highway

Ceiling Collapse in the Interstate 90 Connector Tunnel

Boston, Massachusetts

July 10, 2006

ACCIDENT REPORT

NTSB/HAR-07/02

PB2007-916203 National

Transportation

Safety Board

National

Transportation

Safety Board

490 L’Enfant Plaza, S.W.

Washington, D.C. 20594

Highway Accident Report

Ceiling Collapse in the Interstate 90 Connector Tunnel

Boston, Massachusetts

July 10, 2006

490 L’Enfant Plaza, S.W.

Washington, D.C. 20594

NTSB/HAR-07/02

PB2007-916203

Notation 7901A

Adopted July 10, 2007
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report.

National Transportation Safety Board. 2007. Ceiling Collapse in the Interstate 90 Connector 

Tunnel, Boston, Massachusetts, July 10, 2006. Highway Accident Report NTSB/HAR-07/02. 

Washington, DC.

Abstract: About 11:01 p.m. eastern daylight time on Monday, July 10, 2006, a 1991 Buick passenger 

car occupied by a 46-year-old driver and his 38-year-old wife was traveling eastbound in the 

Interstate 90 connector tunnel in Boston, Massachusetts, en route to Logan International Airport. 

As the car approached the end of the Interstate 90 connector tunnel, a section of the tunnel’s 

suspended concrete ceiling became detached from the tunnel roof and fell onto the vehicle. 

Concrete panels from the ceiling crushed the right side of the vehicle roof as the car came to rest 

against the north wall of the tunnel. A total of about 26 tons of concrete and associated suspension 

hardware fell onto the vehicle and the roadway. The driver’s wife, occupying the right-front seat, 

was fatally injured; the driver was able to escape with minor injuries.

Major safety issues identified in this accident include insufficient understanding among designers 

and builders of the nature of adhesive anchoring systems; lack of standards for the testing of 

adhesive anchors in sustained tensile-load applications; inadequate regulatory requirements for 

tunnel inspections; and lack of national standards for the design of tunnel finishes. As a result 

of its investigation of this accident, the National Transportation Safety Board makes safety 

recommendations to the Federal Highway Administration; the American Association of State 

Highway and Transportation Officials; the departments of transportation of the 50 States and 

the District of Columbia; the International Code Council; ICC Evaluation Service, Inc.; Powers 

Fasteners, Inc.; Sika Corporation; the American Concrete Institute; the American Society of Civil 

Engineers; and the Associated General Contractors of America.
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Contents

Acronyms and Abbreviations....................................................................................... v

Executive Summary ..................................................................................................... viii

Factual Information .........................................................................................................1

Accident Synopsis ...................................................................................................................1

Accident Location (D Street Portal)......................................................................................2

Site Description........................................................................................................................4

Postaccident Inspection ........................................................................................................10

Postaccident Actions .............................................................................................................14

Overview of the CA/T Project ............................................................................................15

Management and Oversight of the CA/T Project ............................................................17

Program Management .....................................................................................................17

Design.................................................................................................................................19

Construction......................................................................................................................19

Federal Oversight .............................................................................................................21

Evolution of Ceiling Design in CA/T Project Tunnels ....................................................21

Ted Williams Tunnel........................................................................................................21

I-93 Tunnel.........................................................................................................................25

Design Policy Memorandum No. 107............................................................................26

I-90 Connector Tunnel .....................................................................................................26

Design and Specifications for the D Street Portal Ceiling ...............................................27

Anchor Alternatives .........................................................................................................27

Ceiling Panel Alternatives...............................................................................................28

Anchor Loading Calculations.........................................................................................29

Anchor Selection...............................................................................................................30

Anchor Approval..............................................................................................................34

Anchor Testing Requirements ........................................................................................36

Anchor Installation Procedures...........................................................................................37

Contract Requirements ....................................................................................................37

Epoxy Supplier’s Recommended Procedures ..............................................................37

Anchor Installation as Described by Modern Continental.........................................38

Installation of the D Street Portal Ceiling ..........................................................................40

Hole Drilling......................................................................................................................40

Installation and Testing of Anchors...............................................................................41

Hanging of Ceiling Panels...............................................................................................42

Preaccident Anchor Failures................................................................................................42

HOV Tunnel ......................................................................................................................42

I-90 Connector Tunnel .....................................................................................................49

Tests and Research ................................................................................................................50

Anchor Examination ........................................................................................................50

Anchor Hole Examination...............................................................................................53
Contents

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Core Sample Examination...............................................................................................54

Ceiling Support Beam Loading ......................................................................................55

Anchor Loading and Design Redundancy Analyses ..................................................56

Anchor Peak Load Tests ..................................................................................................59

Anchor Creep Testing......................................................................................................60

Anchor Installation Parametric Study...........................................................................61

Tests of Void Formation During Anchor Installation .................................................64

Examination of the Effect of an Air Bubble in the Resin or Hardener......................65

Epoxy Testing....................................................................................................................66

Nature of Epoxy................................................................................................................69

Other Information .................................................................................................................72

Current Guidance for the Use of Power-Fast Epoxy...................................................72

Quality Control/Quality Assurance..............................................................................75

CA/T Structural Inspection Program............................................................................76

Federal Design and Inspection Standards for Bridges and Tunnels.........................78

Ceiling Designs in Other U.S. Tunnels..........................................................................80

Analysis............................................................................................................................81

Accident Sequence.................................................................................................................81

Background of the Accident ................................................................................................83

Design of the D Street Portal Ceiling..................................................................................84

Anchor Loading................................................................................................................84

Decision to Use Adhesive Anchors................................................................................85

Anchor Installation Procedures...........................................................................................86

Epoxy Used in the D Street Portal.......................................................................................89

Use of Fast Set Versus Standard Set Epoxy .......................................................................90

Guidance for Using Fast Set Versus Standard Set Epoxy................................................92

ICBO ER-4514....................................................................................................................92

Powers Design Manual....................................................................................................94

Response to Preaccident Anchor Failures..........................................................................95

B/PB and Modern Continental ......................................................................................95

Powers................................................................................................................................97

Standards and Protocols for the Testing of Adhesive Anchors......................................98

Lack of Awareness of the Potential for Adhesive Anchor Creep Under Sustained 

Load.......................................................................................................................................101

Tunnel Inspections ..............................................................................................................102

National Standards for Design of Tunnel Finishes ........................................................103

Conclusions................................................................................................................... 105

Findings ................................................................................................................................105

Probable Cause ....................................................................................................................107

Recommendations........................................................................................................ 109

Appendixes

A: Hearing and Investigation.........................................................................................113

B: AASHTO Testing Survey...........................................................................................114

C: Tunnel Ceiling Survey ...............................................................................................117
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Acronyms and Abbreviations

AASHTO American Association of State Highway and 

 Transportation Officials

AC Acceptance Criteria

ASCE American Society of Civil Engineers

AGC Associated General Contractors of America

ASTM ASTM International

BOCA Building Officials and Code Administrators 

 International, Inc.

B/PB Bechtel/Parsons Brinckerhoff 

CA/T Central Artery/Tunnel [project]

Conam Conam Inspection Services

DOT U.S. Department of Transportation

EOTC Executive Office of Transportation and Construction

ER evaluation report

FHWA Federal Highway Administration

FST/HNTB Fay, Spofford and Throndike, Inc., and HNTB 

 Corporation

Gannett Fleming Gannett Fleming, Inc.

HOV high-occupancy vehicle

ICBO International Conference of Building Officials

ICBO ES ICBO Evaluation Service, Inc.

ICC International Code Council

ICC ES ICC Evaluation Service, Inc.

ICC ESR ICC Evaluation Service report

I-90 Interstate 90

I-93 Interstate 93

kip kilo-pound (1,000 pounds)

MassHighway Massachusetts Highway Department

Mass Pike Massachusetts Turnpike

MIT Massachusetts Institute of Technology

Modern Continental Modern Continental Construction Company, Inc.
Acronyms and Abbreviations

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MSDS Material Safety Data Sheets

MTA Massachusetts Turnpike Authority

NBI National Bridge Inventory

NBIP National Bridge Inspection Program

NBISs National Bridge Inspection Standards

Newman Renner Colony Newman Renner Colony, LLC

NIST National Institute of Standards and Technology

Powers Powers Fasteners, Inc.

psi pounds per square inch

psf pounds per square foot

QC quality control

QC/QA Quality Control and Quality Assurance

RFI request for information

SBCCI Southern Building Code Congress 

International, Inc.

Walsh Walsh Construction Company
Acronyms and Abbreviations

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Accident Report

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Selected Entities Involved in the Design and Construction 

of the D Street Portal

Entity Role

Federal Highway Administration (FHWA) Authorized Federal funding for the Central Artery/

Tunnel (CA/T) project. Reviewed and approved 

the preliminary and follow-on CA/T designs. 

Reviewed and approved all CA/T construction 

contracts. Provided oversight for all major project 

recommendations and decisions.

Massachusetts Highway Department 

(MassHighway)

Processed, approved, and awarded all CA/T design 

and construction contracts.

Massachusetts Executive Office of Transportation 

and Construction (EOTC)

Beginning in 1993, approved expenditure of funds 

for CA/T project. 

Massachusetts Turnpike Authority (MTA) Responsible for completed elements of CA/T 

project. In 1997, was given authority for CA/T 

ownership, management, and operation.

Bechtel/Parsons Brinckerhoff (B/PB) Management consultant for CA/T project. Served 

as owners’ (MTA’s) representative to the project. 

Managed design consultants and was project 

construction manager. Reviewed all design 

specifications and was secondary reviewer for all 

contractor submittals, including the D Street portal 

anchor adequacy submittal. 

Gannett Fleming, Inc. (Gannett Fleming) Section design consultant for the Interstate 90 (I-90) 

connector tunnel finishes. Adapted ceiling system 

design for D Street portal. Primary reviewer for 

contractor submittals, including the D Street portal 

anchor adequacy submittal. 

Modern Continental Construction Company, Inc. 

(Modern Continental)

Construction contractor for I-90 connector tunnel 

finishes. Selected and installed the adhesive 

anchoring system used in the D Street portal.

Conam Inspection Services, Inc. (Conam) Hired by Modern Continental to perform required 

proof testing of all adhesive ceiling support 

anchors installed by Modern Continental in the I-90 

connector tunnel (including the D Street portal).

Newman Renner Colony, LLC

(Newman Renner Colony)

Supplied the adhesive anchoring system selected 

and used by Modern Continental in the D Street 

portal. The system used epoxy supplied by Powers 

Fasteners, Inc.

Powers Fasteners, Inc. (Powers) Supplied (through Newman Renner Colony) the 

epoxy used for anchors in the D Street portal. 

Sika Corporation Formulated the epoxy that was subsequently 

packaged and marketed by Powers for Newman 

Renner Colony and used in the D Street portal.
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Executive Summary

About 11:01 p.m. eastern daylight time on Monday, July 10, 2006, a 1991 

Buick passenger car occupied by a 46-year-old driver and his 38-year-old wife was 

traveling eastbound in the Interstate 90 connector tunnel in Boston, Massachusetts, 

en route to Logan International Airport. As the car approached the end of the 

Interstate 90 connector tunnel, a section of the tunnel’s suspended concrete 

ceiling became detached from the tunnel roof and fell onto the vehicle. Concrete 

panels from the ceiling crushed the right side of the vehicle roof as the car came 

to rest against the north wall of the tunnel. A total of about 26 tons of concrete 

and associated suspension hardware fell onto the vehicle and the roadway. The 

driver’s wife, occupying the right-front seat, was fatally injured; the driver was 

able to escape with minor injuries.

The National Transportation Safety Board determines that the probable cause 

of the July 10, 2006, ceiling collapse in the D Street portal of the Interstate 90 connector 

tunnel in Boston, Massachusetts, was the use of an epoxy anchor adhesive with poor 

creep resistance, that is, an epoxy formulation that was not capable of sustaining 

long-term loads. Over time, the epoxy deformed and fractured until several ceiling 

support anchors pulled free and allowed a portion of the ceiling to collapse. Use of 

an inappropriate epoxy formulation resulted from the failure of Gannett Fleming, 

Inc., and Bechtel/Parsons Brinckerhoff to identify potential creep in the anchor 

adhesive as a critical long-term failure mode and to account for possible anchor 

creep in the design, specifications, and approval process for the epoxy anchors used 

in the tunnel. The use of an inappropriate epoxy formulation also resulted from 

a general lack of understanding and knowledge in the construction community 

about creep in adhesive anchoring systems. In addition, Powers Fasteners, Inc., 

failed to provide the Central Artery/Tunnel project with sufficiently complete, 

accurate, and detailed information about the suitability of the company’s Fast Set 

epoxy for sustaining long-term tensile loads. Contributing to the accident was the 

failure of Powers Fasteners, Inc., to determine that the anchor displacement that 

was found in the high-occupancy vehicle tunnel in 1999 was a result of anchor 

creep due to the use of the company’s Power-Fast Fast Set epoxy, which was 

known by the company to have poor long-term load characteristics. Also 

contributing to the accident was the failure of Modern Continental Construction 

Company, Inc., and Bechtel/Parsons Brinckerhoff, subsequent to the 1999 

anchor displacement, to continue to monitor anchor performance in light of the 

uncertainty as to the cause of the failures. The Massachusetts Turnpike Authority 

also contributed to the accident by failing to implement a timely tunnel inspection 

program that would likely have revealed the ongoing anchor creep in time to 

correct the deficiencies before an accident occurred.
Executive Summary

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The safety issues identified during this investigation are as follows:

• Insufficient understanding among designers and builders of the nature 

of adhesive anchoring systems;

• Lack of standards for the testing of adhesive anchors in sustained 

tensile-load applications;

• Inadequate regulatory requirements for tunnel inspections; and

• Lack of national standards for the design of tunnel finishes.

As a result of its investigation of this accident, the National Transportation 

Safety Board makes safety recommendations to the Federal Highway 

Administration; the American Association of State Highway and Transportation 

Officials; the departments of transportation of the 50 States and the District of 

Columbia; the International Code Council; ICC Evaluation Service, Inc.; Powers 

Fasteners, Inc.; Sika Corporation; the American Concrete Institute; the American 

Society of Civil Engineers; and the Associated General Contractors of America.

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Factual Information

Accident Synopsis

About 11:01 p.m. eastern daylight time on Monday, July 10, 2006, a 1991 

Buick passenger car occupied by a 46-year-old male driver and his 38-year-old 

wife was traveling eastbound in the Interstate 90 (I-90) connector tunnel in Boston, 

Massachusetts, en route to Logan International Airport. As the car approached the 

end of the I-90 connector tunnel, a section of the tunnel’s suspended concrete ceiling 

detached from the tunnel roof and fell onto the vehicle. Concrete panels from the 

ceiling crushed the right side of the vehicle roof as the car came to rest against 

the north wall of the tunnel. A total of about 26 tons of concrete and associated 

suspension hardware fell onto the vehicle and the roadway. The driver’s wife, 

occupying the right-front seat, was fatally injured; the driver was able to escape 

with minor injuries. (See figure 1.)

Figure 1. Postaccident scene with the crushed passenger car barely visible under the wreckage. 

The open area in the ceiling is the original location of the concrete panels. (Photograph courtesy 

Massachusetts State Police)
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Accident Location (D Street Portal)

The accident occurred in the eastbound travel lanes of the I-90 connector 

tunnel1 at mile marker 135.25, just west of the entrance to the Ted Williams Tunnel. 

The Ted Williams Tunnel carries traffic underneath Boston Harbor to Logan 

International Airport. (See figure 2.) The accident site was within a 200-foot-long 

section of the I-90 connector tunnel that will be referred to in this report as the 

D Street portal. The D Street portal actually comprised three tunnelsa two-lane 

westbound tunnel, a two-lane (with an acceleration lane) eastbound tunnel (the 

accident location) located south of the westbound tunnel, and a one-lane eastbound 

high-occupancy vehicle (HOV) tunnel located south of the other two tunnels.2 (See 

figure 3.) The Ted Williams Tunnel, the I-90 connector tunnel, and the D Street 

portal were all built as part of Boston’s Central Artery/Tunnel (CA/T) project. 

(The CA/T project will be discussed in more detail later in this report.)

1 In this report, “I-90 connector tunnel” refers to the I-90 tunnel between the Interstate 90 and 93 

interchanges in downtown Boston and the entrance to the Ted Williams Tunnel.

2 A short one-lane westbound exit ramp (Ramp F) tunnel paralleled the other tunnels at the accident 

location, but this tunnel had no suspended ceiling and will not be considered in this report.

23

22

20

25

24 25

18

24

26

Boston Inner

Harbor

Beacon

Hill Financial

District

Chinatown

South End South Boston

City Point

A St

B St Bolton St

D St

C St

SummerSt

E 1st St

E Broadway

Mass Pike

Accident location

a-B-C

1

93

90

90 Mass Pike

Figure 2. Accident site. 
Factual Information

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Figure 3. Plan view (top) and aerial view (bottom, looking west) of the D Street portal.
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Accident Report

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The D Street portal was built in 1993, before completion of either the Ted 

Williams Tunnel or the remainder of the I-90 connector tunnel. The portal was 

completed first in order to coordinate the construction sequencing with the traffic 

plan. That traffic plan required a temporary above-ground ramp to carry traffic 

from D Street to the entrance to the Ted Williams Tunnel in order to provide access 

under Boston Harbor to the airport before work was finished on the remainder of 

the I-90 tunnel. To accommodate the weight of a parking deck that was expected 

to be built over the portal, the tunnel roof was constructed of heavily reinforced3

concrete, which was 5 to 7 feet thick.

The D Street portal was constructed by Kiewit/Perini/Atkinson/Cashman, 

JV (joint venture), of Boston, which was under contract to the Massachusetts 

Department of Public Works to construct the landside west tunnel approach to 

the Ted Williams Tunnel. The work consisted of approximately 2,600 feet of I-90 

cut-and-cover tunnel4 and one section of depressed open highway, as well as the 

D Street portal and a temporary ramp. The designer (the section design consultant) 

for this portion of the project was HDR Engineering, Inc., headquartered in Omaha, 

Nebraska.

The D Street portal was opened to traffic in phases. The accident site area 

was opened to traffic on December 14, 2000. Traffic was not routed through all 

the bores of the tunnel until the remainder of the connector tunnel was completed 

and opened to the public in January 2003. According to 2005 data provided by 

the Massachusetts Turnpike Authority (MTA), eastbound traffic through the I-90 

connector tunnel (including the D Street portal) averaged 43,000 vehicles per day.

Site Description

The roadway in the eastbound D Street portal tunnel at the accident 

site consisted of two 12-foot-wide travel lanes and, along the south side of the 

tunnel, an 18-foot-wide acceleration lane. Raised walkways with 3 1⁄2-foot-high 

steel handrails were on either side of the tunnel. The walkway on the north side of 

the tunnel was about 3 feet wide, elevated about 2 1⁄2 feet above the road surface, 

and separated from the travel lanes by a 5-foot-wide shoulder. The south walkway 

was about 2 1⁄2 feet wide, elevated 3 feet above the road surface, and separated 

from the acceleration lane by a 1 1⁄2-foot shoulder. (See figure 4.)

3 The reinforcement was in the form of steel reinforcing bars of varying thicknesses (often referred to as 

“rebar”) embedded in the concrete in both transverse and longitudinal directions.

4 Cut and cover is a construction technique, typically used for shallow tunnels, in which a trench is dug 

and then roofed over.
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Suspended over the roadway at the time of the accident was a ceiling 

consisting of concrete panels supported by a steel framework. This framework 

was, in turn, supported by a system of steel rods and turnbuckles attached to steel 

hanger plates. These hanger plates were affixed to the tunnel roof by stainless steel 

threaded rods (anchors) inserted into holes drilled in the concrete roof5 and held in 

place with an epoxy adhesive.6 (This anchoring system will be described in detail 

in the “Design and Specifications for the D Street Portal Ceiling” section of this 

report.) The distance from the road surface to the suspended concrete ceiling was 

about 17 feet. The distance from the top of the suspended ceiling to the tunnel roof 

was about 5 1⁄2 feet.

The ceiling “module” at the site of this accident (designated module EB081) 

comprised 15 panels of reinforced concrete: two rows of five 12- by 8-foot concrete 

panels about 4 inches thick, each weighing about 4,700 pounds, and a single row 

of five 6- by 8-foot concrete panels about 4 inches thick, each weighing about 2,500 

pounds. (See figure 5.) The larger panels made up the north and center rows of 

ceiling panels; the smaller panels made up the south row.7 All 10 of the large panels 

5 These holes were core-drilled using a cylindrical diamond drill bit.

6 Although these threaded rods were sometimes referred to in CA/T project documents as “bolts,” in this 

report, they will be referred to as “anchors.” The combination of epoxy, threaded rod, and seal plug make up 

the anchoring “system.”

7 This description applies to the eastbound tunnel only; the number and arrangement of panels differed 

in the westbound and HOV tunnels because of the different roadway widths.

Tunnel roof

Acceleration

lane

Travel lanes

Concrete ceiling panels

Strut Strut

5’ shoulder 1.5’ shoulder

12’ 12’ 18’

Ventilation duct

Supply air ducts

N

Not to scale

Figure 4. Cross section of the eastbound portal tunnel at the accident location.
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fell onto the roadway in this accident, with only one corner of one panel remaining 

attached to the ceiling support structure. The row of smaller panels remained in 

place.

Figure 5. Overview of the support structure for the accident ceiling module. Panels and support 

beams show alphanumeric designations that were assigned during postaccident reconstruction.
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Supporting the 15 concrete panels of the accident module were 4 steel 

support beams oriented parallel with the roadway1 on the north side, 1 on the 

south side, and 2 toward the middle. The beam to the north (designated “N” by 

investigators) supported only the north ends of the five large panels in the north 

row. The first beam to the south (designated “M1”) supported both the south ends 

of the northern row of panels and the north ends of the center row. The next beam 

(“M2”) supported both the south ends of the large center panels and the north 

ends of the row of smaller 6- by 8-foot panels. The south beam (“S”) supported 

only the south ends of the smaller panels.

Each beam was supported by eight vertical hanger rods attached by clevis 

connections to the support beam at the bottom and to the roof hanger plate at 

the top. (See figure 6.) In addition to the vertical support rods, angled (diagonal) 

hanger rods at several locations prevented movement of the ceiling system in the 

longitudinal direction (parallel to the travel lanes). Metal struts extending from the 

tunnel walls to either side of the ceiling module prevented transverse movement.

Two adhesive anchors (see figure 7) secured each of the 26 roof hanger 

plates (of the accident module) to which only vertical hanger rods were attached. 

Four anchors were used to secure the six roof hanger plates (two each for beams 

M1 and M2 and one each for beams N and S) that had both vertical and diagonal 

rods. Thus, beams N and S were each secured by 18 anchors, while beams M1 and 

M2 each used 20 anchors. The entire module was supported by 76 anchors. For 

reasons that will be discussed later in this report, the 200-foot-long D Street portal 

was the only section of the CA/T tunnel system to have a ceiling of this particular 

design supported solely by adhesive anchors.

A portion of the area between the suspended ceiling and the tunnel roof was 

used as a ventilation duct. The tunnel ventilation system was designed to maintain 

air quality in the tunnel and to remove smoke in the event of fire. Large-volume 

fans in above-ground buildings adjacent to the connector tunnel drew air into the 

tunnel from fresh air ducts underneath the roadway and exhausted it along the 

tunnel ceiling. Once the ceiling panels had been hung, two rows of corrugated 

metal panels were installed as sidewalls extending from the suspended ceiling up 

to the tunnel roof, creating (at the accident site) a ventilation duct 24 feet wide and 

5 1⁄2 feet high. (Refer to figure 4.) Air was drawn into this exhaust plenum through 

3 1⁄2 -feet by 9-inch exhaust ports in the center of some of the panels in each module. 

(Six of the 12- by 8-foot ceiling panels in the accident module had exhaust ports.)

The complete ceiling module at the accident site measured 30 feet wide 

and 40 feet long. The weight of the 15 concrete panels was about 60,000 pounds; 

the support beams, rods, hanger plates, and ductwork weighed an additional 

17,000 pounds, for a total module weight of about 77,000 pounds. The weight of 

the concrete panels and supporting hardware that fell in this accident was about 

52,000 pounds.
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Row N Row M1 Row M2

Strut

Channel

fitting

Hanger rods

Clevis

connections

Welded stud

Concrete panels

Square

washer

“T” beam “L” angle “L” angle

Vertical

plate

North

4-inch-thick

concrete panel

Hanger rod

and turnbuckle

Tunnel roof

Support beam

Roof hanger plate

Adhesive anchor

Figure 6. Cross section of the I-90 tunnel ceiling showing support beam and concrete panel 

connections (looking east, not to scale).
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The ceiling in the D Street portal was installed by Modern Continental 

Construction Company, Inc. (Modern Continental), of Cambridge, Massachusetts, 

between June 1999 and April 2000. The ceiling module that collapsed in this 

accident was installed in November 1999. Modern Continental installed the last 

ceiling module of the I-90 connector tunnel in July 2002.

5”

3”

3/4”

Concrete roof

Roof hanger plate

Nut

Lock washer

Sealing washer

Seal plug

Epoxy

Anchor

Not to scale

0.9”

0.55”

Figure 7. Typical adhesive anchor and roof hanger plate assembly.
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Postaccident Inspection

The collapsed ceiling structure is shown in figure 8. For purposes of 

identification, investigators designated the individual concrete panels “N1” through 

“N5” (the north row) and “C1” through “C5” (the center row), from east to west 

(refer to figure 5). The relative positions of the fallen panels indicate that panels 

C1 through C5 and the south ends of panels N1 through N5 swung down and to 

the north. Panel N2 remained attached at its northeast corner to support beam N. 

Panels N1 and N3 fell back to the south on top of the center panels, thus their lower 

surfaces are visible in figure 8. Panels N4 and N5 came to rest leaning against the 

north wall or railing, and their upper surfaces are visible. The fallen panels were 

later removed from the tunnel and reconstructed as shown in figure 9.

In addition to the concrete panels, the entire 40-foot length of support beam 

M1 and its hanger assembly fell onto the roadway or onto the wreckage. The 

hanger assembly included 8 vertical and 4 diagonal rod hangers, along with all 

8 hanger plates and the 20 anchors that had attached the support beam to the 

tunnel roof. The north side of the ventilation duct enclosure also fell.

Figure 8. Looking north at the collapsed concrete panels before removal from the tunnel. 

Components shown as labeled for postaccident reconstruction. (Photograph courtesy Massachusetts 

State Police)
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Figure 10 shows some of the roof hanger plates and anchors in the 

westbound tunnel portion of the D Street portal as they were just after the accident 

(though they were not involved in the accident). Several of these hanger plates 

show evidence of significant displacement (movement downward from their 

originally installed positions).

Figure 9. Collapsed panels after removal from the tunnel as rearranged in their original positions 

within the ceiling module. The upper surfaces of the panels are shown. (Photograph courtesy 

Massachusetts State Police) 
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After the accident, all the ceiling panels and their support structures, except 

for the anchors themselves, were removed from all bores of the D Street portal. Each 

remaining adhesive anchor was subsequently examined to determine how much, 

if any, it had displaced from the tunnel roof since it was originally installed.

The examinations revealed that, in the westbound tunnel, 78 of the 198 

anchors had displaced. In the eastbound tunnel, 57 of the 248 remaining (after the 

accident) anchors had displaced. In the HOV tunnel, 26 of the 188 anchors had 

displaced. The amounts of displacement ranged from less than 0.1 inch to more 

than 1.0 inch.

Displacement measurements taken by Safety Board investigators for all the 

anchors securing a particular hanger plate (either a two-anchor or four-anchor 

fitting) were averaged to generate a single number to represent the amount the 

hanger plate had moved downward. Figure 11 shows the relative displacement of 

the roof hanger plates in the three D Street portal tunnels as well as the distribution 

of displaced hanger plates within each module.

Figure 10. This photograph, taken in the westbound D Street portal tunnel after the accident, 

shows a number of roof hanger plates that have begun to pull away from the tunnel roof, including 

the two-anchor hanger plate in the foreground and the four-anchor plate adjacent to it.
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00 to - 0.2”-0.2 to -0.4”-0.4 to -0.6”-0.6 to -0.8”-0.8 to -1.0”-1.0”+

HOV

N

M

S

078 079 080 081

WB

N

M

S

081 082 083 084

EB

S

M1M2

N

080 081 082 083

FAILURE AREA

N

E

Graphic display of the displaced roof hanger plates found during postaccident inspection of the D Street portal tunnels. Each Figure 11.

square on the chart represents a roof hanger plate (whether a two- or four-anchor plate). Shading of each square represents the amount of displacement. 
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Postaccident Actions

After the accident, State and local authorities closed the I-90 connector tunnel 

and its access ramps. The entire eastbound HOV tunnel (through both the I-90 

connector tunnel and the Ted Williams Tunnel) was also closed. One I-90 access 

ramp, which was closed on July 10, 2006, was reopened on July 11 after shoring was 

installed for a portion of the ramp tunnel ceiling where a row of adhesive anchors 

showed displacement. This ramp was closed again on July 18 when concerns arose 

about anchor displacement that was found outside the shored area.

Over the succeeding weeks and months, engineers from the Massachusetts 

Executive Office of Transportation and Construction (EOTC), the Massachusetts 

Highway Department (MassHighway), the Federal Highway Administration 

(FHWA), the CA/T project, and independent consulting firms inspected the 

ceiling structures of the closed tunnels and ramps and the Ted Williams Tunnel to 

identify sites where corrective actions might be needed.

As part of these inspections, all of the adhesive anchors in the Ted Williams 

Tunnel (eastbound and westbound) were inspected, and 37 anchors from the three 

tunnel bores were proof tested.8 Two anchors failed the proof test and were replaced 

with undercut anchors.9 At four locations in the westbound Ted Williams Tunnel, 

the roof hanger plates had displaced from the tunnel roof. Two of these areas 

were shored temporarily until new hanger plates could be fabricated and installed 

using undercut anchors. The Massachusetts Executive Office of Transportation 

and MassHighway performed sustained load tests on selected anchors in an area 

of the westbound Ted Williams tunnel that could be closed to traffic long enough 

to conduct the tests. None of the tested anchors displaced during the tests.

The I-90 connector tunnel (except for the D Street portal area), including 

ramps to and from the tunnel, was surveyed, and 1,097 roof hanger plates were 

found to be installed with adhesive anchors.10 Some of the approximately 2,200 

adhesive anchors were found to have displaced by some amount from the 

tunnel roof. All of these anchors were replaced with undercut anchors, and at 

some locations, additional hanger plates were fabricated and installed, also with 

undercut anchors.

The suspended ceiling structure in the D Street portal was removed. During 

subsequent tunnel evaluations, it was determined that, because of the short length 

8 A proof test is a nondestructive test in which a load greater than the expected normal service load 

is applied to a component. If the component is not permanently deformed by the test, it is considered 

acceptable.

9 Undercut anchors are threaded mechanical fasteners that fit into holes that are drilled wider (undercut) 

at their deepest point. When installed, the tip of the anchor expands into the undercut area, holding tension 

loads by bearing against the concrete in the undercut area.

10 Although the roof of the I-90 connector tunnel (other than the D Street portal section) was constructed 

with cast-in-place channel inserts for attaching ceiling supports, some of these channels were missing or 

misaligned, requiring the use of adhesive anchors at those locations.
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of this tunnel section and its proximity to a tunnel opening, the suspended ceiling 

was not necessary for adequate tunnel ventilation. The ceiling structure was not 

replaced.

The closed tunnel sections and access ramps were reopened beginning in 

November 2006 as corrective measures were completed. The last closed tunnel 

section, the eastbound HOV tunnel, was reopened in May 2007.

Overview of the CA/T Project

The CA/T projectinformally known as the “Big Dig”was a 20-year effort 

(more than 14 years in the major construction phase) that is generally regarded as 

one of the most complex and costly public infrastructure projects ever undertaken 

in the United States. It was intended to improve traffic flow in downtown Boston by 

(1) replacing a deteriorated and congested elevated roadway (Interstate 93 [I-93], the 

“Central Artery” through Boston), (2) extending I-90 (the Massachusetts Turnpike, 

or Mass Pike) to Logan International Airport, (3) providing an interchange for 

Interstates 90 and 93, and (4) replacing the I-93 bridge over the Charles River. (See 

figure 12.)

The project, which is owned and managed by the MTA, is part of the 

Metropolitan Highway System. Although originally scheduled to be completed in 

1998 at a cost of $2.6 billion, the main construction phase of the CA/T project was 

actually completed in 2006 at a final project cost in excess of $14 billion.

Construction of the CA/T project presented a number of significant, possibly 

unique, engineering challenges. Many of these challenges resulted from the need 

to conduct a major construction effort while minimizing disruptions to commerce 

and inconveniences to the public. In the case of I-93, the old elevated central artery 

roadway had to continue in use while the new highway was tunneled beneath it. 

In another instance, the new highway tunnel had to cross underneath an existing 

subway tunnel without disrupting subway train service. A portion of the I-90 

connector tunnel was built beneath nine railroad tracks without affecting daily 

commuter and intercity passenger rail traffic.

Early in the construction phase of the project, CA/T owners and managers 

began to encounter construction delays and cost increases that attracted additional 

public and political attention to what was already a high-visibility project. 

According to officials responsible for oversight of the project, a major emphasis 

throughout the construction phase was keeping the project on schedule while 

keeping costs under control.
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The project at completion consisted of 161 lane miles of highway along a 

7 1⁄2-mile corridor, with 5 miles of tunnel, 6 interchanges, and 200 bridges. The 

new I-93 north-south central artery is an 8- to 10-lane limited access underground 

expressway. The new east-west artery extends I-90 (Mass Pike) from its previous 

terminus south of downtown Boston through the new Ted Williams Tunnel under 

Boston Harbor to Logan Airport.

Figure 12. Central/Artery Tunnel project at completion. (Graphic courtesy MTA)
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Management and Oversight of the CA/T Project

The CA/T project adopted a conventional design-bid-build approach to the 

various project sections and was set up with layers of public oversight and checks 

and balances, as described below.

Program Management

The Massachusetts Secretary of Transportation initially assigned overall 

responsibility for the CA/T project to the Massachusetts Department of Public 

Works.11 Because no State agency had sufficient personnel or expertise to provide 

day-to-day management of a project of this magnitude, the Department of Public 

Works was directed to hire an experienced contractor as project manager.12 Over 

the course of the CA/T project, this project manager would provide the following 

major services:

• Preliminary design

• Final design coordination and review

• Construction coordination and monitoring by inspectors and resident 

engineers

• Cost estimate preparation and actual cost reporting to project owners

• Right of way and other property acquisition

• Computer-aided design record-keeping

• Utility engineering and coordination

• Internal quality assurance

• Construction safety programs

• Construction contract administration as owners’ authorized 

representative

• Standard drawings for the program

• Geotechnical engineering services

• Environmental services

• Engineering materials testing

In 1985, the Department of Public Works entered into an agreement with 

Bechtel/Parsons Brinckerhoff (B/PB)a joint venture formed between Bechtel 

Corporation and Parsons Brinckerhoff Quade & Douglasto prepare a preliminary 

project management plan. Later the same year, the department issued a 1-year 

11 The information in this section is based on CA/T project contracts, reports, and other documents, 

historical data from a number of sources, and interviews with B/PB representatives and others responsible for 

or involved in the management or oversight of the project.

12 This means of managing large projects is often used by State and local governments.
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contract to B/PB to develop a comprehensive work plan for managing design 

consultants and reviewing their work. This contract was followed by a number of 

limited‐term contracts with B/PB, called “work programs,” that extended through 

the life of the project.

In its role as management consultant, B/PB was accountable initially to the 

Department of Public Works. In 1991, the Department of Public Works became 

MassHighway, and B/PB fell within the purview of that department. Between 

1986 and 1993, the CA/T project was managed as a special, separate project of the 

Department of Public Works/MassHighway and was administered by a project 

director and staff.

In 1993, the EOTC signed a memorandum of agreement with MassHighway 

under which the CA/T project director would report directly to the EOTC rather 

than to MassHighway. The project director would approve the expenditure of 

funds, and the Board of Commissioners of MassHighway would process and 

approve contracts.

By 1995, as various CA/T highway segments were completed, more and 

more day-to-day management of the CA/T project had been transferred to the 

MTA, and in 1996, the project director for the CA/T project was transferred to that 

agency. In 1997, the Massachusetts Metropolitan Highway System was created, 

and the MTA was designated as the owner and operator. Because all elements 

of the CA/T project were included in the Metropolitan Highway System, the 

MTA was given authority for the ownership, management, and operation of the 

complete CA/T project.

Also in 1997, an agreement was entered into whereby key personnel 

of B/PB, the MTA, and MassHighway would work together as an “integrated 

project organization.” Under this structure, the project staffs worked as a 

single organization under the direction of the MTA, which had authority 

to act on any matter relating to the management and administration 

of the CA/T project. The stated goal of the change in management 

structure was to streamline project management and improve cost effectiv

eness.

Throughout the project, the relationship between the MTA and B/PB 

was governed by the work program in place at the time. Subject to general MTA 

oversight, B/PB continued to function as the owner’s representative in day-to-day 

administration of CA/T design and construction contracts.

All funding for the CA/T project continued to be provided through 

MassHighway, which was the State agency authorized to receive and disburse 

Federal funds. As the funding source, MassHighway also retained responsibility 

for awarding and executing design and construction contracts.13 As part of 

13 For that reason, all CA/T section design and construction contracts were with MassHighway, not the 

MTA.
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the owners’ oversight role, MassHighway and MTA engineers and project 

management staffs reviewed and evaluated B/PB’s work. The FHWA also 

participated in reviews and oversight of almost all major B/PB recommendations 

and MassHighway/MTA decisions.

B/PB served as management consultant for the I-90 connector tunnel as 

described above until the MTA assumed responsibility for operations, inspections, 

and maintenance of the tunnel in January 2003.

Design

B/PB prepared the concept studies and preliminary design basis for about 

25 percent of the total CA/T design effort. For greater manageability, the CA/T 

project was subdivided into a number of sections, each of which was designed 

and constructed under separate contracts. The final design of each project section, 

as well as the construction specifications, was the responsibility of the design 

engineering firm or firms14 that had been selected as the “section design consultant” 

for that part of the project.15

The section design consultants were responsible for developing detailed, 

“stamped”16 designs sufficient for construction contractors to bid and build the 

various sections of the project. The section design consultant was the primary 

reviewer of all construction proposals, with B/PB as the secondary reviewer. 

During construction, the section design consultants performed such services as 

reviewing shop drawings and submittals and preparing responses to construction 

contractors’ requests for information. (RFIs) 17 B/PB’s review of the section design 

consultants’ designs focused primarily on determining whether the designs met 

the requirements of the CA/T project. Contractor questions or RFIs or clarification 

relating to the final design were typically referred to the section design consultant 

for resolution rather than to B/PB.

Construction

MassHighway, with the advice and assistance of B/PB, advertised the 

section design consultant’s final design and specifications for bid, typically 

receiving proposals from three or more construction contractors. The selected 

contractor (usually the low fee proposal) was responsible for constructing the 

14 Some project sections were large enough to support the efforts of two or more engineering firms 

working as a joint venture.

15 The section design consultant for each part of the project was selected by a group of public employees 

impaneled for that particular contract. The selection was approved by MassHighway’s Architect and Engineering 

Board.

16 A plan is stamped when a Massachusetts registered professional engineer approves it and affixes an 

official seal.

17 An RFI is a document used by a contractor to request additional information or to obtain clarification 

about some aspect of the construction.
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project section in accordance with the contract design and specifications and its 

own quality control program. (The contractor was responsible for quality control, 

in accordance with the CA/T contract and general industry practice.)

Before the work started, B/PB reviewed the contractor’s project-specific 

quality control program for conformance with the standards set out in the contract. 

During construction, the contractor performed quality control, to include, as 

necessary, providing material certificates and arranging for proof testing by a 

materials testing consultant approved by MassHighway. Certain materials used 

by the contractor were also tested by the CA/T project’s construction laboratory, 

which was managed by B/PB, certified by the American Association of State 

Highway and Transportation Officials (AASHTO),18 and independently assessed 

by MassHighway. The materials tested were predominately structural components 

such as asphalt, structural steel, and Portland cement concrete. Adhesive epoxy 

was not tested but was accepted based on materials certificates provided by the 

manufacturer.

From the onset of construction, B/PB was responsible for quality assurance, 

a responsibility carried out primarily through the office of the resident engineer. 

B/PB field engineers within the resident engineer’s office were present in the field 

during construction to monitor the contractors’ activities and to record all work 

being done in the field engineer daily report. The daily report was used to verify 

payment and resolve claims and to document acceptability of work and compliance 

with environmental requirements. All field engineer daily reports were required 

to include the acceptance and rejection criteria for the work, including any tests or 

inspections that were performed and their results, as well as any unusual events 

or deficiencies.

When deficiencies in the contractor’s work were recurring, remained 

uncorrected, became irreversible, or resulted in unapproved deviations from the 

contract specifications, the resident engineer was required to create a deficiency 

report documenting the unacceptable performance, which was then transmitted 

to the contractor for resolution. If the contractor failed to take corrective action 

acceptable to the resident engineer, payment for the work could be withheld. 

No further payments would be made toward that part of the contract until the 

deficiency had been corrected in a manner acceptable to and verified by the 

resident engineer.

The resident engineer was also responsible for the receipt and verification of 

construction materials on the job site. This included responsibility for comparing 

the product delivered to the site with the product described in the approved 

submittal to ensure that it was the product approved for use on the job.

18 AASHTO comprises representatives of highway and transportation departments in the 50 States, 

the District of Columbia, and Puerto Rico. The association’s mission is to advocate transportation-related 

policies and to provide technical services to help improve transportation safety and efficiency. AASHTO 

conducts research and performs data analysis and provides States and jurisdictions with written guidelines 

and standards on a variety of transportation topics.
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B/PB was to facilitate the resolution of issues between or among contractors, 

section design consultants, and the project owners. Significant issues and challenges 

that arose during the design and construction of the CA/T project were typically 

brought to the attention of the project interface committee, a group that met weekly 

and that comprised representatives from the MTA, MassHighway, the FHWA, 

and B/PB.

Federal Oversight

The projected cost of the CA/T project exceeded the threshold ($5 million) 

necessary to qualify it for “full oversight” by the FHWA. The project also met this 

requirement because it was a part of the Interstate Highway System. As a project 

costing $1 billion or more (a threshold that has since been lowered to $500 million), 

the CA/T project also qualified as a “major project.”

In its full oversight role, the FHWA was responsible for ensuring that the 

project adhered to Federal regulations and standards and for evaluating the State’s 

programs and providing technical assistance, as necessary. The FHWA office 

in Boston, according to officials there, had as many as 15 staff members (in an 

office of about 30) working full‐ or part-time on the CA/T project. More typically, 

6 to 8 staff members were assigned to the project at any one time. Staffing for 

the CA/T project began in 1986 when, for the first time in that office, a project 

engineer was assigned responsibility for this single construction project. Two 

additional engineers later joined the staff, at which time oversight of the I-90 and 

I-93 portions of the project were separated into the areas of environment, design, 

and construction. The addition to the team of structural and other engineers led to 

the creation of a project administrator position above the project engineer.

The FHWA reviewed and approved the preliminary and follow-on CA/T 

project designs. Because it was responsible for authorizing Federal expenditures 

for the project, the FHWA was required to review and approve all CA/T project 

construction contracts. The agency also reviewed and approved all plans, 

specifications, and estimates, although highway administration officials said that 

they did not have the time, the personnel, or the expertise to “review every detail 

of every design.” Boston FHWA officials said they relied heavily on B/PB, which 

in this project was performing the role that would normally be carried out by a 

government agency, specifically, the State highway department.

Evolution of Ceiling Design in CA/T Project Tunnels

Ted Williams Tunnel

The sequence of construction for the CA/T project was developed based 

on the desire to provide, as early as possible, a third link from downtown Boston 
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to Logan Airport. The main element of this link would be the new 3,850-foot-long 

immersed-tube19 Ted Williams Tunnel, which, along with the smaller Boston 

Marine Industrial Park and Bird Island Flats tunnels, made up the I-90 (partial) 

route that was opened to traffic on December 15, 1995. At both ends of this route, 

temporary facilities were built to allow traffic to enter and exit the tunnels before 

the permanent facilities connecting to them were completed. At the west end of 

the route, a portion of the permanent tunnel structure had to be built to allow 

construction of a temporary ramp above it. This tunnel structure, the D Street 

portal, was thus constructed well before the other portions of the I-90 connector 

tunnel.

The Ted Williams Tunnel was designed by Sverdrup Civil, Inc., and 

constructed by J. F. White/Morrison–Knudson/Interbeton. Design documents 

did not require that the tunnel roof incorporate provisions for attaching a 

suspended ceiling, and no such provisions were made in the final design. The 

design documents did note that a ceiling would be installed after the roof was 

constructed. Construction began on the tunnel in 1991.

The ceiling system for the Ted Williams Tunnel was designed in 1992 by 

Domenech Hicks and Krockmalnic, Inc., of Boston, the section design consultant for 

the Ted Williams Tunnel finishes.20 The ceiling design developed by the consultant 

consisted of 2-inch-thick precast panels of lightweight concrete21 totally enclosed in 

porcelain-enameled sheet steel. The installed ceiling panels were typically bolted 

to the bottom flanges of longitudinal structural steel channel stringers, which, in 

turn, were suspended from the tunnel roof by steel pipe struts. Each hanger and 

brace was connected to the concrete roof slab or tunnel liner by two epoxy adhesive 

anchors. The panels extended to the tiled sides of the tunnel to create a uniform 

finish for the tunnel tube.

The support system for the ceiling panels had to be designed to accommodate 

the suction loads (calculated as 55 pounds per square foot in the Ted Williams 

Tunnel) created when the tunnel ventilation system was activated. Because the 

weight of the panels was less than the negative load created within the ventilation 

plenum above the ceiling, the ceiling support system was required to work in both 

tension and compression.

A typical panel in the Ted Williams Tunnel was about 11 feet long (although 

5 1⁄2-foot lengths were also common) and 4 feet wide. The cost of the panels was 

about $50 per square foot, or about $2,200 for a typical panel. The design dead 

19 In immersed-tube tunnel construction, the tunnel segments are built elsewhere, usually floated and 

sunk into place, and then welded together.

20 Tunnel finishes included ceiling panels and their structural support systems, light fixture support systems, 

tile sidewalls, walkway finishes, utility room cross passages finishes, floor and wall finishes, roadway‐level exit 

doors and egress signage, and roadway paving and striping.

21 Lightweight concrete is made by replacing some or all of the normal-weight aggregate with lightweight 

aggregate, which is typically a heat-expanded slate, clay, or shale. The cast density of lightweight concrete is 

about 115 pounds per cubic foot versus about 145 pounds per cubic foot for normal-weight concrete.
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load22 of the panels was about 28 pounds per square foot, for a typical panel weight 

of about 1,200 pounds. A total of about 20,000 panels and their associated 24,400 

epoxy adhesive anchors23 were installed in the Ted Williams Tunnel by general 

contractor Walsh Construction Company (Walsh) of Chicago, Illinois.

For the anchor adhesive in the Ted Williams Tunnel, Walsh selected 

UltraBond Epoxy supplied by U.S. Anchor Corporation (now Adhesives 

Technology Corporation). This material was approved for use by MassHighway

in January 1994. In April 1994, Walsh submitted for approval another anchor 

adhesive, Epcon Ceramic 6 Epoxy, supplied by ITW Red Head of Wood Dale, Illinois. 

The stated purpose of the second submittal was “to ensure product availability in 

order to meet project schedule.” The CA/T project laboratory commented on this 

submission, noting that this material did not meet the material specifications and 

that the manufacturer was not on the State’s approved list. No documentation was 

found regarding resubmittals by Walsh for this product, but sometime in June

1994, according to the B/PB field engineer daily report, the contractor began using 

the Epcon material instead of, or concurrent with, the UltraBond product.

According to project documentation, installation of the ceiling in the Ted 

Williams Tunnel proved to be problematic. Contract specifications required that 

the installation contractor, before drilling, use x-ray or other technology to locate 

rebar in the tunnel roof. If rebar was encountered during drilling, workers were to 

abandon the hole and drill a new one 2 inches away. This proved to be unworkable. 

For a variety of reasons (density of the roof concrete, the amount of rebar in the 

roof, the epoxy coating on the rebar), neither x-ray nor any other technology could 

consistently locate the rebar.

At one point, almost half the drilled holes had encountered rebar and had 

been abandoned and patched. The delays caused by the redrilling threatened 

to delay the tunnel opening, and in November 1994, B/PB recommended, and 

MassHighway approved, drilling through rebar.

Early in construction, when the installed anchors were proof tested 

before being placed in service, failure rates ranged between 8 and 16 percent. A 

deficiency report was issued in response to the “extraordinarily high failure rate” 

for anchors that had been installed when water was visible on the tunnel roof. 

Project documents attributed other test failures to insufficient curing time for the 

epoxy, holes that were drilled too deep, an inadequate amount of epoxy, or holes 

that had not been properly cleaned. Dampness in the tunnel roof was also cited as 

an issue, and the anchor installation was delayed briefly because cold weather was 

thought to be inhibiting the curing of the epoxy.

22 Dead load is the weight of the materials and all fixtures and attaching parts. Live load refers to the 

transient load created by operation, environment, personnel, and equipment. The design live load for the Ted 

Williams Tunnel panels was 40 pounds per square foot.

23 About 12,200 roof hanger plates were used in the Ted Williams Tunnel, each supported by 2 anchors. 

The maximum design load supported by each anchor ranged from 2,550 to 2,950 pounds, depending on the 

location.
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In addition to the problems encountered during the drilling, setting, and 

testing of the anchors, the design of the panels also presented difficulties. The 

geometry of the tunnel required that many of the panels be fabricated to the 

dimensions of a specific location, which complicated the installation process 

and increased the time needed to fit the panels. Project managers and owner 

representatives also expressed concern about the long-term costs associated with 

maintaining the enameled ceiling.

In response to the high costs associated with the Ted Williams Tunnel 

finishes,24 the FHWA, in February 1995, convened a value engineering25 team to 

study tunnel finishes and develop recommendations for alternative finish systems. 

The stated purpose of the workshop was to “look at Tunnel Finishes...to determine if 

the overall material and construction costs might be reduced by adopting less costly 

design alternatives while still meeting finish system functional requirements.”

Before the value engineering team issued its recommendations, the 

FHWA and MassHighway asked B/PB to expedite the identification of 

cost-saving alternative tunnel finishes that could be incorporated into the 

subsequent tunnel finish contracts for the I-93 and I-90 tunnels. The management 

consultant developed medium- and low-cost tunnel finish system options, 

which it presented to MassHighway and the FHWA. The finish options chosen 

by MassHighway combined elements of the medium- and low-cost options and 

included changing ceiling panels “to epoxy painted precast panels.”

When the value engineering report was issued in March 1995, it offered the 

following options regarding tunnel ceiling finishes:

Option 0—Panel weight 30 [pounds per square foot], cost $50 [per 

square foot] approximate: porcelain enameled steel face precast 

panels on a 4’ x 6’ grid of hangers (current design).

Option I—Panel weight 35 [pounds per square foot], cost $44.69 

[per square foot]: precast panels supported on a 4’ x 6’ grid (current 

design modified to remove porcelain enamel facing).

Option II—Panel weight 50 [pounds per square foot], cost $34.55 [per 

square foot]: precast lay-in panels supported on continuous inverted 

steel tees at 12’ on center (tees are aligned with the lane edges).

Option III—Panel weight 50 [pounds per square foot], cost $46.23 

[per square foot]: cast-in-place concrete supported on continuous 

inverted steel tees at 12’ on center (tees are aligned with the lane 

edges).

24 The tunnel finishes contract for the Ted Williams Tunnel was valued at $49.5 million when it was issued 

in January 1993. When the work was completed in July 1996, the contract costs had risen to $78.2 million.

25 Value engineering is a process used to improve the ratio of function to cost, that is, to achieve increased 

function at the same cost or equal function at a lower cost.
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The report recommended that Option II be adopted for subsequent ceiling 

finishes. B/PB concurred in the recommendation “on the basis of maximum cost 

containment, for an estimated total projectwide savings of $65 million.”

The recommendation was approved by the MTA and MassHighway, and in 

June 1995, cost containment measures were implemented that included changing 

“porcelain faced concrete ceiling panels to precast concrete ceiling panels supported 

on steel tee beams.” It was thought that, because the dead weight of the panels was 

greater than the suction load created by the tunnel ventilation system, the ceiling 

suspension system, required to work in tension only, could be simplified.

I-93 Tunnel

The design consultant chosen for the I-93 tunnel finishes was a joint venture 

between Fay, Spofford and Throndike, Inc., and HNTB Corporation (FST/HNTB). 

FST/HNTB was responsible for designing a ceiling system for the I-93 tunnel 

that would incorporate the heavier precast concrete panels mandated by the 

FHWA, the MTA, MassHighway, and B/PB. The design requirement provided to 

FST/HNTB by B/PB specified that the support system for the ceiling be designed 

such that the failure of one support hanger would not result in a failure of the 

entire module. According to FST/HNTB representatives, this “one-hanger-out” 

scenario was considered in all design calculations and specifications.

In late 1996, the FST/HNTB team tasked with designing the ceiling system 

for the section of I-93 tunnel between Congress and North Streets developed a 

design that used steel beams, hanger rods, turnbuckles, and attachment plates to 

support a ceiling module of precast concrete panels. (Except for the way it was 

attached to the roof, this is the ceiling system that would later be used in the 

D Street portal.)

As with other sections of the I-93 tunnel, the section between Congress and 

North Streets had steel roof girders (I-beams) extending across the width of the 

tunnel. The ceiling support design developed by the team called for 3⁄4-inch-diameter 

threaded steel studs to be welded to the roof girders. The hangers for the ceiling 

support beams would then be attached to the welded studs using nuts and washers. 

Because the hanger attachment was steel-to-steel, a safety factor26 of at least 3 was 

specified, and calculations indicated that the design met this criterion. FST/HNTB 

provided preliminary drawings of the proposed ceiling support system through 

B/PB to MassHighway and the FHWA, both of which approved this design.

26 As used here, safety factor is the ratio of the predicted ultimate load (maximum load before failure) 

to the calculated maximum service load. The safety factor is used to allow for uncertainties in the design 

and construction process. These uncertainties could involve design calculations, material quality, installation 

practices, or the operational environment. Considerations that influence the selection of an appropriate safety 

factor include the degree of uncertainty in the design and the potential consequences if the structure should 

fail.
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Design Policy Memorandum No. 107

On March 13, 1997, MassHighway issued Design Policy Memorandum 

No. 107, subject: Tunnel Finish Details, which contained, “Clarifications to CA/T 

Directive Drawings & Implementation of Cost Containment Proposals Related to 

Tunnel Finishes.” This memorandum gave new guidance to the section design 

consultants who would be responsible for subsequent tunnel finishes.

The cost-containment changes in the memorandum related to the tiled 

concrete tunnel side wall panels and to the suspended ceiling panels. In regard to 

the latter, the memorandum directed that, in the remainder of the tunnels, ceiling 

panels were to be installed only over the travel lanes (as opposed to covering the 

entire ceiling) except as required to accommodate the tunnel ventilation system.

The clarifications and changes to the directive drawings included changes 

to the ceiling support system “in response to constructibility & schedules issues 

and lessons learned from the [Ted Williams Tunnel].” Included as attachments 

to the memorandum were the FST/HNTB preliminary design sketches related to 

the proposed suspended ceiling for the I-93 tunnel between Congress and North 

Streets. The design policy memorandum directed that the section design consultants 

responsible for subsequent tunnel finishes use the ceiling system design shown on 

the attachments, adapting it as necessary to address location-specific issues.

I-90 Connector Tunnel

The tunnel finishes section design consultant for the I-90 connector 

tunnel (which included the D Street portal) was Gannett Fleming, Inc. (Gannett 

Fleming), headquartered in Camp Hill, Pennsylvania. Modern Continental was 

the construction contractor.

Because of the problems installing adhesive anchors in the roof of the Ted 

Williams Tunnel, MassHighway had directed that the roof of the 6,300-foot-long 

I-90 connector tunnel (except for the D Street portal portion, which had already been 

built) be constructed with cast-in-place channel inserts (Unistruts27) embedded in 

the concrete. For the suspended ceiling, Gannett Fleming engineers, as directed by 

Design Policy Memorandum No. 107, adapted the ceiling system developed by 

FST/HNTB, using the embedded steel channel inserts (instead of roof girders) for 

the roof attachments.

Project records show that about 2,000 adhesive anchors were installed in the 

Unistrut portion of the I-90 connector tunnel at locations where the builder either 

did not install a section of steel channel, installed it too deeply into the concrete 

to be used, or installed it such that the roof hangers supporting the ceiling could 

not be aligned properly. At these sites, which represented about 10 percent of the 

total number of anchor locations in the Unistrut portion of the tunnel, Modern 

27 Unistrut is a registered trademark of the Unistrut Corporation and its affiliates.
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Continental used adhesive anchors to secure the ceiling hanger plates to the tunnel 

roof. Because the D Street portal was constructed without the embedded Unistrut 

channels, all of the ceiling hanger plates in that part of the tunnel were secured to 

the tunnel roof with adhesive anchors.

Design and Specifications for the D Street Portal Ceiling

Anchor Alternatives

In 1996, according to project documents, Gannett Fleming planned to 

specify the use of undercut anchors to attach the suspended ceiling in the D Street 

portal. B/PB became aware of these plans and, in a January 13, 1997, telephone call 

to Gannett Fleming, directed the design consultant not to use undercut anchors. 

According to Gannett Fleming records, B/PB cited problems another project 

contractor had experienced while installing the undercut anchors.28 The B/PB 

representative told Gannett Fleming that the directive not to use undercut anchors 

would apply project-wide and that previously installed undercut anchors would 

be removed.

After receiving this directive, Gannett Fleming continued to pursue 

approval to use undercut anchors. The company researched various types of 

anchoring systems, with particular emphasis on identifying the type of anchor 

that would perform best should flexure cracking occur in the concrete base 

material. In an August 25, 1997, letter to B/PB, Gannett Fleming summarized 

the company’s findings for three types of anchorsresin-bonded (adhesive), 

undercut, and expansion29that could be used in the D Street portal. The research 

focused only on applications in which the anchors would be in pure tension in 

cracked concrete.

Resin-Bonded. In regard to resin-bonded anchors, the Gannett Fleming letter 

referenced a research finding that, in cracked concrete, the common resin‐bonded 

anchor may retain only 40 percent, and possibly as little as 20 percent, of its normal 

(in uncracked concrete) ultimate load capacity. The letter also cited manufacturer’s 

literature to the effect that the anchor would lose strength at temperatures between 

120° F and 230° F. The letter stated that, “Meeting high temperature requirements 

as well as maintaining design capacity appears difficult with resin bonded 

anchors.”

28 According to the written phone record, B/PB noted that unless the holes were placed accurately and 

undercut properly with specialized equipment, the anchors could be pulled out by hand.

29 Expansion anchors are mechanical fasteners that expand when tightened, transferring tension loads 

from the anchor to the concrete substrate by friction.
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Undercut. In regard to undercut anchors, the letter cited a report finding 

that such anchors in cracked concrete would retain 65 to 70 percent of their 

normal ultimate load capacity and would perform similarly to steel under high 

temperatures. The letter stated that, “These anchors appear to have the desired 

characteristics for supporting the ceiling in the subject tunnel.”

Expansion. In regard to expansion anchors, the letter cited research indicating 

that such anchors, which typically do not have the capacity to post-expand in 

cracked concrete, are unsuitable for use in pure tension applications.

The letter concluded by suggesting a meeting “as soon as possible to discuss 

our findings and to obtain direction on the anchor preferred by B/PB.” Although 

no written record could be found of a subsequent meeting or discussion regarding 

anchor alternatives, B/PB at some point directed, and Gannett Fleming accepted, 

that undercut anchors would not be used in the D Street portal.

Ceiling Panel Alternatives

On January 13, 1999, Modern Continental submitted a value engineering cost 

proposal30 to B/PB suggesting an alternative ceiling system for the I-90 connector 

tunnel. The company proposed using a Celline metal panel structural ceiling system 

provided by Environmental Interiors, Inc., of Hudson, New Hampshire, in lieu of the 

precast concrete panels. The proposal stated that, based on reduced cost of materials, 

transportation, and labor, use of the Celline system could save the project $4 million. 

According to Environmental Interiors, “The entire Celline system (including optional 

full backer sheet) weighs less than 10 pounds per square foot.”

On February 24, 1999, B/PB responded that project personnel had evaluated 

the proposal and concluded that, as presented, it was unacceptable. The response 

advised that final acceptance of the proposal and permission to proceed would be 

withheld pending

1.) Review and acceptance of the vendor’s revised design and their 

structural calculations by the Project;[31] 2.) Review and acceptance 

of prototype panel testing results; and 3.) Project assessment of the 

initial system cost and its life cycle cost....

On March 9, 1999, Environmental Interiors, citing a lack of responsiveness 

from B/PB, withdrew its proposal to provide the Celline ceiling system for use in 

the I‐90 tunnel. On March 25, 1999, B/PB officially notified Modern Continental that 

the value engineering cost proposal was not considered viable for implementation 

and should not be pursued further. The notification letter stated

30 Contractors were encouraged and offered incentives to submit value engineering cost proposals that 

identified less costly or more effective alternatives for meeting project goals.

31 Meaning B/PB, MassHighway, the MTA, and the FHWA.
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Considering the current status of your material purchase orders, the 

precasters expended engineering and buy-out costs, and unresolved 

engineering issues, we agree that a substantial cost and/or schedule 

savings for this project do not appear feasible.

Anchor Loading Calculations

In an August 4, 2006, written response to a Safety Board inquiry,32 Gannett 

Fleming officials explained the design principles and load factors used in the 

contract specifications for the ceiling suspension system for the I-90 connector 

tunnel (including the D Street portal). According to that submittal, Gannett Fleming 

engineers calculated the maximum service load for each anchor as follows:

For the two-anchor roof hanger plates supporting a single vertical hanger 

rod (26 plates and 52 anchors in the accident module)

Load per anchor: 2.6 kips33 (1.8 kips dead load plus 0.8 kips live load) 

based on a 5-foot by 12-foot tributary area consistent with a hanger 

spacing of 5 feet and a panel of 12 linear feet.

Suction load that would result from maximum activation of the 

tunnel ventilation system was specified as 42 pounds per square 

foot negative load (–1.3 kips), reducing the dead load under those 

conditions to 0.5 kips per anchor.

For the four-anchor roof hanger plates supporting one vertical hanger rod 

and two diagonal rods (6 plates and 24 anchors in the accident module):

Load per anchor: 2.15 kips (1.3 kips vertical dead and live loads plus 

1.6 kips vertical component of seismic load, with this total reduced 

for allowable overstress while under seismic load).

According to the letter, Gannett Fleming specified that the construction 

contractor must use epoxy anchors capable of supporting a load of 4.0 kips (instead 

of the calculated maximum service load of 2.6 kips) to allow for possible flexure 

cracking in the concrete. A safety factor of 4 was also specified. The required 

average ultimate load of the anchor would thus be 16 kips (a 4-kip specified load 

with a safety factor of 4) or 16,000 pounds.

A Gannett Fleming memorandum documenting an October 9, 1998, meeting 

between Gannett Fleming and B/PB representatives indicates that B/PB directed, 

for the one-hanger-out scenario, “use of a safety factor of two (2) applied to the 

32 The submittal was updated by Gannett Fleming on November 2, 2006.

33 One kip (kilo-pound) equals 1,000 pounds of force.
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manufacturer’s ultimate capacities.”34 The letter to the Safety Board stated that 

Gannett Fleming engineers calculated the additional load that would be transferred 

to the remaining anchors in the event of a failure of an end hanger (identified as 

most critical). They determined that those hangers would retain a safety factor of 

2 after application of the additional load from a failed end hanger.

Anchor Selection

As the construction contractor for the I-90 connector tunnel finishes, Modern 

Continental was responsible for choosing, installing, and arranging for proof 

testing of the anchors in the D Street portal in accordance with Gannett Fleming 

and B/PB specifications. B/PB authorized Modern Continental to proceed on the 

contract on November 16, 1998.

The I-90 connector tunnel finishes contract contained two specifications for 

adhesive anchors. One of these, Specification 960.050, “Miscellaneous Metals for 

Buildings,” addressed “the requirements for miscellaneous fabrications for tunnel 

finishes and for tunnel stairways, utility spaces and passages.”

The specification regarding the ceiling support anchors was “Precast 

Concrete Ceiling System” Specification 723.480. This was a performance-based 

specification prepared by Gannett Fleming that required that the contractor

Provide chemical adhesive type anchor system to anchor support 

system to concrete structure. Provide rods, washers and nuts 

fabricated of compatible steel in the diameters and embedment 

lengths shown on the drawings. Provide adhesive consisting of 

2 component (plastic resin and catalyst hardener) mixture. Resin 

material shall remain unaffected by continuous humidity and by 

chemicals present in a vehicle exhaust type of air duct environment.

In the specification, Gannett Fleming defined the minimum design service 

loads, the minimum factors of safety, and other design criteria and installation 

requirements that had to be met with the choice of anchor. The specification did 

not contain criteria for assessing long-term performance of the anchoring system 

or detail an appropriate inspection program. 

The anchoring system selected by Modern Continental used a two-part 

(generically, a “resin” and a “hardener”) epoxy material formulated by Sika 

Corporation, of Lyndhurst, New Jersey; packaged by Powers Fasteners, Inc. 

(Powers) (formerly The Rawlplug Company, Inc.),35 of New Rochelle, New York; 

34 According to Gannett Fleming, the safety factor was within the guidelines established for the portions 

of the I-90 tunnel with embedded channel inserts.

35 In the 1990s, The Rawlplug Company, Inc., which marketed its epoxies and anchors under the Rawl 

brand, became Powers Fasteners, Inc. During the transition from Rawlplug to Powers Fasteners, the company 

was sometimes referred to as Powers Rawl.
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and distributed by Newman Renner Colony, LLC (Newman Renner Colony), 

of Westwood, Massachusetts. Sika Corporation supplied the epoxy resin and 

hardener in bulk36 to Powers, which packaged, marketed, and distributed the 

material first as Foil-Fast (supplied in foil packages under the Rawl name), then 

as Power-Fast Epoxy Injection Gel. Serving as a wholesaler, Powers packaged 

this same product for Newman Renner Colony as NRC-1000 Gold epoxy, and 

this is the name under which it was purchased by Modern Continental. On 

June 3, 1999, Modern Continental signed an agreement with Newman Renner 

Colony to purchase fasteners, hangers, anchor rods, and miscellaneous metals, 

in addition to the epoxy. The anchors themselves were threaded rods 5⁄8 inch in 

diameter and 8 inches long.

The accident investigation revealed that, although the epoxy provided by 

Powers was available in either slow-setting (Standard Set) or quick-setting (Fast 

Set) formulations,37 at the time Modern Continental entered into the purchase 

agreement for the anchoring system, Powers was packaging only the Fast Set 

version of its Power-Fast epoxy for “private label” distribution by Newman Renner 

Colony. The NRC-1000 Gold cartridge labeling at the time did not indicate that the 

material was Fast Set but showed the catalog No. 8431, which was identified by 

Powers as the Fast Set formulation.

According to internal Powers correspondence dated June 3, 1999 (the same 

day Modern Continental signed the purchase agreement with Newman Renner 

Colony), Powers was beginning the process of having the Standard Set Power‐Fast 

epoxy also packaged as NRC-1000 Gold. According to this correspondence, 

the Standard Set material was being provided to Newman Renner Colony in 

anticipation of a need for the slower-setting epoxy for future projects. The addition 

of Standard Set epoxy to the Newman Renner Colony line would require new 

labeling to indicate Fast Set or Standard Set. The correspondence indicated 

that Newman Renner Colony had placed an order for 1,000 units of the catalog 

No. 8431 (Fast Set) material and had placed an initial order for 120 units of the newly 

packaged Standard Set epoxy to be used for U.S. Department of Transportation 

(DOT) projects requiring an International Conference of Building Officials 

certificate (the correspondence did not indicate which DOT projects were being 

referenced). The correspondence stated, “We [Powers] have told them [Newman 

Renner Colony] that production for this product [the Standard Set formulation 

packaged as NRC-1000 Gold] would be 4-6 weeks.”

36 Sika Corporation supplied the epoxy components in bulk to Powers until 2002, when the company 

began to market the product itself under the Sikadur brand. At that time, the company began supplying the 

material to a third company, which then packaged the epoxy both for Sika Corporation and for Powers. Sika

Corporation’s fast-setting version is marketed as Sikadur Injection Gel AnchorFix-3.

37 Powers product literature reports that its Standard Set formulation takes about twice as long to 

gel (begin to harden) as the Fast Set. For example, at 75° F, the listed gel time for Standard Set epoxy is 

35 minutes versus 15 minutes for Fast Set. Qualification testing indicated that, at a base material temperature 

of 75° F, minimum curing time (during which the anchor should not be disturbed) was 2 hours for Fast Set and 

6 hours for Standard Set. Full curing (the minimum time required for maximum load capacity) was 24 hours 

for both formulations.
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The Powers manual current at the time of the D Street portal ceiling design 

was the Fastening Systems Design Manual, second edition (dated 1997).38 In regard 

to the two epoxy formulations, the manual stated

Power-Fast Epoxy Injection Gel is available in either fast and slow 

setting versions to provide the installer with a choice of gel and 

curing times. For example, in warmer weather, the slower setting 

version is normally used as it allows the installer time to properly 

fill anchor holes prior to the point at which the material begins to gel 

or solidify.

The manual provided different values for the Fast Set and Standard Set 

versions in regard to tensile strength, flexural strength, and slant shear strength, 

but it did not indicate any differences in the bond strength or long-term behavior 

of the two epoxy types in anchor applications. The tables of ultimate strength and 

allowable strength (calculated from the ultimate strength using a safety factor of 4) 

for various anchor and base material combinations applied to both formulations.

The Power-Fast39 anchoring system (at that time, the Rawlplug Foil-Fast 

Injection Gel anchoring system) had been tested in 1992 in accordance with 

standards established by the International Conference of Building Officials (ICBO),40

an organization that promulgated standards and published independently 

generated physical property data on manufacturers’ products, including adhesive 

anchors. The test results for the Power-Fast system (as well as for Powers 

Chem-Stud Capsule adhesive anchoring system) were contained in the April 

1992 version of ICBO Evaluation Service, Inc. (ICBO ES), evaluation report (ER) 

4514 (ICBO ER-4514). That report made no distinction in the bond strength or 

long-term performance of the Powers Fast Set versus Standard Set epoxies.41

By 1997, Powers was in the process of expanding and updating the 

information in the ICBO evaluation report for its Power-Fast epoxies. As part of 

this process, additional testing was performed on the epoxies by CTI Engineering 

(subsequently CEL Consulting), of San Lorenzo, California, in accordance with 

ICBO Acceptance Criteria (AC) 58, Acceptance Criteria for Adhesive Anchors in 

38 The information in the 1997 version of the Powers manual was identical to that in the 1992 version of 

ICBO Evaluation Service, Inc., evaluation report 4514, also discussed in this section.

39 All the data pertaining to this product would apply equally to the NRC-1000 Gold epoxy used in the 

D Street portal.

40 In 1994, the ICBO, along with the Building Officials and Code Administrators International, Inc. (BOCA), 

and the Southern Building Code Congress International, Inc. (SBCCI), founded the International Code Council 

(ICC) to develop a single set of international codes without regional limitations.

41 Although testing done for ICBO (now ICC) qualification is performed by independent testing agencies, 

the testing is funded by the manufacturer of the product being evaluated, and the manufacturer has substantial 

influence on the content of the final evaluation report.
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Concrete and Masonry Elements and ASTM42 E 1512, Standard Methods for Testing 

Bond Performance of Adhesive-Bonded Anchors.

A CTI Engineering report initially issued in March 1996 and reissued in 

March 1997 detailed the results of a 120-day creep43 test performed by the company 

on the Power-Fast Standard Set epoxy. This test was performed in accordance with 

the provisions of the January 1995 edition of AC58, and the Standard Set epoxy 

passed.

AC58 did not require creep tests, but the criteria did specify it as an 

optional test. The optional test was a pass/fail test under which the tested material 

was subjected to one load at a single temperature for a specified time. Powers 

representatives confirmed that the Rawl Foil-Fast (later renamed Power-Fast) 

Fast Set epoxy had been creep tested in 1995 and 1996. These tests were done in 

accordance with AC58 standards, which required that the anchors be tested at 

110° F under a load of 40 percent of the ultimate anchor strength as measured at 

70° F. The Fast Set epoxy failed the tests. Documents acquired by the Safety Board 

showed that, in this same time frame, Powers pursued additional creep testing of 

Fast Set epoxy anchors at lower loads or lower temperatures than those specified 

in AC58. Some anchors were tested at 110° F under loads of 40 percent and 25

percent of the ultimate anchor strength at 70° F. All of these anchors pulled out in 

less than 2 days. Anchors also failed when tested at 90° F and 70° F under a load of 

40 percent of the ultimate strength at 70° F. No evidence was found that the Fast 

Set epoxy formulation that was available in the mid-1990s had ever passed a creep 

test at any temperature.

The Safety Board obtained a copy of an August 15, 1996, letter from Powers 

to the epoxy formulator (Sika Corporation) in which Powers referenced the failed 

creep test on the Fast Set material. The letter asked Sika Corporation to compare 

the Powers Fast Set epoxy with other epoxies that had passed the creep test in an 

attempt to determine whether the Fast Set could be reformulated to pass the test. 

No source of the difference in performance was identified by the test method used, 

and the epoxy was not reformulated.

Powers representatives told the Safety Board that the company was not 

able to recover all of its quality control records for 1997 and 1999 but that, based 

on records that were available, no anomalies had been identified in the Fast Set or 

Standard Set epoxies sold in that time frame. Additionally, recovered records for 

two batches of the Power-Fast epoxy sold under the NRC-1000 Gold label from 

1997 through 1999 did not indicate any anomaly in the product.

Sika Corporation representatives reported that between 1997 and 1999, a 

single batch of the resin that failed to satisfy the company’s internal quality control 

42 ASTM International, formerly known as the American Society for Testing and Materials, is an international 

standards organization that develops and publishes standardized testing methods used to evaluate a wide 

range of materials, products, systems, and services.

43 Creep is a gradual, continuing deformation of a material under sustained load.
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tests was discarded. One batch of the hardener was also rejected before quality 

control testing. All batches of the resin and hardener provided in bulk by Sika 

Corporation to Powers from 1997 to 1999 met Sika Corporation’s internal quality 

control standards.

Anchor Approval

The D Street portal construction contract required that Modern Continental 

submit for approval documentation that addressed the technical qualifications 

of the chosen adhesive anchoring system. These documents would be evaluated 

and approved by Gannett Fleming and reviewed by B/PB for acceptability and 

compliance with the contract specifications.

The first three anchor adequacy submittals forwarded by Modern 

Continental for approval were returned, unapproved, with a request for additional 

information. In December 1999, Modern Continental prepared a fourth anchor 

adequacy submittal. The anchor service load data in the submittal were the values 

calculated and specified by Gannett Fleming. The anchor load capacity data were 

taken from the Powers design manual, second edition. According to the manual, 

the Powers adhesive anchors were capable of supporting up to 6,350 pounds44

each (in 4,000-psi concrete) while maintaining a safety factor of 4 against ultimate 

load (in this case, 25,400 pounds). The data included in the submittal made no 

reference to which epoxy formulation was to be used.

This fourth submittal also included a copy of a draft revision of ICBO 

ER-4514 dated October 1999. Modern Continental included this draft report 

in response to a specific request by the Gannett Fleming engineer based on his 

review of a previous submittal. The draft report revision limited the use of the 

Power-Fast Fast Set epoxy to “short term loads such as those resulting from wind 

or earthquake forces.” For anchors embedded 5 inches into 4,000-psi concrete, the 

allowable load tables showed lower loads (than the then-current Powers manual) 

for Standard Set epoxy and specified an additional 25-percent reduction in the 

allowable loads for Fast Set.45

On December 17, 1999, the anchor capacity structural calculations were 

certified by a registered professional engineer employed by Sigma Engineering 

International, Inc., of Lincoln, Rhode Island. A note adjacent to the engineer’s seal 

stated

44 This value was interpolated from data contained in the 1992 version of ICBO ER-4514 and in the 

second and third editions of Powers design guides (1997-2001), which did not provide load capacities for 

exactly 5 inches of anchor embedment.

45 The 1999 draft and February 2000 final versions of the ER-4514 reissue did list data for 5-inch 

embedment, and these data indicated an allowable load of 5,150 pounds when using Standard Set epoxy, 

resulting in an allowable load of 3,862 pounds for the Fast Set formulation for these anchors. The current 

Powers design manual lists the same allowable loads. ICBO ER-4514 was being reissued at the request of 

Powers as part of the effort by that company and Newman Renner Colony to have the anchors qualified for 

use on California Department of Transportation projects.
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The calculations were performed to compare the anchor minimum 

design service loads, per project specification...with the allowable 

loads provided by the anchor bolt manufacturer only.

The anchor adequacy submittal was received by Gannett Fleming on 

December 30, 1999. On January 7, 2000, Gannett Fleming authorized the contractor 

to proceed with the anchor installation (which had been underway since the 

previous July) pending final approval of the anchors. The contractor was also 

directed to provide the final version of the revised ICBO ER-4514 when it became 

available.

The final version of the reissued ICBO ER-4514 was dated February 2000. 

This version of the report, like the October 1999 draft that had preceded it, 

distinguished in the report text between the Fast Set and Standard Set formulations. 

The “Findings” section of the report advised

That the...Power-Fast Adhesive Anchor System described in this 

report comp[lies] with the 1997 Uniform Building Code,TM subject to 

the following conditions [abridged from the 13 conditions listed in 

the report]:

4.10 Use of Power-Fast Epoxy Adhesive...anchors in concrete to resist 

earthquake loads, wind loads, dead loads or live loads is permitted as 

noted in the tables. The tabulated allowable load values in the tables 

may be increased by 33 1/3 percent for short-term loads, such as wind 

or earthquake loads...as permitted in the tables. The allowable load 

values for the Power-Fast Epoxy Adhesive, Standard Set, installed 

with threaded rod, fully threaded bolts, or reinforcing steel may be 

increased for short-term loads, such as wind or earthquake loads. The 

allowable load values for the Power-Fast Epoxy Adhesive, Fast Set, 

installed with threaded rod or fully threaded bolts is permitted for 

short-term loads, such as those resulting from wind or earthquake 

forces only. [Emphasis added.] The allowable load values for PowerFast Epoxy Adhesive, Fast Set, used with reinforcing steel is permitted 

for short-term wind loads only.

Tables included in the report showed that, for a 5⁄8-inch-diameter anchor in a 

3⁄4-inch-diameter, 5-inch-deep hole in 4,000-psi concrete, the allowable tension load, 

based on a safety factor of 4, was 5,150 pounds. From this, an average ultimate load 

capacity of 20,600 pounds can be calculated. Footnotes to the tables of allowable 

loads indicated that the safety factor for the Fast Set formulation should be 5.33 

rather than 4 as recommended for the Standard Set epoxy. This reduction would 

result in an allowable tension load of 3,863 pounds for Fast Set epoxy anchors.46

46 These values address only the load capacity of the epoxy bond, which in all cases is less than the 

tensile strength of the 5/8-inch by 8-inch 316 stainless steel threaded rod.
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Provisions of AC58 at that time required that a safety factor of 5.33 be 

applied to adhesives that had not passed the optional creep testing (either because 

they had not been tested for creep or because they had been tested and failed) and 

that these adhesives be used for short-term loads only.

On February 4, 2000, Gannett Fleming (with secondary review by B/PB) 

approved Modern Continental’s anchor submittal, thus authorizing use of the 

anchoring system that had been installed in the failure area in late summer 1999.

None of the approval documentation identified the epoxy formulation 

that was being used or that was approved for use in the D Street portal. The only 

mention of two epoxy formulations was in the revised ICBO ER-4514 that was 

included with the final anchor adequacy submittal. Representatives of Modern 

Continental initially told Safety Board investigators they were “99 percent” certain 

that Standard Set epoxy had been used in the D Street portal ceiling installation. 

Later, they said they did not know which formulation had been used.

Project documents dated September 1999 show the purchase and delivery, 

from Newman Renner Colony, of Power-Fast epoxy, catalog No. 08402, which has 

been identified as the Fast Set material. Additional invoices and packing slips were 

located for the years 2000 and 2001 that show NRC-1000 Gold, catalog No. 8431 

(the Fast Set version), being purchased for this contract. No documentation was 

found of any other epoxy being delivered for use on the D Street portal contract.

Anchor Testing Requirements

The section design consultant for the tunnel finishes in the Ted Williams 

Tunnel had specified a progressive testing program under which a portion of 

the installed adhesive anchors were to be proof tested to 125 percent of their 

maximum design service load. The procedure was considered progressive because 

the number of anchors that would be tested would be based on the failure rates; 

that is, if a higher than expected number of anchors were to fail the initial proof 

tests, additional anchors would then be tested. If the failure rates were lower than 

expected, fewer additional anchors would require testing.

A December 1998 report by the Massachusetts Inspector General47

characterized these testing specifications as “confusing and unclear,” resulting 

in numerous change orders and changes to specifications, which in turn led to 

additional costs to the project. Based on this experience, the testing procedures 

were modified for the D Street portal. In a September 23, 1998, facsimile transmittal, 

B/PB directed that Gannett Fleming’s contract specifications require that all

anchors installed in the D Street portal be tested to 125 percent of their maximum 

design service load.

47 Commonwealth of Massachusetts, Office of the Inspector General, A Review of the Central

Artery/Tunnel Project’s Use of Anchor Bolts on the C05B1 Tunnel Finishes Contract, Publication

No. 18248-40-5C-12/98 IGO, December 1998.
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On the basis of this requirement and the company’s calculated maximum 

design service load, Gannett Fleming required that the installation contractor 

employ an approved independent testing agency to test each anchor to 3,250

pounds (1.25 x 2,600 pounds).

Anchor Installation Procedures

Contract Requirements

Requirements for the installation and testing of the adhesive anchoring 

system to be used in the D Street portal were set out in the contract between 

Modern Continental and MassHighway. The contract emphasized that the epoxy 

manufacturer’s instructions should be followed, but it also specified certain 

procedures related to the locating, drilling, and cleaning of anchor holes. The 

contract specified that anchors should not be disturbed or loaded until after the 

manufacturer’s minimum cure time.

During the bid phase, an addendum was added to the contract that 

contained additional directives regarding the installation of the adhesive anchors. 

Compliance with the manufacturer’s instructions was again stressed, and the proof 

testing procedure was specified. The addendum also permitted drilling through 

rebar.

Epoxy Supplier’s Recommended Procedures

The second edition of the Powers Rawl Fastening System Design Manual, 

which was current at the time of the D Street portal ceiling installation, addressed 

drilling and preparing anchor holes and using the product in cold weather. The 

manual also provided specific installation guidelines. For solid base materials, the 

(abridged) instructions are as follows:

• Drill a hole to the size and embedment required.

• Blow the hole clean with compressed air, brush the hole, and blow 

it clean again. Holes should be clean and sound. They may be dry or 

damp, but should be free of standing water or frost.

• Be sure to properly balance the mixing nozzle prior to dispensing and 

when changing cartridges.... Fill the hole approximately half way with 

epoxy starting from the rear of the hole. Slowly withdraw the static 

mixing nozzle as the hole fills to avoid creating air pockets within the 

hole.

• Push the threaded rod or reinforcing bar into the hole while turning 

slightly to insure positive distribution of the epoxy. Be sure the rod is 

fully seated at the bottom of the hole and that some epoxy has flowed 
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from the top of the hole. The threaded rod or reinforcing bar used should 

be free of dirt, grease, oil, or other foreign material.

• Allow the epoxy to cure for the specified time prior to applying any 

load. Do not disturb or load the anchor until it is fully cured.

The manual stated that Power-Fast Epoxy Injection Gel can be used for 

overhead installations of threaded anchor rods. The overhead anchor holes should 

be prepared using the standard procedure with the following exceptions:

• After the anchor hole is drilled and cleaned, insert the proper size anchor 

seal plug [a flanged plastic plug] into the hole [to retain the adhesive 

and hold the anchor centered in the hole until the adhesive sets].

• Insert the Power-Fast mixing nozzle through the seal plug and fill the 

hole halfway starting from the bottom or rear of the hole.

• Insert the threaded rod through the seal plug, turning it slightly to 

ensure proper distribution of the epoxy.

• Be sure the anchor rod is fully seated at the bottom of the hole and some 

epoxy has flowed from the opening in the seal plug.

The seal plugs used in the D Street portal were made of red polyethylene 

material. Because such plugs are typically tight against the anchor hole and because 

epoxy does not bond well to the polyethylene material of the plugs, the installation 

of the seal plugs reduces the effective embedment depth of the anchors (by an 

amount between 0.5 and 0.9 inch owing to the geometry of the plug). Although 

the strength of adhesive anchors is highly dependent on the embedment depth, 

the design manual did not indicate that the use of seal plugs might reduce the load 

capacity of a particular anchor below that published in the bond strength tables.

Anchor Installation as Described by Modern Continental

Representatives of Modern Continental provided the Safety Board with 

the procedures the company said were used to install the adhesive anchors in 

the D Street portal. These procedures essentially followed the Powers installation 

guidelines.

All anchor holes in the D Street portal were drilled by a two-person crew. 

The crew would begin by positioning the drill base on the roof of the tunnel at 

the proper location to center the drill bit. Once in position, the drill unit was held 

in place through the use of an air pump that created suction between the drill 

base and the tunnel roof. The suction was sufficient to support the weight of the 

drill without manual assistance. The crew could usually drill several holes before 

having to reposition the lift truck on which they were working.
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One of the workers responsible for drilling the holes and setting the anchors 

described the procedure as follows:

Hole Drilling

• A two-person crew, after using a scissors lift to raise themselves and the 

water-cooled drill to the roof of the tunnel, would line up the drill with 

a mark placed on the ceiling by the surveyors, secure the drill to the 

ceiling, and drill the hole using a diamond-tipped wet core drill.48

• The crew initially judged the depth of the hole either by markings on the 

drill bit or a drill stop; once the hole was drilled, the workers lowered 

the drill and checked the depth of the hole with a tape measure.

• The crew drilled holes for several days or a week before cleaning them 

using an “iron” (round wire) brush, which was inserted in the hole and 

moved along its length several times.

• Finally, the crew used compressed air to blow out the holes, which 

would then be allowed to dry 2 or 3 days.

Anchor Setting

• Two workers installed the adhesive anchors: one worker injected epoxy 

into the hole, and the other inserted the anchor.

• The workers injected the epoxy through the “red cap” (seal plug) that 

had been placed in the hole after the hole was cleaned.

• The epoxy nozzle was “bottomed out” in the hole (inserted until it 

touched the closed end of the hole) and slowly withdrawn as the epoxy 

was being dispensed.

• After the hole was completely filled with epoxy, a worker inserted a 

precut anchor (threaded rod) into the hole through the red cap. The 

anchor was twisted as it was inserted.

• Any excess epoxy was wiped away, and the portion of the bolt extending 

from the hole was checked for length.

The worker also said that he would run some epoxy out of the gun when 

using a new cartridge to ensure that the epoxy was mixed properly before it was 

injected into an anchor hole. The worker stated that he believed the epoxy being 

used might have been the Fast Set version. The worker said that the training he 

received on drilling and using the epoxy consisted of instruction, demonstration, 

and observation during the first days of work.

48 A diamond-tipped core drill is used primarily for cutting large-bore holes in masonry or concrete. The 

bit is in the form of a hollow cylinder, and the cutting edge, which is embedded with industrial diamonds, cuts 

a ring to the depth required. The core is then broken off to form a hole. In a wet core drill, water is injected 

through the bit for cooling. (The water also removes some of the cut material.)
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A second worker gave a similar description of the drilling and setting 

process. He recalled that an electric air compressor was used to clean the holes. 

The second worker stated that he was trained to use the drill and the epoxy by the 

first worker.

Safety Board investigators also interviewed the foreman of the installation 

crews. His account of the drilling and adhesive process was similar to those 

provided by the two workers. The foreman said that a limited amount of epoxy 

was maintained on-site in a heated work trailer, and when that supply ran out, he 

obtained more from the Modern Continental office in Boston, which kept some 

epoxy on hand and ordered additional cases of cartridges as needed.

Installation of the D Street Portal Ceiling

Hole Drilling

According to the B/PB field engineer daily report,49 Modern Continental 

employees and contractors began surveying and laying out the locations of the 

holes to be drilled in the D Street portal roof on June 7, 1999, and prototype core 

drilling began 3 days later. Two Modern Continental laborers, working atop a 

snorkel lift, used a Hilti DD 100 wet diamond core drill to drill the holes. The drilling 

crews began at the east end of the eastbound tunnel. Two Modern Continental 

supervisors and a Hilti Corporation representative were on hand to observe the 

drilling operation and, in the case of the Hilti representative, to provide instruction 

in the use of the equipment.

B/PB engineers on the scene observed the drilling of eight holes, none of 

which struck rebar. In drilling additional holes, the Modern Continental drilling 

crew often encountered rebar. They abandoned some of these holes until, on the 

advice of the Hilti representative, they adjusted the drilling rig to lower the rpm 

and decrease the amount of water entering the bit. According to the field engineer 

daily report, after these adjustments, the crew could drill through rebar “in about 

10 minutes.” The crew then returned to previously abandoned holes and redrilled 

them to the proper depth. By June 25, 1999, a total of 117 holes had been drilled, 

and drilling continued at an average rate of 20 to 40 holes per day.

49 Most of the entries in the field engineer daily report regarding anchor installation and testing were 

made by the field architect for the I-90 tunnel finishes. This same individual had also been the field architect 

for the finishes in the Ted Williams Tunnel. He told investigators he was assigned this role largely because, as 

a former boat-builder, he had previous experience with epoxy (though not with epoxy anchors).
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Installation and Testing of Anchors

The B/PB field engineer daily report recorded that the first 30 anchors 

installed in the D Street portal were set in epoxy, in the HOV mock-up area,50

on July 28, 1999. An additional 52 anchors were set the following day, July 29, 

at which time the engineer noted that the workers were installing the epoxy and 

anchors without blowing out the holes with compressed air as recommended by 

the epoxy supplier.

Proof testing of the installed anchors began on July 30, 1999. The tests were 

conducted by Conam Inspection Services (Conam) of Auburn, Massachusetts, 

an independent testing firm hired by Modern Continental and approved by 

MassHighway. The contract specified that proof testing would consist of applying 

a tension load of 3,250 pounds (125 percent of the design service load) to each 

anchor for a period of 2 minutes.51 (While this testing was in progress, workers 

were continuing to drill holes and set anchors in other parts of the tunnel.)

The daily report noted that 36 anchors were tested on July 30, with 3 failures. 

Testing resumed 3 days later, on August 2, 1999. On that day, 35 anchors were 

tested, and 3 failed. At each failed anchor, workers used a carbide-tipped drill bit 

to remove the epoxy material from the hole. They then cleaned the hole, injected 

fresh epoxy, and installed a new anchor. Each replaced anchor was then retested 

to the same tension load as before.

On August 9, 1999, a crew of ironworkers began installing the ceiling 

hardware in the HOV tunnel. The B/PB field engineer noted that by the end of the 

day, the crew had installed 25 roof hanger plates and 17 hanger rod assemblies.

While the ironworkers were attaching hanger plates and rod assemblies, 

Conam personnel were continuing to perform proof tests in the eastbound and 

HOV tunnels. The field engineer noted that in the HOV tunnel, four anchors were 

tested with two failures. Both of these failures were anchors that had failed the test 

previously and had been replaced. The engineer’s daily report stated that one of 

these anchors passed the proof test but was seen to turn when a nut was threaded 

onto it. The other anchor held the weight, but during the testing it displaced by about 

1⁄2 inch from the tunnel roof. Both anchors were to be replaced and retested.

Anchor drilling, setting, and testing continued in the D Street portal through 

the end of September 1999. The field engineer daily report (which might not have 

documented all the testing) recorded 548 tests with 38 failures.

50 The HOV mock-up area was the first section of the D Street portal where anchors were set and ceiling 

panels were installed. This area was used to develop and refine the techniques and procedures that would be 

used in setting the anchors and installing the ceiling panels in the rest of the tunnel.

51 The investigation could not confirm that each proof test load was held for the specified time period.
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Hanging of Ceiling Panels

Based on contract specifications, the precast concrete panels used for the 

ceiling in the I-90 connector tunnel were shipped to the construction site on flatbed 

trailers. A module fabrication area was established as close as possible to the site 

of the final installation, and a wood timber bed was set up to provide a work space 

area for module assembly. The structural steel support elements for a module were 

first set into position on the beds, and the concrete panels were unloaded onto 

them directly from the flatbed trailers. The panels were then bolted into position 

and secured to the structural steel.

Once assembled, the ceiling module was placed onto a special 

trailer-mounted ceiling installation lift and trucked to its intended erection location. 

The lift then raised the module into position and supported it while a crew of 

ironworkers attached the panel support beams to the previously installed hanger 

assemblies. According to the specifications, the lift allowed fine adjustments to 

be made to module location in both transverse and longitudinal directions and 

allowed the module to be tilted to follow the roadway profile. The lift supported 

the ceiling module until all the vertical hangers had been connected, after which 

the ironworkers made adjustments to plumb and level using the support rod 

turnbuckles.

An ironworker who worked for a short time installing the ceiling modules 

told investigators that his crew was responsible for attaching the diagonal rods to 

the panel supports at the bottom and to the four-anchor roof hanger plates at the 

top. He said the module would be supported for some period of time, perhaps 

for as long as a week, from the vertical rods alone before the diagonal rods were 

installed and final adjustments were made for plumb and level.

According to the field engineer daily report, the ceiling module involved 

in this accident was one of five modules installed on November 17, 1999. By early 

December 1999, all the ceiling modules had been erected in the eastbound and 

westbound D Street portal tunnel bores.

Preaccident Anchor Failures

HOV Tunnel

On October 7, 1999, Modern Continental’s senior project manager for the I-90 

tunnel notified B/PB that the company had become aware of problems involving 

“a small percentage of adhesive anchors in the HOV ceiling mockup....” The letter 

reported that the anchors showed signs of tensile movement that had created gaps 

between the roof of the tunnel and the ceiling hanger plates.
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The letter noted that the affected ceiling module had been erected in early 

August 1999 and that no problems were evident at that time. On September 9,

1999, a Modern Continental worker installing tunnel ventilation ductwork above 

the ceiling noticed that one or more ceiling hanger plates had displaced from the 

tunnel roof by about 1/16 inch.

Periodic subsequent inspections by Modern Continental revealed increased 

movement in some of the hangers, with a “worst case” movement, in early October

1999, of 1/2 inch (later reported to be 9/16 inch). This finding prompted Modern 

Continental to notify B/PB of the displaced anchors. The notification letter 

concluded

Whereas these anchors have been installed and tested in accordance 

with contract documents, [Modern Continental] respectfully requests 

direction pertaining to any repair or mitigative measures required.

B/PB responded to this notification by letter on October 12, 1999. The 

letter stated that, while the management consultant concurred that the anchors 

had been tested in accordance with contract requirements, it could not confirm 

that the anchors had been correctly loaded. The letter referenced a review of the 

ceiling system that had found several loose turnbuckles, which “could induce 

excessive loading to the point that the anchors may be over stressed which may 

cause movement.”

The letter suggested other possible causes for the anchor movement, such 

as improper ceiling erection procedures (removing lift support too quickly or in 

such a manner as to overstress the anchors before the uniform loading of all the 

turnbuckles) or failure to properly prepare and clean the drilled holes “which 

could cause a bond failure of the adhesive to the concrete over time.”

The letter directed that Modern Continental have the supplier of the adhesive 

anchor bolt system review the installation of the failed anchors and recommend a 

solution. In the meantime, B/PB would confirm that the ceiling load calculations 

were correct. The letter concluded

In summary, [Modern Continental] shall confirm that the ceiling 

system is properly installed and all connection points are providing 

the correct support. Anchors that have moved since ceiling installation 

shall be abandoned and/or removed and replaced. When replacing 

the defective anchors, insure that proper measures are provided to 

support the ceiling so that other over stressed conditions are not 

created.

On October 13, 1999, according to the field engineer daily report, 

the B/PB field architect met with representatives from Modern Continental 

and Powers atop the ceiling in the HOV mock-up area to discuss the anchor 

displacement. According to the daily report, the Powers representative did not 
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offer any conclusions or analysis at that time, instead deferring until he could 

consult with Powers engineering staff.

On October 21, 1999, another Powers representative met with Modern 

Continental and B/PB personnel to discuss the possible cause of the anchor 

displacement in the HOV tunnel. This Powers representative also examined the 

displaced anchors and reviewed and discussed with B/PB and Modern Continental 

personnel the anchor installation and testing procedures and the module erection 

process.

In an October 29, 1999, letter to Modern Continental, Powers documented 

the findings of the company’s examination of the displaced anchors. The letter 

stated that the Powers representatives had visually inspected the displaced 

anchors with the objective of answering the question, “Why would an anchor that 

was successfully proof loaded and believed to be correctly installed, move after 

the ceiling hanger plates were installed?”

The Powers letter stated that the company representative used a torque 

wrench to check the applied torque of the anchors that showed movement as well 

as those that had not moved. He reported torque values of 120 foot-pounds, which 

were greater than the recommended 50 to 90 foot-pounds.

The Powers letter also included responses to general questions that had 

been posed by Modern Continental representatives at the time of the anchor 

assessment. Those responses are summarized as follows (and directly quoted as 

indicated):

• “Please refer to the attached excerpt from Powers’ Fastening Systems 

Design Manual, Second Edition, Section 22.4.1 entitled ‘Displacement.’” 

[The text accompanying the referenced displacement curve stated: “As 

an anchor is loaded to its ultimate (failure) load capacity, displacement 

of the anchor relative to the base material will occur.”] If an appropriate 

factor of safety is applied to the ultimate load capacity of the adhesive, 

then displacement should not occur provided that the proper installation 

procedures were employed.

• Any movement in the anchor may be an indication that the allowable load 

capacity of the particular installation has potentially been exceeded.

• It is possible that an improperly installed anchor could pass a proof load 

test provided a sufficient safety factor has been used. Powers Fasteners 

recommends a safety factor of 4, “but it appears that a higher safety 

factor has been used based on comparing the proof load of your field 

test with the published ultimate tensile bond strength.”

• “Adhesive anchoring problems typically reveal themselves immediately 

in a testing environment and do not manifest themselves over a period of 

time.” For example, dust in the drilled hole would probably have caused 

the anchor to move during proof testing. Improperly mixed adhesive 
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typically would not fully cure and would remain somewhat sticky, which 

would be apparent during proof testing.

• “Overstress” usually refers to conditions where the nut has been 

overtorqued.

• Because Powers Fasteners did not design the roof hanger plate assembly, 

the company cannot address “the different loads that may be acting on 

these anchors.”

The Powers letter concluded as follows:

While we [Powers] believe that the existing anchors subjected to 

torque exceeding our recommended range may be acceptable, the 

only way to verify their suitability is by performing a proof load test. 

Successful proof load test results would indicate that the anchors are 

still functional. Nuts should then be reapplied to the tested anchors 

with a torque that is within our recommended torque range.

No evidence was found that Powers took any further action in regard to 

the anchor displacement in CA/T tunnels after the 1999 anchor examination and 

submission of findings.

On November 8, 1999, Modern Continental wrote to B/PB and included 

the Powers letter as an attachment. The contractor cited the findings by Powers to 

argue that the anchor displacement in the HOV tunnel was not caused by a failure 

to properly clean the anchor holes. The company also stated that the ceiling panels 

were erected in accordance with the approved procedure in the presence of the 

B/PB engineer. Additionally, the contractor stated that, given the parameters of 

the ceiling design (approximate module weight, number of anchors supporting 

the module, and tensile capacity of the anchor) and the applied factors of safety, 

“it is improbable that the anchors were overstressed as a result of erection loads or 

the erection procedures.”

The letter concluded:

Per the recommendations of [Powers], Modern Continental 

Construction will remove and replace the anchors which exhibited 

movement, and will proof test the anchors subjected to torque values 

higher than the manufacturer’s recommended values in order to 

verify the anchor capacity....

B/PB acknowledged receipt of this correspondence in a November 11, 1999, 

letter to Modern Continental. The letter stated that the management consultant 

did not agree with the contractor’s position that all elements of the ceiling had 

been installed in accordance with the contract in that “adhesive anchors are over 

torqued and the ceiling hangers are not loaded uniformly. [Only when] the anchors 
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in question are removed and inspected can a determination be made of correct or 

incorrect installation techniques.”

B/PB concurred with the Modern Continental plan to remove and replace 

the displaced anchors and to proof test anchors subjected to torque values higher 

than the manufacturer’s recommended values. In reference to the action items 

contained in B/PB’s October 12 letter to Modern Continental, the management 

consultant held “open” (yet to be completed) the requirement that the contractor 

confirm that all roof hanger plates were correctly loaded and that they were carrying 

uniform loads. In regard to its own action item, the consultant reconfirmed that 

the design loads for the ceiling had been correctly calculated.

According to the B/PB engineer daily report, on November 12, 1999, 

Conam representatives performed a proof-load test on the HOV anchor that had 

shown the most displacement (9/16 inch). The reports indicated that this anchor 

had passed the 3,250-pound proof test on July 30, 1999, the first day of anchor 

proof testing. The engineer noted that, when the standard test load was applied 

on November 12,

the bolt held for a few seconds, then began to pull out with almost no 

resistance.... Upon examining the pulled-out bolt, it appeared to lack 

sufficient epoxy to fully fill the drilled hole. Also, there was a significant 

amount of concrete dust adhered to the epoxy surrounding the bolt, 

usually an indication that the drilled hole was not completely cleaned 

out prior to installation. The epoxy nearest to the embedded tip of the 

bolt was brittle and easily crumbled, usually an indication of improper 

mixing of resin and hardener. The epoxy near the exposed end of 

the bolt (but still in the embedded portion) appeared to be fully and 

properly cured. This would indicate the mixture of resin and hardener 

was not uniform during the injection of epoxy into the drilled hole. In 

spite of this combination of installation deficiencies, it appears the bolt 

was able to develop just enough strength to pass the pull-out [proofload] test. However after several weeks of constant loading by the 

ceiling module, the bond was broken, and the bolt began to slip out.

Field reports for November 9 and November 15, 1999, documented tests 

performed by B/PB and Modern Continental engineers to verify the torque values 

of adhesive anchors in the D Street portal (in response to the Powers findings). 

For the November 9 tests, the engineers randomly selected 66 anchors (one-third 

of the installed total) in a section of the westbound tunnel. On November 15, a 

random selection of 64 anchors from a section of the eastbound tunnel was tested. 

According to the daily report,

All tested bolts were found to require between 1⁄8 and 1⁄4 turn to ‘click’ 

the torque wrench, which was set at 75 ft-lbs. The manufacturer’s 

recommended torque for 5⁄8” bolts is 50 to 90 ft-lbs, hence 75 ft-lbs is 

acceptable.
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On December 1, 1999, B/PB issued Deficiency Report 001 regarding the 

failed anchors. The report noted that, “At least five adhesive anchors in the area 

of ceiling module HOV079 have failed, that is pull-out has been observed, since 

the hanging of the ceiling module.” A diagram included with the report showed 

hanger displacements from 1/16 to 9/16 inch. The diagram also identified four 

loose vertical hanger rods and one loose diagonal rod in the affected module.

Modern Continental responded to the deficiency report on 

December 2, 1999, detailing the actions the company was taking to resolve the 

issue. The response referenced the October 21, 1999, on-site review by a Powers 

representative and noted that, “Based on information gathered on site, which 

included a visual inspection of the anchors in question, a determination of failure 

could not be made.”

Modern Continental proposed to address the deficiency by following 

procedures recommended by Powers in a November 30, 1999, submittal to the 

contractor. These procedures were similar to those that Modern Continental had 

used when anchors had failed in initial proof testing; that is, the displaced anchors 

would be extracted and all debris removed from the hole. The hole would be blown 

out with an air compressor, brushed out with a nylon brush, and blown clean 

again. A new anchor rod would be installed in accordance with the manufacturer’s 

recommendations. After the epoxy was cured, the anchor would be proof tested 

“per job site specifications.”

According to internal B/PB correspondence, the B/PB design manager 

questioned whether the proposed response to Deficiency Report 001 would be 

satisfactory. In a December 8, 1999, e-mail to the design project engineer and the 

B/PB structural engineer (and copied to the B/PB project and resident engineer), 

the design manager stated, in part:

You’ve noted the key piece of information that is missing from the 

package. That is the cause of the anchor failure and how the repair 

procedure will overcome that. I’ll accept the fact that a single reason 

cannot be given with certainty, but an educated assessment can be 

made of the probable causes and a description of how those are 

being prevented by the reinstallation procedure can be presented....

We are not trying to hold up construction, we are trying to make a 

determination that the installation is safe and functional.

In a reply e-mail, the B/PB structural engineer noted

Glaringly absent from [Deficiency Report 001] is any explanation 

why the anchors failed and what steps are proposed to ensure that 

this problem does not reoccur.

On December 27, 1999, B/PB returned the submittal to Modern Continental, 

rejecting the proposed response to Deficiency Report 001. The document stated
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Prior to beginning the repair process the contractor needs to submit 

documentation on the manufacturer of epoxy and type being used by 

Powers Fasteners. i.e., If it is a SIKA [Chemical Corporation] product 

what type is it?

The submittal then detailed the repair/replacement procedures to be used 

for the failed anchors. The only significant difference between these procedures 

and those that had been proposed by Modern Continental/Powers was in the 

proof test loads. Modern Continental was directed to proof test all the replaced 

anchors to 7,900 pounds instead of 3,250 pounds as specified in the original contract 

documents. (This value was 125 percent of the maximum allowable load of 6,350 

pounds calculated for these anchors from the data in the Powers catalog.) The 

submittal also stated that

Because of evidence concerning installation problems, i.e. dust in the 

hole and insufficient adhesive in the hole, the capacity of all of the 

other anchor bolts is in question and will need to be addressed.

In this regard, the submittal provided two options for Modern Continental: 

Remove and replace all the previously installed anchors using the procedures 

and test values outlined in the submittal, or retest all previously installed anchors 

to 7,900 pounds. In subsequent correspondence, the 7,900-pound proof test load 

was reduced to 6,350 (the calculated allowable load for the anchor), but the issue 

remained as to who would pay for the retesting of the previously installed anchors. 

B/PB, in a January 7, 2000, letter to Modern Continental, stated

In the case of the ceiling anchor bolts, the bolts failed after the ceiling 

panels were installed. Examination of the one anchor that has been 

removed, indicated that the anchor bolt was improperly installed. 

There is evidence that the drill hole was not brushed clean..., and 

the anchor was not free of dirt, oil or foreign matter. Additionally 

the anchors were over torqued when the ceiling supports were 

installed.

The calculated allowable bond strength for a properly installed 

adhesive anchor system is 6350 lbs tension. [Modern Continental] 

is required to demonstrate correct installation techniques of the 

adhesive anchor bolt system, therefore it is the Project’s position that 

the re-testing of the bolts is required....Retesting that confirms the 

manufacturer’s calculated bond strength of 6350 lbs will be covered 

by a subsequent Contract Modification.

In February, the management consultant and the contractor reached an 

agreement under which all the failed anchors would be replaced in accordance 

with the approved procedures and proof tested to 6,350 pounds. Additionally, 

all previously installed anchors in the HOV ramp area would be retested to the 

higher value. The CA/T project agreed to pay the testing cost for any anchor that 
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passed the test at the higher value. The project and the contractor would split the 

cost of any anchor that had previously passed the test at 3,250 pounds but failed at 

6,350. Finally, all subsequently installed anchors in the I-90 tunnel would be tested 

to the higher proof load.

Modern Continental retested a total of 187 anchors in the HOV area and 

experienced 19 failures. An internal B/PB memorandum addressing the disposition 

of Deficiency Report 001 made the observation that

There were only two failures in the modules located outside of 

the [HOV] ceiling mock-up area. This could be the result of better 

installation techniques being used by the contractor as gleaned from 

going through the ‘learning curve’ in the mock-up area. These better 

installation techniques include: (1) cleaning holes out better and not 

using first epoxy out of the gun during the installation of the epoxy 

anchors and (2) not over torquing the nuts when the ceiling plates 

are installed over the anchors.

The corrective actions taken by Modern Continental were verified by 

B/PB in late 2000, and Deficiency Report 001 was closed on January 26, 2001. No 

evidence was found of any followup actions taken by Modern Continental or 

B/PB in regard to the anchor displacements in the HOV tunnel.

I-90 Connector Tunnel

On December 17, 2001, a Modern Continental quality control inspector 

initiated a noncompliance report to B/PB informing the management consultant 

of anchor displacements noted in another section of the I-90 connector tunnel. 

The defective anchors were those that had been used where the Unistrut channel 

inserts embedded in the roof were either missing or not aligned properly. The 

report stated that

Several anchors appear to be pulling away from the concrete. The 

subject anchors were [previously] tested to the revised value of 6350 

lbs., all of which passed.... Reason for failure is unknown.

B/PB directed Modern Continental to “set new anchors and retest.” As 

with the HOV tunnel 2 years before, all the displaced anchors were removed and 

replaced, then retested to more than 6,000 pounds. No additional actions were 

reported.

The investigation revealed other instances of anchor displacement in the 

Unistrut portion of the I-90 tunnel that were identified and reported by B/PB field 

engineers (as anchor “slippage”) in 2001 and again in 2002. These did not generate 

deficiency reports, and no documentation was found to indicate what actions were 

taken in regard to these displaced anchors.
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Tests and Research

Anchor Examination

During the accident, all 20 anchors attaching ceiling support beam M1 to 

the tunnel roof pulled out and fell onto the roadway. All the anchors reportedly 

remained within their roof hanger plates immediately following the accident, 

trapped between the flange of the polyethylene seal plug above the hanger plate 

and the nut and washers below the plate (refer to figure 7). During the recovery 

process, 16 of the 20 anchors were removed from their hanger plates without a 

record having been made of which anchors came from which plates. Even though 

the remaining four anchors stayed in their four- or two-anchor hanger plates, in the 

end it was not possible to match any of the 20 failed anchors with their respective 

anchor holes.

The 20 anchors from the failure row were all examined in the Safety Board 

Materials Laboratory, as were an additional 65 anchors from outside the failure 

area.52 Some of these anchors were chosen for laboratory examination randomly, 

but most were chosen because of specific anomalous conditions. Of these additional 

anchors, 7 came from within the accident module, 11 came from the adjacent 

module to the west, and 19 came from the two modules immediately to the east 

of the accident module. The remaining anchors came from three modules in the 

westbound tunnel (20 anchors) and two modules in the HOV tunnel (8 anchors).

All of the examined anchors were stamped with “316” on each end, consistent 

with a marking for 316 stainless steel, and this composition was confirmed during 

laboratory testing. The undamaged surfaces of the anchors were generally smooth 

and reflective and showed no evidence of corrosion.

The anchors from both within and outside the M1 failure row were examined 

for (1) damage, including bending deformation, (2) the extent of epoxy coverage 

on the anchor, and (3) the epoxy’s condition. Forces involved in the collapse of 

the ceiling or in the subsequent extraction of anchors from the tunnel roof caused 

some epoxy to separate from the original anchors, making that epoxy unavailable 

for inspection. Features associated with the epoxy included void areas, fractured 

epoxy, adhesively failed epoxy, yellowed epoxy, and overflow epoxy, as described 

below.

Void areas are unbonded epoxy surfaces along the embedment length of the 

anchor where the epoxy did not completely fill the gap between the anchor and 

the hole wall.

Fractured epoxy is epoxy along the embedment length of the anchor that has 

been sheared or otherwise separated.

52 FHWA personnel removed 49 of these 65 anchors, and many others, from the tunnel roof as part of 

the on-scene portion of the accident investigation.
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Adhesively failed epoxy is epoxy along the embedment length of the anchor 

that appears to have separated from the surface of the anchor hole and remained 

attached to the anchor as the anchor was pulled out.

Yellowed epoxy is fractured (or, in some cases, adhesively failed) epoxy with 

a distinct yellow tint.

Overflow epoxy is epoxy that extends below the seal plug and onto the 

threads of the anchor.

Figure 13 illustrates some of the features found on the failed anchors.

Of the 20 failed anchors from the accident site, all but one were found to 

have void areas that encompassed from 1 to 40 percent (average 10 percent) of 

their total embedment areas. Five of the anchors showed evidence of adhesive 

failure, with the most significant involving 29 percent of the embedment area. All 

of the anchors were missing epoxy, and 13 of the 20 had yellowed epoxy. Twelve of 

the anchors were bent. All but one showed evidence of overflow epoxy, typically 

extending 3⁄4 inch below the embedment area. On three of these anchors, the nut 

had been threaded onto the area of overflow epoxy.

Of the 65 tested anchors from outside the M1 failure row, 62 were found to 

have void areas that encompassed from 1 to 70 percent (average 15 percent) of the 

Yellowed epoxy

Fractured epoxy

Adhesive failure area

Void areas

Figure 13. Three of the 20 failed anchors from the accident site illustrating epoxy features found 

on some of the anchors.
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total embedment area. Twenty-three of the anchors showed evidence of adhesive 

failure, and 44 were missing epoxy. Twenty-seven anchors had yellowed epoxy. 

Forty of the 65 anchors had displaced from the tunnel roof before being removed, 

with displacement ranging from 0.625 to 2.65 inches.

Yellow discoloration of the typically white fractured epoxy was found 

on 13 of the 20 failed anchors. As with all the anchors with yellowed epoxy, the 

discoloration was on the lower portion of the embedment depth, extending above 

the seal plug. In the most extreme case, the yellowed epoxy encompassed 4 inches 

of the 5- to 5 1⁄2-inch original embedment depth of the anchor. In examining the 

other anchors removed from the tunnel roof, investigators noted that yellowed 

epoxy was found only on those anchors that had been displaced a significant 

amount from the tunnel roof. No yellowed epoxy was found on anchors that had 

not displaced, suggesting that the discoloration resulted from environmental 

exposure of the yellowed portion while the rest of the anchor remained in the 

roof.

When the amount of yellowed epoxy was compared with the amount of 

anchor displacement for the anchors examined in the laboratory, yellowed epoxy 

was not found on any of the examined anchors with a displacement of less than 

0.375 inch and was found on all but one of the examined anchors with displacement 

of 0.5 inch and greater. The one anchor that did not fit this pattern had one of 

the greatest amounts of displacement. Because this anchor was from the north 

row of the accident module, directly adjacent to the failure area, the displacement 

might have occurred at the time of the accident rather than over time before the 

accident.

The embedment length of the laboratory-examined anchors containing 

yellowed epoxy corresponded closely with the measured displacement; the 

yellowed appearance was typically about 0.3 inch greater than the measured 

displacement length. On some anchors, the yellowed epoxy extended around the 

perimeter of a void, consistent with environmental exposure extending up into the 

hole through the void.

A significant amount of dark brown epoxy was found on six of the anchors 

from outside the failure row;53 a smaller amount of brown epoxy was noted on one 

of the failed anchors. On several of the anchors from outside the failure row, the 

dark brown epoxy was soft and pliable immediately after the anchor was pulled 

from the tunnel roof, to the extent that several of these anchors had to be placed 

in plastic bags before being put into paper evidence bags. In the months after 

the accident, the dark brown material became harder, although some soft areas 

remained. For the anchors not from the failure row, a clear relationship was seen 

between the presence of the dark brown epoxy and the amount of adhesive failure 

noted on that anchor.

53 Two of these anchors were from the south (S) row of the accident module.
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Five of the six anchors from outside the failure row having dark brown 

epoxy were also among the anchors with the greatest displacement. Among the 

examined anchors, four of the eight anchors with the greatest displacement had 

dark brown epoxy as well as larger areas of adhesive failure. Samples of the dark 

brown epoxy from several of the anchors were among the epoxy samples chosen 

for testing and analysis (discussed later in this section).

Anchor Hole Examination

Safety Board investigators performed hand-held borescope54 inspections of 

the failure row (M1) anchor holes on August 9 and 10, 2006. Initial visual and 

borescope examinations showed the presence in the holes of significant loose 

epoxy that, in some cases, almost completely blocked the hole. Removal of the loose 

epoxy revealed that all of the holes had some epoxy remaining at the very top of 

the hole. This epoxy had separated cleanly from the anchors, leaving the positive 

mold of the characters “316” that had been stamped onto the anchor ends.

Although the borescope video images showed the features within the anchor 

holes, they did not allow the precise measurement of the locations or area fractions 

of the features. Nor was the handheld device able to generate an overall image of 

the entire hole surface. Thus, arrangements were made to obtain laser-scanned 

images of the holes. With a few exceptions, the laser images were sufficiently clear 

to allow the holes to be assessed for void areas, plug areas, fractured epoxy areas, 

and adhesively failed surfaces, as defined below.

Void areas are unbonded surfaces in the epoxy.

Plug areas are smooth epoxy surfaces that had been in contact with portions 

of the red polyethylene seal plug.

Fractured epoxy areas are areas where a thickness of epoxy with a rough 

surface extends from the wall of the hole.

Adhesively failed surfaces are areas where the epoxy had separated from the 

concrete or rebar surface, leaving behind little or no epoxy.

Of the 20 holes imaged, all but one showed epoxy voids involving from 3 to 

38 percent of the hole surface area, with 11 of the 20 holes having void area fractions 

of 20 percent or more.55 The void areas were generally oriented longitudinally 

along the length of the hole. Eleven holes had adhesive failure regions. Of these, 

two holes had adhesive failure area fractions between 40 and 50 percent, and four 

54 A borescope is an instrument in the form of a rigid or flexible tube with an eyepiece at one end and a 

lens at the other. It is used to make visual inspection of narrow cavities, such as the bore of a gun.

55 These percentages are in relation to the area of the scanned surface, which covered 4.5 inches of the 

typical 5-inch embedment length. The void areas present when the anchors were installed could have been 

higher than those measured in the laboratory because evidence of voids may have been lost or obscured as 

the anchors were pulled out.
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had adhesive failure areas from 18 to 31 percent. All of the holes showed fractured 

epoxy covering 42 to 93 percent (average 58 percent) of the hole surface area.

Core Sample Examination

Core samples were removed from four of the anchor positions in the M1 

failure row. At each position, the concrete surrounding the anchor hole was cut 

and removed from the tunnel roof either intact or in several large pieces with 

multiple smaller pieces. Three of these samples were sectioned at the FHWA 

Turner-Fairbank Highway Research Center and then examined in the Safety Board 

Materials Laboratory. The examination, inspection, and sectioning of these three 

core samples revealed the presence of significant voids in the epoxy between the 

anchors and the concrete surface of the anchor holes, measured as 31, 27, and 29 

percent for the three samples. Areas of adhesive failure were also noted, as well as 

some dark brown epoxy in the top of the hole for one of the anchor positions.

All four of the core samples contained horizontally aligned sections of No. 

11 rebar (nominally 1 3⁄8 inch in diameter). Of the core samples examined at the 

Safety Board, one of the anchor holes had been cored almost directly through the 

center of No. 11 rebar; and more than half of the circumference of the other two 

holes was through the No. 11 rebar. Additional pieces of smaller rebar were also 

found in the core samples. A comparison of the feature maps generated during the 

direct examination of the opened anchor holes with the laser images of the same 

holes showed, in general, a strong correlation between the shape of the various 

feature areas and that minimal epoxy was lost during the coring, cutting, and 

opening process.

In addition to the core samples from the failure area, core samples were 

removed from 10 anchor positions in the roof of the westbound connector tunnel 

and 1 anchor position in the HOV tunnel. At six of the anchor positions, the 

anchors were extracted before the cores were cut and removed. The reaction load 

required to extract the six anchors, measured using a hand-operated hydraulic 

press, ranged from 13,000 to 16,213 pounds and averaged 14,797 pounds.

Of the 11 core samples removed, 5 samples (1 with an anchor and 4 without) 

were retained by the Massachusetts Office of the Attorney General, and 6 samples 

(4 with anchors and 2 without) were retained by the Safety Board. Two of the 

samples retained by the Board contained anchors that had displaced from the 

tunnel roof before removal. The following information applies only to the six core 

samples retained by the Board.

The examination, inspection, and sectioning of the core samples retained by 

the Safety Board revealed the presence of significant voids in the epoxy between 

the anchors and the concrete surface of the anchor holes, measured as 10, 15, 21, 25, 

27, and 31 percent for the six samples. Areas of adhesive failure were also noted.
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All six of the core samples contained rebar similar to that found in the core 

samples from the failure area. Two of the anchor holes had been cored almost 

directly through the center of No. 11 rebar. All of the anchor holes had intersected 

one or more pieces of rebar.

Four of the core samples were sectioned for further examination. One core 

was sectioned at the Safety Board Materials Laboratory, and three cores were 

sectioned at the Turner-Fairbank Highway Research Center.

Examination of the core sectioned at the Safety Board laboratory revealed 

that about one-half of the circumference of the hole contained very little epoxy 

and that significant epoxy remained on the other half of the hole. After further 

sectioning of the sample, multiple void areas were visible on the side with the bulk 

of the remaining epoxy. A large void was also found in the epoxy above the upper 

end of the anchor.

One side of the anchor from this core contained a damaged and deformed 

layer of epoxy that appeared to have extended out to the surface of the anchor 

hole. The epoxy along this side of the anchor appeared to have been compressed 

along the length of the anchor, with the relatively smooth surface of the epoxy 

apparently corresponding to the surface of the anchor hole.

Examination of one of the cores sectioned at the Turner-Fairbank Highway 

Research Center showed that the epoxy filled most of the volume between the 

anchor and the hole surface, with the exception of one large void (an approximately 

cylindrical area of 0.7 square inch) and some small voids. This sample had epoxy 

fractures occurring at three locations: at the interface between the epoxy and the 

concrete hole surface (adhesive failure), through the epoxy in areas without voids, 

and at the interface between the anchor and the epoxy.

On all of the core samples, it was noted that the anchor was not concentrically 

located within the hole and that the voids were more predominant on the side of 

the anchor with greater distance between the anchor and the hole surface.

Ceiling Support Beam Loading

As part of this investigation, the dead load on each row of anchors in the 

D Street portal was calculated.

In the eastbound tunnel (the vicinity of the accident), the weight supported 

by the north row of anchors (row N) included half the weight of two of the 

12‐ by 8-foot panels without exhaust port (4,865 pounds), half the weight of three 

of the 12- by 8-foot panels with exhaust port (6,960 pounds), the full weight of the 

longitudinal panel support beam (1,800 pounds), the weight of seven 2-anchor 

roof hanger plates (322 pounds) and one 4‐anchor hanger plate (163 pounds), the 
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weight of 20 ventilation duct enclosure panels (1,000 pounds), and half the weight 

of five transverse ceiling struts (372 pounds), for a total of 15,482 pounds.56

Similar calculations for the other rows of anchors in the eastbound, 

westbound, and HOV tunnels generated approximations of the dead weight 

supported by each row of anchors in a module. As shown in table 1, the dead load 

carried by the individual rows ranged from less than 10,000 pounds (south rows in 

the HOV and eastbound tunnels) to more than 27,000 pounds (westbound middle 

and eastbound M1 rows).

Table 1. D Street portal ceiling support beam loading.

Tunnel Support beam Total dead load (pounds)

Westbound

North 15,647

Middle 27,452

South 15,440

Eastbound

North (N) 15,482

Middle 1 (M1) 27,452

Middle 2 (M2) 22,834

South (S) 9,617

HOV

North 15,456

Middle 21,891

South 9,699

Anchor Loading and Design Redundancy Analyses

At the request of the Safety Board, FHWA researchers at the Turner-Fairbank 

Highway Research Center performed a detailed analysis of the ceiling support 

system in the D Street portal. Researchers modeled the structure to provide an 

approximation of the load applied to each adhesive anchor and to determine 

how loads were distributed throughout the system.57 By showing how loads were 

redistributed under different “hanger-out” scenarios, the model also allowed 

researchers to evaluate design redundancy within the system.

Anchor Loading Analysis. According to Gannett Fleming, the design 

of the D Street portal ceiling did not assign any vertical dead or live load to 

the diagonal hanger rods in the system.58 Also, evidence gathered during the 

investigation indicated that, in some instances, the diagonal rods were not 

installed until after the ceiling module had been erected. Yet, adjustments could 

have been made to the diagonal rod turnbuckles after they were installed (to 

56 Not included in any of these calculations is the weight of the 12-inch-wide by 3/8-inch-thick steel plates 

that spanned the gap between modules.

57 The model was created using FEMAP software and was executed using the static analysis module of 

ABAQUS version 6.6.

58 The design did anticipate a vertical load component under seismic loading.
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level the ceiling, for example) that would have transferred some vertical load to 

those rods. To account for either possibility, the model was run both with and 

without the diagonal rods in place to provide an upper and lower bound for 

anchor forces.59

The FHWA analysis indicated that the maximum anchor loads within 

each row of hangers for the accident module occurred at the west end of the 

row (where the ceiling support beam was cantilevered about 6 inches farther 

than at the east end). The maximum calculated anchor load was 2,823 pounds, 

assuming that the vertical hanger rods resisted both dead and live load and that 

the diagonal hangers resisted only live load. This is slightly above the maximum 

load of 2,600 pounds calculated by Gannett Fleming. Figure 14 shows the anchor 

loads in all rows of the accident module when the diagonal hanger rods were 

assumed to resist only live loads. When the diagonal hanger rods were fully 

included in the analysis, the highest calculated anchor load was 2,371 pounds 

(dead load plus live load).

Design Redundancy Analysis. The structural redundancy of the system 

was examined by removing anchors from the model and repeating the computer 

analysis under dead load only and under both live and dead loads. Because the 

M1 row of anchors in the accident module had the highest proportion of load, and 

these were the anchors that failed in the accident, this was the only anchor row on 

which the redundancy analysis was performed. The analysis was performed with 

the diagonal hanger rods included.

In each failure scenario, all of the anchors (either two or four) were removed 

from a roof hanger plate to simulate a complete failure of one hanger assembly. 

The simultaneous removal of all the anchors for a hanger plate also provided a 

“worst-case” for redundancy evaluation.

Researchers analyzed eight different one-hanger-out scenarios 

(sequentially removing each roof hanger plate), seven different two-hanger-out 

scenarios (sequentially removing adjacent pairs of roof hanger plates), and six 

different three-hanger-out scenarios (sequentially removing three adjacent roof 

hanger plates).

59 Assigning vertical load to the angled rods increased the anchor loading on the four-anchor hanger 

plates (to which the angled rods were attached) and slightly decreased the loading on the two-anchor hanger 

plates on either side of the four-anchor plate.
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Figure 14. Plan view of the accident module’s roof hanger plates showing maximum anchor 

loading, in kips (1 kip = 1,000 pounds), as calculated for the Safety Board by the FHWA. These 

“worst-case” calculations assume no vertical load being supported by the diagonal hanger rods 

attached to the four-anchor hanger plates. Figures at the upper left of the four anchor plates 

represent the load on the two anchors on the west side of the plate; figures on the lower right show 

the load on the two east-side anchors. (For ease of identification in this report, hanger plates are 

numbered from east to west.)
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Table 2 shows the highest anchor load in the simulated M1 row of the 

accident module for the conditions analyzed by the model.

Table 2. Maximum anchor loads in the M1 row of adhesive anchors in the D Street portal under 

various hanger-failure scenarios.

Condition Dead load only (lbs) Dead load plus live load (lbs)

Vertical rods only 2,159 2,823

Vertical and diagonal rods 1,665 2,371

One hanger plate out 3,095 4,412

Two hanger plates out 7,648 10,887

Three hanger plates out 10,504 14,946

The data in the table indicate that, with all roof hanger plates intact or with 

one hanger out, the maximum anchor loads were below the published allowable 

loads for Power-Fast epoxy anchors (6,350 pounds as shown in the Powers design 

manual at the time). The design specifications required that a safety factor of 2 

be maintained for the remaining anchors in the event of failure of a roof hanger 

plate (one hanger out). A safety factor of 2 would have translated to a maximum 

allowable load, using Powers’ published capacities, of 12,700 pounds. The FHWA 

analysis indicated that even under the two-hanger-out scenarios, the maximum 

anchor load remained below this value.

Anchor Peak Load Tests

At the request of the Safety Board, FHWA personnel removed a total of 188 

anchors from the roofs of the eastbound and westbound D Street portal tunnels and 

recorded the peak load attained before each anchor pulled free. The loads required 

to extract the anchors varied widely, from a low of 1,121 pounds to a high of 

24,242 pounds.60 None of the anchor ultimate loads exceeded the 25,400-pound 

average capacity indicated in the Powers literature. Only five exceeded the 

20,600-pound capacity indicated in ICBO ER-4514. The average and median peak 

loads were about 12,000 pounds.

Of the 188 anchors, 45 had pretest observable displacements up to a 

maximum of 2.625 inches, and the displaced anchors tended to require less force 

to remove them. For example, the anchor with the greatest displacement was also 

the anchor that pulled out at the lowest peak load. The displaced anchors required 

approximately half as much force to remove from the tunnel roof as those without 

displacement. Of the 21 anchors requiring less than 5,000 pounds of force to remove 

them, only 5 had not displaced to some extent before the test.

60 One peak load value of 470 pounds was recorded, but test personnel considered this value to be 

suspect.
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Anchor Creep Testing

In addition to performing peak load tests, FHWA personnel performed 

sustained load (creep) tests on a number of the anchors in the westbound D Street 

portal tunnel. They first performed preliminary testing to determine if more 

rigorous testing was needed. For the preliminary test, they selected two anchors 

that showed no visible signs of distress or displacement. They then suspended 

a lead weight of approximately 2,000 pounds from each anchor and monitored 

the behavior of the anchors over the next 2 days. The anchors began to displace 

shortly after the weight was applied, and this displacement did not stabilize for 

the duration of the tests. At the end of the 47-hour test period, one of the anchors 

had displaced by about 0.11 inch and the other by about 0.07 inch. This result, 

and the fact that these anchors had shown no displacement before the tests began, 

prompted the more detailed investigation described below.

For the more rigorous testing, investigators used loads of 1,000, 2,000, and 

3,000 pounds, representing the approximate range of service loads on the anchors. 

Initial plans called for testing six anchors in the westbound tunnel, two at each load 

level. The anchors were to be monitored for up to 3 months. However, anchor failures 

due to creep during the 3-month test period made it possible for investigators to 

conduct a total of nine tests. As with the preliminary tests, the nine anchors selected 

for the more rigorous testing displayed neither signs of distress nor displacement 

before the tests began. Also, the nine tests were conducted in the south row of the 

westbound tunnel, one of the more lightly loaded rows available.

During the sustained load tests, two anchors pulled completely free of 

the tunnel roof. Of these two, one pulled out after supporting 2,000 pounds for 

84 hours; the other after supporting 3,000 pounds for 7 hours. One other anchor 

was relieved of its 3,000-pound load after 377 hours when it became apparent that 

it was about to pull out. In general, each adhesive anchor failure occurred within 

the epoxy and not at the epoxy-to-concrete interface. Only one anchor failure 

exhibited spalling of concrete. All of the anchors that sustained the load for the 

duration of the tests showed displacement from the tunnel roof of 0.03 to 0.14 inch, 

and the movement continued through the test period.

The FHWA also performed creep testing of Powers Power-Fast adhesive 

anchors at its Turner-Fairbank Highway Research Center. These tests were 

conducted with a variety of weights (1,000, 2,000, 3,000, and 4,000 pounds) and 

using both Fast Set and Standard Set epoxy formulations. Using best practices to 

minimize the formation of voids, investigators installed the anchors overhead in 

concrete slabs.

Regardless of the load level, none of the anchors installed with Standard 

Set epoxy showed significant movement during the test period (although the 

slight movement that did occur never completely stabilized). Conversely, anchors 

installed with the Fast Set epoxy exhibited significant displacement and high 

displacement rates at all load levels. Both of the anchors that were installed with 
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Fast Set epoxy and subjected to a 4,000-pound load displaced completely from the 

concrete slab before completion of the test. Figure 15 shows a graphical comparison 

of the displacement performance of anchors installed with Fast Set and Standard 

Set epoxies under a sustained load of 2,000 pounds. The graph displays the much 

more rapid onset and continuation of creep in the anchors installed with the Fast 

Set epoxy compared to those installed with the Standard Set version.

The FHWA tests also demonstrated that the displacement rate for anchors 

using Fast Set epoxy increased by similar amounts (approximately linearly) from 

the 1,000-pound test to the 2,000-pound test and from the 2,000-pound test to the 

3,000‐pound test, but the rate increased significantly from the 3,000-pound test to the 

4,000-pound test. In other words, the creep rate was approximately a linear function of 

the applied load up to 3,000 pounds, after which the rate became nonlinear.

Anchor Installation Parametric Study

At the request of the Safety Board, the Turner-Fairbank Highway Research 

Center conducted a study of the parameters associated with the installation of 

adhesive anchors in concrete that could affect the short-term load capacity of the 

anchors. Although most of the testing was done using Powers Power-Fast Fast 

Set epoxy, one series used Powers Power-Fast Standard Set epoxy, and one series 

used epoxy from another manufacturer.

Figure 15. Displacement curves for test anchors installed with Power-Fast Fast Set (two upper 

curves) and Standard Set (two lower curves) epoxies under a 2,000-pound tension load. (Graphic 

courtesy Turner-Fairbank Highway Research Center)
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To establish a baseline for anchor performance, the test matrix included a 

series of overhead anchor installations in which best practices were followed for 

cleaning the holes and minimizing the introduction of voids. These installations 

resulted in anchors with an average peak load capacity of 22,084 pounds, and this 

is the load that was used to gauge the effects of various installation parameters. As 

discussed below, the study revealed the installation parameters that did, and did 

not, cause reductions in anchor load capacity.

Parameters That Degraded Anchor Load Capacity

• Use of the Fast Set epoxy mixed off-ratio with an excess of hardener 

(more than 50 percent by volume) greatly reduced the load capacity 

of the anchors. In a test series with a ratio of hardener to resin of 3:2 

(60 percent hardener), the average anchor strength was reduced by 

about 60 percent.

• Baking a Fast Set epoxy cartridge at 140° F for 56 hours before use caused 

the hardener portion of the epoxy to partially phase-separate. This phase 

separation resulted in an oily substance rising to the top of the cartridge 

where it was the first material extruded before transitioning to a material 

more consistent with epoxy mixed with the typical gray hardener. This 

phase separation resulted in a gross reduction (approximately 85 percent) 

in the load capacity of the first anchor installed with this material, but as 

anchor installation with this cartridge progressed, anchor performance 

increased to typical load capacities. Safety Board investigators placed 

samples of the Fast Set resin and hardener and the Standard Set resin 

and hardener into separate glass jars and stored them at 140° F for 

56 hours. Changes in the appearance of the materials were documented 

with photographs. After storage, a layer of greenish brown liquid was 

found on top of the gray Fast Set hardener, and a layer of colorless 

liquid covered the Standard Set hardener. No change was apparent in 

the white resin components of either formulation.

• When an air bubble was intentionally created above the injected epoxy 

and the anchor was twisted during insertion (as specified by the 

manufacturer’s installation instructions), the load capacity of the anchor 

was reduced by an average of 40 percent.

• When an air bubble was intentionally created above the injected epoxy 

and the anchor was not twisted during insertion, the load capacity of the 

anchor was reduced by an average of 32 percent.

• Eliminating individual steps in the anchor hole cleaning process only 

modestly reduced anchor load capacity. Anchors installed with no 

cleaning at all (but allowing the hole to dry) showed a reduction of 

less than 15 percent in average load capacity (after correcting for the 

reduction in load capacity caused by the presence of voids). Anchors 

installed immediately after coring of the anchor hole (with no drying 

or cleaning at all) also showed a reduction of less than 20 percent in 
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average load capacity (correcting for voids). These results suggest that 

the water used for cooling and lubrication during core drilling washes 

away debris, especially when drilling overhead.

Parameters That Did Not Degrade Anchor Load Capacity

• Anchors installed in holes created with a diamond coring bit had 

load capacities similar to anchors installed in holes created with a 

carbide‐tipped drill bit, which is specified by ICBO ER-4514. The 

Powers design manual recommended, but did not require, the use of a 

carbide-tipped drill bit.

• Anchors installed through No. 11 rebar did not show a reduction in load 

capacity.

• Anchors on which simulated attachment hardware was installed and 

then torqued to 50, 90, and 125 foot-pounds showed no reduction in 

load capacity at any torque level.

• Injection of epoxy using a mixing nozzle shortened from 7 to 5 inches 

(which installation crews may be tempted to do to speed up the 

installation process)61 did not affect the load capacity of the anchors.

• Use of Fast Set epoxy mixed off-ratio with an excess of resin (more than 

50 percent by volume) increased the load capacity of the anchors.

The testing also found that anchors installed with Powers Standard Set epoxy 

and with Simpson Epoxy-Tie SET-22 (epoxy from Simpson Strong-Tie Company, 

Inc.) had average load capacities that were 10 to 20 percent higher than the anchors 

installed with best practices using Powers Power-Fast Fast Set epoxy. All three 

epoxies demonstrated some amount of creep displacement during testing when 

load was held constant; however, the Fast Set epoxy showed substantially greater 

creep, and at lower load levels, than the other two epoxies.

The testing revealed the difficulty in installing anchors overhead without 

introducing air bubbles that reduce the area of adhesion between the anchor and 

the concrete. Despite their best efforts, in a laboratory environment, investigators 

could not completely eliminate air bubblesand the resulting voids in the cured 

epoxywhen they installed the anchors overhead.

After the anchors were pulled from the concrete test slab, the unbonded 

areas on anchors with significant voids were measured, allowing investigators 

to determine how these unbonded areas affected peak loads. The calculations 

indicated that anchors with significant voids in the epoxy produced a lower 

uniform stress at peak load than anchors without significant voids, suggesting 

that voids cause stress concentrations that limit the performance of the remaining 

(bonded) epoxy.

61 No evidence was found that workers modified the mixing nozzles during installation of the D Street 

portal anchors.
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Tests of Void Formation During Anchor Installation

Safety Board investigators and representatives of the Turner-Fairbank 

Highway Research Center conducted a series of tests in order to study void 

formation in an overhead adhesive anchor system. Clear acrylic tubes were used 

to simulate the anchor holes so that the void formation process could be directly 

observed. The tubes were the approximate shape and size of the drilled holes for 

the anchor adhesive. Each tube was assembled with a flat end plate and a disk 

at what would be the upper end. The tubes were then clamped to an overhead 

plate to simulate the orientation of the anchor holes in the tunnel roof. A threaded 

nylon rod was used to simulate the anchor. In order to observe what occurred 

during the test procedure, a clear silicone-based caulk was used as a substitute for 

the opaque two-part epoxy. For comparison purposes, tests were also completed 

using Powers Power-Fast Fast Set epoxy instead of the clear caulk.

The tip of the injection tube supplied with the epoxy cartridges was flat 

(perpendicular to the axis of the nozzle). Additional mixing nozzles, available 

in packs of two, were also acquired and found to be of a one-piece construction 

(although the box illustrated a two-piece construction), and the tip of the nozzle 

was cut at approximately 45 degrees.

The installation guidelines printed on the cartridge indicated that

• The anchor hole should be filled approximately half to two-thirds full, 

starting from the bottom or back of the anchor hole;

• The nozzle should be slowly withdrawn as the hole fills to avoid creating 

air pockets;

• The anchor should be turned slightly as it is inserted; and

• The anchor should be fully seated at the bottom of the hole.

For the series of tests, the silicone caulk (or epoxy for one series of tests) 

was injected upwards into the test hole, and a nylon anchor was inserted. Anchors 

were inserted in one continuous motion, with the speed of insertion controlled by 

the viscosity of the caulk and estimated at approximately 10 inches per minute. 

After testing, an estimation of the void area was made. Small voids at the upper 

ends of the holes were not included in the area calculations.

The results of these tests may be summarized as follows:

• When the epoxy manufacturer’s installation instructions were precisely 

followed, a small bubble of air (0.04 cubic inch) was normally trapped at 

the upper end of a hole (in the groove produced by the core drill).62 The 

simulated anchor could not be maintained concentric with the hole, and 

62 A core drill cuts a ring to the depth required, and the core is subsequently broken off to produce a hole. 

Previous examinations revealed that the core normally broke off about 0.25 inch above the bottom of the hole, 

leaving a generally flat bottom about 0.6 inch in diameter encircled by a groove.
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during the last inch of insertion, the air bubble at the top was displaced 

away from the side of the hole closest to the threaded rod.

• Greater volumes of entrapped air at the end of the hole produced a void 

or voids along the length of the hole. Entrapped air with a volume less 

than or equal to 0.26 cubic inch would remain within the hole as a void. 

If the entrapped air had a volume greater than 0.26 cubic inch, a portion 

of the air was normally forced out of the test hole, leaving a void along 

the side of the anchor.

• Twisting the threaded rod after insertion tended to spread out any voids 

produced during insertion, thereby increasing the effective area of the 

void.

• Air trapped in the middle of the hole had the tendency to be forced out 

of the hole during insertion of the threaded rod.

• The epoxy surrounding the voids adhered both to the threaded nylon rod 

and to the sides of the acrylic tube. (This adherence was also observed 

on the accident anchors and in the accident holes.)

• No difference was noted in the void areas produced using the angled 

nozzle versus the square (flat) nozzle.

Examination of the Effect of an Air Bubble in the Resin or Hardener

The Safety Board performed four experiments simulating the presence 

of an air bubble at the tip of the container for either the resin or hardener in a 

dual-cartridge package of Power-Fast Fast Set epoxy. An air bubble in one of the 

components would result in some amount of epoxy mixed at a ratio different from 

the 1:1 ratio that was intended. Bubbles of 0.2 and 0.4 cubic inch in the resin or 

in the hardener were simulated by placing a spacer on the end of one plunger of 

the injection gun to advance one component ahead of the other. A new mixing 

nozzle was used for each of the four experiments. As with the void formation 

experiments described above, the epoxy was injected overhead into clear acrylic 

tubes simulating anchor holes, and a threaded nylon rod was then inserted.

The epoxy was allowed to set for 24 hours, after which the acrylic end plates 

from the tops of the tubes were removed. In the two experiments where the resin 

was extruded ahead of the hardener (an excess of resin), the epoxy had cured 

to a hard, solid state. In the two experiments where the hardener was extruded 

ahead of the resin (an excess of hardener), some amount of liquid uncured epoxy 

remained at the top of the hole. Seven days after installation, the threaded nylon 

rods were pressed out of the tubes in which the hardener had been extruded ahead 

of the resin. In both cases, pliable epoxy that was tacky to the touch was found over 

approximately the top half of the embedded lengths of the threaded nylon rods. 

Except for the color of the epoxy, these two test anchors appeared similar to the 

anchors that retained a dark brown pliable epoxy when extracted from the tunnel 

roof. These results were consistent with the results from the FHWA parametric 
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study, which found that epoxy mixed with an excess of hardener (therefore 

resulting in some amount of uncured epoxy) decreased the strength of the anchor, 

while epoxy mixed with an excess of resin increased anchor strength.

Epoxy Testing

Materials Characterization Testing. A variety of materials characterization 

tests were performed on samples of the anchor adhesive from the D Street portal 

as well as on samples from newly purchased packages of epoxy. The tests included 

Fourier transform infrared spectroscopy, differential scanning calorimetry, 

thermogravimetric analysis, headspace gas chromatography/mass spectroscopy, 

and X-ray energy dispersive spectroscopy using a scanning electron microscope.

The adhesive samples from the tunnel were taken from the anchors that had 

been examined in the Safety Board Materials Laboratory and from the adhesive 

collected from anchor holes during the borescope examination. Some of the 

samples were selected for examination because they displayed typical adhesive 

characteristics; others because they displayed an unusual structure.

For reference, samples of new materials were also tested. The anchor adhesive 

used in the D Street portal tunnel was identified in various construction documents 

as Power-Fast Epoxy Injection Gel packaged as NRC-1000 Gold Premier Epoxy.63

New packages of both Standard Set and Fast Set formulations of Power-Fast Epoxy 

Injection Gel64 were purchased for testing,65 along with a manual injection gun. 

Each package of epoxy consisted of two side-by-side tubes, one containing a white 

epoxy resin and the other a dark gray hardener. The injection gun simultaneously 

pushed two plungers that extruded the resin and hardener through a static mixing 

nozzle (included with the package), which attached to both tubes. The tubes could 

be resealed for later use (with a new mixing nozzle); additional mixing nozzles 

were also purchased. For both Standard Set and Fast Set epoxies, the resin and 

hardener tubes were the same diameter, so the resin and hardener mixed in a 1:1 

ratio by volume.

Five samples of adhesive from the D Street portal, along with reference 

samples of both the Standard Set and Fast Set epoxy formulations, were sent to 

Trace Laboratories–East in Hunt Valley, Maryland, for preliminary testing. One of 

the samples from the tunnel had been collected during the borescope examination 

63 During the early stages of construction of the I-90 connector tunnel ceiling, some of the epoxy used 

was packaged as Powers Power-Fast epoxy, but this same material at some point began to be packaged as 

NRC-1000 Gold epoxy.

64 Sika Corporation, which formulated the epoxies sold by Powers, told the Safety Board that the changes 

in epoxy formulation that occurred between 1999 and 2006 were not significant. The company also provided 

the Board with documentation detailing the changes.

65 The current retail price of a 22-ounce package of Power-Fast Fast Set epoxy is about $2.00 more than 

the Standard Set version ($46.00 versus $44.00). The cost is the same ($38.20) for the 15-ounce packages. 

According to Powers’ estimates, each 22-ounce package should be sufficient to install about 30 anchors of 

the type used in the D Street portal.
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of holes at the accident site; the other four were from taken from anchors. These 

included one sample with yellow tint and one sample of pliable dark brown 

material. The reference samples included samples mixed at 1:1 by volume through 

the static mixing nozzle and samples mixed with either an excess of white resin or 

an excess of gray hardener.

Thirty-one adhesive samples from the tunnel were subsequently sent to the 

Massachusetts Institute of Technology (MIT) for testing. These included samples 

taken from 17 of the 20 anchors involved in the accident (3 of the failed anchors did 

not retain sufficient epoxy to allow sampling). The 31 samples included material 

that had a yellow tint, material that had an appearance typical of fractured epoxy, 

material that had a pliable texture and a dark brown appearance, and material 

that showed characteristics of adhesive fracture (at the concrete interface) rather 

than cohesive fracture (within the epoxy). Also sent for testing were five samples 

of Power-Fast Fast Set epoxy that had been used during FHWA anchor installation 

and pull testing. Reference samples of Power-Fast Standard Set and Fast Set 

epoxy mixed at 1:1 by volume in the Safety Board Materials Laboratory were also 

submitted for comparison.

Fourier transform infrared spectroscopy at MIT showed that all of the 

samples from the tunnels, including the samples from the accident site, matched 

to the Fast Set reference samples. Headspace gas chromatography/mass 

spectroscopy examination of the Fast Set and Standard Set reference samples at 

Trace Laboratories showed clear differences in the unreacted components present 

in the two formulations. All of the epoxy samples from the tunnel that were tested 

with this technique matched the Fast Set reference samples.

The samples from the failure area were similar to the other samples from 

the tunnel that were identified as typical. No anomalies were found that would 

suggest that the epoxy from the anchors in the failure area differed from the epoxy 

found on anchors in other areas of the tunnels.

Two differential scanning calorimetry thermal scans were performed 

on each sample. Almost all of the samples demonstrated a difference in the 

glass transition between the first and second scans, and a number of samples 

exhibited endothermic peaks or exothermic reactions during the first scan that 

were not present in the second scan. These results indicate that heating during the 

first scan induced additional chemical (or structural) reactions, suggesting that 

the as-installed epoxy was not completely cured. The results of the differential 

scanning calorimetry tests of the dark brown samples suggest that these materials 

were consistent with an epoxy mixed with an excess of hardener.

Neither the Fourier transform infrared spectroscopy nor the differential 

scanning calorimetry testing revealed the cause of the yellow tint on the sample 

with the yellowed epoxy.
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X-ray energy dispersive spectroscopy in the scanning electron microscope 

was carried out on two epoxy samples from the tunnels and on the reference 

samples. The spectra for all of the samples appeared similar both in elemental 

content and in relative peak heights, with peaks for carbon, oxygen, magnesium, 

silicon, and calcium.

NIST Testing. The Safety Board provided new packages of both Standard 

Set and Fast Set formulations of Power-Fast Epoxy Injection Gel to researchers in 

the Building and Fire Research Laboratory at the National Institute of Standards 

and Technology (NIST) for testing by dynamic mechanical thermal analysis 

coupled with time-temperature superposition. The testing was intended to predict 

the long-term behavior of the two epoxy formulations in regard to creep and to 

estimate the time scale for any changes in creep compliance.66

Rearrangement of the long-chain molecules that make up a polymer67

results in a stiffness that is time-dependent. If a load is applied quickly, the 

molecules have insufficient time to rearrange and deform, and the polymer 

reacts as a stiff, glassy material. If the load is then held constant, the molecules 

will gradually rearrange and deform in a process that is observed as creep. 

Although, given sufficient time, this deformation could increase by orders of 

magnitude, with a well-formed polymer network (as in a cross-linked epoxy), 

the deformation should reach a long-term (rubbery) plateau after which creep is 

no longer observed.68

The molecular rearrangement that occurs over time as the material 

transitions from glassy to rubbery is similar to the change that occurs in a shorter 

time when the material is heated. Thus, by combining the results from a series of 

short-term tests at different temperatures (a procedure known as time-temperature 

superposition), researchers can predict how a material will respond over a much 

longer period of time.

NIST researchers tested small thin-film samples of the two epoxy 

formulations loaded in tension, then combined the results to calculate the creep 

compliance at room temperature (20° C or 68° F). The results showed that the 

creep compliance under short-term loading was similar for both the Fast Set and 

Standard Set epoxies, indicating that the instantaneous response (initial anchor 

displacement) when a load is applied would be similar for anchors installed with 

either formulation. For the Fast Set formulation, this initial anchor displacement 

was predicted to increase rapidly from its initial valueby a factor of 1.8 after 

1 day, by a factor of 3.5 after 1 month, by a factor of 6.3 after 1 year, and by a factor 

66 Creep compliance relates the strain (equivalent, in this context, to anchor displacement) at any point 

in time to the constant applied stress (tensile load). A larger creep compliance translates directly to a larger 

anchor displacement.

67 A polymer is a natural or synthetic compound that consists of large molecules made up of a linked 

series of smaller, identical molecules knows as monomers.

68 The chemical makeup and behavior of epoxy is discussed in more detail in the “Nature of Epoxy” 

section of this report.
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of 14 after 10 years. The best estimate of the Standard Set behavior was that the 

initial anchor displacement would increase by a factor of 1.2 after 1 day and by a 

factor of 2 after 10 years.

The NIST testing results indicated that, while the creep compliance will 

eventually plateau for both epoxies, the long-term creep compliance of the Fast 

Set epoxy is 11 times that of the Standard Set epoxy. This suggests that the Fast Set 

epoxy has substantially fewer cross-links than the Standard Set epoxy or possibly 

a significantly lower filler content. In addition, the testing indicated that the Fast 

Set epoxy is more complex and inhomogeneous than the Standard Set epoxy.

Additional tests were performed to assess the effects of absorbed water on 

the two epoxy formulations. Because the testing was performed with thin-film 

samples, saturation could be achieved fairly quickly by exposing the samples to 

100 percent relative humidity at room temperature. Under these conditions, the 

Fast Set epoxy absorbed almost twice as much water as the Standard Set (4.4 percent 

compared to 2.3 percent, by mass). The absorbed water softened both materials, 

causing a lowering of the glass transition temperature (the point at which the 

material changes from glassy to rubbery) of both as well as a broadening of the 

transition itself. Tests on samples that were saturated and then dried showed that 

some of the changes caused by the absorbed water were irreversible.

Nature of Epoxy

Epoxies are used as adhesives in a wide variety of applications. In composite 

structures (such as aircraft components, printed circuit boards, and sporting 

equipment), epoxies act as an adhesive holding together the fiber reinforcement. 

Epoxies have good chemical and electrical resistance, so they are often used in 

paints and coatings and to make molded parts that act as electrical insulators. In 

the construction industry, epoxies are used in a number of adhesive and sealant 

applications and can be used as a matrix with aggregate reinforcement to make 

highly durable but expensive epoxy concrete. For at least 35 years, epoxies have 

been used with threaded rods and rebar to form adhesive anchors.

The term “epoxy” covers a broad range of materials formed by the chemical 

reaction between two components: a resin and a hardener. An epoxy resin contains 

compounds with one or more epoxide rings (hence the name “epoxy”), which are 

three-membered rings with two carbon atoms and one oxygen atom. A wide variety 

of chemical compounds can be used as the hardener, including amines or amides 

(nitrogen‐containing compounds) and mercaptans (sulfur-containing compounds). 

The Material Safety Data Sheets (MSDS) for Powers Power-Fast epoxies indicate 

that both the Fast Set and Standard Set hardeners are amine-based.

Once the resin and the hardener are mixed, the amine groups on the 

hardener molecules begin to link with the epoxide groups on the resin molecules. 

Typically, the resin molecules have an epoxide ring at each end, and the hardener 
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molecules have an amine group at each end. The resin and hardener molecules can 

therefore link in an alternating pattern to form long polymer chains. Each amine 

group can link to more than one epoxide ring, so resin molecules can link to amine 

groups within different chains, thus forming crosslinks between polymer chains. 

A well-developed network of crosslinks prevents significant rearrangement of 

the polymer molecules, so the polymer cannot be melted and reformed. This type 

of polymer is called a thermoset. (Polymers that can be melted and reformed are 

called thermoplastics. In a thermoplastic, the polymer chains are entangled but not 

crosslinked.) As the epoxy cures, that is, as more and more epoxy molecules link 

with hardener molecules in long polymer chains, fewer unbonded reactive groups 

remain available for linking. Also, as the network forms, the viscosity of the material 

increases, making it more difficult for any free reactive groups to move to an area 

where a reaction can occur. Eventually, the reaction slows and finally stops. Even 

at this point, however, some unbonded reactive groups generally remain, and an 

increase in temperature will cause the network to expand and the viscosity of the 

material to decrease, which will allow more of the remaining reactive groups to 

link to one another.

In addition to the epoxy resin and the hardener (or blends of different 

resins and hardeners), an adhesive formulation can include a number of other 

components. Epoxy adhesives frequently include inorganic filler particles that 

reduce cost, reduce shrinkage, increase bulk stiffness and strength, improve gap 

filling, and increase the viscosity of the components (before curing). The MSDS 

sheets for the Power-Fast Fast Set and Standard Set epoxies indicate that they both 

include talc (magnesium silicate) and calcium carbonate, two common inorganic 

fillers. The formulation can also incorporate organic compounds that alter the 

viscosity of the resin or hardener, accelerate or slow the curing reaction, and 

alter the final properties of the adhesive. These organic compounds might have 

reactive endgroups and be incorporated into the network, or they might remain as 

unreacted compounds.

Viscoelasticity and Creep. Like all polymers, the stiffness of an epoxy is 

time and temperature dependent. If a load is applied suddenly, the epoxy responds 

like a hard, glassy solid. If that load is then held constant, however, the long-chain 

polymer molecules have time to begin to rearrange and slide past one another, 

and the stiffness of the epoxy decreases to a range where it can be described as 

rubbery. This increasing deformation under constant load is called creep. Materials 

like epoxy (or any polymer) with an instantaneous elastic response followed by 

a slowly increasing deformation (like a very viscous fluid) are called viscoelastic. 

The time necessary for the glassy-to-rubbery transition depends on the molecular 

structure and the lengths of the polymer chains between crosslinks. The temperature 

is also critically important, because the molecular rearrangements are a result of 

the constant thermal excitation of the molecules. If the temperature increases, the 

rate of rearrangement increases, and the glassy-to-rubbery transition occurs more 

rapidly. Above the glass transition temperature, the molecular rearrangements 

occur so quickly that the epoxy is always rubbery.
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In a thermoplastic (a polymer without crosslinks) under load, the behavior 

can pass from the glassy regime to the rubbery regime and, given sufficient time, 

eventually to a fluid regime where the polymer molecules move completely past 

one another. In a well-formed crosslinked network of a thermoset, the polymer 

molecules are prevented from moving very far, and once the rubbery state is 

reached, no further softening occurs.

Because time and temperature are so strongly interrelated in polymers, it 

is common to try to predict the long-term rubbery behavior by testing at higher 

temperatures. In fact, the entire glassy-to-rubbery transition can be mapped out by 

testing over a range of temperatures and then combining all the data. This method, 

called time-temperature superposition, works well for epoxies that are fully 

cured. For materials like the Power-Fast Fast Set epoxy, however, the additional 

reactions that occur as the temperature increases change the molecular structure 

of the polymer, which interferes with the superposition. Poor time-temperature 

superposition can be a clue to an incompletely formed network or an inhomogeneous 

material.

Nonlinear Deformation, Yield, and Damage. The time-temperature 

superposition method used to predict long-term behavior is generally carried 

out using relatively small loads and deformations. When the loads are small, 

the deformations are linearly proportional to the load, and structures are, for the 

most part, designed so that the loads remain within the range of linear behavior. 

However, this range depends on the state of the epoxy, because loads that are 

within the linear range in the glassy state might be outside the linear range in the 

rubbery state.

Within the linear range, the glassy-to-rubbery transition is assumed to occur 

independently for each load application. So if two loads are applied at different 

times, the response in each case is a glassy deformation followed by creep as the 

molecules rearrange. For loads in the linear range, creep deformation is generally 

reversible, so that once the load is removed, the epoxy will eventually return to its 

original shape.

At higher loads, the deformation can become a nonlinear function of the 

applied load. Depending on their formulation, epoxies can show softening and 

plastic (unrecoverable) deformation similar to the ductile behavior of metals, 

suggesting relatively extensive movement of the polymer molecules. The onset 

of plastic deformation is also time (and temperature) dependent. If the load is 

applied slowly, plastic deformation begins at a lower load than if the load is 

applied quickly.

Generally, cured epoxies have been considered to be brittle materials, 

meaning that they fracture rather than undergo plastic deformation as the load 

increases. The accumulation of this fracture damage is another possible source of 

nonlinear creep behavior. In a structure where the loads are not evenly distributed, 

small cracks in the epoxy can occur where the loads are high, shifting the load to 
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areas where the structure is still intact. The structure therefore behaves as though 

the epoxy is a softening material even though the epoxy is actually progressively 

fracturing.

Other Information

Current Guidance for the Use of Power-Fast Epoxy

Powers Guidance. As part of this investigation, the Safety Board reviewed 

the versions of the Powers Specification and Design Manual that were published 

subsequent to the second edition, which was current at the time the ceiling was 

installed in the D Street portal. The third edition of the manual was identical to 

the second edition with respect to the information about adhesive anchors. The 

fourth edition, dated 2002, had some changes in the ultimate strength values, but, 

as with previous versions, it did not identify differences in the allowable loads or 

long-term performance of the Fast Set and Standard Set epoxies.

In 2006, Powers published the fifth edition of its manual. The manual listed 

the physical properties of the Powers adhesives and showed that the Standard 

Set epoxy formulation has slightly higher values than Fast Set for compressive, 

tensile, flexural, and slant shear strengths. All the bond strength capacity tables 

had a footnote that read (depending on the values in the table): “Reduce the above 

[allowable/ultimate] bond capacities by 25 percent when calculating [allowable/

ultimate] bond capacities for the Fast Set formula.” This was the first mention in 

a Powers manual of a possible difference in the performance of the two epoxy 

formulations in anchoring applications.

In the front of the manual was a page with sections labeled “Product 

Description,” “General Applications and Uses,” “Features and Benefits,” and 

“Approvals and Listings,” all having to do with the Power-Fast + Epoxy Adhesive 

Anchoring System.69 The “Product Description” section noted that the product 

is “available in Standard Set and Fast Set formulas.” This is the only place on the 

page that mentioned the two formulations. In the bulleted list of “Features and 

Benefits” were these two items:

Listed and approved to resist dead loads, live loads, and short-term 

loads such as those resulting from wind or earthquake.

Independently tested and qualified to ASTM E1512, AC58 and 

AC60 criteria, including creep resistance, freeze-thaw cycling and 

simulated seismic/wind conditions.

69 The “+” indicated that a mixing nozzle was included with each cartridge.
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The specification and design manual stated

Safety factors are used to account for field variations which may 

differ from the testing conditions in the laboratory. Typical minimum 

safety factors established by industry are as follows [abridged]:

Product Typical Safety Factor

Mechanical Anchors in Concrete 4 (UBC, IBC, IRC)a

Adhesive Anchors in Concrete with Creep Test 4 (UBC, IBC, IRC)

Adhesive Anchors in Concrete without Creep Test 5.33 (UBC, IBC, IRC)

Pow[d]er-actuated Fasteners in Steel 5 (UBC, IBC, IRC)

a

 UBC – Uniform Building Code; IBC – International Building Code; IRC – International Residential Code.

While the Building Codes utilize the typical safety factors listed 

above for a minimum recommended allowable design load, higher 

safety factors (10:1 or higher) may be appropriate for the following 

conditions:

• Overhead applications

• Vibratory loads (example, dynamic or shock loads)

• Safety and life critical applications

• Questionable base materials

Actual safety factors to be used should be determined by the design 

professional responsible for the product installation, based on 

the governing building code and after examining all influencing 

factors.

In May 2007, Powers updated its Power-Fast epoxy product literature to 

specifically address the differences in long-term performance of the Fast Set and 

Standard Set formulations. In the May 2007 revision, tables showing ultimate and 

allowable bond strengths for threaded-rod anchors are labeled as applying to the 

“Standard Set Power-Fast+” epoxy. This is a change from previous editions, which 

had table headings that referred only to “Power-Fast+” epoxy. Additionally, a 

footnote accompanying the tables states

Reduce the above allowable bond capacities by 25 percent when 

calculating allowable bond capacities for the Fast Set formula. 

Allowable working load values for Fast Set formula are permitted 

for short-term loads only; where applicable to code and ICC-ES 

ESR-1531. [Emphasis in the original.]

As with all previous editions of the Powers manual, the most recent manual 

revision recommends the use of seal plugs for overhead applications, but it does 
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not indicate that the presence of a seal plug can reduce the load capacity for a 

particular anchor and anchor embedment below that published in the tables 

contained in the manual.

International Code Council Guidance. In February 2003, the four building 

products evaluation services in the United StatesNational Evaluation Services, 

BOCA Evaluation Services, ICBO Evaluation Service, Inc., and SBCCI Public Safety 

Testing and Evaluation Servicescombined to form ICC Evaluation Service, Inc. 

(ICC ES), as a separately incorporated subsidiary of the International Code Council 

(ICC).

Evaluation reports of the former services are being revised, reformatted, 

renumbered, and reissued as ICC ES reports (ICC ESRs). Power-Fast epoxies are 

now addressed in ICC ESR-1531, which was reissued in December 2006. This 

report effectively replaces ICBO ER-4514 in regard to the Power-Fast epoxy.70 ICC 

ESR-1531 did not carry over the recommendations that were contained in ICBO 

ER-4514 indicating that Power-Fast Fast Set epoxy should be used for short-term 

loads only. The “Conditions of Use” section includes the following:

5.5 The Power-Fast epoxy adhesive is permitted to be used in 

normal-weight concrete to resist dead loads, live loads, and shortterm loads such as those resulting from wind or earthquake....

The conditions of use do not distinguish Fast Set from Standard Set 

Power-Fast epoxy. Tables in the report showing allowable tension and shear loads 

for threaded rods installed in concrete do list separate loads for the Fast Set and 

Standard Set epoxies. A footnote to the tables states that the allowable loads for 

the Fast Set epoxy “are calculated using an applied safety factor of 5.33.” No text 

in ICC ESR-1531 restricts the Fast Set formulation to short-term loads.

On May 18, 2007, Powers distributed the (previously discussed) updated 

version of its Specification and Design Manual to the company’s branch managers 

and sales staff. Included with the revised manual was a cover letter from Powers’ 

director of engineering indicating that the changes to the manual reflected 

clarifications that were needed in ICC ESR-1531. The letter stated that Powers had 

questioned ICC ES about the fact that the restrictions of ICBO ER-4514 regarding 

acceptable use of the Fast Set epoxy were not included in ICC ESR-1531. According 

to the letter, ICC ES had “agreed that a clarification is in order.” The letter further 

stated

The clarifications for the conditions of use are expected to limit the 

use of the Fast Set Power-Fast formula in ESR-1531 for the reported 

allowable loads to short-term loads only, such as those resulting 

from wind or earthquake.

70 ICBO ER-4514 is still available as a legacy report, but in January 2007, all references to Power-Fast 

epoxy were removed. The report now addresses only the Powers Chem-Stud Capsule adhesive anchoring 

system.
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Quality Control/Quality Assurance

Quality control requirements for highway construction projects 

are addressed in AASHTO’s Implementation Manual for Quality Assurance

(February 1996) and Construction Manual for Highway Construction 1990 and in the 

FHWA’s Quality Assurance Procedures for Construction, which was published on 

June 29, 1995, as 23 Code of Federal Regulations Part 637.

These documents define quality assurance as “all those planned and 

systematic actions necessary to provide adequate confidence that a product or 

service will satisfy given requirements for quality.” The guidance goes on to state 

that

The term Quality Control and Quality Assurance (QC/QA) has 

often been used synonymously with Quality Assurance. The above 

definition considers Quality Assurance to be an all encompassing 

concept which includes quality control (QC), acceptance, and 

independent assurance (IA). Therefore, Quality Assurance is the 

proper term and is used in this manual.

Under the heading “Engineering Personnel,” the AASHTO guidance 

states

Many Agency engineering personnel have been involved in 

construction management for many years. They may believe that 

there is no need to change and that you are trying to ‘fix something 

that isn’t broken.’ Some may interpret the Quality Assurance program 

as a form of automation and believe that they are being stripped of 

responsibilities. They may feel that their only responsibilities are to 

‘observe and record’ test results and when the work is done, just apply 

the proper pay adjustment. The inspectors must realize that their 

responsibility has not changed and that inspection is still a critical 

element of acceptance. If a Contractor is producing unacceptable 

work, the Contractor must be notified as soon as possible.

It goes on the say that

The Contractors must understand that QC is their responsibility, 

and ‘Acceptance’ is the Agency’s responsibility. It is important to 

realize that some of the test results will not be identical; therefore, 

an Agency must address these instances in their specifications. 

Contractors should establish correlation factors between their QC 

tests and the Agencies’ acceptance testing.

Under the QC/QA system developed by State departments of transportation, 

AASHTO, and the FHWA, the contractor produces certifications from suppliers 

that a material meets the State’s specifications. The State’s materials testing group 
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then acquires random samples and subjects them to testing by the State’s certified 

laboratory or by a certified private laboratory. This process applies primarily to 

the structural materials used for a project, such as pavement materials (asphalt, 

Portland cement, pavement and structural concrete aggregate, structural steel, 

and admixtures to pavements). In the case of the accident project, the steel 

anchor rods and the tunnel’s Portland cement concrete were tested by the 

CA/T materials laboratory. The anchor epoxy was tested only for its performance 

in high temperatures during possible tunnel fires.

This model QC/QA program places responsibility for quality control on 

the project construction contractor and its materials testing subcontractor. The 

construction manager (a State or its project management contractor) performs 

quality assurance by monitoring the quality control of the contractor and the 

contractor’s material testing consultant.

At the request of the Safety Board, AASHTO surveyed its members 

regarding the testing of critical systems or materials (such as a system or 

material used to support components suspended over a roadway) that do not 

have AASHTO or ASTM test methods or specifications associated with them. 

Appendix B summarizes information obtained from that survey.

CA/T Structural Inspection Program

The accident investigation found no evidence that any inspections had 

been performed to determine the physical and functional condition of the ceiling 

system in the D Street portal between the time the tunnel was opened to traffic on 

January 18, 2003, and the day of the collapse. Nor did records indicate that periodic 

inspections were performed on any of the ceiling systems in the I-90 connector 

tunnel.

The scope of services contained in two short-term contracts between 

MassHighway and B/PB required the management consultant to

develop a maintenance structural inspection program for the 

viaducts, tunnels, bridges, buildings and other facilities constructed 

by [MassHighway] as part of the CA/T Project.... The scope of the 

program will deal with the structural elements of the tunnels, tunnel 

finishes, bridges, buildings and facilities as well as the structural 

components of the electrical, mechanical and control systems and 

specialty products and materials used in the construction of the 

CA/T Project. The inspection program will include procedures and 

protocols for routine and emergency inspections.

In November 2003, B/PB prepared the Inspection Manual for Tunnels and 

Boat Structures, the stated purpose of which was to
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aid the MTA...in the detailed and scheduled inspection of the tunnels, 

boat sections and the structural elements included within the Central 

Artery/Tunnel...network. Tailored to this highway tunnel system, 

the scope encompasses all aspects of a structural inspection.

One component of the inspection manual was the following:

Section 5.0, Classification of Structure Type and Specific Elements, 

illustrates specific elements encompassed within the CA/T which is 

comprised of five different tunnel types. This mainly includes special 

structures, products and testing, concrete and steel components, 

protective coatings, tunnel finishes and the roadway wearing 

course.

The manual included a set of condition ratings that applied to the structural 

elements of the inspection:

In addition, a set of condition ratings, ranging from 0 to 9, can be 

applied to the structural elements of the inspection. These techniques 

assist in providing a straightforward inspection record that is effective 

for tunnel assessment and maintenance.

The manual indicated that each hanger component used to support the 

modular concrete ceiling panels in the I-90 and I-93 exhaust duct areas should 

be inspected visually, by sounding, or by nondestructive testing. Appendix A of 

the manual included a blank routine hanger inspection field report. The blank 

field report contained entry fields for hanger number, location, connections for 

ceiling slab and floor slab, clevis, bolts, turnbuckle, threaded rod, moisture, and 

comments. The appendix also included a deficiency legend that identified the 

following deficiencies for exhaust duct hangers (vertical and diagonal) and bolt 

connections: surface rust, loss of section (percentage), loss of tension, out of plane 

(horizontal and vertical), broken, and buckled.

Investigators asked MTA officials why the inspection manual was not 

used from the time it was published in November 2003 until the day of the ceiling 

collapse. The officials stated that the inspection manual was not used because (1) a 

tunnel inspection database needed to be developed, (2) the inspection manual was 

being reviewed by the FHWA and the MTA, and (3) MTA personnel needed time 

to be trained to use the manual. They said that, in late 2005, the MTA took steps to 

initiate pilot or trial inspections based on the manual, including engagement of an 

outside consultant, but these trials were never carried out.

The Metropolitan Highway System Safety Review Team Stem to Stern Safety 

Review—Phase I report71 recommended that an inspection interval of 6 months be 

followed for as long as the epoxy anchorage system remains in service in the Ted 

71 Commonwealth of Massachusetts, Office of the Governor, Metropolitan Highway System Stem to 

Stern Safety Review–Phase I, November 15, 2006.
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Williams Tunnel, the Sumner Tunnel, and the Callahan Tunnel. According to that 

report, the 6-month inspection interval was necessary until a long-term strategy 

to address the problems with the ceiling anchorage system could be developed, 

possibly including replacing all epoxy anchors or maintaining existing anchors 

and continuing to monitor their performance.

In a summary of the status of tunnel inspections since the accident, the 

MTA indicated that it had “reinvigorated efforts to develop and implement a 

comprehensive tunnel inspection program” with the completed, ongoing, and 

projected actions summarized below.

• The MTA issued a tunnel inspection and testing program policy directive 

that calls for routine, in-depth inspections of all tunnel elements. The 

policy requires that all appurtenances suspended over roadways and 

their hanger systems be inspected annually and that all other structural 

tunnel components be inspected every 3 years.

• In March 2007, the MTA approved four 3-year general engineering 

consulting services contracts under which all the MTA tunnels will be 

continuously inspected in 2007, 2008, and 2009.

• The Metropolitan Highway System engineering and maintenance staff 

has reorganized and is currently in the process of increasing personnel 

to allow a greater portion of tunnel inspection and testing to be done by 

in-house staff. A new senior structural engineer position is being added 

to organize and oversee the tunnel inspection program, and a new 

structures maintenance engineer position is being added to coordinate 

and oversee repairs required in response to the inspection findings. 

MTA staff is currently inspecting the Sumner and Callahan Tunnels’ 

adhesive ceiling hangers on a continuous basis. Additionally, the MTA 

will be performing biweekly readings of ceiling hanger instrumentation 

in the Ted Williams Tunnel.

• Engineering consultants are developing standard tunnel inspection 

forms based on the Inspection Manual for Tunnels and Boat Structures

and standard FHWA bridge inspection forms. Data are being collected 

and organized with respect to providing a report of the preventive 

maintenance procedures performed on various life safety tunnel 

systems.

• The MTA is developing a 5-year capital program that will incorporate a 

tunnel inspection program.

Federal Design and Inspection Standards for Bridges and Tunnels

In the early 1970s, the FHWA, under legislative authority provided 

under 23 United States Code Section 151 and using standards promulgated in 

23 Code of Federal Regulations Part 650, developed the National Bridge Inspection 
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Program (NBIP). This program required that each State transportation department 

inspect all non-federally owned public-road bridges within its jurisdiction.

The NBIP was developed, in part, in response to Safety Recommendation 

H‐71‐13, which was issued to the U.S. Secretary of Transportation following the 

Safety Board’s investigation of a December 15, 1967, bridge collapse in Point

Pleasant, West Virginia, that killed 46 people.72

H-71-13

Expand existing research programs or institute new research 

programs to: (a) identify bridge building materials susceptible to 

slow flaw growth by any of the suspected mechanisms; (b) determine 

critical flaw size under various stress levels in bridge building 

materials; (c) develop inspection equipment capable of detecting 

critical or near critical flaws in standing bridge structures; (d) devise 

analytical procedures to identify critical locations in bridge structures 

which require detailed inspection; (e) develop standards which 

incorporate appropriate safeguards in the design and fabrication of 

future bridges to ensure protection against failures of material such 

as occurred in the Point Pleasant bridge; (f) develop standards for 

the qualification of materials for future bridge structures, using the 

information disclosed in this investigation; (g) devise techniques for 

repair, protection, or salvage of bridges damaged by internal flaws; 

and (h) expand the knowledge of loading history and life expectancy 

of bridges.

The NBIP consists of National Bridge Inspection Standards (NBISs) and 

a National Bridge Inventory (NBI). The NBISs were first established in 1971 to 

set national requirements regarding bridge inspection frequency, inspector 

qualifications, report formats, and inspection and rating procedures. The NBI data 

include identification of the bridge, structure type and material, age and service, 

geometric data, navigation data, condition, load rating and posting, proposed 

improvements, and inspections. The NBISs require that bridges be inspected at 

regular intervals not to exceed 24 months.

Tunnel inspections are addressed in the FHWA’s Highway and Rail Transit 

Tunnel Inspection Manual, 2005 edition, which states that tunnel owners should

establish the frequency for up-close inspections of the tunnel structure 

based on the age and condition of the tunnel. For new tunnels, this 

time period could be as great as five years. For older tunnels, a much 

more frequent inspection time period may be required, possibly 

every two years. This up-close inspection is in addition to daily, 

weekly, or monthly walk-through general inspections.

72 National Transportation Safety Board, Collapse of U.S. Highway Bridge, Point Pleasant, West Virginia, 

December 15, 1967, Highway Accident Report NTSB/HAR-71/01 (Washington, DC: NTSB, 1971).
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The tunnel inspection manual is a guide for tunnel inspections; the FHWA 

has not been given legislative authority to mandate compliance with national 

tunnel inspection standards.

Ceiling Designs in Other U.S. Tunnels

The Safety Board contacted nine tunnel authorities to gather information 

about various suspended ceiling designs used in tunnels throughout the United 

States. The Board requested specific information about typical ceiling panel/slab 

dimensions and weights, the type of ceiling anchorage system used, and whether 

the ceiling system was continuously supported at the ends of the panel. Appendix C 

summarizes the information obtained from that survey.

In July 2004, the FHWA developed the Road Tunnel Design Guidelines

manual that contained guidelines for the design of different categories of tunnels 

(soft ground tunneling, rock tunnels, mixed-face and difficult-ground tunnels, 

shafts, shotcrete, immersed tunnels, and cut-and-cover tunnels). The manual did 

not contain any guidance on the design of tunnel finishes.
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Analysis

This analysis begins with a brief description of the July 10, 2006, collapse of the 

D Street portal ceiling, followed by a discussion of the factors that were considered 

to be potentially causal or contributory to the accident. The analysis concludes by 

addressing the safety issues identified during the accident investigation. Those 

safety issues are as follows:

• Insufficient understanding among designers and builders of the nature 

of adhesive anchoring systems;

• Lack of standards for the testing of adhesive anchors in sustained 

tensile-load applications;

• Inadequate regulatory requirements for tunnel inspections; and

• Lack of national standards for the design of tunnel finishes.

Accident Sequence

By July 2006, at least 13 of the ceiling support anchors in the M1 anchor 

row of the eastbound D Street portal tunnel had likely displaced (pulled out of 

the tunnel roof) by a significant amount. Although preaccident displacement of 

the anchors from the accident row could not be measured, 13 of the 20 anchors 

in that row showed a yellow discoloration found only on displaced anchors. The 

yellowed epoxy suggests that these anchors, at least, had displaced to some extent 

before they pulled free during the accident. The yellowed epoxy on one of the 

anchors indicated that it had displaced by as much as 4 inches from its original 

5-inch embedment depth.

About 11:00 p.m. on July 10, 2006, all 20 anchors in the M1 row pulled free. It 

is likely that the load had been shed from initially displaced anchors to neighboring 

anchors over time, creating a cascading displacement pattern that continued to 

worsen until at least several anchors in this row became totally separated from 

the tunnel roof. The remaining anchors, unable to sustain the additional load, 

then gave way, allowing the M1 support beam to fall and causing the ends of the 

concrete panels resting on the beam to rotate downward.

The rotation of the north row of panels was initially somewhat restricted 

by the channel fittings that attached the tops of the welded studs to the N beam. 

(Refer to figure 6 for a detail of this type of connection) As the panels continued 

downward, the concrete began to fracture around these attachments, greatly 

reducing resistance to additional rotation of the north panels. As the M1 beam 

continued to drop, the degree of rotation between the concrete panels and the 

support beams also increased, causing the welded studs at the south end of the 
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center panels to fracture at the welds near their bases. Loss of these connections 

completely released the south ends of the center panels from beam M2, allowing 

those ends to move northward and drop off the M2 beam, which remained attached 

to the roof.

At this point, as the accident passenger car was traveling in the north travel 

lane, the entire set of 10 large concrete panels, along with support beam M1 and its 

supporting hardware, swung down and to the north. The south ends of the center 

panels struck the roadway first, resulting in significant crushing and fracturing 

of the concrete along the line of contact. (Refer to figure 9.) These center panels 

were also likely to have been the first to strike the passenger car, with the crushing 

damage progressing from right to left (from the passenger side toward the driver’s 

side) as the panels continued to fall.

Initial contact of the south panels with the roadway created additional 

rotation between the panels and beam M1. At some point, as the concrete panels 

dropped, the loads at most of the 15 attachment positions along support beam N 

became sufficient to fracture either the welded studs or the rebar in the concrete 

where the studs were attached. At the easternmost attachment position along 

the north side of panel N2, the stud remained intact, and the rebar around the 

fractured portion of the stud kept the panel attached to beam N throughout the 

accident sequence.

The accident vehicle, after its initial contact with the falling concrete ceiling 

panels, moved to the north and came to rest against the elevated walkway that 

paralleled the roadway. Because the south ends of the panels fell first, the north 

ends of several of the panels came to rest slightly farther to the north than their 

original positions in the ceiling. The north ends of these panels were partially 

supported by the 6-foot-high walkway handrail,73 which slightly reduced the 

crushing damage to the driver’s side of the vehicle and likely made it possible for 

the driver to survive the accident in which his wife was fatally injured.

After the accident, 161 of the 634 remaining adhesive anchors supporting 

the D Street portal ceiling were found to have measurable displacement, that 

is, they showed evidence of having gradually pulled out of the roof under the 

sustained tension load of the concrete ceiling panels. The Safety Board concludes 

that by July 2006, a significant portion of the adhesive anchors used to support the 

D Street portal ceilings had displaced to the extent that, without corrective action, 

several of the ceiling modules in the three portal tunnels were at imminent risk of 

failure and collapse.

All of these anchors had been tested after installation and were found 

capable of supporting, for 2 minutes or less, a minimum of 3,250 pounds. Some 

portal anchors had been successfully tested to 6,350 pounds. Yet many of these 

same anchors began to fail under even lesser loads, indicating thatmuch like 

73 The railing itself, which was 3 1⁄2 feet high, was affixed to a 2 1⁄2-foot-high raised walkway.
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the glue on an adhesive label, which will hold tightly enough to tear the paper if 

jerked suddenly but will yield to a slow and steady pullthe epoxy anchors in the 

D Street portal could resist a sudden and brief proof-test load but could not sustain 

a constant load over time.

Background of the Accident

The July 10, 2006, accident was a sudden, violent event, but the circumstances 

leading up to it developed over a period of more than 20 years, beginning with 

the design of the Ted Williams Tunnel in the late 1980s. The specifications for the 

Ted Williams Tunnel did not require that the tunnel incorporate a provision for 

attaching a suspended ceiling, even though the owners knew that one would be 

needed to accommodate the tunnel ventilation system (which had not yet been 

designed). The D Street portal, which was completed before the Ted Williams 

Tunnel, was expected to use the same post-installed ceiling as the Ted Williams 

Tunnel; thus, it also had no embedded ceiling supports.

The lack of embedded anchoring devices led the section design consultant 

for the Ted Williams Tunnel finishes to devise a ceiling system that relied on 

adhesive anchors for support. About 24,000 adhesive anchors were installed in 

the Ted Williams Tunnel, but various installation problems encountered during 

this process prompted CA/T project authorities to direct that the balance of the 

I-90 connector tunnel (except for the D Street portal, which was already built) be 

constructed with embedded steel channels in the roof so that adhesive anchors 

would not be needed.

Also during construction of the Ted Williams Tunnel, the FHWA, the 

MTA, MassHighway, and B/PB decided to adopt a simpler and cheaper ceiling 

system for future tunnels. Instead of the custom-engineered laminated lightweight 

concrete panels that had proved so costly and time-consuming to install in the 

Ted Williams Tunnel, they would use cheaper (and more easily installed) precast 

concrete panels for the I-93 tunnel and the I-90 connector tunnel.

The ceiling system that was adopted by the CA/T owners and B/PB and 

distributed to other section design consultants consisted of a group of concrete 

panels supported by a steel framework suspended from rods attached to roof 

hanger plates. In the I-93 tunnel, these plates would be attached to the roof girders 

using welded studs. In the I-90 tunnel, they would be attached to the steel channels 

in the roof. Because the D Street portal roof had neither girders nor embedded 

channels, section design consultant Gannett Fleming (as discussed later in this 

analysis) specified the use of adhesive anchors. The anchors that were installed 
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in the D Street portal in response to that specification were the ones that failed on 

July 10, 2006.74

The Safety Board evaluated a number of factors that could have caused or 

contributed to the failure of the anchors supporting the D Street portal ceiling. These 

factors included the design of the ceiling and its support system, the procedures 

used to install the adhesive anchors, and the properties of the epoxy used for the 

anchors. The Safety Board also evaluated the actions of CA/T project construction 

and oversight agencies in response to anchor failures that occurred several years 

before the accident. Those issues, among others, are discussed in the sections that 

follow.

Design of the D Street Portal Ceiling

Anchor Loading

In making its anchor-loading calculations, Gannett Fleming determined 

that the greatest load on any anchor in the D Street portal would be 2,600 pounds 

(1,800 pounds dead load and 800 pounds live load). To increase the margin for 

safety, however, Gannett Fleming specified that the anchors used in the portal 

should be capable of supporting a service tensile load of 4,000 pounds, with a 

safety factor of 4 (16,000 pounds ultimate load capacity).

At the request of the Safety Board, the Turner-Fairbank Highway Research 

Center, using a finite element model, calculated the loads on the adhesive anchors 

supporting the ceiling module that collapsed in this accident. The anchor loads 

were determined for three general conditions: with both vertical and diagonal 

hanger rods supporting the load, with only the vertical rods supporting the load, 

and with various combinations of roof hanger plates missing.

This analysis showed that the maximum load on any anchor in the row of 

anchors that failed was between 2,371 and 2,823 pounds, depending on the load 

carried by the diagonal hanger rods. While the upper end of this range is slightly 

higher than the maximum load calculated by Gannett Fleming (2,600 pounds), it 

is less than the service load capacity of 4,000 pounds specified by Gannett Fleming 

for the D Street portal anchors. The Safety Board therefore concludes that the 

anchor loading calculations developed by Gannett Fleming for the ceiling in the 

D Street portal tunnel were consistent with the actual maximum loads sustained 

in service.

74 After the accident, all the ceiling modules in the D Street portal were permanently removed. CA/T 

authorities determined that, because of the short span of the tunnel and its proximity to the tunnel opening, 

the suspended ceiling was not needed.
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Decision to Use Adhesive Anchors

The Safety Board considered whether adhesive anchors were appropriate 

for use in the D Street portal. Gannett Fleming initially planned to use undercut 

anchors in the D Street portal. In January 1997, however, B/PB informed the design 

consultant that, because of problems encountered when another contractor had 

used undercut anchors, these anchors were not to be used in the D Street portal. 

Gannett Fleming continued to make the case for the undercut anchors, researching 

the various alternatives available and suggesting to B/PB, in an August 1997 letter, 

that undercut anchors still appeared to be the best choice for this application. 

B/PB was not persuaded and sustained its directive not to use these anchors. 

Gannett Fleming accepted this direction and specified the use of adhesive anchors 

rather than undercut anchors.

The Safety Board notes that, while B/PB cited previous installation problems 

in rejecting undercut anchors, it apparently did not consider or give significant 

weight to the problems with adhesive anchors that were encountered by the 

contractor who installed the ceiling in the Ted Williams Tunnel. That experience 

was at least partly responsible for the fact that the tunnels that were yet to be built 

would have ceiling supports embedded in the tunnel roofs, obviating the need for 

adhesive anchors. Too many variables exist to assume that had undercut anchors 

been used in the D Street portal, this accident would not have occurred; however, 

the Safety Board notes that, after the accident, all of the adhesive anchors in the 

I-90 connector tunnel were replaced with undercut anchors.

According to test data provided by the anchor epoxy supplier (Powers) 

and forwarded to Gannett Fleming during the anchor approval process, assuming 

the particular combination of concrete type, anchor size, and embedment depth 

proposed for the D Street portal project, each epoxy anchor, using a safety factor 

of 4, could support up to 6,350 pounds. A safety factor of 4 means that an average 

anchor is expected to support four times this weight, or 25,400 pounds, before 

failure of the adhesive or the concrete surrounding the anchor. The safety factor 

incorporated into the design was intended to provide a margin of safety to account 

for imperfect installation, weaker-than-normal concrete, unexpected operating 

conditions, or other uncertainties. Thus, even in less-than-ideal conditions, the 

anchors were expected to safely support loads of up to 6,350 pounds. The finite 

element analysis conducted for the Safety Board by the FHWA showed that the 

expected anchor loads, even with the diagonal hanger rods excluded, were well 

below the load capacities of the adhesive anchors shown in the then-current 

Powers manual.

The FHWA analysis also showed that, even with any one ceiling hanger 

plate completely missing, the anchor loads in the remaining plates remained 

below 6,350 pounds. Only when two adjacent ceiling hanger plates were removed 

from the model did the calculated load on anchors in the adjacent plates exceed 

6,350 pounds. Even then, the loads were well below the expected average ultimate 

load capacity published by the anchor supplier.
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The Safety Board therefore concludes that, based on published anchor 

strength test data, the calculated anchor loading for the D Street portal ceiling 

system, and the limited number of available alternatives, Gannett Fleming’s 

specification of an adhesive anchoring system to support the ceiling system was 

not inappropriate.

But while the specification of adhesive anchors to support the D Street portal 

ceiling was not necessarily inappropriate, the use of these anchors in the D Street 

portalsupporting significant loads in pure tensionwas an atypical application 

that placed additional responsibility on the designers to ensure the safety of 

the system. Gannett Fleming engineers should have been aware that polymeric 

adhesives have significantly different properties than the steel and concrete that is 

typically used in construction. That fact, plus the somewhat innovative use of such 

adhesives as a primary structural element, should have led Gannett Fleming to 

perform careful measurements and calculations to ensure that the structure would 

remain sound. Despite the fact that all polymers have the potential to deform under 

sustained load, the designers included in the contract no specifications regarding 

the long-term mechanical properties of the adhesive, no requirement for testing of 

the adhesive for long-term performance, no consideration of the service life of the 

adhesive anchors in relation to the expected life of the tunnel, and no provision for 

periodic inspections of the installed anchors. The Safety Board therefore concludes 

that Gannett Fleming and B/PB failed to account for the fact that polymer adhesives 

are susceptible to deformation (creep) under sustained load, with the result that 

they made no provision for ensuring the long-term, safe performance of the ceiling 

support anchoring system.

Anchor Installation Procedures

The investigation determined that the adhesive anchor installation 

procedures provided by Modern Continental, the installation instructions 

provided by the epoxy manufacturer, and the installation procedures described 

by the workers themselves were generally consistent. However, notations from 

the B/PB field engineer daily report indicated that workers installed at least some 

anchors without first blowing out the holes with compressed air.

The Safety Board evaluated multiple parameters having to do with anchor 

installation to determine whether they might have caused or contributed to the 

anchor failures in this accident. These parameters included the cleaning of the 

anchor holes, the presence of damp concrete during installation of the anchors, 

the drilling of an anchor hole through rebar, the improper mixing of the epoxy 

components, and the presence of voids in the epoxy between the anchor threads 

and surface of the anchor hole.

Epoxy installation procedures typically emphasize that the hole must be 

clean and suggest that the holes be brushed, blown out with compressed air, and 
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brushed again. But in FHWA tests conducted for the Safety Board, the cleanliness 

or dampness of an anchor hole reduced the short-term load capacity by less than 

20 percent. These results suggest that overhead drilling with water lubrication 

might itself remove most dirt and debris from the hole. Of the 188 anchors FHWA 

personnel pulled out of the eastbound D Street portal tunnel roof, few gave way 

at the epoxy-to-concrete interface, indicating that, however well the hole had been 

cleaned, the hole surface was prepared well enough to bond with the epoxy.

Many, if not most, of the anchors holes in the D Street portal intersected 

segments of rebar, but FHWA testing revealed that installing anchors in holes 

cored through rebar had little or no effect on short-term load capacity of the 

anchors. Poorly mixed epoxy (such as might result from shortening the mixing 

nozzle from 7 to 5 inches to speed installation) similarly had little effect on the 

capacity of the anchor to sustain a load. An improper ratio of the two constituents 

did have an effect, but the effect depended on the balance of the constituents, with 

an excess of hardener decreasing the anchor maximum strength and an excess of 

resin increasing it.

Storage of a Fast Set epoxy cartridge at 140° F for 56 hours before installation 

resulted in a phase separation within the material, but this generally affected 

only the first anchor to be installed, after which the epoxy returned to its normal 

consistency and its normal load capacity. Use of a diamond core drill bit instead of 

the recommended carbide-tipped bit had no effect on anchor load capacity. Also, 

the anchors performed similarly whether the attaching nuts were torqued at 50, 

90, or 125 foot-pounds.

The epoxy found on some anchors outside the failure area was dark brown 

and pliable when the anchor was removed, consistent with a mixture with an 

excess of hardener. The Safety Board identified two mechanisms that could lead 

to mixing of the epoxy at ratios other than the intended 1:1 by volume. The first 

mechanism was phase separation during storage. Settling of the filler particles 

would increase the concentration of the fluid resin or hardener compounds at the top 

of the cartridge. This process was accelerated by storing a Fast Set epoxy cartridge 

at 140° F for 56 hours before installation. The hardener component appeared to 

be more susceptible to phase separation than the resin, making a mixture with an 

excess of hardener (the worst case) more likely.

A second mechanism that could cause an excess of resin or hardener is the 

presence of an air bubble at the tip of one of the tubes in the dual cartridge. Only 

the component without the air bubble would be extruded initially, which would 

coat all of the surfaces of the mixing nozzle and be entrained into the subsequent 

mixed epoxy. A relatively small air bubble in either tube could therefore affect the 

ratio of resin to hardener in a relatively large volume of epoxy, even if some of the 

first epoxy extruded is discarded, as recommended in the installation instructions. 

Except for the color of the epoxy, the test anchors where the hardener was extruded 

ahead of the resin appeared remarkably similar to anchors that retained a dark 

brown pliable epoxy when they were extracted from the tunnel roof.
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Examination of the anchor holes from the failure area showed that several 

had adhesive failure regions, with two anchor holes having adhesive failure area 

fractions between 40 and 50 percent, and four additional anchor holes having 

adhesive failure area fractions from 18 to 31 percent. The examination did not 

reveal the presence, in any of the anchor holes or on any of the anchors from the 

failure area, of significant uncured epoxy, which can result from excessive amounts 

of hardener.

The Safety Board therefore concludes that, although it is unlikely that 

all the D Street portal adhesive anchors were installed in a manner that would 

ensure maximum anchor performance, improper or deficient anchor installation 

procedures or practices alone would not account for all of the anchor failures that 

were observed before and after the accident.

One installation factor that almost certainly has an impact on anchor load 

capacity is the amount of epoxy surrounding the anchor. If insufficient epoxy is 

inserted into the hole, or if it is injected in such a way that significant voids are 

created, the epoxy bond area is decreased, which increases the load stresses on the 

remaining epoxy and compromises the ultimate load capacity of the anchor.

The Safety Board found measurable void areas associated with almost all of 

the anchors and anchor holes that were examined after the accident. For example, 

the anchor holes from the failure area showed void area fractions as high as 38 

percent, with 11 of the 20 holes having void area fractions of 20 percent or more.75

These voids significantly reduced the load transfer area of the epoxy, which 

increased the average stress on the remaining epoxy and accelerated the rate of 

displacement of the anchors after installation.

As shown by Safety Board simulations, the size and location of voids can be 

influenced in a variety of ways during epoxy injection or anchor insertion. More 

significant, however, was the finding that voids were frequently introduced during 

the installation tests conducted by the FHWA, even when the proper procedures 

were followed precisely and every effort was made to eliminate voids. This 

suggests that, in overhead applications, voids are introduced into the adhesive by 

the nature of the task itself. The Safety Board therefore concludes that installing 

adhesive anchors in overhead applications appears, by the nature of the task, to 

introduce voids into the adhesive that can reduce the ultimate load capacity of the 

anchor and thus the overall reliability of the anchoring system.

Because it is unlikely that independent epoxy qualification testing evaluates 

products in an overhead application, the load values from those tests may not 

reflect the reductions in load capacity that would result from the voids that would 

likely be introduced by such installations. In addition, overhead applications 

typically require use of seal plugs to contain the epoxy until it sets. If the seal plug 

75 The measured void area fractions were considered minimums because some evidence of the presence 

of voids could have been lost during the failure process.
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prevents bonding between the epoxy and the concrete (as did the polyethylene 

plugs used for the anchors in this accident), the effective anchor embedment 

depth may be reduced,76 causing a further reduction in anchor load capacity. The 

Safety Board therefore believes that the International Code Council should use its 

building codes, qualified materials listings, test criteria, or other mechanisms to 

make end users aware of the strong potential for creating voids in the adhesive 

during the overhead installation of adhesive anchors and of the need to account 

for the reduction in effective embedment depth associated with the use of seal 

plugs in such applications.

Epoxy Used in the D Street Portal

Epoxy is a polymer and, like all polymers, its stiffness is time and temperature 

dependent. If a load is applied suddenly, the epoxy responds like a hard solid. But 

if that load is then held constant, the molecules within the polymer may begin to 

rearrange and slide past one another, causing the epoxy to gradually deform in 

a process called creep. As the deformation increases, it becomes irreversible and 

eventually leads to damage accumulation and failure. This process can also be 

affected by other aspects of the operating environment, such as the presence of 

moisture or chemicals.

For the D Street portal adhesive anchors, Modern Continental (the 

construction contractor) chose an epoxy anchoring system provided by Newman 

Renner Colony. The epoxy was Powers Power-Fast Epoxy Injection Gel, which 

was packaged by Powers for Newman Renner Colony and supplied to the CA/T 

project as NRC-1000 Gold epoxy. Although the Powers Power-Fast epoxy was 

available in either Standard Set or Fast Set versions, at the time of the original 

purchase agreement between Modern Continental and Newman Renner Colony, 

the Fast Set formulation was the only one that was being packaged as NRC-1000 

Gold epoxy.

Fourier transform infrared spectroscopy and headspace gas 

chromatography/mass spectroscopy testing of epoxy samples from most of the 

anchors that failed in this accident and other randomly selected anchors revealed 

that their chemical composition was consistent with the Fast Set epoxy. None of 

the anchors tested showed a chemical composition consistent with the Standard 

Set epoxy. Project invoices indicated that Modern Continental purchased 

Power-Fast Fast Set/NRC-1000 Gold epoxy during the period when the D Street 

portal ceiling was being installed, and no record was found of the purchase of 

Standard Set epoxy during this period. Based on these tests and observations, the 

Safety Board concludes that Modern Continental was supplied with and used the 

Fast Set formulation of Power-Fast Epoxy Injection Gel when the company was 

76 The seal plugs used in the D Street portal reduced the effective anchor embedment by more than 

1⁄2 inch.
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installing the anchors in the D Street portal, including the anchors that failed in 

this accident.

Postaccident testing conducted by the Turner-Fairbank Highway Research 

Center at the request of the Safety Board revealed that, while both the Fast Set and 

Standard Set formulations of the Powers epoxy performed similarly in short-term 

load tests, they differed dramatically under long-term load. The testing showed that 

anchors installed with the Powers Fast Set epoxy, using best practices, exhibited 

significant and continued displacement (creep) when subjected to loads as low as 

1,000 pounds. Anchors loaded to 4,000 pounds completely separated from their 

anchor holes before the end of the 82-day test period. Given that the expected 

maximum anchor load was 2,600 pounds, the FHWA testing showed that the Fast 

Set epoxy, because of its susceptibility to creep, was not suitable for use in any 

long-term tension load applicationsuch as supporting the D Street portal ceiling. 

The Safety Board concludes that the source of the anchor displacement that was 

found in the D Street portal tunnels and that precipitated the ceiling collapse 

was the poor creep resistance of the Power-Fast Fast Set epoxy used to install the 

anchors.

The Safety Board notes the likelihood that, between the time the ceiling was 

installed and the tunnel ventilation system began operation, the load on the anchors 

would have been primarily from the dead load, and not all of the anchors would 

have been expected to support the maximum load. Gannett Fleming calculated the 

maximum anchor dead load to be 1,800 pounds. Based on the FHWA sustained 

load testing, even this load would have been enough to cause significant and fairly 

rapid anchor displacement. Once the ventilation system was placed in operation, 

the resulting suction load generated by the fans could have significantly reduced 

the tension load on the anchors and slowed their displacement. This might explain 

why the D Street portal ceiling system did not fail sooner than it did.

Use of Fast Set Versus Standard Set Epoxy

As the investigation revealed, the use of Power-Fast Fast Set epoxy virtually 

assured future problems with the D Street portal ceilings. The obvious question, 

then, is how did Modern Continental come to use an epoxy formulation that had 

been shown to be inappropriate for this application.

The investigation found no evidence that Modern Continental was offered 

a choice or made a conscious decision to use one epoxy formulation over another. 

When Modern Continental contracted with Newman Renner Colony to provide 

the Powers epoxy, the Fast Set epoxy formulation was the only one being offered 

by Powers under the Newman Renner Colony label. Powers was beginning the 

process of also providing its Standard Set epoxy for distribution by Newman Renner 

Colony, but this was in response to a potential requirement for other projects and 

was unrelated to the work in the D Street portal. Evidence was found that some of 
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the epoxy Newman Renner Colony provided for the D Street portal contract was 

packaged as Power-Fast epoxy, but this was the same Fast Set product that the 

company was supplying under its own NRC-1000 Gold label.

Installation of the anchors in the D Street portal began in July 1999, using 

epoxy purchased from Newman Renner Colony. No evidence was found that 

Modern Continental had any information at that time to suggest that the epoxy 

it was using was susceptible to creep. The Safety Board therefore concludes that 

Modern Continental was not aware, when its employees installed the adhesive 

anchors in the D Street portal, that the epoxy being used was susceptible to creep 

and was therefore unsuitable for this application.

The draft reissue of ICBO ER-4514, which Modern Continental submitted 

to Gannett Fleming in December 1999 in its fourth attempt to have the anchors 

approved by the design consultant, did refer to two epoxy formulations and did 

state that the Fast Set version was approved for short-term loads only. But this 

documentation, as well as the ultimate load figures submitted to show that the 

anchor capacities were sufficient to support the calculated design loads, was 

supplied by Powers, and none of the documentation specified which epoxy 

formulation had been supplied for use in the D Street portal. Modern Continental 

apparently assumed, based on information provided by Powers, that the epoxy it 

was using was suitable.

As noted previously, Gannett Fleming did not include a contract specification 

identifying long-term performance (creep resistance) of the anchor adhesive as 

an issue that should be addressed by contractors. In the specification for ceiling 

support anchors, Gannett Fleming indicated that the selected adhesive material 

should “remain unaffected by continuous humidity and by chemicals present in 

a vehicle exhaust type of air duct environment,” but the design consultant said 

nothing about the potential for creep in such materials and thus of the necessity 

of verifying that the selected material could support substantial tension loads 

indefinitely. Had it done so, the construction contractor would have at least been 

made aware of the potential for anchor creep77 so that it could have specifically 

considered this factor when selecting the anchor adhesive. The Safety Board 

concludes that had Gannett Fleming, in the construction contract for the D Street 

portal finishes, specified the use of adhesive anchors with adequate creep resistance, 

a different anchor adhesive could have been chosen, and the accident might have 

been prevented.

Even though Gannett Fleming made no provisions in the initial design 

specifications regarding the long-term performance of the adhesive anchors, the 

company could have addressed that issue during the approval process for the 

anchoring system selected by Modern Continental. Gannett Fleming engineers 

reviewed all of the documentation relating to the contractor’s proposed anchoring 

77 As used in this report, anchor creep refers to continuous anchor displacement under an applied load 

as a result of creep or damage accumulation, or both, in the epoxy adhesive.
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system and even rejected the first three submittals, each time requesting more 

information. With its fourth anchor adequacy submittal, Modern Continental 

included the draft revision of ICBO ER-4514, which stated that the Power-Fast 

Fast Set epoxy formulation was approved for short-term loads only. Although 

the guidance in the report was somewhat ambiguous (as will be discussed later 

in this analysis), Gannett Fleming had the responsibility to carefully review all of 

the anchor adequacy documentation. Such a review of the draft ICBO ER-4514 

should have prompted Gannett Fleming to inquire as to which epoxy formulation 

Modern Continental was using. A query from Modern Continental to Newman 

Renner Colony or Powers would likely have revealed that the Fast Set version 

was being provided to the job, and work could have been stopped and corrective 

measures taken. Instead, the Gannett Fleming reviewer authorized Modern 

Continental to proceed with work installing the anchors (by this time, the anchors 

that would be involved in the accident had already been installed). The Gannett 

Fleming reviewer apparently evaluated Power-Fast/NRC-1000 Gold epoxy as 

a single product and focused only on the bond strength as shown in the tables. 

The Safety Board concludes that Gannett Fleming approved the D Street portal 

anchors without identifying which epoxy formulation was being used, even 

though the company was provided with information indicating that one version 

of the Power-Fast epoxy should be used for short-term loading only.

Guidance for Using Fast Set Versus Standard Set Epoxy

ICBO ER-4514

Powers was updating its ICBO listing for Power-Fast epoxies in 1997, 

which required that the epoxies be independently tested in accordance with ICBO 

guidelines. As part of the qualification testing, an optional 120-day creep test was 

performed on the Standard Set epoxy. In response to a change in ICBO guidance 

(AC58), the results of the 120-day test of Power-Fast were extrapolated to 600 

days. The Standard Set epoxy met the standards for creep in both the 120- and 

extrapolated 600-day tests. No creep tests were reported for the Fast Set 

formulation (although such tests had been performed, as will be discussed 

below).

The ICBO evaluation report (ER-4514) on Power-Fast epoxy reissued in 

February 2000 had few references to Fast Set epoxy, and those could easily have 

been overlooked without a careful reading. In the product description, the report 

noted that the epoxy was available in two formulations and that the Fast Set 

version had additives to speed curing. (A table of relative curing times was also 

included.) The most significant mention of Fast Set epoxy was in the “Findings” 

section where, in a long paragraph presenting the 10th finding, the use of the Fast 

Set formulation with threaded rods was “permitted for short-term loads, such as 

those resulting from wind or earthquake forces only.”
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Another mention was in a footnote to the table of allowable tension loads 

for threaded rods in concrete. According to the footnote, when using Fast Set, 

the allowable loads from the table should be reduced “by 25 percent based on 

a safety factor of 5.33.” The footnote made no reference to any difference in 

long-term performance under load between Fast Set and Standard Set epoxy. In 

total, the report said very little about Power‐Fast Fast Set epoxy except in its finding 

that this formulation should only be used for short-term loads.

At the time the anchors were installed in the D Street portal, the ICBO (or its 

umbrella organization, the ICC) required, in acceptance criteria AC58, that a design 

safety factor of 5.33 be used for anchors in concrete when the epoxy formulation 

had not passed the optional creep test (either because it was not tested or because 

it failed the test). Thus, the footnote specifying a safety factor of 5.33 for Power‐Fast 

Fast Set epoxy indicated that this material had not passed the optional creep test. 

There was no requirement to report that a material had failed the optional creep 

test.

Tables contained in ICBO ER-4514 showed that the allowable load for 

Power-Fast Standard Set epoxy, with the anchor size and embedment used in 

the D Street portal and with a safety factor of 4, was 5,150 pounds. Based on this 

load and the recommended 25-percent reduction, the allowable load for Fast Set 

epoxy would be about 3,860 pounds. This was about 1,200 pounds more than the 

design load of 2,600 pounds calculated by Gannett Fleming for the D Street portal 

anchors and only about 600 pounds more than the initial 3,250-pound proof-test 

loads (and considerably less than the 6,350-pound proof‐test load applied to some 

of the anchors).

Every anchor in the D Street portal was thus tested to within a few hundred 

pounds of the catalog allowable load for that anchor, using guidelines in the ICBO 

report, and some of these were tested to the 6,350-pound allowable load listed 

in the Powers literature. Yet many of the anchors began to pull away from the 

tunnel roof after being under constant load for 2 months or less. The Safety Board 

therefore concludes that, as shown by the displaced anchors in the D Street portal, 

the maximum load capacity of an adhesive anchor, which relates to short-term 

loading, does not indicate that the anchor will be able to support even lighter loads 

over time, and thus a larger design safety factor cannot compensate for an adhesive 

material that is susceptible to creep.

The Safety Board learned during this investigation that the Power-Fast Fast 

Set epoxy had been tested for creep performance in 1995 and 1996 and had failed to 

meet the standard. That alone would explain the ER-4514 recommendation that the 

Fast Set epoxy be used to resist short-term loads only. But this load restriction was 

only shown in the report recommendations. In the bond strength tables, footnotes 

indicated only that the allowable loads shown should be reduced sufficiently to 

allow a safety factor of 5.33 (rather than 4) if the Fast Set material was to be used. 

Nothing in the tables or the footnotes indicated that the Fast Set epoxy should 

limited to use with short-term loads regardless of the safety factor employed.
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Given that the ability to sustain a load over a period of time is a typical 

requirement for almost any type of fastener, the Safety Board is concerned that 

the ICC has previously allowed creep testing of epoxy adhesives to be optional. 

A design engineer or contractor should be provided with all of the relevant 

information about a product before it is used in a safety-critical application; 

therefore, the Safety Board believes that the ICC should require creep testing for 

the qualification of anchor adhesives and disqualify for use in sustained tensile 

loading any adhesive that has not been tested for creep or that has failed such tests. 

The capabilities of Powers Power-Fast epoxy anchor systems are now covered 

in ICC ESR-1531. Although the bond strength tables in the report have separate 

listings for the Fast Set and Standard Set epoxies, the report does not address the 

difference in long-term performance between the two formulations or indicate 

that Fast Set should be used only for short-term loads. Because of the possibility 

that the critical difference in the two epoxies could still be overlooked, the Safety 

Board believes that ICC Evaluation Service, Inc., should revise evaluation report 

ICC ESR-1531 to state explicitly in the text and in the bond strength tables that the 

Fast Set formulation of the epoxy is approved for short-term loads only.

Powers Design Manual

According to Powers, in the second edition of its Fastening Systems Design 

Manual, the only difference in anchor performance between the Power-Fast 

Standard Set and Fast Set epoxies was their respective gel and curing times. Except 

for the ICBO report itself (which, as noted earlier, was somewhat ambiguous), 

none of the documentation submitted by Powers to support the qualification of the 

NRC-1000 Gold epoxy suggested a possible difference in long-term performance 

between the Standard Set and Fast Set formulations.

Powers should have made a clear distinction in all of its literature between 

the relative capabilities of its Standard Set and Fast Set formulations. It did not 

do so, even though, before the epoxy was provided to the D Street portal project, 

the company had conclusive evidence that its Fast Set epoxy was susceptible to 

creep and that it was therefore inappropriate for long-term tension loading in a 

safety-critical application.

Powers was aware that Modern Continental was using the Power-Fast 

product for long-term tension loads; it was also aware that the NRC-1000 Gold 

formulation being used was the Fast Set material. But there is no evidence that 

the company ever communicated with the contractor in regard to which formula 

should be or was being used in the D Street portal.

Only in May 2007, more than 10 months after this accident, did Powers 

revise its product literature to indicate that the Power-Fast Fast Set epoxy should 

be used for short-term loads only. The Safety Board notes that this is the only 

Powers product literature obtained during this investigation that explicitly alerts 

designers or contractors of a difference in creep resistance between the company’s 
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two epoxy formulations. The Safety Board therefore concludes that the information 

that was provided by Powers regarding its Power-Fast epoxy was inadequate and 

misleading, with the result that Modern Continental used the Fast Set formulation 

of the epoxy for the adhesive anchors in the D Street portal even though that 

formulation had been shown through testing to be susceptible to creep under 

sustained tension loading.

As a follow-on to the revised product literature and as an additional safety 

measure, the Safety Board believes that Powers should revise the packaging, for 

all distributors, of its Power-Fast Epoxy Injection Gel Fast Set formulation to state 

explicitly that this formulation is approved for short-term loads only. Also, because 

Sika Corporation, the epoxy manufacturer, markets the fast-setting version of this 

epoxy as Sikadur Injection Gel AnchorFix-3, the Safety Board believes that Sika 

Corporation should revise its product literature and packaging to state explicitly 

that Sikadur Injection Gel AnchorFix-3 is approved for short-term loads only. To 

address the issue of epoxy creep more globally, the Safety Board believes that 

the ICC should revise its building codes, qualified materials listings, and product 

labeling guidelines to clearly address the possibility for creep in polymeric anchor 

adhesives and to make end users aware of the potential lack of correlation between 

short- and long-term performance of these adhesives.

Response to Preaccident Anchor Failures

B/PB and Modern Continental

As noted previously, no evidence was found to indicate that Modern 

Continental, Gannett Fleming, or B/PB was aware that the adhesive the contractor 

had used in the D Street portal was susceptible to creep and was therefore 

inappropriate for this use. But Modern Continental and B/PB had opportunities, 

long before the tunnel was opened, to correct the mistake. Unfortunately, those 

opportunities were missed.

On September 9, 1999, a Modern Continental employee installing

ventilation ductwork above the HOV tunnel ceiling noticed that several of the 

anchors in the tunnel had begun to pull out. When subsequent checks over the next 

few weeks revealed that the displacement was increasing, Modern Continental 

notified B/PB of the problem. This was the first evidence that at least some of the 

3,250-pound proof-tested anchors were yielding to even lesser loads over a period 

of timewhich, in this case, was only about 2 months.

B/PB initially suspected that the anchor displacement was the result of 

improper anchor installation or improper erection of the ceiling panels by Modern 

Continental. Powers sent representatives to the site in October 1999 to help identify 

the source of the displacement, but in the end, as cited by Modern Continental, 
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“based on information gathered on site, which included a visual inspection 

[by Powers] of the anchors in question, a determination of failure could not be 

made.”

The “fix” for the problem that was ultimately agreed to by B/PB and the 

contractor was that the contractor would remove and replace all the failed anchors 

and proof test them to a higher load of 6,350 pounds. Additionally, all previously 

installed anchors in the HOV tunnel would be retested to the higher load, and 

subsequent new anchor installations in the I-90 tunnel would also be tested to 

6,350 pounds. As shown by the investigation, the higher proof test loads could not 

confirm that the anchors would be able to sustain long-term loads, and replacing 

the anchors using the same formulation of epoxy did nothing to prevent future 

displacement.

B/PB and Modern Continental had no basis for assuming that replacing 

the failed anchors and testing them to a higher load would solve the problem. 

As indicated by Modern Continental and B/PB correspondence that discussed 

various proposed remedies for the failed anchors, both the contractor (who 

was responsible for quality control) and the management consultant (who was 

responsible for quality assurance) were fully aware that the specific cause of the 

anchor displacement had not been identified. Some engineering officials within 

B/PB expressed particular concern that, because the source of the anchor 

displacement had not been determined, the proposed remedy might not work. 

At a minimum, the prudent course would have been for the contractor or B/PB 

personnel, or both, to continue to monitor the performance of all the anchors in 

the D Street portal until they could be sure the problem had been solved. Had this 

occurred, the contractor or B/PB personnel would no doubt have discovered that 

anchors were continuing to pull out, even those that had successfully passed a 

higher proof test. At that point, a thorough review of the ceiling installation would 

likely have been undertaken. Such a review could have resulted in a change in 

anchor type or a change in the epoxy, either of which might have prevented this 

accident.

About 2 years later, in 2001, a B/PB field engineer noted anchor “slippage” 

in the Unistrut portion of the I-90 connector tunnel. In December of that year, a 

Modern Continental quality control inspector working in the Unistrut portion of 

the eastbound I-90 connector tunnel found additional anchors that had begun to 

pull out. These anchors had been tested, only a few months before, to 6,350 pounds, 

and all had passed. The nonconformance report that was issued regarding the 

anchors noted that the “reason for failure is unknown.” The failed anchors were 

replaced and retested.

At this point, it should have been obvious to B/PB and to Modern Continental 

that the remedy that had been developed in response to the anchor displacement 

in the HOV tunnel in 1999 had not been effective, as anchors that had passed proof 

tests at higher values were still displacing. This was another opportunity for the 

management consultant and the contractor to inspect all the installed anchors to 
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determine the extent and, more importantly, the cause of the anchor displacement. 

Instead, the companies apparently considered the continuing failures as isolated 

instances and took no action to address the problem in a systemic way. The Safety 

Board therefore concludes that, after unexplained anchor displacement was found 

in the I-90 connector tunnel in 1999 and 2001, B/PB and Modern Continental 

should have instituted a program to monitor anchor performance to ensure 

that the actions taken in response to the displacement were effective. Had these 

organizations taken such action, they likely would have found that anchor creep 

was occurring and they might have taken measures that would have prevented 

this accident.

Powers

Although neither Modern Continental nor B/PB responded appropriately 

to preaccident anchor displacement, they received very little help from Powers 

in devising an effective solution. When Powers was called to examine the anchor 

displacements in the HOV tunnel in 1999, the company seemed surprised that 

anchors that had been successfully proof tested only a few months before could 

be failing. The company’s summary of its anchor examination suggested that the 

displacement could have resulted from deficiencies in anchor installation that had 

been masked by the high safety factors (which allowed the anchors to pass the 

proof test). Again, the company was equating an adhesive anchor’s short-term 

load capacity with its ability to resist long-term deformation.

The only potential source of the anchor displacement that was specifically 

identified by the Powers representative was overtorquing of the nuts that were 

threaded onto the anchors, which might have overstressed them. According 

to the Powers report, some of the anchors in the HOV tunnelthose that 

had displaced and those that had notwere checked and found to have been 

installed with 120 foot-pounds of torque, which was more than the recommended 

50 to 90 foot-pounds.

Leaving aside the question of how it was possible to check the installation 

torque of a nut after the anchor had pulled away from the roof, these torque readings 

appear not to have been typical within the D Street portal. Of the 130 randomly 

selected anchors in the eastbound and westbound tunnels that were subsequently 

checked by B/PB and Modern Continental engineers, all were reported to have 

been installed with slightly less than 75 foot-pounds of torque, which was well 

within the recommended range. Furthermore, testing of anchors installed with 

125 foot-pounds of torque showed no reduction in load capacity. These findings 

combine to indicate that application of excess torque did not cause or contribute 

to the failure.

No evidence was found that Powers took any followup action in regard 

to the anchor displacement in CA/T tunnels after the 1999 anchor examination 

and submission of findings. Even though the company was aware that its product 
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was not performing as expected in the HOV tunnel and that a definitive reason 

for the failures had not been determined, it did not recommend that B/PB or 

Modern Continental continue to monitor anchor performance, and it did not offer 

to provide or arrange for such inspections itself.

Nor was evidence found that Powers performed subsequent testing or 

conducted further research as a result of the anchor failures. At least some officials 

within Powers were aware that the Power-Fast Fast Set epoxy was subject to 

creep, but this information was apparently not considered (or was not known) 

by the Powers representatives and engineers who evaluated the failed anchors 

in the HOV tunnel. Even if the information about the poor creep resistance of the 

Fast Set epoxy was not common knowledge within the company, a reasonable 

amount of research would likely have revealed it, and corrective action could have 

been taken. The Safety Board would have expected the supplier of a safety-critical 

construction component to have been more proactive in determining why its 

product was failing to perform as expected. The Safety Board therefore concludes 

that Powers’ response to the anchor displacements that occurred in 1999 in the 

HOV tunnel of the D Street portal was deficient in that the company did not 

identify the source of the failures as creep in the Fast Set anchor adhesive and took 

no followup action to ascertain why its product had not performed in accordance 

with the users’ expectations.

Standards and Protocols for the Testing of Adhesive Anchors

In hindsight, the installation and test procedures used for the adhesive 

anchors in the CA/T I-90 tunnels were clearly inadequate to ensure that the 

anchors would perform as required over the life of the tunnels. The proof-test 

procedure used, while it may have been appropriate for mechanical anchors, 

provided no information about the long-term strength of adhesive anchors under 

sustained load, or even about the anchors’ ultimate short-term load strength. Also, 

as noted previously, the voids that appear to have been unavoidably introduced 

during the overhead installation of the adhesive anchors would have reduced the 

anchor load capacity irrespective of the creep resistance of the epoxy.

In its 2002 Standard Specifications for Highway Bridges, 17th Edition, AASHTO 

recommended that embedment anchors (defined as cast-in-place, grouted, 

adhesive‐bonded, expansion, and undercut steel anchors) be subjected to sacrificial 

tests at the job site to document the capability of the anchor to achieve the full 

tension value as shown in the manufacturer’s literature. Instead of conducting such 

sacrificial tests, CA/T managers and owners apparently accepted at face value 

the catalog load capacities provided by Powers and performed no independent 

testing to verify that the numbers were valid or that the anchors would perform 

similarly in this particular application.
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Although the lack of maximum-load verification testing using overhead 

installations cannot be definitively shown to have contributed to this accident, 

testing a sample of the anchors to their ultimate loads would have been prudent 

given the safety-critical nature of the system. The Safety Board concludes that, 

because of the potential catastrophic effects of a failure of the D Street portal ceiling 

system, B/PB and Gannett Fleming should have required that ultimate load tests 

be conducted on the adhesive anchors used to support the ceiling before allowing 

any of the anchors to be installed.

The Safety Board recognizes that ultimate load tests alone would not have 

revealed the property of the epoxy that eventually led to this accident, which 

highlights the need for more refined and specific testing of any adhesive anchor 

system that is being considered for use in a sustained tensile-load application. 

Because no protocols or standards currently exist for such testing, public agencies 

and their contractors are left to devise their own tests or to conduct no tests at all. 

The Safety Board concludes that protocols or standards for the testing of adhesive 

anchors in sustained tensile-load applications will provide designers and builders 

with test methods designed specifically to accurately assess the long-term safety 

of those anchors.

A creep testing protocol is specified in ICBO-AC58, but this is a pass/fail 

test that is conducted using one load at a single temperature for a specified time. 

Such a test may be appropriate as a screening tool to identify adhesives that should 

never be used for long-term tensile loads (such as the Power-Fast Fast Set epoxy, 

which failed the test), but it does not provide any data that could be used to predict 

the operational lifetime of an adhesive. Nor does it provide information to assist 

users in establishing appropriate inspection intervals for adhesive anchors under 

different loads or at different temperatures.

ASTM Standard D 2990-01, Standard Test Method for Tensile, Compressive, and 

Flexural Creep and Creep-Rupture of Plastics (first adopted in 1971 and most recently 

reapproved in 2001), includes standardized testing guidelines and information 

in a series of appendixes. The appendixes describe a number of well-established 

and complementary methods for predicting the long-term properties of polymers 

and for ensuring their safe use under creep conditions. The introduction to the 

appendixes notes that

Since the properties of viscoelastic materials are dependent on time, 

temperature, and rate of loading, an instantaneous test result cannot 

be expected to show how a material will behave when subjected to 

stress or deformation for an extended period of time.

The standard itself discusses various methods for testing plastics (polymers) 

to assess their behavior (creep) under sustained loads; it does not address adhesive 

anchors. The test methods described in the standard could, however, be adapted, 

through specific testing protocols, to generate data that would aid designers 
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and others in evaluating the suitability of adhesive anchors for a particular 

application.

For example, one method for predicting long-term properties discussed in 

ASTM D 2990-01 involves conducting a number of tests over a range of applied 

loads (similar to the sustained load tests performed at several load levels by the 

FHWA as part of this investigation) to determine the time to failure as a function 

of load. These data can then be extrapolated to estimate the load at which failure 

will occur for times beyond the range of the tests.

A second method outlined in an appendix to ASTM D 2990-01 employs 

laboratory testing coupled with time-temperature superposition to calculate creep 

compliance over a wide range of time. Because creep compliance is directly related 

to the displacement of an anchor under a constant load, this method could be used 

with a maximum displacement criterion to predict the expected useful life of an 

adhesive anchor. The results of this testing could also be used to assess the effect 

of variations in temperature over the life of the installation. The time- temperature 

superposition tests performed for the Safety Board at NIST predicted that the 

room temperature displacement of an anchor installed with Power-Fast Fast Set 

epoxy would increase by a factor of 3.5 after 1 month and by a factor of 14 after 10 

years.

The results of the FHWA creep tests and the NIST material evaluations 

appear comparable (except for the Fast Set anchors loaded at 4,000 pounds, which 

in the FHWA tests demonstrated a nonlinear behavior suggesting yield or damage 

accumulation in the adhesive), although a rigorous comparison has not yet been 

attempted. In any event, use of either of these methods as a part of the preparations 

for construction in the D Street portal would have demonstrated that the Fast Set 

epoxy was not suited to this application.

NIST also performed experiments suggesting that moisture absorption could 

have a significant effect on the material properties of the Fast Set and Standard Set 

epoxies. These experiments were performed on small samples that allowed for 

rapid saturation and therefore might not reflect actual-use conditions; however, 

they indicate that a testing plan to assess the long-term durability of polymeric 

materials must consider environmental effects in addition to temperature.

The Safety Board therefore believes that, building on current test standards 

from ASTM or other sources, the FHWA and AASHTO should work jointly to develop 

standards and protocols for the testing of adhesive anchors to be used in sustained 

tensile-load overhead highway applications. These standards and protocols should 

consider site-specific ultimate strength values as well as the creep characteristics 

of the adhesive over the expected life of the structure. Once these standards and 

protocols are developed, the Safety Board believes that AASHTO should incorporate 

them into the AASHTO Construction Quality Assurance Guidelines.
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Until these standards and protocols have been developed and implemented, 

the Safety Board believes that the FHWA and the transportation departments of 

the 50 States and the District of Columbia should prohibit the use of adhesive 

anchors in sustained tensile-load overhead highway applications where failure of 

the adhesive would result in a risk to the public. Concurrently, the Safety Board 

believes that AASHTO should use the circumstances of this accident to emphasize 

to its members through its publications, Web site, and conferences, as appropriate, 

the risks associated with using adhesive anchors in sustained tensile-load 

applications where failure of the adhesive would result in a risk to the public.

These recommendations will affect future installations of adhesive anchors, 

but they do not address adhesive anchors that may already have been used to 

support overhead signs or traffic control devices where a failure could result in 

injury or death. The Safety Board is concerned that some of these anchors may 

be susceptible to creep and that, without monitoring and corrective action, these 

anchors may fail. The Safety Board therefore believes that the transportation 

departments of the 50 States and the District of Columbia should review the use of 

adhesive anchors in highway construction within their jurisdictions and identify 

those sites where failure of the adhesive under sustained load could result in a 

risk to the public. Once those sites have been identified, a repair and inspection 

program should be implemented to ensure that such failures do not occur.

Lack of Awareness of the Potential for Adhesive Anchor Creep 

Under Sustained Load

This accident investigation revealed a striking lack of knowledge among 

the designers, contractors, managers, and overseers of the CA/T project about the 

nature and performance of polymer adhesives, even as those adhesives were being 

approved for use in applications where a failure would present an immediate risk 

to the public. No one involved with the CA/T project appeared to be aware of 

the potential of a polymer such as the anchor epoxy to gradually deform under 

sustained load. Even after being presented with evidence of anchor creep, project 

managers and overseers failed to recognize the inherent weakness in the epoxy 

adhesivea weakness that could not be overcome even with the best installation 

practices or the most rigorous short-term proof testing.

The Safety Board does not believe that those associated with the CA/T 

project were unique in their lack of understanding of the nature of adhesive 

anchors. While the anchors have been in use for a number of years, they have rarely, 

perhaps never, been used in such numbers and in such a challenging environment 

as in the I-90 tunnels. In civil projects, adhesive anchors are typically used in 

short-term or shear load applications. Under these conditions, even if the adhesive 

is susceptible to creep, the displacement will likely never reveal itself, and those 

responsible for specifying, approving, installing, and testing the anchors will 

not be aware of it. Unfortunately, the lack of knowledge of the nature of epoxy 
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anchors could lead to the use of these anchors in highway, tunnel, and bridge 

applications where susceptibility to creep could be a threat to public safety. 

The Safety Board therefore concludes that the circumstances of this accident 

demonstrate a general lack of knowledge and understanding among design and 

construction engineers and builders of the complex nature of epoxies and similar 

polymer adhesives, and in particular, the potential for those materials to deform 

(creep) under sustained tension loads.

The Safety Board expects that the implementation of its safety 

recommendations to the FHWA and AASHTO will serve to inform those involved 

in public works projects of the potential for creep in adhesive anchors. But the use 

of adhesive anchors is not limited to civil projects; such anchors are sometimes used 

in commercial construction. The Safety Board therefore believes that the American 

Concrete Institute78 should use its building codes, forums, educational materials, 

and publications to inform design and construction agencies of the potential for 

gradual deformation (creep) in anchor adhesives and to make them aware of the 

possible risks associated with using adhesive anchors in concrete under sustained 

tensile-load applications.

Finally, because civil engineers and general contractors involved in civil 

and commercial construction are generally not expected to be familiar with the 

complex chemistry of epoxies or similar adhesives and yet may specify or use 

adhesive anchors in their projects, the Safety Board believes that the American 

Society of Civil Engineers79 and the Associated General Contractors of America80

should use the circumstances of this accident to emphasize to their members 

through their publications, Web sites, and conferences, as appropriate, the need to 

assess the creep characteristics of adhesive anchors before those anchors are used 

in sustained tensile-load applications.

Tunnel Inspections

No tunnel inspections were performed to determine the physical and 

functional condition of the ceiling system from the time the I-90 eastbound 

connector tunnel was opened to traffic on January 18, 2003, until the day of the 

fatal accident.

78 The American Concrete Institute is a nonprofit technical and educational society representing public 

agencies, engineers, architects, owners, contractors, educators, or others interested in the design, construction, 

or maintenance of concrete structures.

79 The American Society of Civil Engineers (ASCE) has the stated mission of advancing professional 

knowledge and improving the practice of civil engineering. In support of this mission, the society develops and 

transfers to its members research results and technical policy and managerial information.

80 The Associated General Contractors (AGC) of America is the Nation’s largest and oldest construction 

trade association. A stated goal of the organization is to improve the construction industry through education 

and technology. AGC of America members represent all areas of construction, public and private, except for 

residential construction.
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In response to the contract scope of services, B/PB, in November 2003, 

published an inspection manual entitled Inspection Manual for Tunnels and Boat 

Structures. Although the manual was a comprehensive and detailed guide for 

inspecting CA/T tunnels, the MTA did not use it between November 2003 and 

July 2006, and the tunnels were not inspected.

Postaccident inspection of the area above the suspended ceilings in the 

D Street portal revealed the large number of anchors that had become displaced 

from the tunnel roof. The displaced roof hanger plates were so obvious that even a 

cursory examination of this area before the accident would have revealed that the 

structural integrity of the ceiling system was threatened. At the time the inspection 

manual was published in November 2003, the ceiling module that collapsed in this 

accident had already been in place for 4 years, and at that time at least some of its 

anchors had probably begun to yield to the load.

The Safety Board concludes that had the MTA, at regular intervals between 

November 2003 and July 2006, inspected the area above the suspended ceilings in 

the D Street portal tunnels, the anchor creep that led to this accident would likely 

have been detected, and action could have been taken that would have prevented 

this accident.

According to guidance in the FHWA’s Highway and Rail Transit Tunnel 

Inspection Manual, 2005 edition, the frequency of tunnel inspections could be as 

great as 5 years for new tunnels and 2 years for older tunnels. The FHWA requires 

that bridges, in contrast to tunnels, be inspected at least every 2 years, regardless 

of age. In this accident, problems with some of the anchors in the HOV tunnel 

were identified within weeks or months of their installation, indicating that even 

recently built structures are not immune to potentially hazardous defects. In the 

view of the Safety Board, the inspection interval for tunnels, whether new or old, 

should be consistent with the interval for inspection of bridges. Recognizing that 

the FHWA lacks the authority to establish and mandate a nationwide tunnel 

inspection program, the Safety Board believes that the FHWA should seek 

legislation authorizing it to establish a mandatory tunnel inspection program 

similar to the NBIP. Once such legislation has been obtained, the Safety Board 

believes that the FHWA should develop and implement a tunnel inspection 

program that will identity critical inspection elements and specify an appropriate 

inspection frequency.

National Standards for Design of Tunnel Finishes

The FHWA’s 2004 manual Road Tunnel Design Guidelines did not address 

the design of tunnel finishes, despite the fact that tunnel authorities throughout 

the country use a wide variety of tunnel finish designs and anchorage systems 

with different redundant support systems and different installation requirements. 

The Safety Board’s survey of tunnel finishes (refer to appendix C) revealed that 
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adhesive anchors are seldom used as an anchorage system to support suspended 

ceiling panels. When adhesive anchors are used, they rarely are required to act in 

pure tension, and they typically support lightweight panels. The most common 

anchorage systems used to support suspended ceiling panels are mechanical 

expansion anchors.

The survey also revealed that a majority of U.S. tunnels have continuous 

ceiling panels/slabs that extend into the concrete tunnel walls. This continuous 

support provides significant redundancy in that, if the hangers fail, the suspended 

ceiling panels are self-supported. The I-90 connector tunnel had no continuous 

supports that extended from the ends of the ceiling panels into the concrete tunnel 

walls. The struts on either side of each ceiling module prevented movement of the 

ceiling system in the transverse direction; they provided no support for the ceiling 

panels in the event of anchor or hanger failure.

In the Safety Board’s opinion, national standards for the design of tunnel 

finishes would be useful to government entities or other organizations that are 

designing new tunnels or retrofitting existing ones. As more tunnels are built and 

retrofitted in the future, the need will only increase for national standards that will 

help tunnel owners ensure uniformity and safety in their tunnel finish designs.

The Safety Board therefore concludes that national standards for the design 

of tunnel finishes, including tunnel suspended ceilings, will provide government 

entities or other organizations with ready access to information that could be 

useful in designing tunnel finishes that minimize potential risks to public safety. 

The Safety Board therefore believes that the FHWA should, in cooperation with 

AASHTO, develop specific design, construction, and inspection guidance for 

tunnel finishes and incorporate that guidance into a tunnel design manual.
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Conclusions

Findings

1. By July 2006, a significant portion of the adhesive anchors used to support the 

D Street portal ceilings had displaced to the extent that, without corrective 

action, several of the ceiling modules in the three portal tunnels were at 

imminent risk of failure and collapse.

2. Although it is unlikely that all the D Street portal adhesive anchors were 

installed in a manner that would ensure maximum anchor performance, 

improper or deficient anchor installation procedures or practices alone would 

not account for all of the anchor failures that were observed before and after 

the accident.

3. The anchor loading calculations developed by Gannett Fleming, Inc., for the 

ceiling in the D Street portal tunnel were consistent with the actual maximum 

loads sustained in service.

4. Based on published anchor strength test data, the calculated anchor loading 

for the D Street portal ceiling system, and the limited number of available 

alternatives, Gannett Fleming, Inc.’s, specification of an adhesive anchoring 

system to support the ceiling system was not inappropriate.

5. Gannett Fleming, Inc., and Bechtel/Parsons Brinckerhoff failed to account for 

the fact that polymer adhesives are susceptible to deformation (creep) under 

sustained load, with the result that they made no provision for ensuring the 

long-term, safe performance of the ceiling support anchoring system.

6. Modern Continental Construction Company, Inc., was supplied with and 

used the Fast Set formulation of Power-Fast Epoxy Injection Gel when the 

company was installing the anchors in the D Street portal, including the 

anchors that failed in this accident.

7. The source of the anchor displacement that was found in the D Street portal 

tunnels and that precipitated the ceiling collapse was the poor creep resistance 

of the Power-Fast Fast Set epoxy used to install the anchors.

8. Modern Continental Construction Company, Inc., was not aware, when its 

employees installed the adhesive anchors in the D Street portal, that the 

epoxy being used was susceptible to creep and was therefore unsuitable for 

this application.
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9. Had Gannett Fleming, Inc., in the construction contract for the D Street portal 

finishes, specified the use of adhesive anchors with adequate creep resistance, 

a different anchor adhesive could have been chosen, and the accident might 

have been prevented.

10. Gannett Fleming, Inc., approved the D Street portal anchors without 

identifying which epoxy formulation was being used, even though the 

company was provided with information indicating that one version of the 

Power-Fast epoxy should be used for short-term loading only.

11. The information that was provided by Powers Fasteners, Inc., regarding its 

Power-Fast epoxy was inadequate and misleading, with the result that Modern 

Continental Construction Company, Inc., used the Fast Set formulation of 

the epoxy for the adhesive anchors in the D Street portal even though that 

formulation had been shown through testing to be subject to creep under 

sustained tension loading.

12. As shown by the displaced anchors in the D Street portal, the maximum load 

capacity of an adhesive anchor, which relates to short-term loading, does not 

indicate that the anchor will be able to support even lighter loads over time, 

and thus a larger design safety factor cannot compensate for an adhesive 

material that is susceptible to creep.

13. After unexplained anchor displacement was found in the Interstate 90 

connector tunnel in 1999 and 2001, Bechtel/Parsons Brinckerhoff and Modern 

Continental Construction Company, Inc., should have instituted a program 

to monitor anchor performance to ensure that the actions taken in response to 

the displacement were effective. Had these organizations taken such action, 

they likely would have found that anchor creep was occurring, and they 

might have taken measures that would have prevented this accident.

14. Powers Fasteners, Inc.’s, response to the anchor displacements that occurred 

in 1999 in the high-occupancy tunnel of the D Street portal was deficient in 

that the company did not identify the source of the failures as creep in the 

Fast Set epoxy adhesive and took no followup action to ascertain why its 

product had not performed in accordance with the users’ expectations.

15. Had the Massachusetts Turnpike Authority, at regular intervals between 

November 2003 and July 2006, inspected the area above the suspended ceilings 

in the D Street portal tunnels, the anchor creep that led to this accident would 

likely have been detected, and action could have been taken that would have 

prevented this accident.

16. Because of the potential catastrophic effects of a failure of the D Street portal 

ceiling system, Bechtel/Parsons Brinckerhoff and Gannett Fleming, Inc., 

should have required that ultimate load tests be conducted on the adhesive 
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anchors used to support the ceiling before allowing any of the anchors to be 

installed.

17. Installing adhesive anchors in overhead applications appears, by the nature 

of the task, to introduce voids into the adhesive that can reduce the ultimate 

load capacity of the anchor and thus the overall reliability of the anchoring 

system.

18. The circumstances of this accident demonstrate a general lack of knowledge 

and understanding among design and construction engineers and builders 

of the complex nature of epoxies and similar polymer adhesives, and in 

particular, the potential for those materials to deform (creep) under sustained 

tension loads.

19. Protocols or standards for the testing of adhesive anchors in sustained 

tensile-load applications will provide designers and builders with test 

methods designed specifically to accurately assess the long-term safety of 

those anchors.

20. National standards for the design of tunnel finishes, including tunnel 

suspended ceilings, will provide government entities or other organizations 

with ready access to information that could be useful in designing tunnel 

finishes that minimize potential risks to public safety.

Probable Cause

The National Transportation Safety Board determines that the probable 

cause of the July 10, 2006, ceiling collapse in the D Street portal of the Interstate 

90 connector tunnel in Boston, Massachusetts, was the use of an epoxy anchor 

adhesive with poor creep resistance, that is, an epoxy formulation that was 

not capable of sustaining long-term loads. Over time, the epoxy deformed and 

fractured until several ceiling support anchors pulled free and allowed a portion 

of the ceiling to collapse. Use of an inappropriate epoxy formulation resulted from 

the failure of Gannett Fleming, Inc., and Bechtel/Parsons Brinckerhoff to identify 

potential creep in the anchor adhesive as a critical long-term failure mode and 

to account for possible anchor creep in the design, specifications, and approval 

process for the epoxy anchors used in the tunnel. The use of an inappropriate 

epoxy formulation also resulted from a general lack of understanding and 

knowledge in the construction community about creep in adhesive anchoring 

systems. In addition, Powers Fasteners, Inc., failed to provide the Central 

Artery/Tunnel project with sufficiently complete, accurate, and detailed 

information about the suitability of the company’s Fast Set epoxy for sustaining 

long-term tensile loads. Contributing to the accident was the failure of Powers 

Fasteners, Inc., to determine that the anchor displacement that was found in 

the high-occupancy vehicle tunnel in 1999 was a result of anchor creep due to 
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the use of the company’s Power-Fast Fast Set epoxy, which was known by the 

company to have poor long-term load characteristics. Also contributing to the 

accident was the failure of Modern Continental Construction Company, Inc., and

Bechtel/Parsons Brinckerhoff, subsequent to the 1999 anchor displacement, to 

continue to monitor anchor performance in light of the uncertainty as to the cause 

of the failures. The Massachusetts Turnpike Authority also contributed to the 

accident by failing to implement a timely tunnel inspection program that would 

likely have revealed the ongoing anchor creep in time to correct the deficiencies 

before an accident occurred.
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Recommendations

As a result of its investigation of the July 10, 2006, ceiling collapse in the I-90 

connector tunnel in Boston, Massachusetts, the National Transportation Safety 

Board makes the following safety recommendations:

To the Federal Highway Administration:

In cooperation with the American Association of State Highway 

and Transportation Officials, develop standards and protocols for 

the testing of adhesive anchors to be used in sustained tensile-load 

overhead highway applications. These standards and protocols 

should consider site‐specific ultimate strength values as well as the 

creep characteristics of the adhesive over the expected life of the 

structure. (H-07-15)

Prohibit the use of adhesive anchors in sustained tensile-load 

overhead highway applications where failure of the adhesive would 

result in a risk to the public until testing standards and protocols 

have been developed and implemented that ensure the safety of 

these applications. (H-07-16)

Seek legislation authorizing the Federal Highway Administration 

to establish a mandatory tunnel inspection program similar to the 

National Bridge Inspection Program. (H-07-17)

Once provided with legislative authority to establish a mandatory 

tunnel inspection program as indicated in Safety Recommendation 

H-07-17, develop and implement a tunnel inspection program that 

will identity critical inspection elements and specify an appropriate 

inspection frequency. (H-07-18)

In cooperation with the American Association of State Highway and 

Transportation Officials, develop specific design, construction, and 

inspection guidance for tunnel finishes and incorporate that guidance 

into a tunnel design manual. (H-07-19)

To the American Association of State Highway and Transportation Officials:

Work with the Federal Highway Administration to develop 

standards and protocols for the testing of adhesive anchors to be 

used in sustained tensile-load overhead highway applications, 

and incorporate those standards and protocols into the AASHTO 

Construction Quality Assurance Guidelines. These standards and 
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protocols should consider site‐specific ultimate strength values as 

well as the creep characteristics of the adhesive over the expected life 

of the structure. (H-07-20)

Use the circumstances of the July 10, 2006, accident in Boston, 

Massachusetts, to emphasize to your members through your 

publications, Web site, and conferences, as appropriate, the risks 

associated with using adhesive anchors in sustained tensile-load 

applications where failure of the adhesive would result in a risk to 

the public. (H-07-21)

In cooperation with the Federal Highway Administration, develop 

specific design, construction, and inspection guidance for tunnel 

finishes and incorporate that guidance into a tunnel design manual. 

(H‐07-22)

To the Departments of Transportation of the 50 States and the District of 

Columbia:

Prohibit the use of adhesive anchors in sustained tensile-load 

overhead highway applications where failure of the adhesive would 

result in a risk to the public until testing standards and protocols 

have been developed and implemented that ensure the safety of 

these applications. (H-07-23)

Review the use of adhesive anchors in highway construction 

within your jurisdiction and identify those sites where failure 

of the adhesive under sustained load could result in a risk to 

the public. Once those sites have been identified, implement an 

inspection and repair program to ensure that such failures do not 

occur. (H-07-24)

To the International Code Council:

Require creep testing for the qualification of all anchor adhesives. 

(H‐07‐25)

Disqualify for use in sustained tensile loading any adhesive that has 

not been tested for creep or that has failed such tests. (H‐07‐26)

Revise your building codes, qualified materials listings, and 

product labeling guidelines to clearly address the possibility for 

creep in polymeric anchor adhesives and to make end users aware 

of the potential lack of correlation between short- and long-term 

performance of these adhesives. (H-07-27)
Recommendations

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Use your building codes, qualified materials listings, test criteria, or 

other mechanisms to make end users aware of the strong potential 

for creating voids in the adhesive during the overhead installation 

of adhesive anchors and of the need to account for the reduction in 

effective embedment depth associated with the use of seal plugs in 

such applications. (H-07-28)

To ICC Evaluation Service, Inc.:

Revise evaluation report ICC ESR-1531 to state explicitly in the 

text and in the bond strength tables that the Fast Set formulation 

of Powers Power-Fast epoxy is approved for short-term loads only. 

(H‐07‐29)

To Powers Fasteners, Inc.:

Revise the packaging, for all distributors, of your Power-Fast 

Epoxy Injection Gel Fast Set formulation to state explicitly that this 

formulation is approved for short-term loads only. (H-07-30)

To Sika Corporation:

Revise your product literature and packaging to state explicitly that 

Sikadur Injection Gel AnchorFix-3 epoxy is approved for shortterm loads only. (H-07-31)

To the American Concrete Institute:

Use your building codes, forums, educational materials, and 

publications to inform design and construction agencies of the 

potential for gradual deformation (creep) in anchor adhesives 

and to make them aware of the possible risks associated with 

using adhesive anchors in concrete under sustained tensile-load 

applications. (H‐07‐32)

To the American Society of Civil Engineers:

Use the circumstances of the July 10, 2006, accident in Boston, 

Massachusetts, to emphasize to your members through your 

publications, Web site, and conferences, as appropriate, the need 

to assess the creep characteristics of adhesive anchors before 

those anchors are used in sustained tensile-load applications. 

(H-07-33)
Recommendations

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To the Associated General Contractors of America:

Use the circumstances of the July 10, 2006, accident in Boston, 

Massachusetts, to emphasize to your members through your 

publications, Web site, and conferences, as appropriate, the need 

to assess the creep characteristics of adhesive anchors before those 

anchors are used in sustained tensile-load applications. (H-07-33)

BY THE NATIONAL TRANSPORTATION SAFETY BOARD

MARK V. ROSENKER DEBORAH A. P. HERSMAN

Chairman Member

ROBERT L. SUMWALT KATHRYN O’LEARY HIGGINS

Vice Chairman Member

STEVEN R. CHEALANDER

Member

Adopted: July 10, 2007
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Appendix A

Hearing and Investigation

The National Transportation Safety Board was notified of the Boston, 

Massachusetts, accident on July 10, 2006. An investigative team was initially 

dispatched from the Safety Board’s Arlington, Texas, office. As the investigation 

progressed, additional investigators responded from the Washington, D.C., and 

Atlanta, Georgia, offices. Separate groups were established to investigate issues 

related to human performance, structural engineering, and construction oversight. 

No Board Member was on scene.

Participating in the investigation were representatives of the Federal 

Highway Administration, the DOT’s Office of the Inspector General, and the 

Massachusetts State Police.

One deposition was conducted in which an employee of Powers Fasteners, 

Inc., was interviewed on March 21, 2007.
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Appendix B

AASHTO Testing Survey

The bracketed numbers reflect the percentage of the 30 States that responded 

to survey options A through E below. Percentages total more than 100 because of 

the selection of multiple options.

How does your State ensure that these critical systems or materials will 

work properly? Please [select] one or more of the [options] below:

A. The state evaluates the material in-house (or hires a lab to evaluate 

it) based on a non-AASHTO protocol [32.3 percent]

B. The state asks the contractor to evaluate the material (or hire a lab 

to evaluate it) based on a non-AASHTO protocol [12.9 percent]

C. The state uses/trusts the manufacturers’ specs or certifications 

[25.8 percent]

D. The state delegates responsibility to the contractor to ensure that 

these critical systems will work properly (the contractor, in turn, may 

simply use the manufacturers’ specs or certifications) [19.4 percent]

E. Other (please explain) [67.7 percent]

Responses to the “Other” category from various States included the 

following observations:

A qualified products list (QPL) is developed based on a corresponding 

procedure that includes independent lab testing from the supplier 

and our lab testing for verification. Contractor performs witnessed 

proof testing in the field to confirm personnel ability and procedures. 

Quality control (QC) testing is done on the first day of production 

installation. Quality assurance (QA) testing is done on a random 

basis. Criteria and requirements for QC and QA testing are cited in 

the specifications.

The Professional Engineer will have to verify the design and testing 

to assure the system will meet the critical application.
Appendix B

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How handled varies. If proposed on a working contract an ad-hoc 

group is formed to evaluate/test. Often, we ask for independent lab 

results from the contractor/vendor, but attempt to reconfirm testing 

in our own lab. If a vender submitted item and not time critical, it goes 

to our Products Evaluation Unit and may be accepted or rejected by 

the Highway Developmental Council (standing group to evaluate 

non-standard materials). In both cases we research what would be 

the most appropriate testing protocols.

When material can not be tested in-house we require notarized test 

results and certifications from the manufacturer.

We recently completed a Materials Risk Analysis, evaluating all 

common materials for two kinds of risk: failure to meet specification 

and consequences if specifications are not met. This analysis provides 

a basis for how we accept materials: based on testing, fabrication 

inspection, manufacturer’s cert of compliance, visual, etc.

We’d try and perform ourselves or use a consultant services provider 

to ensure compliance.

[We use] a standard form to get all pertinent information on the 

material in question. We would ask the manufacturer of that material 

to provide contacts, preferably [department of transportation], where 

the material had been used if possible and provide any test data that 

they have on the material for our review. Based on this information 

we would make a decision to proceed with evaluating the material 

for use on a project specific basis or on a statewide basis.

Additional methods for critical systems or materials that have 

been utilized include a mandatory system operation, or materials 

function, failure free time period. During this time the contractor 

must maintain, rectify, correct any and all operational issues at their 

cost. The time cannot conclude nor final payment [be] made until the 

specified time period has passed continuously without issues.

If we could develop our own test method or specifications to include 

in the contract we would. If no specifications exist, we may require 

the supplier to provide specifications, test results, and certifications 

on the product. In some instances we may accept the product based 

only on the suppliers certification.

We use [established] test procedures, Certificates of Compliance, 

Analysis, and Delivery. We use a great deal of in-house testing and 

use some contractor results in the acceptance process.
Appendix B

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For critical items as described above, [we require] the 

manufacturer/contractor to provide engineering calculations to 

support the use of the material/system in question. We may also 

test some of the materials to verify the properties supplied by the 

manufacturer/contractor.

We would in some situations evaluate the component itself to 

determine the appropriate action. It could be a combination of the 

items in question 3. If at all possible we would try to find an AASHTO 

or ASTM reference that would at least support the direction of our 

action.

In some cases we maintain an approved products list that “qualifies” 

certain materials where we review and test the material or system 

and then it is available for any project.

[I]f we do not have the equipment or expertise to test the material in 

house we would identify outside testing expertise and, dependent 

on how critical the element is, we may even witness the testing.

We do not ‘ask’ contractor to evaluate critical systems or materials 

that do not have AASHTO or ASTM specification, but we have 

‘required’ the contractor to test items and we witness the testing.

Most structure critical components are tested in our Central Materials 

Laboratory. Generally, if there is not an accepted AASHTO or ASTM 

test method, there is a state test method outlining the procedure to be 

used. Certain components are taken on manufacturers’ certification 

and/or a certified test report.

Require that a registered professional engineer, registered in any 

state, evaluate and certify that the item design complies with the 

plans and specifications and meets and exceeds the appropriate 

national standard and that the materials meet or exceed the 

specification requirements. In addition, require the Contractor to 

furnish a certification that the item is fabricated in compliance with 

the certified design and complies with the specification requirements. 

For devices that require crash testing, the manufacturer is required 

to supply a certification that the device has been crashed tested and 

meets requirements per the appropriate crash test specified.
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Appendix C

Tunnel Ceiling Survey

Tunnel authority

Typical ceiling panel or 

slab dimension

Typical ceiling 

panel or slab 

weight

Ceiling 

anchorage 

system

Continuous 

support at 

end of panels 

or slabs Length Width Thickness Weight 

(lbs)

psf

Massachusetts

Turnpike 

Authority

Sumner Tunnel 11’ 3” 3’ 3” 2” 550 15 Adhesive anchors No

Callahan Tunnel 11’ 3” 3’ 3” 2 1⁄4” 550 15 Adhesive anchors No

I-90 Ted Williams 

Tunnel

11’ 0” 4’ 0” 2” 1,200 28 Adhesive anchors No

I-90 

Connector Tunnel

12’ 0” 8’ 0” 4” 4,800 50 Bolts in embedded 

steel channels, 

adhesive anchors 

at east portal and 

isolated locations

No

I-93 Central 

Artery Tunnel

12’ 0” 8’ 0” 4” 4,800 50 Hanger plates 

typically attached 

to steel roof girders

No

MTA Bridges 

and Tunnels in 

New York

Brooklyn Battery 

Tunnel

10’ 8” 20’ 5” 5” 12,380 57 Centerline 

cast-ring bolted 

hanger plus 

expansion anchors 

mechanically 

engaged in 

concrete lining

Yes, plus 

continuous 

steel I-beam

Queens Midtown 

Tunnel

10’ 8” 20’ 6” 5” 12,479 57 Centerline castring bolted hanger 

plus acrylic resin 

expansion anchors 

mostly in shear 

and partially in 

pullout

Yes, plus 

continuous 

steel I-beam
Appendix C

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Tunnel authority

Typical ceiling panel or 

slab dimension

Typical ceiling 

panel or slab 

weight

Ceiling 

anchorage 

system

Continuous 

support at 

end of panels 

or slabs Length Width Thickness Weight 

(lbs)

psf

Port Authority 

of New York 

and New Jersey 

Tunnels

Lincoln Tunnel 22’ 0” 5’ 0” 4 3⁄4” 8,000 73 Original cast-inplace slab 

supported at ends 

by concrete tunnel 

liner and by center 

support assembly 

bolted to cast-iron 

ring

Yes

Holland Tunnel 23’ 0” 5’ 0” 4 1⁄2” 8,000 70 Precast 

replacement panels 

supported at ends 

by concrete liner, 

by inserts secured 

to concrete liner 

near each end 

of panel, and by 

center assembly 

bolted to the cast 

iron ring

Yes

Detroit–Windsor 

Tunnel Authority 

in Michigan

Detroit–Windsor 

Tunnel

10’ 0” 20’ 0” 5” 11,000 55 Slab supported 

at mid-span by 

manganese bronze 

metal ceiling 

hangers

Yes

South Jersey 

Transportation 

Authority

Atlantic City 

Expressway 

Tunnel

n/a n/a n/a n/a n/a No suspended 

ceiling panels 

used in tunnel; 

ventilation is 

accomplished 

through jet fans

n/a

Maryland 

Transportation 

Authority

Fort McHenry 

Tunnel

6’ 10” 2’ 4” 2” 353 22 Panel supported 

by pipe hangers 

extended into 

concrete ceiling with 

expansion anchors

Yes
Appendix C

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Tunnel authority

Typical ceiling panel or 

slab dimension

Typical ceiling 

panel or slab 

weight

Ceiling 

anchorage 

system

Continuous 

support at 

end of panels 

or slabs Length Width Thickness Weight 

(lbs)

psf

Chesapeake 

Bay Bridge and 

Tunnel District 

in Maryland

Chesapeake Bay 

Tunnel

12’ 0” 12’ 0” 5” 8,640 60 Cast-in-place 

concrete slab 

supported by 

stainless steel 

hangers that 

extend into upper 

socket embedded 

into concrete 

ring ceiling that 

contains stainless 

steel strap anchors

Yes

Pennsylvania 

Turnpike 

Commission

Allegheny and 

Tuscarora 

Tunnels

30’ 0” 28’ 6” 5” 47,500 56 Slab corbelled into 

tunnel walls with 

redundant support 

system at midspan consisting 

of 3 hanger rods; 

hanger rods 

are attached to 

separate threaded 

insert cast in place 

at top of arch

Yes, at side 

walls, but not 

between slabs

Virginia 

Department of 

Transportation

Midtown Tunnel 6’ 6” 2’ 6” 2” 407 25 Cast-in concrete 

anchors

No

Hampton Roads 

Bridge Tunnel

eastbound tube 7’ 7” 2’ 0” 2” 474 31 Mechanical 

expansion anchors

No

westbound tube

Big Walker 

Mountain Tunnel

12’ 9”

38’ 6”

1’ 0”

31’ 0”

2”

6”

318 

89,500

25

75

Cast-in concrete 

anchors

Steel anchorage 

assemblies cast 

into concrete 

tunnel lining

No

Yes
Appendix C

National Transportation Safety Board

HIGHWAY

Accident Report

120

Tunnel authority

Typical ceiling panel or 

slab dimension

Typical ceiling 

panel or slab 

weight

Ceiling 

anchorage 

system

Continuous 

support at 

end of panels 

or slabs Length Width Thickness Weight 

(lbs)

psf

East River 

Mountain Tunnel

38’ 6” 31’ 0” 6” 89,500 75 Steel anchorage 

assemblies cast 

into concrete 

tunnel lining

Yes

Downtown Tunnel

eastbound tube 7’ 6” 2’ 6” 2” 474 25 Mechanical 

expansion anchors

No

westbound tube 7’ 6” 2’ 6” 3” 703 37 Cast-in concrete 

anchors

No

Monitor–

Merrimac

Memorial Bridge

Tunnel

7’ 3” 3’ 0” 2” 544 25 Mechanical 

expansion anchors 

for both tubes

No