PHHS UM.IOSH) PUBLICATION NO. 83-103

N AT’ L INST.

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'|||j j |j I AiiiQt at oi37 jment of Draft Construction

Safety Standards for Excavations

An NBS/NIOSH Publication

Volume I

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Geotechnical Engineering Group

Structures Division

Washington, DC 20234

April 1983

Prepared under Interagency Agreement No. 82-06-M for: Department of Health and Human Services

Public Health Service

Centers for Disease Control

National Institute for Occupational Safety and Health

Division of Safety Research, Morgantown, WV 26505

Ronald L. Stanevich, Project Officer

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NBSIR 83-2693

b'HHS (NIOSH) PUBLICATION NO. 83-103

DEVELOPMENT OF DRAFT CONSTRUCTION

SAFETY STANDARDS FOR EXCAVATIONS

An NBS/NIOSH Publication

Volume I

Felix Y. Yokel

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Geotechnical Engineering Group

Structures Division

Washington, DC 20234

and

Ronald L. Stanevich —

Division of Safety Research

National Institute for Occupational Safety and Health

Morgantown, WV 26505

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April 1983

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Prepared under Interagency Agreement No. 82-06-M for: Department of Health and Human Services

Public Health Service

Centers for Disease Control

National Institute for Occupational Safety and Health

Division of Safety Research, Morgantown, WV 26505

Ronald L. Stanevich, Project Officer

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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PREFACE

The Occupational Safety and Health Act of 1970, Section 22(c) (1 ) (d) (2)

authorizes the Director of NIOSH to make recommendations concerning improved

occupational safety and health standards. The purpose of this document is to

recommend to OSHA revised, updated language for improving 29 CFR 1926 Subpart P on Excavations, Trenching, and Shoring.

The draft standard contained in the document represents a consolidation

of technical research performed by the National Bureau of Standards (NBS) on excavations combined with analysis of the comments generated by discussions

of the proposed revisions. The proposed revisions were discussed at five

regional workshops at which representatives of interested parties such as organized labor, trade associations, academic institutions, and state and

federal agencies participated. These workshops were held in Atlanta, GA,

Boston, MA, Dallas, TX, Milwaukee, WI , and San Francisco, CA during the months

of June and July of 1981

We are pleased to acknowledge the contributions to this document made by

staff of NIOSH, NBS, and the organizers of and participants in the workshops.

The views, conclusions and recommendations expressed in this document are

not necessarily those of any particular reviewer, statepor federal agency.

However, all comments, whether or not incorporated, were considered carefully

and have been forwarded along with thi:

J . \Donal d Millar, M.D.

AssVstant Surgeon General

Director, National Institute for

Occupational Safety and Health
ABSTRACT

Five regional industry workshops were held to discuss construction practice in

excavations. The input document to the workshops contained suggested revisions

to Subpart P of the Safety and Health Regulation for Construction! which were prepared by the National Bureau of Standards (NBS) and based on previously

prepared recommendations for construction practice in excavations. 2 This report

contains a copy of the workshop input document, workshop summaries and

recommendations relating to the workshop input document.

Key words: braced excavations; construction; Federal regulations; retaining

structures; safety; shoring; slope stability; soil classifications;

soil pressures; standards, trenching.

1 Federal Register, Vol . 39, No. 122, Safety and Health Regulations for

Construction, Subpart P, Excavation, Trenching for Shoring, June 1974.

2 Yokel, F. Y., Recommended Technical Provisions for Construction Practice in

Shoring and Sloping of Trenches and Excavation, NBS Building Science Series

127, June 1980.

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TABLE OF CONTENTS

Page

ABSTRACT iii

1. INTRODUCTION 1

2. ANALYSIS OF COMMENTS AND RECOMMENDATION 3

3. APPENDIX: Workshop Input Document 55

v
LIST OF FIGURES

Page

Figure 1A. Zone of exposure 5

Figure 1. Effects of nearby foundation loads that must be determined

by an engineer 18,19

Figure 2. Allowable configurations of sloped excavations (cases II,

III and IV are for short-term excavations) 24,25

Figure 3. Determination of Adjusted Depth 28,29

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LIST OF TABLES

Page

Table 1. Soil Classification System for the Standard Practice 22,23

Table 4(a). Maximum Center-to-Center Spacing of Spaced Sheeting

Members 36
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1. INTRODUCTION

Existing OSHA regulations governing excavations, trenching, and shoring practices

in the construction industry (29 CFR 1926, Subpart P) were promulgated in 1971.

In 1976, OSHA engaged NBS to review the technical provisions of the regulations

in view of: 1) actual construction practice; and 2) the state of the knowledge

in geotechnical and structural engineering.

Based on the results of that study, which was completed in 1980, a working

draft of recommended revisions to Subpart P was prepared by NBS under sponsorship of OSHA and the National Institute for Occupational Safety and Health

(NIOSH), and widely distributed throughout industry. In the summer of 1981,

five regional industry workshops were conducted to discuss the recommendations.

Industry response was encouraged, collected and evaluated carefully.

This report contains the input document to the workshops (the working draft),

summaries of the workshop comments, and an analysis of the suggestions and

commentary produced by the workshops. In combining NBS recommendations with

industry input via the regional workshops, this document is intended to serve

as groundwork for further OSHA development of recommended standards and as part

of the record on which OSHA revision of Subpart P will be based. The report is

also intended to serve industry as a resource document for the development of a voluntary consensus standard.

Section 2 contains a comparison of the text of the input document with comments

and suggestions from the industry input, as well as resulting recommendations.

The input document to the workshops is included as an appendix to Volume I of

this report. Volume II of this report contains workshop summaries by the

author, workshop proceedings prepared by the organizers, miscellaneous

correspondence, prepared statements and background information.

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2. ANALYSIS OF COMMENTS AND RECOMMENDATIONS

This section contains an analysis of industry-wide response to the

recommendations contained in the workshop input document which is included as

an appendix.

Regional industry workshops were held in June and July 1981, in: Atlanta, GA;

Boston, MA; Dallas, TX; Milwaukee, WI; and San Francisco, CA. The workshops

were jointly sponsored by AFL-CIO, AGC, the Association of Soil and Foundation

Engineers (ASFE) and the National Utility Contractors Association (NUCA). Also,

representatives of the shoring industry, government, and other interested

groups, as well as interested individuals, participated in the workshops.

This section is laid out in a horizontal format which provides for the

simultaneous presentation of four columns of information contained on facing

pages. On the left hand page, the far left column contains the text of the

input document. The next columns, also on the left hand page, includes any

suggestions or comments which were produced in the industry workshops relating

to the corresponding portion of the text. On the right hand page, left to

right, are recommendations and suggestions made as a result of specific

industry input, and a column containing an explanation of the recommendations.

3
TEXT SUBMITTED TO WORKSHOP COMMENTS

SUBPART P - EXCAVATIONS AND SHORING

1926.650 - GENERAL PROTECTION REQUIREMENTS

(a) The regulations contain minimum

requirements for the protection of

workers in, and adjacent to,

excavations against death and

injury.

(b) Walkways, runways, and sidewalks

shall be kept clear of excavated

material or other obstructions and

no sidewalks shall be undermined

unless shored to carry a minimum

live load of one hundred and twentyfive (125) pounds per square foot.

(c) If planks are used for raised

walkways, runways, or sidewalks,

they shall be laid parallel to the

length of the walk and fastened

together against displacement

(d) Planks shall be uniform in thickness

and all exposed ends shall be provided

with beveled cleats to prevent

tripping.

(e) Raised walkways, runways, and

sidewalks shall be provided with

plank steps on strong stringers.

Ramps, used in lieu of steps, shall

be provided with cleats to insure a safe walkway surface.

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(a) It was suggested that this scope M

statement should be amplified to

make clear that the regulations only

apply when workers are exposed to l| mass movement of soil or rock.

(Comments in Wisconsin workshop by

F. Yokel —concern expressed that I revised regulations may be enforced P*

where they are not applicable, such

as borrow pits.)

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(d) AGC of Kentucky suggest: "Planks

shall be installed in a manner to

reduce the probability of tripping.

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RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(a) The regulations contain minimum

requirements for the protection of

workers in, and adjacent to,

excavations against death and

injuries. The regulations for

shoring, shielding and sloping apply

to all excavations in which workers

are exposed to effects of mass movement of soil or rock. The zone

of exposure is defined in Figure 1A.

(a) This section contains a scope

statement. It states that the regulations are minimum requirements,

which may have to be exceeded in some instances. The definition of

exposure is added in order to exempt

excavations which pose no risk to

workers from the regulations.

FIGURE 1A: 70NE OF EXPOSURE

(b) ... no sidewalk which supports

human traffic while the excavation

is in progress shall be... foot.

Sidewalks which are undermined

and not shored should be barricaded

so they can not be used.

(c) NO CHANGE RECOMMENDED

(d) A performance statement such as the

one suggested would be desirable if

it could be more precise, (i.e.,

the maximum allowable height of

protrusions could be specified.)

(e) NO CHANGE RECOMMENDED

(b) There may be sidewalks which are not

in use until the excavation work is

completed. Undermined sidewalks,

even if not used, may be hazardous.

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TEXT SUBMITTED TO WORKSHOP. COMMENTS

(f) All Employees shall be protected

with personal protective equipment

for the protection of the head,

eyes, respiratory organs, hands,

feet, and other parts of the body as set forth in Subpart Z of this part.

(g) Employees exposed to vehicular

traffic shall be provided with and

shall be instructed to wear warning

vests marked with or made of reflectorized or high visibility material.

(h) Employees subjected to hazardous

dusts, gases, fumes, mists, or atmospheres deficient in oxygen,

shall be protected with approved

respiratory protection as set forth

in Subpart D of this part.

(i) No person shall be permitted under

loads handled by power shovels,

derricks, or hoists. Employees

shall be required to stand away

from any vehicle being loaded.

(j)

A competent person shall inspect the

excavation for evidence of possible

cave- ins or slides, and indications

of structural failure in members of

the shoring system. If evidence of

possible cave-ins or slides or structural failures is apparent, all work

in the excavation shall cease until

necessary precautions have been

taken to safeguard employees.

The competent person shall conduct

an overall inspection of the excavation and the ground adjacent to the

excavation at least twice daily and

shall conduct a special inspection

after every rainstorm, penetration

of water into the excavation, or other disturbance that could weaken

the soil or the shoring system, and

shall increase protection against

slides and cave-ins if necessary.

(g)

AGC of Kentucky: Need to define

"exposed to vehicular traffic."

(h) The comment was made that "approved

respiratory protection" is not

necessarily the only means of

protection. (F. Yokel - Boston

workshop)

(i) It was noted that this provision

forces a driver to leave the truck

during loading (F. Yokel - Boston

workshop). Some, but not all,

equipment is listed (AFL-CIO).

(j)

There was some discussion whether

there should be a distinction between

a competent and a qual ified person

(see F. Yokel memo on San Francisco

workshop)

.

AFL-CIO recommended to substitute

"see that all work in the excavation shall cease until necessary

precautions have been taken to

protect employees" or "increase

protection against slides and cave- in's if necessary."

In the Wisconsin workshop (Hayden),

the competent person is defined and

the point is made that a competent

person should always be at the site

when work is in progress.

Dewatering operations and equipment

shall be monitored by a competent

person to insure their proper operation and precautions shall be taken

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RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(f) NO CHANGE RECOMMENDED

(g)

NO CHANGE RECOMMENDED

(h) NO CHANGE RECOMMENDED

(i) No person shall be permitted under

loads handled by equipment.

(j)

No employer shall cause or permit

employees to work in, or adjacent

to, an excavation until a competent

person has determined that no recognizable conditions exist exposing

them to injury from mass movement

of soil or rock.

All excavation work and work in

excavations shall at all times be

under the supervision of a competent

person.

Excavations, shoring systems and the

ground adjacent to excavations shall

be inspected by a competent person

at lease twice daily and after every - rainstorm, penetration of water

into the excavation, or other

disturbance that could weaken the

soil or the shoring system; and, if

necessary, the competent person

shall order all work in the excavation

to cease until necessary precautions

have been taken to protect employees.

Dewatering operations and equipment

shall be monitored by a competent

person to insure their proper

(i) The statement recommended is not

tied to specific equipment. The

specific reference to trucks is

dropped since it would not permit a dump truck drive to remain in the

truck during loading.

(j) The first paragraph is taken, in

part, from the proposed California

regulations and explicitly requires

a safety determination by a competent

person before anybody can work in, or adjacent to, an excavation.

The second paragraph is amended in

accordance with AFL-CIO suggestions.

The definition of a "competent

person" will be changed in accordance with suggestions by the

Wisconsin AGC (Hayden memo). A

competent person's supervision is

required for all excavation work

under this provision.
TEXT SUBMITTED TO WORKSHOP COMMENTS

to safeguard the workers in the

excavation if dewatering equipment

mal functions.

1926.651-SPECIFIC EXCAVATION REQUIREMENTS

(a) Prior to opening an excavation,

efforts shall be made to determine

whether underground installations,

i.e., sewer, telephone, water fuel,

electric lines, etc., will be

encountered, and if so, where such

underground installations are located. When the excavation

approaches the estimated location

of such an installation, the exact

location shall be determined and

when it is uncovered, proper

supports shall be provided for the

existing installation. Utility

companies shall be contacted and

advised of proposed work prior to

the start of actual excavation.

(b) Trees, boulders, and other surface

encumbrances, located so as to create

a hazard to employees involved in

excavation work or in the vicinity

thereof at any time during operations, shall be removed or made

safe before excavating is begun.

(a)

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Ohio Contractor Association |P

recommended rewording. (Letter

from Leonard Freed) Kodak Park

Division commented that this sectionlK

is appropriate in Subpart P, but IP

should be dropped from Subpart S.

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(c) (1) In excavations which employees

may be required to enter, excavated

or other material shall be effectively stored and retained at least

2 feet or more from the edge of the

excavation.

(2) As an alternative to the

clearance prescribed in subparagraph

(1) of this paragraph, the employer

may use effective barriers or other

effective retaining devices in lieu

thereof in order to prevent excavated

or other materials from falling into

the excavation.

(c) (1) AFL-CIO state that the edge

clearance should be 3 ft.

Duke suggested that if the edge

distance is too great, there is a danger that other materials may be

piled up on the resulting shelf,

actually increasing hazards. [This

suggestion was erroneously addressed

to paragraph 1926.652(6) (3) .]

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(2) AFL-CIO stated that "Other

effective retaining devices" should

be eliminated, and noted that their

task force recommended extending

tight sheeting 18 in. Rep. from the

shoring industry - suggested eliminating projection of sheeting in

Figure 3 of input document since t hi

"is not always the method used to

protect workers." Greater Milwaukee

contractors consider the section

redundant.

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RECOMMENDATIONS/SUGGESTIONS COMMENTARY

operation and workers shall leave the

excavation or other precautions shall

be taken to safeguard the workers if

dewatering equipment malfunctions.

(a) At the beginning of the paragraph,

add the following sentence: "All

known owners of underground utilities

in the area involved shall be advised

of the proposed work at least 48

working hours prior to the start of

excavation work."

(b) NO CHANGE RECOMMENDED

(c) (1) NO CHANGE RECOMMENDED

(2) As an alternative to the

clearance prescribed in subparagraph

(1) of this paragraph, the employer

may use protective barriers projecting

at least 18 inches above the ground

surface to prevent excavated or other materials from falling into

the excavation.

(a) The sentence was taken in part from

the proposed California Standard and

is similar to, but more precise

than, the opening sentence proposed

by the Ohio Contractors Associated.

The provision will assure that

utility companies are advised of

excavation work prior to its start.

(c) (1) AFL-CIO recommeded to increase

clearance to 3 ft., but no specific

justification was presented for such

a provision, which would increase

right-of-way requi rements. The

AFL-CIO suggestion should be further

studied before a decision is made.

(2) It appears that a "barrier" or a "retaining device" are one and the

same.

Projecting the sheeting was suggested

by AFL-CIO but considered hazardous

by others. The decision about what

kind of an effective barrier to use should be left to the contractor.
TEXT SUBMITTED TO AGENCY COMMENTS

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(d) Diversion ditches, dikes or other

suitable means shall be used to

prevent surface water from entering

an excavation and to provide adequate

drainage of the area adjacent to the

excavation. Water shall not be

allowed to accumulate in an excavation, unless this condition is

considered in the design and in the

initial work plan and adequate

provisions are made to protect

workers.

(d) It was suggested in the San Francisc®

workshop to add "while work is in W

progress." (F. Yokel , S. F. memo)

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(e) If it is necessary to place or operate power shovels, derricks,

trucks, materials, or other heavy

objects on a level above and near an excavation, the side of the excavation shall be shored as necessary

to resist the extra pressure due

to such superimposed loads.

(f) Blasting and the use of emplosives

shall be performed in accordance

with subpart U of this part.

(g) When mobile equipment is utilized or allowed adjacent to excavations,

substantial stop logs or barricades

shall be installed. If possible,

the grade should be away from the

excavati on.

(h) Adequate barrier physical protection

shall be provided at all remotely

located excavations. All walls,

pits, shafts, etc., shall be barricaded or covered. Upon completion

of exploration and similar operations, temporary walls, pits, shafts,

etc., shall be backfilled.

(i) If possible, dust conditions shall

be kept to a minimum by the use of

water, salt, calcium chloride, oil,

or other means.

(e)

(f)

( 9 )

(h)

( 1 )

Many comments noted that this sectioi^

is redundant. In the San Francisco fl|

workshop, it was noted that methods

other than shoring could be used.

(F. Yokel , S. F. memo) Concern was expressed that this provision may belP

applied to backfilling operations.

A question was raised whether this

section is necessary since it state

the obvious.

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Many workshop participants consider

the use of stop logs impractical.

The grading provision is advisory

and, therefore, may not be

appropriate in a regulation.

The statement was criticized as being imprecise. (Ohio Contractors

Assoc., F. Yokel, S. F. memo) It was recommended to delete "remotely

located." (F. Yokel, S. F. memo)

It was noted in many comments that

this paragraph conflicts with ERA

regul ations.

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RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(d) ...Water shall not be allowed to

accumulate in an excavation whil

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work is in progress, unless ...

(e) It is recommended to eliminate this

paragraph.

(f) NO CHANGE RECOMMENDED

(g)

It is recommended to eliminate this

paragraph.

(h) Excavations at unattended work

locations shall have adequate

physical barrier protection or other

means to prevent employees from

falling into the excavation and

mobile equipment from inadvertently

entering the excavation. All walls,

pits, shafts, etc., shall be

barricaded or covered.

Upon completion of exploration and

similar operations, temporary walls,

pits, shafts, etc., shall be

backfi lied.

(i) It is recommended to eliminate this

paragraph.

(d) The qualification added would prevent

an unnecessarily broad interpretation

of this provision.

(e) "Surcharge" is adequately covered in

1926.652.

(g) Stop logs are impractical. The

second sentence contains a sound

idea, but the phrase, "if possible"

is too vague. Such a statement may

be appropriate in a standard, but

not in a regulation.

(h) The fact that an excavation is

remotely located is less important

than the fact that it is unattended.

This more precise statement is in

part taken from the proposed

California regulations.

(i) Part of the regulation conflicts

with EPA regulation. Also, a regulation containing the statement

"if possible" is too vague.

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TEXT SUBMITTED TO WORKSHOP COMMENTS

(j) In locations where oxygen deficiency

or gaseous conditions are possible,

air in the excavations shall be

tested. Controls, as set forth in

Subparts D and E of this part, shall

be established to assure acceptable

atmospheric conditions. When flammable gases are present, adequate

ventilation shall be provided or sources of ignition shall be eliminated. Attended emergency rescue equipment, such as breathing apparatus, a safety harness and line,

basket stretcher, etc., shall be

readily available where adverse

atmospheric conditions may exist or develop in an excavation.

(k) Where employees or equipment are required or permitted to cross over excavations, walkways or bridges

with standard guardrails shall be

provided

(l) Where structural ramps are used for

employees or equipment, they shall

be designed and constructed by

qualified persons in accordance with

accepted engineering requirements.

(m) All ladders used on excavation

operations shall be in accordance

with the requirements of Subpart L of this part.

(n) Materials used for shoring,

sheeting, and underpinning of structures adjacent to excavations shell

not be damaged or weakened by corrosion, deterioration or prior use to

an extent that will cause them to

have a minimum strength less than

that required in Section 1926.652

(b)(4)(H).

(o) Employees entering bell -bottom pier

holes shall be protected by the

installation of a removable-type

casing of sufficient strength to

resist shifting of the surrounding

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(m)

(o)

It was suggested to spell out jjj

emergency procedures here, rather

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than referencing other regulations,

(i.e., Texas memo, Braun and Root) Mj

It was also recommended to delete V

this paragraph, "in accordance with

Texas

prior

workshop,

agreement with

Ohio

OSHA."

Contractors

(White, ^

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Assoc.) ^

It was noted that this provision is

not practical for small (shallow)

trenches (Texas memo). It was also

recommended to adopt the California

approach (7 1/2 ft. or more, F.

Yokel , S.F. memo)

AGC of Kentucky suggested to elimina

this section because it is for longterm excavations.

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AFL-CIO recommends: to eliminate

"be designed and ...."

There was concern about ladders

projecting above the trench (Texas

workshop memo).

The wisdom of requiring a harness

was questioned since sometimes other

protection is safer (F. Yokel, Texas

memo). AFL-CIO asked why straight

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RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(j)

Provisions should either be spelled

out or paragraph deleted, as this is

covered by other regulations.

(k) Trenches shall only be crossed where

safe crossing have been provided.

Walkways and bridges across excavated

areas shall be provided with standard

guardrails and toe boards when the

depth of excavation exceeds ? feet

(7 1/2 in California Standard).

(1)

drop "and constructed"....

(m) The need for this paragraph reference

is questioned.

(n) NO CHANGE RECOMMENDED

(o) ....above the bell. Adequate life

saving equipment, suitable for

instant rescue, shall be required

for each employee entering the shaft.

Employee personal protective equip-

(j)

Neither duplication of regulations

nor cross reference to other

regulations are desirable.

(k) Walkways and bridges are not the

only safe means for crossing

excavations. There may be berms or access slopes. Guard rails should

not be required for very shallow

trenches. The wording is taken from

the proposed California Standard.

No justification was found for the 7 1/2 ft. height limit, even though it

appears reasonable.

(l) The intent here is to get proper

engineering design. Since a "competent

person" must be in the field, it is

assumed they will be properly

constructed

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(m) Ladders are covered elsewhere.

(o) It is obvious that this section

addresses itself specifically to

belled piers since these require

hand excavation. However, the term

"partially cased" piers could also

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TEXT SUBMITTED TO WORKSHOP COMMENTS

earth. Such temporary protection

shall be provided for the full depth

of that part of each pier hole which

is above the bell. A lifeline,

suitable for instant rescue and

securely fastened to a shoulder

harness, shall be worn by each

employee entering the shafts. This

lifeline shall be individually

manned and separate from any line

used to remove materials excavated

from the bell footing.

(p)

When employees are required to be in

trenches 4 (5?) feet deep or more,

an adequate means of exit, such as a ladder, steps or a negotiable slope

shall be provided and located so as to require no more than 25 feet of

lateral travel.

(q)

Shoring shall follow the excavation

as closely as practical in order to

avoid long sections of unshored

excavations.

(r) Members of the shoring system shall

be installed in their proper

position and secured to prevent

failure.

(s) Portable trench boxes or sliding

trench shields may be used for the

protection of personnel in lieu of a shoring system or sloping. Where

such trench boxes or shields are

sided pier holes are not covered

here.

Brown and Root noted that it is

difficult to get men with harnesses

out on a vertical pull. Proposed

rewording.

(p)

Opinions of workshop participants

were split on the issue of depth (5

ft or 4 ft). AFL-CIO favored 4 ft.

Most, but not all, contractors and

engineers favored 5 ft. It was suggested to allow the use of

shoring as aid of exit and large

pipes as shelter (Texas memo). It was suggested to allow escape to

the center of wide excavations if

escape routes are unobstructed

(Kodak letter).

(q)

The comment was made that the section

is confusing since shoring is not

always needed (Duke, AGC-Kentucky)

It was also suggested to drop this

section.

(r) It was recommended to drop this

provision (F. Yokel, Boston memo,

Texas memo, AGC-Kentucky). The

section also was called unclear.

(AGC-Kentucky, Ohio Contractors

Association)

(s) Efficiency Production and GME

suggested to add: "As defined by

accepted engineering practice".
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

merit should include, but not be

limited to, harnesses, wristlets, or other devices acceptable to OSHA.

Lifelines shall be individually

manned and separate from any lines

used to remove excavated material.

(p) When employees are required to be in

excavations 5 feet deep or more, an adequate means of exit such as a ladder, steps or a negotiable slope

shall be provided and located so as to require no more than 25 feet of

lateral travel. As an alternate to

a means of exit to the top of the

excavation, the following means of

escape from mass movement of soil or rock are considered acceptable:

unimpeded movement away from the

excavation wall toward the center of

the excavation if the width of the

excavation measured at the top of

the bank exceeds 3 times its depth;

not more than 25 feet of unimpeded

lateral travel to a large-diameter

pipe or another safe structure which

would not collapse, and the access

to which would not be blocked as a result of a cave-in.

(q) "As closely as practical" is very

vague for a regulation. The paragraph, however, is appropriate for

a standard. It is suggested to

either drop this provision or change

it to read, "Shoring, where needed,

shall follow...."

(r) Struts (cross braces) shall be

secured to other members of the

shoring system so they will stay in

place when their preload is lost.

(s) It is recommended to eliminate this

paragraph.

be used. The section was revised in

accordance with suggestions by Brown

and Root.

(p) The opinion on the limiting depth

was split; however, it may be

counterproductive to enforce the

regulations for 4 ft deep trenches

which would include most of the

waterlines, and thereby considerably

increase the volume of trenching

work covered by these regulations.

In very wide excavations, escape to

the center of the excavation would

probably be safer than attempts to

scale the bank. The same reasoning

would also apply if a safe sheltered

area is available on the bottom of

the excavation.

(r) This paragraph was too general to serve a useful purpose. However, it

is important to "secure" struts,

which have a tendency to fall out

when the preload is lost.

(s) Shoring, as well as shielding,

systems are handled adequate in

1926.652. It is no longer necessary

to use the concept of "equivalency"

since Table P.2 is eliminated.

15
TEXT SUBMITTED TO WORKSHOP • COMMENTS

used they shall be designed, con- structed, and maintained in a manner

which will provide protection equivalent to that provided by the

shoring required for the excavation.

(t) Backfilling and removal of trench

support shall progress together from

the bottom of the trench. Struts

shall be released slowly and, in

unstable soils, ropes shall be used

to pull out the jacks or braces from

above after employees have cleared

the trench.

1926.652-SPECIFIC SHORING, SHIELDING,

AND SLOPING REQUIREMENTS

(a) Acceptable Practice

(1) The following excavations are exempt

from shoring, shielding, and sloping

requirements:

a. Excavations less than 5 ft deep,

except when examination of the

ground by a competent person

indicates that hazardous ground

movement may occur.

b. Excavations in unfractured rock.

(2) Excavations from 5 ft to 20 ft (24 ft

?) deep shall be shored, shielding,

or sloped in accordance with the

Standard Practice in Section

1926.652(b) with the following

exceptions:

a. If there is a deviation from the

provisions of the Standard

Practice, shoring, shielding, or sloping reuqirements must be

determined by an engineer (a

qualified persion ?).

b. An engineer shall determine the

shoring, shielding, or sloping

requirements whenever the bottom

of a building foundation adjacent

to the excavation which has not

been secured by underpinning

extends into the critical zone delineated in Figure 1.

(t) Many workshop participants considered

this section unwarranted because it

is overly descriptive and could not

be implemented with some systems

(F. Yokel memos - Boston and Dallas,

AGC-Kentucky)

(a) Kodak suggested to use the terms

"stable" and "unstable" rock, since

almost all rock slopes that have

been excavated are fractured.

The opinions on the depth limit for

the standard practice were split:

AFL-CIO sggested 15 ft. The majority

of AGC and ASFE, 24 ft. Some AGC

and ASFE representati ves, 20 ft.

The opinions on "engineer" vs. "qualified person" were split. AFLCIO wants the term "engineer." Most

other participants suggested "qualifie1 person," with an improved definition

of the term. The suggestion was made that the "qualified person"

should be required to submit

calculations (F. Yokel, S. F. memo).

p

AGC-St. Louis suggested that depth

limits for standard practice should

not apply to sloped excavations.

Efficiency Construction suggested

the term "qualified engineer." One

important point was made in a joint

report of the local sponsors of the

Milwaukee workshop (Hayden), as well

as by AFL-CIO (Mickle): Any OSHA

standard should

a

a

n

cover as many

situations as possible with standard

R

a

practice,
RECOMMENDATIONS/ SUGGEST IONS COMMENTARY

(t) Removal of trench supports and

backfilling shall be performed in

a manner which will not expose

workers to mass movement of soil or

rock.

(a) Acceptable Practice

(1) The following excavations are exempt

from shoring, shielding, and sloping

requirements:

a. Excavations less than 5 ft deep,

except when examination of the

ground by a competent person

indicates that hazardous ground

movement may occur.

b. Excavations in stable rock.

(2) Excavations from 5 ft to 24 ft

deep in Type A and B soils and from

5 ft to 15 ft deep in Type C soils

(see table 1) shall be shored,

shielded or sloped in accordance

with the Standard Practice in Section

1926.652(b) with the following

exceptions

a. If there is a deviation from the

provisions of the Standard

Practice, shoring, shielding, or sloping requirements must be

determined by a qualified person.

b. An engineer shall determine the

shoring, shielding, or sloping

requirements whenever the bottom

of a building foundation adjacent

to the excavation which has not

been secured by underpinning

extends into the critical zone delineated in figure 1.

(t) Careless or premature removal of

shoring may expose workers to the

effects of a cave- in. A descriptive

section like the one originally

proposed cannot work since different

procedures are used for different

shoring systems. Thus, a performance requirement is proposed.

(a) The terms of stable and unstable

rock are introduced as suggested by

Kodak. This will help to resolve

the difficulty arising from the

definitions of "fractured rock."

The definitions are modified

accordingly.

A more rational approach is taken to

the depth limit for standard practice.

The greatest concern in selecting

shoring for deep excavations without

prior engineering analysis is not

the lateral force against this

shoring, but the possibility of a base failure, either because of

inadequate shear strength of the

soil, or because of a quick condition

arising from hydraulic gradients.

These concerns are associated with

Type C soils and, therefore, a 15 ft

depth limit is recommended for these

soils. On the other hand, there is

not much risk associated with a 24 ft

limit for Type A and B soils, even though it is not likely that many

contractors will use standard practice

to this depth.

The controversy around the "qualified

person" concept is primarily semantic.

An attempt is made in 1956.652 to

improve the definition of "qualified

person.

17
TEXT SUBMITTED TO WORKSHOP COMMENTS

Ad

\\

i \

Limit of critical zone

FOOTING A: Standard practice can be followed FOOTING B: An enfineer shall be consulted Figure 1. Effects of nearby foundation

loads that must be determined

by an engineer

(3) For all excavations deeper than

20 (24?) ft, except those in

unfractured rock, an engineer

(qualified person) shall determine

the shoring, shielding, or sloping

requirements.

(b) Standard Practice

(1) Scope

The Standard Practice provides a method by which field conditions are related to shoring, shielding, and

sloping requirements.

The Standard Practice makes a distinction between short-term and

long-term excavations (see definition in 1926.653 - 24 hours (7 days)

is the division point).

(b)(1) It was noted that in some regions

there are local practices which

have a long track record of

successful application and an excellent safety record (see

memoranda and letters on Wisconsi

workshop). These practices do

not always comply with the proposed Standard Practice (for

instance, the struts in the

Wisconsin practice cannot support

the weight of a man - per

F. Yokel memo). Introduction of

the Standard Practice in such

locations may actually increase

accidents because workers have to

be re-trained.
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

FOOTING A: Standard practice can be followed FOOTING B: An enf ineer shall be consulted Figure 1. Effects of nearby foundation

loads that must be determined

by an engineer

For all excavations deeper than 24 ft in

Type A and B soils or 15 ft in Type C

soils, except those in stable rock, a qualified person shall determine the

shoring, shielding, or sloping

requirements.

(b) Standard Practice

(1) Scope

The Standard Practice provides a method

by which field conditions are related to

shoring, shielding, and sloping

requi rements.

The Standard Practice makes a distinction

between short-term and long-term excavations (see definition in 1926.653 - 3

days is the division point.)

Established regional practices can be

used in lieu of the Standard Practice if

they are approved by local authorities

and have a proven record of at least

5 years of successful application. Such

practices are subject to review and

revocation if a serious accident occurs. Any change in such regional practices

shall comply with the Standard Practice.

(b)(1) Elimination of the distinction

between short-term and long-term

excavations, even though attractive

from the point of view of simplicity, would force us to make the

Standard Practice more conservative than present work practices.

The 3-day division point seems a reasonable compromise.

The provision accomodating

established regional practices is

designed to minimize possible

adverse impacts from the introduction of new regulations, while at

the same time safeguarding the

safety of the workplace. Additional field measurements particularly of loads acting on wales,

could enable us to minimize the

discrepancy between the Standard

Practice and some established

regional practices.

The provision that a change in an estal bished regional practice must

comply with the standard practice

will safeguard against lateral

load increases and failures,

resulting from the replacement of

shoring members used in the estalished practice by members made

of different materials which may

have the same working strength as the original member, but differstiffnesses and safety margins.

19
TEXT SUBMITTED TO WORKSHOP COMMENTS

(2) Soil Classification

Soils are divided into three types:

A, B, and C. For each soil type the

"equivalent weight effect", we , to be

used for the calculation of lateral

soil pressure on shoring systems,

and the maximum permissible sideslope

for sloped excavations are stipulated. Table 1 provides guidance

for the selection of the soil type.

Table 1

(3) Sloped Excavations

Sloped excavations shall not have

sideslopes steeper than those stipulated in table 1. If there is any

indication of general or local

instability, slopes shall be cut

back to the stable slope. The slope

configurations shown in figure 2 can be used.

Figure 2--refer to page 24 for

magnified print of figure 2.

(b)(2) In the California workshop, it was recommended to adopt the new

soil classification recommended

by CAL OSHA (F. Yokel , S. F. memo)

In the Boston workshop the

suggestions was made to return to

the Matrix classification originally proposed by NBS (Building

Science Series 122).

Refer to page 22 for magnified print

of table 1.

(3) See comments on table 1 and figure 2.

Figure 2

Different opinions were expressed

regarding the bank next to the work

area. Many contractors expressed

the opinion that the bank should be

increased to 4 ft (Dallas and Atlanta

workshops, Kentucky AGC and others).

In the Dallas workshop, it was suggested by some contractors to

increase the bank to 5 ft (workshop

memo). AFL-CIO recommended to

leave the allowable height at 3 ft.

The point was made that if a large

pipe is laid it would provide workers

protection against collapse of the

bank next to the work area.

AFL-CIO objected to case IV as too

complicated for regulation

recommended to make it advisory.

20
RECOMMENDATIONS/ SUGGEST IONS COMMENTARY

(2) NO CHANGE RECOMMENDED

Refer to page 23 for magnified

print of table 1.

(3) NO CHANGE RECOMMENDED

Figure 2—Refer to page 25 for

magnified print of figure 2.

I

I

I

I

I

I

1

I

Figure 2

The revised sketch is a suggestion

rather than a recommendation. It is

recommended that industry try to

reach agreement on the height of the

al 1 owabl e bank.

Reasons for increasing the bank to

4 ft would be that the safety risk is

not substantially increeased, while

accommodating pipe bedding specifications presently used by many

municipalities, etc. The suggested

scheme would accommodate most specifications, while the original scheme

would conflict with some.

Frequent situations of conflict

between excavation safety regulations

and job specifications could undermine

the effectiveness of the regulations.

21
TEXT SUBMITTED TO AGENCY

Table 1. Soil Classification System for the Standard Practice

Soil Type Description w

elb/ft3 Steepest Allowable Slope hot. :vert.^/

Depth 12 ft. or less Depth Greater

than 12 ft.

A Intact Hard 20“/ 3/4:1 1:1

B Medium 40 3/4 :

c / 1 1/2:1

C Saturated, Submerged

or Soft

80 1 1/2:1 2:1

Notes

1. Type A : Intact Hard Soils Include stiff clays and clayey (cohesive) sands and gravels (hardpan, till) above the ground water table which have no fissures, weak

layers, or inclined layers that dip toward the bank of the excavation as stipulated

in Note 3. Stiff clays included have an unconflned compresssive strength6 / q u - 1.5 tsf or more. Intact hard soils subject to vibrations by heavy traffic,

pile driving or similar effects are Type B .

2. Type B : Medium Soils are all soils which are not Type A or C.

3. Type C : a. Soft Soils include cohesive soils^ with an unconflned compressive

strength6 / of 0.5 tsf or less and soils that cannot stand on a slope of 3 hor.

1 vert, without slumping (muck).

b. Saturated or Submerged Solis are assumed whenever water seeps into the excavation

from the soil forming the bank; or water is retained by tight sheeting; or there is

a possibility that the excavation may be entered by workers within 1 day after more

than half of its depth was flooded and pumped out.

4. Layered Systems (two or more distinctly different soil or rock types or micaceous

seams in rock) which dip toward the bank of the excavation with a slope of 4 hor.:

1 vert, or steeper are considered Type C. Layered soils are classified in accordance with the weakest layer.

5. Rock: Fractured rock shall be considered Type B when it is dry and Type C when it

is submerged. Unfractured rock is exempt from shoring and sloping requirements.

a/ In long-term excavations "Intact Hard” soil is Type B soil.

^/ If there is any indication of general or local instability slopes shall be cut back

to a slope which is at least 1/4 hor.:l vert, flatter than the specified slope.

c / In long-term excavations steepest allowable slope shall be 1:1.

Cohesive soils are clays (fine grained) or soils with a high clay content which have cohesive strength. They do not crumble, can be excavated with vertical sideslopes, are plastic (can be molded into various shapes and rolled into threads) when moist

and are hard to break up when dry.

e / Unconflned compressive strength can be determined by undrained laboratory tests, field tests, or the following thumb penetration tests: stiff clays with an unconfined compressive strength of 1.5 tsf can be readily Indented by the thumb nail. They can be indented by the thumb, but can be penetrated by the thumb only with very

great difficulty. Cohesive soils with an unconflned compressive strength of less than 0.5 tsf can be easily penetrated several inches by the thumb and can be molded

by light finger pressure. tsf»tons per square foot. (W ...Slopes shall be cut back to the stable (flatter) slope? Change Table 1 to use

3/4:1 maximum slope as the only limitation?)

COMMENTS

It was suggested that 1/2:1 slope should be permitted (Wisconsin workshop, Kentucky

AGC). Kentucky AGC also proposed a 5 ft bank next to the work area with a 1/2 in 1 slope for Type A soils and a 3 ft bank with a 3/4 in 1 slope for Type B soils.

It was noted by ASFE that the "Standard Practice is not conservative enough for slopes

to be used blindly; thus, the "stable slope" concept must be maintained (Kleinfelder)

AFL-CIO strongly objected to the "stable slope" concept as being too vague. It was noted in the Texas workshop that some caliche formations will stand on a 1/4:1 slope

(F. Yokel, Texas memo). It was noted that "vibrations" should be defined. It was state that there is a conflict between the sloping requirements for Type C soils and the definition under 3. of soils that cannot stand on a 3:1 slope.

22
RECOMMENDATIONS/ SUGGESTIONS

Table 1. Soil Classification System for the Standard Practice

Soil Type Description w lb/ ft^

e Steepest Allowable Slope hot. :vert.k/

Depth 12 ft. or less Depth Greaterthan 12 ft. A Intact Hard 20®/ 1/2:1 1/2:1

B Medium 40 1/2:1®/ 3/4:1®/

C Saturated , Submerged

or Soft

80 1:1 1 1/2:1

Notes:

1. Type A : Intact Hard Soils Include stiff clays and clayey (cohesive) sands and gravels 1*/ (hardpan, till) above the ground water table which have no fissures, weak

layers, or inclined layers that dip toward the bank of the excavation as stipulated

in Note 3« Stiff clays Included have an unconflned compresssive strength®/

q u

• 1.5 tsf or more. Intact hard soils subject to vibrations by heavy traffic,

pile driving or similar effects are Type B .

2. Type B : Medium Soils are all soils which are not Type A or C.

3. Type C : a. Soft Soils Include cohesive soils**/ with an unconfined compressive

strength®/ of 0.5 tsf or less and soils that cannot stand on a slope of 3 hor.:

I vert, without slumping (muck).

b. Saturated or Submerged Soils are assumed whenever water seeps into the excavation from the soil forming the bank; or water is retained by tight sheeting; or there is a possibility that the excavation may be entered by workers within 1 day after more

than half of its depth was flooded and pumped out.

4. Layered Systems (two or more distinctly different soil or rock types or micaceous

seams in rock) which dip toward the bank of the excavation with a slope of 4 hor.:

1 vert, or steeper are considered Type C. Layered soils are classified in accordance with the weakest layer.

5. Rock : Unstable rock shall be considered Type B when it is dry and Type C when it

is submerged. Stable rock is exempt from shoring and sloping requirements.

®/ In long-term excavations "Intact Hard" soil is Type B soil.

k/ The steepest allowable slope is not necessarily safe in all- conditions. A competent person shall determine the safe slope, and if there is any indication of general

or local instability, slopes shall be cut back to a slope which is at least 1/4 hor.:

1 vert, flatter than the specified slope.

c/ In long-term excavations steepest allowable slope shall be 3/4:1 for depths 12 ft or less and 1:1 for depths greater than 12 ft.

<*/ Cohesive soils are clays (fine grained) or soils with a high clay content which have

cohesive strength. They do not crumble, can be excavated with vertical sideslopes

are plastic (can be molded into various shapes and rolled into threads) when moist

and are hard to break up when dry.

e / Unconfined compressive strength can be determined by undrained laboratory tests, field tests, or the following thumb penetration tests: stiff clays with an unconfined compressive strength of 1.5 tsf can be readily indented by the thumb nail. They can be indented by the thumb, but can be penetrated by the thumb only with very

great difficulty. Cohesive soils with an unconflned compressive strength of less than 0.5 tsf can be easily penetrated several inches by the thumb and can be molded

by light finger pressure, tsf“tons per square foot.

COMMENTARY

It is obvious from the workshop discussions that the maximum allowable slopes are too severe for many regions. Thus, these sloping requirements are relaxed. To offset possible hazards resulting from this relaxation, footnote b) was modified to explicitly

charge the competent person on the job with the responsibility of selecting a safe slope . This approach is also in line with the ASFE comment that stipulates slopes cannot be used "blindly."

The terms "unstable" and "stable" are used in 5.

The statement on vibrations was not modified, even though it is realized that there may

be some question whether a vibration warrants this consideration. It is possible, within

the present stateof-the-art, to define vibration by velocity measurements; however, this approach seems too sophisticated for the excavation environment. In any case, heavy

traffic and pile driving are specifically Identified.

23
TEXT SUBMITTED TO WORKSHOP

i

Case I - Simple slope

Case II - Compound slope with bench no more than 3 ft. high

Case III & IV - Configuration must meet following criteria:

1. No vertical bank to exceed 5 ft., the vertical bank adjacent to the work area not to exceed 3 ft.

2. Imaginary slopes ij and kl not to exceed steepest allowable

sideslope from Table I

Figure 2. Allowable configurations of sloped excavations

(cases II, III, and IV are for short-term excavations)

24
RECOMMENDATIONS/SUGGESTIONS

i Cast III

5 ft. wax.

|

Statpast allowable sidaslepa from Table I

Setback d

Casa I - Simple slope

Case II - Compound slope with bench no more than 4 ft. high Case III l IV • Confifuration must meet following criteria:

f. No vortical bank to exceed 5 ft., the vertical bank adjacent to the work area net to exceed 4 ft

2. Imapinary slopes ij and kl not to exceed steepest allowable

sideslope from Table I

Figure 2. Allowable configurations of sloped excavations

(cases II, III, and IV are for short-term excavations)

25
TEXT SUBMITTED TO WORKSHOP COMMENTS

(4) Shored and Shielded Excavations

(i) For the purpose of selecting shoring

systems, trench shields, or trench

boxes the depth of excavations shall

be assumed greater than the actual

depth in order to allow for spoil

piles, construction equipment and

sloping ground. This adjusted depth

(H e ) shall be determined as follows:

a. For ground sloping down from the

supported or shielding excavation

wall, level ground, or ground sloping

up from the supported or shielded

excavation wall with a slope less

than 3 hor. in 1 vert, the Adjusted

Depth (He ) is the actual depth of

the supported excavation wall (H)

plus 2 ft (surcharge allowance).

(See figure 3(a).)

b. For ground sloping up from the

supported or shielded excavation

wall with a slope of 3 hor.:l vert,

or steeper the adjusted depth (He ) is determined in accordance with

table 2 and figure 3(b).

c. For heavy equipment (20,000 lb or more) near the side of the supported

or shielded excavation wall the

additional depth shown in table 3 shall be added to the 2 ft. surcharge

allowance stipulated in a. No

additional depth needs to be added

for equipment operating at a distance

from the side of the excavation wall

which is equal to, or larger than,

the depth of the supported or shielded excavation (H).

(4)(i) Many workshop participants

observed that this section is

complicated and perhaps difficult

to implement. (F. Yokel, S. F. memo. Efficiency Production memo)

AFL-CIO suggested to: 1) Increase

surcharge in (4)(i)) a. to 3 ft.,

2) Keep (4)(2) b. and c. as a guidel ine.
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(4)(i) NO CHANGE RECOMMENDED (4)(i) Even though b. and c. require

some skill, their application

should not be too difficult for a competent person to handle. The

alternative of a need to consult

a qualified person who is not on the job is even less attractive.

The AFL-CIO suggestion of increasing

the surcharge requirement in a.,

and in return eliminating b. and

c., would mean in practice that

in case b., a backslope of maximum

4 ft. height (H] in figure 3b = 4 + 4 ft) could be allowed, and

equipment of maximum 20,000 lb.

With higher backslope and heavier

equipment, an engineer (qualified

person) would have to be consulted.

If this is acceptable, OSHA could

go that route.

27
TEXT SUBMITTED TO WORKSHOP COMMENTS

c

TABLES 2 and 3 (Refer to appendix)

Figure 3

Tables 2 and 3 SEE COMMENTS ON 4(i)

Figure 3

It was suggested to eliminate the

protrusion of shoring, as this is many

times not used, and frequently not

desirable as a means of protection agains

rolling or sliding objects (Bradberry).

TOP OF SUPPORTED WALL SURCHARGE

(aj AVERAGE CONDITION, TERRAIN NOT

STEEPER THAN 3 hor : 1 vert ADJUSTED DEPTH = H+2ft

B

(b) GROUND SLOPING TOWARD

SUPPORTED WALL

ADJUSTED DEPTH IN ACCORDANCE

WITH TABLE 2, BUT NOT MORE

THAN Hi+2ft

(c) HEAVY EQUIPMENT LOADS

ADJUSTED DEPTH: ADD THE

DEPTH FROM TABLE 3 TO THE

2ft SURCHARGE ALLOWANCE

ADJUSTED DEPTH =H+2ft+Hw

H w IS FROM TABLE 3

H = DEPTH OF SUPPORTED EXCAVATION

I

V

R

H

R

R

R

Figure 3. Determination of Adjusted Depth
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

TABLES 2 and 3 NO CHANGE RECOMMENDED

TOP OF SUPPORTED WALL SURCHARGE

(aj AVERAGE CONDITION, TERRAIN NOT

STEEPER THAN 3 hor : 1 vert ADJUSTED DEPTH = H+2ft

(b) GROUND SLOPING TOWARD

SUPPORTED WALL

ADJUSTED DEPTH IN ACCORDANCE

WITH TABLE 2, BUT NOT MORE

THAN Hi+2ft

(cj HEAVY EQUIPMENT LOADS

ADJUSTED DEPTH: ADD THE

DEPTH FROM TABLE 3 TO THE

2ft SURCHARGE ALLOWANCE

ADJUSTED DEPTH =H+2ft+H w

H w IS FROM TABLE 3

H = DEPTH OF SUPPORTED EXCAVATION

Figure 3. Determination of Adjusted Depth

29
TEXT SUBMITTED TO WORKSHOP COMMENTS

(ii) Required strength of Shoring Systems,

Trench Shields and Trench Boxes.

Shoring systems, trench shields and

trench boxes shall have adequate

strength to resist the following

working loads:

a. A uniformly distributed lateral

pressure equal to the equivalent

weight effect (we ) , in Table 1 times

the Adjusted Depth (H e ) of the

Excavation.

b. A 240 lb gravity load distributed

over a 1 ft length at the center

of any strut (cross brace).

c. A 240 ft- lb impact load acting

toward the excavation on the walls

of trench shields and trench boxes.

Loads a. and b. shall be assumed to

act simultaneously. Only trench

shields and trench boxes need to

resist load c.

Shoring systems shall be designed in

accordance with accepted engineering

practices. A 33 percent increase

in allowable working stresses or an equivalent strength reduction shall

be acceptable for shoring systems,

trench shields, and trench boxes

used in short-term excavations.

(ii) Many workshop participants commente

that this section should be at the

end of the text since it addresses

itself to people who pre-design

shoring systems and not to the man

in the field.

«

I

AFL-CIO noted that in accordance

jj with their task force recommendationTM

the gravity load under b. should be

increased to 500 lb. They also

noted that the impact load fj

requirement is not clear.

Efficiency Production, in behalf of

the trench box industry, requested

that under a. a triangular (hydrostatic type) pressure distribution

be permitted. However, another

trench box manufacturer said that

he agrees with our recommendation.

The justification for the 33 percent

overload for short-term excavation

was questioned (F. Yokel, Boston

memo)

a

a

a

a

a
RECOMMENDATIONS/ SUGGEST IONS COMMENTARY

( i i ) Move to end of 1926.652. Amend text

as follows:

Required strength of Shoring Systems,

Trench Shields, and Trench Boxes

used with the Standard Practice

Shoring systems, trench shields, and

trench boxes shall have adequate

strength to resist the following

working loads:

a. A uniformly distributed lateral

pressure equal to the equivalent

weight effect (we ) in table 1 times

the Adjusted Depth (H e ) of the

excavation.

b. A 240 lb gravity load distributed

over a 1 ft length at the center of

any strut (cross brace).

c. A 240 ft-lb impact load 3/ acting

toward the excavation at any point

on the walls of trench shields and

trench boxes.

Loads a. and b. shall be assumed to

act simultaneously. Only trench

shields and trench boxes need to

resist load c.

Shoring systems shall be designed in

accordance with accepted engineering

practices. A 33 percent increase in

allowable working stresses or an equivalent strength reduction shall

be acceptable for shoring systems,

trench shields, or trench boxes used

in short-term excavations.

Struts shall be designed to resist

the full lateral pressure stipulated

in ( i

i

)

wales 80 percent of the

lateral pressure, and sheeting

67 percent of the lateral pressure.

(ii) The section cannot be eliminated

since this would make the Standard

Practice meaningless. It should,

however, be separated from the rest

of the text since it is addressed to

shoring and shield manufacturers and

engi neers.

It is not recommended to increase

the gravity load since this is

considered dangerous. Contractors

and workers will assume that struts

can support loads and load their

struts. Such a situation is likely

to get out of hand. As it is,

workers should be prohibited from

loading struts or climbing on struts,

and vertical load capacity is

provided strictly for emergencies.

It is specifically noted that this

section is applied for pre-designed

systems used with the Standard

Practice. An engineer need not

follow the Standard Practice, and

thus is also not bound by this

section.

The impact loading is more precisely

defined in this revision, and provisions are made for load reductions

for wales and sheeting.

It should be noted that with the 33

percent load reduction, the Standard

Practice will yield struts roughly

equal to those presently used in

empirical practice. Elimination of

the load reduction would make the

Standard Practice more conservative

than empirical practice.

3/ The load shall be applied by a 60 lb. sand-filled leather bag

(ASTM E72-77)

31
TEXT SUBMITTED TO WORKSHOP COMMENTS

(iii) Selection of Shoring System, Trench

Shields, and Trench Boxes

Shoring systems, trench shields, and

trench boxes shall be selected in

the field on the basis of Soil Type

(Table 1), Adjusted Depth (Section

1926.652(b) (4) (i ) ) and a determination

whether the excavation is long-term

or short-term in the following manner:

a. Trench shields, trench boxes, prefabricated strut-wale assemblies and

other pre-fabricated assemblies shall

be rated for the maximum Adjusted

Depths in Type A, B, and C soils in

which they can be used, and selected

accordingly.

b. Hydraulic shores or other prefabricated sub-assemblies or members

of shoring systems shall be rated

for allowable working loads and

selected with the aid of the charts

in the guidelines supplementing

Subpart P, or selected directly from

special charts prepared by the

manufacturer.

c. Timber shoring shall be selected

with the aid of charts in the

guidelines supplementing Subpart P or from special charts prepared by

an engineer (qualified person).

d. Any other shoring system can be predesigned and rated by an engineer

(qualified person) and selected on the basis of soil type and equivalent

depth from charts prepared for this

purpose.

(iii) Efficiency Production suggested to

state in the second paragraph simply

Shoring systems and trench shields

shall be selected in the field in

accordance with accepted engineering

practices. They also suggested to

drop the word, "Adjusted" in a., and

"qualified person" in c. AFL-CIO

recommended actually bringing charts

for hydraulic shoring or other predesigned assemblies into the Standar1 Practice. They also noted that

timber shoring should be in the

guidelines and selected by an engineer.

The Wisconsin workshop memo noted

that timber shoring should be so designed that all members (struts

and wales) are the same size.

George Bradberry stated that the

examples given should be further

pursued in the regulations. He

further elaborated on his written

statement by stating that descriptiv

tables for prefabricated assemblies,

which comply with the Standard

Practice, should be provided in an addendum to the regulations.

32 A

A
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

iii) Selection of pre-designed shoring

system, trench shields, and trench

boxes to be used with the Standard

Practice.

Shoring systems, trench shields, and

trench boxes shall selected in the

field on the basis of Soil Type,

(Table 1), Adjusted Depth, [Section

1926 .652(b) (4) (i)], and a determination whether the excavation is longterm or short-term in the following

manner:

a. Any shoring system which is intended

for a specific project can be predesigned by a qualified person and

selected in the field on the basis

of soil type and equivalent depth

from charts or other instructions

prepared for this purpose.

b. Trench shields, trench boxes, prefabricated strut-wale assemblies and

other pre-fabricated assemblies

shall be rated by an engineer for

the maximum Adjusted Depths in Type

A, B, and C soils in which they can

be used and selected accordingly.

c. Hydraulic shores or other prefabricated subassemblies or members

of shoring systems shall be rated by

an engineer for allowable working

loads and selected with the aid of

the charts supplementing Subpart P, or selected directly from special

charts prepared by an engineer in

behalf of the manufacturer.

d. Timber shoring shall be selected

with the aid of charts supplementing

Subpart P or from special charts

prepared by an engineer.

In addition, it is recommended to have

an addendum to Subpart P which will aid

in the selection of shoring (similar to

table P-2, but covering much more than

timber shoring and containing figures,

as well as tables and charts).

(iii) The section title was re-written to

specifically apply to systems used

with the Standard Practice .

a. is for the case where a contractor

pre-designs his own shoring systems

(site or company specific). In this

case, the term "qualified person" is

used, and it is the contractor's

responsibil ity that the system be

designed to resist the stipulated

minimum loads.

b. is intended for trench box

manufacturers and requies rating of

the trench boxes by an engineer

either generically for standard box

types manufactured, or, if the need

arises, for a specific case.

c. leaves two options--the use of

generic charts in a supplement to

subpart P, to be used with shoring

rated by an engineer for specific

load capacity, or charts prepared by

an engineer for the manufacturer.

d. leaves also two choices--in this

case, a state or municipality may

want their own chart, or charts from

the subpart P supplement may be used.

In lieu of b., c., and d., a contractor

may design his own system under a.

An addendum, rather than a guideline is

proposed for specific charts and figures

that will help personnel in the selection

of shoring.

33
TEXT SUBMITTED TO WORKSHOP COMMENTS

(5) Special Provisions

(i) Intersecting Trenches

When two trenches intersect and one trench is shored, the intersecting

trench shall also be shored from the

intersection of the two trench walls

to a distance of not less than its

depth.

(i) In the S. F. workshop, it was noted

that there should be an option to

block the intersecting trench.

Ohio Contractors Association noted

that this cannot always be done.

(ii) Sloping Ground

If the ground behind an excavation

wall slopes up from the excavation

wall and the ground slope exceeds 3

hor. in 1 vert, workers in the exca- vation must be protected against

objects rolling or slidinng from the

sloped ground. This can be accomplished by projecting the sheeting at

least 18 inches above the ground sur- face or by a specially constructed

protective toeboard. If spaced

sheeting is used provisions shall be

made to close the gaps between projecting sheeting members. (Workers

in excavations must be protected

against rolling or sliding objects.)

(iii) Excavation Below the Bottom of

Sheeting, Trench Shields, or Trench

Boxes

Excavation up to 2 ft (3 ft ?) below

the bottom of sheeting, trench shields

or trench boxes is permitted in shortterm excavations provided that:

a. No soil movement below the bottom of

the sheeting, trench shield, or trench box is evident, and

b. The forces acting on the bracing,

trench shield, or trench box are calculated for the full depth of the

excavation, and the lowest wales and

struts are designed to resist the

forces that would result if the

sheeting would be projecting to the

bottom of the excavation.

(ii) AFL-CIO strongly endorsed this

paragraph and objected to the

performance statement in parentheses.

George Bradberry noted elsewhere

that vertical shoring members should

not be shown as protruding above the

top of the excavation since this is

often not done.

Many contractors supported the

performance statement.

(iii) Most contractors supported the 3 ft

option (in parentheses); however,

participants in the San Francisco

workshop, including contractors and

ASFE, were in favor of limiting the

excavation below the bottom of

sheeting to 2 ft.

I

I

I

In the Boston workshop, the ASFE

representati ve suggested to limit the^

length over which this type of j_l

excavation is allowed.

Kodak noted that many times this has H

to be performed on the bottom of

“

long-term excavations for the purpose

of installing utilities. Thus, they Wk

proposed to put "short-term" in the |i

beginning of the sentence. The

term, "soil movement," was criticized^

as being too vague. fl

B

34
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(5) Special Provisions

(i) Intersecting Trenches

When two trenches intersect and only

one trench is shored, adequate

support must be provided for the

struts near the unshored trench.

This can be accomplished by shoring

the intersecting unshored trench

from the intersection of the two

trench walls to a distance of not

less than its depth.

(ii) Sloping Ground

If the ground behind an excavation

wall slopes up from the excavation

wall and the ground slope exceeds 3

hor. in 1 vert, workers in the

excavation must be protected against

objects rolling or sliding from the

sloped ground. This can be accom- plished by a protective barrier

projecting at least 18 inches above

the ground surface.

iii) Short-term Excavation Below the

Bottom of Sheeting, Trench Shields,

or Trench Boxes

Short-term excavation up to 3 ft

below the bottom of sheeting, trench

shields, or trench boxes is permitted

provided that:

a. There is no evidence of soil

instability below the bottom of

I

the sheeting, trench shield, or trench box; and

b. The forces acting on the bracing,

trench shield, or trench box are calculated for the full depth of the

excavation, and the lowest wales and

struts are designed to resist the

forces that would result if the

sheeting would be projecting to the

bottom of the excavation.

[

(i) The intent of this provision is to

prevent a shear failure caused by the

thrust exerted by struts against the

excavation wall. Blocking off the

intersecting trench will not alleviate

this problem. The paragraph was re- written to give the option to use other methods for securing the struts

near the unshored trench.

(ii) A good case for a protective barrier,

at least 18 in high, has been made

by the AFL-CIO task force. It is,

however, not considered prudent to

encourage projections of vertical

shoring member. If such members are

hit by a heavy rolling object, the

impact could trigger a cavein.

(iii) The wording was changed to also

permit such short-term excavation

within a long-term excavation and

also to make sure that the excavation below the sheeting _be short

term.

The term, "soil movement," was removed since this term was considered confusing in past court

cases.

The permitted excavation depth was increased to 3 ft., since this is

considered adequate for a wide range

of construction situations without

being excessively risky. A 2 ft.

clearance would be inadequate even

for smal 1 -diameter pipe.

35
TEXT SUBMITTED TO WORKSHOP COMMENTS

(iv) Maximum Spacing of Spaced Sheet ing a/

Maximum allowable spacing of spaced

sheeting shall be in accordance with

table 4(a) or (b) whichever controls.

(iv) It was suggested to eliminate

table 4(a) since it is sufficient

specify "clear spacing."

Table 4(a) Maximum Center-to-Center

Spacing^/ of Spaced

Sheeting Members

Soil

Type

Depth of Excavation

5 ft- 10 ft- 15 ft10 ft 15 ft 20 ft

A 8 ft 6 ft 4 ft

B 4 ft 4 ft 3 ft

C Tight Sheeting Required

Table 4(b) Maximum Clear Spacing^/ of

Spaced Sheeting Members

Soil

Type

Depth of Excavation

5 ft10 ft

10 ft15 ft15 ft20 ft

A 7.5 ft 5.5 ft 2 ft

B 4 ft 2 ft 1 ft

C Tight Sheeting Required

a / If there is an indication of spalling

the spacing must be reduced to a spacing that will prevent spalling.

b/ Refer to figure 4, page .

36
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(iv) NO CHANGE RECOMENDED ( iv ) If center to center spacing

requirements are eliminated, the

arching characteristics of the

unsupported excavation wall may

change unless the stiffness of the

spaced supports is specified. This

may be difficult to do in practice.

The tables themselves reflect

successful empirical practice.

37

I
TEXT SUBMITTED TO WORKSHOP COMMENTS

1926.653 DEFINITIONS APPLICABLE

TO THIS SUBPART

(a) "Accepted engineering requirements

(or practices) . I hose requirements

or practices which are compatible

with standards required by a registered architect, a registered profession engineer, or other duly

licensed or recognized authority.

Guidance for accepted engineering

practices pertaining to excavation

safety is provided in the guidelines

supplementing Subpart P.

(b) Acceptable Practice is a practice

which meets the minimum requirements

in Section 1926.652(a).

(c) Adjusted Depth is the actual depth

from the bottom of the excavation to

the top of the supported excavation

wall plus an additional depth to

allow for surcharge, sloping ground,

or heavy equipment as stipulated in

Section 1926.652(b) (4) ( i

)

(d) Allowable Working Stresses are allowable stresses determined in

accordance with accepted engineering

practices.

(e) Belled Excavation is a part of a shaft or footing excavation, usually

near the bottom and bell -shaped;

i.e., an enlargement of the cross section above.

(f) Clear Spacing of sheeting members is

the distance between the edges of

sheeting members over which the soil

is unsupported (see figure 4).

(g) Competent Person means one who is

capable of identifying existing and

predictable hazards in the surroundings

or working conditions which are unsanitary, hazardous, or dangerous

to employees, and who has authorization

to take prompt corrective measures

to eliminate them.

(a) It was suggested by many participants

to remove the word, "registered

architect," since architects are

not normally involved in excavation

work. The question was raised

whether the last sentence is still

a part of the definition (maybe

there will be no guidelines).

(g) In the San Francisco workshop, it was proposed to eliminate the "compet

person" and have only a "qualified

person"

It was noted that a competent person

should always be at the excavation

site (F. Yokel, Atlanta memo;

Bradberry)

38
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(a) "Accepted engineering requirements

(or practices)" Those requirements

or practices which are compatible

with standards required by a registered

professional engineer, or other duly

licensed or recognized authority.

Guidance for accepted engineering

practices pertaining to excavation

safety is provided in the guidelines

supplementing Subpart P.

(b) NO CHANGE RECOMMENDED

(c) NO CHANGE RECOMMENDED

(d) NO CHANGE RECOMMENDED

(e) NO CHANGE RECOMMENDED

(f) NO CHANGE RECOMMENDED

(g) Competent Person means one who is

capable of identifying existing and

predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous

to employees, and who has authorization to take prompt corrective

measures to eliminate them.

In excavation work, the competent

person is one who has the knowledge

and experience necessary to apply

the Standard Practice for sloping

(g)

The existing definition appears

adequate, except that specific

knowledge of the Standard Practice

should be required. The competent

person should also recognize conditions which are not covered by the

Standard Practice and, therefore,

require the judgment of a qualified

person or an engineer.

39
TEXT SUBMITTED TO WORKSHOP COMMENTS

(h) Engineer is a registered professional

engineer.

(i) Equivalent Weight Effects (wP ) is the

weight effect stipulated in table 1 which is used to calculate pressures

on shoring systems.

(j) Excavation is any manmade cavity or depression in the earth's surface

except as noted, including its sides,

walls, or faces, formed by earth

removal and producing unsupported

earth conditions by reasons of exca- vation. Excavations do not include

tunnels and shafts, caissons and

cofferdams covered by Subpart S of

the Safety and Health Regulations

for Construction.

(k) Excavation Wall is the side of an excavation, rising from the bottom

of the excavation to the ground

surface.

(l) Fractured Rock is rock which could

spall or crumble when excavated with

vertical slopes. Fractured rock

slopes secured against mass movement

and spalling by rock bolts, netting,

or other means approved by a qualified

person are considered stable (equal

to unfractured rock).

(h) It was recommended that regi strati

should not be required.

(j) Kodak recommended to either state

that excavations include trenches,

or use separate trench definition.

(1) Kodak recommended to use terms of

"stable" and "unstable" rock. It was noted that the definition lack

precision, and that all rock that

was excavated was also "fractured"

(F. Yokel, Atlanta workshop). It was suggested that a "competent,"

rather than a "qualified," person

determine if slope is secured.

40
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

and shoring, and to recognize conditions where a qualified person or

an engineer must be consulted.

(h) NO CHANGE RECOMMENDED

(i) NO CHANGE RECOMMENDED

(j) Excavation is any manmade cavity or depression in the earth's surface

except as noted, including its sides,

walls, or faces, formed by earth

removal and producing unsupported

earth conditions by reason of

excavation. Excavations do not

include tunnels and shafts, caissons

and cofferdams covered by Subpart S

of the Safety and Health Regulations

for Construction.

Excavations include trenches commonly

used for the installation of piping

and other utilities.

(k) NO CHANGE RECOMMENDED

(1) Unstable Rock is rock which could

spall or crumble when not supported

by shoring. Unstable rock slopes

secured against mass movement and

spalling by rock bolts, netting, or other means approved by a qualified

person, are considered stable.

(h) If the concept of a "qualified

person" is retained, an "engineer"

should always be a registered

professional

(j) Since many contractors view trenches

separately from excavations, it is

important to emphasize that trenches

are included in excavations.

(1)

The term, "unstable rock," seems more appropriate since any rock that

is excavated has been fractured.

The phrase, "excavated with vertical

slope," was dropped since there is no reason why a steeper slope than

that stipulated in table 1, say

1/4:1, could not be permitted as long as there is no danger of

spalling or rock slides, even if a stable vertical excavation was impossible. The reqiurement for

approval by a qualified person is

important since, in many instances,

consideration must be given to

geological features which a competent

foreman may not understand.

41
TEXT SUBMITTED TO WORKSHOP COMMENTS

(m) Long-term Excavations are excavations which are open for more

than 24 hours (7 days).

(n) Mud Sills are wales which are

instal 1 ed at the level of the bottom

of the excavation wall.

(o) Negotiable Slope is a slope on which

a person can egress from or ingress

to an excavation.

(p) Qualified Person means one who, by

possession of a recognized degree,

certificate, or professional standing,

has successfully demonstrated his

ability to solve or resolve problems

relating to the subject matter, the

work, or the project.

(m) Opinions on the length of time for

an excavation to become long term

differed. AFL-CIO supported the

original 24 hours. Some contractors

supported 7 days. Contractors in

Texas and Atlanta workshops, as well

as trench box manufacturers , suggested to drop the distinction

between short-term and long-term.

Many participants suggested that

3-4 days may be a good dividing

line so that excavations which are open over the weekend don't become

"long term." It was also noted that

in many instances a trench may be

covered in several hours, but man

holes stay open for a week or more.

It was also noted that in arrid

regions there is no rationale for

distinguishing between long-term

and short-term excavations.

(o) AFL-CIO suggested 1 1/2:1 slope;

Efficiency Production suggested to

add "with relative speed."

(p) AFL-CIO objected to the use of a "qualified person" in matters relating to the design of shoring unless

that person is a registered engineer

They are worried about identifying

who is qualified. ASFE favored the

concept of a qualified person since

42
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(m) Long-term Excavations are excavations

which are open tor more than

72 hours.

(n) NO CHANGE RECOMMENDED

(o) Negotiable Slope is a slope on which

any person working in the excavation

can readily egress from or ingress

to an excavation.

(p) Qualified Person is a person designated

by the employer, preferably a registered professional engineer, who is

familiar with the operation to be

performed and the hazards involved

and who has the necessary training,

knowledge and experience to perform

the engineering analysis and exercise

(m) There are many parameters which

affect slope stability as a function

of time. These include: fissuring

caused by lateral expansion (removal

of restraint); change in soil moisture content; erosion) effects of

vibration and disturbance an seepage.

To find a common denominator for

all conditions is impossible. On

the other hand, some of the proposed

provisions would have to be much

more conservative (slope, lateral

pressure for medium clays, allowable

stresses in shoring) when there is no time limit on their application.

Three days seems a reasonable time

span for a federal standard. Individual states or regions may revise

this down or up, considering local

conditions.

(o) Since there are no research data on negotiable slope at the present

time, it is suggested to keep the

performance statement. "With relative speed" is too vague as a requirement. "Any" person "working

in the excavation" was added for cases where egress may require

special physical skill which not

everybody possesses. It is con- ceivable that an employer could be

required to demonstrate that his men can egress. Alternately,

research could be performed to

determine how flat a slope has to

be before it is negotiable. There

is no doubt that the 1 1/2:1 slope

suggested by AFL-CIO is negotiable;

however, such flat slopes are normally not used in construction.

(p) Since the qualified person has to

deal with situations which fall

outside the Standard Practice, he

must have the capability to determine

the stability of excavation slopes

and the adequacy of shoring or shielding systems. It should

essentially be the responsibil ity of

43
TEXT SUBMITTED TO WORKSHOP COMMENTS

(q) Safety Margin is any measure of excess strength over that required

to reist the working loads.

(r) Sheeting is composed of members of

the shoring system which are in

direct contact with the soil in the

supported bank.

(s) Shoring Systems are structural

systems supporting the bank of an excavati on.

(t) Short-Term Excavations are excavations which are open for 24

hours (7 days) or less.

(u) Sides, Walls, or Faces are the

vertical or inclined earth surfaces

formed as a result of excavation work.

(v) Slope is an incline expressed as a ratio of horizontal distance to

vertical rise.

(w) Spaced Sheeting is sheeting in which

tne members bearing against the

excavation wall are spaced (see

figure 6)

(x) Spalling is the continuous flaking

and falling of soil or rock from an unsupported trench wall.

the contractor has primary

responsibility.

Wisconsin OSHA objected to a "qualified person" for depths beyond

the Standard Practice and noted that

a professional engineer should be

required.

Metropolitan St. Louis Sewer District

suggested that "competent" and

"qualified" persons be used for

protection of the safety of personnel , and registered engineers be

used to protect adjacent structures

against excessive settlements.

California AGC suggested that the

"qualified person" should be designated by the contractor (F. Yokel,

S. F. memo), ASFE (California) suggested that perhaps design calculations should be required.

(t) See Long-Term Excavations

fl

1

1

1

1

0

44
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

the judgment required for the determination of the stability of excavations and the design of appropriate

shoring or shielding.

the contractor to choose a qualified

individual, since the contractor

would be liable in case of an accident. Even though it is evident

that it v/ould be desirable that the

qualified person be a registered

engineer, not every registered

engineer is necessarily qualified,

and some qualified individuals may

not be registered engineers.

(q) NO CHANGE RECOMMENDED

(r) NO CHANGE RECOMMENDED

(s) NO CHANGE RECOMMENDED

(t) Short-Term Excavations are (t) See Long-Term Excavations

excavations which are open for

72 hours or less.

(u) NO CHANGE RECOMMENDED

(v) NO CHANGE RECOMMENDED

(w) NO CHANGE RECOMMENDED

(x) Delete continuous (x) Spalling does not have to be

continuous to constitute a significant safety hazard.

45
TEXT SUBMITTED TO WORKSHOP COMMENTS

(y) Standard Practice is the trenching

and shoring practice in Section

1926.652(b).

(z) Struts are the primary support

members of a shoring system including

but not limited to cross braces,

raker braces, jacks, or backties

( see figure 6)

(aa) Stable Slope is the slope which will

remain stable for the duration of the

excavation.

(bb) Structural Ramp is a ramp built of

materia! other than soil or rock.

(cc) Supported Wall is that part of the

excavation wall which is supported

by a shoring system or shielded by

trench boxes or trench shields.

(dd) Trench Box see trench shield.

(ee) Trench Shield is a protective device

which shields workers in a trench

from the effect of mass movement of

soil or rock and which can be moved

along as work progresses.

(ff) Wal es (walers) are members of the

shoring system which are directly

supported by struts and which in

turn provide support to the sheeting

(see figure 4)

(gg) Working loads are loads which should

reasonably be anticipated to occur

and which must be resisted with

appropriate safety margins, determined in accordance with accepted

engineering practice.

(z) It was noted that raker braces and

backties should be shown in figure 6

(aa)

(bb)

(cc)

(dd)

(ee)

(ff)

(gg)

46 I

I
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

(y) NO CHANGE RECOMMENDED

(z) NO CHANGE RECOMMENDED

(aa) NO CHANGE RECOMMENDED

(bb) NO CHANGE RECOMMENDED

(cc) NO CHANGE RECOMMENDED

(dd) NO CHANGE RECOMMENDED

(ee) NO CHANGE RECOMMENDED

(ff) NO CHANGE RECOMMENDED

(gg) NO CHANGE RECOMMENDED

ADDITIONAL DEFINITIONS

Employer is the person or organization

who is constructing the excavation.

(i.e., contractor, public utility, etc.)

Mass Movement of Soil or Rock is the

displacement of soil or rock caused by

overall or local stability failures which

could cause death or injury to workers.

47
TEXT SUBMITTED TO WORKSHOP COMMENTS

1. STANDARD PRACTICE

2. STRENGTH OF SHORING SYSTEMS

ANALYSIS OF WORKSHOP COMMENTS WHICH DO NO'

Three significant statements were made

with regard to Standard Practice.

(a) In the joint memo of the organizer

of the Wisconsin workshop, it is

stated that, "Any OSHA standard

should cover as many situations as- possible with Standard Practices."

It was also proposed that Subpart

rather than the guideline, contain

tables and figures (isometric

drawings) from which workers can select shoring systems. (Letter

from Bradberry; comments in Calif

m

workshop)

(b) AFL-CIO, in essence, suggested to

have a Standard Practice which is even more standardized than that

proposed— namely , have to a depth

15 ft., a very conservatively

designed standard shoring system

which would be suitable for all (or

most) conditions.

Two comments were made by the trench box

manufacturers with respect to strength

requirements, which relate to

1926.652(b) (4 )

( i i ) , as well as to the

guide! i nes

(a) A triangular, rather than a squarel

pressure diagram should be stipulate

for trench boxes.

48
RECOMMENDATIONS/SUGGESTIONS COMMENTARY

Shielding is the surrounding of workers

1 in an excavation by a protective structure

which isolates them from the effects of mass movement of soil or rock.

XTLY RELATE TO SECTIONS IN THE WORKING DRAFT

(a) It is recommended to include tables

and isometric drawings for systems

which are deemed to comply with

Subpart P in a companion document.

I

I

[i (a) No change in the Standard Practice

is recommended. There is no objection

a

to include a triangular pressure

| diagram in the guidelines, together TM with appropriate criteria for

restraint conditions of the retaining

I

structure. (It should be noted that

the pressure diagrams shown in the

guidelines are only "information."

Some of the references listed in

A. 5. 2., such as the Navy manual and

(a) Tables and isometric drawings are considered an excellent way to convey

the Standard Practice. However,

because of the diversity of ways in

which a contractor can comply with

the Standard Practice, a choice of

systems not covered in this supplement should also be permitted, as long as an engineer/qualified prson

determines that the systems comply.

The difficulty with standard tables

is particularly evident in the case

of timber shoring, where the choice

of member sizes frequently depends

on local conditions. The supplement

will probably have to be updated

from time to time to cover recent

technological developments.

(b) The AFL-CIO recommendation merits

further study. It would result in a much more conservative system and some problems may arise for con- tractors or manufacturers who wish

to introduce new technology, or even with existing systems presently

on the market.

(a) The Standard Practice is intended to

be a simplified approach which

applies to a wide range of conditions. It is conceivable that under

many circumstances, the stipulated

pressures would be excessive for

trench boxes. However, there are other cases, such as instances where

trench boxes are forced into a slightly narrower trench to prevent

excessive settlement in the vicinity.

49
ANALYSIS OF WORKSHOP COMMENTS WHICH DO NOT DIREC

TEXT SUBMITTED TO WORKSHOP COMMENTS

(b) The 33 percent overstress for

short-term excavations should not

be permitted.

3. SOIL CLASSIFICATION Two alternatives to the proposed soil

classification (table 1) were suggeste

In the San Francisco workshop (F. Yoke

memo), it was suggested to adopt the

proposed California classification. I the Boston workshop (Kodak letter), it was suggested to adopt the Matrix

classification originally proposed by

(refer to BSS 121, "Soil Classificatio

for Constrction Practice in Shallow

Trenching," Yokel, Felix Y., Tucker,

Richard L., and Reese, Lymon C.)

5C
E TO SECTIONS IN THE WORKING DRAFT (Cont'd)

RECOMMENDATIONS/SUGGESTIONS

Tshebotarioff , recommend triangular

diagrams.

It is recommended to keep the proposed

soil classification.

COMMENTARY

where the stipulated lateral pres- sures apply. (One such instance is

documented in a recent court case.)

It would be unwise to base the design

of prefabricated trench boxes on the

premise that their use will be

restricted to cases where the trench

wall is not restrained. On the

other hand, the guidelines are for

engineers and, in many specific

instances, engineering judgment may

lead to the conclusion that a triangular pressure diagram is a reasonable assumption.

It should be noted that not all

trench box manufacturers wish to

design their product for a triangular

pressure diagram.

(b) The 33 percent working stress

reduction for short-term excavations

results in struts which are compatible with those used in traditional

shoring practice. Elimination of

this working stress reduction would

require upgrading of many systems

presently used. The track record of

these systems does not seem to

justify such a step. It appears

that in many instances shoring

manufacturers will prefer not to

take advantage of this strength

reduction so that their systems can

be used in both short-term and

long-term excavations.

There is little doubt that the Matrix

classification has many advantages. The reason it was not chosen is that it has

too many choices, and therefore, cannot

be readily used from memory (one would

have to have some chart or plaque). It also was concluded that four choices of

shoring would not be an advantage in the

field. At present, there are three

choices, and the transition from one to

the next (which is likely to occur in

many field situations) can be made by

simply inserting intermediate struts.

The California classification system has

been considered and not recommended

because the soil categories cannot be
ANALYSIS OF WORKSHOP COMMENTS WHICH DO NOT DIREC'

TEXT SUBMITTED TO WORKSHOP

EXEMPTION OF CERTAIN INDUSTRY GROUPS

FROM COMPLIANCE WITH SUBPART P

PREPARATION OF A VOLUNTARY INDUSTRY

STANDARD

COMMENTS

The American Gas Association requested

a letter (see Appendix) to be exempt fori

compliance with Subpart P.

Many workshop participants, representing

all the participating groups, noted th

a voluntary industry standard should b

prepared. Mi

52
TO SECTIONS IN THE WORKING DRAFT (Cont'd)

® RECOMMENDATIONS/SUGGESTIONS

I

|

No recommendation

It is strongly recommended to:

1. Prepare a voluntary industry standard.

The standard could be sponsored by

ANSI (A10.12).

2. On the basis of the existence of this

standard, simp! ify Subpart P and

confine it to concise, unambiguous

and easily enforceable regulations.

COMMENTARY

correlated with lateral pressures (for

detailed discussions refer to F. Yokel memo on San Francisco workshop).

This problem is considered to be outside

the scope of this report.

NBS recommended to OSHA to support

preparation of such a standard. (NBS

could prepare a first draft and subsequent

revised drafts, thus insuring rapid

progress in the adoption of a voluntary

standard.) OSHA so far decline to fund

this effort.

I

53

3. APPENDIX

This appendix contains the original input document that was submitted to the

workshop. The document was based on previous NBS studies and on recommendations

from NIOSH, AFL-CIO, AGC and the shoring industry.
56
February 20, 1981

WORKING DRAFT OF SUGGESTED REVISION IN SUBPART P OF

THE SAFETY AND HEALTH REGULATIONS FOR CONSTRUCTION

BASED ON BUILDING SCIENCE SERIES REPORT BSS 127

BY

FELIX Y, YOKEL

FOR WORKSHOP USE ONLY

NOT FOR REFERENCE OR PUBLICATION

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PREFACE

This is a working draft of a suggested revision of the Occupational

Safety and Health Administration, (OSHA), 29 CFR Part 1926. Subpart P, Excavation, Trenching, and Shoring regulations. It was

prepared as a text for discussion and comment at regional industry

workshops. The purpose of this draft is to convey a better understanding of how the recommendations of a National Bureau of Standards

(NBS) study!/, if adopted, could be implemented in excavation practice

in general and how they would affect the provisions of Subpart P in

particular

At the conclusion of the regional workshops, summaries of the

proceedings, comments, and final recommendations will be prepared

in collaboration with the interested industry groups. These summaries will be forwarded to OSHA through the National Institute

for Occupational Safety and Health (NIOSH) , as recommendations for

changes to Subpart P. The summaries will become part of the record

on which OSHA, through the formal rulemaking procedure established

by law, will base revisions to Subpart P.

Industry, labor, and other concerned groups and individuals will

have further opportunity to address issues unresolved at the workshops, as well as other issues concerning these revisions, during

the rulemaking process

This working draft has several parts

Pages 5-20 contain a suggested revised version of Subpart P.

Pages 21-50 contain suggested guidelines which supplement

Subpart P

Pages 51-59 contain an attachment with a summary of suggested

changes in the present version of Subpart P.

The following comments should help explain the intent of this

working draft.

1. The "Acceptable Practice" in Section 1926.652(a) explains

when the provisions apply and how they are to be used.

2. The "Standard Practice" in Section 1926.652(b) is addressed

to field personnel with the intent of making the selection

of slopes or shoring in the field as simple as possible. It

is assumed that the shoring or shields selected will be predesigned.

3. Section 2 of the guidelines deals with the pre-design or rating

of shoring systems, trench shields and trench boxes. It is

addressed to contractors, shoring manufacturers and engineers

and is as precise and unambiguous as possible.

1/ Yokel, F. Y., Recommended Technical Provisions for Construction

Practice in Shoring and Sloping of Trenches and Excavations

NBS Building Science Series 127, Washington, D.C., June, 1980.
- 2

-

4. Appendix A of the guidelines contains engineering guidelines

and correlates accepted engineering practice with the revised

version of Subpart P.

5. Appendix B of the guidelines contains specific information on

acceptable shoring systems in the form of tables and charts

which would aide field personnel and contractors in the selection of shoring.

This working draft was prepared in consultation with individuals

from the various groups involved in excavations, i.e., labor

unions, shoring manufacturers, contractors, and engineers. The

first draft was prepared with input from the labor unions and

shoring manufacturers, and relatively little input from contractors.

The draft was subsequently discussed in a two-day meeting of an

AGC task committee which was also attended by NBS personnel. In

this meeting consensus was reached on various desirable revisions

Where these revisions substantially deviate from the original draft

or from the original NBS recommendations they are included herein

in parentheses with a question mark. Thus, for instance, ...shielding and sloping requirements must be determined by an engineer

(qualified person?) means that the task committee recommends that

a "qualified person" be substituted for "an engineer".
-3-

SOME ISSUES

1. Page 6.

2. Page 8.

3. Page 9.

4. Page 10.

5. Page 11.

6. Page 12.

7 . Page 13

THAT SHOULD BE CONSIDERED IN THE WORKSHOPS:

Section 1926.651(a): This section appears to fall

within the scope of Subpart S. Should it be dropped?

Section 1926. 651 (p): Should the exit requirements

for excavations start at 5 ft, rather than 4 ft depth?

(This would remove most excavations less than 4 ft

deep from the scope of Subpart P.) Should exit

requirements be waved for excavations which are wide

enough to permit people to escape toward the center

of the excavation? Should it be recognized that

large enough pipes or other covered structures can

shelter people? Should "negotiable slope" be better

defined?

Section 1926.652(a)(2): Could the depth limitation

in the "Standard Practice" be extended to 24 ft?

If so, should there be a more stringent limit for

Class C soils? Should a "qualified person" be substituted for an "engineer", and if so, is the definition of a "qualified person" good enough so that a

determination of who is a "qualified person" is

possible? (This issue also applies to other sections

of the working draft.)

Section 1926.652(b)(1): Should the short-term excavation definition extend to 7-days rather than 1-day?

If so, do we need more conservative requirements?

Table 1: Should the stipulation of maximum slope

be limited to 3/4:1? Should the suggested performance

requirement (footnote b) (the "stable slope" concept)

be used? Will this approach work?

Figure 2: Should the allowable bank next to the work

area in Cases II, III and IV be Increased to 4 ft?

Should "Case IV" be limited to excavation by trenching

machines?

Section 1926 . 652 (b) (4) (ii)

This section, unlike most

others in Subpart P, is not addressed to the man in

the field, but to those who pre-design shoring systems

Yet the section is necessary to avoid unreasonable

vagueness. Should this section be at the end of Subpart P? Should part of it be conveyed as definitions?
-4-

8. Page 16

9. Page 16

Section 1926 . 652 (b) (5) (ii) : This section makes it

difficult to implement some of the slope configurations allowed in Fig. 2. Should the proposed performance statements be substituted to give more

options, or alternately, should more options be

specified or the specified options identified as

examples of implementing the performance statement?

Section 1926 . 652 (b) (5) (iii) : Should the allowable

excavation below the bottom of shoring or shields

be increased to 3 ft?

10. Page 18 Definition of "Accepted engineering requirements"

Should "a registered architect" be omitted since

architects do not deal with excavations?

11. Page 18 Definition of "Competent Person": Should the definition be re-written to require that the competent

person be working at the excavation site?

12 Should "Mass Movement of Soil or Rock" be defined?

13. Page 52. Old 1926.651(c): Should this statement be deleted?

even though this matter is addressed elsewhere, this

statement conveys the intent of Section 1926.652 in

simple language.
SUBPART P - EXCAVATIONS AND SHORING

1926.650-GENERAL PROTECTION REQUIREMENTS

(a) The regulations contain minimum requirements for the

protection of workers in, and adjacent to, excavations against death and injury.

(b) Walkways, runways, and sidewalks shall be kept

clear of excavated material or other obstructions

and no sidewalks shall be undermined unless shored

to carry a minimum live load of one hundred and

twenty-five (125) pounds per square foot.

(c) If planks are used for raised walkways, runways,

or sidewalks, they shall be laid parallel to the

length of the walk and fastened together against

displacement.

(d) Planks shall be uniform in thickness and all exposed

ends shall be provided with beveled cleats to prevent

tripping.

(e) Raised walkways, runways, and sidewalks shall be

provided with plank steps on strong stringers.

Ramps, used in lieu of steps, shall be provided

with cleats to insure a safe walking surface.

(f) All Employees shall be protected with personal

protective equipment for the protection of the

head, eyes, respiratory organs, hands, feet, and

other parts of the body as set forth in Subpart

E of this part.

(g) Employees exposed to vehicular traffic shall be

provided with and shall be instructed to wear

warning vests marked with or made of ref lectorized

or high visibility material.

(h) Employees subjected to hazardous dusts, gases,

fumes, mists, or atmospheres deficient in oxygen,

shall be protected with approved respiratory

protection as set forth in Subpart D of this part.

(i) No person shall be permitted under loads handled

by power shovels, derricks, or hoists. Employees

shall be required to stand away from any vehicle

being loaded.
- 6

-

(j) A competent person shall inspect the excavation

for evidence of possible cave-ins or slides, and

indications of structural failure in members of

the shoring system. If evidence of possible caveins or slides or structural failures is apparent,

all work in the excavation shall cease until

necessary precautions have been taken to safeguard employees.

The competent person shall conduct an overall

inspection of the excavation and the ground

adjacant to the excavation at least twice daily

and shall conduct a special inspection after

every rainstrom, penetration of water into the

excavation, or other disturbance that could

weaken the soil or the shoring system, and shall

increase protection against slides and cave-ins

if necessary.

Dewatering operations and equipment shall be

monitored by a competent person to insure their

proper operation and precautions shall be taken

to safeguard the workers in the excavation if

dewatering equipment malfunctions.

1926. 651-SPECIFIC EXCAVATION REQUIREMENTS

(a) Prior to opening an excavation, efforts shall be

made to determine whether underground installations; i.e., sewer, telephone, water, fuel,

electric line^ etc., will be encountered, and

if so, where such underground installations are

located. When the excavation approaches the

estimated location of such an installation, the

exact location shall be determined and when it

is uncovered, proper supports shall be provided

for the existing installation. Utility companies

shall be contacted and advised of proposed work

prior to the start of actual excavation.

(b) Trees, boulders, and other surface encumbrances,

located so as to create a hazard to employees

involved in excavation work or in the vicinity

thereof at any time during operations, shall be

removed or made safe before excavating is begun.

(c) (1) In excavations which employees may be required

to enter, excavated or other material shall be

effectively stored and retained at least 2 feet

or more from the edge of the excavation.

(2) As an alternative to the clearance prescribed

in subparagraph (1) of this paragraph, the employer

may use effective barriers or other effective retaining

devices in lieu thereof in order to prevent excavated

or other materials from falling into the excavation
- 7

-

(d) Diversion ditches, dikes or other suitable means

shall be used to prevent surface water from

entering an excavation and to provide adequate

drainage of the area adjacent to the excavation.

Water shall not be allowed to accumulate in an

excavation, unless this condition is considered

in the design and in the initial work plan and

adequate provisions are made to protect workers.

(e) If it is necessary to place or operate power

shovels, derricks, trucks, materials, or other

heavy objects on a level above and near an

excavation, the side of the excavation shall

be shored as necessary to resist the extra

pressure due to such superimposed loads.

(f) Blasting and the use of explosives shall be

performed in accordance with Subpart U of this

part.

(g) When mobile equipment is utilized or allowed

adjacent to excavations, substantial stop logs

or barricades shall be installed. If possible,

the grade should be away from the excavation.

(h) Adequate barrier physical protection shall be

provided at all remotely located excavations.

All wells, pits, shafts, etc., shall be

barricaded or covered. Upon completion of exploration and similar operations, temporary

wells, pits, shafts, etc., shall be backfilled.

(i) If possible, dust conditions shall be kept to

a minimum by the use of water, salt, calcium

chloride, oil, or other means.

(j) In locations where oxygen deficiency or gaseous

conditions are possible, air in the excavation

shall be tested. Controls, as set forth is

Subparts D and E of this part, shall be established to assure acceptable atmospheric

conditions. When flammable gases are present,

adequate ventilation shall be provided or

sources of ignition shall be eliminated.

Attended emergency rescue equipment, such as

breathing apparatus, a safetv harness and

line, basket stretcher, etc., shall be readilv

available where adverse atmospheric conditions

may exist or develop in an excavation.

(k) Where employees or equipment are required or

permitted to cross over excavations, walkways

or bridges with standard guardrails shall be

provided.
- 8-

(l) Where structural ramps are used for employees or

equipment, they shall be designed and constructed

by qualified persons in accordance with accepted

engineering requirements.

(m) All ladders used on excavation operations shall be

in accordance with the requirements of Subpart L

of this part.

(n) Materials used for shoring, sheeting, and underpinning of structures adjacent to excavations

shall not be damaged or weakened by corrosion,

deterioration or prior use to an extent that

will cause them to have a minimum strength less

than that required in Section 1926 . 652 (b) (4) (ii)

(o) Employees entering bell-bottom pier holes shall be

protected by the installation of a removable- type

casing of sufficient strength to resist shifting of

the surrounding earth. Such temporary protection

shall be provided for the full depth of that part

of each pier hole which is above the bell. A lifeline, suitable for instant rescue and securely fastened

to a shoulder harness, shall be worn by each employee

entering the shafts . This lifeline shall be individually

manned and separate from any line used to remove materials

excavated from the bell footing.

(p) When employees are required to be in trenches

4 (5?) feet deep or more, an adequate means of

exit, such as a ladder, steps or a negotiable

slope shall be provided and located so as to

require no more than 25 feet of lateral travel.

(q) Shoring shall follow the excavation

as closely as practical in order to avoid long

sections of unshored excavation.

(r) Members of the shoring system

shall be installed in their proper position

and secured to prevent failure.

(s) Portable trench boxes or sliding trench

shields may be used for the protection of

personnel in lieu of a shoring system or

sloping. Where such trench boxes or shields

are used they shall be designed, constructed,

and maintained in a manner which will provide

protection equivalent to that provided by the

shoring required for the excavation.

( t) Backfilling and removal of trench support shall

progress together from the bottom of the trench.

Struts shall be released slowly and, in unstable

soils, ropes shall be used to pull out the

jacks or braces from above after employees have

cleared the trench.
-9-

1926. 652-SPECIFIC SHORING, SHIELDING AND SLOPING REQUIREMENTS

(a) Acceptable Practice

(1) The following excavations are exempt from shoring,

shielding and sloping requirements:

a. % Excavations less than 5 ft. deep, except when

examination of the ground by a competent person

indicates that hazardous ground movement may occur.

b. Excavations in unfractured rock.

(2) Excavations from 5 ft. to 20 ft. (24 ft. ?) deep shall be

shored, shielded or sloped in accordance with the Standard

Practice in Section 1926.652(b) with the following exceptions;

a. If there is a deviation from the provisions of

the Standard Practice, shoring, shielding or

sloping requirements must be determined by an

engineer (a qualified person ?)

b. An engineer shall determine the shoring, shielding

or sloping requirements whenever the bottom of

a building foundation adjacent to the excavation

which has not been secured by underpinning

extends into the critical zone delineated in

Figure 1.

FOOTING A: Standard practice can be followed

FOOTING B: An engineer shall be consulted

Figure 1. Effects of Nearby Foundation Loads That

Must be Determined by an Engineer
- 10 -

(3) For all excavations deeper than 20 (24?) ft., except

those in unfractured rock, an engineer (qualified

person?) shall determine the shoring, shielding or

sloping requirements.

(b) Standard Practice

(1) Scope

The Standard Practice provides a method

by which field conditions are related to shoring,

shielding and sloping requirement.

The Standard Practice makes a distinction between

short-term and long-term excavations (see definition

in 1926.653 - 24 hours (7 days?) is the division

point)

(2) Soil Classification

Soils are divided into three types: A, B, and C. For

each soil type the "equivalent weight effect”, we , to be used for the calculation of lateral soil pressure on shoring systems, and the maximum permissible

sideslope for sloped excavations are stipulated.

Table 1 provides guidance for the selection of the

soil type.

(3) Sloped Excavations

Sloped excavations shall not have sideslopes steeper

than those stipulated in Table 1. If there is any

indication of general or local instability, slopes

shall be cut back to the stable slope. The slope

configurations shown in Figure 2 can be used.

(4) Shored and Shielded Excavations

(i) Determination of Adjusted Depth

For the purpose of selecting shoring systems, trench

shields, or trench boxes the depth of excavations shall

be assumed greater than the actual depth in order to

allow for spoil piles, construction equipment and

sloping ground. This adjusted depth (R

e

i shall be

determined as follows;

For ground sloping down from the supported or shielded

excavation wall, level ground, or ground sloping up

from the supported or shielded excavation wall with a

slope less than 3 hor. in 1 vert, the Adjusted Depth (H ) is the actual depth of the supported excavation (E) plus

2 ft. (surcharge allowance). (See Figure 3(a).)

a.
- 11 -

Table 1. Soil Classification System for the Standard Practice

Soil Type Description w

e lb/ ft^

A

1

1

1 Intact Hard

T1

1 20aJ |1 3/4:1

1

1 1:1

1 B

1

1

1 Medium

1

1

i

l 40 |

I 3/4 : IS/

1

1 1 1/2:1

1 C

1

1 Saturated, Submerged

1

1

1 80 | 1 1/2:1 1 2:1

1

1 or Soft l

1

i

i

1

1

Steepest Allowable Slope hor. :vert.k/

Depth 12 ft. or less Depth Greater

than 12 ft.

Notes:

1. Type A : Intact Hard Soils include stiff clays and clayey (cohesive) sands and

gravels^/ (hardpan, till) above the ground water table which have no fissures,

weak layers, or inclined layers that dip toward the bank of the excavation as stipulated in Note 3. Stiff clays included have an unconfined compressive

strength-' q u * 1.5 tsf or more. Intact hard soils subject to vibrations by

heavy traffic, pile driving or similar effects are Type B .

2. Type B : Medium Soils are all soils which are not Type A or C.

3. Type C : a. Soft Soils include cohesive soils!!/ with an unconfined compressive

strength^./ of 0.5 tsf or less and soils that cannot stand on a slope of 3 hor.:

1 vert, without slumping (muck).

b. Saturated or Submerged Soils are assumed whenever water seeps into the excavation from the soil forming the bank; or water is retained by tight sheeting;

or there is a possibility that the excavation may be entered by workers within 1 day after more than half of its depth was flooded and pumped out.

4. Layered Systems (two or more distinctly different soil or rock types or micaceous

seams in rock) which dip toward the bank of the excavation with a slope of 4 hor.:

1 vert, or steeper are considered Type C. Layered soils are classified in accordance with the weakest layer.

5. Rock : Fractured rock shall be considered Type B when it is dry and Type C when it

is submerged. Unfractured rock is exempt from shoring and sloping requirements.

s/ In long-term excavations "Intact Hard" soil is Ty^e B soil.

I If there is any indication of general or local instability slopes shall be cut back

to a slope which is at least 1/4 hor.:l vert, flatter than the specified slope.

£/ In long-term excavations steepest allowable slope shall be 1:1.

Cohesive soils are clays (fine grained) or soils with a high clay content which

have cohesive strength. They do not crumble, can be excavated with vertical sideslopes, are plastic (can be molded into various shapes and rolled into threads)

when moist and are hard to break up when dry.

•S/ Unconfined compressive strength can be determined by undrained laboratory tests,

field tests, or the following thumb penetration tests: stiff clays with an unconfined

compressive strength of 1.5 tsf can be readily indented by the thumb nail. They can

be indented by the thumb, but can be penetrated by the thumb only with very great

difficulty. Cohesive soils with an unconfined compressive strength of less than 0.5 tsf can be easily penetrated several inches by the thumb and can be molded by light

finger pressure. tsf=tons per square foot.

(b/ ...Slopes shall be cut back to the stable (flatter) slope?

3/4:1 maximum slope as the only limitation?)

Change Table 1 to use
- 12 -

Case III ^Corner not to extend

\Tbeyond line ij /

, , 5 ft. max.

• \ f/6 ft. min. //

_L IAL

Steepest allowable

sideslope from Table I' ~Jj ft. max.

Case IV

Steepest allowable

sideslope from Table I

max.

Steepest

allowable

sideslope

Setback

d, ft.

Setback d

for 4 ft

max bank

K : 1 4 (5)

1 : 1 5!4 (6)

1!4 : 1 8 (9)

Case I • Simple slope

Case II • Compound slope with bench no more than 3 ft. high

Case III l IV - Configuration must meet following criteria:

1. No vertical bank to exceed 5 ft., the vertical bank adjacent to the work area not to exceed 3 ft. (4 ft. ?)

2. Imaginary slopes ij and kl not to exceed steepest allowable

sideslope from Table I

Figure 2: Allowable Configurations of Sloped Excavations

(Cases II, III and IV are for short-term excavations)
-13-

fa. For ground sloping up from the supported or shielded

excavation wall with a slope of 3 hor.tl vert, or

steeper the adjusted Depth (He ) is determined in

accordance with Table 2 and Figure 3 (b)

c. For heavy equipment (20,000 lb. or more) near the

side of the supported or shielded excavation wall

the additional depth shown in Table 3 shall be

added to the 2-ft. surcharge allowance stipulated in

a. No additional depth needs to be added for equipment

operating at a distance from the side of the excavation

wall which is equal to, or larger than, the depth of

the supported or shielded excavation (H)

(ii) Required strength of Shoring Systems, Trench Shields

and Trench Boxes

Shoring systems, trench shields and trench boxes shall

have adequate strength to resist the following working

loads

a. A uniformly distributed lateral pressure equal to the

equivalent weight effect (w ) in Table 1 times the

Adjusted Depth (H ) of the excavation.

b. A 240 lb gravity load distributed over a 1 ft length

at the center of any strut (cross brace)

c. A 240 ft-lb impact load acting toward the excavtion on

the walls of trench shields and trench boxes

Loads a. and b. shall be assumed to act simultaneously.

Only trench shields and trench boxes need to resist load c.

Shoring systems shall be designed in accordance with

accepted engineering practices. A 33 percent increase

in allowable working stresses or an equivalent strength

reduction shall be acceptable for shoring systems, trench

shields or trench boxes used in short-term excavations.

(iii) Selection of Shoring System, Trench Shields, and

Trench Boxes

Shoring systems, trench shields and trench boxes shall

be selected in the field on the basis of Soil Type

(Table 1), Adjusted Depth (Section 1926 . 652 (b) (4 ) (i)

and a determination whether the excavation is long-term

or short-term in the following manner:

a. Trench shields, trench boxes, pre-fabricated strutwale assemblies and other pre-fabricated assemblies

shall be rated for the maximum Adjusted Depths in Type

A, B, and C soils in which they can be used, and selected

accordingly.
- 14-

Table 2. Determination of Adjusted Depth for Ground Sloping Toward the

Supported or Shielded Excavation Walls (includes vertical cuts

at the bottom of sloped trenches-see Figure 3(b))

Slope of Ground

1

1

1 Adjusted Depth for Long Sloped

3 hor. : 1 vert

1

1 1.67 times the depth of the supported excavation (H)

2 hor. : 1 vert. 1 2 times the depth H

1 hor.:l vert. 1 3 times the depth H

3/4 hor.:l vert. 1

1 3.7 times the depth H

§J If the supported excavation wall is at the bottom of a sloped excavation

(see Figure 3(b)) the equivalent depth needs not to exceed the total depth

of the excavation (H in Figure 3(b)) plus a 2 ft. surcharge allowance.

Table 3. Additional Surcharge Allowance in ft. for Heavy Equipment

Near the Supported or Shielded Excavation Wall (to be added to the standard 2 ft. allowance) (See Figure 3(c))

Depth of Trench and Soil Type

Weight of Equipment, W

1

1

1

10 ft. IT

II

II

15 ft. TT

II

1

20 ft.

1

1 A

1

1 1

I B I

1 1

C

IIII

1

A

1 1

1 B I C

1 1

II

II

1

A

1 B 1 C

1

20,000 lb

1

1 2

1

1 1

1 1 —

II

1

1

1

1 1

1 !

II

1

II

1

1

1

50,000 lb

1

| 7

1

1 1

1 2 |

1 1 —

II

1

1

5

1 1

I 2 | —

1 1

IIII

II

4

1

1 1 —

1

100,000 lb

1

1 10

1

i r

1 4 |

1 1

1 IT

II

II

8

1 1

I 3 | —

1 1

1

II

1

6

1 2 1 —

1

Notes: 1. Distance between the tracks of the equipment (edge of wheel or chain) and the supported excavation wall not to be less than 4 ft.

2. Distance between the center of the equipment load and the supported excavation wall not to be less than 6 ft.

3. If the spoil pile and the heavy equipment are on the same side of the supported excavation wall, the average depth

of the spoil pile shall be added to the surcharge allowance

in Table 3.

4.

If the equipment load is distributed over a length

parallel to the trench which is shorter than the following lengths: 10 ft. for 20,000 lb equipment;

12 ft. for 50,000 lb equipment; 20 ft. for 100,000

lb equipment follow the Guidelines Supplementing

Subpart P or accepted engineering practice.

Example: a 50,000-lb 12-ft long crane operates on the side of a 15-ft. trench in Type B soil. Adjusted

depth: 15 ft. + 2 ft. + 2 ft. (Table 3)^.9 ft.
-15-

TOP OF SUPPORTED WALL SURCHARGE

(a) AVERAGE CONDITION, TERRAIN NOT

STEEPER THAN 3 hor : 1 vert

ADJUSTED DEPTH = H+2ft

(bj GROUND SLOPING UP FROM

SUPPORTED WALL

ADJUSTED DEPTH IN ACCORDANCE

WITH TABLE 2, BUT NOT MORE

THAN Hi+2ft

(c) HEAVY EQUIPMENT LOADS

ADJUSTED DEPTH: ADD THE

DEPTH FROM TABLE 3 TO THE

2ft SURCHARGE ALLOWANCE

ADJUSTED DEPTH = H+2ft+H w

H w IS FROM TABLE 3

H = DEPTH OF SUPPORTED EXCAVATION

Figure 3: Determination of Adjusted Depth
-16-

b. Hydraulic shores or other pre-fabricated sub-assemblies

or members of shoring systems shall be rated for allowable working loads and selected with the aid of the

charts in the guidelines supplementing Subpart P, or

selected directly from special charts prepared by the

manufacturer

c. Timber shoring shall be selected with the aid of charts

in the guidelines supplementing Subpart P or from special

charts prepared by an engineer (qualified person?).

d. Any other shoring system can be pre-designed and rated

by an engineer (qualified person?) and selected on the

basis of soil type and equivalent depth from charts

prepared for this purpose.

(5) Special Provisions

(i) Intersecting Trenches

When two trenches intersect and one trench is shored,

the intersecting trench shall also be shored from the

intersection of the two trench walls to a distance of

not less than its depth.

(ii) Sloping Ground

If the ground behind an excavation wall slopes up from

the excavation wall and the ground slope exceeds

3 hor. in 1 vert, workers in the excavation must be

protected against objects rolling or sliding from the

sloped ground. This can be accomplished by projecting

the sheeting at least 18 inches above the ground surface or by a specially constructed protective toeboard.

If spaced sheeting is used provisions shall be made to

close the gaps between projecting sheeting members.

(Workers in excavations must be protected against rolling

or sliding objects?)

(iii) Excavation Below the Bottom of Sheeting, Trench Shields,

or Trench Boxes

Excavation up to 2 ft. (3 ft. ?) below the bottom of

sheeting, trench shields or trench boxes is permitted

in short-term excavations provided that:

a. No soil movement below the bottom of the sheeting,

trench shield or trench box is evident; and

b. The forces acting on the bracing, trench shield, or

trench box are calculated for the full depth of the

excavation, and the lowest wales and struts are

designed to resist the forces that would result if

the sheeting would be projecting to the bottom of

the excavation.
- 17 -

3l/ (iv) Maximum Spacing of Spaced SheetingMaximum allowable spacing of spaced sheeting shall be in accordance with

Table 4 (a) or (b) which ever controls.

Table 4(a) Maximum Center-to-Center Spacing^/ of

Spaced Sheeting Members

Soil

1

1

1 Depth of Excavation

Type 1

1

1

5 ft. - 10

r ft. 1 10 ft. - 15 ft.

1

1

1 15

1

ft. - 20 ft.

A

1

1

1

8 ft.

1

i 6 ft.

1

1

1

1

4 ft.

B

1

i

1

4 ft.

I

I 4 ft.

1

1

1

1

3 ft.

C

1

1

1 Tight Sheeting Required.

Table 4(b) Maximum Clear Spacing^/ of Spaced Sheeting Members

1 Depth of Excavation

Soil j Type 1

1

1

5 ft. - 10 ft. I 10 ft. - 15 ft.

1

1 15 ft. - 20 ft.

1

A

1

1

1 7.5 ft. 1 5.5 ft.

1

I 2 ft.

1

B

1

1

1

3 ft. i 2 f t

1

| 1 ft.

1

C | Tight Sheeting Required.

' If there is an indication of spalling the spacing must be

reduced to a spacing that will prevent spalling.

b/ Refer to Figure 4, page 18.
-18-

1926.653 DEFINITIONS APPLICABLE TO THIS SUBPART

(a) "Accepted engineering requirements (or practices)"

Those requirements or practices which are compatible

with standards required by a registered architect, a

registered professional engineer, or other duly

licensed or recognized authority. Guidance for

accepted engineering practices pertaining to excavation

safety is provided In the guidelines supplementing

Suhpart P.

(b) Acceptable Practice is a practice which meets the

minimum requirements in Section 1926.652(a).

( c) Adjusted Depth is the actual depth from the bottom of

the excavation to the top of the supported excavation

wall plus an additional depth to allow for surcharge,

sloping ground, or heavy equipment as stipulated in

Section 1926 . 652 (b) (4 ) (i)

(d) Allowable Working Stresses are allowable stresses

determined in accordance with accepted engineering practices.

(e) Belled Excavation is a part of a shaft or footing excavation, usually near the bottom and bell-shaped; i.e.,

an enlargement of the cross section above.

(f) Clear Spacing of sheeting members is the distance between

the edges of sheeting members over which the soil is

unsupported (see Figure 4)

(g) Competent Person means one who is capable of identifying

existing and predictable hazards in the surroundings or

working conditions which are unsanitary, hazardous, or

dangerous to employees, and who has authorization to

take prompt corrective measures to eliminate them.

(h) Engineer is a registered professional engineer.

(i) Equivalent Weight Effects (we ) is the weight effect

stipulated in Table 1 which is used to calculate pressures

on shoring systems.

(j) Excavation is any manmade cavity or depression in the

earth's surface except as noted, including its sides,

walls, or faces, formed by earth removal and producing

unsupported earth conditions by reasons of excavation.

Excavations do not include tunnels and shafts, caissons

and cofferdams covered by Subpart S of the Safety and

Health Regulations for Construction.

( k) Excavation Wall is the side of an excavation, rising

from the bottom of the excavation to the ground surface.
-19-

(l) Fractured Rock is rock which could spall or crumble when

excavated with vertical slopes. Fractured rock slopes

secured against mass movement and spalling by rock

bolts, netting, or other means approved by a qualified

person are considered stable (equal to unfractured rock)

(m) Long-Term Excavations are excavations which are open

for more than 24 hours (7 days?)

(n) Mud Sills are wales which are installed at the level

of the bottom of the excavation wall.

(o) Negotiable Slope is a slope on which a person can

egress from or ingress to an excavation.

(p) Qualified Person means one who, by possession of a recognized degree, certificate, or professional standing,

or who by extensive knowledge, training, and experience,

has successfully demonstrated his ability to solve or

resolve problems relating to the subject matter, the

work, or the project.

(q) Safety Margin is any measure of excess strength over that

required to resist the working loads.

(r) Sheeting is composed of members of the shoring system which are

in direct contact with the soil in the supported bank.

(s) Shoring Systems are structural systems supporting the

bank of an excavation.

(t) Short-Term Excavations are excavations which are open

for 24 hours (7 days?) or less.

(u) Sides, Walls, or Faces are the vertical or inclined

earth surfaces formed as a result of excavation work.

(v) Slope is an incline expressed as a ratio of horizontal

distance to vertical rise.

(w) Spaced Sheeting is sheeting in which the members

bearing against the excavation wall are spaced (see

Figure 6)

(x) Spalling is the continuous flaking and falling of soil

or rock from an unsupported trench wall.

(y ) Standard Practice is the trenching and shoring practice

in Section 1926.652 (b)

(z) Struts are the primary support members of a shoring

system including but not limited to cross braces, raker

braces, jacks and backties (see Figure 6).

(aa) Stable Slope is the slope which will remain stable for

the duration of the excavation.
- 20 -

(bb ) Structural Ramp is a ramp built of material other than

soil or rock.

(cc) Supported Wall is that part of an excavation wall which

is supported by a shoring system or shielded by trench

boxes or trench shields.

(dd) Trench Box see trench shield.

(ee ) Trench Shield is a protective device which shields workers

in a trench from the effect of mass movement of soil or

rock and which can be moved along as work progresses.

(ff

Wales (walers) are members of the shoring system which

are directly supported by struts and which in turn provide support to the sheeting (see Figure 4).

(gg) Working Loads are loads which should reasonably be anticipated to occur and which must be resisted with appropriate

safety margins , determined in accordance with accepted

engineering practice.

Figure 4. Components of the Shoring System
- 21 -

GUIDELINES SUPPLEMENTING SUBPART P OF THE SAFETY

AND HEALTH REGULATIONS FOR CONSTRUCTION

1 . DEFINITIONS

(a) Average Strength is the average failure load obtained

in tests of not less than 5 randomly selected samples

corrected for effects of load duration.

Ob) Design Criteria are design rules which , if followed,

will reduce the risk of occurrence of design limit

states to acceptable levels.

(c) Design Limit States are failure modes which endanger

workers m, or adjacent to, excavations.

(d) Design Loads are loads used for the design of shoring

systems or the determination of slope stability. Design

loads may be working loads or factored loads.

(e) Factored Loads are working. loads multiplied by the

factors stipulated in Section 2.1.B of the Guidelines.

(f) Failure Loads are loads which will cause failure of a

member of the shoring system that can endanger workers

in the trench or render the member unserviceable.

(g) Load Capacity is a measure of strength defined in

Section 2. IB.

(h) Safety Factor is the ratio of load capacity to the effect of the most critical combination of working loads.

In the case of excavation stability, the safety factor

is the ratio of resisting forces to driving forces.

For excavation slope stability the safety factor can

be taken as the ratio of critical height to actual

height.

(i) Saftey Margin is any measure of excess strength over that

required to resist the working loads.

(j ) Short-Term Strength Properties of Soils are the strength

properties of the soil adjacent to the excavation

during the period of exposure. Some of this strength

can be lost with the passage of time by such effects as

desiccation and lateral expansion. A typical shortterm strength property is apparent cohesion in moist

sands. In some instance there may be an increase in

strength with time (for instance drained vs. undrained

strength)
- 22 -

2 STRENGTH REQUIREMENTS FOR PRE -DESIGNED SHORING SYSTEMS,

TRENCH BOXES AND TRENCH SHIELDS TO BE USED IN THE STANDARD

PRACTICE

2.1 Design of Shoring Systems

Shoring systems, trench shields t and trench boxes shall

be designed to resist the working loads stipulated in

Section 2.2. The term "designed to resist is interpreted as follows [A or B]

A. The following stresses are not exceeded: 1.33 times

the allowable working stresses in short-term excavations; 1 times the allowable working stresses in

long-term excavations. "Allowable Working Stresses"

are the "allowable stresses" stipulated in applicable standards in conjunction with traditional

"working stress" design (using unfactored loads)

For timber shoring which is left

in place (not re-used for other excavations) allowable working stresses can be adjusted for load

duration as follows: 1 - week duration for shortterm excavations; 1 - year duration for long-term

excavations. Allowable stresses for hardwood timber

shall comply with Table 1.

B. The system has adequate load capacity to resist the

following factored loads: 1.3 times the working

loads stipulated in Section 2.2 in short-term

excavations. 1.7 times the working loads stipulated

in Section 2.2 in long-term excavations.

"Load capacity" is defined as one of the following:

a: "Design strength" as defined for reinforced concrete members in ACI 318 (see Section 2.5

or

b: "maximum strength" as defined for steel members

in Part 2 of the AISC Specifications (see Section

2.51 or

c: S = S (1 - 1.65v) for members which cannot be designed by the standards listed in Section 2.5,

where
-23-

S = load capacity

S = average strength (failure load corrected for

load duration if applicable)

v - coefficient of variation of strength.

2.2

Loads Acting on Shoring Systems, Trench Shields and

Trench Boxes

2.2.1 General

All loads given in this section are "working loads".

They are loads which shall reasonably be anticipated

and which must be resisted with the safety margins

stipulated herein and in the standards listed in

Section 2.5.

2.2.2 Operational Loads

The following minimum load shall be used for the

design of all struts (cross braces) : A gravity load

of 240 lb. distributed over a 1 ft. long portion in

the center of the span of the strut or at the location

where its effect is most critical.

In addition to the 240 lb. gravity load and the

lateral loads in 2.2.3, trench shields, trench boxes

and shoring systems installed by methods which do

not assure that the sheeting bears tightly against

the excavation wall (there may be an open space

between the bank and the sheeting) shall withstand

without failure an impact energy of 240 ft. -lb. applied

at any point against the sheeting side facing the

excavation wall (toward the excavation) . Only in

shoring systems whose struts are pre-loaded, the

sheeting shall be assumed to bear tightly against

the excavation wall.

2.2.3 Lateral Soil Pressures

Lateral soil pressure per unit surface area of the

supported excavation wall shall be calculated by the

following equation:

p = we He

where

p * a uniformly distrubuted lateral soil pressure

in lb/ft2

we= equivalent weight effect from Table 1 in Subpart

P, 1926.652 (lb/ft3)
- 24 -

• adjusted depth determined in accordance with Figure 1. Section 1926.652(b)(4) provides a procedure for the determination

of He by personnel in the field.

2.2.4 Loads Tributary to Members of the Shoring System

0.) The following portion of the lateral loads caused by the uniform lateral

soil pressure p shall be assumed to act on members of the shoring system:

100 percent of the tributary load shall be assumed to act on all struts,

80 percent of the tributary load shall be assumed to act on wales (members

directly supported by struts shall be designed as wales), 67 percent of

the tributary load shall be assumed to act on sheeting. Tributary load

shall be calculated in accordance with Figure 2.

(2) Loads Tributary to Spaced Sheeting

Struts and wales supporting spaced sheeting shall be designed to resist

the full tributary lateral load (the same load that would be calculated

for tight sheeting).

Spaced sheeting members shall be designed to resist the lateral load

tributary to an area equal to the length of the member times the center

to center spacing between the sheeting members (this includes the

unsheeted portion of the trench wall) as follows:

Sheeting members supported by wales shall be designed to resist 67 percent

of the lateral soil pressure "p". Sheeting members directly supported bystruts shall be designed to resist 80 percent of p.

2.3 Rating of Shoring Systems

2.3.1 Components or subassemblies of shoring systems, or fully assembled selfcontained shoring systems, shall be rated and subsequently used to resist

working loads equal to, or smaller than, those for which they are rated to be

adequate.

Rating shall be accomplished as follows:

Struts shall be rated for the compressive working loads they are allowed

to resist. If struts are extendable, the rating shall consider length

effects on load capacity. Rating of struts shall Include consideration

of the 240 pound vertical downward load stipulated in Section 2.2.2.
- 25-

P

: *e

e H * DEPTH OF SUPPORTED EXCAVATDN

| a) AVERAGE CONDITION TERRAIN NOT

STEEPER THAN 3 hor 1 vert H e

* H 4 2ft — eq |1]

(bi GROUND SLOPING TOWARD

SUPPORTED WALL

H e“ Hn~2 *]* HH-0.04

or H e =H i +2ft

WHICHEVER IS LESS - eq 2

|C| HEAVY EQUIPMENT LOADS

H e

= H-H q -H*

MW eq3

w e H| ^

• * |

H w CAN BE DISREGARDED WHEN x £ H

/ = LENGTH OF EQUIPMENT OR

LINELOAO IN THE DIRECTION OF

THE TRENCH

W * TOTAL FORCE EXERTED BY WEIGHT

OF EQUIPMENT OR LINE LOAD

w e

-- EQUIVALENT WEIGHT EFFECT FROM TABLE I

Figure 1 Determination of Adjusted Depth
- 26 -

d.

d2

d3

di

Strut 1

Strut 2

Strut 3

hM

d.

i dih

r

»

Strut 1

d2 h

4 Strut 2

d3h.

4 d ih

t Strut 3

d4

;

CASE 1. Sheeting is not

embedded

Tributary Height for Strut 3

Sheeting

di Strut 1 di

d 2 Strut 2

d 2/2

d 2h

A , d3h

03

Strut 3

4

’ d3h

d«

> Strut 4 „£

Mlud sill d4h

r p -i

Strut 1

Strut 2

Strut 3

CASE 2. Embedded sheeting

Mote: Use mud sill or equivalent

support unless sheeting is firmly embedded

Strut 4

Tributary Load = p x Tributary Height (from figure) x Horizontal Strut Spacing

Figure 2. Loads Tributary to Members of the Shoring System
- 27 -

Wales supported at given length Intervals shall be rated for allowable load

per linear foot of wale. For stru t—wale assemblies the wale shall be

designed to resist moments and shears not less than 80 percent of those

resulting from the trlbutrary allowable strut loads.

Self-contained repetitively-used shoring systems such as trench boxes,

hydraulic shoring systems or pre-fabrlcated strut-wale assemblies can be

rated either for allowable working loads (in lb/ft 2 of trench wall), or preferably, for pre-determined conditions of use. Rating for conditions

of use shall Include designation of maximum allowable adjusted depth for

given soil types, (e.g., a trench box could be rated for use in a 20 ft.

equivalent depth in Type B soil or, alternately, for an allowable working

load of 800 lb/ft2 ).

2.3.2

Rating Procedures

The rating shall be based on the professional opinion of an engineer and

marked on the component or assembly. It shall be accomplished by engineering

analysis or testing. In addition to the loads stipulated in Section

2.2

the .engineer shall consider loads resulting from installation and

construction procedures.

Repetitively used assemblies or components shall be kept in good repair.

This shall be accomplished by renewing the rating at least annually after

inspection by a qualified person. Hydraulic shores shall be tested at least once a year to 1.25 times their allowable working load, and the load shall be

maintainable for at least 5 minutes without a pressure drop.

2.4 Determination of Load Capacity by Test

If the load capacity of structural components of a shoring system is

determined by test, the following minimum requirements shall be used:

2.4.1 Strength variability shall be considered in accordance with Section

2. IB.

2.4.2 Under no circumstances shall the allowable working load of struts in

short-term excavations exceed 67 percent of the average strength, or in

long-term excavations 50 percent of the average strength of the component

or shoring system.

2.4.3 For struts the test load shall be applied with an eccentricity of not

less than 1/6 the thickness of the strut with respect to any one of

the principal axes (but not simultaneously with respect to both axes).

The test loads shall induce a centerspan moment equal to that caused

By a concentrated load of 240 lb times the applicable load factor

(Section 2.1B) applied at the center of the strut normal to its axis,*

Load eccentricities shall be of the same magnitude and direction on both ends of the strut (single curvature)
- 28 -

2.4.4 Impact load shall be applied by a 60 lb sand filled leather bag fabricated

in accordance with Section 12.2 of ASTM E 72-77 [5], During the impact

test the sheeting shall be supported as in actual working conditions.

Three successive impact tests shall be applied. "Failure" under impact

load is defined as any one of the following: rupture of the sheeting or any of its structural supporting members; any structural damage that would

lower the load capacity of the shoring below that required; excessive

bending which can endanger workers in the trench.

2.5 Applicable Standards

Structural members of the shoring system shall be designed in accordance with

the pertinent provisions in the following standards:

SteelSpecifications for the Design, Fabrication and Erection of Structural

Steel for Buildings, American Institute of Steel Construction, New

York, N.Y. , February 1969.

ConcreteBuilding Code Requirements for Reinforced Concrete, (ACI 318-77),

American Concrete Institute, Detroit, Michigan, November 1977.

AluminumSpecifications for Aluminum Structures, The Aluminum Association,

New York, N.Y., November 1967 [1].

Wood

National Design Specifications for Wood Construction, National

Forest Products Association, June 1977, for soft-wood lumber

stresses. Because formally approved allowable working stresses do

not exist for most hardwood species, applicable ASTM Standards may

be followed in conformance with procedures recognized under the

American Lumber Standard, PS70/70. Allowable stresses are given in

Ta ble 1

* If the end eccentricity produces the desired center span moment the

provision is satisfied.
- 29 -

Table 5. Allowable Unit Stresses in psi for Hardwood Trenching Lumber^/

Hardwood group-k/

2 to 4 in. thick, 2 to 14 in. wide | 1 5 in. and thicker, 5 to 20 in. wide

Fb Ft FC

Fv Fd E S 1 Fb Ft FC

Fy Fci E

White oak£/ 875 575 550 105 355 800,000 | I 975 650 525 120 355 800,000

Mixed oa.V.^1 850 550 500 80 355 800,000 | | 925 625 475 90 355 800,000

Mixed hardwoods I$1 725 475 375 65 165 800,000 | | 800 550 350 75 165 800,000

Mixed hardwoods III/ 600 400 350 50 115 800,000 | I 675 450 325 60 115 800,000

Ref. Southern Pine Inspection Bureau Grading Rules, 1977 edition, for general grade description as follows

Grade Paragraph Size

No. 2 313

No. 2 343

No. 2 SR 406

2 to 4 in. thick, 2 to 4 in. wide

2 to 4 in. thick, 5 to 14 in. wide

5 in. and thicker, 5 to 20 in. wide

Assumes 10-yr. load duration basis. For new (first use) lumber, adjustments for load duration may

be made: for 1-yr. duration multiply by 1.1; for 1 wk. , multiply by 1.25; for 2 days, multiply by 1.30. Load duration adjustments for used trenching lumber are not recommended. For hardwood

trenching lumber, requirements are waived for manufacture, compression wood, firm knots, skips,

stain and warp. Holes limited as knots; wane limited as given for No. 2 grade in SPIB, 1977 edition.

Hardwood species defined per ASTM D 1165.

£/ White oak: The following white oaks—bur, chestnut, live, overcup, post, swamp chestnut, swamp

white, white.

4/ Mixed oak: Red oak (black, cherry bark, laurel, northern red, pin, scarlet, southern red, water,

willow); white oak (footnote c)

Mixed hardwoods I: Ash (black, blue, green, Oregon); beech; birch (sweet, yellow); cherry; elm

(American, rock, slippery); hackberry; hickory (mockernut, pignut, shagbark, shellbark); locust

(black, honeylocust); magnolia (cucumber, southern, sweetbay); maple (bigleaf, black, red, silver,

sugar); mixed oak (footnote d); pecan (bitternut hickory, nutmeg hickory, pecan, water hickory); red

alder; sassafrass; sugarberry; sweetgum; sycamore; tanoak; tupelo (black, water); yellow poplar.

Excludes all cottonwood, all aspen, basswood, and balsam poplar.

Mixed hardwoods II: All hardwoods in Mixed hardwoods I (footnote e) plus black and eastern

cottonwood; quaking and bigtooth aspen; basswood. Excludes balsam poplar.
- 30 -

APPENDIX A. ENGINEERING GUIDELINES FOR THE DESIGN OF SHORING SYSTEMS

AND OTHER MEANS T PREVENT MASS MOVEMENT OF SOIL AND ROCK

Table of Contents

Page

A.l General 32

A. 2 Scope 32

A. 3 Design Loads 32

A. 3.1 General 32

A. 3.2 Soil and Water Loads 33

A. 3. 3 Surcharge Loads 33

A. 3. A Operational Loads 34

A. 3. 3 Dynamic Loads 34

A. 3.6 Restraint Loads 34

A. 4 Design Criteria 34

A. 4.1 General 34

A. 4. 2 Sloped Excavations 34

A. 4. 3 Braced and Shielded Excavations 33

A. 5 Information on Accepted Engineering Practice 38

A. 3.1 .General 38

A. 3. 2 References 38

A. 5.3 Summary of Information 38
- 31 -

LIST OF SYMBOLS

B ~ Vldth of excavation In ft.

c - Cohesion (undralned shear strength) of material In bank, lb/ft 2

.

Cfc - Undralned shear strength of material below bottom of

excavation, lb/ft2 .

Dr

- Relative density of soil, percent.

H - Depth of Excavation, in ft.

ka - Coefficient of active earth pressure, as defined by pertinent

equations listed.

m - Coefficient in lateral force equation as defined by Peck

(1969) (see Section A. 5. 2).

N * yH/c - Stability number, based on shear strength of material in the

bank.

Nfc « yH/ Cfo - Stability number, based on shear strength of material below

bottom of excavation and weight of material in bank.

N - Blowcount in standard penetration test using traditional U.S.

methods (rope and cathead) in blows per foot.

S - Load capacity in lb.

S - Average strength (average failure load corrected for load

duration, if applicable) in lb.

v - Coefficient of strength variation.

y - Unit weight of soil (in natural condition or as assumed for

worst case), in lb/ft 2.

ysat - Unit weight of saturated soil, in lb/ft^.

ysub - Unit weight of submerged soil, in lb/ft^.

yw - Unit weight of water in lb/ft^.

^ “ Angle of shearing resistance (internal friction) of soil, in

degrees.
- 32 -

A.l GENERAL

These guidelines are for engineers who design shoring systems, trench shields,

and trench boxes or determine slde.iJ.opes In excavations. The guidelines are not meant to be a standard from which an engineer cannot deviate. Rather,

they recommend minimum design loads and safety margins against mass soil and

rock movement which are considered appropriate, and design limit states which

should be considered by engineers. It Is recognized that the design of shoring

srystems, the stability analysis of slopes, and the assessment of soil conditions are not an exact science which can be approached with a set of rigid

rules, but rather an art which requires judgment, experience and recognition

of unique local conditions. Thus these guidelines can neither be imposed as mandatory rules, nor can a professional engineer forego his responsibility to

determine in each Instance whether the stated guidelines are adequate.

A. 2 SCOPE

The guidelines contain recommended minimum requirements for the protection of

workers in excavations against death and injury by mass movement of soil and

rock. They do not cover other important parameters which an engineer must con- sider, such as protection of adjacent structures, utilities and improvements

against damaging settlements, or effects of ground water fluctuations on adjacent properties. They also do not cover other safety requirements in

excavations which are unrelated to soil and rock movement.

Three methods of preventing soil and rock movement are considered in the

guidelines: sloping of the banks of excavations; shoring; and shielding of

the work space by protective devices. Other methods could also be used such as soil stabilization by freezing or grouting. The guidelines do not apply to

excavations whose collapse does not endanger workers.

A. 3 DESIGN LOADS

A. 3.1 General

All the design loads listed, but not necessarily only the listed loads, should

be considered. Unless specifically stated otherwise in the design criteria,

the most critical combination of design loads should be considered. The design

loads quantified herein are "working loads" (see definition). The design loads

apply to shoring systems as well as protective devices such as trench shields

and trench boxes.

A. 3. 2 Soil and Water Loads

(1 ) General

Loads caused by soil and water pressures should be calculated in accordance

'#ith accepted engineering practice and these guidelines.
-33-

(2 ) Loads Cauaed by Water

Hydrostatic loads, hydrodynamic loads and seepage forces should be considered

where applicable. Special attention should be given to the effects of potential groundwater fluctuations, saturation of previously drained deposits, and

water penetration into fissures. The following conditions are recommended as Che basis for determining critical loads:

For long-term excavations: conditions caused by the 5-year flood.

For short-term excavations: conditions caused by the 1-year flood or alternatively the most severe condition that will not cause interruption

of work and evacuation of the workers from the excavation.

(3 ) Soil Loads

Soil loads should be determined in accordance with the state of the art in

geotechnical engineering. Special attention should be given to fissures,

planes or weakness and previously excavated soils. The following conditions

are recommended as a basis for determining critical loads.

For long-term excavations: Drained as well as undrained conditions should

be considered if applicable. Short-term strength characteristics should

not be assumed to contribute to stability. Effects of exposure, lateral

expansion, desiccation cracks, freezing, erosion, and change in confining

pressures should be taken into account.

For short-term excavations: In most instances only undrained conditions

need to be considered. Short-term strength characteristics could be

considered, provided that an adequate assessment is made of conditions

that could lead to loss of strength.

Further information is provided in Section A. 5.

A. 3. 3 Surcharge Loads

Surcharge loads should be determined on the basis of actual anticipated working

conditions. Consideration should be given to: the amount and location of

accumulated spoil material; stored construction material; construction equipment; vehicular and human traffic; and foundations adjacent to the excavation.

In no case shall the surcharge load be assumed less than 200 lb/ft^ distributed

over the entire ground surface or the equivalent of an additional 2 ft. depth

of material excavated on the site (using average unit weight of soil deposits),

whichever is more.

A. 3. 4 Operational Loads

All loads caused by the anticipated excavation work must be considered. These

Include excavated or construction material supported by portions of the shoring
- 34 -

system and workers climbing on Che shoring system. The following minimum load

shall be used for design: a gravity load of 240 lb distributed over any

1 ft. long portion of any strut.

A. 3.5 Pynamlc Loads

•jrnamic loads which can reasonably be anticipated as a result of pile driving,

blasting, vehicular traffic and construction equipment should be considered.

In addition, trench shields, trench boxes and shoring systems installed by

methods which do not assure that the sheeting bears tightly against the exca- vation wall (there may be an open space between the bank and the sheeting)

should withstand without failure an impact energy of 240 ft-lb applied at any

point against the sheeting side facing the bank (Inward). Only in shoring

systems whose 6truts are pre-loaded the sheeting should be assumed to bear

tightly against the excavation wall.

A. 3. 6 Restraint Loads

Restraint loads caused by temperature, moisture, or other factors causing

dimensional changes in structural members of the shoring system should be con- sidered when applicable. In general, it can be assumed that the empirically

based lateral loads calculated in accordance with present engineering practice

contain a reasonable allowance for temperature effects on struts.

A. 4 DESIGN CRITERIA

A. 4.1 General

This section conveys design limit states and design criteria. "Design limit

states" are events which constitute a failure to meet safety requirements.

"Design criteria" are design rules such as factors of safety to be used which,

if followed, will reduce the probability of occurrence of the design limit

states to acceptable levels. It is conceivable that an engineer could deviate

from the design criteria if the occurrence of the design limit states can be

prevented by other means.

A. 4.2 Sloped Excavations

(1 ) Design Limit States :

1. Slope stability failure (part or all of the embankment)

2. Sloughing
- 35 -

(2 ) Design Criteria :

1. Long-term Excavations

(a) Granular soils (no cohesion):

Slope angle should not exceed angle of shearing resistance.

(b) Cohesive Soils:

The safety factor against stability failure should be greater

than 1.5, unless the excavation is monitored by an engineer

using Instrumentation and other means. The safety factor should

always be greater than 1.3. Suitable surface and subsurface

drainage should be provided to prevent stability failures or sloughing Induced by seepage or erosion.

Maximum unbraced height of vertical bank:

5 ft. for all soils or fractured rock. No limitation for

unfractured rock.-L/

2. Short-term Excavations

The safety factor against stability failure should exceed 1.3

except that for dry cohesionless soils a slope angle equal to the

angle of shearing resistance may be maintained. Short-term strength

properties could be utilized, provided that there are adequate

safeguards against conditions which could cause strength degradation.

Maximum unbraced vertical bank: For intact hard clays and loess the

unbraced height could exceed 5 ft provided that an engineer can document that there is substantial empirical evidence that the

unsupported bank will stand without failure. For all other soils,

including fractured rock, the maximum unbraced height should not

exceed 5 ft. There are no limitations for unfractured rock.

A. 4.3 Braced and Shielded Excavations

( 1 ) Design Limit States

1. Stability failure of the bank.

2. Base instability.

3. Partial caving or sloughing of the bank between spaced vertical or horizontal supports.

U A geotechnical engineer or engineering geologist should determine whether

the rock is unfractured.
-36-

4. Failure of Che soil supporting struts, anchors, or soldier piles.

5. Failure of structural components of the shoring system or of protective

devices.

(2) Design Criteria

1

Stability of the Bank

A stability failure of the bank is the collapse of all or part of the

bank caused by sliding of a soil mass along a failure surface. The

failure surface may lie outside the support points of structural mem- bers of the shoring systems (supports of raker braces, soil anchors,

or the bottom of soldier piles or cantilever sheeting) and thus

render the shoring ineffective, or it may be caused by the structural

failure of members of the shoring system.

The safety factor against any stability failure of the bank should

exceed 1.5.

2.

Base Stability

where

Base instability leads to heaving of the base of the excavation,

which in turn can cause dislocation and collapse of the shoring

system. The safety factor against base instability should exceed

1.5. Potential effects of uplift resulting from artesian pressure

in confined aquifers should be considered. Dewatering should be

adequate to prevent piping (quick condition) caused by seepage of

groundwater into the base of the excavation. In deep clay deposits,

base instability should be considered a problem whenever N ^ exceeds

the following values: > 6 for trenches where — > 3; N

^

> S.l^

for verv wide excavations: intermediate values for 0 < ii < 3.

B ~

N 5 * yH/cb * stability number for base failure,

y * unit weight of soil, lb/ft^

H * depth of excavation, ft.

B width of excavation, ft.

c^ * undrained shear strength below excavation base, lb/ft z

3

Soil Stability between Spaced Supports

There is no generally accepted theoretical approach by which the

ability of a soil to arch between successive supports can be evaluated or correlated with strength properties of the soil. There is

empirical evidence that short-term supports can be spaced up to 8 ft. on center in hard clay, very stiff sandy clays or glacial tills, and

2 to 3 ft. on center in slightly fissured clays.
- 37 -

Guidance is given in Section 1926. 652 ( b) (4 ) ( iv ) and should be compared

with empirical field evidence.

4. Soil Support for Struts. Anchors or Soldier Piles

A minimum safety factor of 2 is recommended against bearing failures

of members of the shoring systems such as raker braces. A safety

factor against shear failure of the supporting soil of not less than

1.5 should be used when passive earth pressure is relied upon to

support embedded portions of soldier piles and sheeting or deadmen.

All soil anchors should be proof load tested to 1.33 times their

working load. If the load capacity of soil anchors is determined by

tests, it should be not less than 1.5 times the working load for

anchor inclinations of 2 hor.rl vert, or flatter, and increase to

2.0 times their working load for inclinations of 1 hor.:2 vert. When

anchor capacity is determined by analysis the safety factor should

not be less than 3. Soil anchors subjected to the working load

should not show creep when the load is sustained for 15 minutes.

5. Design of Structural Components of Shoring Systems, Trench Shields

and Trench Boxes

(a) Applicable Standards

See Section 2.5.

(b) Allowable Stresses

Allowable stresses should be determined in accordance with the applicable

standards. In long-term excavations allowable stresses should not be

exceeded under any applicable combination of working loads. In short-term

excavations allowable stresses in structural members may be exceeded by

up to 33 percent.

( c) Ultimate Strength Design

Ultimate strength, rather than working stress design may be used whenever

such a procedure is stipulated in the applicable standard or load capacity

is determined by test. Ultimate loads should be taken as 1.7 times the

working load for long-term excavations and 1.3 times the working load for

short-term excavations, and should not exceed the load capacity as defined

in section 2.1B.

( d) Determination of Load Capacity by Test

Determination of the load capacity of structural components of the shoring

system by tests should be in accordance with Section 2.4.
- 38 -

A.5 INFORMATION ON ACCEPTED ENGINEERING PRACTICE

A. 5.1 General

This section contains a brief summary of Information on commonly used

engineering practice which Is considered to provide adequate protection against

the mass movement of soil and rock. The choice of the referenced design

approaches should not be Interpreted as an endorsement of these approaches

9*er other approaches which are consistent with the present state of the art.

A. 5. 2 References

The following references provide guidance in the calculation of lateral loads on excavation bracing. Loads calculated in accordance with these references are considered to be working loads:

Department of the Navy, Design Manual, Soil Mechanics, Foundations and Earth

Structures, NAVFAC DM-7, Chapter 10, U.S. Naval Publications and Forms Center,

Philadelphia, PA, September 1971.

Goldberg, D.T., Jaworski, W.E., and Gordon, M.D. , Lateral Support Systems and

Underpinning, Report No. FHWA-RD-75-129 , Vol. II, Federal Highway

Administration, Washington, D.C., April 1976.

Peck, R.B., Deep Excavations in Soft Ground, Proceedings of the International

Conference on Soil Mechanics and Foundation Engineering, State-of- the-Ar

Volume, pp. 225-250, Mexico City, 1969.

Peck, R.B., Hanson, W.E., and Thurnburn, T.H., Foundation Engineering , Chapter

27, John Wiley and Sons, New York, NY, Jan. 1974.

Tschebotariof f , T. P. , Foundations, Retaining and Earth Structures , McGraw-Hill

New York, NY, 1973.

United States Steel Company, Sheet Piling Manual, U.S. Steel, Pittsburgh, Pa.,

July 1975.

A. 5. 3 Summary of Information

Hereafter is a summary of information derived from references in section A. 5. 2.

The suggested pressure envelopes are not intended as an endorsement of one single approach to the problem, but rather as a summary of commonly used

approaches
-39-

(1 ) Lateral Pressures

1 Sands (Peck, 1969)

065 k0

y H

k tan^ (4 5 - 4> /2 )

fl

2. Soft to Medium Clays, when N > 6 (Peck, 1969) (if pressures

calculated under 3 using 0.4 yH are larger, use (3).

N « yH/C

When cut is underlain

normally consolidated

All other cases: m *

by deep

clays

i.o'

soft

m * 0.4

3. Stiff Clays, whenever N < 4. (Peck, 1969) (if 4 < N < 6 use 2. or 3.,

whichever gives larger pressures)
- 40 -

4. Dense cohesive sands, very stiff sandy clays. (Goldberg et al., 1976)

Relatively Uniform Upper Third of Cut

Dominated by Cohesionless Sands
- 41 -

(2 ) Soil Properties

TABLE A.l. Typical Values of Unit Weight of Soils

Silty or clayey sands & Soil Type

r

gravel |

1

I

Moist U.W. abc

W.T., y ( Ib/f

3

1 ve | Saturated U.W. Be;

) I W.T., y Bat (lb/ff

ow

} )

Poorly graded sand — r

i

i 105-115

1

1

I 115-125

Clean veil graded sands

i

i

i 115-125

1

1

1 125-130

Silty or clayey sands

1

i

i 120-130

1

1

1 125-135

Silty or clayey sands &

1 gravel I

| 125-135

l

I

I 130-145

Soft to medium clay

1

1

i 100-115

I

1

1 100-115

i Stiff to very stiff clay I

i 110-125

1

1

1 110-125

Organic silt or clay

i

1

1 90-100

1

1

1 90-100

T sub “ fsat ” T

yw

« 62.4 lb/ft 3

TABLE A. 2. Relationship Between Properties of

Standard Penetration Test Results

Cohesionless Soil and

1 1

1 1

1 1

1 Soil Type I

1 1

SPT, N

blows/ ft.

1 1

1 Relative I

1 Density 1 $

1 Dr 2 | (after Peck)

1 1

1

1

1

1 ka

1

1

1

1

1

1

i r

1 Very loose sand 1

1 | <4

1 1

I 0-15 |

l i 29°

1

| >0.35

1

1

!

i

1 1

I Loose sand |

1 | 4-10

1 1

1 15-35 | 29°-30°

1

i 0.35-0.33

1

I

I

i 1 1

1 Medium dense sand |

1 | 10-30 | 35-65 |

I j 30°-36°

1

| 0.33-0.25

1

1

1

i

! 1

| Dense sand |

1 | 30-50

1 I

| 65-85 |

t i 36°-41°

1

| 0.25-0.21

1

1

1

i

1 1

I Very dense sand i

1 1 >50

1 1

| 85-100 |

! 1

>41*

1

| <0.21

1

i

1

!
-42-

TABLE A. 3. Properties of Cohesive Soli and Standard Penetration

Test Results

Clay

Consistency Identification

Very soft

1 1

1 Easily penetrated several I

1 Inches by fist. Extrudes 1

1 between fingers when j

1 squeezed in hand. i

| |

<2

"1

| 250

1

1

I

|

I <500

Soft

1 1

1 Easily penetrated several I

1 inches by thumb. Molded I

1 by light finger pressure. I

| |

2-4 I 250-500

1

1

|

| 500-1000

Medium

1 1

1 Can be penetrated several 1

! inches by thumb with mod- I

1 erate effort. Molded by I

1 strong finger pressure. 1

|

t

4-8 | 500-1000

1

1

1

|

I 1000-2000

Stiff

1 1

1 Readily indented by thumb |

1 but penetrated only with |

1 great effort. I

1 |

8-15 | 1000-2000

1

1

|

| 2000-4000

Very stiff

1 1

1 Readily indented by |

1 thumbnail. 1

15-30 | 2000-4000

1

1

I 4000-8000

Hard

1 1

1 Indented with difficulty. I

1 1 >30

1

I >4000

1

| >8000

SPT, N

blows/ f t

Shear Str.

lb/ft2 Compr. Str,

lb/ft 2

The correlation between N values and soil properties for clays can be regarded

as no more than a crude approximation, but for sands it is often reliable enough

to permit the use of N values in design. Unconfined compression tests or triaxlal tests are more reliable for clays. It should also be noted that the value

of N can be Influenced by numerous factors such as: the depth at which the test

is made; the location of the water table; presence of boulders in the deposits;

Irregularities in performing the test; etc. In general, N values used here are representatives of those obtained by the traditional U.S. (rope and cathead)

methods. If other methods are used, a correction for delivered energy is

desirable.
-43-

APPENDIX B. INFORMATION ON ACCEPTABLE SHORING SYSTEMS

B.l Timber Shoring

(a> Examples of acceptable timber shoring sizes for mixed hardwoods II (see

Table 1, page 27) are given in Tables B.l, B.2, B.3 and B.4. Other sizes

and arrangements can be used if they comply with the provisions in

Subpart P.

^b) Timber sheeting (except plywood) shall have a minimum thickness of 2 in.

Type A and B soils and 3 in. in Type C soils. In trenches more than

15 ft. deep all timber sheeting shall have a minimum thickness of 3 in.

Table B.l. Spaced Tiaber Sheeting in Accordance vlth Standard Practice (Strut

Wale Assemblies for trenches 4 ft. or less wide).

Trench

Depth

(ft)

Soil

Type

Strut Sizes (in) Sizes of Upright (In) Uale i Sizes ! (in) I

l

5-10

10-15

5-10

10-15

10-15

Horizontal Spacing (ft)

A 6 8 Horizontal Spacing (ft)

2 3 4 6 8

4x4

4x6

4x4

4x4|

4x6

6x6

4x4

2x6

2x6

2 x 6 2x6

2x6

3x8

2x8

6x81

I 8x8

i o x o i

Notes: (1) All luaber sizes are actual (not noalnal) sizes In Inches.

(2) 3x6 struts can be substituted for 4x4 struts In trenches

up to 4 ft. wide. For trenches wider than 4 ft. use Table 1.3 for strut size adjuataent.

(3) All horizontal spacing la center-to-center

(4) Vertical center-to-center spacing of struts or wales not

to exceed 4 ft.

(5) Longer side of wale cross section to be horizontal.

(6) Spaced sheeting Is not allowed In Type C soils.
- 44-

Teble 1.2. Tlaber Shoring Strut Sizes for Strut-Wale Aascablies, In Accordance

with Standard Practice (for trenches A ft. or lees wide)

Trench

Depth

(ft)

Soil

Type

Horizontal Strut Spacing (ft)

10 12 1« I lb 20 I

5-10 4x6

6x8

6x6

8x8

6x6 I 8x8

8 x 10 I 8 x 10 8x8 I 8x10

10 x 10 I 10 x 12

10 x lu l 12 x 12 |

10-15 6x6

8x8

6x8

8 x 10 8x8 | 8x10

10 x 10 I 10 x 12

10 x 10 I 10 x 12

12 x 12 I

12 x 12 i

15-20 6x8

8 x 10 8x8

10 x 12

8 x 10 I 10 x 10

12 x 12 I

10 x 12 I 12 x 12

(1)

All luaber sizes are actual (not noalnal) sizes In inches.

(2) For trenches wider than 4 ft. adjust strut sizes by Table B.3.

(3) Vertical spacing not to exceed 5 ft. cents r-to-center.

(4) All horizontal spacing is center-to-eenter.

Table B.3. Adjustment of Strut Size for Trench Width

Adjustment of Strut Size for Excavation Width

Strut Size from Size of Strut Required

Table B.l or B.2 for Trench Widths

4 ft 1 6 ft

1

1 9

1

ft

1 1

1 12 ft |

1 1

15 ft

4 x 4 1 4 x 4

1

1 4 x 6

1 1

1 6x6 | 6x6

4 x 6 | 4 x 6 1 6 x 6 1 6 x 6 | 6x6

6 x 6 1 6 x 6 1 6 x 6 16x8 | 8x8

6 x 8 1 6 x 8 1 6 x 8 18x8 I 8x8

8 x 8 1 8 x 8 1 8 x 8 18x8 | 8 x 10

8 x 10 1 8 x 10 1 8

1 x 10 1 8 x 10 |1 1

10 x 10

I

I

Notes: (1) Blanks indicate no adjustment in size required

(1) 10 x iO or larger sizes need no adjustment.
- 45 -

Table B.4. Tlaber Shoring Vale Sites In Accordance with Standard Practice

1 I 1 1 1

I frwach | | Horltontsl Strut Spacing (ft) I Sheeting I

1 Sooth I Soil 1 1 Thicxness 1

1 (ft) 1 Type 1

! !

1 1 | 6 I 8 I 10

1 1 1 1 1

1 1 1 1 (in) I 12 I 14 | 16 | 20 I |

1 1 1 1 1

! 1 1 1 1

I 5-10 | B | 6 x 8 | 8 x 10 | 10 x 10

| | C | 8 x 10 | 10 x 12 I 12 x 12*

1 1 1 1 1 till 1 10 x 10 | 10 x 12 | 12 x 12 I | 2 | 12 x 12 I I I |3 |

1 I

i i I

1 1 1 1 T~

1 10-15 IB 1 8 x 8 I 10 x 10 I 10 x 12*

I | C | 10 x 12 | 12 x 12* I 12 x 12

1 1 1 1 1

1 1 1 1 1 10 x 12 1 12 x 12 I | | 2 1

1 1 1 13

! ! ! !

i

i i i r

I 15-20 | B | 8 x 10 |

1III1 C. I 12 i 12 |

1

1 10 x 12 1 12 x 12*

12 x 12 |

1

n i i i i i

1 12 x 12 | I | 13 |

1

1

1

1

1

1

1

1 I3| 1 1 USE INTERMEDIATE STRUTS TO THE RIGHT OF LINE 1

(1) All luaber sites are actual (not noainal) sites In inches.

(2) Vertical spacing not to exceed 5 ft. center- to-center.

(3) All horltontsl spacing Is center-to-center

(4) Long side of cross-section of rectangulsr aeabers to be horltontsl.

(5) * Indicates slight overstress.

(6) Wale sites to the right of dividing line require Insertion of lnteraedlate strut before workers

enter the trench.

(7) If vertical dlstsnce froa the center of the lowest wale to the bottoa of the trench exceeds

2 1/2 ft., sheeting shall be firmly eabedded below the bottoa of the trench or audsi.ll shall be used. The vertical dlstsnce froa the center of the lowest wale to the bottoa of the trench shall

not exceed 3 ft., or 3 1/2 ft. If audslll Is used.
- 46 -

B.2. charts for the selection of rated shoring systems

CHART 1: Strut Loads for 5 Ft. Vertical Strut Spacing

Strut Load, kip

EXAMPLE: (following arrows)

Equivalent Depth: 17 ft.

Horizontal Strut Spacing: 10 ft.

Strut Loads:

Type A Soil 17 kip

Type B Soil 34 kip

Type C Soil 68 kip
- 47 -

chart 2: Strut Loads for 4 Ft. Vertical Strut Spacing

EXAMPLE: (follow arrows)

Equivalent Depth: 17 ft.

Horizontal Strut Spacing: 12 ft.

Strut Loads:

Type A Soil 16.3 kip

Type B Soil 32.6 tip

Type C Soil 65.3 kip
-48-

chart 3: Vale Loads in Kip Per Poot of Length

WALE LOAD, kip per ft of length

EXAMPLE: (follow arrows)

Equivalent Depth: 17 ft.

Type B Soil Vertical Spacing: 5 ft.

Wale Load: 2.72 kip per foot of length
- 49 -

chart 4: Sheeting Pressure, lb/ft^

200 400 600 800 1000 1200 1400

Sheetino Pressure, lb/ft 2

EXAMPLE: (follow arrows)

Equivalent Depth: 17 ft.

Type B Soil

Sheeting Pressure: 460 lb per ft 2
-50-

Table B.5. Strut Load* in KIP for 5 Ft. Vertical Str-'t Spacing

Equivalent Depth

and Soil Type

Horizontal Strut Spacing, Ft.

10 12 14 16 18 20

5 ft. - 10 ft. A

1

1 2

1

1 4

1

1 6

1

1 8

1

1 10

1

1 12

1

1 14

1

1 16

1

1 18

1

1 20

B 1 4 1 8 1 12 1 16 1 20 1 24 1 28 1 32 1 36 1 40

C 1

1 6 11 16 11 24 11 32 11 40 11 48 11 56 11 64 11 72 11 80

10 ft. - 15 ft. A

1 3

1

1 6

1

I 9

1

1 12

1

1 15

1

1 18

1

1 21

1

1 24

1

1 27

1

1 30

B 1 6 1 12 1 18 1 24 1 30 1 36 1 42 1 48 1 54 1 60

C 1

1 12 11 27 11 36 11 48 11 45 11 72 11 84 11 96 11 108 11 120

15 ft. - 20 ft. A

1

1 4

1

1 8

1

1 12

1

1 16

1

1 20

1

1 24

1

1 28

1

1 32

1

1 36

1

1 40

B 1 8 1 16 1 24 I 32 1 40 1 48 1 56 1 64 1 72 1 80

C 1

1 16 11 32 11 48 11 64 11 80 11 96 11 112 11 128 11 144 11 160

Table B.6. Wale Loads in KIP Per Ft. of Length of 5 Ft.

Vertical Wale Spacing

1 1

1 Soil Type 1

1 1

1 r

I Trench Depth |

1 1 A

n r

1 B 1

1 1

C

1 1

1 5 ft. - 10 ft. I

t i .8

1 1

1 1.6 |

1 | 3.2

1 1

I 10 ft. - 15 ft. I

1 i 1.2

1 1

1 2.4 |

1 | 4.8

1 1

I 15 ft. - 20 ft. I

1 1 1.6

1

1

1 3.2 |

1 1

6.4
-51-

ATTACHMENT

SUMMARY OF RECOMMENDED CHANGES

IN SUBPART P

Subpart P—Excavations, Trenching, and Shoring

1926.650 General protection requirements.

(a) Walkways, runways, and sidewalks shall be kept clear of excavated material or other obstructions and no sidewalks shall be undermined unless shored to carry a minimum live load of one

hundred and twenty-five (125) pounds per square foot. (b) If planks are used for raised walkways, runways, or side- walks, they shall be laid parallel to the length of the walk and

fastened together against displacement.

(c) Planks shall be uniform in thickness and all exposed ends

shall be provided with beveled cleats to prevent tripping.

(d) Raised walkways, runways, .and sidewalks shall be pro- vided with plank steps on strong stringers. Ramps, used in lieu of

steps, shall be provided with cleats to insure a safe walking surface. (e) All employees shall be protected with personal protective

equipment for the protection of the head, eyes, respiratory organs, hands, feet, and other parts of the body as set forth in Subpart E

of this part. (f) Employees exposed to vehicular traffic shall be provided

with and shall be instructed to wear warning vests marked with or made of refiectorized or high visibility material. (g) Employees subjected to hazardous dusts, gases, fumes,

mists, or atmospheres deficient in oxygen, shall be protected with

approved respiratory protection as set forth in Subpart D of this part.(h) No person shall be permitted under loads handled by

power shovels, derricks, or hoists. To avoid any spillage employees

shall be required to stand away from any vehicle being loaded.

(i) Daily inspections of excavations shall be made by a competent person. If evidence of possible cave-ins or slides is apparent, all work in the excavation shall cease until the necessary

precautions have been taken to safeguard the employees.

1926.651 Specific excavation requirements.

(a) Prior to opening an excavation, effort shall be made to determine whether underground installations, i.e., sewer, tele- phone, water, fuel, electric lines, etc., will be encountered, and

if so, where such underground installations are located. When the excavation approaches the estimated location of such an installation, the exact location shall be determined and when it is uncovered, proper supports shall be provided for the existing installation. Utility companies shall be contacted and advised of proposed

work prior to the start of actual excavation.

(a) Moved to 1926.650 (b) , N.C.

(b) Moved to 1926.650 (c), N.C.

(c) Moved to 1926.650 (d) , N.C.

(d) Moved to 1926.650 (e) , N.C.

(e) Moved to 1926.650 (f), N.C.

(f) Moved to 1926.650 (g) , N.C.

(g) Moved to 1926.650 (h) , N.C.

(h) Moved to 1926.650 (i). Modified

Reason: Purpose of "to avoid

spillage" is not clear.

(i) Moved to 1926.650 ( j ) , Modified

Reason: Daily impections are

not enough, inspection of

dewatering systems was added.

(a) Moved to 1926.651 (a), N.C.
-52-

(b) Trees, boulders, and other surface encumbrances, located Cb)

so as to create a hazard to employees involved in excavation work

or in the vicinity thereof at any time during operations, shall be

removed or made safe before excavating is begun.

(c) The walls and faces of all excavations in which employees (c)

are exposed to danger from moving ground shall be guarded by

a shoring system, sloping of the ground, or some other equivalent means.

(d) Excavations shall be inspected by a competent person after kd)

every rainstorm or other hazard-increasing occurrence, and the protection against slides and cave-ins shall be increased if necessary.(e) The determination of the angle of repose and design of the '• e -' supporting system shall be based on careful evalution of pertinent

factors such as: Depth of cut; possible variation in water content

of the material while the excavation is open; anticipated changes

in materials from exposure to air, sun, water, or freezing; loading

imposed by structures, equipment, overlying material, or stored

material; and vibration from equipment, blasting, traffic, or other

sources.

(f) Supporting systems, i.e., piling, cribbing, shoring, etc., shall (f)

be designed by a qualified person and meet accepted engineering

requirements. When tie rods are used to restrain the top of sheeting or other retaining systems, the rods shall be securely anchored

well back of the angle of repose. When tight sheeting or sheet

piling is used, full loading due to ground water table shall be as- sumed. unless prevented by weep holes or drains or other means.

Additional stringers, ties, and bracing shall be provided to allow

for any necessary temporary removal of individual supports.

(g) All slopes shall be excavated to at least the angle of repose (g)

except for areas where solid rock allows for line drilling or presplitting.

(h) The angle of repose shall be flattened when an excavation (h)

has water conditions, silty materials, loose boulders, and areas where erosion, deep frost action, and slide planes appear.

(i) (1) In excavations which employees may be required to (i)

enter, excavated or other material shall be effectively stored and

retained at least 2 feet or more from the edge of the excavation.

(2) As an alternative to the clearance prescribed in subparagraph ( 1 ) of this paragraph, the employer may use effective barriers or other effective retaining devices in lieu thereof in order to prevent excavated or other materials from falling into the excavation.

(j) Sides, slopes, and faces of all excavations shall meet ac- (j ) cepted engineering requirements by scaling, benching, barricading.

Moved to 1926.651 (b) , N.C.

Deleted

Incorporated in 1926.650, j

Deleted

Deleted

Deleted

Deleted

Moved to 1926.651 (c) , N.C.

Deleted
- 53 -

rock bolting, wire meshing, or other equally effective means. Special attention shall be given to slopes which may be adversely

affected by weather or moisture content. (k) Support systems shall be planned and designed by a qualified person when excavation is in excess of 20 feet in depth, adjacent to structures or improvements, or subject to vibration or ground water.

(l) Materials used for sheeting, sheet piling, cribbing, bracing,

shoring, and underpinning shall be in good serviceable condition,

and timbers shall be sound, free from large or loose knots, and of proper dimensions.

(m) Special precautions shall be taken in sloping or shoring the

sides of excavations adjacent to a previously backfilled excavation or a fill, particularly when the separation is less than the depth of the excavation. Particular attention also shall be paid to

joints and seams of material comprising a face and the slope of such seams and joints.

(n) Except in hard rock, excavations below the level of the base of footing of any foundation or retaining wall shall not be

permitted, unless the wall is underpinned and all other precautions

taken to insure the stability of the adjacent walls for the protection

of employees involved in excavation work or in the vicinity thereof. (o) If the stability of adjoining buildings or walls is endangered

by excavations, shoring, bracing, or underpinning shall be pro- vided as necessary to insure their safety. Such shoring, bracing, or underpinning shall be inspected daily or more often, as conditions

warrant, by a competent person and the protection effectively

maintained.

(p) Diversion ditches, dikes, or other suitable means shall be

used to prevent surface water from entering an excavation and to provide adequate drainage of the area adjacent to the excavation.

Water shall not be allowed to accumulate in an excavation.

(q) If it is necessary to place or operate power shovels, derricks, trucks, materials, or other heavy objects on a level above

and near an excavation, the side of the excavation shall be sheetpiled, shored, and braced as necessary to resist the extra pressure due to such superimposed loads.

(r) Blasting and the use of explosives shall be performed in accordance with Subpart U of this part. (s) When mobile equipment is utilized or allowed adjacent to excavations, substantial stop logs or barricades shall be installed.

If possible, the grade should be away from the excavation.

(t) Adequate barrier physical protection shall be provided at

all remotely located excavations. All wells, pits, shafts, etc., shall be barricaded or covered. Upon completion of exploration and

(k) Deleted - Replaced by

1926.652(a)

(1) Deleted - Reason: redundant

see 1926.651(n).

(m) Deleted “ Replaced by

1926.652(b), Table 1.

(n) Deleted - Replaced by

1926.652(a), Fig. 1.

(o) Deleted - Replaced by

1925.652(a), Fig. 1.

(p) Moved to 1926.651 (d) , modified

Reason: Excavation below water

should not be prohibited.

(q) Moved to 1926.651 (e) , modified

Reason: Simplified.

(r) Moved to 1926.651 (f). N.C.

(s) Moved to 1926.651 (g). N.C.

(t) Moved to 1926.651 (h). N.C.
similar operations, temporary wells, pits, shafts, etc., shall be

backfilled. (u) If possible, dust conditions shall be kept to a minimum by

the use of water, salt, calcium chloride, oil or other means.

(v) In locations where oxygen deficiency or gaseous conditions

are possible, air in the excavation shall be tested. Controls, as set forth in Subparts D and E of this part, shall be established to assure acceptable atmospheric conditions. When flammable gases

are present, adequate ventilation shall be provided or sources of

ignition shall be eliminated. Attended emergency rescue equipment,

such as breathing apparatus, a safety harness and line, basket

stretcher, etc., shall be readily available where adverse atmospheric

conditions may exist or develop in an excavation.

(w) Where employees or equipment are required or permitted

to cross over excavations, walkways or bridges with standard

guardrails shall be provided.

(x) Where ramps are used for employees or equipment, they

shall be designed and constructed by qualified persons in accord- ance with accepted engineering requirements.

(y) All ladders used on excavation operations shall be in ac- cordance with the requirements of Subpart L of this part.

1926.652 Specific trenching requirements.

(a) Banks more than 5 feet high shall be shored, laid back to

a stable slope, or some other equivalent means of protection shall be provided where employees may be exposed to moving ground

or cave-ins. Refer to Table P-1 as a guide in sloping of banks.

Trenches less than 5 feet in depth shall also be effectively protected

when examination of the ground indicates hazardous ground

movement may be expected.

(b) Sides of trenches in unstable or soft material, 5 feet or more in depth, shall be shored, sheeted, braced, sloped, or other- wise supported by means of sufficient strength to protect the employees working within them. See Tables P-1, P-2 (following

paragraph (g) of this section).

(c) Sides of trenches in hard or compact soil, including embankments, shall be shored or otherwise supported when the trench

is more than 5 feet in depth and 8 feet or more in length. In lieu of shoring, the sides of the trench above the 5-foot level may be

sloped to preclude collapse, but shall not be steeper than a 1-foot

rise to each Vi -foot horizontal. When the outside diameter of a pipe is greater than 6 feet, a bench of 4-foot minimum shall be

provided at the toe of the sloped portion.

(u) Moved to 1926.651 (i) , N.C.

(v) Moved to 1926.651 (j), N.C.

(w) Moved to 1926.651 GO , N.C.

Cx) Moved to 1926.651 (1)

Modified

Reasor : Earth or rockfill ramps

should be exempted.

(y) Moved to 1926.651 (m)

,

N.C.

(a) Deleted “ Replaced by

1926.652(a)

(b) Deleted - Replaced by

1926.652(a)

(c) Deleted “ Replaced by

1926.652(a)
- 55 -

(d) Materials used for sheeting and sheet piling, bracing, shoring, and underpinning, shall be in good serviceable condition, and

timbers used shall be sound and free from large or loose knots,

and shall be designed and installed so as to be effective to the bottom of the excavation.

(e) Additional precautions by way of shoring and bracing shall be taken to prevent slides or cave-ins when excavations or trenches

are made in locations adjacent to backfilled excavations, or where

excavations are subjected to vibrations from railroad or highway

traffic, the operation of machinery, or any other source.

(f) Employees entering bell-bottom pier holes shall be protected by the installation of a removable-type casing of sufficient strength to resist shifting of the surrounding earth. Such temporary

protection shall be provided for the full depth of that part of each

pier hole which is above the bell. A lifeline, suitable for instant rescue and securely fastened to a shoulder harness, shall be worn

by each employee entering the shafts. This lifeline shall be indi- vidually manned and separate from any line used to remove materials excavated from the bell footing.

(g) (1) Minimum requirements for trench timbering shall be

in accordance with Table P-2. (2) Braces and diagonal shores in a wood shoring system

shall not be subjected to compressive stress in excess of values given by the following formula:

5= 1300- 201

D

Maximum ratio L

- 50

D

Where:

L = Length, unsupported, in inches. D = Least side of the timber in inches. 5 = Allowable stress in pounds per square inch of cross-section. (h) When employees are required to be in trenches 4 feet deep

or more, an adequate means of exit, such as a ladder or steps, shall be provided and located so as to require no more than 25

feet of lateral travel.

(i) Bracing or shoring of trenches shall be carried along with

the excavation.

(j) Cross braces or trench jacks shall be placed in true hori- zontal position, be spaced vertically, and be secured to prevent

sliding, failing, or kickouts.

(d) Moved to 1926.651 (n) , Modified.

Reason: More specific

requirement substituted.

(e) Deleted - Replaced by

1926.652(b), Table 1.

(f) Moved to 1926.651 (o) , N.C.

(g) Deleted - Replaced by

1926.652(b) and Guidelines,

Appendix B.

(h) Moved to 1926.651 (p), Modified.

Reason: Negotiable slope added

as means of exit.

(i) Moved to 1926.651 (q). Modified.

Reason: Intent of requirement

not clear.

( j ) Moved to 1926.651 (r)

Modified.

Reason: More general statement

needed.
- 56 -

(k) Portable trench boxes or sliding trench shields may be

used for the protection of personnel in lieu of a shoring system

or sloping. Where such trench boxes or shields are used, they

shall be designed, constructed, and maintained in a manner which

will provide protection equal to or greater than the sheeting or shoring required for the trench.

(l) Backfilling and removal of trench supports shall progress

together from the bottom of the trench. Jacks or braces shall be

released slowly and, in unstable soil, ropes shall be used to pull out the jacks or braces from above after employees have cleared

the trench.

(k) Moved to 1926.651 (s) , Modified.

Reason: Simplified.

(1) Moved to 1926.651 (t)

Table P-1

Deleted - Reason: Replaced

by 1926.652, Table 1.
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Table P-2 Deleted. Reason: Timber

is not the only material used.

Revised timber tables are in the

Guidelines, Appendix B.
-58-

1926.653 Definitions applicable to this subpart

(a) “Accepted engineering requirements (or practices)”

Those requirements or practices which are compatible with standards required by a registered architect, a registered professional

engineer, or other duly licensed or recognized authority.

(b) “Angle of repose”—The greatest angle above the hori- zontal plane at which a material will lie without sliding.

(c) “Bank”—A mass of soil rising above a digging level. (d) “Belled excavation”—A part of a shaft or footing excavation, usually near the bottom and bell-shaped; i.e., an enlargement

of the cross section above.

(e) “Braces (trench)”—The horizontal members of the shoring system whose ends bear against the uprights or stringers. (f) “Excavation”—Any manmade cavity or depression in the

earth’s surface, including its sides, walls, or faces, formed by earth removal and producing unsupported earth conditions by reasons

of the excavation. If installed forms or similar structures reduce

the depth-to-width relationship, an excavation may become a

trench. (g) “Faces”—See paragraph (k) of this section. (h) “Hard compact soil”—All earth materials not classified as running or unstable.

(i) “Kickouts”—Accidental release or failure of a shore or

brace.

. (j) “Sheet pile”—A pile, or sheeting, that may form one of a continuous interlocking line, or a row of timber, concrete, or steel

piles, driven in close contact to provide a tight wall to resist the

lateral pressure of water, adjacent earth, or other materials. (k) “Sides,” “Walls,” or “Faces”—The vertical or inclined earth surfaces formed as a result of excavation work.

( l ) “Slope”—The angle with the horizontal at which a particular earth material will stand indefinitely without movement.

(m) “Stringers” (wales) —The horizontal members of a shoring system whose sides bear against the uprights or earth. (n) “Trench”—A narrow excavation made below the surface

of the ground. In general, the depth is greater than the width, but

the width of a trench is not greater than 15 feet. (o) "Trench jack”—Screw or hydraulic type jacks used as cross bracing in a trench shoring system.

(p) “Trench shield”—A shoring system composed of steel plates and bracing, welded or bolted together, which support the walls of a trench from the ground level to the trench bottom and

(a) Modified. Reason: Guidelines

are referenced.

(b) Deleted - definition too vague.

(c) Deleted - other definition used.

(d) Moved to 1926.653 (e)

(e) Deleted - other definition used.

(f) Moved to 1926.653 (j). Modified.

(g)

_ Deleted - other definition used.

(h) Deleted - definition not used.

(i) Deleted - definition not used.

(j) Deleted - definition not used.

00 Moved to 1926.653 (t)

(1) Moved to 1926.653 (u)

Modified.

Reason: Slope xs not defined as angle

Cm) Moved to 1926.653 (cc) , Modified.

uStringers" not used.

(nl Deleted - definition not used.

(o) Deleted

(p) Moved to 1926.653 (dd) , Modified.

Reason: Definition considered

inadequate.
- 59 -

which can be moved along as work progresses. (q) “Unstable soil”—Earth material, other than running, that (q) Deleted - not used,

because of its nature or the influence of related conditions, cannot

be depended upon to remain in place without extra support, such

as would be furnished by a system of shoring.

(r) “Uprights”—The vertical members of a shoring system. (*) Moved to 1926.653 (ee) , Modified.

(s) “Wales”—See paragraph (m) of this section. (s) Moved to 1926.653 (t)

ft) “Walls”—See paragraph (k) of this section.
—i
NB5-114A (rev. 2-8C) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (See instructions

83-2693 April 1983

4. TITLE AND SUBTITLE

Development of Draft Construction Safety Standards for Excavations - Volumes I

5. AUTHOR(S)

Felix Y. Yokel and Ronald L. Stanevich

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

S. Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME ANO COMPLETE ADDRESS ( Street. City. State, ZIP)

Department of Health and Human Services

Public Health Service, Center for Disease Control

National Institute for Occupational Safety and Health

Division of Safety Research, Morgantown, WV 26505

10.

SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

A record of an interim stage in the development of revisions to existing Occupational

Safety and Health Administration (OSHA) regulations governing excavations, trenching and shoring practices in the construction industry. Subpart P 29 CFR 1926, is

presented. The National Bureau of Standards (NBS) prepared a working draft of

recommended changes to the regulations based on previous NBS technical studies.-

Five regional industry workshops were held to discuss the proposed revisions.

Included in the report is a copy of the recommended revisions, which were submitted to the workshops, and a record of industry's response in the form of suggestions, commentary and summaries of workshop activities. The key section of

the report presents an analysis of industry response and resulting recommendations.

The document is a record intended to aid OSHA during subsequent stages of the rulemaking process.

1/ Yokel, F. Y., “Recommended Technical Provisions for Construction Practice in

Shoring and Sloping of Trenches and Excavation," NBS Building Science Series

127, June 1980.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

braced excavations; construction; Federal regulations; retaining structures; safety;

shoring; slope stability; soil classification; soil pressures; standards; trenching

13.

AVAILABILITY

m Unlimited

| | For Official Distribution. Do Not Release to NT1S

| ) Order From Superintendent of Documents, U.5. Government Printing Office, Washington, D.C.

20402.

J

! Xl Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15. Price

USCOMM-DC S043-P80
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