Soil-Cement Walls for Excavation Support
David S. Yang, Raito, Inc.
Abstract: The Cement Deep Soil Mixing (CDSM) method introduces and mixes cementitious materials
with in situ soils using hollow-stem rotating shafts equipped with a cutting tool at the tip and mixing
paddles above the tip. CDSM generally produces a soil-cement panel consisting of three overlapping
soil-cement columns. The soil-cement panel is then extended to form walls, which are effective for
excavation support and groundwater control due to the continuity and low permeability of soil-cement
walls. Two design approaches could be taken in the application of CDSM for excavation support: 1)
single wall design and 2) gravity wall design. The former one is treated as a wall technology and thelatter one is treated as a soil stabilization method. This paper will review the CDSM equipment andinstallation procedures for the construction of these two types of soil-cement walls. Four case examples
are used to illustrate the design and application of these two types of soil-cement walls.

I

INTRODUCTION

This paper presents the application of soil-cement walls for excavation support using two categories of insitu soil mixing methods, one for single row wall installation and the other for ground stabilization. The
term “CDSM” (Cement Deep Soil Mixing) was initiated by Port of Oakland together with its consultants torepresent the in situ soil mixing procedures it selected to use for the construction of soil-cement walls,
buttresses, and blocks for the development or expansion of its facilities at the Port of Oakland and the
Oakland International Airport. This term is adopted in this paper as a generic term to represent the soil
mixing methods used in the four project examples without differentiating their origins, unique equipment
designs and procedures, and special areas of applications. The soil mixing equipment and procedures
used for these four projects can be traced back to their origins in Japan. However, they are used in the
United States in more liberal and innovative manners to achieve performance requirements for specificapplications in each project. The first part of this paper is a review and discussion of the two soil-mixing
methods, wall methods and soil stabilization methods. This is followed by the presentation of four caseexamples for the application of earth retention: 1) CalPERS Headquarters Expansion Project,
Sacramento, California; 2) Skyport Drive Grade Separation Project, San Jose, California; 3) Oakland
Airport Roadway Project, Oakland, California; and 4) Delayed Coker Unit Project, St. Croix, US Virgin
Islands. The first two projects used single wall design and the latter two projects used gravity wall design.

II

SOIL MIXING METHODS FOR WALL INSTALLATION AND SOIL STABILIZATION

Based on the concept of mixed-in-place piles initiated in the 1950’s in the United States, Japaneseconstructors in the late 1960’s and early 1970’s installed single mixed-in-place soil-cement piles along a
row to create a wall for excavation support and groundwater control needed for the construction of
basements or other subsurface structures. Due to the high groundwater conditions in most of the major
cities in Japan, wall continuity and uniformity became the major requirements of soil-cement walls forreliable groundwater control to avoid settlement or failure of buildings or other facilities adjacent toexcavations. To overcome the deficiency of a single-auger soil-mixing tool, Seiko Kogyo developed theSoil Mix Wall (SMW) method, which uses a triple-axis auger and staggered installation placement toproduce a single-row soil-cement wall with reliable material uniformity and wall continuity. This method isrecognized as a wall installation technology in Japan. Due to the need to install steel reinforcement into
the single-row soil-cement wall for resisting lateral forces, high water cement ratio grout with bentonite is

Earth Retention Systems 2003: A Joint Conference
Presented by ASCE Metropolitan Section Geotechnical Group, The Deep Foundations Institute, and
ADSC: The International Association of Foundation DrillingMay 6 and 7, 2003, New York City1

used to produce lower strength soil-cement with high fluidity to facilitate the installation of steel H-piles or
sheet piles. Since its full-scale application in 1976, more than 5,000 SMW walls have been installed.
Attempts were made to use the SMW method for large-scale-area ground stabilization; however, thisextended application was not widely accepted in Japan due to its origin and classification as a wall
method. This method was introduced to the United States in 1987 for the construction of a seepage cutoff
wall and soil-cement cells for foundation stabilization under the Jackson Lake Dam in Wyoming. The first
application of SMW wall as an excavation support wall in the United States was in 1990 for theconstruction of a Wet Weather Storage Basin for East Bay Municipal Utility District in Oakland, California.
The CDSM method used for the first two project examples of this paper is a wall method with improved
controls over mixing energy and grout distribution for uniformity of soil-cement produced.
There are numerous varieties of soil mixing methods developed in Japan for the treatment of soft ground.
The variations mainly include design of the mixing tool; application of soil mixing energy mechanically,
hydraulically, or a combination of both; and addition of hardening agents in wet or dry form. Recently, ageneral term “Deep Mixing Method” (DMM) was accepted to cover these soil-mixing methods developed
worldwide. Most of the Japanese wet DMM methods are based on the results of initial research anddevelopment performed in late 1960’s to early 1970’s by the Port and Airport Research Institute (PARI) of
the Japanese Ministry of Transportation in conjunction with several general contractors. The research anddevelopment of PARI aimed at the treatment of soft marine deposits under or adjacent to the harbor to
produce massive soil-cement configurations for use as foundations or for maintaining the stability of theport structures such as sea walls, breakwater, quay and other port facilities. In contrast to the wall
method, multiple rows of soil-cement panels or walls are installed to form a block or monolith of soilcement underground to serve the design functions. While the material design of soil-cement remains
unchanged, the geometric design continues to evolve for more efficient use of the soil-cement structures.
The combination of walls or panels to form a soil-cement grid structure reduces the percentage of soil
treatment, however, it serves the equivalent functions of a soil-cement block for bearing capacity,
settlement control, stability or liquefaction prevention. The soil mixing method used for the latter two
project examples of this paper is a soil stabilization method with modifications on the design of the mixing
tool and mixing procedures to meet the project demands in the United States.

III

REINFORCEED SOIL-CEMENT WALLS FOR EXCAVATION SUPPORTA. CalPERS Headquarters Expansion Project, Sacramento, California

1. Proposed Construction
This project included construction of a four- and six-story building with two levels of below-grade
parking. An excavation to a depth of 32 feet below existing ground surface was needed for theconstruction of the below-grade parking structure. A soil-cement wall along the perimeter of thebuilding was constructed for use as seepage control and excavation support during theconstruction of the below-grade parking structure. A site plan with the alignment of the soilcement wall is shown in Figure 1.
2. Subsurface Conditions
The site is underlain by 6 to 14 feet of silty sand fill and soils disturbed by past developments.
The fill is underlain by clayey to sandy silts to depths of 25 to 35 feet below the existing grade.

Earth Retention Systems 2003: A Joint Conference
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2

The silts are underlain by clean sands with occasional layers of silty sands to depths of about 60
to 65 feet (Wallace-Kuhl Report, 2001). The top of this stratum was exposed at the bottom of thebasement excavation. A dense stratum of sandy gravels and large cobbles underlies the sandsand extends to depths of 100 to 120 feet. This stratum is very permeable and imposes a major
dewatering challenge to the construction of the below-grade parking structure. The gravel andcobble stratum is underlain by partially cemented clayey silts, part of the Riverbank Formation, tothe maximum exploration depth of 145 feet. A representative boring log is shown in Figure 2. The
groundwater table ranges from 7 feet to 15 feet below grade depending on the season.
CL

1

2% MAX

1

9'N

CUTOFF WALL INSTALLATIONSTARTING POINT

Q STREET

N

A

1/20

50' MIN.

CUTOFF WALLSECTION A - A
WORKING PLATFORM (TYP)

3RD STREETWORKING PLATFORM

SOIL-CEMENT WALL

BATCH
PLANT
#2

40'

SPOILS COLLECTION AREA (TYP.)

5TH STREET

50'

EXISTING ALLEY

4TH STREETANUMBER AND DIMENSIONS DEPENDENTON SPOILS MANAGEMENT

20'
BATCH
PLANT
#1

40'

MATERIAL DELIVERIESACCESS ROUTE

Min 50' - 0" (Typ)R STREETMin 9' - 0"(Typ)

PRE-DRILLING
STARTING POINT

SOIL-CEMENT WALL

Figure 1: Site Plan
Depth
[Feet]
0
7
15
20
25
30
35
40
45
50
55
60
65
69

Depth
[Feet]

Blows/Ft
SM
15
11
1
18
39
58
16
30
34
29

0

5

MH
ML
SM
SP/SM
SP
SM
SP

33

54

41
26
90
99
91
73
50/3"

SM
SM/ML
ML
ML/SM
ML

Bottom of Excavation

7'
15'
Water Table
varies byseasonBottom of Sheet Pile

Soil Cement Wall
Not Reinforced

GP
91
95
100
105 106110
115 116
120
125

Soil Cement
Tied-Back Wall
Reinforced

105
110

Low Permeability Stratum

Figure 2: Representative Boring Log and Cross Section

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3. Design of Seepage Cutoff / Excavation Support Wall
The seepage cutoff / excavation support wall was designed by Mueser Rutledge Consulting
Engineers. As discussed in the letter report of Mueser Rutledge Consulting Engineers (2001), thesite is underlain by a major aquifer, consisting of very permeable sands, gravels and cobbles. The
aquifer is recharged by the Sacramento River, resulting in seasonal fluctuation in groundwaterlevels with river stages. This dynamic aquifer must be dewatered or otherwise controlled to permit
construction of the underground parking. A perimeter cutoff wall was designed to extend to thelow permeable Riverbank Formation to isolate the deep excavation from the fluctuation of thegroundwater levels and simplify the basement construction. A maximum permeability of 1 x 10-6
cm/sec was specified for the cutoff wall. The Riverbank Formation was expected to perform at an
average permeability of 2.3 x 10-6 cm/sec based on the laboratory testing of samples recovered.
Assuming an average permeability of 1 x 10-6 cm/sec for the 30-inch thick cutoff wall, and apermeability of 2 x 10-6 cm/sec for a 5- foot thick Riverbank Formation as a closure layer, Mueser
Rutledge estimated a steady state seepage through the cutoff wall and the closure formation to
be 65 gal/min during the maximum expected draw down from an elevation of +5 (13 feet deep)
outboard to an elevation of –17 (35 feet deep) inboard of the cutoff wall. Approximately half of thisflow is upwards through the Riverbank Formation. The contract specifications allow for seepage
quantity up to 200 gal/min.
Steel sheet piles were designed to reinforce the upper portion of the cutoff wall to support thelateral earth pressure and the 600-psf surcharge outside the wall and a groundwater table at anelevation of +10 feet (8 feet deep) outboard. The sheeting relies on two tieback levels andundisturbed soil below subgrade for support. Depth of embedment was approximately 15 feetbelow the bottom of the excavation, leaving the lower 60- to 70-foot portion of un-reinforced wall
to serve as the sole seepage barrier as shown in Figure 2. Sheeting movements on the order of
two inches were anticipated.
4. Wall Installation
A single row soil-cement wall was produced along the perimeter of the area to be excavatedusing the CDSM method. A triple axis auger (mixing tool) with discontinuous auger flights andmixing blades was used to mix the in situ soils with cement grout to form a soil-cement panel. The
panels were then extended to form a continuous wall as shown in Figure 3a. Based on additional
borings made along the perimeter of the excavation, the soil-cement cutoff wall was extended toa depth varying from 110 to 128 feet, with about a 10-foot key into the Riverbank Formation. The
10-foot key into the Riverbank Formation was constructed to cut off any sand lenses in the upper
portion of the Riverbank Formation. Sheet piles as shown in Figure 3b were inserted into the soilcement wall before the hardening of the soil-cement.
5. Excavation and Seepage Control
Major excavation and inboard pumping were started after the completion of the wall installation.
The pumping rate exceeded 100 gal/min in the early excavation stage and gradually reduced to arange between 50 to 60 gal/min after storage was removed. The groundwater table wasmaintained at approximately 3 feet below the bottom of the excavation using two deep wells.
Without the barrier, approximately 9,500 gal/min discharge was estimated and would require 35
deep wells to maintain the site dry for construction. A view of the wall and bottom of the
excavation is shown in Figure 4.

Earth Retention Systems 2003: A Joint Conference
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ADSC: The International Association of Foundation DrillingMay 6 and 7, 2003, New York City4

3' DIAMETER

PRE-DRILLPRIMARY

PRIMARY

PRIMARY

4'
SECONDARYSECONDARY

Figure 3a: Soil-Cement Cutoff WallCL
XZ85 X 50
SHEET PILES (TYP)

2'-0"
4"
1'-4"

1'-0"

CL

2'-6"

Figure 3b: Soil-Cement Excavation Support Wall

Earth Retention Systems 2003: A Joint Conference
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5

Figure 4: Soil-cement Tied-Back Wall with Sheet Pile Excavation Support System
B.

Skyport Drive Grade Separation Project, San Jose, California
1. Proposed Construction
This grade separation project consists of a cut-and-cover tunnel, a depressed road with twochannel walls along Airport Boulevard and a temporary slab bridge to the south of the proposed
tunnel as shown in Figure 5. The cut-and-cover tunnel is a cast-in-place reinforced box
approximately 800 feet long, 50 feet wide, and extends about 22 feet below finished grade.
Temporary shoring will be required along the depressed roadway for construction. The maximum
excavation will be about 18 to 20 feet below the existing roadway grade. Groundwater control will
be required during construction.

Soil-Cement
Wall Layout

Figure 5a: Site Plan
8 2 0 .0 'M E A S U R E D A L O N G 'A 1 ' L IN E

E L E V = 4 7 .1 5 'D E S IG N
H IG H W A T E R

Figure 5b: Longitudinal Section

Earth Retention Systems 2003: A Joint Conference
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ADSC: The International Association of Foundation DrillingMay 6 and 7, 2003, New York City

6

2. Subsurface Conditions
The subsurface soils along the depressed roadway generally consist of alternating clay and sandlayers (Parikh Consultants Report, 2002). The clay layer extends from existing grade down to 16
feet deep on the north and to 30 feet deep on the south. The clay layer is underlain by silty toclayey sands with thickness ranging from 10 to 29 feet. Below the sand layer, the borings
encountered a stiff clay layer to depths of 50 feet. A representative boring log is shown in Figure
6. The groundwater is located at approximately 15 feet below grade and is affected by waterlevel in the Guadalupe River running within 100 to 200 feet parallel to the proposed depressed
roadway. Historical records indicate that the water level could reach an elevation of 47.15 feet,
which is approximately 1 foot below the existing grade of Airport Boulevard.
Depth[Feet]

N-Values
Blows/ft

0
29
10

22
11

20

5
8

30

14

40

17
81

50

15

60

24
50/4"

20

CL
CL

CDSM
Wall

Wall
Interface

Underpass
StructureCH
SM

Reinforced
Soil-Cement
Tied-Back
Wall

CL
SM
CL
ML
SW/SM
CL

Soil-Cement
Cutoff Wall

CH
CL
SM
GP/GC
SC

Figure 6: Representative Boring Log and Cross Section
3. Design of Seepage Cutoff / Excavation Support Wall
The construction of the depressed road and tunnel requires excavation below the groundwatertable and the water level at the Guadalupe River. A soil-cement wall was recommended by Parikh
Consultants, Inc. for temporary excavation support and groundwater control to maintain the
groundwater below the bottom of the excavation. The cutoff portion of the soil-cement wall isdesigned to key into the clay layer at approximately 30 to 50 feet below the existing grade for thecontrol of lateral flow. Due to the varying subsurface conditions, exploratory borings at 100-footintervals were required to confirm the depths, thickness, and continuity of the clay layer for use asa closure seal below the bottom of the excavation. The lateral earth pressure and water pressure
are resisted by the portion of the reinforced soil-cement wall extending only 15 feet below bottomof excavation, approximately 15 feet above the lower tip of the soil-cement cutoff wall as shown in
Figure 6. H-piles (size W16x40) are used for reinforcement, which in turn are generally
supported by two levels of tiebacks. In the areas where the excavation is less than 16 feet, only
one level of tieback is needed. The geometric design of the soil-cement wall and steel
reinforcement are shown in Figure 7. The soil-cement is required to have a maximum
permeability of 1 x 10-6 cm/sec and a minimum 28-day unconfined compressive strength of 100
psi. Due to the high groundwater condition, the depressed road and cut-and-cover tunnel are

Earth Retention Systems 2003: A Joint Conference
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ADSC: The International Association of Foundation DrillingMay 6 and 7, 2003, New York City

7

designed as buoyancy boxes as shown in Figure 6. In addition to the use for temporary
construction purposes, the soil-cement wall also provides long-term uplift resistance to theconcrete structures of the depressed road and tunnel. Steel ties are welded onto the surface ofthe H-piles of the soil-cement wall and incorporated into the concrete walls of the depressed roadand tunnel. An allowable friction resistance of 480 pounds per square foot between the surface ofthe soil-cement wall and native soils is used for the calculation of the uplift resistance provided by
the soil-cement wall. Details of the connection are shown in Figure 7a.
4. Wall Installation
A CDSM wall will be installed using a multiple-axis auger following the layout design shown in
Figure 7b. The in situ soil mixing parameters, including mixing energy and grout ratio, will beselected based on the results of laboratory trial mix study. A computer based QA/QC system will
be used to monitor the wall installation on a real- time basis. H-piles will be installed
immediately after the soil mixing. A total of 80,000 square feet of wall will be installed from May to
July 2003.

Bent Bars

Below

1' top of
Pile

6"
6"
6"
6"

3"

T

T

Plan

ProfileFigure 7a: Uplift Connection

W16x402'

3' Diameter

Figure 7b: Reinforcing Layout

Earth Retention Systems 2003: A Joint Conference
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8IV

GRAVITY SOIL-CEMENT WALLS FOR EXCAVATION SUPPORT

A. Oakland Airport Roadway Project, Oakland, CA
1. Proposed Construction
The Oakland airport roadway project included three new grade separation structures. The CDSM
method was used to construct cutoff walls, soil-cement foundations and soil-cement gravity
retaining walls for the construction of these grade separation structures. At the Air Cargo
Road/Taxiway B intersection, Taxiway B will be raised a maximum of 8 feet above the existing
grade, and Air Cargo road will be depressed a maximum of about 15 feet below the existing
grade. This grade separation structure is located in the vicinity of a former borrow pit used toobtain sand fill during construction of the original North Field airport site in the late 1920’s and1930’s. The borrow pit was abandoned in the late 1940’s and was allowed to in-fill with sediments
including soft silty clays, loose silts and sands. A block-type CDSM treatment was used toconstruct a permanent retaining structure, which also functioned as a temporary shoring system
during construction. The block-type treatment also included a CDSM cutoff wall to provide
permanent seepage control and reduce dewatering requirements during construction. A site planand the layout design of the CDSM wall are shown in Figure 8a and 8b, respectively.

Figure 8a: Site Plan

2.0'

Ø3.0'

2.5'

Figure 8b: Geometric Design

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2. Subsurface Conditions
The subsurface soils outside the former borrow pit area generally consist of about 10 to 15 feet ofsand fill overlying relatively thin deposits of soft Bay Mud, usually less than 3 feet (Geomatrix
Consultants Report, 1999). The fill and Bay Mud are underlain by competent medium dense tovery dense sands and medium stiff to very stiff silty or sandy clays. In areas of the former borrow
pit, loose sands or silts and soft silty clay in-fill materials were encountered extending down to
depths of 20 to 25 feet below the existing ground surface. An idealized soil profile along Air Cargo
Road at the Taxiway B over crossing is shown in Figure 9. The sand fill and lose sand in-fillmaterials are subject to liquefaction during a strong earthquake. Groundwater levels at the sitevary with location due to pumping activities at the airport. The groundwater levels generally varyfrom 5 to 10 feet below the existing ground surface.

Figure 9: Idealized Soil Profile (Courtesy of Geomatrix Consultants)
3. Design of Gravity Soil-Cement WallA block-type treatment of CDSM columns was designed by Geomatrix Consultants, Inc. toconstruct permanent retaining structures along the depressed Air Cargo Road. The overlapping
CDSM elements were designed as a gravity structure and included soil nails for reinforcement
and a permanent concrete wall facing as shown in Figure 10. The CDSM gravity structure wasdesigned to limit the permanent lateral deformations to approximately 6 inches during a design
earthquake with a probability of exceedance of 20 percent in 50 years. Where the CDSM walls
are adjacent to the abutments for the Taxiway B bridge structure, they are designed for apermanent deformation of approximately 4 inches during a design earthquake with a probability ofexceedance of 5 percent in 50 years. Estimated peak ground accelerations for the two design
earthquakes are 0.47g and 0.70g, respectively. The permanent deformations were estimatedusing pseudo-static stability methods and Newmark-type displacement analyses. Design
dimensions for the CDSM gravity retaining structure are shown in Figure 10. The minimum widthof the gravity wall equals the maximum excavation depth during construction and the depth of the

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gravity wall extended a minimum of 4 feet below the maximum depth of excavation. In areas
where additional slide resistance was needed, part of the soil-cement panels were extended
below the bottom of the gravity wall to act as a slide resistance key. Geocomposite drain strips
behind the permanent wall facing of the gravity wall were designed to release the water pressure.
Collector pipes will carry the seepage from these drain strips as well as that from the drainage
layer below the Air Cargo Road pavement to a sump for pumping. To minimize the amount ofwater pumped from the drainage system on a permanent basis and to minimize the amount ofdewatering required during construction, a CDSM cutoff wall was incorporated in the center of thesoil-cement gravity wall and extended beneath the bottom of the gravity wall to reduce the flow of
seepage from the gravelly soil layer under the gravity wall. The design was based on an average
unconfined compressive strength of 150 psi (Yang, et al., 2001).

SECURITY FENCEANCHORAGE DETAIL(B11-7)2'-0"3"TOP OF CDSM WALL

9"
1'-0"

DRILL AND GROUT#5 BAR 4'-0" @ 36" MAX EACH WAY[PROVIDE 2 MIN VERTICALLY]

1'-0"15° TYP

SOIL NAILING-#9 BAR[SPACED @ 5'-0" VERTICAL
AND 6'-0" HORIZONTAL]PROVIDE 1" MIN GROUT COVER
3'-0"

2'-0"

CAST-IN-PLACE
CONCRETE WALL FACING
GEOCOMPOSITE DRAIN
UPPER LIMIT @ ELEV. 5.0'

#5 @ 18" MAX
CONCRETE BARRIER TYPE 50D[AT RET. WALL AR-1 ONLY]MAX

PAVEMENT SECTIONPERMAEABLE MATERIAL
SHOTCRETE
AS REQUIRED

Figure 10: Design of CDSM Gravity Wall

4. Wall Installation
The installation of the CDSM gravity wall began in March 2001 and was completed in December
2001. Approximately 45,000 cubic yards of soil-cement gravity wall were installed. A view of the
excavated CDSM wall is shown in Figure 11. Due to the complex subsurface conditions resulting
from the historical development of the site, several test sections were performed along the

Earth Retention Systems 2003: A Joint Conference
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alignment of the gravity wall for the confirmation or modification of the mix design and installation
procedures to ensure that the design strength and uniformity could be obtained.

Figure 11a: CDSM Gravity Wall Before Installation of Facing

Figure 11b: CDSM Gravity Wall Close-up View of the Left WallB.

Delayed Coker Unit Project, St. Croix, US Virgin Islands
1. Proposed Construction
The project consisted mainly of a delayed coker unit, including coker handling and storage
facilities. The main delayed coker unit spreads over an area of 336 feet by 204 feet (Arango, etal., 2002). The major components of the partly underground unit are coker structures extending
330 feet high, a 26-foot deep coke pit, a 36-foot deep settling basin and a coke pad at grade.
Surrounding the coke pit, pad, and settling basin is a 13-foot high concrete wall and a series ofheavy concrete columns supporting a 125-foot long bridge crane. An artistic view of the finishedfacilities is shown in Figure 12.

Earth Retention Systems 2003: A Joint Conference
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2. Subsurface Conditions
The subsurface materials consist of three main strata: hydraulic fill, marine deposits, andlimestone (Arango, et al., 2002). The 10 to 13 feet of fill has a 3 to 7-foot thick layer of desiccatedstiff to hard silts and clays with sand, underlain by lenses of soft to medium stiff silts and clays.
The hydraulic fill is underlain by the original Bay deposits, which extend down to the weathered
limestone unit at depths varying from 55 to 78 feet. While variable from place to place, the marine
deposits appear to consist of two continuous layers of silty to clayey sands intercalated with twolayers of silty clay. The two sand layers have a standard penetration blow count, N, varying from
3 to 8 and fine contents ranging between less than 5 to 40 percent. Very low factors of safety
against liquefaction, less than 0.4, were found for these two sand layers. Beneath the marine
deposits is a layer of highly weathered clayey limestone, which becomes less weathered andstronger with depth. The groundwater table is encountered at 15 feet below the ground surface. A
representative boring log is shown in Figure 13.

Figure 12: An Artistic View of the Finished Facilities(Courtesy of Bechtel Corporation & Earthquake Engineering Research Institute)

Earth Retention Systems 2003: A Joint Conference
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13

Depth[Feet]

N-Values
Blows/ft

0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75

52
49
18
10
4
1

WOR
PUSH

3
15
2
PUSH
WOR
PUSH

1

GM
SM
SM

1.5

CL
SM
CL
ML
CL
CH

13
8

LS

54

ML

50/2"

LS

PUSH

1

ML

6
3
3

PUSH

1

Soil-Cement Gravity
Wall & Foundation

CL

Figure 13: Representative Boring Log and Subsurface
3. Design of Soil-Cement Foundation and Gravity Wall
The soil-cement foundation and gravity retaining wall were designed by Bechtel Corporation(Arango, et al., 2002). The coker structure includes two coker drum structures, each weighing
16,500 tons, and a 403-foot high upper steel frame structure. The coker structures’ massive size,
weight, and mass distribution coupled with the extreme site-specific conditions of high seismic
potential and hurricane force winds result in some of the most severe foundation loads in the
Petroleum and Chemical Industry. A cursory assessment of the subsurface soils conditions at thesite concluded that the nature and engineering properties of both the fill and marine deposits
were not adequate to directly support the heavy loading imposed by the structures. Also,
difficulties were anticipated in providing temporary support of excavation and control of water
seepage with a 36-foot head. For the excavation, options including sloping walls, sheet piles,
drilled shafts, and structural slurry walls were considered and discarded fortechnical/constructability reasons. In the end, a solution based on supporting excavation andstructural loads on improved soil-cement utilizing the CDSM was adopted.
The CDSM solution was unique in that it provided support to the deep excavation without the useof reinforcement, sheet piling or anchors; it provided support to the heavy structural loads
eliminating the need for piling; it provided stability against liquefaction; and it eliminated the needfor a de-watering system for the excavation. Overlapped soil-cement columns were used tocreate a continuous cellular system under the structures and along the perimeter of the
excavation. Soil-cement panels were extended to bear on the layer of stiff clay or weathered
limestone under the site. The cells have various plan dimensions to provide different replacement
ratios to satisfy different load demands as shown in Figure 14a. Areas under the coke drum
structures, the retaining walls around the perimeter and the deeper settling basin required a 90
percent replacement ratio. Less severely loaded zones under the coke tank and coke padrequired only 63 percent and 39 percent replacement, respectively. Details of the geometric
design are shown in Figure 14b. A cross section along the deepest excavation and the forcesconsidered in the stability analysis are shown in Figure 15. The design required for an average
90-day unconfined compressive strength of 125 psi. The required static shear strength was taken
as one half of the unconfined compressive strength. The dynamic shear strength was taken as
130 percent times the value of the static strength. The elastic modulus was taken as 300 times
the unconfined compressive strength.

Earth Retention Systems 2003: A Joint Conference
Presented by ASCE Metropolitan Section Geotechnical Group, The Deep Foundations Institute, and
ADSC: The International Association of Foundation DrillingMay 6 and 7, 2003, New York City

14

A

DetailFigure14b

A
Figure 14a: Site Treatment Plan (Courtesy of Bechtel Corporation & EERI)

Figure 14b: Geometric Design

Earth Retention Systems 2003: A Joint Conference
Presented by ASCE Metropolitan Section Geotechnical Group, The Deep Foundations Institute, and
ADSC: The International Association of Foundation DrillingMay 6 and 7, 2003, New York City

15

1

1

1
1 El. 98.4 ft

24.6 ft1

El. 91.5 ft
1.5

El. 68.2 ft

El. 57.1 ft

1

1.5

El. 60.0 ft

El. 59.1 ft

El. 70.5 ft

Soil Cement
El. 46.3 ft
P1

6.9 ft1.0
34.5 ft

1.5

P2
P3

P5

P1 Combined horizontal force of soil andsurcharge above ground water
P2 Horizontal force acting below ground water
resulting from soil above ground water
P3 Combined force (soil and water)
P4 Water pressure
P5 Weight of wallP4
27.6 ft

Figure 15: Cross Section A-A (Courtesy of Bechtel Corporation & EERI)
4. Wall Installation
Triple-axis soil mixing equipment was used to install soil-cement grids and gravity walls according
to the layout design shown in Figure 14b. The construction began in April 2001 and wascompleted in October 2001. A total of 70,000 cubic yards of soil-cement was produced. A view of
the CDSM gravity wall is shown on Figure 16.

Figure 16: A View of Excavated CDSM Wall and Foundation
Earth Retention Systems 2003: A Joint Conference
Presented by ASCE Metropolitan Section Geotechnical Group, The Deep Foundations Institute, and
ADSC: The International Association of Foundation DrillingMay 6 and 7, 2003, New York City

16

V

CONCLUDING REMARKSIn situ soil mixing methods provided efficient solutions for projects with challenging subsurface
conditions. It produces reinforced soil-cement walls or gravity walls for effective earth retention andseepage control in difficult ground, including highly permeable cobble soils, soft soils, or liquefiableground.
VI REFERENCES
ARANGO, I, WANG, C.T., and BITNER, B., 2002. Construction of an Industrial Facility on Liquefiable
Ground, Proceedings of 7th U.S. National Conference on Earthquake Engineering, Earthquake
Engineering Research Institute (EERI), Boston, Massachusetts, 10 p.
GEOMATRIX CONSULTANTS REPORT, 1999. Geotechnical Study, Oakland Airport Roadway
Project, Metropolitan Oakland International Airport, Oakland California, 70 p.
MUESER RUTLEDGE CONSULTING ENGINEERS, 2001. Cutoff and sheeting and Bracing
Performance, CalPERS Extension, Sacramento, California, Mueser Rutledge Letter Report, 4 p.
PARIKH CONSULTANTS REPORT, 2002. Geotechnical Engineering Investigation, Skyport
Drive Grade Separation, San Jose, California, 15 p.
WALLACE KUHL REPORT, 2001. CalPERS Headquarters Expansion Project, GeotechnicalEngineering Baseline Report, pp. 7-8
YANG, D.S., SCHEIBEL, L.L., LOBEDAN, F. and NAGATA, C., 2001. Oakland Airport Roadway
Project, Deep Foundations Institute Specialty Seminar-Soil Mixing, St. Louis, Missouri, pp. 55-71

Earth Retention Systems 2003: A Joint Conference
Presented by ASCE Metropolitan Section Geotechnical Group, The Deep Foundations Institute, and
ADSC: The International Association of Foundation DrillingMay 6 and 7, 2003, New York City

17