EEFECT OF SHEET PILE WALL SUPPORTED EXCAVATION ON ADJACENT STRIP FOUNDATION

1

EEFECT OF SHEET PILE WALL SUPPORTED EXCAVATION ON ADJACENT STRIP FOUNDATION

Yousry M. Mowafy 1, Ahmed M. El-Tuhami

2, Samir A. Gad

3, and Ahmed A. Mohamed

4.

ABSTRACT

Ground movements induced from excavations is a major cause of deformation and damage

to the adjacent buildings and utilities. This problem is investigated experimentally and

numerically in the present study. Two parameters were studied, the first is the foundation depth

and the second is the building distance from the excavation. Nodal displacements and elements

straining actions were determined and analyzed. Finally, a series of finite element analysis was

performed on a prototype dimensions and a comparison between the laboratory model tests and

the finite element analysis was presented. It is found that the value of (lateral deformation /H) is

0.01 in cantilever sheet pile wall and the relative density is the important factor in decreasing

values of lateral deformations and straining actions for sheet pile wall and settlement in strip

footing.

Keywords: Excavation, Relative distance, Lateral deformation, Relative depth.

1. Introduction Deformations of the excavation support system adjacent ground are influenced by a

number of factors including stiffness of the excavation support system, the installation

procedures of the system, the soil conditions, the excavation procedures, the type of building, the

distance of the building from the excavation, the orientation of the building with respect to the

excavation, and the size of the building with respect to the excavation-related deformations. To

confirm this speculation, model testing of braced excavations was conducted to examine the

effects of varying the building’s depth of foundation and the building’s distance from the

excavation face. Boscardin and Cording [1989] and Boone [1996] have both recognized that

excavation-related limiting criteria is a function of building type and orientation with respect to

the excavation, type of support system, excavation techniques, and soil conditions. Kishnani and

Borja (1993) found that wall pressures and deformation increase with decrease in adhesion

between sheet pile wall and soil. Milligan (1983) studied analytically the deformations behind

flexible retaining walls anchored at the top and performed a number of model tests with dense

sand to study the deformations. Hashash and Wittle [1996] investigated the effects of wall

embedment depth, support conditions, and stress history profile on the undrained deformations

around a braced diaphragm wall in a deep clay deposit, using a series of numerical experiments-

nonlinear finite element analyses. The results are presented in prototype design charts for

estimating ground movements as functions of the excavation depth and the support conditions,

and incorporate the effects of wall length on base stability. Seok et al. [2001] observed that

braced excavations inevitably result in deformation of the adjacent ground and settlement of

adjacent buildings behind the wall. Building settlement is believed to exceed the amount of

associated ground settlement because of the additional settlement under building weight. This is

due to decrease in stiffness of the foundation soil that is caused by lateral movement of the

1) Professor of Soil Mechanics and Foundations, Civil Eng. Dept., AL-Azhar University, Cairo, Egypt.

2) Associate Professor of Soil Mechanics and Foundations, Civil Eng. Dept. Beni-Suef University, Beni-Suef, Egypt.

3) Associate Professor of Soil Mechanics and Foundations, Civil Eng. Dept. AL-Azhar University, Cairo, Egypt. 4) Teaching Assistant, Civil Eng. Dept., Alazhar University, Qena, Egypt.

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excavation face. To quantify the amount of building settlement, model testing was conducted to

determine the magnitude of the additional settlement due to the structure and the effect of

varying the building’s depth in the ground and of its distance away from the excavation wall.

Son et.al. [2005] observed that the bearing walls oriented in a direction perpendicular to

an excavation wall tend to become distorted with shear strain and lateral strain at the foundation

level. When ground movement initially impinges on the front of the building, the building is

primarily subjected to shear distortion and lateral strain at the base.

Peck (1969), Goldberg et al. (1976), and Clough and O’Rourke (1990) suggested that in

deep excavations in stiff clays, residual soils, and sands, the maximum lateral wall movement,

δhmax, is less than 0.5% of the excavation depth, H . Figure (2.10) shows data collected by

Clough and O’Rourke (1990) on lateral wall movement for different types of retained walls. In

this figure the average normalized lateral wall movement, δhmax ∕ H ≈0.2%, and cases with δhmax ∕

H ≈0.5%, are reported to represent poor construction work. Moormann (2004) concluded that ground

conditions were one of the identified most influential parameters. The maximum lateral and vertical movements due

to deep excavation in cohesive soils of very soft to soft consistency, with undrained shear strength cu<75kN/m2, may

be more than 1% of H. Zhong W. Wang et.al (2005) studied the characteristics of wall deflections

and surface ground settlements at six deep multi-strutted excavations in Shanghai soft soils and

compared the results with those of similar case histories reported worldwide, particularly in

Taipei and Singapore as shown in Fig. (1). They concluded the ratio between the measured

maximum wall deflection and the depth of the excavation (δhm /H) in Shanghai was <0.007,

which was similar to the ratio measured in Taipei, but it was substantially smaller than the Peck

bounding limit of 0.01. At each station, the measured maximum displacement was <0.45% of the

final excavation depth.

Fig.(1) Measured maximum lateral excavation wall movement versus excavation depth,

(after Clough and O’Rourke (1990))

The main objective of the present study is to investigate different aspects of the behavior

of excavations in soil and the response of structures located near these excavations. The main

objectives for this research are:-

I. Establishing an analytical model to represent realistic behavior for the excavation and

the adjacent strip footing.

II. Studying the effect of the parameters affecting on the behavior of the chosen model such as distance between the building and excavation and building foundation depth.

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2. Model Test Setup, materials and Procedures A schematic drawing of the test setup used in this study is shown in Fig.( 2). The model

test box was made of 2 mm thick steel sheets, 500 mm wide, 1000 mm high, and 1700 mm long.

The excavation wall was made of a 1 mm thick steel sheet. The model strip footing was made of

500 mm wooden block. An automatic IOtech DaqBoard/2005 data acquisition system with

LabView software was used to continuously monitor and record data during all stages of the

tests. Multiplexing Isolated Analog Input DBK207 with 16 channel capacity was used to monitor

the output voltages from instruments. The data acquisition system was connected to a PC

Pentium IV processor, as shown in Fig.( 3). The footing was stiffened by a vertical tapered

wooden plate 500 mm wide extending from strip footing top level to the level arm loading rod, as

shown in Fig. (4). Width of excavation (w) = 16cm,

Depth of excavation = (H) cm,

Total height of sheet pile wall = (d) cm,

Building distance from excavation = (x) cm,

Foundation depth = (Df) cm.

The undrained internal friction angle of the sand compacted to a relative density of 17kN/m2 was

found from triaxial tests to be 36°. Index properties of sand are shown in Table (1), and its

gradation curve is shown in Fig. (5).

Table (1). Index properties for sand.

Minimum

unit

weight,

(kN/m3)

Maximum

unit

weight,

(kN/m3)

emin emax Specific

gravity,

Gs

Coefficient

of

uniformity,

Cu

Coefficient

of

curvature,

Cc

D10

(mm)

D30

(mm)

D60

(mm)

14.8 18.9 0.376 0.75 2.6 2.78 2.21 0.20 0.33 0.50

Fig. (2) Model of excavation, adjacent area and footing

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Fig. (3) Sheet pile wall supported excavation and Data Acquisition system.

Fig. (4) Side view of model strip footing.

3. Numerical Modeling and Selection of Parameters Soil code Finite Element Program Plaxis 7.2 was used in numerical modeling. The validity

of the results of this program was checked via conducting a number of program runs on physical

experimental model to make a comparison between experimental and numerical modeling

results. Plaxis program was furtherly applied to analysis different investigated parameters using

prototype dimensions.

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Fig. (5) Particle size distribution of tested soil.

3.1 Material model of sandy soil In order to make realistic predictions of the stability and deformations of excavation and

adjacent building, the Hardening soil model in PLAXIS program was used for sand idealization.

This model adopted to characterize the behavior of excavation and adjacent strip footing system

and material properties are presented herein. The excavation soil is assumed to be the same soil

in laboratory model. The sand is modeled by 15-node triangular element in the analysis as an

elastic perfectly plastic hardening model. The value of relative density is 0.53 for medium and

0.76 for dense sand. The parameters of medium and dense sand was determined from triaxial test

are presented in Table (2) and (3) respectively.

3.2 Sheet Pile Wall The sheet pile wall is modeled by means of beam element. The parameters for sheet pile

wall are presented in Table (4).The interaction between the wall and the soil is modeled at both

sides by means of interfaces. The interfaces allow for the specification of a reduced wall friction

compared to the friction in the soil.

Table (2) Input physical and mechanical properties of medium sand Parameter Name Value Unit

Soil dry unit weight

Wet soil unit weight Secant stiffness in standard drained triaxial test

Tangent stiffness for primary oedometer loading

Unloading / reloading stiffness Poisson’s ratiofor unloading-reloading

Cohesion

Friction angle

Dilatancy angle Interface reduction factor

Power for stress-level dependency of stiffness

Reference stress for stiffnesses

γd

γwet

Eref

50

Eref

oed

Eref

ur

υur

c

φ

ψ R

m

pref

17

20 14925

10447

44775 0.25

10

36

6 0.8

0.5

100

kN/m3

kN/m3

kN/m2

kN/m2

kN/m2

-

kN/m2

degree

degree -

-

kN/m2

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Table (3) Input physical and mechanical properties of dense sand Parameter Name Value Unit

Soil dry unit weight

Wet soil unit weight

Secant stiffness in standard drained triaxial test Tangent stiffness for primary oedometer loading

Unloading / reloading stiffness

Poisson’s ratiofor unloading-reloading Cohesion

Friction angle

Dilatancy angle

Interface reduction factor Power for stress-level dependency of stiffness

Reference stress for stiffnesses

γd

γwet

Eref

50

Eref

oed

Eref

ur

υur c

φ

ψ

R m

pref

18

20

29850 20894

89550

0.25 10

42

12

0.8 0.5

100

kN/m3

kN/m3

kN/m2

kN/m2

kN/m2

- kN/m

2

degree

degree

- -

kN/m2

Table (4) Material properties of the sheet pile (beam)

Parameter Name Value Unit

Type of behavior

Normal stiffness

Flexural rigidity

Equivalent thickness

Weight

Poisson’s ratio

Type

EA

EI

d

w

υ

Elastic

2.68 x106

9.68x103

0.208

1.2

0.3

-

kN/m

kN/m2/m

m

kN/m/m

-

3.3 Strip Footing

strip footing can be simulated by beam element. This line element has bending

stiffness, EI, and axial stiffness, EA. Where:

E: modulus of elasticity for concrete cuF4400 (N/mm2)

A: area of cross section

I: moment of inertia

Fcu: characteristic strength (25N/mm2)

The footing is loaded with distributed load 100 kN/m2, which is transferred to soil.

The properties of footing are given in Table (5).

Table (5) Material properties for the strip footing

3.4 verification of numerical modeling In this part study the results of laboratory and numerical analysis. Figures (6, 7, 8, and 9)

show bending moment on the cantilever sheet pile wall at different values of X, (Df = 40 mm)

and (H = 160 mm). Observed bending moment distribution is plotted on the same figure for

comparison. From the figure, it can be observed that computed and FEM bending moment values

are so close. The maximum bending moment on sheet pile wall was at x = 80mm. When X

increased, the bending moment on sheet pile wall consequently decreases. When (X / H) ratio

reaches the value of 1.5 no considerable further decreases in the values of the bending was

recorded.

Parameter Name Value Unit

Axial stiffness

Flexural rigidity

Equivalent thickness

Weight

Poisson’s ratio

EA

EI

d

w

υ

3.811E+07

3.175E+06

1.00

25.00

0.2

kN/m

kN.m2/m

m

kN/m/m

-

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Fig .(6) Variation of the sheet pile wall bending moment for x= 8cm and H=16cm



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3.5 Numerical modeling of proto type dimensions The general layout of the physical model and the mesh are shown in Fig. (10). The

dimensions of the model reproduce the dimensions of the prototype wall simulated by the

reduced scale model (1/25th). The boundary conditions (no horizontal and no vertical

displacements) correspond to the wall of the container. The finite element mesh was generated

automatically as a very fine mesh to be more accurate in representation of the excavation system

behaviour, as shown in Fig. (11).

Fig. (10) Model of excavation, adjacent area and strip footing

Fig. (11) Finite element mesh for the model of deep excavation and adjacent area

Excavation

Sheet pile

G.S

.

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4. Testing program The parameters taken into consideration are distance of strip footing (x) and the

depth of foundation (Df). These variables are discussed in the following items. Table (6) presents

the studied cases of variation of ratio of foundation depth to excavation depth (relative depth

HDR fd and the ratio of strip footing distance to depth of excavation

HΧRx .The resulting straining actions and deformations due to excavation are

studied in term of (Rx =0.5, 1, 1.5 and 2). Rd having the values of (0.25and 0.5) as shown in

Table (6).

Table (6) Analysis cases used in the numerical study.

Case No. 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

medium dense

Rd = fD 0.25 0.50 0.25 0.50

Rx =

0.5

0

1.0

0

1.5

0

2.0

0

0.5

0

1.0

0

1.5

0

2.0

0

0.5

0

1.0

0

1.5

0

2.0

0

0.5

0

1.0

0

1.5

0

2.0

0

5. Analysis and results The effect of studied parameters on straining actions and deformations of sheet pile wall,

strip footing and excavation bottom may be presented as follows:

5.1. Straining action and deformation of sheet pile wall

5.1.1. Horizontal deformation of sheet pile wall

Figures (12, 13, 14 and 15) show the relationship between lateral deformation of the sheet

pile wall and (Rx) for Rd = 0.25 and 0.5. The maximum lateral deformation was recorded at

Rx=0.5 and Rd=0.25. When the values of (Rx) and (Rd) were increased, a corresponding decrease

in lateral deformation of sheet pile wall was recorded. The ratio between the measured maximum

wall deflection and the depth of the excavation (δhmax /H) was 0.0098, which was larger than the

ratio measured in Taipei and Goldberg et al. (1976), Clough, O’Rourke (1990) and Zhong W.

Wang et.al (2005) bounding limit of 0.005 but it was substantially smaller than the Peck and

Moormann (2004) bounding limit of 0.01. If Rx ≥ 1.5 no considerable decreasing of the lateral

deformation of the sheet pile wall at all values of Rd and follows the same trend. Comparing

Figs.(12) and (13) corresponding to medium sand and Figs. (14) and (15) corresponding to dense

sand it may be concluded that sheet pile wall deformation were nearly doubled with the case of

medium sand compared to that of dense sand.

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Fig.(12): Variation of the lateral deformation of sheet pile wall for different values of Rx

(Rd = 0.25) for medium sand.

Fig. (13): Variation of the lateral deformation of sheet pile wall for different values of Rx

(Rd = 0.50) for medium sand.


(Rd = 0.25) for dense sand.

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(Rd = 0.50) for dense sand.

5.1.2. Bending moment in sheet pile wall

Figures (16, 17, 18, and 19) show the relationship for bending moment on the wall at

different values of (Rx) for Rd = 0.25 and 0.5. The maximum bending moment on sheet pile wall

was recorded with the case of Rx = 0.5 and Rd=0.25. When the values of (Rx) and (Rd) were

increased, a corresponding decrease in bending moment on sheet pile wall was recorded. For all

cases it is obvious that the maximum value of bending moment is at almost 75% of wall height.

At Rx ≥ 1.5 in cases of dense sand no considerable difference was noticed in the values of the

bending moment for different values of Rd. The value of bending moment in dense sand is almost 0.63 of it in medium sand for all cases.

Fig. (16): Variation of the sheet pile wall bending moment for different values of Rx (Rd = 0.25)

for medium sand.

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Fig.(17): Variation of the sheet pile wall bending moment for different values of Rx (Rd = 0.50)

for medium sand.

Fig.(18): Variation of the sheet pile wall bending moment for different values of Rx (Rd = 0.25)

for dense sand.

Fig. (19): Variation of the sheet pile wall bending moment for different values of Rx (Rd = 0.50)

for dense sand.

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5.1.3. Shearing force in sheet pile wall

Figures (20, 21, 22 and 23) show the shearing force distribution on the sheet pile wall at

the different values of (Rx) for Rd = 0.25 and 0.5 respectively. The maximum shearing force on

sheet pile wall was recorded at Rx=0.5 and Rd=0.25. When the values of (Rx) and (Rd) were

increased, a corresponding decrease in shearing force on sheet pile wall was recorded. At Rx ≥

1.00 no considerable difference was noticed in the values of the shearing force for different

values of Rd. Comparing Figs.(20) and (21) corresponding to medium sand and Figs. (22) and

(23) corresponding to dense sand it may be concluded that sheet pile wall shearing force were

nearly 140% with the case of medium sand compared to that of dense sand.

Fig. (20): Variation of the sheet pile wall shearing force for different values of Rx (Rd = 0.25) for

medium sand.


medium sand.

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dense sand.


dense sand.

5.2. Straining action and deformation of strip foundation

5.2.1. The settlement of the strip foundation

Figures (24, 25, 26, and 27) show the relationship between settlement of strip foundation

and (Rx) for Rd = 0.25and 0.5. The maximum settlement was found where the building is nearest

to the excavation. When the values of (Rx) and (Rd) were increased, a corresponding decrease in

the settlement of strip footing was recorded. At Rd = 0.25 the maximum settlement at Rx = 0.5

has a value of 65 mm in medium sand. Differential settlement can be observed which decrease at

Rx = 1. It can be observed that the settlement decrease by increasing the depth of foundation. At

Rx ≥ 1.50 no considerable difference was noticed in the values of foundation settlement for all

cases. Comparing Figs.(24) and (25) corresponding to medium sand and Figs. (26) and (27)

corresponding to dense sand it may be concluded that strip footing settlement were nearly 230%

with the case of medium sand compared to that of dense sand.

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Fig. (24): Variation of strip footing settlement for different values of Rx (Rd = 0.25) for medium

sand.

Fig.(25): Variation of strip footing settlement for different values of Rx (Rd = 0.50) for medium

sand.

Fig. (26): Variation of strip footing settlement for different values of Rx (Rd = 0.25) for dense

sand.

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Fig. (27): Variation of strip footing settlement for different values of Rx (Rd = 0.50) for dense

sand.

6. CONCLUSIONS Strip footing adjacent to retained excavation was studied in this research. The straining

actions and deformations were studied and investigated. Two main parameters were studied, the

first is the relative depth, HDRfd

and the second is the relative distance, HΧRx

where Df is the foundation depth, H is the excavation depth and X is the building distance. The

following conclusions can be drawn from the obtained results:

The maximum horizontal displacement of cantilever sheet pile wall was found at depth(0.00).

The maximum lateral deformation and straining actions on sheet pile wall was recorded with

the case of Rx = 0.5 and Rd=0.25. When the values of (Rx) and (Rd) were increased, a

corresponding decrease in lateral deformation and straining actions on sheet pile wall was

recorded.

The maximum settlement was found where the building is nearest to the excavation. When

the values of (Rx) and (Rd) were increased, a corresponding decrease in the settlement of strip

footing was recorded.

At Rx ≥ 1.50 no considerable difference was noticed in the values of the lateral deformation,

bending moment and shearing force for different values of Rd.

The ratio between the measured maximum wall deflection and the depth of the excavation

(δhmax /H) was 0.0098, which was larger than the ratio measured in Taipei and Goldberg et al.

(1976), Clough, O’Rourke (1990) and Zhong W. Wang et.al (2005) bounding limit of 0.005

but it was substantially smaller than the Peck and Moormann (2004) bounding limit of 0.01.

The relative density is the important factor in decreasing values of lateral deformations and

straining actions for sheet pile wall and settlement in strip footing.

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7. REFERENCES 1- Anas, E.L.L., "Structures Resting on Non-uniform Layers of Soil Including Effect of Geo-

Grid Reinforcement and Earthquake", M.Sc. thesis, University of Assiut, Egypt, June (2005).

2- Boone, S, J. “Ground-movement-related building damage”. Journal of geotechnical

engineering, Vol. 122, No. 11, November. pp. 886 – 896, (1996).

3- Boscardin, M, D. and Cording, E, J,. “Building response to excavation induced

settlement” Journal of geotechnical engineering Vol. 115, No. 1, January. pp. 1 – 20, (1989).

4- Hashash,Y.M.A and Whittle, A.J. “Ground Movement Prediction for Deep Ecavations in

Soft Clay” Journal of geotechnical engineering Vol. 122, No.6, pp. 474 –486, June (1996 ).

5- Kishnani, S. S. and Borja, R. I. “seepage and soil-structure interaction effects in braced

excavations” Journal of geotechnical engineering, ASCE, Vol. 119, No. 5, pp. 912 – 928, (1993).

6- Milligan, G. W. E., “Soil Deformations near anchored sheet-pile Walls,” Geotechnique

Journal, 33, No. 1, pp. 41 - 55, (1983).

7- Mohamed, A. A., “The effect of ground movement induced by retaind excavation on

adjacent structures ", Phd. Thesis submitted for examination, Civil Eng. Dept., Al-Azhar

University, (2011).

8- PLAXIS Version 7.2 Material models Manual, "Finite Element Code for Soil and Rock

Analysis". A. A. Balkema Poblishers, (1998).

9- Seok, J. W., Kim, O. Y., Chung, C. K. and Kim, M. M. “Evaluation of ground and

building settlement near braced excavation sites by model testing” Canadian Geotechnical

Jornal. Vol. 38, (2001) .

10- Son, M. and Cording, E. J., “Estimation of building damage due to excavation-induced

ground movements”. Journal of geotechnical and geoenvironmental engineering, ASCE,

February. pp. 162 – 177, (2005).

EEFECT OF SHEET PILE WALL SUPPORTED EXCAVATION ON ADJACENT STRIP FOUNDATION

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