Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Stability of Self-Standing High Stiffness-Steel Pipe Sheet Pile Walls Embedded
in Soft Rocks
Vijayakanthan KUNASEGARAMPhD Student, Dept. of Civil and Environmental Engineering, Tokyo Institute of Technology, Tokyo, Japan
Email: vijayakanthan.k.aa@m.titech.ac.jp, heshuvijay@gmail.com

Jiro TAKEMURA
Associate Professor, Dept. of Civil and Environmental Engineering, Tokyo Institute of Technology, Tokyo, Japan

Yoshiro ISHIHAMA
Senior Researcher, Steel Structures Research Lab, Nippon Steel and Sumitomo metal Corporation, Chiba, Japan

Yukihiro ISHIHARAManager, Press-in Technologies Support Department, IPA Support Section, GIKEN LTD, Tokyo, Japan

ABSTRACT
Five centrifuge model tests are reported in this paper, which discusses the overall behaviours of self-standing stiff sheet
pile walls embedded in soft rocks. Two different soft rocks, namely sand rock and mud rock were modelled by using
sand-cement-clay mixtures at appropriate mixing ratios. In this study, a centrifuge modelling technique has beendeveloped in which the loading process can be simulated from design conditions to the ultimate failure conditions on anembedded wall in soft rock. A series of centrifuge tests has been carried out to investigate the influence of embedment
depth on the stability of self-standing steel pipe sheet pile walls. Experimental observations reveal that, the stiff sheet
pile walls suffer from rigid body rotations about a pivot point. An equilibrium analysis was performed by switching theactive and passive zones based on the observed pivot point at the verge of rotational failure. A similar contribution ofincrement in embedment depth on the stability of walls can be confirmed from the analysis and experimental outcomes.
Also, it can be confirmed that the wall can stand in the design condition with a reasonable safety margin with a relatively
small embedment depth compared to current design practices and a small increment in embedment depth e.g., 0.5m, cansignificantly increase the wall stability and prevent the wall from ultimate collapse.
Key words: Self-standing walls, Soft rock, Stability, Centrifuge model, Steel pipe piles

1. Introduction
Urban development with existing infrastructures

application of large diameter piles as a self-standing wall,

often encounters certain physical restrictions for theembedment ground, such as dense sand or soft rock toapplication of earth retaining structures. In such situations

secure the passive resistance against the lateral anddue to simple retaining mechanism and applicability under

moment loads from the retained soils. The current design

limited space, self-standing walls could be an ultimate

practice in Japan requires a minimum embedment depth

choice of an engineer. Large diameter steel pipe piles canfor a self-standing sheet pile wall. In the design method,be effectively utilized for a self–standing sheet pile wall

based on the characteristic value β obtained by Chang’swith a relatively large retained height. Deflection of theequation, the minimum embedment depth of (2.5–3)/β iswall below the allowable limit and the flexural bending

being used as described in the design manual of self-

failure can be prevented due to the high flexural stiffness

standing steel sheet pile wall (2009). Referring to thisand strength of large diameter piles. However, for the

method, the requirement of minimum embedment depth

relatively large stiffness and strength are required for the- 143 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

increases with the increasing EI value, which causes

body to form a rigid container. Two box-shape rubber bags

difficulties in the installation of large diameter piles into

were placed on the front and back sides of the wall. The

the hard ground such as soft rock and eliminates thefront one was a polypropylene-made closed box with pileapplicability of large diameter piles. Therefore, if this typeat the bottom corner and the top of the box was filled withof retaining wall can be constructed with a relatively small

water. The back side one was an open box made of latex

embedment depth in soft rock type ground, its

rubber, which was filled with dry sand. Detailed modelling

applicability can be increased, which would contribute toprocedures about the centrifuge model are described in

the reduction of construction time and cost. For theKunasegaram et al. (2018).

reduction of embedment depth smaller than the one
determined by the current design practice, both
serviceability and ultimate limits should be reasonably

2.1. Test conditions and model sheet pile walls
This paper reports the results of five centrifuge model

examined in the design with an additional margin of safety.

tests, which are divided into two test series, i.e., sand rockand mud rock series, as shown in Table 1. All dimensions

2. Centrifuge modelling
Centrifuge model studies were conducted using TIT

and the properties of the model walls are given in

Mark III geotechnical centrifuge at 50g centrifugal

made up of aluminium (A5052-O) alloy plates having theacceleration, the specifications of centrifuge facility are

yield strength of 95 MPa and the Young’s modulus of 69

listed in Takemura et al. (1999). An illustration of a

GPa. Rigid and flexible sheet pile walls having thecentrifuge model arrangement is given in Fig. 1, which

thickness of 24.9 mm and 9.9 mm in model scale arerepresents a self-standing sheet pile wall embedded inillustrated Fig. 2. The transformed sections of rigid andartificially made soft rock. In the centrifuge model, aflexible model sheet pile walls were designed to replicate

model wall was placed throughout the breadth of thethe flexural rigidities of steel pipe sheet pile walls with thecontainer to secure the plane strain deformations of the

Diameter (Ø) of 2.5 m, thickness t=25 mm and Ø=1.0 m,

wall. Soft rock model was prepared in a container which

t=10 mm respectively. Fig. 3, shows the dimensions of

had the internal dimensions of 700 mm in length, 150 mm

large diameter piles and corresponding transformedin breadth and 500 mm in depth. The container was madesections in prototype scale. Considering the currently

up of a removable steel frame on the rear face and aavailable technology for the installation (Gyropress

transparent acrylic panel stiffened by a steel hollow frame

method) of large diameter piles, an 0.18 m gap between

in the front; both face panels were bolted with the frame

two piles is inevitable. Therefore, in the modelling ofin the front; both face panels were bolted with the mainequivalent rectangular section, an effective width

prototype scale in Table 1. Model sheet pile walls were

24.9

φ10

All dimensions are in mm- Strain gauges
25- Earth pressure sensors
9.9
130
25

Used intests
φ10
S1_RW1S1_RW250
S2_RW1304
S2_RW2

320

164

40

50

90＝ 6＠15
25

Fig. 1

Centrifuge model arrangement

Fig. 2- 144 -

Used intest
S1_RW330

4060＝6＠1018

Model Sheet pie walls used in experimentProceedings of the First International Conference on Press-in Engineering 2018, Kochi

E= 193 GPa
t=25 mm
EI= 10.7
GNm2/mAluminium wall model

Table 2.

Physical and mechanical properties of soft rocks

σy= 95 MPa E= 69 GPa
1m
Model
Wall “R”

My= 11.3 MNm/m 2.68 m

Embedment medium

Sand rock

Mud rock

Water/Cement ratio (%)

395

510

Water content (%)

21.5

39

Clay: Sand (wt. %)

30:70

100:0

Bulk density (kg/m3)

2060

1820

Dry density (kg/m3)

1715

1320

1.3

1.0

260-660

200-420

My= 24.5 MNm/m

Ø=1m

1m

t=10 mm
EI= 0.62
GNm2/m

My= 1.6 MNm/m 1.18 m

Model
Wall “F”

0.495 mσy= 255 MPa
Ø = 2.5 m

1.245 mStainless steel pipe sheet pile walls

My= 3.8 MNm/m

All dimensions are in prototype scaleFig. 3

Transformed sections of wall "R" and wall "F"

Table 1.

Test conditions

Unconfined Compressive
Strength (UCS) (MPa)E50_Ԑad - E50_Ԑas (MPa)

Rock
type

S1_RW1S1_RW2Sand
rock

S1_RW3S2_RW1S2_RW2
H- Wall height

Mud
rock

Wall
type

EI wall(GNm2/m)

H
(m)

de
(m)

R

12

2.5

11.096R

12

3.0

11.096

F

9

1.8

0.697

R

12

2.5

11.096R

12

3.0

11.096

2.1

Model Sand rock (S1_RW2)

Model Mud rock (S2_RW2)

1.8

Melbourne Mud rock (Johnston)

1.5

UCS (MPa)

Test
code

Calgary Mud rock (Lo,et al)

1.2
0.9
0.6

de-Embedment depth

0.3

of 2.68 m and 1.18 m are considered for the wall ‘R’ and00

the wall ‘F’ respectively.
Fig. 4

1

2
Strain (Ԑa) (%)

3

4

Stress-strain behaviour of centrifuge model and2.2. Properties of artificial soft-rockMechanical properties of artificial soft rocks were

natural soft rocks

investigated through the unconfined compression (UC)(Lo, et al., 2009). From the stress strain behavior, up to

tests which were conducted for the cylindrical molded

0.4% axial strain the model soft rocks exhibit similar

specimens (Ø=50mm and L=100mm). The physical andHowever, the post peak behaviors of natural rocks aremechanical properties of model soft rocks are presented in

more brittle compared to the model rocks.

Table 2. In this study, the averaged external strain (dialgauge: Ԑad) and the surface strain (strain gauge: Ԑas) of thespecimens were measured by using a dial gauge and a pair2.3. Simulation of Excavation and loading
The main objective of this modelling process was toof strain gauges, respectively. Secant modulus (E50) of thesimulate the excavation under serviceability limit states

artificially made rock samples were estimated based on

and achieving the ultimate failure conditions with thethe averaged external strain (E50_Ԑad) and the averaged

application of additional lateral loading under a constantstrain gauge (E50_Ԑas) measurements. The detailed

centrifugal acceleration. Although the small deformation

procedures about soft rock modelling for centrifuge

to large ultimate failures could be achieved by different

studies are described in Kunasegaram et al. (2015).

alternative way such as increasing the centrifugal

Typical stress-strain behaviors of model soft rocks areacceleration, such an alternative cannot predict theillustrated in Fig. 4, along with the natural soft rocks

behavior of specific prototypes as the self-weight of theencountered in Melbourne (Johnston, 1984) and Calgary

soil change with the centrifugal acceleration.
- 145 -

qLf = H(Kaγ’+γw)
Sand
qLf ~3.5qefHhw

qef =KaHγdde

Soft rock

de

0.25

0.25

0.2

0.2

0.15
S1_RW1S1_RW2
S1_RW3S2_RW1S2_RW2

0.1
0.05

qLf

0.15
0.1
0.05
0

0

Soft rockLoading height (hw) (m)Ze

Excavation depth (Ze) (m)Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

200

0

400

500

Time (sec)

(a)

(b)

Fig. 6

1000

1500

Time (sec)

Measured excavation depth and loading height in modelFig. 5 Pressure distribution during (a) Excavation & (b) Loading

scale

Therefore, it cannot be applied for the verification or

which was done by raising the air pressure of the tankdesign method.

manually. Due to the difficulty in monitoring andIn this study, unloading in the wall front andcontrolling the pressures, the variations of water height

additional loading in the back side of the wall were

were different as shown in Fig. 6. The horizontal lateral

achieved by using water as a draining and filling liquidpressure applied to the wall can be increased about 3.5

respectively. The excavation process and the loading

times the dry sand condition at the submerged state asprocess after the excavation were simulated in a constantdescribed in Fig. 5. Excavation depths and the water

centrifugal acceleration as shown in Fig. 5. Referring toheights in the two loading processes were measured by theFig. 5 the excavation depth and the loading height of waterpore pressure transducers placed at the bottom of bothin the back side of the wall are indicated by Ze and hw

rubber bags.

respectively. Also the notations qef and qLf represents theapplied load intensities at the end of excavation and at the

3. Results and discussion

end of loading respectively.

3.1. Observed behaviors

Utilization of a heavy liquid having the identical unit

The way of increasing wall top displacements andweight of back fill material could create the vertical stressrotations with the excavation depth and the additional

similar to that of the sand. However, the unbalance oflateral loading are shown in Fig. 7 and Fig. 8 respectively.

horizontal stresses at the initial condition and the

Unlike a convex shape displacement and rotation profile

backward wall movements caused by the heavy liquidwith the increase of excavation depth in field, a concave

could be higher than those caused by water as a draining

shape behavior can be observed in all test cases. Thisliquid. It is important to note that the earth pressure

phenomenon could be attributed to the utilization of fluid

coefficient (K) in the retained soil is expected to be higher

in the wall front which has the lateral earth pressure

than the earth pressure coefficient at rest (K0=1-sinϕ’～

coefficient of unity and zero stiffness. Considering the0.35), which can be attributed to the backward movement

difference between unloading by fluid and the real fieldof the wall due to relatively larger water pressure than at

excavations, in the case of real field excavation therest earth pressure of the sand with γd=15.6 kN/m3.

mobilized passive earth pressure also increases with the

The unloading in the excavation process at the walllateral movement of wall, which could control the wall

front was simulated by draining out the water from thedeflections at the initial stage of excavation with a larger

rubber bag with the help of solenoid valves to the storage

supporting height of earth in the wall front. This

tank. After the excavation process, to create the ultimate

phenomenon results in a convex shape load displacement

loading condition, in other words to create large wall

behavior in real field excavation. However, it cannot be

deflection, the additional load was applied by feeding the

expected from a fluid with zero stiffness.

drained water in the tank to the backside rubber box,
- 146 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Wall top displacement (δt) (mm)

200

500

S1_RW1δt

δt

S1_RW2

ze
150

400

S1_RW3H

hw

S2_RW1S2_RW2

de

300

de

100

Soft rock

Soft rock

200

50
100

0

0

0

2

4

6

8

10

12

0

2

4

Excavation depth (Ze) (m)

6

8

10

12

10

12

Loading height (hw) (m)Fig. 7 Variation of measured wall top displacement with excavation depth and loading height
0.05

0.020

δt

S1_RW2ze
Wall top rotation (θt) (rad)δt

S1_RW10.04

S1_RW3

H

0.015

hw

S2_RW1S2_RW2

de

de

0.03

0.010

Soft rock
Soft rock

0.02

0.005
0.01

0.000

0.00
0

2

4

6

8

10

12

0

2

4

6

8

Loading height (hw) (m)Excavation depth (Ze) (m)Fig. 8 Variation of wall top rotation with excavation depth and loading height

Considering the uncertainty in the initial condition of theactive earth pressure coefficient of sand. Calculated

modelling process in this study, a nonlinear variation of

moment loads for constant and non-linear K values areearth pressure coefficient with the excavation depth waspresented in Fig. 9 against the excavation depth andselected in which the K value at initial condition is equalloading height.

to 0.63(γw/γd) and decreasing non-linearly to achieve Ka at

Fig. 10 shows the variation of normalized wall top

the end of excavation. However, during the loading

displacements against the estimated moment loads at theprocess, K=Ka was used to estimate the moment loads

dredge level. From Fig. 10, a similar increasing trend ofwith the assumption of full mobilization of active earth

displacements against the moment load with differentpressures, where K=0.63 is the calculated K value tosystem stiffness can be observed. Considering themaintain the equilibrium with water pressure, and Ka is theresistance against moment loads or stiffness of observed- 147 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

4000

Moment load (kNm/m)

12m wall

Moment load based on anonlinear variation of "K"

3000

9m wall

2000
1000
K=Ka

0

12 m wall, K= 0.35 = K0
12 m wall, K= 0.2 = Ka
9 m wall, K= 0.35 = K0
9 m wall, K= 0.2 = Ka
12 m wall, K=0.5
9 m wall, K=0.5
12m nonlinear
9m nonlinear

-1000
-2000
0

2

4

6

8

10

Theoritical moment loads
at the embedment level fordifferent K-values

120

Excavation depth (Ze) (m)

2

4

6

8

10

12

Loading height (hw) (m)Fig. 9 Variation of theoretical moment loads at dredge level with excavation depth and loading height

curves, the wall in S1_RW3 exhibits large plastic(S2_RW1 & S2RW2), a significant contribution of 0.5 m

deformations under small increment of moment loads.

increment in embedment depth can be seen from small to

Although the ratio of the wall height to the embedment

large wall top displacements. However, there is no

depth (H/de=5) is almost similar to that of the walls insignificant difference that can be seen for the walls

S1_RW1 and S2_RW1 (H/de=4.8), observed large

embedded in sand rock up to 60 mm (0.5%H) wall top

deformations at small load levels could be attributed todisplacement. Up on initiation of yield deformation

relatively small flexural stiffness of the wall. Thisaround 60 mm wall top displacement, the wall in S1_RW1

observation clearly indicates the necessity of walls with

undergoes large plastic deformation and exhibits thehigh flexural stiffness to sustain large bending moments.

collapse of the wall under a constant applied load. A

Considering the similar embedment and loading

similar behavior can be observed upon yielding atconditions of walls embedded in sand and mud rocks

different wall top displacements for the cases S1_RW3,(S1_RW1, S2_RW1 and S1_RW2, S2_RW2), walls in

S2_RW1 & S2_RW2. However, the wall in S1_RW2

mud rock exhibit large displacements and rotations

exhibits high resistance even at large moment loads

compared to the ones in sand rock. Difference in thecompared to the other cases. At the end of loading process,behaviors is as expected, since the model sand rock poses

the stability of the wall was confirmed with an induced

higher initial stiffness compared to the mud rock as shownwall top displacement of 185mm (1.5%H). Comparing

in Fig. 4. From the physical observations given in Fig. 11

this observation with the case of S1_RW1, a significant

and observed moment load displacement behaviors at thecontribution of 0.5 m increment in embedment depth onend of loading process, clear failures of the walls can be

the stability and failure behavior of self-standing walls canobserved except the case of S1_RW2. The observation

be confirmed.

clearly indicates that, the stability of self-standing walls

Up on completion of loading process in order toembedded in hard mediums can be maintained withcreate the failure of wall in S1_RW2, the centrifugal

relatively small embedment depth (de=3m) than that of theacceleration was gradually increased up to 95g as

current design practice.

described in Fig.10. Although a gradual increase ofReferring to the observed stiffness of moment load
displacement relation to the walls embedded in mud rockdisplacement could be observed with the increase ofacceleration, there is no clear failure of the embedded- 148 -

Normalized wall top displacement(δt/H) (%)

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

4

relatively small wall top displacements could be attributed

3.5

to the lateral translation of the wall. It is important to note3

that the soft rocks used in this study are relatively stiff andself-standing height of model soft rocks are much higher

2.5

than the embedment depths. Also, the wall in S1_RW2

2

does not show a clear response during the entire loading

G-up until 95g

1.5

0.5

process.

S1_RW1S1_RW2
S1_RW3S2_RW1S2_RW2

1

50G

Mobilization of passive pressures with wall top
displacements for the walls in S1_RW1, S1_RW3 andS2_RW1 can be observed Fig. 12. As the wall move and

0
0

1000

2000

3000

4000

5000

rotate towards the front as depicted in Fig. 14, passive

Moment load (ML) (kNm/m)resistance induced by the embedded medium also

Fig. 10 Variation of normalized wall top displacement withincreases with the wall movement. This observation is asapplied moment load at dredge level

expected since the earth pressure cells are located above
the point of rotation. However, a clear mobilization cannot

S1_RW1S2_RW1be seen for the wall in S2_RW2. The possible reason forthis observation could be the relatively deeper location of
the earth pressure cell in front compared to the point of

A

P

P

A

P

rotation. This argument could be supported by referring toA
S1_RW3

S1_RW2the observed rise of passive pressure at relatively large

S2_RW2wall top displacements at the back side of the wall in
S2_RW2. Over all from the observed pressure variations
A P

P

A

P

A

in front and back side with the wall movement, it can beconcluded that the net earth pressure profile is a

Fig. 11

Observed deformation and failure of walls

combination of passive pressure zones in front and backmedium that can be seen even at 95g centrifugalside of embedded length of the wall. Also, the active andacceleration. It can be confirmed by means of physicalpassive earth pressure zones can be switched based on theevidence provided in Fig. 11. Overall from thepoint of rotation. Fig. 14, shows a typical failure mode

observations, it can be concluded that, the wall with 3 mobserved for a self- standing wall (S2_RW1) embedded inembedment in sand rock (S1_RW2) could maintain the
However, for the application of self-standing walls in mud
rock, the stability of wall with increased embedment
depths (de > 3 m) must be confirmed.
Measured earth pressures in the front and back sideof the embedded portion of the wall are plotted against thewall top displacements in Fig. 12 and Fig. 13 respectively.
Observed pivot points from digital images of deformed
wall at the end of loading process are provided in

Measured earth pressure (kPa)stability even under large horizontal and moment loads.

parenthesis. From Fig. 13, a clear decreasing trend of earthpressures can be observed in the initial stages of wall

1000
900
800
700
600
500
400
300
200
100
0

medium. Also, the observed loss of pressure at the backside and the increase in front (S1_RW1, S2_RW2) at

Dredge
level

Wall

dx
E.P sensor
dx=1.75m(1.56 m)0

movement. This observation reveals the gradual loss ofcontact between the earth pressure cell and the embedment

Observed pivot points are
given in parenthesis

200

dx=0.9m(1.05 m)dx=1.75m(1.55 m)400

S1_RW1S1_RW2
S1_RW3S2_RW1S2_RW2dx=1.25m(1.45 m)dx=1.25m(1.28 m)

600

800

Wall top displacement (δt) (mm)Fig. 12

Change of measured earth pressures in the wall front

embedded portion against the wall top displacement- 149 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

condition of wall even below the FOS equals to unity. The

Measured earth pressure (kPa)

500

Dredge
level

400

Wall

dx
300

E.P sensor

S1_RW1S1_RW2
S1_RW3S2_RW1S2_RW2dx=1.25m(1.28 m)200

factor of safety against the rotational failure about thepivot point which is located at a depth do from the dredge
level can be written as a ratio between resisting moments(MR) and driving moments (MD). The FOS (MR/MD) canbe derived from the pressure distributions described in

dx=1.75m(1.55 m)Fig. 15, where γd and γR are unit weight of backfill sanddx=1.25m(1.45 m)100

(γd=15.6 kN/m3) and soft rock (γR=20.1 kN/m3)
respectively. Also, Ka is the active earth pressure

dx=0.9m(1.05 m)dx=1.75m(1.56 m)coefficient of sand and Cu represents the undrained shear0

strength of soft rock.

0

200

400

600

800

A stability analysis was conducted on a self-standing

Wall top displacement (δt) (mm)wall embedded in soft rock with undrained shear strength

Change of measured earth pressures in embeddedof 650kPa and fixed retain height of 12 m. In this analysis,

portion at the back side of the wall against wall top

the critical depth of the pivot point was estimated using

displacement

the principle of minimization of moment ratio as described

Fig. 13

InitialEnd of
End ofstage
excavation
loadingby Madabushi, et al. (2005). For different embedment

Initialstage

depths, FOS against rotational failure was estimated by

End ofloadingvarying the loading height of water in the back side of thewall. Based on the estimated FOS and the corresponding

θ=6.77

loading height of water, the imposed moment loads (ML)
at
2.5 m

the

dredgelevel

wasestimated.

Graphical

representation of estimated moment loads against theembedment depths at different FOS are presented in Fig.
16.

0.996 mAssumed strength of the embedded medium(Cu=650kPa) and wall dimensions (H, de) in this analysis

Fig. 14are identical to the condition of S1_RW1 and S1_RW2

Typical failure pattern observed for wall"R" inwhich are 2.5 m and 3 m embedment in sand rock. Fig. 17.

S2_RW1 and the deformation profile in the embedment zoneshows the experimental observations for the walls

soft rock with a relatively small embedment depth. From
depicted deformation profile in the embedded zone, aSandtranslation and rigid body rotation modes of deformations
could be observable at the end of excavation and at the end

H=12 mof loading respectively. Based on the observed failureKaγd(H-hw)

modes and the earth pressure mobilizations as described

2Cu

in Fig. 12 and Fig. 13, an idealized pressure distribution
was drawn for the stability analysis as shown in Fig. 15.
Referring to the observed failure mode in Fig. 14,
certain amount of base shear as well as side wall frictions

dodeγRdo+2Cu

could be expected in the embedded zone as a favorable

hwγw
Ka[γd(H-hw)+hwγ’]

hwSoft rock[γd(H-hw)+(γ’+γw)hw+γRdo+2Cu]

action against the failure of the wall. However, thecontribution of above mentioned forces is not considered[γd(H-hw)+(γ’+γw)hw+γRde+2Cu]in this stability analysis. This assumption could
underestimate the factor of safety (FOS) and yield a stable

Fig. 15- 150 -

Assumed earth pressure profile for stability analysis

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

embedded in sand and mud rocks, in which appliedin mud rock reached its ultimate capacity around 120 mm

moment loads against the embedment depth at different

wall top displacements.

stages of wall top displacement (δt/H) are plotted Fig. 17.

Considering

2%(50mm=0.4%H)

and

10%

Increasing wall top displacements can replicate the(250mm=2%H) of the pile diameter as allowable anddecrease of FOS. Considering the theoretical andultimate limits of the wall top displacements, it can be said

experimental observations for 2.5 m and 3 m embedmentthat the 2.5 and 3 m embedment depths in sand rock can

in sand rock and mud rock, a clear agreement can be seen

secure the allowable displacements under design loads

in the trend of increasing moment load. Larger the wall top(end of excavation) with a reasonable safety margin.

displacements are, the higher the stiffness (∆ML/∆de)Considering the stability of walls in mud rock, the 3 m

between the moment load observed for 2.5 m and 3m

embedment depth is not adequate to provide an additional

embedment depths become, which can be observable withsafety margin over the allowable limit, therefore further

the decrease of FOS in the theoretical analysis. However,increment of embedment depth is necessary to control thethe observed moment load (ML) for mud rocks in Fig. 17

wall deformations within allowable limits with an

exhibits no further increase from δt/H =1% to 2% which

additional factor of safety. From Fig. 17 it can beclearly indicates that the wall with 3m embedment in

confirmed that the wall in S1_RW2 could sustain large
lateral loads even after the ultimate limits of deformations

Moment load (ML)(kNm/m)

5000

FOS=0.5
FOS=1.0
FOS=1.5
FOS=2.0

4000(2%H). This observation clearly indicates that the wallwith 3 m embedment in sand rock could maintain thestability even at ultimate loading conditions with a

3000

reasonable safety margin. Also, an 0.5 m increase ofembedment in sand rock significantly improved the2000

stability and failure behavior of wall under design andultimate loading conditions.

1000

Cu= 650 kPa & H=12 m

0
1

2

3

4. Conclusions

4
Stability of walls embedded in soft sand rocks can be

Embedment depth (de) (m)Fig. 16 Variation of moment load at dredge level against the

secured with a relatively smaller embedment depth thanthat of current design practices. However, the behavior in

embedment depth for different FOS based on stability analysis

mud rocks must be well studied with an increased

Moment load (ML)(kNm/m)

6000

embedment (de >3 m) depth to secure the stability under

0.25% H
0.50% H
1 %H
2 %H
4 %H

5000
4000

Sand rock
Mud rockultimate loads.
A small increment (0.5 m) in the embedment depth
significantly increased the stability and failure loads ofself-standing walls embedded in soft rocks.

δt in %H

3000

Failure of self-standing walls embedded in soft rocks

end of loadingtake place by rigid body rotation about the pivot point

2000

which is located far above from the bottom tip of the wall.
δt=50 mm

1000

References
end of excavation

0
1.5
Fig. 17

Association of Steel Pile. 2009. Design manual of self-standing

2
2.5
3
Embedment depth (de) (m)steel sheet pile wall.
Gopal Madabhushi, S.P. and Chandrasekaran, V.S. 2005.

Influence of embedment depth on the stability of self-

standing walls embedded in soft rocks

Rotation of cantilever sheet pile walls. Journal of
geotechnical and geoenvironmental engineering, 131 (2),- 151 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

pp. 202-212.
Johnston, I.W. and Chiu, H.K. 1984. Strength of weathered
Melbourne

mudstone.

Journalof

GeotechnicalEngineering, 110 (7), pp. 875-898.
Kunasegaram, V., Seki, S., Takemura, J. 2015. “Modeling of softrock for a centrifuge study”, Proc. 12th GeoKanto, pp. 1519.
Kunasegaram, V., Seki, S., Takemura, J. 2018, “Deflection andfailure of self-standing high stiffness steel pipe sheet pilewalls embedded in soft rocks”, Proc. 9th ICPMG, pp.
1439-1444.
Lo, Kwan,Y., Micic, S., Lardner, T. and Janes, M. 2009.
Geotechnical properties of a weak mudstone in downtown
Calgary. GeoHalifax’09.
Takemura, J., Kondoh, M., Esaki, T., Kouda, M. and Kusakabe,O. 1999. Centrifuge model tests on double propped wall
excavation in soft clay. Soils and Foundations, 39 (3), pp.
75-87.

- 152 -