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

Seismic Assessment of Steel Sheet Pile Reinforcement Effect on RiverEmbankment Constructed on a Soft Clay GroundKentaro NAKAI
Associate Professor, Department of Civil Engineering, Nagoya University, Nagoya, Japan
Email: nakai@civil.nagoya-u.ac.jp

Toshihiro NODA
Professor, Disaster Mitigation Research Center, Nagoya University, Nagoya, Japan

Shinji TAENAKA
Senior Researcher, Steel Structures Research Laboratories, Nippon Steel & Sumitomo Metal Corporation, Chiba, Japan

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

Nanase OGAWA
Chief, Construction Solutions Department, GIKEN LTD., Tokyo, Japan

ABSTRACTThe steel sheet pile reinforcement method is often used as a countermeasure against settlement and lateral displacement
when constructing embankments on soft ground. However, it has been reported that during Kumamoto earthquake(2016), some of the sheet piles that had been installed since the construction of the embankments contributed to seismic
resistance, although they were not intended as an earthquake countermeasure. Therefore, by assessing the seismic
performance of the steel sheet pile method, it is also expected to expand the applicable range of the construction
method. In this study, a numerical investigation on the effect of the steel sheet pile reinforcement method with different
embedment lengths was conducted against dynamic loading due to earthquakes, as well as the effect of settlement andlateral displacement at the time of static loading due to embankment construction. Numerical results indicate that thesteel sheet pile reinforcement method enables us to obtain not only the isolated effect for the deformation during
embankment construction, but also the aseismic effect by securing the proper embedment depth.
Key words: Soft ground, Steel sheet pile, Embedment depth, Settlement problem, Dynamic problem

1. Introduction
When embankment construction is carried out on

settlement under the embankment and the influence on

soft ground, settlement and lateral deformation occur inthick, the improvement cost becomes large. Although thethe surrounding ground induced by the consolidation

method (2) will be less effective in inhibiting thesettlement of the embankment (Fig. 1(a)). As asettlement of the embankment itself, it can inhibit thecountermeasure method, there are two ways: (1) adeformation of the surrounding ground by installing themethod to prevent embankment from settlement bywall body to the supporting layer. When the weak layer isground improvement (Fig. 1(b)) and (2) a method ofthick, it is economical and requires less space forisolating/blocking the influence (stress propagation) on

construction compared with the ground improvement

the surrounding ground by walls such as steel sheet pilemethod. Therefore, this method is very effective when

(Fig. 1(c)). In the case of constructing a new

the structure is located in the proximity of theembankment, the method of (1) can reliably inhibitembankment. In order to improve the economic

the surrounding ground. However, when the soft layer is- 221 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

efficiency, a floating pile construction method forintended as an earthquake countermeasure. Therefore, byshortening the embedment of steel sheet piles above theassessing the seismic performance of the steel sheet pile

supporting layer has also been considered. However, it

method, it is also expected to expand the applicablecannot be expected to inhibit ground deformation

range of the construction method.

differently from the fully fixed steel sheet pile

In this paper, a numerical investigation on the effectconstruction method. Moreover, settlement of the steelof the steel sheet pile reinforcement method withsheet pile itself is also concerned. Therefore, it isdifferent embedment lengths was conducted against

important to grasp the influence of the difference indynamic loading due to earthquakes, as well as the effectembedment length of steel sheet pile on the deformationof settlement and lateral displacement at the time of staticof the surrounding ground.

loading due to embankment construction. The analysis
code employed in this study is the soil-water coupledfinite deformation analysis GEOASIA (Noda et al., 2008),
which incorporates an elasto-plastic constitutive model,
namely SYS Cam-clay model (Asaoka et al., 2002), thatallows description of the behavior of soils ranging fromsand through intermediate soils to clay within the same
theoretical framework. This analysis code can be applied
to both ground deformation and failure and can be used toanalyse co-seismic behaviour over a time range of a few
seconds to a few minutes and post-seismic behaviour, inwhich case the time range is from a few years to a few
centuries.
2. Analysis condition
2.1. Target site
Soft ground near the mouth of the Kikuchi river inKumamoto prefecture, Japan was targeted as a reference(Ochiai et al., 1997). Fig. 2 shows the cross section andthe ground profile. It can be seen from the figure that theground consists of 6 layers and that the N-values lies
between 0 to 4 except for the SF layer at a depth of 25m.
It can be therefore said that this ground is very soft.

Fig. 1

Schematic drawing of general countermeasure against
settlement problem

As mentioned above, the steel sheet pile method
has been conventionally used as a countermeasureagainst static consolidation problems. However, it has
been reported that during the Kumamoto earthquake(2016), some of the severed sheet piles, which had been
installed during the construction of the embankments
contributed to seismic resistance, although they were not- 222 -Fig. 2

Cross section and the ground profile

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

2.2. Finite element mesh and boundary condition
Fig. 3 shows the finite element mesh before theconstruction of an embankment. Only half of line
symmetry is shown in the figure. The analysis region was
200 m in width and 28 m in depth. The ground wasassumed to be initially horizontally layered, with analternate layer of sand and clay. The hydraulicboundaries for the subsurface were designatedd asdrained boundaries, and the bottom end and the twolateral faces were designated to be under undrained
conditions. Periodic boundaries were realized by tying
two nodes with the same height between both lateral ends
(Noda et al., 2009).

Fig. 3Fig. 4

Experiment & simulation result for SF layer

Fig. 5Experiment & simulation result for CL layer

Fig. 6

Experiment & simulation result for CH layer

Finite element mesh2.3. Elasto-plastic properties for soils
The elasto-plastic properties (material constants andinitial conditions) of the soils were all determined basedon the results of mechanical tests using undisturbed
samples obtained from in-situ boring surveys. Theelasto-plastic properties were determined by replicating
the results of these mechanical behaviors using the SYS
Cam-Clay Model. The numerical simulation results of
the SYS Cam-Clay model are presented in Figs. 4, 5, and6. Mechanical properties of undisturbed samples

werewell replicated by the numerical simulations. Table 1
lists the identified elasto-plastic properties. In the initial
ground conditions, it was presumed that the degree of thesoil skeleton structure, stress ratio and specific volume
wereuniformin

eachlayer,andonly

theoverconsolidation ratio was distributed in accordancewith the overburden pressure. As for the embankment
material, since the test data could not be obtained, thematerial constants which was used in the past researchwere adopted (Nakai et al., 2017).

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

Table 1.

Material constants and initial condition for soils
EmbCLSFCH

Critical state index M

1.58

1.51

1.60

1.65

NCL intercept N

1.66

2.45

2.28

2.90

Table 3.

Embedment depth (layer of the tip)

Elasto-plastic parameters~Analysis conditions

Case 1

No countermeasureCase 25m (SF1)Compression index Swelling index ~

0.047

0.200

0.160

0.243

0.0047

0.020

0.025

0.020

Case 312m (CH)

Poisson’s ratio 

0.30

0.20

0.20

0.40

Case 417m (SF2)

Degradation index of structure a

1.34

0.60

1.00

0.60

Case 522m (CL2)

Ratio of  Dv

cs

1.00

0.07

1.00

0.07

Case 627m (SF3)

Degradation index of OC m

1.28

5.00

0.80

5.00

Rotational hardening index br

0.00

0.00

0.00

0.00

Limit of rotational hardening mb

0.00

0.00

0.0

0.00

Evolution parametersp

to D s p

Initial conditions
Specific volume v----

Stress ratio  0

0.545

0.545

0.545

0.545

Degree of structure 1 / R * 0

2.7

1.10

1.05

20.00

Degree of overconsolidation 1 / R0

23.70

2.20

30.00

1.80

Degree of anisotropy  0

0.00

0.00

0.00

0.00

Soil particle density  s (g/cm3)

2.65

2.65

2.65

2.65

Mass permeability index k (cm/s)

1.0 × 10-5

1.0 × 10-6

1.0× 10-4

1.0 × 10-6

2.4. Analysis cases
Numerical analyses were carried out in theFig. 7

Enlargement around the embankment after installationof sheet pile and construction of embankment

acceleration (gal)1) A steel sheet pile was modeled by replacing the soil
with a one-phase linear elastic material (Fig. 7) of
which material constants were shown in Table 2. As
indicated in Table 3, six different embedment depthsof the sheet pile were considered. However, theanalyses were conducted under two-dimensional plane

2) Embankments 3.4 m in height with slope gradients of
2:1 were constructed on the initial ground by adding
finite element meshes (Takaine et al., 2010).
3) Seismic waveform was input in the horizontal
direction equally on all nodes of the bottom face of theground. The seismic motion input was a strong motion
seismogram of Kumamoto earthquake (2016) observed
at K-NET station near the target area (Fig. 8).
Table 2.

Material constants for steel sheet piles

60

300
200
100
0 -1
10time (s)300300Fig. 8 Input seismic motion (Kumamoto earthquake)
NS200
1002003. Analysis0 result-100100
3.1. Deformationby embankment construction-200
Figs. 9, 10 and 11 show a variation of the ground-300
0surface at different
time20passage. Since
3 and 5 10-1
040 Cases 2, 60
time (s)show similar
300 results to Case 4, the figures are omitted 300
UDhere. In the200 case of no countermeasures (Case 1), there is100
a large settlement
just beneath the embankment and uplift 200
0of the surrounding ground. However, the amount of-100
100
settlement below the embankment decreases due to the-200
pile construction,and the deeper the installation is, the 0-300
02040
60
10-1
greater the effect is. In Case6,(s)when the embedment istime
Fourier amplitude (gal*s)equivalent to the actual values.

40

Fourier amplitude (gal*s)

weight, flexural rigidity, and yield moment became

20

acceleration (gal)modulus, and yield stress were revised so that theEW

acceleration (gal)strain conditions. Therefore, the density, Young’s

300
200
1000-100-200-300
0Fourier amplitude (gal*s)

following steps.

Density  (g/cm3)

2.05

deep enough, there were almost no deformation of thePoisson’s ratio 0.3

surrounding ground. In Case 4, as the pile itself sinks,

Young’s modulus E (GPa)

12.9

settlement occurs from beneath the embankment toYield stress  y (MPa)15.1

embankment toe, but the uplift of the surrounding ground

Yield moment M y (kNm)860

was quite restricted. The cut-off effect, which can be- 224 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

observed as a discontinuous settlement on both sides ofthe pile is shorter than 5m (Case 1 and 2), the cut-off

the pile, can be reproduced even in the numericaleffect by the sheet pile cannot be observed. However,analysis.

when the embedment depth is longer than 12 m, as theembedment depth becomes longer, the cut-off effectappears conspicuously, and the occurrence of the shear
strain of the surrounding ground is strongly inhibited. Fig.
18 summarizes subsurface deformation 300sec after theoccurrence of the earthquake. Similar to the shear strain
distribution, the amount of settlement at the embankment
and the deformation of the surrounding ground are large
in Case 1 and Case 2. On the contrary, in Case 6, whenan embedment is deep enough, both deformations
become small. These numerical results indicate that theFig. 9

steel sheet pile reinforcement method enables to obtain

Case1 (without countermeasure)the aseismic effect by securing the proper embedment
depth.

Fig. 10

Case4 (embedment depth 17m)
Fig. 12 Shear strain Case1 (without countermeasure)Fig. 11

Fig. 13

Case6 (embedment depth 27m)

Shear strain Case2 (embedment depth 5m)

3.2. Deformation by seismic motion
Figs. 12 to 17 show shear strain distributions 30sec
after the occurrence of an earthquake (soon after theseismic motion was finished). Although the amount ofground deformation due to embankment did not differ
much from Case 2 to Case 5, the deformation at the timeof the earthquake varies depending on the embedment
depth of the sheet pile. When the embedment depth of- 225 -Fig. 14 Shear strain Case3 (embedment depth 12m)

Proceedings of the First International Conference on Press-in Engineering 2018, Kochiof settlement and lateral displacement at the time of static
loading due to embankment construction. Numericalresults indicate that the steel sheet pile reinforcement
method enables us to obtain not only the cut-off effect forthe deformation during embankment construction, butalso the aseismic effect by securing the proper
embedment depth.
Fig. 15

5. Acknowledgements
This research was supported by International

Case4 Shear strain (embedment depth 17m)

Press-in Association TC3 (Chair: Prof. Jun Otani).
Authors express deep appreciation for the cooperation
and useful discussion. We also thank to the National
Research Institute for Earth Science and Disaster
Prevention (NIED) for allowing us to use K-NET data.

Fig. 16

References
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Nakano, M. 2002. An elasto-plastic description oftwo distinct volume change mechanisms of soils.
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Nakai, K., Noda, T. and Kato, K. 2017. Seismic
assessment of river embankments reinforced by thesheet pile constructed on a low N-value soft ground,
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Geotechnical

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1375-1396.
Fig. 17

Noda, T., Asaoka, A., and Nakano, M. 2008. Soil-water

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coupled finite deformation analysis based on arate-type equation of motion incorporating the SYS
Cam-clay model. S&F, 48(6), pp. 771–790.
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4. Concluding remarks
In this study, a numerical investigation on the effectTakaine, T., Tashiro, M., Shiina, T., Noda, T., and Asaoka,of the steel sheet pile reinforcement method with

failure of peat-calcareous soil layered ground due todifferent embedment lengths was conducted against

multistage test embankment loading. S&F, 50(2), pp.

dynamic loading due to earthquakes, as well as the effect245–260.

- 226 -A. 2010. Predictive simulation of deformation and