Proceedings of the 3rd International Conference on Press-in Engineering 2024, Singapore

Deformation suppression effect of double steel sheet pile method for river levee
on soft ground against mega earthquake
Kentaro Nakai
Associate Professor, Dept. of Civil Engineering, Nagoya University, Nagoya, Japan
Email: nakai@civil.nagoya-u.ac.jp

Toshihiro Noda
Professor, Dept. of Civil Engineering, Nagoya University, Nagoya, Japan

Takahiro Yoshikawa
Assistant Professor, Dept. of Civil Engineering, Nagoya University, Nagoya, Japan

Toshihiro Takaine
GEOASIA Research Society, Nagoya, Japan

ABSTRACTAs there are concerns about the occurrence of a mega earthquake, appropriate earthquake resistance evaluation andseismic countermeasures for river levees are urgent issues. The authors previously investigated the reinforcing effect ofsteel pipe sheet piles placed at the toe of the embankment on a river levee built on an alternating layer of sand and claythat simulates the typical alluvial plains of Japan. Through the result of seismic response analysis, it was shown that if
the sheet pile penetration is shallow to clayey layer, deep slippage that passes through the tip of the sheet pile will occur,
so it is necessary to deepen the penetration to the supporting layer. In this paper, we investigated the effectiveness of the
double steel pipe sheet pile method in which steel pipe sheet piles connected with tie rods are installed on both shouldersof the slope instead of at the toe of the slope, expecting to reinforce the levee body itself. As a result, it was found thatslippage occurring within the clay layer, stretching and subsidence of the embankment were greatly suppressed, and ahigh restraint effect could be expected against large deformations caused by the soft clay layer.
Key words: River levee, Double steel sheet pile method, Sand/clay alternating layer, Seismic response analysis

1. Background

(Noda

at

al.

2008),

incorporating

elasto–plastic

As there are concerns about the occurrence of mega

constitutive equations SYS (Super/subloading Yield

earthquakes such as the Tokyo Metropolitan Earthquake

Surface) Cam-clay model (Asaoka et al., 2002)) toanddescribe sand, intermediate soil, and clay within the sametheearthquake

NankaiTroughresistance

Earthquake,evaluation

appropriate
seismic

theoretical framework. Through the results of seismic

countermeasures for river levees are urgent issues. The

andresponse analysis, it was demonstrated that if the sheet pileauthors have so far studied the behavior of a river levee

penetration is shallow to clayey layer, a deep slippage thatbuilt on alternating layers of thickly deposited soft clay

passes through the tip of the sheet piles will occur, so it isand sand with an N-value of almost zero that simulates thenecessary to deepen the penetration to the supporting layer.

typical alluvial plains of Japan, and the reinforcing effects

In addition, it was demonstrated that if sheet piles areof steel pipe sheet piles placed at the toe of theinstalled on only one side of an embankment, theembankment (Nakai et al., 2017). In this study, we

deformation on the other side will be greater, and evenconducted seismic response analysis using soil-water

greater damage might occur. Moreover, the deformation

coupled finite deformation analysis called GEOASIA

suppression effect of the levee body itself is small, thus if-1-

Proceedings of the 3rd International Conference on Press-in Engineering 2024, Singapore

the levee body is in a loose condition, it is not possible to

The geological structure was a simplified from the

suppress the settlement and lateral deformation of theactual ground, consisting of alternating layers diluvium,

levee body.

alluvial soft clay, and alluvial loose sand from deeper part.

Therefore, in this study, we investigated the

The clay obtained from the boring survey has an N-value

effectiveness of the double steel pipe sheet pile method inof almost zero, and the shear wave velocity Vs is estimatedwhich steel pipe sheet piles connected with tie rods areto be 20 to 40 m/s. After constructing a river levee with ainstalled on both shoulders of the slope instead of the toeheight of 5.0 m and a slope of 1:1, the river channel wasof the slope, expecting to reinforce the levee body itself in

excavated, and the water level of the river was raised toaddition to preventing liquefaction of the foundation

GL + 1.2 m. The width of the embankment crest is 7.0 m

ground.

on the right bank and 14.0 m on the left bank. The
hydraulic boundary is set to zero water pressure so that the

2. Analysis condition

ground surface matches the groundwater level. The

2.1. Finite element mesh and ground condition

bottom and both sides of the mesh are modeled as
undrained conditions. The hydraulic boundary of the

We conducted the following three cases (Table 1)elements on the outside of the embankment gives waterwith reference to previous study.

pressure to the elements according to the height of thewater level. The material constants were determined by

Table 1. Analyses condition
Case 1Case 2
Case 3

No reinforcement

reproducing various mechanical tests of the undisturbed(without sheet piles)

samples using the SYS Cam-clay model. For the initialconditions, the degree of soil skeleton structure (structure,

Reinforced sheet pile with length L = 20 m

overconsolidation, and anisotropy) and initial stress ratio(shallow penetration)

were assumed to be uniform in each layer, and the specificReinforced sheet pile with length L = 23 mvolume was distributed according to the overburden(deep penetration)pressure.

The steel pipe sheet pile was assumed to have an

2.2. Input ground motion

outer diameter of φ = 700 mm and a width of t = 10 mm.

Fig. 2 shows the input seismic motion, which

In Cases 2 and 3, steel pipe sheet piles were inserted fromcomprises the Tokai, Tonankai, and Nankai triple-linked

the slope shoulder after the embankment construction, andseismic waves near Nagoya Port. A simple shear

the pile heads were tied with tie rods. Fig. 1 shows thedeformation boundary with lateral boundary elements was

finite element mesh used in the analysis. The analysis area

set at both ends of the boundary (Noda et al., 2009; Asaoka

is 1.0 km horizontally wide, and this figure is an enlarged

et al., 1998), and a viscous boundary equivalent to Vs =view of the areas near the left and right embankments. The

300 m/s (Noda et al., 2009; Lysmer and Kuhlemeyer,

steel pipe sheet pile was modeled as a one-phase elastic1969) was used at the bottom of the FEM mesh. The

body, and the elastic modulus and density were set to giveseismic waveform was input horizontally simultaneously

equivalent stiffness and weight as actual ones. The tie rod

at all nodes of the bottom boundary.

was expressed using the distance invariant condition of
two finite element nodes at the connection with the sheet
pile (Asaoka et al., 1998).

Fig. 2 Input seismic motion
Fig. 1 Finite element mesh-2-

Proceedings of the 3rd International Conference on Press-in Engineering 2024, Singapore

3. Analysis results

respectively for each case. The same finite element mesh3.1. Reinforcing effect of double steel pipe sheet pile

was used in all cases. Because of the small mesh width at

methodthe assumed sheet pile locations, Case 1 also appears to

Figs. 3 to 5 show the distributions of shear strain,

have sheet piles, but the assumed sheet pile locations areexcess pore water pressure ratio, and degree of structure,

the same soil material as the surrounding area. The degree

Fig.3 Distributions of shear strain

Fig. 4 Distributions of excess pore water pressure ratio-3-Proceedings of the 3rd International Conference on Press-in Engineering 2024, Singapore

Fig.5 Distributions of degree of structure

Fig.6 Amount of settlement at the toe and shoulder of the left bankFig. 7 Amount of horizontal displacement at the toe and shoulder of the left bankof structure is an index that quantitatively expresses theFigs. 6 and 7 show the amount of settlement andbulkiness of the soil skeletal structure. The greater thehorizontal displacement at the toe and shoulder of the leftdegree of structure, the greater the void ratio under thebank, respectively. Since there is no significant difference

same effective stress. Collapse of structure meansin the settlement and horizontal displacement of the

disturbance of the soil, leading to plastic compression.

embankment between the right and left banks, only the-4-Proceedings of the 3rd International Conference on Press-in Engineering 2024, Singapore

results of left bank embankment is shown.

considerations, if the clay is in a soft condition at a highIn the case of no reinforcement (Case 1), arcuate

level of the structure, and especially near areas subject toslippage occurs within the soft clay layer directly beneath

uneven loads such as directly beneath river embankments,

both levee bodies, and it can be seen that the levee bodies

seismic damage can occur even in clay layers that wereare sinking deeply. Since the excess pore water pressurepreviously thought not to cause earthquake damage.

increases (mean effective stress decreases) at the location

Next, we will discuss the reinforcing effect of thewhere slippage occurs, it is clear that the seismic damage

double steel pipe sheet pile method. In both Cases 2 and 3,of the clay layer during an earthquake is caused by thethere is almost no difference in the presence or absence of

decrease in rigidity (the disturbance of soft clay) due topenetrating into the diluvium at the tip of the sheet pile,

repeated shearing. Therefore, the degree of structure at thisand the large deformation caused by liquefaction of thelocation is also significantly lowered. The top of thesand layer and slippage in the clay layer that occurred inembankment sank approximately 2.0 m during theCase 1 is strongly suppressed. The amount of settlement

earthquake and continued to settle approximately 0.6 m

at the shoulder of the levee body is 1.0 m, which isafter the earthquake as the positive excess pore watersuppressed to about 40% compared to the case withoutpressure that accumulated

the earthquake

countermeasures. Moreover, stretching of the toe of thedissipates. Due to the settlement of the embankment, theduringlevee was also suppressed to 1.5m, which was about 43%

riverbed rises, and the river area decreases. In addition, theof that without any measures. In Cases 2 and 3, the excess

slippage of the embankment causes the levee body topore water pressure ratio (Fig. 4) increased during thestretch by approximately 3.5 m. Based on the above

earthquake in the sand layer and clay layer surrounded by

Fig. 8 Temporal changes in the bending moment in the depth direction acting on the sheet piles in Cases 2

Fig. 9 Temporal changes in the bending moment in the depth direction acting on the sheet piles in Cases 3-5-

Proceedings of the 3rd International Conference on Press-in Engineering 2024, Singapore

Fig. 10 Change over time in the tie rod axial force for Cases 2 and 3
sheet piles. This is because significant unloading occurs inpiles, the axial force of tie rods is greater when they arethis region, leading to increase the overconsolidation ratio,

short. This is because the deformation at the bottom of thewhich suppresses the occurrence of plastic deformation

long sheet pile (Case 3), where the tip of the sheet pile isand causes almost no structural disturbance (Fig. 5). One

penetrated into the diluvium, is relatively small. In thisof the important notices is that there is no significant

way, there is an optimal specification depending on the

difference in the effectiveness of preventing deformation

conditions of the ground and sheet piles, and it is also

between the two cases, indicating that deformation can be

influenced by design concepts such as whether or not tosuppressed without penetrating the tip of the sheet pile into

allow yielding of the steel pipe sheet piles.

the diluvium.
4. Concluding remarks
3.2. Bending moment of sheet pile and axial force of

The "Earth Embankment Principles" refers to the ruletie rodthat nothing other than soil should be allowed inside theFigs. 8 and 9 show the temporal changes in theembankment. Therefore, in the past, sheet piles could not

bending moment in the depth direction acting on the sheet

penetrate the embankment body and were instead placed

piles in Cases 2 and 3, respectively. In this analysis, steel

at the toe of the embankment. However, as disasters

pipe sheet piles are modeled using a linear elastic body,

become more severe, durable structures are required, andand the yielding is not taken into consideration. The yield

there are calls for a review of the Earth Embankment

moment of the sheet pile with the specifications set here

Principles. Therefore, this study uses soil-water coupled(φ = 700 mm, t = 10 mm) is 860kN･m. Therefore, it canfinite deformation analysis to propose a double steel sheet

be seen that according to the original specifications, all thepile method, in which steel pipe sheet piles connected withsheet piles would yield near the main shocks. However, if

tie rods are installed on both shoulders of the slope.

the sheet pile of short length (Case 2) is replaced with φ =In river levees on soft ground consisting of

800 mm, t = 20 mm, and the sheet pile of long length

alternating layers of loose sand and soft clay with a small(Case 3) is replaced with φ = 1300 mm, t = 22 mm, theN-value (locations where local loads are applied), inyield moment can be kept below the yield value. In fact,

addition to liquefaction of the sand layer during ansteel pipe sheet piles with such specifications exist. Fig.

earthquake, the stiffness of the clay layer decreases due to

10 shows the change over time in the tie rod axial force

disturbance. The shear slippage caused by the lowering

for Cases 2 and 3. From this figure, a large tensile force iscauses sinking of the levee body and lateral flow, and there

generated in the tie rod to suppress the deformation of theis a risk that the function of the levee will deteriorate

embankment during an earthquake, but it decreases andsignificantly due to a decrease in river area. Although notconverges over time. Although the details are omitted,

mentioned in this study, the natural period of the soft layer

there are tie rods with specifications that can withstandbecomes longer due to the liquefaction of the thickly

this axial force. Also, unlike the bending moment of sheet

deposited soft sand layer and the disturbance of the clay
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Proceedings of the 3rd International Conference on Press-in Engineering 2024, Singapore

layer, resulting in long-term earthquake motion with arather long period component of several seconds to 5
seconds. Resonance with long-period earthquakes will
occur, and the damage will become more serious. Thiskind of ground is often found in sedimentary basins andalluvial plains, including areas below sea level where large
cities are located. However, the specifications of existing
steel pipe sheet piles indicate that this construction method
can be expected to have high earthquake resistance(deformation restraint effect).
In the future, we will continue to model the sheet pile
as an elastoplastic body and conduct systematic analyses
with a view to develop design concepts consideringfactors such as the length of the sheet pile, the size of theembankment, the influence of the stratigraphy of theground, and the impact of repeated earthquakes. Also, it isnecessary to implement it in an actual specific manner.
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embankments

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