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

Reinforcement of River Embankment against the Nankai Trough Earthquake
Kojiro OKABAYASHI
Professor Department of civil engineering Kochi National College of Technology, Kochi, Japan
Email: oka@ce.kochi-ct.ac.jp

Youhi NAKAZAWA
Student Department of civil engineering Kochi National College of Technology, Kochi, Japan
Email: z4828@gm.kochi-ct.jp

Masashi OKA
Student Department of civil engineering Kochi National College of Technology, Kochi, Japan
Email: z4907@gm.kochi-ct.jp

ABSTRACTIn the Great East Japan Earthquake of 2011, many river embankments were damaged by strong seismic waves. After theearthquake, tsunami spilled over damaged embankments. In the river levee, back covering coatings were damaged due
to settlement of fill by the earthquake motions or liquefaction, and back covering coatings and fill soils flowed out
backrush. As a reinforcement method for river banks, a construction method of placing sheet piles in the embankment
wall body is being studied for the purpose of maintaining the function of the levee at the time of an earthquake or flood.
The occurrence of the Nankai Trough earthquake is expected in Kochi Prefecture, and the prefecture is proceeding withcountermeasures under the idea of triple protection. Especially reinforcement of river embankments is an important issue
in disaster prevention and reduction. In the past, with respect to various reinforcement methods in river embankment,
dynamic centrifugal model experiments and behavior by effective stress method are being verified. In this study, we
conducted a model experiment of double wall sheet piles on shoulder of cut-off wall method. In addition, modelexperiments were also conducted on a floating structure that keeps embedded depth of sheet piles in the liquefaction layerand shorten embedded depth for the purpose of cost rationalization of the present construction method. Furthermore, therelationship with the dominant period of the earthquake was also investigated for these experiments.
Key words: liquefaction, seismic response analysis, dynamic centrifugal force model experimentof magnitude 9.0 class may also occur. The Nankai Trough1. Introduction
On March 11, 2011, the Tohoku district Pacific

Earthquake is expected to occur at a probability of 70%

offshore earthquake of magnitude 9.0 occurred. Due towithin the next 30 years (Kochi Prefecture, 2017). In orderthislarge-scale

to minimize the damage from the Nankai Troughembankment damages occurred simultaneously in many

earthquake,inTohoku

district,

Earthquake, it is necessary to take countermeasures forplaces, embankments did not work. Particularly, theliquefaction.

damage from the tsunami increased around the Abukuma

In this research, we will investigate the liquefaction

River and Natori River (Sendai River National Highway

countermeasure work against the earthquake of Level 1Office, 2017). In addition, most of the damage to the(which occurs at a frequency of about once every several

embankments were caused by liquefaction, and many

decades to several hundred years and causes great

embankments subsided by liquefaction.

damage). We also investigate the predominant period of

In Kochi prefecture, the Nankai Trough earthquake

the seismic waves, which depends on the embedded depth- 203 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochiof the sheet piles.
For the research method, effective stress analysis
method LIQCA and dynamic centrifuge were used. We
compared the results of the experiment and the analysis.
We also confirmed the liquefaction behavior andexamined the effectiveness of countermeasures.
Fig. 3

2. Research case

Model3: Sheet piles are embedded to thebase layer

In this study, three models were considered:Embankment model (Fig. 1), a model in which sheet piles
were inserted to the mid-depth of the liquefaction layer(Fig. 2), and a model in which sheet piles were inserted tothe base layer (Fig. 3). They are called model 1, model 2,and model 3, respectively. Model 2 is a case where no load
is transmitted from the sheet pile to the base layer (calledfloating foundation). The dimensions shown in Fig. 1 areprototype size. Silica sand No. 5 with Dr = 90% was used
for the base layer. Toyoura sand with Dr = 50% was used
for the liquefaction layer. Silica sand No. 7 with Dr = 95%

2.1. Input seismic wave
For the seismic waves, the acceleration required toliquefy the experimental soil layer was calculated basedon the simplified judgment method of the road bridge
specification (Japan Road Association, 2012).
Fig. 4 shows the seismic waves used in the analysis.
In the centrifuge model test, from the similarity rule, theacceleration was set to 80m/s2 (40times) and the period
was set to 0.067 sec (1/40).

Acceleration (m/s2)

was used for embankment.

1.8

Period ;2.66 (sec)
Duration ; 53.33 (sec)Maximum acceleration ; 217 (gal)

1.2
0.6
0-0.6
-1.2
-1.8
０

16
16

32

48

64

8096

112

128 144160

Time(s)Fig. 4

Input seismic wave (prototype scale)

3. Liquefaction analysis
Fig. 1Model1: Embankment ground model

3.1. Analysis method
The analysis model was prepared with AUTOCAD
and analyzed using the effective stress analysis method
program LIQCA.
3.2. Analysis modelFig. 5 shows the half section of the analytical model.
For the analytical model, the width of the analytical model
has been made sufficiently wide so that there is no
influence of the propagation of the seismic wave on theFig. 2

Model2: Sheet piles are inserted to center

lateral boundary. The drainage boundary was designatedof the liquefaction layer

as the surface of Toyoura sand.
3.3. Material parameters
In this research, material parameters were set with- 204 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

reference to the simulation analysis of the centrifugalmodel experiments by Saito (2018). The parameters areshown in Table 1 and Table 2.
Table 3 shows the physical properties of the sheet
pile wall. As the material constant of the sheet pile, thevalue of the aluminum plate used in the centrifugal force
model experiment was used.
Table 3.

properties of the sheet pile wall

Analysis
ExperimentFig. 5Analysis model

Ｓｈｅｅｔ ｐｉｌｅ ｗａｌｌ

Model 2

７．０３×107

Model 3

Table 1.

E (KN/ｍ2)

A (ｍ2 )

Ｉ(ｍ4) ρ

0.19

0.37

0.29

1.24(ｇ/ｃｍ３)
2.69

Parameters for Dynamic Analysis
Embankment

Silica sandToyoura sand(Dr = 50%)

Toyoura sand(Dr = 70%)

Wet unit volume weight (γ t)15.758(kN/m³)

16.17(kN/m³)

14.484(kN/m³)

15.06(kN/m³)

Saturated unit volume weight (γ sat)
Effective soil covering pressure
Static earth pressure coefficient
Nondimensional initial shear coefficient
Initial gap ratio (e₀)
Compression exponent (λ)
Swelling index (k)Pseudo-consolidation ratioDilatancy factor (D₀)
Dilatancy factor (n)Water permeability coefficient / unit volume of water
Bulk elastic modulus of waterTransformation stress ratio (Mm)
Fracture stress ratio (Mf)
Parameter (B₀) in hardening function
Parameter (B₁) in hardening function
Parameter (Cf) in hardening function
Anisotropic loss parameter (Cd)
Plasticity reference strain (γP * r)
Elastic reference strain (γE * r)

18.7(kN/m³)0(kN/m²)
0873
0.856
0.018
0.006
15
1.5

19.845(kN/m³)0(kN/m²)
01043
0.6
0.025

18.774(kN/m³)0(kN/m²)
0910
0.791
0.003918.8(kN/m³)0(kN/m²)
01040.9
0.718
0.00392.0×10-4
119

2.2×10-4
10.5
5

2.2×10-4
1.5
0.75
7

8.67×10-5（m/sec/kN/m³）
2000000(kN/m²)
0.909
1.122
2200
30
0
2000
0.005
0.01

1.0×10-3（m/sec/kN/m³）
2000000(kN/m²)
0.909
1.551
5000
60
0
2000
0.01
0.2

1.0×10-4（m/sec/kN/m³）
2000000(kN/m²)
0.909
1.229
3500
60
02000
0.003
0.006

1.0×10-4（m/sec/kN/m³）
2000000(kN/m²)
0.8171.245
5185.7
1000
2000
0.005
0.02

Table 2.

Parameters for Static Analysis

Embankment

Silica sandToyoura sand (Dr = 50%)

Toyoura sand (Dr = 70%)

Wet unit volume weight (γ t)15.758(kN/m³)

16.17(kN/m³)

14.484(kN/m³)

15.06(kN/m³)

Saturated unit volume weight (γ sat)

18.7(kN/m³)

19.845(kN/m³)

18.774(kN/m³)

18.8(kN/m³)

0.333

0.333

0.333

0.333

1.0×10-8(kN/m²)
13494.07
10(kN/m²)
31.3(deg)

1.0×10-8(kN/m²)
11210.610(kN/m²)
42(deg)1.0×10-8(kN/m²)
12775.2
10(kN/m²)
37.75(deg)

1.0×10-8(kN/m²)
12775.2
10(kN/m²)
37.75(deg)Poisson's ratio
Effective soil covering pressure
Static earth pressure coefficient
Proportionality coefficient of Young's modulus (E0)Constant (n)Adhesive force
Internal friction angle

shows the excess pore water pressure ratio of 0, and the3.4. Analysis result
Fig. 6 and Fig. 7 show the excess pore water pressure

red color shows the excess pore water pressure ratio of 1.0.

ratio distribution map after the earthquake. The blue color

As shown in Fig. 6, complete liquefaction did not- 205 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

occur under embankment. However, due to the rise of

Seismic accelerometers and piezometers were installed atexcess pore water pressure, the deformation of the2 cm, 6 cm and 10 cm depth from the ground surface.

embankment top, the slope and the horizontal ground near
the embankment becomes larger.

Fig. 6

Table 4 shows the ground condition of the centrifuge
experiment.

Analysis results of model 2Fig. 8
Table 4.

Fig. 7Analysis results of model 3

As shown in Fig. 7, although the deformation wasExperimental model

Grand condition of Centrifuge Experiment

Embankment（Silica Sand No. 7）
Liquefaction layer（Toyoura sand）
Dr＝50％
Basement layer（Silica Sand No. 5）

Wet unit weight(kN/m³)

Saturated unit weight(kN/m³)

15.76

18.7

14.48

18.77

16.17

19.85

slightly smaller in Model 3, the behaviors of liquefaction
were almost the same for each model.

4.2. Experimental method
Photo 2 shows a photograph before the experiment

4. Liquefaction experiment by dynamic centrifuge

of a model in which the sheet pile is inserted to the mid-4.1. Conditions of experiment
Liquefaction experiments were carried out using acentrifuge of Kochi National College of Technology.
Photo 1 shows the dynamic centrifuge .

depth of the liquefaction layer (model 2).
As mentioned earlier, the foundation layer was madeof silica sand No. 5, and the liquefaction layer was madewith Toyoura sand. The base layer and the liquefaction

The experiments were carried out in a centrifugal
force field of 40 g. As shown in Fig. 8, the model size waslayer were saturated with a methyl cellulose solution
having a viscosity 40 times that of water.

set to a scale of 1/40 of the actual size (Figs. 1 to 3).

Photo 1.

Dynamic centrifuge of Kochi National College

Photo 2.

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Soil layer of model 2 before experimentProceedings of the First International Conference on Press-in Engineering 2018, Kochi

Silica sand No. 7 was used as the filling material.
The embankment was made by freezing with a hardaluminum form, thawed and placed on the liquefaction
layer before the experiment.
4.3. Experimental result
Photo 3 shows a photograph after the experimentof model 2. Both of the embankment, and the liquefaction
layer (Toyoura sand) subsided 3 mm. As the embankment
settled the water level rose about 7 mm.
Fig. 9

Excess pore water pressure (10 cm) ofmodel 2 (model scale)mPhoto 3.

Soil layer of model 2 after experimentFig. 10 Excess pore water pressure (10 cm) ofmodel 3 (model scale)

The effective stress is 65.9 kPa for both models. In
the model 2, pore water pressure uw (35.4 kPa) + excess
pore water pressure = 41.1 kPa.
In the model 3, pore water pressure uw (38.2 kPa) +excess pore water pressure = 44.0 kPa.
Both models have not yet been completely liquefied.
Moreover, it can be seen that excessive pore water
Photo 4.

Soil layer of model 3 after experimentpressure is increased by preventing pore water pressure
dissipation in model 3 in which the sheet piles are inserted

Photo 4 shows a post-experimental picture of modelto the base layer.

3 with sheet piles inserted to the base layer. The
embankment settled about 2 mm. The liquefaction layer

4.3.2.

has slightly settled.

Dominant period

Fig. 11 shows the earthquake Fourier spectrum of themodel 2, and Fig. 12 shows the earthquake Fourier

4.3.1.

spectrum of the model 3. As shown in Fig. 11, in model 2,Excess pore water pressure

Fig. 9 shows the change of excess pore water pressure

the velocity response spectrum exceeded at a frequency ofat the installation depth of 10 cm of piezometer for model

10.5 Hz. The predominant period is 0.095 s, and on the2. Fig. 10 shows a similar figure for model 3. The effective

prototype scale it is 40 times and it is 3.85 seconds.

stress is 65.9 kPa for both models.

Likewise, as shown in Fig. 12, the model 3 has a
predominant period of about 1.81 seconds.

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

12Table 5.

Comparison of settlement (model scale)

Fourier spectrum (cm/s)

10Settlement of levee crown
Analysis
Experiment

864
200

102030Frequency (Hz)405060Embankment model（model 1)

15.2mm5mm

Sheet piles are inserted tocenter of the liquefaction layer(model 2)

19.6mm3mm

Sheet piles were inserted to thebase layer (model 3)

12.7mm2mm

Frequency (Hz)Fig. 11 Earthquake Fourier spectrum of model 2 (modelIn the experiment, since the experiment is carried outscale)with the model container, it is considered that the lateral

12flow was suppressed by the restraint of the side wall of theFourier spectrum (cm/s)

10model. Moreover, it can be inferred that thawing of

8embankment was insufficient and subsidence became

6small.

46. Conclusion
From the comparison of the effective stress analysis

2001020Frequency30(Hz)405060and the centrifugal force model experiment, the following

Frequency (Hz)were found.

Fig. 12 Earthquake Fourier spectrum of model 3(1) Excess pore water pressure ratio almost agreed(model scale)with analysis and experiment. It can be reproduced byThat is, in the model 2, the predominant period has
doubled. This indicates that resonance phenomena can besetting the material parameters by the result of element
simulation etc.

avoided by changing the predominant period according to(2) The displacement was small in the experimental

the type of embankment and the natural period of thevalue. It is necessary to consider the influence of lateralstructure on the embankment.

restraint by the container and embankment freezing.
(3) The penetration depth of the sheet pile influences

5. Comparison of analysis result and experiment result

the dissipation of pore water pressure and dominant period.

5.1. Excess pore water pressure ratio
In the analysis results of model 2 and model 3, the(4) Furthermore, we think that it is necessary toconsider countermeasures method with improvement.

excess pore water pressure ratio just under theembankment did not reach 1.0, and perfect liquefactiondid not occur. Also in the experimental results, the excess
pore water pressure ratio did not reach 1.0 and perfectliquefaction did not occur. From this, it is considered thatconsistency between the analysis result and theexperiment result is sufficient for the excess pore waterpressure ratio.

References
Kochi Prefecture. 2017,3. Preparing for the Nankai
Trough Earthquake.
Japan Road Association. 2012. Specifications for
Highway bridges, Part V Seismic Design, pp. 132137.
Saito, K. 2016. Simulation analysis of centrifuge model
test using liquefaction analysis program LIQCA.
Shikoku branch of Geotechnical Society, The 16th

5.2. Deformation

earthquake disaster prevention research committee,

Table 5 shows the comparison of settlement. In theexperiments, deformation of the embankment andReport.
Sendai River National Highway Office. 2017. Damaged

movement of the sheet pile were hardly observed, butthese were confirmed in the analysis.

condition due to the Great East Japan Earthquake, MLIT
Tohoku Regional Development Bureau.

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