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

Reactive Measure Effects on River Dyke Instability and Adjacent Residences on
Soft Clay Deposits after the Tohoku-Pacific Ocean Earthquake of 2011
K. YASUHARA
Institute for Global Change Adaptation Science, Ibaraki University, Ibaraki, Japan
Email: Kazuya.yasuhara.0927@vc.ibaraki.ac.jp

X. S. YANG
Construction Technology Research Institute, Saitama, Japan

T. HORIKAWA
Construction Technology Research Institute, Saitama, Japan

H. YAMANE
Construction Technology Research Institute, Saitama, Japan

ABSTRACTThis paper presents case histories of the instability of clay deposits beneath a loose sand layer induced after the Great
East Japan Earthquake in 2011. As a reactive countermeasure against damage of this kind, the upper parts of existing
river dykes were removed. Subsequently, sheet piles were installed immediately after the earthquake at the toes of riverdykes to separate the influences of dyke instability on adjacent residences. Thereafter, the river dykes were returned totheir respective original heights by surcharging the fills for dykes. To confirm the effects of those countermeasures,
numerical analyses were conducted, combining both the computer codes for dynamic analysis of behavior during
earthquakes with the code for static analysis of post-earthquake behavior. Results of numerical analyses agree well withvariations of measurements of settlement with the elapsed time. Results indicate that the reactive countermeasures adopted
herein work well for reducing the instability of river dykes and residences caused by the great earthquake.
Key words: Land subsidence, Earthquake, Clay deposit, Countermeasure

1. Introduction
Land subsidence and ground sinking are(ii) settlement of sandy deposits and subsequentasliquefaction,

and

(iii)

long-term

post-earthquake

remarkable and as extremely destructive phenomena as

settlement in soft clay caused by the dissipation of excess

the gigantic tsunami that struck Tohoku and Kanto inpore pressure. Land subsidence of the latter two categories

Japan after the 2011 Off the Pacific Coast of Tohoku(ii) and (iii) occurs in inland areas, strongly influencing

Earthquake (hereinafter the “Tohoku Earthquake”).

local residents. A difference is apparent between the

Moreover, the mechanisms of both events are complex

settlement mechanisms of both types in the settlement of

because several tectonic, geologic, and geotechnicalcategory (ii), which is related to saturated sandy deposits,

factors induced land subsidence and ground sinking,whereas the settlement in category (iii) is associated withexerting overlapping influences that persist even now, six

saturated clayey deposits. Based on differences among theyears after the earthquake.

causes and mechanisms related to the land subsidence ofRoughly speaking, this land subsidence and groundthree kinds described above, suitable countermeasures

sinking are classifiable into three categories: (i) landagainst subsidence must be taken, corresponding to theirsinking along coastal areas because of tectonic movements

different characteristics.

(Imakiire and Koarai, 2012, Yasuhara and Kazama. 2015),- 233 -

This paper presents a case study of post-earthquake

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

settlement and deformation of clay deposits underlying theriver dykes and their adjacent residences in Ibaraki during
and after the Tohoku earthquake in 2011, including the

3. Earthquake-induced settlement of clay deposits
3.1. Earthquake-induced settlement
Liquefaction-induced settlement of sandy soil deposits

effects of countermeasures which were undertakenceases quickly, but cohesive soil deposit settlement takes

immediately after the earthquake.

a long time to end because of the low hydraulic
2. River dyke and residential damage

conductivity of cohesive soils and the slow dissipation of

2.1. Acceleration waveform

excessively

high

pore

pressure

generated

duringearthquakes (Yasuhara et al., 2001; Yasuhara and Matsuda,

dyke exhibited 6-weak seismic intensity (on the Japanese

2002; Matsuda et al., 2014). It continues from the instantscale) during the Tohoku Off-Pacific Earthquake in 2011,of settlement immediately after the earthquake. Therefore,

as shown in Fig. 1.

earthquake-induced residual settlement of cohesive soil

Acc. Rate (gal.)

The waveform measured 15 km distant from the riverdeposits includes instant settlement (non-time dependent)

200
Maximum acceleration rate: 156.481 gal

and delayed settlement: Fig. 3.

0

-200
0

Fig. 1

30

60

90

120

150

(sec.)210
180

240

270

300

Acceleration waveform measured near the river dyke.

2.2. Damage features of the river dykes and theirvicinity
Damage to the river dyke and the sluice pipe wasremediated soon after the earthquake. However, damage
to residences including cracks in the exterior walls wasrecovered completely or was left for discussion amongresidents and the government because it was not certain
which factors were responsible for increasing damage to

Fig. 3

residences, although settlement and inclination had been

Constitution of earthquake-induced settlement ofstructures on cohesive soils.

observed since the start of river dyke construction, as
explained later in this paper. In any case, long-term

3.2. Geotechnical characteristics of cohesive soil

settlement and deformation are expected to result fromexistence of the thick clay layer underlying the sand layer,

deposits beneath river dykes and private residences
As stated earlier, one case in Ibaraki after the gigantic

having the soil profile shown in Fig. 2.

earthquake of 2011 showed settlement of thick cohesive
soil deposits beneath the river dyke and private residences,
thereby damaging river dykes and many adjacent private
residences. The horizontal profiles of the river dyke andresidential areas portrayed in Fig. 2 show a thick clay layer
with 18 m deposits on the sand layer with higher groundwater level (GWL). The plastic chart for this clay is shownin Fig. 4 in which all plots are located along the A-line.
Therefore, it seems that this clay is not specific to thispoint.
However, according to the summary of index andmechanical properties, this clay is also characterized by

Fig. 2Geological profile of the objective site.

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

the following (Yasuhara & Kazama, 2015).

3.3. Outlines of Settlement of River Dykes andi) Highly sensitive with high liquidity indexii) High water content with high undrained strength

Residences
A set of typical observed settlement vs. time relations

Post-earthquake settlement is expected to result fromfor river dykes and residences continuously before andconsolidation followed by dissipation of excess pore

after the earthquake is presented in Figs. 5 and 6. It ispressures generated by a strong earthquake. The averagenoteworthy that settlement took place and influenced theindex properties of clay are presented in Table 1. It isadjacent residences probably because of a lack of

extremely unusual because characteristic (ii) does notinstallation of countermeasures having been undertaken

make sense from geotechnical perspective, although

along the river dykes. The figures also show that thecharacteristic (i) does make sense. This clay (labeled K-

earthquake occurrence in 2011 accelerated the settlementclay) has high structures of clay particles, which readilyof river dykes and residences.

undergo deformation by disturbance, leading to vertical

4

which was constructed almost 35 years ago. Both clays are
similar: both are highly plastic and become much softer

8
5.0k
1-1
1-2
1-3
1-4
1-5
1-6
1-7
1-8
1-9
1-10

10
12
14
16

with water contents beyond the liquid limit, although it

18

cannot be said that the water content of either clay is very

20
22

high.

20

09

6

/0

20

09

Dyke removal& sheet piling

Settlement monitoring
being suspended

Settlement vs. time curves for river dykes.
Remediation measures

Befo

re e

4

arth

12
01
Converging
02

qua

6

ke

07
06
03
08
05
04
11
10
09

8
No. ofresidences
01
02
03
04
05
06

12
14
16
18
20

1

0

1
7/

07
08
09
10
11
12

1

20

0

1
8/

Fig. 6

2

1
9/
00

1

Tohoku-Pacific Ocean
Earthquake of 2011

Cumulative settlement (cm)

No. ofresidences

2

10

Index properties of clay beneath dykes in Ibaraki

5.0k

6
2 1 6
2
6
2
6
2
6
2
6
/0
/1 /1 /0
/1
/0
/1
/0
/1
/0
/1
/0
10 01011/3011 011 012 012 013 013 014 014 015
20
2 20 2
2
2
2
2
2
2
2
2

0

Table 1.

1-1
Return to theoriginal height2/1

Fig. 5

Fig. 4 Plastic chart of K-clay in the objective site

1-9
1-8
1-7
1-10
1-6
1-5
1-4
1-3
1-2

6

Tohoku-Pacific Ocean
Earthquake of 2011

being deposited near the area of Joban express highway,

Settlement (cm)2

K-clay clay in the objective site in the current study, Table
1 also shows index properties of J-clay for comparison,

Remediation measures0

settlement and lateral deformation. For comparison withA
ea fter
rth
qu

ak

1 1
1
/1 /1 1/1
10 /3
120 2011 20eConverging

20

1

11
2/

2

11
3/
01

20

14

1

/1

Settlement vs. time curves for residences.

As mentioned previously, settlement of cohesive soil
deposits after the earthquake in 2011 was very complex,
but it might be caused by combining the following.
i) land sinking by crustal movementii) time-independent immediate settlement followed bydeformation of upper sand and lower clay deposits,iii) time-dependent settlement of clay deposits followedby dissipation of excess pore pressure generated byearthquakes.

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

This paper addresses issues (ii) and (iii) because itemphasizes an examination of post-earthquake behaviorof clay deposits. The rates of settlement before and after
the earthquake are noticeably different. The settlement has
been exacerbated by earthquakes because of the postearthquake settlement of clay deposits caused by delayed
dissipation of excess pore pressure in clay deposits after
the earthquake. Generally speaking, such settlement takes
a long time to cease. Therefore, engineers and researchers
must ascertain when the rate of residual settlement after
the earthquake becomes negligible for residents not to feelat risk in everyday life.
Since 2007, the governmental office in charge of river(a) April 2009 – August 2011

management in the objective area has been monitoring
variations of settlement, lateral displacement and excess

River side

20 (mm)2014/10/30

the river dykes. Results of settlement monitoring indicate

15

2014/08/27

the following.

10i) Settlement of residences accumulated up to 14 cm for5ii) Settlement increased to around 2 cm immediately after
the earthquake in 2011.

2015/10/22
2016/03/03

2013/10/28
-20

-15

-10

-5

2015/11/19-5
2012/05/31-10

3.4. Lateral displacement observation
Borehole inclinometer installation at river dyke toes

-15
-20

and borehole inclinometer measurements were conducted

5

10

15

20

(mm)

Downstream

the prior six years starting in 2007.

Upstreampore water pressure (EPWP) over time inside and outside

2012/5/31→2013/10/28(before c.)
2013/10/28→2014/8/27(after c.)
2014/8/27→2014/10/30
2014/10/30→2015/10/22
2015/10/22→2015/11/19(abnormal?)2015/11/19→2016/3/3

Residence side

respectively from April 2009 to August 2011 and from
Fig. 7(b) May 2012 – March 2013
Measurement results of lateral displacement

Fig. 8Installation of piezometers in the clay layer.

May 2012 to March 2016.
The monitored results presented in Fig. 7 indicated thefollowing.
i) Inclination at the toes of dykes increased in the directionof residences before the earthquake. It tends to return tothe dyke after the earthquake.
ii) Inclination tends to increase again towards theresidences after the countermeasure execution but its
magnitude is not so severe to influence on the residences.
Judging from the tendencies presented above,
information of inclination monitored at the toe of dykes
proves the effectiveness of the countermeasures adopted
to avoid earthquake influences.
3.5. Results of monitoring excess pore water pressure
Two sets of three piezometers for PWP measurement
were installed in the clay layer beneath dykes andresidences, as shown in Fig. 8.

- 236 -

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

As shown in Fig. 10, it is extremely difficult to predict the(a) PWP at 5.3 km (beneath the dyke)▽Embankment top

behavioral tendency precisely.

▽dyke foot road5

In spite of the present situation, the remaining EPWP,

Embankment
Fc

3.5 kN/m2, beneath the residence is less than that beneath▽GWL TP+1.50m
tic
ta
os
dr re
Hy ssu▽ presecurity to residents.
Ac1

PWP from July 25
to Aug.7,2013

K4-5-1-10
Pw2=26.6kN/m

2

K4-5-2(a) Beneath the dyke

10
8
6
10

Dyke excavation-15
PWP at Aug.8,2013

50

100

150

200

2

-5

-10

250

2

PWP(kN/m )-15(b) PWP at 5.3 km(beneath residences)

10

-20

PWP (kN/m ) (amount in change)

T.P.(m)102

Pw2=15.5kN/m

K4-6-22

Estimated -3.5kN/m
0
-5

-10

-15

2

PWP at Aug.8,2013
Pw3=18.7kN/m-15

K4-6-3

2

-20
Ac3
Ds1
Dc1

0

-20

Hydrostatic pressure
PWP from July 25 to Aug.7,2013
PWP at Aug.8,2013
50

Ground surface of residences

5

PWP from July 25
to Aug.7,2013

K4-6-1

-10

-25

8
7
6
5

T.P.-7.5m

Ac1

EPWP
2
Pw1= 1.8kN/m

Ac2

Height (m)

tic
ta
os
dr re
Hy ssu
▽ pre

As1

-5

Sheet pile installation

Location of piezometerK4-5-1:T.P.- 7.5m
K4-5-2:T.P.-12.5m
K4-5-3:T.P.-17.5m(b) Beneath residences

Fc▽GWL TP+2.00m
02

Estimated 12.5kN/m

-25
1
5
9
3
7
0
4
7
1
7
/11/0 013/11/1 013/11/2 013/12/1 013/12/2 014/01/1 014/01/2 014/02/0 014/02/2 014/03/0
2013
2
2
2
2
2
2
2
2
2

▽Ground surface of residence

5(With nomeasurement)

100

150
2

200

T.P.-12.5m

T.P.-17.5m

Dec. 400Initial value at Nov.1, 2013

-25

Hydrostatic pressure
PWP from July 25 to Aug.7,2013
PWP at Aug.8,2013

Dec. 4PWP (kN/m ) (amount in change)

K4-5-3

Initial value at Nov.1, 2013

2

-20
Ac3
Ds1
Dc1

Sheet piling close
to piezometer

5

Pw3=30.4kN/m

Excavation of pilingJan. 23

EPWP
2
Pw1= 5.7kN/mJan. 16

T.P.(m)-5

Ac2

the river dyke. This result must give some sense of

As1

Height (m)0Sheet pile installation

Jan. 23

10

Location of piezometer
K4-6-1:TP- 7.5m
K4-6-2:TP-12.5m
K4-6-3:TP-17.5m

-25
1
5
9
3
7
0
4
7
1
7
/11/0 013/11/1 013/11/2 013/12/1 013/12/2 014/01/1 014/01/2 014/02/0 014/02/2 014/03/0
2013
2
2
2
2
2
2
2
2
2

250

PWP(kN/m )Fig. 10 Variations of EPWP after the countermeasures.

Fig. 9 Variations of EPWP distribution with time at thelocation beneath the dyke and residence

4. Countermeasure damage-mitigation effects

Fig. 9 presents an example of a set of the results of
EPWP distribution and its variation with time from July
25 through August 8, 2013 at locations beneath the dyke
and the residence. Fig. 9 shows that the EPWP at both sites
remains after the earthquake but that the one beneath theresidence is smaller than the other beneath the dyke
although both remaining EPWPs tend to dissipate
gradually throughout the clay layer, producing residual
settlement at both sites.
Actually, however, EPWP behavior, particularly after
the earthquake and installation of the countermeasures
which will be described in the next chapter, is complicated.

The following countermeasures were used to prevent
effects of river dykes on post-earthquake settlement ofresidences (Fig. 11).
i) Remove 2.2 m of dykes to reduce dyke self-weight.
ii) Thereafter, install sheet piles aside from the river dykes
into the hard stratus, called Ac3 layers, to intercept theeffects of river dyke self-weight on residences.
iii) Return the dyke height to the original height with 4.1
m.
As might be readily apparent from the results
depicted in Fig. 5 and Fig. 6, the following behavior wasobserved after installing the countermeasures stated above.

- 237 -

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

dimensional FEM analysis using computer code called
Analysis for Liquefaction-induced Deformation (ALID).
Using the seismic wave motion being measured under 500
m depth from the surface at a location 15 km distant fromthe river dyke with 6-weak seismic intensity during the
Tohoku Off-Pacific Earthquake in 2011, as shown
previously in Fig. 1, one-dimensional seismic response
analysis was conducted.

Fig. 11 Remedial measures from damage induced byearthquake.

i) Remaining EPWP in subsoils both outside and inside thedykes became less than that before partial dyke removal.
ii) Installation of sheet piles is associated with increased
ground settlement beneath the dykes, but does not increase
settlement of the ground outside the dykes. In other words,
ground settlement beneath the residences might decrease.
iii) Filling dykes again to their original height did notincrease ground settlement of residences because of theintercept of stress distribution of dykes to residential
ground.
As a summary of the tendencies described above, thecountermeasures adopted herein have been effective forFig. 12 Flow chart of numerical analysis.

reducing post-earthquake settlement of residences near theriver dykes. Furthermore, as described later, lateral

The surface wave obtained from this analysis was

displacement does not tend to increase towards the

input into ALID as the seismic motion. For these analyses,

residences. However, continuous settlement monitoringa Cam-clay model was adopted for predicting the excess

should be done because groundwater abstraction effects

pore pressures in Ac2 generated during the earthquake.
As the second stage, the elasto-viscoplastic two-on continuous settlement of residential areas remain

dimensional FEM analysis using the computer code called

uncertain.

Deformation Analysis Considering Stress Anisotropy and5. Numerical analysis

Reorientation (DACSAR) incorporating the Sekiguchi–

5.1. Analytical procedures

Ohta model (Sekiguchi and Ohta, 1977; Iizuka & Ohta,

To reproduce the behavior of dykes and their adjacent

1987) was conducted to estimate settlement of river dykes

residences continuously from before to after theand residences caused by dissipation of EPWP calculated

earthquake, numerical analysis using two-dimensional

using DACSAR.

FEM was performed. The analytical flow is shown in Fig.
5.2. Additional parameters necessary for numerical12.
pressures and their distribution in the subsoils under the

analysis
Additional parameters necessary for numericalself-weight of dykes were determined from the two-

analysis using DACSAR are summarized below.

As the first stage for analysis, the excess pore- 238 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi- Coefficient of consolidation cv: 0.046 (m2/day)- Coefficient volume compressibility mv: 1.38 × e-03
(m2/kN) calculated using the relation,
mv=3λ/{(1+eo)(1+2Ko) × σ’vo}(a) Immediately

after(b) In 6 yr later(2017/4)

earthquake04- Coefficient of hydraulic conductivity k :6.20 × e(m/day)- Coefficient of secondary compression, α: 7.45 × e-03
- Initial volumetric strain rate, v0 (v0=α/t): 1.21 × e-06
(1/day)5.3. Post-earthquake settlement and pore pressure
As results of numerical analysis, calculated(c) 30 yr later (2041/4)
Fig. 15 Variations of distribution of EPWP withsettlement and excess pore pressures are shown in Fig. 13

elapsed timeand Fig. 14. It can be indicated from both figures thati) Instant settlement of dykes was approximately 2 cm
which is not large but lateral heaving was observedii) EPWP was concentrated beneath the center of dykes
Settlement up to app. 2 cm

Fig. 13

Fig. 14

Settlement of dykes after earthquake.

Distribution of EPWP generated by the earthquake.

Fig. 16

The EPWPs generated during the earthquake showni) The predicted total settlement of river dykes will be

in Fig. 13 were input as initial EPWP values into
prediction of their variations in river dykes with elapsed
time using DACSAR. The calculation results are shown in
Fig. 15 as distribution of EPWP against depth of riverdykes. Particularly, results show that EPWP in thick clay
layers generated during the earthquake tend to dissipate
gradually and return to the original hydraulically static

greater than 90 cm for the next 30 yr.
ii) Settlement must persist for more than 30 yr. In addition,
Fig. 16 (b) expanding the settlement vs. time relation
during the 6 months after the earthquake indicates that thecalculated settlement reaches 57.4 cm in 6 months after theearthquake, which is approximately four times themeasured one as 14.8 cm.

condition, but the maximum EPWP is generated directly
beneath the river dyke.
Calculated settlement at the slope shoulder of the rear
river is shown in Fig. 16 for comparison with thosemeasured. Fig. 16 demonstrates the following.

Calculated and measured settlement variations overtime.

Compression index, Cc, and secondary compression
coefficient, C used for numerical analysis were obtained
from odometer tests on undisturbed samples of Ac2 layers.
It should be emphasized that the coefficient of secondary
compression, C, for Ac2 in K-clay is 0.026 and the ratio,- 239 -

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

C/Cc, is 0.024 in which both are normal in comparison
with typical clays in Japan (i.e., Yasuhara and Ue, 1983).

although the government started monitoring ten years ago

According to comparison of calculated variations ofFig. 18 and Fig. 19 present a family of calculated

settlement with elapsed time with the measured one aslateral displacement and inclination angle and settlement

shown in Fig. 16, there is no good agreement with both.

as a function of time elapsed from earthquake occurrence.

Here, parameters related to long-term settlement of Ac2

Here, inclination angle  is defined as shown in Fig. 20.

in response to resident requests.

the measured variations of settlement with time. The result
calculated using the modified values of two parameters in

T.P.(m)clay were re-determined using back analysis to adapt to12
8
4

Excisted dyke Additional dyke Residence0

In this case, good agreement exists between both
calculated and simultaneously measured variations ofsettlement over time, indicating that long-term settlementof river dykes will continue, even for 30 yr.

Settlement(cm)the following way is shown in Fig. 17.

θ =

7

1000
At April, 2016
At April, 2016
One year later2 yrs. later3 yrs. later
At April, 2016

20
40

θ =

60

16
1000

5 yrs. later
10 yrs. later
20 yrs. later
30 yrs. later (at April, 2046)

80

100
120
-40

-20

0

20

40

Fig. 19 Variations of inclination angle with elapsed time.

Fig. 17

Recalculated and measured settlement variation overtime.

5.4. Calculated results of lateral displacement

Fig. 20

Inclination angle.

Fig. 18 and Fig. 19 present the following.
i) Lateral displacement tends to increase inland or at
housing sites over time, which is similar to the measured
tendencies in Fig. 7.
ii) The magnitude of displacement is not large: less than 3
Fig. 18

Calculated lateral displacement at the ground surface.

Lateral displacement during and after an earthquake
most strongly affects residents living near river dykes

cm.
5.5. Evaluation of countermeasure effects
5.5.1. Countermeasure effects on settlement
Effects of countermeasures as shown in Fig. 11 were

because earthquakes can show high lateral displacement,

evaluated using the FE analysis. Fig. 21 presents- 240 -

(m)
60

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

variations of settlement at the toes of banks at 30 yr after

suggesting that the countermeasures undertaken after thethe earthquake. The parameters used for calculation were

earthquake work particularly well for reducing damage infoundresidences adjacent to the river dykes.

using

results

ofbackcalculation

fromcurves with and without the countermeasures. Comparison
between the curves shows their differences and clarifies
effects of countermeasures on reducing dyke settlement,
particularly after the earthquake.

Lateral disp. (cm) T.P.(m)measurements. Results are divided into two calculated
12
8
4

Dyke
Location of sheet pile
Without
With } Within Ac2

2
0

Without
With } Within Ac1

-2
-4
-15

0

15

30

45

(m)
75

60

Depth of soil at each distanceT.P.(m)

10
5

As1

With

-5
-10

Without

Ac2

-15
-20
Ds

-25

Ac3
Dc

-30
-35

Fig. 21B

0-6 -3 0 3 6 -6 -3 0 3 6 -6 -3 0 3 6 -6 -3 0 3 6 -6 -3 0 3 6

Lateral displacement (cm)Calculated and measured settlement.
Fig. 23

Lateral displacement against subsoil depth.

5.5.2. Countermeasure effects on lateral displacement
In the same manner as that in the settlement
computation,

thecalculated

variationsoflateraldisplacement over time with and without countermeasures
are presented in Fig. 22, divided into two cases at the toeof the river rear and the center of residences. It is indicatedfrom the results in Fig. 22 that the effects ofcountermeasures on reduction are also clear in thesecurves.
T.P.(m)5

Laterl displacement(cm)

15

-60
3
2
1
0
-1
-2
3
2
1
0
-1
-2

①

10

②

H.W.L

3

2011/0Location of sheet pile
-30

0

30

60

(m)
90

① Lateral displacement at toe of liver rear
Without sheet pilingWith sheet pilingFig. 24

Calculated EPWP variations over time beneath dykes.

② Lateral displacement at center of residence
Without sheet pilingWith sheet piling5.5.3. Countermeasure effects on excess pore water

3
3
3
3
3
3
3
2016/0 2021/0 2026/0 2031/0 2036/0 2041/0 2046/0(y/m)

pressure
Successive to the computation of settlement andFig.22 Calculated results of lateral displacement at dykes andlateral displacement, computation of the variations ofresidences with and without sheet pile installation.

EPWPs with elapsed time was also conducted for threedepths

The same trend was observed in Fig. 23 which shows
the distribution of lateral displacement towards the depth

of

clay

soil

layerswithandwithout

countermeasures. Among them, Fig. 24 presents two cases
beneath the dyke and the residence.

of clay layers with and without countermeasures,- 241 -

Regarding EPWP behavior of in two locations, theProceedings of the First International Conference on Press-in Engineering 2018, Kochi

countermeasure effects differ. That is, the larger EPWPFY2019,remains beneath the residence even 30 yr after the

representative is Kazuya Yasuhara, Professor Emeritus of

Project

No.

16H02362),

Japan,

whose

earthquake, but the smaller EPWP remains beneath the

Ibaraki University, Japan.

center of dykes. This persistence suggests that we should
devote attention to the residual settlement of residences

References

caused by dissipation of the larger EPWP remaining

Iizuka, A. and Ohta, H. 1987. A determination procedure of input

beneath the residence, although this tendency is notparameters in elasto-viscoplastic finite element analysis.

consistent with the measured settlement, as shown in Fig.

Soils and Foundations, Vol. 27, No. 3, 71-87.

6, which tends to converge at the present situation in 2015.

Sekiguchi, H. and Ohta, H. 1977. Induced anisotropy and timedependency in clays. Proc. Ninth ICSMFE, Specialty

6. Conclusion
The paper presents a description of our specificexaminationofpost-earthquake

settlement

Session 9, Tokyo, pp.229-238.
Yasuda, S., Yoshida, N., Adachi, K., Kiku, H., Gose, S. andand

Masuda, T. 1999. A simplified evaluation method for

deformation of clay layers beneath river dykes and theirevaluating lateral flow and subsequent liquefaction.

adjacent residences observed at some locations in the

J.JSCE, 638/III-49, pp. 71-89. (in Japanese)

Kanto regions, as derived from a case history from thisYasuhara, K. and Ue, S. 1883. Increase in undrained

category of settlement in Ibaraki. After the earthquake instrength due to secondary compression. Soils and2011, the MLIT adopted combined countermeasures byFoundations, Vol. 23, No. 4, pp. 50-64.

which a part of the dykes (1.5 m among 6.0 m in total) was

Yasuhara, K., Murakami, S., Toyota, N. and Hyde, A. F. L. 2001.

removed initially. Then sheet piles were installed at the

Settlement in fine-grained soils under cyclic loading. Soils

toes of dykes. Thereafter, the dykes were returned to theand Foundations, J. of JGS, Vol. 41, No. 6, pp. 25-36.

original height by surcharging. Investigations andYasuhara, K. and Kazama, M. 2015. Land subsidence of clay

numerical analyses of the case history suggest thedeposits after the Tohoku-Pacific Ocean Earthquake

following points.

(Keynote Lecture). Proc. IAHS, 372, pp. 211-216,

i) The combined countermeasures have worked effectively

doi:10.5194/piahs-372-211-2015.

for reducing settlement and deformation not only in riverdykes but also their adjacent residences founded on clay
deposits.
ii) Numerical analysis using two computer programs
suggests that countermeasures are beneficial for reducing
dyke and residence settlement and lateral displacement on
clay deposits.
iii) Careful attention must be devoted to the fact that such
settlement and deformation are time-dependent. Therefore,monitoring of settlement and EPWP should continue for along period.
7. Acknowledgements
Our great appreciation is extended to the Hitachi
River and Road Office, Kanto Branch, the Ministry ofLand, Infrastructure and Transport, which provided
important information for this case study. The authors arealso grateful for financial support from a Grant-in-Aid for
Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology (FY2016–- 242 -