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

Seismic Behavior of the River Embankment Improved with the Steel SheetPiling Method
Shuhei YAMAMOTO
Department of Civil and Structural Engineering, Graduate School of Engineering, Kyushu University, Japan
Email: heihei.kendo@gmail.com

Kiyonobu KASAMA
Division of Civil and Structural Engineering, Faculty of Engineering, Kyushu University, Japan

Makoto OHNO
Kyushu Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism, JapanYou TANABEOYO corporation, JapanABSTRACT
In recent years, the steel sheet piling method is used as a countermeasure against soft ground for the purpose of reducing
the subsidence of the surrounding ground and lateral displacement. Among them, the partial floating steel sheet piling
method (called “the PFS method”) constructs a stress blocking wall by alternately placing short-length floating steel
sheet piles and long-length conventional steel sheet piles, and is a new construction method to decrease settlement of theembankment side. In addition, it is possible to decrease the subsidence of the ground around the embankment, and it isexcellent in terms of workability and economy 1). This method has been applied as a subsidence countermeasure for riverembankments in Kumamoto Prefecture, Japan. However, in April 2016, a massive earthquake occurred in Kumamoto
prefecture that recorded a maximum magnitude of 7.3, causing damage such as subsidence in the embankment of therivers in Kumamoto plain where the PFS method was used. From these backgrounds, the objective of this paper is toreport the damage of river embankment caused by the 2016 Kumamoto earthquake and to evaluate the effectiveness ofsteel sheet pile structure including the PFS method as an earthquake countermeasure.
Key words: the PFS method, river embankment, steel sheet piles, earthquake, subsidence

1. Outline of the project

2016, a massive earthquake occurred in Kumamoto

1.1. Place
The objective place are the rivers flowting into thePrefecture that recorded a maximum magnitude of 7.3,

Ariake Sea in Kumamoto plain in Kumamoto Prefecture,these rivers where the PFS method was used. From these

Japan. Among them, settlement due to the 2016

backgrounds, the objective of this paper is to report theKumamoto earthquake was observed especially in thedamage of river embankment by the 2016 Kumamoto

river embankment of the four rivers, the Kase River, theearthquake and to evaluate the effectiveness of steel sheet

Shira River, the Hamado River and the Midori River.

pile structure including the PFS method as an earthquake

causing damage such as subsidence in the embankment ofcountermeasure.
1.2. Background and objectives of the project
The measure applied to the ground subsidence issue

2. Piling methodof the four rivers is the PFS method which is steel sheet

2.1. Piling methodpiling method in the river embankment. However, in April- 227 -One of the methods for preventing groundProceedings of the First International Conference on Press-in Engineering 2018, Kochi

deformation of river embankments on soft ground is thesteel sheet piling method. In this construction method, theFloating
sheet pile

tip of the steel sheet pile penetrates into the support layer
under the weak layer and closes the side of theembankment, for the purpose of preventing the basal
destruction of the main body of the embankment andSoft layer

displacement toward the outside of the legs of theembankment 2).

Support layer

In the steel sheet piling method, there are different
shapes such as the floating steel sheet piling method
Fig. 1(called “the FS method”) and the conventional steel sheet

The FS methodpiling method (called “the CS method”), the PFS method
combining the conventional sheet pile and the floating
sheet pile.

Conventional
sheet pile

Information such as shaped features of eachpiling method as exemplified in Fig. 1 to Fig. 4.
Since the FS method does not penetrate into thesupport layer, construction costs are low, however theSoft layer

effect of suppressing ground deformation is low. Althoughthe CS method penetrates into the support layer, theSupport layer

ground deformation suppression effect is excellent,however the construction cost is high. The PFS method
Fig. 2has an excellent effect of suppressing ground deformation

The CS methodby alternately placing the floating sheet pile and theconventional sheet pile, and is excellent in terms ofFloatingsheet pile

workability and economical efficiency.
2.2. Piling typeIn the countermeasure work, not only the shape of theSoft layer

steel sheet pile but also the construction position of thesteel sheet pile and the kind of countermeasure arechanged depending on the object to be countermeasured.
A countermeasureforgroundsubsidence(calledSupport layer“subsidence countermeasure”) is applied on the riverFig. 3

Conventional
sheet pile

The PFS method

backside to block the transmission of subsidence to thenearby ground3). A countermeasure for earthquake(“earthquake countermeasure”) is applied on the river

Embankment

Floating
sheet pile

front side to prevent slippage and settlement of the riverembankment itself. Fig. 5 shows the relationship between
the CS length of countermeasures H1 and the FS length ofcountermeasures H2. The straight line in the figure shows
the approximate line of the plot data, and the black line,Soft layer

the pink line and the orange line indicate subsidence

Conventional
sheet pilecountermeasure, subsidence & earthquake and earthquake
countermeasure. As can be seen from the figure, thesubsidence countermeasure and the earthquake counter- 228 -Fig. 4

Shape schematic of the PFS method

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

measure are in a linear relationship in which the FS length40

increases as the CS length increases. There is no clear

35

correlation in subsidence & earthquake countermeasure.
countermeasureislongerthantheearthquake

countermeasure the CS length and the FS length.

30
FS length H2(m)In addition, it can be seen that the subsidence

Subsidence countermeasure
Subsidence & Earthquake
Earthquake countermeasure
Sheet pile seawall
Ground improvement

25
20
15
10

2.3. Countermeasure working position
Fig. 6 shows the location of countermeasures in each5

river in the Kumamoto plain (the Kase River, the Shira0y = 4.3178 + 0.60514x R= 0.52186
y = 23.635 - 0.036564x R= 0.03995
y = 0.91401 + 0.46593x R= 0.99924

01020

River, the Hamado River and the Midori River).

30405060

CS length H1(m)Countermeasure working position indicates the river table
Fig. 5inside the river levee and countermeasure behind the river

Relationship between CS length and FS length

outside. The Kumamoto plain has a shallow depth and thealluvial sandy soil layer by the reclaimed land widely

the result of settlement amount measured by the Ministry

distributed.

ofLand,InfrastructureandTransport'sin riverembankment. The amount of settlement is measured at the200 m pitch of the levee.

3. Analysis of settlement amount3.1. Layout
Table 1 shows the shape of each countermeasure andThe Sira RiverAriakeSea

The Kase River

The Midori River
TheHamadoRiverFig. 6

The FS method
The PFS method
The CS method
Without

Countermeasure working placement position in the Kumamoto plain- 229 -

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

3.2. Probability density

Table 1.

Fig. 7 shows the probability density distribution ofThe shape of countermeasure and settlement amountA ll d ata

settlement amount by countermeasures. From the figures,
it can be seen that the settlement amount in embankments
without countermeasure is distributed over a wide range,
whereas the settlement amount of each countermeasure

S ettlem en t

W ith ou t

FS

P FSCSm eth odm eth odm eth od

P oin ts

788

548

53

164

23

A verage

0.199

0.201

0.193

0.207

0.106

M od e

0.210

0.210

0.150

0.170

0.100

S tan d ard

am ou n t

d eviation

0.206

0.238

0.072

0.107

0.065(m)M in im u m-1.184-1.184

0.060

0.008

-0.070range of 0.1 to 0.4 m, the FS method is 86%, the PFS

M axim u m

1.658

1.658

0.360

0.490

0.230

method and the CS method is 96%, and the settlement

M easu red istan ce

142166110903

5566

23582

2115

---

37.9

32.5

worker concentrates in the range of 0.1 to 0.4 m. In theamount is suppressed almost by 0.4 m by theC on ven tion alA veragecountermeasure work. Focusing on the mode, the FS

sh eet p ile H 1S tan d ard(m)d eviation

---

6.83

7.68

F loatin g

A verage--

15.7

24.8

-

sh eet p ile H 2

S tan d ard
d eviation

--

4.38

6.60

-(m)

S h eet sh eet

A verage

--

-

0.653

-

len gth ratio

S tan d ard

H 2/H 1d eviation

---

0.132

-

method and the PFS method were 39% and 46% in therange of 0.2 to 0.3 m, and 57% in the range of 0.1 to 0.2m, which is the smallest CS method.
3.3. Settlement amount range
Fig. 8 shows the range of settlement amount by
countermeasures by percentile plot. This encloses 90% of60

the population of settlement amount, 95% and 5% aboveand below the box, 75% and 25% for the upper and theline .As shown in the figure, with regard to the averagevalue, the settlement amount of the CS method is thesmallest at 0.106 m, and the unsupervised and the FS
method, the PFS method was about the same as theProbability density (%)

lower broken lines in the box, and 50% for the middle

Without
FS method
PFS method
CS method

5040302010

settlement amount around 0.2 m. Focusing on the width ofthe box, the CS method has the smallest variation, and then0-0.2 -0.1

the FS method, the PFS method, no countermeasure

00.1

0.2

0.3

0.4

0.5

0.6

0.7

Settlement amount (m)becomes large. Focusing on the upper and the lower

Fig. 7 Probability density function by countermeasure

broken line ranges in the box, since the PFS method islocated below the box, the settlement amount also
concentrates downward. For that reason, it is the PFS

2method that includes the maximum value of settlement

Maximam value

subsidence amount is larger than the FS method in termsof distribution of the settlement amount. In addition, since
the maximum settlement amount without countermeasureis 1.66 m, the countermeasure work is suppressed to lessthan 0.5 m, so the effect of the ground deformation

Settlement amount range(m)amount in countermeasures, but it can be said that thesuppression of the countermeasure worker appears
remarkably.

1.5

Box top and bottom：95%, 5%Dashed line top and bottom in the box：75%, 25%Center line：50%

10.5
0-0.5
All data

3.4. Average settlement amount by countermeasures

Fig. 8Fig. 9 shows the average settlement amount for eachriver countermeasure. As can be seen from the figure, in- 230 -Without

FS method

PFS method

Settlement amount range

CS method

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

the Kase River, the Hamado River and the Midori River,
the CS method has the smallest settlement amount, thenWithout
FS method
PFS method
CS mothod

0.3

and the settlement amount increased. On the other hand,in the Shira River, the PFS method has the largest settlingamount, and shows the smallest settlement amountwithout countermeasure. It is thought that this was
influenced by the ground property of each river.

Average settlement amount(m)the PFS method, the FS method, without countermeasure
0.25
0.2
0.15
0.1
0.05

3.5. Pile length ratio and settlement amount0Fig. 10 shows the relationship between the pile

Kase River

Sira River

length ratio and the settlement amount. We consider theground suppression effect from the shape of the pile sheet

Fig. 9length and the kind of countermeasures in the PFS method

Hamado RiverRiverMidori River

Average settlement amount by countermeasuresby using the index obtained by dividing the FS length H 2
0.5

by the CS length H 1 as the pile length ratio. As can beseen from the figure, the pile length ratio is 0.4 to 0.7 for

Subsidence countermeasure
Subsidence & Earthquake
Earthquake countermeasure

0.4
Settlement amount (m)countermeasures against sinking and about 0.85 forearthquake countermeasure, and the countermeasureagainst settlement has a big difference between the CS
length and the FS length. This is considered to be due tothe fact that the countermeasure against settlement was

0.3
0.2
0.1

applied in thick sections of the soft ground layer, so that
the CS length penetrating into the support layer became

00longer than the earthquake countermeasure. In addition,

0.2

0.4

0.6

0.8

FS length H / CS length H1
2

most of the settlement amount is less than 0.3 m, and there

Fig. 10are no clear difference in the settlement amount depending

Relationship between pile length ratio
and settlement amounton the type of countermeasure.
smallest 0.1 m.
4) Although it is not clearly understood that the4. Concluding remarks
The embankment reinforcement method using steel

effectiveness of the PFS method is superior to othersheet piles are examined for the effect of suppressing

construction methods, it is necessary to consider theground deformation at the time of earthquake and thegeology at the countermeasure construction site.

findings obtained are described below.
1) Regarding settlement of river levees caused by the5. Acknowledgements

Kumamoto earthquake in 2016, the maximum value ofThis research is proceeding while receiving various

each countermeasure was no more than 0.5 m. Maximum

opinions from "the Technical Committee on Expansion ofeffect for reducing deformation was 71 % compared with

Applicablesection provided no countermeasures

Association PFS Method and Evaluation of Earthquake

2) As for frequency of the settlement, their range was
between 0.1 m and 0.4 m. 86 %, 96 % and 96 % of theConditionsofInternational

PressingBehavior". We would like to express our sincere gratitude
to everyone concerned.

amount of settlement provided the FS method, the PFS
method and the CS method were in the range respectively.

References

3) Comparing with average value of settlement

1) Ochiai, H. 2006. Countermeasure against soft groundamount in each countermeasure, the CS method is thesubsidence by new-style steel sheet piling method and- 231 -1

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

performance design: PFS method, foundation work,
vol. 34, No. 6, pp. 88-91.
2) Kimizu, M. 2010. Three-dimensional Numerical
Analysis on the Effect of PFS Method as Measures toPrevent Emergent Settlement. The 65th Annual
Academic Lecture by the Japan Society of Civil
Engineers, III-240, pp. 479-480.
3) Nomura, S. 2004. Development of a new type steel
sheet piling method for measures against groundsubsidence Part 1. 39th Geotechnical Researchpresentation, pp. 1269-1270.

- 232 -