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

Centrifuge Model Tests and Image Analyses of a Levee with Partial Floating
Sheet-pile Method
Daiki HIZEN
Graduate Student, Graduate School of Advanced Technology and Science, Tokushima University, Tokushima, Japan
Email: c501741002@tokushima-u.ac.jp

Naoki KIJIMA
Graduate Student, Graduate School of Advanced Technology and Science, Tokushima University, Tokushima, Japan

Katsutoshi UENO
Associate Professor, Graduate School of Technology, Industrial and Social Sciences, Tokushima University, Tokushima,
Japan
Email: ueno@ce.tokushima-u.ac.jp

ABSTRACTA steel sheet pile is used as a settlement countermeasure method for levees on soft ground. It is expected that settlementof landside ground can be suppressed by penetrating steel sheet piles nearby toe of slope of the levee. In order to improve
the performance of existing two methods, full bottom landing and floating method, the Partial Floating Sheet-pile method(PFS method) was proposed. However, the PFS method has a limited number of experimental studies and construction
examples. Thus, the effect of the PFS method is not well-understood. In this study, a 1/50 scale ground models with levees
and two types of sheet pile walls were built and self-weight consolidation experiments were conducted with and without
the countermeasure using centrifuge apparatus. The objective was to confirm the effect of the PFS method on thesettlement of landside ground and failure mode of the levees. The experimental results showed that the countermeasurecases suppressed the settlement of landside ground more than the non-countermeasure case. It was observed from image
analyses that in the countermeasure cases, relative displacement of clay layer occurred near sheet piles. Continuous shearstrain induced by relative displacement is considered to cause cracks on the slopes of the levees.
Key words: PFS method, centrifuge model test, image analysis

1. Introduction
A steel sheet pile method is used as a countermeasure

to a support layer and the others stop in soft ground wasfor settlement of levees on soft ground. It is expected thatTanabe et al., 2005). Obase (2008) reported pilot

a settlement of landside ground of levees can beconstruction and preliminary analysis of the PFS method

suppressed by penetrating steel sheet piles nearby toe ofand showed its effectiveness as the countermeasure.

slope. There are some types in the steel sheet pile method.

However,

The full bottom landing method that penetrates sheet pile

experimental tests are still limited. Therefore, the level ofto a support layer has high suppression effect, but its

suppression effect of the PFS method is not well-construction cost is high. The floating method that does

understood. Much more research efforts are needed for

not penetrate sheet pile to a support layer has low

practical applications and design guideline.

proposed (Okuda et al., 2005, Miyamoto et al., 2005,

studies of thePFS method

including

suppression effect, but its construction cost is low. As anIn this study, the authors addressed the above

alternative of the two, the Partial Floating Sheet-pileresearch needs by performing a series of experimental

method (PFS method) in which some sheet piles penetratestudies of the PFS method. The experimental models- 215 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

consist of 1/50 scale ground models and two types of sheet

material for model tests.

piles and self-weight consolidation experiments are
conducted using centrifuge apparatus. The objective wasTable 1. Material properties of the support and levee layer

to confirm the effectiveness of the PFS method for thesettlement of landside ground and failure modes. Also,

Soil particle density, 𝜌𝑠this study used image analysis (Ueno et al., 2014) toMaximum void ratio, emax

capture development of strain around sheet piles in a clay

Minimum void ratio, eminlayer. This paper presents details of the experimental

Maximum dry density, 𝜌𝑑𝑚𝑎𝑥

setups, results as well as the applied image analysis.

Optimum moisture content

2. Centrifuge model test

Table 2.

2.1. Soil material(g/cm3)

supportlevee

2.64

2.65

1.02

1.01

0.74

0.42(g/cm3)

1.75
12.0

Material properties of solidified clay

Soil particle density, 𝜌𝑠 (g/cm3)

2.70

The test model consists of three layers, a support

Liquid limit, 𝑤𝐿 (%)

70.1

layer, a clay layer, and a levee. For the support layer

Plastic limit, 𝑤𝑃 (%)

40.4

material, Mikawa silica sand No.3 was used. For the levee,

Plasticity index, 𝐼𝑃

29.7Engineering classificationMH

mixed sand with Mikawa silica sand No.7 and fine sand ofwhose ratio by weight is 8:2 was used. Material properties
are tabulated in Table 1.
Clayey slurry made from a mixture of kaolin clay,

Compression index, 𝐶𝑐
Consolidation yield stress, 𝑝𝑐

0.55(kN/m2)

gypsum and water were poured into soil container after thesheet pile model was installed at the prescribed position.
Gypsum consumes free water in the slurry and solidifies it
in four days due to hydration reaction. This procedureprovides two advantages; the strength can be adjusted bychanging compounding ratio, and the consolidation speed
for preparation become fast.
The mixing ratio and curing period were determinedbased on the results of a series of unconfined compression
test preliminary conducted prior to this study. Finally, themixing ratio with water was set so that material A(gypsum: water = 10:4) and material B (kaolin clay: water= 10:8) were 17:83. Curing period was set to five days.

Fig. 1Results of unconfined compression test

Fig. 2Stress characteristics of 𝑐𝑣 , and 𝑚𝑣

The properties of solidified clay are tabulated inTable 2. The results of unconfined compression test forsolidified clay are shown in Fig. 1. When compressivestrain exceeded 10%, slight strain softening was observed.
The compressive strength only in Case 2 is large, but inother cases it is almost the same. Therefore, it was judgedthat the same degree of clay layer can be prepared eachtime.
Oedometer tests were also conducted, and thepressure characteristics of 𝑐𝑣 and 𝑚𝑣 are shown in Fig.
2. Because 𝑐𝑣 is larger than the lower representative value
200 (cm2/d) of alluvial clay, the consolidation time isconsidered to be shorter. This is another advantage of this- 216 -60.0

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

2.2. Model preparation
The model configuration and measurement points areshown in Fig. 3. The dimensions are shown in the modelscale. The model was 1/50 scale. The test model was built
in a rigid container with the internal dimensions of 450mm
width, 350mm height and 200mm depth.
For the support layer, Mikawa silica sand No.3 wet(a) Top view

with distilled water was damped well to make the ground
50mm high. In the case of installing a sheet pile model, it
was penetrated into the support layer at this stage.
For the clay layer, Kaolin clay, gypsum and water
were mixed thoroughly and run into slurry state andpoured into the container to ensure sufficient groundheight. The entrapped air in the clay layer was removed
using a vibrator. After the above processes werecompleted, wet cloth and lap covered to the model groundso as not to dry. After 4 days passed, the container front
glass was taken up once and colored sand for image(b) Sectional view

analysis were spread. In addition, the ground surface wasFigs. 3(a, b)

Model configuration

shaped so that the prescribed height and the initial height
were measured at 51 points as shown in Figs. 3(a). The
wet density and moisture content of the clay layer were
1.61t/m3 and 70.0% as representative value.
For the levee, mixed sand was compacted in fivelayers with a target of moisture content w=12% and thedegree of compaction Dc=85% on the completed the claylayer. Levee dimensions were 30mm crest width, 65mm(a) Full sheet pileheight, 290mm bottom width and 1:2 slope gradient. AfterFigs. 4(a, b)(b) PFS
Sheet pile models

completion of the levee, the initial height of slope andcrest were measured at 39 points only a part of the levee

Table 3.

as shown in Figs. 3(a).

Case code

The sheet pile models used in the test are shown in

Self-weight consolidation experimental cases
Sheet pile

Position of sheet pile

NCFigs. 4(a, b). A stainless steel plate with 3mm thickness isFull(toe)FullToe of slope

used. Full bottom landing sheet pile and the PFS model

PFS(toe)PFS

Toe of slope

are shown in Figs. 4(a) and Figs. 4(b), respectively. The

Full(1.5m)

Full

1.5m from toe of slope

dimensions are shown in the model scale.

PFS(1.5m)

PFS

1.5m from toe of slope

2.3. Experimental conditions
The self-weight consolidation experimental cases are

was 50g field in all experiments. The centrifuge time wasshown in Table. 3. Five cases were conducted; i.e. non-reaching 50g. In addition, all experiments were conducted

countermeasure (NC), installing a full sheet pile aroundon 5 days from the start of curing.

about 20 minutes before reaching 50g and 60 minutes after

toe of the slope of the levee (Full(toe) and Full(1.5m)) andinstalling the PFS around toe of the slope of the levee

3. Experimental results(PFS(toe) and PFS(1.5m)). Positions of sheet pile are

3.1. Settlements
A side view after experiment in the case of PFS(toe)shown in Figs. 3(a). The applied centrifuge acceleration- 217 -

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

is shown in Fig. 5. As the clay used was entirely whitematerial, colored sand is spread over the side surface ofthe clay using spoon for image analysis. However, thecolored sand and the clay are not completely in close
contact. Clear settlements of levee were observed and thesurface of clay layer was concaved.
Comparisons of the settlements are shown in Figs.
6(a) and 7(a): Figs. 6 for Full(toe) and PFS(toe), while(a) Surface of leveeFigs. 7 for Full(1.5m) and PFS(1.5m). In these figures, theheights above the initial surface of clay layer weremeasured along the center line in Fig. 3(a) after 2,500 hourconsolidation in prototype scale. The heights and locations
are described in prototype scale, here after.
The settlements observed in Full(toe) tend to besmaller values comparing with other cases. Otherwise inFigs. 7(a), those from Full(1.5m) show largest settlements(b) Surface of clay layer

along the riverside slope. However, on the landside ground,Figs. 6(a, b) Settlements (Full(toe) and PFS(toe))the settlements obtained in cases of Full(1.5m) andPFS(1.5m) are clearly smaller than those in NC case.
Comparisons of the settlements of clay layer are
shown in Figs. 6(b) and 7(b). Although the values ofsettlements at the center of the levee were fluctuated, thesettlements on the landside ground are clearly suppressedby sheet pile installation.

Additionally, the surface on

the landside ground is almost parallel to the horizontal line
except the case of NC.

(a) Surface of levee

The results discussed above imply that mostcomponents of settlement on landside ground wereproduced not due to the levee, but due to self-weightconsolidation of clay layer itself during centrifuge loading.
Therefore, it can be concluded that sheet pile installation
is effective to suppress settlement on landside ground andisolate it from the influence of consolidation due to levee.
(b) Surface of clay layer
Figs. 7(a, b)

Settlements (Full(1.5m) and PFS(1.5m))

3.2. Cracks on landside slope
Clear cracks parallel to the edge of the slope wereobserved on landside slope except in the case of NC, as
shown in Figs. 8(a-d).

It can be considered that shear

deformation, which affects levee was developed along theFig. 5

Side view after experiment (PFS(toe))sheet pile because of suppression of settlement by sheet
pile installation.

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

are shown in Figs. 12(a-b). The γ𝑠 observed in the caseof NC distributed symmetrically as shown in Figs. 12(a).
On the other hand, as you can see clearly from Figs. 12(b),simple shear deformation was vertically concentrated
along position of sheet pile if the sheet pile walls exist.
To show typical shear deformation induced by the(a) Full(toe)levee, distributions of maximum shear strain γ𝑚𝑎𝑥 after(b)PFS (toe)1,600 hour consolidation in the case of PFS(toe) are
shown in Fig. 13. It is considered that the development
continuous shear strain induced by relative displacement
is due to the occurrence of cracks in the levees.

(c) Full(1.5m)
Figs. 8(a-d)(d) PFS(1.5m)

Cracks appearing around landside slope

4. Image analysis
Deformations in a clay layer were measured andvisualized by using an image analysis method introducedin Ueno et al. (2014). Simple shear strain γ𝑠 and pureshear strain γ𝑝 are defined as,
𝛾𝑠 = 𝛾𝑥𝑦 =𝜕𝑢𝜕𝑦𝛾𝑝 = 𝜀𝑥 −𝜀𝑦 =+𝜕𝑣

𝜕𝑢𝜕𝑥−Figs. 9(1)𝜕𝑥𝜕𝑣𝜕𝑦Definitions of stress and strain(2)

where 𝑢 and 𝑣 are displacements in x and y coordinates,
respectively. The maximum shear strain can be derived
from γ𝑠 and γ𝑝 by using Eq. 3. The definitions of stressand strain are showed in Fig. 9. The strain circle on Mohr’s
diagram is showed in Fig. 10.
Fig. 10 Strain circle on Mohr’s diagram𝛾𝑚𝑎𝑥 = √𝛾𝑝2 + 𝛾𝑠2(3)

The case of PFS(1.5m) as an example ofdistributions of vertical displacement after about 2500
hours is shown in Fig. 11. Comparing image analysis andexperimental result, the vertical displacement of the clay
layer’s surface after 2,500 hours consolidation wasgenerally consistent. Also, similar tendencies were seen inother cases. Therefore, it is thought that the colored sandmoved together with the clay layer.
Distributions of simple shear strain γ𝑠 in the casesof NC and PFS(toe) after about 1,600 hours consolidation- 219 -Fig. 11

Distribution of vertical displacement (PFS(1.5m))

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

analyses that in the countermeasure cases, relative
displacement occurred near the sheet piles in the clay layer.
Continuous shear strain induced by relative displacement
is considered to cause cracks on the slopes of the levees.
Therefore, shear strain may occurs in the actual levee, but
it is considered that because the clay layer deforms by longtime consolidation, clear cracks have not occurred.
In the future, it is necessary to require the shape ofhighly effectiveness for the PFS method without causing
cracks in the levee. In order to examine crack development(a) NC

factors in detail, verification experiments will be
conducted by changing the condition of the levee as wellas the clay layer.
References
Okuda, Y., Onda, K., Ochiai, H. and Kubo, H. 2005.
Development of New Sheet-Pile Method “PFSMethod” for Soft Ground No. 1 –Summary andDesign Concept–. 40th Proceedings of the Japan
National Conference on Geotechnical Engineering,(b) PFS(toe)Figs. 12(a-b)

pp. 1439-1440. (In Japanese)

Distribution of simple shear strain

Miyamoto, H., Maeda, Y., Otani, J. and Tatsuta, M. 2005.
Development of New Sheet-Pile Method “PFSMethod” for Soft Ground No. 2 –Analysis andExamples–. 40th Proceedings of the Japan National
Conference on Geotechnical Engineering, pp. 14411442. (In Japanese)
Tanabe, Y., Maeda, Y., Yamamoto, Y., Fujio, Y. andNomura, S. 2005. Development of New Sheet-Pile
Fig. 13

Method “PFS-Method” for Soft Ground No. 3 –Distribution of maximum shear strain (PFS(toe))

Application of SBIFT–. 40th Proceedings of the Japan
National Conference on Geotechnical Engineering,

5. Conclusion
In this study, in order to evaluate the effect of the PFS

pp. 1443-1444. (In Japanese)

method, a 1/50 scale ground models with levees and twotypes of sheet pile walls were built and self-weight

Obase, K. 2008. Evaluation of The Countermeasures forconsolidation experiments were conducted with andEmbankment on a Soft Ground –PFS Method andwithout the countermeasure using centrifuge apparatus.

ALiCC method–. Soil mechanics and Foundation

As a result, the values of settlements at the center ofengineering, 56 (9), pp. 18-21. (In Japanese)the levee were fluctuated, the settlements on the landsideground are clearly suppressed by sheet pile installation.

Ueno, K., Sreng, S. and Kobayashi, K. 2014. Surface

Additionally, the surface on the landside ground is almost

Kinematometry

parallel to horizontal line except the in case of non-Geotechnical Model Tests. Physical Modelling incountermeasure. And, it was observed from the image

Geotechnics, Vol. 1, pp. 337-343.

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Processingfor