Volume 2, Issue 3 September 2017

ReportA new steel sheet-pile method for countermeasures against
the settlement of embankment on soft ground-Development of PFS MethodProf. Jun Otani
Kumamoto University, Japan
1. Introduction
When the embankment is constructedon soft ground, the ground subsidence
for not only the ground under theembankment but also the ones aroundembankment are serious problems andsome countermeasures have to beconsidered. A steel sheet-pile method is
one of the countermeasures for thisproblem as shown in Figure 1. However,this type of structure has a cost problem
when the area and depth of soft groundare wider and deeper, so that a new
sheet-pile method has been expected.
In 1975, a collaborative research started between Kyushu
University and the Ministry of Construction (Ministry ofLand, Infrastructure, Transportation and Tourism at present)in Japan. Under this collaboration, a series of in-situ full scale
tests were conducted in Kyushu area. Based on thoseactivities, a research committee for developing a new sheetpile method was established in 2003 (the chair is Prof.
Hidetoshi Ochiai, Professor Emeritus of Kyushu University,Japan). In 2005, a new sheet-pile method called PFS method(Partial Floating Sheet-pile) was proposed under theactivities of this committee. In this method, the end bearing
sheet-pile and that of floating type were combined to deal
with its effectiveness and cost as shown in Figure 2. Figure 3
shows the details of this structure. In this report, this PFS
method is briefly introduced.

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Volume 2, Issue 3 September 2017

2. Performance of PFS method at the site
As mentioned before, a large number of in-situ
full scale tests were conducted in Kumamoto
City, Japan. This area is well known as a region ofAriake Clay which is a highly sensitive clay and its
depth is up to 40m. Figure 4 shows the soil
profile at the site of in-situ test for PFS method.
In this case, one end bearing sheet-pile for fivefloating sheet piles were constructed. Figure 5
shows the results of measurement for thesettlements at the site and as easily realized, theeffectiveness of the PFS method is clearly shown.
Photograph 1 shows the view of the site after
PFS construction. Since a large volume of sheetpile materials were reduced, the cost of the PFS
method is obvious and the construction time isalso highly reduced because of the less volumeof the sheet-piles.

3. Numerical Modeling
A series of numerical modeling was conducted. Here, becauseof the shape of PFS method, three dimensional FE analysis wasconducted as a consolidation problem. Figure 6 shows the 3D
mesh for this analysis and the results such as total settlement
and pore water pressure change in ac.1 layer as shown in Figure
4 were compared with the measurement results as shown inFigure 7.

Figure 7 Simplified design model9Volume 2, Issue 3 September 2017

4. Design Procedure
Under the activities of the research committee of the new sheet-pile, a simple design method was proposed in 2007 andthis idea is shown in Figure 8 which is the combination of spring with beam elements. The basic idea is the considerationof only vertical displacement.
5. Closing Remarks
A summary of the development of PFS method was briefly introduced. The quantification of this method was also doneby in-situ test and numerical modeling, and to design this method, a simple model was proposed.
However, as shown in Photograph 2, sheet-pile method has been used for more and more for the permanent structures,
so that the upgrading of the method is indispensable such as the behavior under earthquake. The potential of liquefactionis also the one for checking at the site. Under those circumstances, IPA has recently started a technical committee for thesteel sheet-pie (TC-3) and within three years (2017-2019), a total of 20 members around the world joined this committee
to discuss what we have to do for upgrading the PFS method.
Finally, I would like to give my acknowledge to all the researchers and engineers who joined the development of PFS
method such as the research committee members in 2003 including the members from the Ministry of Land,
Infrastructure, Transportation and Tourism, and the members of Japanese Association for Steel Pipe Piles.

GIKEN LTD.

Photograph 2 Recent sheet-pile method◆ A brief CV of Prof. Jun Otani
Prof. Jun Otani is a full Professor of Geotechnical Engineering at Kumamoto University, Japanand he is the immediate past Vice President of the Japan Geotechnical Society. He is also theDirector of IPA and chair of TC-3 (sheet-pile). He got his master at Nagoya University, Japanand moved to U.S.A. for Ph.D. study. He got his Ph.D. at the University of Houston, TX in 1990.
His research was pile foundations as his Ph.D. study and later, he has done many research
activities on soil reinforcement. In fact, he was the organizing committee chair of the 15th AsianRegional Conference on Soil Mechanics and Geotechnical Engineering under ISSMGE in 2015.
Recently, he deeply involves the research on the application of X-ray CT in geotechnicalengineering. He established the international society called IntACT and plays a role of the Vice
President.

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