Volume 6, Issue 1 March 2021

Reports

IPA Press-in Seminar in Tokyo 2020
(2) TC3 “Expansion of Applicability and Assessment of Seismic
Performance of PFS Method”
Jun Otani
Professor, Kumamoto University
Director, IPA / Chair, TC3

1. Introduction
Annual IPA Press-in Seminar was held on November 30, 2020 and because of the COVID-19, this time of seminar wasorganized by online presentations. TC3 which is the title of “Technical Committee on Expansion of Application Conditions
and Evaluation of Seismic Behavior of PFS (Partial Floating Sheet pile) Method” was asked to organize one of the technicalsessions in this seminar. The basic idea of TC3 session was the presentations of all WG (Working Group) and those are
WG1: Field investigation, WG2: Laboratory test, WG3: Numerical analysis, WG4: Design and WG5: Overseas. At thebeginning of this session, the contents of this session were introduced by the chair of TC3 in which the PFS method asshown in Fig. 1 which is one of the main topics was also introduced. And then, the presentations by the head of each WG
were followed. In this report, those contents are summarized including the final conclusions although the activities ofWG5 was briefly introduced in the presentation by the chair at the beginning of the session.
12Shirakawa, Midorikawa, Hamatogawa and Kasegawa rivers

Construction distance (km)10Soft ground

8Settlement
Seismic
Settlement + Seismic
Shore protection
Seepage64
2

End bearing Sheet pile
01990

Floating Sheet pile

1995

2000

2005

2010

2015

Construction year

Fig. 1. PFS method

Fig. 2. Purpose of countermeasures

2. The contents of the presentations(1) Field investigation WG (WG1) by Prof. Kasama of Tokyo Institute of Technology
In order to evaluate the effect of various steel sheet pile construction methods on the suppression of deformation during
earthquakes, the settlement behavior of river embankments reinforced by steel sheet pile methods under the 2016
Kumamoto earthquake was summarized focusing on the type of steel sheet pile method, shape, location ofcountermeasures (inside and outside of the embankment), and combination of each method. In addition, quantitative
analysis of the settlement of river embankments was carried out focusing on the liquefaction of the embankment and its
foundation soil. Fig.2 shows total number of annual changes on the steel sheet pile methods in Kumamoto with thepurposes of the countermeasures.
(2) Laboratory test WG (WG2) by Prof. Tobita of Kansai University
In order to investigate the seismic performance of PFS method, model shaking tests were conducted at a centrifuge.
Target ground conditions were 1). clayey ground and 2). two layers of loosely packed saturated sand (upper part) and clay
(lower part). Followings are the summary of those two cases:
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Volume 6, Issue 1 March 2021

1)Clayey soil: Although PFS sheet piles are less effective in preventing lateral flow than full-bottomed sheet piles becauseof their lower bending rigidity, they are as effective as full-bottomed sheet piles in reducing the settlement of the top of
the embankment during excitation.
2)Two-layer ground: The lateral displacement of the sheet pile was reduced by about 30% by rooting the lower end of
the floating part of the sheet pile into the clay layer.
(3) Numerical analysis WG (WG3) by Prof. Nakai of Nagoya University
Here, 2-D or 3-D finite element methods were used and the following points was verified numerically:
1) Verification of the effectiveness of the countermeasure for controlling lateral flow during embankment construction
2) Seismic performance verification at the time of an earthquake
Fig. 3 shows the shear strain distribution 10 years after the occurrence of the earthquake (enlarged display around theembankment) along with the amount of subsidence and horizontal displacement at the top of the embankment.
Table 1. Table of contents for design manualFig. 3. Comparison of embankment deformation(4) Design WG (WG4) by Prof. Nishioka of Chuo University
The PFS method is a close construction countermeasuremethod to suppress settlement of the surrounding groundwhere consolidation settlement is more dominant thanhorizontal displacement due to the presence of sandy groundon the surface layer in response to increased load. In the casethat the sandy ground on the surface layer may liquefy, thecountermeasure is necessary. As for the seismic
reinforcement method using steel sheet piles forembankments on liquefied ground, design methods anddevelopment policies have been developed to some extent ineach field under the condition that it is not PFS method (e.g.
Soil Mechanics Laboratory Manual for river embankments). The mission of the WG4 was to revise the design manual sothat it can be easily used for practical design of seismic reinforcement and construction in close proximity. In thispresentation, the basic idea and flow chart of the revised design method was introduced. Table 1 shows the proposed
design manual for the sheet pile method under earthquake.
(5) Conclusions by Dr. Taenaka of Nippon Steel Corporation

At the end of session, the activities by TC3 were concluded and the contents of all the presentations were summarized.
The summaries of all presentations were listed as follows:1) WG1: a) Survey on the actual situation of river bank reinforcement (regions and project results), b) Survey of banksubsidence after the Kumamoto Earthquake

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2) WG2: a) Evaluation of seismic behavior of PFS method in clayey ground, b) Evaluation of seismic behavior of PFS
method in liquefied layer ground3) WG3: a) Investigation of the effect of lateral displacement during raising and its range of application, b) Proposalof 2D analysis model by comparison with 3D analysis, c) Confirmation of the seismic effect of the PFS method bycomparing the methods of no countermeasures, floating, PFS, and end bearing.
4) WG4: a) Introduction of seismic design (liquefaction design) (*Ensure consistency with the 2016 Guide to
Liquefaction Countermeasures for River Embankments), b) Provide information that contributes to technical judgmenton the scope of application.

3. Conclusions
Steel sheet pile method had been used more temporally works but recently, the use as a permanent structure has been
considered. At the same time, PFS method which was originally developed for the countermeasures of ground subsidence
due to river embankment constructions. In addition to those, the effective installation method which is “Press-intechnique” makes it enhanced. Those were the motivation of TC3. We hope that more wide variety of the use of steel
sheet pile including the countermeasure on earthquake are increased from now on.

Reports

Technical assessment on the design and construction method
for rotary press-in pile by Japan Society of Civil Engineers
Mitsuhiro Okada
Engineer, Japan Press-in Association (JPA)
JPA has received a technical assessment for the rotary press-in piling method by theJapan Society of Civil Engineers (Japanese version in 2020, and English translatedversion in 2021).
The assessment was conducted by the Technical Evaluation Committee consisting of
six experts, specializing in earthquakes, ports, roads, railroads, and piles (chair: Prof.
M. Hamada). In this assessment, it was confirmed that the formula for calculating thebearing capacity of rotary press-in piles is on the safe side with respect to the resultsof the vertical and horizontal loading tests.
The rotary press-in piling method has been used in more than 400 projects in Japan,
most of which were for building earth retaining walls. In the future, we would like topropose and expand the application of the piling method to construction projects that
require vertical bearing capacity, such as foundations for roads and bridges.
Please contact us by e-mail for more information.
international@giken.com

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