Volume 8, Issue 3

September 2023

Young Members

Introduction of Recent Initiatives and Bidirectional Cyclic
Simple Shear Apparatus on Research of Liquefaction
Atsushi Mohri
Researcher, Port and Airport Research InstituteNational Institute of Maritime, Port and Aviation Technology
I completed my doctoral program at the Department of Civil Engineering, Graduate School ofTokyo University of Science in March 2022. My research theme from the master's course
onwards is about piles, and I had an opportunity to make a presentation at ICPE2018, Kochi, andICPE2021, Kochi, while I was in school. In particular, since ICPE2018 was the first international
conference for me, it was a memorable experience for me to get a real sense of overseas
research situations.
As the theme of my doctoral program, I conducted model experiments on the behavior ofground reaction forces acting on passive piles, targeting the piles used in the steel pipe pile-typebreakwater reinforcement method. In this construction method, by installing steel pipe piles ina row on the inner port side of the breakwater, it could be expected that the passive resistancereceived from the ground on the port side when the piles are displaced should have a reinforcing
effect. Since various pile deformation modes could be considered depending on the distribution of the external force
acting on the pile, it was necessary to investigate the behavior of the ground reaction force under different deformation
modes. Based on the experimental results, I attempted to show this behavior in terms of the magnitude and depth
distribution of ground reaction coefficients. However, I thought that the analysis method that examines the differencesin ground shear modes (simple shear, compression/extension, rotation) at the ground element level might be moreappropriate for such phenomena, so I am currently preparing to implement this theme.
I joined the Port and Airport Research Institute last year. The research themes so far have focused on: (1) the effect ofseismic reinforcement of existing coastal parapet levees using high-stiffness sheet pile walls by means of a threedimensional underwater shaking table, and, (2) the liquefaction test focusing on the effects of shear direction and shear
history by using a Bidirectional cyclic simple shear testing apparatus.
In the first research on the seismic reinforcement effect of seawalls, as shown in the Fig. 1, I focus on a structure wherea high-stiffness sheet pile wall is to be newly installed on the front side of the parapet, which is a coastal protection facility,
and the front side of the ground is to be improved. In this structure, the lower end of the newly installed sheet pile wall
is located in the liquefaction layer. Therefore, I am conducting model experiments and a validity check of the analysis
model to confirm its subsidence behavior.

Fig. 1. Cross section of the seawall seismic reinforcement24Volume 8, Issue 3

September 2023

In the second study on liquefaction, I am using a bidirectional cyclic simple shear apparatus, developed by Dr. Yudai Aoyagi(currently affiliated with the Public Works Research Institute) shown in Photo 1. This test equipment is designed so thatthe bottom cap under the specimen can move freely in the horizontal plane under back pressure and confining pressure.
Moreover, instead of using conventional methods such as wire-reinforced membrane or stacked rigid rings for the K0
condition of the specimen, it adopts a cell pressure-controlled method, which enables detailed examination of the stressstate of the specimen. By using the test equipment with these characteristics, I am investigating the effects of multidirectional and irregular seismic motions on liquefaction and re-liquefaction strength. In addition, by further improving
this test equipment, I would like to utilize it for my research on the resistance behavior of the ground around piles
subjected to horizontal forces at the ground element level.

Photo 1. Bidirectional cyclic simple shear apparatus

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Volume 8, Issue 3

September 2023

Young Members

Revised Empirical Method for Predicting the Ultimate Bearing
Capacity of Concrete Driven Piles Based on the PDA Results
Kong Sotheara
Instructor, Faculty of Georesources and Geotechnical Engineering
Institute of Technology of Cambodia (ITC)
Deep foundation systems consisting of precast concrete driven piles are commonly used in
Cambodia due to the often-challenging geotechnical conditions underlying most project sites.
Numerous searchers have proposed empirical methods to predict the ultimate bearing capacityof concrete driven piles based on correlations with in-situ tests such as the Standard
Penetration Test (SPT), Cone Penetration Test (CPT), and Pressure Meter Test (PMT) and pileload test results. One of the most widely used empirical methods in Cambodia is that proposed
by De Court (1982, 1995), which takes into account both the soil type and method of installation.
In De Court’s method, the shaft resistance for a pile with perimeter Pi in a soil layer with a SPT
N-value of Ni and thickness of Δzi is given by the relationship:
fs = (AN + BN⋅Ni ) Pi Δzi
For displacement piles, AN = 10 and BN = 2.8, while for non-displacement piles, AN ranges between 5 to 6 and BN rangesbetween 1.4 to 1.7. The base resistance for a pile with a cross-sectional area of Ab in De Court’s method is given by therelationship:qb = (CN Nb ) Ab
where Nb is the average SPT N-value within the effective depth of influence below the pile base which is often taken tobe 3 pile diameters. Values of CN for different soil types and methods of installation are summarized in the Table 1.
Table 1. 𝑪𝑵 Factor for Base Resistance
NonDisplacement
Soil TypeDisplacement
Pile
Piles
Sand
325
165
Sandy Silt205
115
Clayey Silt
165
100
Clay10080
In this study, the correlation between the shaft and base resistance estimated using De Court’s Method with estimatesobtained from CAPWAP Analysis of High-strain Dynamic Pile PDA Tests performed on driven concrete piles in Cambodia
and the Philippines investigated. The number of sites, piles and boreholes used in this is summarized in Table 2.
DataSource
Cambodia
Philippine

Table 2. Summary of Data SetPile Type
Regular Concrete Driven Pile
(Dia. 0.3 x 0.3 & 0.4 x 0.4)
Spun pile(Outside Dia. 0.35)
Regular Concrete Driven Pile
(Dia. 0.4 x 0.4, 0.45 x 0.45 & 0.5 x 0.5)

26SitesNumberPiles

Boreholes

62315

11343159

Volume 8, Issue 3

September 2023

For De Court’s Method, SPT N-values were normalized to an overburden of 1 ton/ft2 and an efficiency 60%. The resulting
adjusted SPT value N1,60 was used in subsequent calculations used to estimate the side and end resistance using De Court’sMethod. The analysis of correlation used a linear regression with an assumed zero intercept. Table 3 summarizes the ratioof the estimate based on the PDA test results versus the theoretical estimates based on SPT N-values using De Court’s
Method, and the corresponding Coefficient of Correlation R2.

DataSource

Cambodia
Philippines

Table 3. Summary of Ratios and Coefficients of Correlations
Ratio and Coefficient of Correlation
qb (PDA)
Qult (PDA)
fs (PDA)
Pile Typeq(SPT)
Qult (SPT)
fs (SPT)b22
R
R2
R
Regular Concrete Driven Pile
2.08470.98461.7607(Dia. 0.3 x 0.3 & 0.4 x 0.4)
0.705
0.79750.8400Spun pile1.54040.3231
1.038(Outside Dia. 0.35)
0.97810.8764
0.9796
Regular Concrete Driven Pile
1.141
1.0093
1.137(Dia. 0.4 x 0.4, 0.45 x 0.45 & 0.5 x 0.5)
0.97730.89600.9773

The ratios summarized in the preceding table can be used to estimate the equivalent PDA side resistance, end resistance,
and total axial capacity of driven piles. In all cases, the correlation coefficient was greater than 0.7. The regression model
generally tended to slightly underpredict the equivalent PDA resistance based on the theoretical resistance estimatedfrom De Court’s Method. Based on the results of this study, it can be concluded that De Court’s Method can be used toestimate the equivalent side resistance, end resistance, and total axial capacity of regular concrete piles driven in thePhilippines. For Regular concrete piles driven in Cambodia, De Court’s Method tended to accurately estimate theequivalent PDA end resistance while underestimating the side resistance by a factor of 0.5. For Spun piles driven inCambodia, De Court’s Method tended to overpredict the PDA end resistance by a factor of 3.0 while overestimating theside resistance by 0.67. The overprediction of the end resistance of spun piles can be attributed to the assumption thatthe pile tip is closed and thus treated as a displacement pile despite it being open at the start of driving. One explanation
for the difference between piles driven in the Philippines and Cambodia concerning the factor for side resistance is thatin the Philippines, the practice is to proof-test the pile to double the design load. In contrast, in Cambodia, piles are
generally tested to three times the design load.

◆ A brief CV of Mr. Kong Sotheara

Kong Sotheara is an Instructor at the Faculty of Georesources and Geotechnical Engineering, Institute of Technology ofCambodia (ITC). He is also a student in the MS Civil Engineering (Geotechnical Engineering) Program of the University of
the Philippines Diliman. His areas of expertise are in the general area of pile foundations and stability of MSE Walls. He
graduated with an Engineer’s degree in Georesources and Geotechnical Engineering, Faculty of Georesources andGeotechnical Engineering (GGE) from Institute of Technology of Cambodia (ITC).

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