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S. Shrestha
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Civil Engineering, Building, Construction & Architecture Engineering Transportation

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3D FEM investigation on bending failure mechanism of column inclusion under embankment load S. Shrestha; J.-C. Chai; D. T. Bergado; T. Hino; Y. Kamo
Lowland Technology International Vol 17 No 3, Dec (2015)
Publisher : International Association of Lowland Technology

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Bending failure mechanism of column inclusions in soft clay deposit under embankment loading has been investigated by three dimensional (3D) finite element analyses. Firstly the effectiveness of the numerical procedure has been verified by comparing the simulated and the measured results of a centrifuge model test reported in the literature in terms of lateral displacement, settlement, and the bending moment in the column. Then the effects of the size of the column improved area from the toe toward the center of the embankment, stiffness of the column, the length of the column on the maximum bending moment in the column have been investigated numerically. The numerical results indicate that increase the size of the improved area, reduced the bending moment in the upper part (near ground surface) of the column; increase the stiffness of the column increased the maximum bending moment; and the maximum bending moment occurred at the end of the column in the case of an end bearing column, and in the upper part of the column for a floating column. The numerical results also indicate that when the whole area under the embankment is improved by end bearing columns with an area improvement ratio of 28 % and tensile strength of the column of 100 kN/m2, the embankment load can be applied with a factor of safety of about 2 for bending failure of the columns is about 13 times of the initial undrained shear strength of the soft deposit.
Effect of cations on consolidation and permeability of polymerized bentonite N. Prongmanee; J.C. Chai; S. Shrestha
Lowland Technology International Vol 20 No 3, Dec (2018)
Publisher : International Association of Lowland Technology

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Properties of a novel material “polymerized bentonite (PB)” and a traditional untreated bentonite (UB) were investigated through two series of laboratory tests (i.e., consolidation test and filter press test). Three different test liquids included of deionized water, 0.6 M NaCl and 0.6 M CaCl2 were used in this study. The results of consolidation tests indicated that the compression index (Cc) and swelling index (Cs) decreased, while the coefficient of consolidation (cv) increased with the increasing in concentration and valence of cation in the solutions. Comparison between two materials in the cationic solutions, the PB had higher Cc and Cs value, but it gave lower cv value compared with that of the UB. The results of estimated permeability (kfilter) from the test results of the filter press showed that the PB gave lower values of kfilter for all the test solutions compared with those of the corresponding UB due to the polymer “locked” Na+ ions carried by the bentonite particles and partially prevented it to be replaced by higher cation charge. Based on the results of permeability, it is suggested that the PB can provide better barrier properties against aggressive cationic solutions compared to that of the UB.
Investigation of the safety factor and reliability of the embankment in soil cement column improved ground on Saga lowland Y. Jabeur; S. Manandhar; S. Shrestha; T. Hino; M. Mbodji; T. Himeno
Lowland Technology International Vol 20 No 4, March (2019): Special Issue on: Green Technology for Sustainable Infrastructure Develop
Publisher : International Association of Lowland Technology

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Saga plain constitutes thick deposited soft marine clay which is susceptible for the construction of any civil engineering structures with reference to large and differential settlement problems in the area. This paper presents the case study of the Ariake sea coastal road project failure on Ashikari region in Saga lowland. In this region, the group of soil cement columns as ground improvement technique is adopted for the construction of the highway embankment. The estimation of probability of failure of the embankment on the stabilized soils is approached through the probabilistic analysis for this research. The assessments of total safety factor (Fs) and reliability rely on random variables of geotechnical parameters. These random variables considered for this study are the unit weights of the soil materials (γ) (fill and clay), the undrained shear strength (cu) in the embankment fill material and undrained shear strength of the stabilized soil and soft soil. Furthermore, the paper also delineates judgment of the geotechnical risk assessment based on real site condition.
Study on effects of specimen size of unconfined compressive strength of improved soil T. Himeno; K. Takatani; T. Hino; S. Mandhar; S. Shrestha
Lowland Technology International Vol 20 No 4, March (2019): Special Issue on: Green Technology for Sustainable Infrastructure Develop
Publisher : International Association of Lowland Technology

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Deep mixing method (DMM) is one of the countermeasures for long-term stability of the soft ground area, specifically highly applicable in coastal lowland. With the economic growth in ASEAN countries, this technology has become more popular in order to develop stable infrastructures through mega projects. In this paper, discussions are carried out through conducted laboratory mixing tests by where samples were extracted from the site in order to maintain the quality of soil-cement column by using DMM based on designed methodology. In Japan, samples are extracted continuously from the vertical direction using a thin-walled sampler. It can be connected from considering characteristics of strength development of each depth grouped into three sections from the tube into upper, middle and lower portions. However, the case of non-uniformity and the total amount of sample taken from the site is not enough, there will be the possibility to encounter a difficult situation to conduct laboratory mixing test using standard specimen size of D 50 mm × H 100 mm. Therefore, the characteristics of strengths appeared in the standard size of D 50 mm × H 100 mm laboratory mixing test is compared and discussed with newly defined laboratory test of specimen size D 25 mm × H 50 mm.
Co-Authors D. T. Bergado J.-C. Chai J.C. Chai K. Takatani M. Mbodji N. Prongmanee S. Manandhar S. Mandhar T. Himeno T. Hino Y. Jabeur Y. Kamo