EC Leong | Nanyang Technological University (original) (raw)

Papers by EC Leong

Environmental geotechnics, Jan 12, 2024

International Journal of Geotechnical Engineering

PanAm Unsaturated Soils 2017, 2018

Engineering Geology, 2021

Abstract Electrical resistivity tomography, ERT, is a geophysical method that is used to image su... more Abstract Electrical resistivity tomography, ERT, is a geophysical method that is used to image subsurface geomaterials for various geological, environmental and geotechnical engineering problems. The success of ERT depends on the availability of a robust electrical resistivity model of soils that is able to characterise the different type of soils using its electrical resistivity measurements. The aim of this paper is to present an electrical resistivity/conductivity model for isotropic saturated sand/clay mixture that considers the effects of sand content, and surface conduction of clay content. The proposed model is formulated using a modified series-parallel mixing model theory which uses phase-volumetric and surface conduction model parameters. The phase-volumetric parmeters describe the configuration of the different soil/water phases in a representative soil unit cell which includes solid soil particles, free water, diffuse double layer (DDL) water. The surface conduction model parameters are used to describe the volume fraction of DDL water in the unit cell, and its electrical conductivity compared to the electrical conductivity of free water. Simple test methods are used in this study to determine the proposed model parameters. Laboratory experimental programme was also conducted in this study to validate the proposed model. Two types of clays, namely, kaolin and bentonite, and one type of clean sand were used to constitute five different sand/clay and clay/clay mixtures. Dynamic compaction method using Standard Proctor tools was used to constitute the testing samples. The electrical conductivities of different reconstituted soil samples were measured and compared with the proposed model predictions, and a good agreement was achieved. The small differences between the model predictions and the experimental measurements could be attributed to the slight deviation of the laboratory test samples from the model assumptions, which require the soil sample to fulfil fully saturated and electrical isotropy conditions.

Geosynthetics International, 2020

This study aims to assess the effect of pore water salinity (sodium chloride (NaCL) solution) on ... more This study aims to assess the effect of pore water salinity (sodium chloride (NaCL) solution) on the consolidation behaviour of GCLs (geosynthetic clay liners) using one-dimensional oedometer test apparatus. The experiments include two testing conditions: (1) an investigation of mechanical consolidation of GCL specimens saturated with water having different salinity levels, and (2) an investigation of the effect of pore water salinity on the volume change of GCL specimens under different constant vertical stress levels (i.e. osmotic consolidation). The mechanical consolidation test results indicated that the compression and swelling indices decrease as the liquid salinity increases, whereas an elastic hysteresis volume change behaviour was observed in the osmotic consolidation test results. The results of this study also show that the compression and swelling indices, and the hydraulic conductivity of a GCL specimen are almost reversible when it is subjected to an osmotic cycle.

Applied Clay Science, 2018

The aim of this study is to investigate the evolution of electrical resistivity of different kaol... more The aim of this study is to investigate the evolution of electrical resistivity of different kaolinite-dominant clay liners, in terms of its soil composition, as its moisture content and dry density change. Eight different mixtures of Kaolin-Bentonite (90%K-10%B; 80%K-20%B; 70%K-30%B; 60%K-40%B), and Kaolin-Sand (90%K-10%S; 80%K-20%S; 70%K-30%S; 60%K-40%S) were tested in this study. Artificial Neural Network, ANN, method was used to develop an electrical resistivity model using the experimental results. The developed model offers the required level of generalization to analyse and assess precisely the effects of different variables on the electrical resistivity of kaolinite-dominant clay liners. The outcomes of this study highlight the effects of water content, soil composition, and dry density on the electrical resistivity of soils. The results in this study show that, at low water content, the adsorbed water and interparticle contacts provide continuous pathways for electrical flow through the soil. Furthermore, the results also indicate that increasing the bentonite content in the mixture decreases its electrical resistivity whereas increasing the sand content increases its electrical resistivity. This behaviour could be attributed to the highest surface conduction of bentonite clay compared to sand. For the soil mixtures tested in this study, the results also show that increasing the dry density of the soil by 20% could result in 50% reduction in its electrical resistivity. This behaviour could be explained in terms of the expected increase in number and area of interparticle contacts as dry density increases that could also improve soil pore water connectivity.

International Journal of Impact Engineering, 2007

International Journal for Numerical and Analytical Methods in Geomechanics, 1994

Rock socketed piles have a number of features which differentiate them from other types of piles.... more Rock socketed piles have a number of features which differentiate them from other types of piles. The generally stubby geometry leads to more even distribution of capacity between shaft and base. However, the low ratio of pile modulus to rock modulus leads to high compressibility and this, coupled with a tendency for the load transfer response along the shaft to exhibit strain‐softening, gives rise to an overall response where the shaft capacity may be fully mobilized, and potentially degraded, before significant mobilization of base load.The paper presents results of finite element analyses of the response of rock‐socketed piles, with particular attention to the shaft response with and without intimate base contact. The shaft interface uses a model, developed from principles of tribology, that includes dilation (and strain‐hardening) prior to peak shaft friction, followed by strain‐softening at larger displacements. The results of the study are shown to be consistent with field mea...

Geotechnical and Geological Engineering, 2008

This paper reports on indirect soil suction measurement methods. Indirect suction measurement tec... more This paper reports on indirect soil suction measurement methods. Indirect suction measurement techniques measure the moisture equilibrium condition of the soil instead of suction. The moisture equilibrium condition of the soil can be determined by primary means as in vapor pressure, secondary means as through another porous medium or tertiary means as in measuring other physical properties of the porous

Journal of Geotechnical and Geoenvironmental Engineering

Unsaturated Soil Concepts and Their Application in Geotechnical Practice, 2001

Soil^water characteristic curve (SWCC) is an important tool for determining the engineering prope... more Soil^water characteristic curve (SWCC) is an important tool for determining the engineering properties of unsaturated soil. This depends on the size and distribution of pore structures which control the permeability and amount of volume change. Mercury Intrusion Porosimetry tests can be used to determine the size, amount and distribution of pore spaces of the soil in a shorter time period compared to the pressure plate test. A soil-air characteristic curve (SACC) can be determined using the volumetric air content as measured in the Mercury Intrusion Porosimetry test. In this paper, SACC parameters are introduced. There appears to be a relationship between the soil-air characteristic curve and the soil-water characteristic curve of a soil. Relations between the SACC and the SWCC parameters are analysed in the light of unsaturated soil mechanics. The results indicate that the pore size distribution of a residual soil varies with depth due to differing degrees of weathering.

Soft Soil Engineering, 2017

International Journal of Geomechanics, 2016

AbstractMeasuring wave velocities of soils is a common methodology of determining the small-strai... more AbstractMeasuring wave velocities of soils is a common methodology of determining the small-strain stiffness of soils. Both confining pressure and degree of saturation affect the magnitude of the wave velocities and hence the stiffness of the soil. However, confining pressure and degree of saturation affect P- and S-wave velocities of the soil differently. At full saturation, increases in effective confining pressure (σ′3) increase S-wave velocity, but P-wave velocity remains fairly constant. As the soil desaturates, the effects of net confining pressure (σ3 – ua) and matric suction (ua – uw) were observed to be different from the effect of effective confining pressure. This difference in response was investigated, and the results are reported here. Degree of saturation has been commonly associated with the Skempton’s pore-water pressure parameter B under an isotropic state of stress. However, some soils have a B-value less than 0.9 even at full saturation. In such cases, the P-wave velocity may be a bett...

Geotechnical and Geological Engineering, 2018