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.
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.
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...
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
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...
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.
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.
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...
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
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...
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