S Yimsiri

An investigation of anisotropic elastic parameters of Bangkok Clay from vertical and horizontal cut specimens

This paper presents an investigation of cross-anisotropic elastic parameters of Bangkok Clay. The study programme consists of both laboratory experiments and parametric analysis. A set of isotropically consolidated undrained and drained triaxial compression tests is performed on vertically- and horizontally-cut undisturbed specimens. The triaxial apparatus is equipped with local strain measuring systems and bender element which enable the measurement of stiffness at small to intermediate strains. The anisotropic stiffness parameters obtained from both undrained and drained triaxial tests are assumed to follow the three-parameter cross-anisotropic elastic model proposed by Graham and Houlsby (1983). Moreover, the elastic moduli are also assumed as power functions of isotropic confining stress. The cross-anisotropic elastic parameters are then derived as functions of these relevant simplified parameters. The least-square method is used to define the optimised elastic parameters from all tests. Finally, a complete set of cross-anisotropic elastic parameters of Bangkok Clay is proposed and discussed against reported values from other soils.

Cantilever-Type Local Deformation Transducer for Local Axial Strain Measurement in Triaxial Test

The cantilever-type local deformation transducer (cantilever-LDT) was developed as an alternative local axial strain measurement device for triaxial testing. The transducer behaves as a cantilever beam and the deflection at its free-end is measured by the output from the strain gages attached near the fixed-end. By placing two cantilever-LDTs along the same vertical alignment but at different levels of a specimen, the local axial strain is obtained from the relative movements of two cantilever-LDTs. The advantages over the original-LDT proposed by Goto et al. (1991) are: (i) a linear calibration curve, (ii) capability to release itself at large strains, and (iii) larger working range. With a gage length of 50mm, the resolution, accuracy, and working range are 0.0012 %, 0.003 %, and 6 %, respectively. The triaxial test results on heavily overconsolidated clay specimens show that the cantilever-LDT can be used satisfactorily to measure the local axial strain accurately, but the reliability depends very much on the quality of specimen preparation and setup.

Effects of water table fluctuation on diesel fuel migration in one-dimensional laboratory study

The effects of water table fluctuation on diesel fuel redistribution in unsaturated soil are investigated in the laboratory by one-dimensional column test. The simplified image analysis method is used to assess the saturation distributions of water and diesel in the flow domain under transient condition. The experiments are undertaken on two homogeneous sands to study the effects of different particle sizes. The two-phase experimental data illustrate soil–liquid characteristic curves (SLCCs) of water/air and diesel/air systems. The SLCCs of diesel/water systems can be predicted by scaling procedure. A descending order of matric suction at a given saturation of wetting phase is in the order of air/water, diesel/water and air/diesel systems. Coarser particle size gives smaller entry pressure, residual matric suction and residual degree of saturation. The three-phase (air/water/diesel) experimental data illustrate that, during imbibition stages, air and diesel are entrapped below water table with the entrapped air saturations of 18–24% and entrapped diesel saturations of 6–10% for fine sand. Coarser particle size yields smaller entrapped diesel saturations and larger entrapped air saturations. The residual diesel saturations during drainage stages and entrapped diesel saturations during imbibition stages do not show any systematic difference as these stages are repeated. During imbibition stages, 37–47% of the total amount of diesel fuel is entrapped under the water table. Also, there is no systematic difference in the amount of diesel fuel entrapped under the water table when imbibition stages are repeated.

Assessment of Liquid Saturations in Sand by Image Analysis

This research investigates the relationship between optical density and liquid saturations in unsaturated sand using multispectral image analysis technique. The tested liquids are water, diesel, and parafin liquid. The experiments are performed on two-fluid phase systems (water-air, diesel-air, and parafin liquid-air) and three-fluid phase systems (diesel-water-air and parafin liquid-water-air). Water is dyed with Brilliant Blue FCF, whereas diesel and parafin liquid are dyed with Red Sudan III. Using consumer-grade digital cameras, two images of sand specimens with various liquid saturations are taken with two different band-pass filters. The analysis results show that, for the sand and investigated fluids, the optical density defined for the reflected luminous intensity is a linear function of the degrees of fluid saturation for each spectral band and for any two- and three-fluid phase systems.

Failure Surface and Plastic Potential in Deviatoric Plane of Bangkok Clay

This paper presents an experimental investigation on the failure surface and plastic potential in deviatoric plane of Bangkok Clay. The results of torsional shear hollow cylinder and triaxial tests with various principal stress directions and magnitudes of intermediate principal stress on undisturbed Bangkok Clay specimens are presented. The obtained stress-strain behaviors assert clear evidences of anisotropic characteristics of Bangkok Clay. Both failure surface and plastic potential in deviatoric plane of Bangkok Clay are demonstrated as isotropic and of circular shape (Drucker-Prager type) which implies an associated flow rule. Concerning the behavior of Bangkok Clay found from this study, the discussions on the effects of employed constitutive modeling approach on the resulting numerical analysis are made.