CURRENT WORK
1. Implementation of Soil Model in FEM Program
A soil model developed for structured clay and other cemented soil have been extended into the generalised stress space and implemented into the finite element code for solving the boundary value problems in geotechnical practice, such as UMAT for ABAQUS-FEM, Add-ins model for SIGMA/W.
2. Development of the Consitutive Model for Structured Clay
Modified Structured Cam Clay (MSCC) model has been developed by Suebsuk et al. (2010) for describing the clay behaviour in three diffferent states, those are destructured (remould), naturally structured and artificially structured (for cement stabilised soil). The influence of structure and destructuring on the mechanical behaviour of clay can be explained by the change in the modified effective stress, which is the sum of the current mean effective stress and the additional mean effective stress due to structure (structure strength). The presence of structure increases the modified mean effective stress and yield surface, enhancing the cohesion, peak strength and stiffness. The destructuring begins when the stress state is on the virgin yield surface. After the failure (peak strength) state, the abrupt destructuring occurs as the soil-cementation structure is crushed; hence the strain softening. The soil structure is completely removed at the critical state when the yield surface becomes identical to the destructured surface. The destructuring law is proposed based on this premise. In the MSCC model, the yield function is the same shape as that of the Modified Cam Clay (MCC) model. A plastic potential is introduced so as to account for the influence of structure on the plastic strain direction for both hardening and softening behaviours. The required model parameters are divided into those describing destructured properties and those describing structured properties. All the parameters have physical meaning and can be simply determined from the conventional triaxial tests. Thus, the MSCC model is a useful tool for geotechnical practitioners. The capability of the model is verified by the test results of destructured, natural structured and artificially structured clays.
3. Foundation design software for education
The research developed a relatively simple method to solve the internal forces and settlement of pile foundation. The method can be used for the trial step in foundation design. The method, called simplified frame-pile (SFP) model, replaced the footing by equivalent grid and the supporting soil by a series of horizontal and vertical spring. Displacements and internal forces can be calculated by stiffness matrix method. The SFP model was calibrated with exact solution and verified by comparing with exact solution and other reliable numerical method as well as with the result of centrifugal model.
In additional, the research developed a computer program for analysis and design pile foundation, named "SUTFoundation". The program combines bearing design and structural design. It is capable of calculating the allowable load and iterating for the proper foundation dimensions. The program also includes shallow foundations (isolated, combined and mat). For shallow foundations, internal forces are calculated using Finite Grid Method (Bowles, 1988). The program is in graphic format using Window. Input is entered interactively through keyboard and mouse. The program was verified by comparing results with those obtained from hand calculation and from other reliable programs.