6.2 CRISP Program and Modified Cam-clay Model

To achieve the purpose mentioned above, finite element analyses were carried out to simulate the deep excavation tests in the centrifuge described in the previous chapters. In this study, the FEM analyses were carried out using the Critical State Soil Mechanics Program (CRISP) developed by University of Cambridge (Britto et al. 1987, 1990). The dimension of the mesh for the FEM analyses was chosen according to the centrifuge model scale. The soil model in the FEM analysis was then subjected to 100g acceleration to simulate the condition in the centrifuge. In the analyses, modified Cam-clay model was employed to simulate the soil behaviours. The FEM results were compared with the results obtained from centrifuge model tests presented in the previous chapters.

The stress-strain behaviour of Singapore marine clay is highly non-linear (Tan, 1983). The modified Cam-clay model had been shown to be able to simulate this behaviour reasonably (Lee et al., 1989, 1993). In addition to the material non-linearity, the dissipation of excess pore water pressure which causes the deformation behaviour of soil time-dependent is another important factor which should be properly considered in the analysis (Yong et al, 1989; Parnploy, 1990). CRISP, with a modified Cam-clay model to simulate the soil behaviour is able to handle the difficulties of non-linearity and time-dependency.