A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 2003

This thesis performed the numerical analysis by plain strain effective stress analysis in undrained conditions of predicted ground movements of 3 station excavations at the Bangkok MRT ISP Blue Line project. Comparisons are made between measurement data and numerical prediction with finite difference code (FLAC) and a finite element code (P ALXIS) from the previous study by Hooi (2003). The two numerical codes using linear elasto-plastic stress-strain model yielded similar patterns of predicted lateral ground movements between FLAC and PLAXIS. A non-linear soil model is used in the analysis to model the actual non-linear stress-strain behavior of soil. The results show close predicted lateral ground movement for both linear and non-linear analysis for the station excavations. Since the level of strain controls the stiffness values of non-linear analysis, it can be concluded that the, strain level behind the diaphragm wall until the last excavation stage is very low. Therefore the linear analysis can be used in the need of increased modulus to 2-3 times modulus of large strain. Finally, sensitivity analysis of soft clay, hard clay and stiff clay with non-linear soil model are studied. Only the variations in modulus of soft clay yield difference in maximum ground movement. The predominant stage of excavation that controls the maximum ground movement is the first stage includes the soft clay layer plays impo1tant roles.