The objective of this thesis is to study the basal heave of excavations using the numerical method. This study firstly confirmed advantage of finite element analysis with updated mesh over the analysis without updated mesh for large deformation problem. Then analysis with updated mesh and strength reduction method was adopted to analyze three failure basal heave or near failure excavations in soft soil. The automatic c – phi reduction method, the manual c – phi reduction method, the angle method and the intersection method were used to justify if excavations reached failure or near failure conditions. The automatic c – phi reduction method defines factor of safety as strength reduction ratio at which displacement increases largely. Based on convergence criteria, the manual c – phi reduction method determines the highest value of strength reduction ratio as safety factor at which equilibrium state remains. On the other hand, the angle method considers kick out phenomenon of the retaining wall as failure state. For the intersection method, the relationship between the displacement and strength reduction ratio was plotted and factor of safety was strength reduction ratio corresponding to intersection point of curve. Moreover, a series of parametric studies was performed to study the effect of excavation width on the evaluation of factor of safety. In general, the factors of safety predicted by the numerical methods consisted with the plastic point distributions when excavation changed from narrow to wide shape.

The objective of this thesis is to study the basal heave of excavations using the numerical method. This study firstly confirmed advantage of finite element analysis with updated mesh over the analysis without updated mesh for large deformation problem. Then analysis with updated mesh and strength reduction method was adopted to analyze three failure basal heave or near failure excavations in soft soil. The automatic c – phi reduction method, the manual c – phi reduction method, the angle method and the intersection method were used to justify if excavations reached failure or near failure conditions. The automatic c – phi reduction method defines factor of safety as strength reduction ratio at which displacement increases largely. Based on convergence criteria, the manual c – phi reduction method determines the highest value of strength reduction ratio as safety factor at which equilibrium state remains. On the other hand, the angle method considers kick out phenomenon of the retaining wall as failure state. For the intersection method, the relationship between the displacement and strength reduction ratio was plotted and factor of safety was strength reduction ratio corresponding to intersection point of curve. Moreover, a series of parametric studies was performed to study the effect of excavation width on the evaluation of factor of safety. In general, the factors of safety predicted by the numerical methods consisted with the plastic point distributions when excavation changed from narrow to wide shape.

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