Application of the zero thickness interface element approach to the upper bound limit analysis of shallow tunnel excavation

The aim of this study is to apply the zero thickness element approach to investigate the upper bound value of limit analysis with the different failure mechanism of a shallow tunnel excavation in soft clay. This interface is modelled as a contact element with zero thickness and with the Coulomb's friction behaviour. The procedure of numerical analysis adopted the zero thickness element particularly developed and installed into the finite element program in the laboratory. A series of finite element analysis is used to investigate the solutions of stability and simulate the soil progressive failure mechanism due to a shallow tunnel excavation. Four geometry of failure mechanism are taken into account the effects of overburden depth and critical collapse ratio. According to the results obtained, the upper bound values between the limit equilibrium analysis and the numerical calculation are theoretically coincidence, and also the progressive failure mechanism of cohesive soil can be practically predicted. The numerical analyses show that the predicted stability ratio is in reasonable agreement with the analytical solutions in the limit analysis.