Undrained stability analysis of dual unlined horseshoe-shaped tunnels in non-homogeneous clays using lower bound limit analysis method

A rigorous adaptive lower bound limit analysis method with 3-noded element (LB-FELA) is adopted to discuss the tunnel stability and failure mechanism of dual unlined horseshoe-shaped tunnels in non-homogeneous clays. The clays mass has heterogeneity, where the shear strength increases linearly with depth. This problem is defined as a plane strain analysis model. The calculation results are provided using the dimensionless stability numbers, which are affected by dimensionless parameters C/D, S/D and ?D/c0.The typical failure mechanisms of the dual horseshoe-shaped tunnels are presented based on the parametric studies using the final refined meshes of the proposed method. The results show that the dimensionless parameters ?D/c0, C/D,and S/D have great influences on tunnel stability and failure mechanism of the dual horseshoe-shaped tunnels. Using the calculation results provided by this paper, the tunnel designers can directly evaluate the stability of the tunnel in non-homogeneous clays.

Automated summary

The rigorous adaptive lower bound limit analysis method was used to study the stability and failure mechanism of dual unlined horseshoe-shaped tunnels in non-homogeneous clays. The results demonstrate significant influences of dimensionless parameters on tunnel stability and provide a direct evaluation tool for tunnel designers.