Study on Elastic-Plastic Analysis of Deep Buried High Geostress Soft Rock Tunnel Using Numerical Procedure

After tunnel excavation and unloading, the stress state of the rock mass is redistributed, resulting in varying radial stresses at different radial depths in the rock mass. Rock mechanics tests showed that the confining pressure, especially for soft rock, had a substantial impact on the mechanical properties of the rock which at various radial depths varied with the confining pressure. Therefore, the Mohr-coulomb strength criterion was used in this study to elastic-plastic analysis of deeply buried tunnels that took into account the coupling impact of strain-softening and confining pressure using the finite difference method. Then, regardless of whether the confining pressure is taken into account, the rock mass’s plastic zone radius and deformation value were compared, which were considerably impacted by confining pressure: the effect is more pronounced when the rock strength is lower and the initial geostress is higher. The rock mass’s strain-softening behaviors and its confining pressure effect should be highlighted while soft rock tunnel support structures were designed with the condition of high initial geostress in order to prevent the rock mass’s distinct deformation of the rock mass caused by the calculation results distortion or even serious consequences like large deformation, damage or failure.