Experimental Investigation of the Deformation and Failure Behavior of a Tunnel Excavated in Mixed Strata Using Transparent Soft Rock

To investigate the deformation and failure behavior of a tunnel excavated in mixed strata, transparent soft rock test and numerical simulations were performed. The distribution features of displacement and failure and the evolution laws were analyzed. In this study, a transparent material for simulating mixed strata was developed. The visualization of the spatial deformation inside rock masses will improve the understanding of this process. The tests suggest that the mechanical properties of transparent soft rock are similar to those of natural rock. Experiments on the isotropic and mixed strata conditions were carried out to study the deformation rules during tunnel boring machine (TBM) excavation. The test results show that the dominant deformation position and direction exist in isotropic and mixed strata. A shear slip band occurs in both mixed and isotropic strata but with different distributions. Finally, numerical simulations were conducted to study the failure process, and the damage pattern of the transparent soft rock experiment was similar to that of the numerical simulation. The interface of the softness and hardness layers controls the extension of rock damage.