Large-scale model experiment and numerical simulation on convergence deformation of tunnel excavating in composite strata

In this research, a large-scale model experiment was carried out to investigate the convergence deformation and failure characteristics of TBM (tunnel boring machine) excavation surrounding rock in deep buried composite strata. Based on the similar theory, the model test results show that the deformation of tunnel surrounding rock after excavation consists of two parts, instantaneous deformation and continuous creep deformation. When a circular tunnel is excavated in deep buried composite strata, the tunnel surrounding rock is firstly subjected to tensile failure on the soft rock side in the horizontal direction, and shear failure occurs at the top and bottom soft rock areas. With further increase of the external boundary load, the hard rock area of the tunnel in the horizontal direction suffers tensile damage due to stress concentration. Convergence deformation of the tunnel surrounding rock reaches the maximum value in the soft surrounding rock area. And then, based on the proposed damage-softening constitutive model of rock, numerical simulations were conducted out by using the finite difference method in order to analyze the convergence deformation mechanism of tunnel excavating in composite strata. The numerical simulation analysis results show that the damage rule of tunnel surrounding rock is controlled simultaneously by stress and lithological characteristics, which agrees very well with the experimental results.