Three-dimensional upper bound limit analysis of deep soil tunnels based on nonlinear Mohr-Coulomb criterion

When the surrounding rock conditions are poor, the buried earth tunnel is prone to collapse during the tunnel excavation process. It is extremely important to accurately predict the extent of the collapsed soil in the deep buried soil tunnel. The theoretical study to predict the collapse range of the deep-buried soil tunnel is not mature enough. In order to predict the extent of the collapse of the surrounding rock of the soil tunnel in advance, based on the nonlinear Mohr-Coulomb criterion and the limit analysis upper bound method, the upper limit expression for the collapse block of the deep-buried soil tunnel under the three-dimensional failure mechanism is derived, and the exact solution to the extent of the tunnel collapse is obtained. The three-dimensional shape of the collapsed body is drawn by the numerical software Matlab. The influences of various parameters on the shape of the buried tunnel collapse are studied and compared with the existing researches. The results show that the parameters in the soil, the radius of the top arc of the tunnel and the supporting pressure have a great influence on the range of the collapse block. Based on the nonlinear Mohr-Coulomb criterion, the upper bound analysis of the buried earth tunnel collapse block can solve the height and width of the collapsed body with and without support force, and the solution is reasonable and reliable. The proposed method can also give the support force to prevent the collapse of deep-buried soil tunnels, which can provide a theoretical basis for the engineering design of tunnels.