Numerical Simulation of Tunneling Process of Seven Steps Bench Method in Small Clear-Distance Twin Highway Tunnel with Eight Lanes

Using the finite difference software,the construction process of the seven steps bench method in twin highway tunnel with eight lanes and small clear-distance was simulated,and the law of the primary support's displacement and internal force varying with construction sequences were analyzed.The results show that the maximum compressive stress of primary support mainly distributes at each of the arch springing or wall corners after each excavation step;the largest axial force distributes at the sidewalls and wall corners close to the middle rock pillar;the maximum bending moment distributes at the vault;the influence of right tunnel excavation on the axial force of left tunnel is smaller than the influence on the bending moment;the displacement of the tunnel vault is the biggest and the displacements of the tunnel arch springing and the hance far from the middle rock pillar are relatively small.