Numerical Analysis of A Shallow-buried Portal in Expressway Tunnels with Weak Rockmass

Aiming at the problems in construction for a shallow-buried and unsymmetrical loading portal in Banzhulin Tunnel in Yu-Xiang expressway, the finite element simulation were carried on to study the behavior for bench excavation method. Main results of numerical analysis as follows:the displacement of surrounding rock of right tunnel(as A(R))at the horizontal direction is large and may larger than that of the left tunnel(as A(L)) at the vertical direction,and the largest deformation is 22.63mm,occuring at the key point D-L. Compared with the data of monitoring measurement, the correctness of this simulation was proved.The behavior for deformation and stress of mountain tunnels as Banzhulin is basically mastered,and the displacement of rockmass is the key factor in tunnelling.