COMPARISON AND ANALYSIS ON SURROUNDING ROCK STABILITY OF BIAS LARGE SPAN TUNNEL WITH DIFFERENT EXCAVATION METHODS

The bias topography has a great negative influence on the deformation of surrounding rocks and the forces of supporting structure of a large span tunnel. A scientific selection of excavation method is an important prerequisite to ensure the safety of tunnel construction. The Hoek-Brown strength criterion takes account of the influence of rock mass structure surface, rock mass strength and construction disturbance on rock mass deterioration. This can better reflect the deformation of surrounding rock during tunneling. Therefore, this paper selects a typical engineering project relying on No. 2 tunnel in Qichong village, Huancheng Road, Guiyang City, determines the Hoek-Brown strength parameters based on site investigations and empirical method as well as used, and simulates the excavation processes with both three-step method and double-wall guide method. Compared with the field data of rock deformation and the axial force of steel arch, the double-wall guide method can better control the development of the plastic zone and the deformation of surrounding rock. It can also better alleviate the adverse effect of bias load on the surrounding rock. But the force acting on steel arches is more uneven, which is not conducive to the stability of supporting structure. Considering the construction safety and construction progress, the double-side wall guide method should be used to construct the tunnel outlet and the entrance section with relatively broken rock, while the three-step method can be used for the remainder with more integral rock.