Abstract: Collapse is the main safety accident during the course of tunnel construction. It is very meaningful for ensuring the construction safety to study the collapse mechanism of tunnel. Taking the collapse of a tunnel crossing inclined rock layers as the engineering background, the methods of numerical simulation and field monitoring were used to investigate the collapse mechanism of tunnel on the basis of the engineering mechanical properties of surrounding rock. The research results show that under the action of excavation blasting vibrating load, over break is very easy to be seen at the left side of tunnel crown, and the plastic zone at the left arch waist is much bigger than the right side, which leads to the tensile stress in the left arch waist. And surrounding rock pressure is much bigger than the right side, which leads to asymmetric loads of supporting structure and the fractures at the inner side of shotcrete layer. With the enlargement of disturbed zone of tunnel, the surrounding rock pressure increases gradually, and the tunnel deformation icreases quickly, and the loss of stableness of surrounding rock eventually leads to the tunnel collapse.

Key words: inclined rock layer, large-section tunnel, collapse mechanism of tunnel, numerical simulation, surrounding rock pressure