New methods of safety evaluation for rock/soil mass surrounding tunnel under earthquake

CHENG Xuan-sheng(程选生)^{1, 2, 3}, DOWDING Charles H², TIAN Rui-rui(田瑞瑞)¹

(1. School of Civil Engineering, Lanzhou University of Technology, Lanzhou 730050, China;
2. Department of Civil and Environmental Engineering, Northwestern University, Evanston 60208, USA;
3. Key Laboratory of Urban Security and Disaster Engineering of Education Ministry,
Beijing University of Technology, Beijing 100124, China)

Abstract:The objective of this work is to obtain the seismic safety coefficient and fracture surface and proceed with the seismic safety evaluation for the rock mass or soil mass surrounding a tunnel, and the limitation of evaluating seismic stability is considered using the pseudo-static strength reduction. By using the finite element software ANSYS and the strength reduction method, new methods of seismic safety evaluation for the rock mass or soil mass surrounding a tunnel are put forward, such as the dynamic finite element static shear strength reduction method and dynamic finite element shear strength reduction method. In order to prove the feasibility of the proposed methods, the results of numerical examples are compared with that of the pseudo-static strength reduction method. The results show that 1) the two methods are both feasible, and the plastic zone first appears near the bottom corners; 2) the safety factor of new method II is smaller than that of new method I but generally, and the difference is very small. Therefore, in order to ensure the safety of the structure, two new methods are proposed to evaluate the seismic stability of the rock mass or soil mass surrounding a tunnel. A theoretical basis is provided for the seismic stability of the rock mass or soil mass and the lining surrounding a tunnel and also provided for the engineering application.

Key words:tunnel; rock or soil mass surrounding tunnel; earthquake stability; safety evaluation