Numerical investigation on failure mechanism of tunnel lining with different fault dip angles and Geological Strength Index under geohazard of fault movement and seismic action

Abstract

In this article, the failure mechanism of the tunnel under geohazard fault movement and non-uniform seismic load was studied. The study area considered was Atal Tunnel in Himachal Pradesh, India, in the North-West of the Himalayas. A normal fault of 10 m width was considered by varying the fault dip angles of 30°, 45°, 60°, 75°, and 90° along with Geological Strength Index (GSI) values of 20, 40, 60, and 80. The finite element models were analysed under fault movement and 4 ground motions. A fault movement of 0.5 m was applied at the bottom of the fault and hanging wall area. The results showed that fault with 60° dip angle produced more structural forces in tunnel lining under fault movement. The fault with 20 GSI rock mass exhibited higher structural forces in the tunnel lining, irrespective of dip angle. In the case of seismic load, a smaller dip angle generates more structural forces. The tunnel lining in the hanging wall experienced more tensile damage, especially in the direction of seismic wave propagation. The left and right sides of the lining in the footwall area underwent tension, whereas the tunnel crown and bottom experience compression under seismic load.

Keywords

• Geological Strength Index
• interface
• dip angle
• mud inrush