Structural damage assessment of shallow buried tunnel subjected to multiple slip surfaces and blind reverse fault: a numerical study

Abstract Faults and fractured zones are common geological hazards in tunnel construction, especially in seismic regions where tunnels are highly vulnerable to fault movements. This study uses Urumqi Metro Line 2 as a case, establishes a new damage assessment system for tunnels crossing multiple slip surface faults. Three-dimensional nonlinear finite element models are used to analyze the effects of fault displacement magnitudes, distances between adjacent slip surfaces, and fault dip angles on tunnel lining damage. The study identifies the damage characteristics and evolution of tunnel linings under multiple fault movements, filling gaps in existing research. Lining damage is quantitatively assessed using two indicators: the damage state of the tunnel lining and the overall lining damage index. The proposed model has been verified through two methods. Results show that as fault displacement increases, lining damage progresses from the invert to the crown and sidewalls, longitudinal damage mainly occurs near the slip surface and fault-rock interface. Once the fault displacement exceeds 0.5 m, the overall lining damage index hardly changes anymore. Fault movements along narrow slip surfaces result in a cumulative effect on the lining; however, when the gap between slip surfaces exceeds 21.0 m, slight damage occurs in the central tunnel region. Tensile damage to the lining is highly sensitive to fault dip angle, with a 20.7% variation as the dip angle changes. Additionally, tunnels in the moving block experience more tensile damage than those in the fixed block. Overall, the numerical results of this study provide a better understanding of the response of tunnels under the movement of multiple slip surface faults.