Reasonable Avoidance Distance of Metro Shield Tunnels under Normal Fault Dislocation

［Objective］ Normal fault dislocation is prone to cause instability and damage to metro shield tunnels. Therefore, it is necessary to study the mechanical characteristics of shield tunnels under normal fault dislocation and their relative positions to the fault rupture plane, in order to determine a reasonable avoidance distance. ［Method］ A numerical model considering the strain-softening behavior of the overburden soil on bedrock and the segment joint stiffness is established and validated through centrifugal model tests. Numerical simulations are conducted to analyze the mechanical behavior of shield tunnels crossing normal faults in a parallel manner. Based on the risk of overturning under the most unfavorable operating conditions of metro trains, a reasonable avoidance distance of shield tunnels under normal fault dislocation is discussed. ［Result & Conclusion］ Under normal fault dislocation, the shield tunnel undergoes significant rotation and displacement, and the surrounding rock pressure and internal forces of the tunnel change considerably during the dislocation process. These variations are related to the relative position between the tunnel and the rupture plane in a free-field condition, because the presence of the shield tunnel significantly alters the propagation path of the normal fault rupture plane. A reasonable avoidance distance of metro shield tunnels under normal fault dislocation will decrease with increasing burial depth. When H0/D (H0 as the thickness of shield tunnel, D as tunnel diameter) ≤ 1.0, the reasonable avoidance distance on the hanging wall side should be ≥1.2D, and on the footwall side ≥1.0D; when 1.0 ≤H/D≤ 2.0, the reasonable avoidance distance on both sides should be ≥0.9D; when H/D≥ 2.0, the hanging wall side should be ≥ 0.7D, and the footwall side ≥0.9D.