Dynamic Responses of Subway Tunnel in Clay Stratum to Moving Loads

An elaborate three-dimensional nonlinear numerical model of a rail-tunnel-foundation system in a clay stratum was developed. The model closely represented an actual subway tunnel and described the rail, sleeper, track slab, inverted arch, lining and foundation. Operation of a subway train with six wagons traveling at 100 km/h was simulated. Large-scale nonlinear dynamic finite element computation for the system was performed. The analysis showed that the system is in a state of loading and unloading repeatedly as the train passes through the tunnel. The spatial distributions of dynamic displacement, velocity, acceleration and stresses in different parts of the system all vary simultaneously with time and space. The characteristics of dynamic stresses in the clayey stratum are much different from those in the inverted arch and lining. The dynamic stresses in the tunnel lining and inverted arch have small values, but the rate effects of dynamic stress for ballastless track slab, inverted arch and tunnel lining are much higher than that of the foundation clay. The rotations of principal stress axes in the XY and YZ planes are predominant for ballastless track slab, inverted arch, tunnel lining and foundation soil just below the tunnel lining, while rotation in the YZ plane is predominant for deeper foundation soil elements. These results justify a conclusion that the thickness of inverted arch and backfill concrete can be optimized. Much attention should be paid during design to the long-term stability of a clayey foundation. The results can be referred in the dynamic design of subways.