Response and failure mechanism of utility tunnel with flexible joints under reverse fault: An experimental, numerical, and analytical investigation

Severe seismic damage occurs to tunnels across or adjacent to the active faults in a high-intensity earthquake area. Therefore, investigating the response and failure mechanism of the utility tunnel structure with flexible joints across the reverse fault is of significant importance. This paper conducts a model test of 1:30, modelling reverse fault rupture with a 45 degrees dip angle and a utility tunnel with flexible joints embedded in the sand layer. The results show that the lining structure in the hanging wall area appears to have longitudinal cracks, concrete falls off, and there is continuous dislocation. Then, a nonlinear three-dimensional finite element model (FEM) is adapted to reveal the utility tunnel response under reverse faulting and to simulate the model test. The numerical results show that the tensile failure area of the lining caused by reverse faulting is larger than the compression failure area. The damage distribution has regional characteristics, and especially the joint area is seriously damaged. The settlement profile of the tunnel under reverse fault can be fitted reasonably by a complementary error function. Finally, an analytical solution of the longitudinal response of the tunnel under reverse fault based on the double-parameter Pasternak model is derived. The analytical solution results show good agreement with the numerical and experimental results. The longitudinal response of the tunnel under reverse fault can be divided into two parts: the influence zone and the non-influenced zone. The flexible joints significantly reduce the damage degree and the damaged area of the tunnel caused by reverse fault dislocation.