Deformation of tunnel surrounding soil under traffic loads considering Bi-directional PSR

Under complex loading condition such as train-induced traffic loads, the foundation soil of transportation infrastructure experiences Bi-directional Principal Stress Rotation (PSR). Ignoring Bi-directional PSR may lead to an underestimation of the soil’s long-term deformation. However, due to the limitations in test equipment, current research predominantly focuses on considering only Uni-directional PSR. To tackle such challenge, this research first used the Finite Element Method (FEM) to obtain the stress paths in the soil around the tunnel under subway traffic loads, including the Bi-directional PSR. Based on these paths, Bi-directional dynamic simple shear tests on Leighton Buzzard sand were conducted. The axial and shear deformation, axial resilient modulus, and shear modulus under Bi-directional PSR were investigated. Results indicated that, under Bi-directional PSR, the vertical deformation of the soil under the tunnel was larger than that under Uni-directional PSR. In particular, the vertical deformation in the soil at few meters away from the centerline of the tunnel was larger than that at the centerline. Therefore, in prediction of vertical deformation of the surrounding soil of the tunnel subjected to long-term traffic loads, considering Bi-directional PSR provides more accurate results. This work provides valuable insights into the mechanical behavior of the subsoil of the tunnel under train-induced traffic loads.