Study on the influence of the in-tunnel underpinning construction of the subway tunnel in the soft ground on the pile foundation

By aiming at the construction problem of the tunnel passing through the pile foundation, the influence of the whole process of the tunnel crossing and invading the pile foundation on the pile foundation was studied in order to clarify the key control nodes of the pile foundation underpinning construction method in the tunnel. By relying on an engineering example of an underground tunnel in Shenzhen under passing existing buildings, the deformation, internal force distribution and bearing capacity of exposed pile foundation during tunnel excavation and pile foundation underpinning were analyzed by using FDM software FLAC3D. The results show that during the construction of the tunnel, the pile foundation exhibited settlement deformation. When the tunnel excavation led to the exposure of the pile foundation, the settlement reached the maximum value, and the maximum settlement of the pile top reached 9.5 mm. The entire pile foundation is under pressure, and the maximum pressure is located in the exposed part of the pile foundation. The maximum value of the additional axial force is about 1 600 kN. The tunnel excavation could cause the loss of the bearing capacity of the pile foundation, and the bearing capacity loss of the pile foundation is the largest when the pile foundation is exposed. The ultimate bearing capacity of the pile foundation is about 25% less than before the tunnel excavation. © 2021, Central South University Press. All rights reserved.