Numerical simulation and analysis of the pile underpinning technology used in shield tunnel crossings on bridge pile foundations

Abstract Currently, the pile foundation underpinning technology is widely used when underground transportation infrastructure passes through existing buildings or structures in urban areas. This study aims to investigate stress transfer mechanisms in pile foundations during an underpinning process as well as the influence of shield tunnel construction on pile stability. To this end, the pile foundation underpinning technology used in China’s Shenzhen Metro Line 10 crossing through the bridge pile foundation group of the Guangzhou–Shenzhen highway was analyzed in detailed. The refined numerical simulation of the pile foundation underpinning and shield tunnel construction processes were conducted using the fast Lagrangian analysis of continua in 3 dimensions (FLAC3D) software. The results demonstrate that after the pile foundation underpinned, the previous bridge load system of bridge panel→pile foundation→bearing soil would transform into a bridge panel→existing pile foundation→new underpinning pile→deep bearing soil stratum structure. The overlying load on the underpinned pile could be effectively transferred to a new underpinning pile. In the process of underpinning and tunnel excavation, the settlement and deformation of the foundation can improve the tip resistance and shaft friction of piles, which in turn, can reduce the maximum principal stress in the pile foundation group. The deformation of the bridge pile foundation is mainly caused by ground loss and excavation disturbance generated during shield tunneling as the settlement induced by pile foundation underpinning accounts for approximately 20%–30% of the total settlement. The reduction effects of settlement deformation, lateral displacement, and principal stress are mainly manifested in underpinning piles, while the non-underpinning pile exhibits minimal variation. Meanwhile, the deformation of the segment lining structure of the shield tunnel primarily occurs near the underpinning area of the pile foundation, and it is mainly settlement deformation with a small horizontal displacement.