Evaluation of Effects of Static Pile Driving on Existing Metro Tunnel Structure

Relatively few studies have been conducted to examine the effects of static pile driving on existing tunnels, and there is a lack of guidance and case studies that can be used as references. This article presents a case study of the tunnel of the Wuxi Metro Line 2 in China that was performed to investigate the mechanism by which static pile driving affects an existing metro tunnel structure. The study provides a theoretical basis for the design of construction schemes for static-driven piles. The effects of pile driving-induced soil compaction and excess pore-water pressure (EPWP) are studied through numerical calculations and are then combined using the superposition principle. In addition, the numerical results are compared with field measured data. The following results are obtained. First, static pile driving results in horizontal compression and vertical extension of the existing tunnel. The horizontal convergence of the tunnel segment near the center of the pile group is -3.56 mm. The opening of the circumferential joints is 1.15 mm, which leads to the risk of water leaks. Second, the EPWP-induced horizontal and vertical extension of the tunnel segment are approximately 50% and 33%, respectively, of the deformation caused by soil compaction before the dissipation of the EPWP and decrease to 25% and 20%, respectively, after the dissipation of the EPWP. Third, the combined effects of static pile driving-induced soil compaction and EPWP calculated based on the superposition principle are consistent with the field observations. This study provides a new procedure for static pile-driving simulations, reveals the influence of static pile driving on the deformation of an existing tunnel, and can be used to guide the design and formulation of construction schemes for static piles.