Strategy and analysis of the deformation of subway tunnel caused by pre-dewatering under water-rich sand

Pre-dewatering is an essential step in deep foundation pits with water-rich sand, and its impact on the surrounding environment has attracted increasing attention. To study the impact of pre-dewatering on the tunnel, we selected a typical foundation pit project in Shanghai to conduct in situ pre-dewatering tests and comprehensively record the soil stress, horizontal displacement, and tunnel deformation around the foundation pit during pre-dewatering. The data showed a strong correlation between the displacement and stress changes in the surrounding soil and the locations of the pre-dewatered soil layers. Based on the changes in the water-earth pressure and displacement, the deformation mechanism of the adjacent subway tunnel caused by pre-dewatering before foundation pit excavation was analyzed. Combined with existing research results, strategies such as increasing the stiffness of the ground wall, improving the anti-deformation ability of the soil in the passive area, and on-demand dewatering were proposed, and the findings can be used as reference for similar projects.