Deformation Mechanism and Influence of Surface Pumping Control in Shallow-Buried Tunnel in Water-rich Fully Weathered Granite

Abstract

Abstract Granite in a fully weathered state is highly sensitive to water and has poor water stability. Therefore, construction control presents significant challenges when building tunnels in such fully weathered granite formations with high water content. Based on this context and relying on the planned Beitouling Tunnel, this study employed geotechnical tests and numerical simulations to analyze the water sensitivity of fully weathered granite and the impact of surface pumping on the deformation of shallow-buried tunnels in such formations. The research findings indicate: (1) Weathered granite in the project area is highly water-sensitive, with decreasing mechanical properties as moisture rises. However, stress-strain characteristics are minimally affected. Granular composition sets conditions for sudden outbursts. (2) Lowering groundwater eliminates seepage within the "pumping funnel." Below the pumping curve, dense seepage vectors cause walls convergence and arch rise due to pumping forces. (3) Lowering the groundwater to the upper bench reduces tunnel vault settlement by over 50% compared to the initial level, yielding optimal control. At the middle bench, walls convergence rises by 9–13%. Lowering to the tunnel bottom increases arch rise by 23–36%.