Effects of House Renovation on the Operating Metro Tunnel in Soft Soil

Building renovations above tunnels in soft soil inevitably induce loading/unloading effects. Currently, there are limited research and case studies on this topic. This paper analyzes the effect of different unloading magnitudes, tunnel burial depths, and building dimensions on existing operational tunnels, by conducting a case study of a building renovation over a tunnel. Field monitoring data indicated that tunnel deformation remains controllable when the temporary load variation was kept within 30 kPa (equivalent to two stories of load). Parameter analysis reveals that as the amount of unloading increases, the tunnel depth decreases, and the building size increases, both the uplift and convergence of the tunnel increase accordingly. When large areas of buildings above the subway are unloaded, the area of each unloading should be appropriately controlled, preferably not exceeding 400 m², and the long side of the unloading should be perpendicular to the direction of the tunnel. Compared to deep tunnels, shallow tunnels are more affected by upper unloading, especially when there are soft soil layers such as mucky soil in the shallow part. Therefore, the amount of unloading and the area of each unloading should be strictly limited.