Responses of ground and adjacent shallow foundation buildings to twin large-diameter shield tunnelling in soft clay: case study

Tunnelling in urban environments often poses significant challenges due to its potential adverse effects on the ground and adjacent buildings, especially when dealing with large-diameter tunnels in soft clay. This study investigates the responses of the ground and shallow foundation buildings to shield tunnelling in soft clay, based on a case involving twin 11.36 m diameter tunnels beneath a residential area with 14 affected buildings. Continuous monitoring of shield operation, ground displacement, and building deformation offers valuable insights into the tunnel-soil-building interaction system. Horizontal deviations of the shield machine result in asymmetric ground settlement on both sides of the tunnel. Secondary grouting is less effective in controlling building settlements than in reducing ground settlement, and its influence on soil horizontal displacement is mainly confined to the area within 1D above the tunnel. Based on the shield machine position and ground heave-settlement characteristics, ground displacement can be generally divided into five stages. Notably, the ground settlement observed at the time of the shield tail arrival accounts for only 35.7 % to 41.8 % of the final total settlement. The temporal trend of building settlement resembles that of the ground, but the final settlement of buildings consistently exceeds that of the greenfield ground. Buildings spanning the tunnel exhibit downward-convex (sagging) bending deformation, while those located on one side of the tunnel show upward-convex (hogging) deformation. Buildings tilt towards the corner closest to the tunnel axis after the tunnel construction. Furthermore, the building differential settlement gradient (inclination) shows a significant inverse proportionality to the eccentric distance, with a linear fit slope of approximately −0.102.