Field measurement of time-space distribution behaviors of environmental settlement of an ultra-deep excavation in Shanghai soft ground

Based on the extensive field observations, the environmental deformation characteristics of a 31.3 m-deep excavation in Shanghai soft ground are investigated. The results show that compared with the general excavations with a depth ranging from 12 to 20 m, the ultra-deep excavation presents significant environmental effects and time-space distribution behaviors: (1) The influence zone of settlement near the long side of the excavation is related to the wall deflection distribution on the plane. The more gently the lateral wall displacement changes from the middle area to the corner, the more extensive the influence zone is. The faster the lateral wall displacement transits from the middle to the corner of the excavation, the more concentrated the influential zone is. (2) Due to the corner effects, the ground surface settlement decreases rapidly from the center to the corner, and exhibits a Gaussian distribution law, with the influence range extending to 1.5H_e (depth of excavation) behind the excavation corner. (3) The deformation of buildings exhibits distinct three-dimensional characteristics. The buildings located near the excavation corner have less settlement than those near the center of the excavation, accompanied by a certain torsional deformation. (4) When the buildings paralleling to the retaining wall cross the corner of the excavation, the most dangerous point is located within 0.5H_e near the corner of the excavation, and its damage degree depends on the relative location between the buildings and the excavation and their stiffness. (5) Compared with the conventional deep excavations, the ultra-deep excavation leads to a larger primary influence zone for ground surface settlement, reaching about 3H_e, but the location of the maximum surface settlement is closer to the wall, nearly 0.5H_e behind the retaining wall. (6) The maximum ground surface settlement δ_vm is about 0.03%~0.50%H_e, and the relationship between the maximum ground surface settlement δ_vm and the maximum lateral wall displacement δ_hm can be expressed by δ_vm=0.6δ_hm averagely.