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Foundation dewatering has become a major cause of land subsidence in Shanghai. The burial depth of foundations in relation to geotechnical construction works is less than 75 m, and the corresponding groundwater includes phreatic, low-pressure artesian, and the first confined aquifers. Based on the geological and hydrogeological conditions beneath Shanghai, methods of dewatering may be divided into three modes and further five patterns according to the insertion depth of the dewatering-retaining system. The most common dewatering mode aims to reduce the water pressure in the confined aquifer by setting the dewatering wells inside the pit, whilst the retaining walls are buried in the confined aquifer and partially cut off the confined aquifer layer. To predict the settlement due to foundation dewatering, numerical models are generally adopted, which are similar to those used to predict land subsidence induced by regional groundwater withdrawal; however, since foundation dewatering is conducted along with the setting of retaining walls and foundation pit excavation, which differs from regional groundwater withdrawal, interactions between the retaining wall-dewatering well, the dewatering-excavation, and dewatering-recharge are important factors affecting the analytical model. Since the grading of the shallow soil layers is different, stratified settlement characteristics of the shallow soil strata and seepage erosion, which results in additional deformation, need to be given particular consideration.

Xi’an City is located at the central region of the Fenwei Plain, and there are 14 ground fissures (labelled GF1–GF14) which have been closely monitored in the urban area of Xi’an City. When a shield tunnel is constructed in a region with ground fissures, problems (such as cracking or failure of the tunnel lining, leakage of groundwater into the tunnel, damage to the completed tunnels and shield, and long-term instability) may be encountered due to the activity of ground fissure. To mitigate the adverse impact caused by the activity of ground fissure, a series of countermeasures are suggested in this paper, which include installation of movement joints, installation of a flexible layer for controlling deformation, foundation reinforcement with cement grouting, and improvement of existing water resistance. A case history regarding the metro tunnel (Xi’an Metro Line 1) which has been intersected the ground fissure 5 (GF5) obliquely was analyzed. The aforesaid countermeasures were applied to this case history. After improving the existing water resistance, the permeability of the surrounding soils was effectively reduced to about 4.0 × 10−8 cm/s and the groundwater leakage into the tunnel was minimal. Observations of the accumulative ground surface settlement near the fissure verified the effectiveness of the countermeasures applied to this case history.