Analysis on Dewatering Tests at Deep Excavation Sites of Soft Soil Areas in Aquifer-Connected Conditions

During foundation excavation of metro stations, the dry working surface was needed, and dewatering in site is essential. After construction of dewatering wells, the pre-dewatering must be performed to check whether it can meet the excavation condition and the water interception effect for curtain of cutting-off water. However, some construction enterprises do not attach importance to the issues, and often ignore or abandon the preparation for the dewatering test due to considering of time and economic costs, laying a certain potential safety hazard for project construction. Based on data analysis on the dewatering test at the deep excavation site of a metro station in Tianjin, it was found that because the construction quality of dewatering wells did not strictly meet the design requirements, the aquifers were interconnected, and led to the foundation dewatering not to meet the design requirements. Subsequently, a grouting reinforcement measure, which alternately injected water glass and calcium chloride solutions into water-resisting layer, was adopted to block water leakage and ensure its water resisting effect and meet the design requirements of dewatering, and simultaneously prevent the impacts of the significant change in groundwater levels caused by dewatering for deep excavation on the surrounding environment.