Abstract: With the rapid development of the urban subway network, the number of commercial and residential buildings around the subway increases sharply. During the excavation of foundations, it is necessary to consider the safeguard measures of the adjacent active subway. The critical aspect of the deep excavation project of the first terrace of Yangtze River in Wuhan area is to prevent the adverse impact on the project itself and the environment caused by the seepage damage of the confined aquifer of the deep sand layer with high water head and strong permeability. The selection of the groundwater control method in the deep excavation can be divided into two modes: “bottom insertion curtain” and “suspended curtain”. The project cost, construction duration, construction difficulty and environmental impact of these two seepage minimization methods are significantly different. A case history of the dewatering treatment of a deep excavation adjacent to an active subway in the ancient riverbed beneath the first terrace of Yangtze River in Wuhan area is presented in this paper. A three-dimensional numerical model with four different curtain insertion depths is established to simulate the construction effect. The optimal curtain construction method and depth of the seepage is selected by considering construction method, cost, construction difficulty as well as its disturbance impact and construction duration in order to reduce the adverse impact of the dewatering on the surrounding environment. The monitoring results show that the simulated values are generally consistent with the measured values. The impact of the excavation dewatering on the adjacent active subway tunnel can meet the safe operation requirements.

Key words: First Terrace of Yangtze River, Ancient Riverbed, Near Subway, Deep Excavation Dewatering, ThreeDimensional Seepage Analysis