Abstract: Cut and cover method is a common method in tunnel construction, but it inevitably cause land subsidence. To protect urrounding environment and buildings from severe adverse effects, land subsidence is a key factor to assure that the construction supporting design is reasonable. In the process of the construction, the main factors that can cause disturbance are dewatering, excavation and supporting. Previous studies were mostly focused on the influence of one single factor. To better understand actual cases, these three factors should be jointly taken into consideration and a three-dimensional simulation involving the whole construction process is needed. Based on the construction of a tunnel under a lake in Wuxi, two three-dimensional numerical models were built with ABAQUS software in this paper, and each model was designed to represent one section with a specific excavation and supporting plan. The models were employed to simulate land subsidence and soil displacement caused by dewatering and foundation pit excavation. The simulation can represent the construction of cut-off wall, retaining wall, pile foundation, dewatering, excavation, and supports. The simulated results have also been examined by the measurement data from the tunnel construction. The results show that (1) with the increasing distance to the foundation pit, the displacement of soil changes from uplift to subsidence and then gradually decreases. The proportions resulting from excavation and dewatering to the final settlement are 30%-40% and 60%-70%, respectively. (2) the ground settlement of the section supported by bored piles is greater than that of the step-slope excavation section with the same excavaing depth. (3) pile foundations are helpful for controlling ground subsidence.

Key words: land subsidence, tunnel, dewatering, pit excavation, three-dimensional numerical simulation