Abstract: The effect of point-well layout, starting time and operation duration on the dewatering results are evaluated in this paper and the dewatering plan of a deep excavation project over a shielded tunnel in Xiamen was also optimized. A three-dimensional seepage numerical model was established by using PLAXIS 3D commercial software to study the potential factors that affecting the dewatering results. The results show that: the spacing of well points is 15 m is an appropriate distance; In Model No. 1, the single well-point did not obtain a high yield of water volume due to the interaction of well point surrounding it when they were operating at the same time. In Model No. 2, the dewatering results was not ideal due the well pints for the next construction section did not operate. When a zoned dewatering plan is desired, the dewatering well point for the next stage should be operated in approximate 30 days ahead of the desired excavation date. The final field practice showed that the dewatering planed used was reliable and the excavated area was safe and stable.

Key words: deep excavation above tunnel, zero distance, finite element analysis, dewatering optimization, porewater pressure field