Abstract: This paper presents a case history of dewatering of an underground combined utility pipe galley construction in Pingtan City. In order to evaluate the dewatering effect under different dewatering design parameters, a three-dimensional numerical model of dewatering during the excavation was established by using commercial finite element method software PLAXIS. In the numerical analysis, the groundwater pressure distribution with different dewatering well spacing, soil layer deformation, variation of groundwater extraction volume with time and dewatering well spacing, are investigated. The results indicate that, the mucky clay layer that lays four (4) meters below the bottom of the excavation serves as a good aquitard layer and the cut-off wall is penetrated into this soil layer so that the connectivity of groundwater between the excavated area and the surrounding area has been effectively reduced. Due to lacking of the groundwater recharging, the groundwater level inside the excavated area could be quickly reach the design groundwater level. The consolidation induced settlement in the cohesive layer inside the excavated area occurs during the dewatering process and the lateral deflection in the excavation supporting structures also occurs so that the ground subsidence behind the supporting structure also consequently induced; The groundwater extraction volume with time pattern shows that a large quantity initially and the extraction volume reduces with time. Under the constraint of the aquitard layer, the time required to reach the design groundwater level has a linear relationship with the pump well spacing.

Key words: Comprehensive Utility Pipe Gallery, Numerical Simulation, Excavation Dewatering, Dewatering Well Spacing, Groundwater Extraction Volume