INFLUENCE OF POST GROUTING OF PILE ON THE SEEPAGE FIELD OF DEEP FOUNDATION PIT DURING DEWATERING

The permeability coefficient decreases in the range of foundation pit after post grouting in bored piles, which has a significant impact on the seepage field of deep foundation pit during dewatering. Taking a plaza-style architecture comprising five towers and underground garage for example, the piles used in the project is bored piles with post grouting technique, the excavation depth of foundation pit is 21 meters, and the thickness of strong permeable confined aquifer groups is 10meters. The open fully penetrating wells are adopted in dewatering engineering which are mainly distributed along the periphery of the foundation pit. Based on the summarization of hydrogeological conditions, a three dimensional unsteady-flow numerical model of underground water is built, which is used to simulate the seepage field under heterogeneous environments. Simultaneously, comparison has been made to the seepage field in homogeneous environments. The model prediction results show that, on the premise of the same dewatering depth, the total water inflow in foundation pit is almost unchanged, while the water inflow in the individual well decreases due to a steeper hydraulic gradient in the post grouting area when the permeability coefficient reduces because of post grouting of pile foundation in pit. Therefore, the number of wells should be increased appropriately. Moreover, the supplied strength will be seriously reduced and the total water inflow in foundation pit will be underestimated if the permeability coefficient is considered as the smaller value after post grouting in the whole calculation domain. The research results have supplied a reference for the optimization plans of underground water control projects and it can also be used for reference in the similar projects of groundwater control.