MULTI-WELL EFFECT OF ULTRA-LARGE FOUNDATION PIT IN DEEP THICK AND HIGHLY PERMEABLE AQUIFERS

Water head drawdown during dewatering in confined aquifers closely relates to multi-well effect. An ultra-large pit is studied in this paper. The pit features 40-meter-thick aquifers, is high permeability at middle and down side, and uses partial pumping wells. Based on the summarization of hydrogeological conditions, a three dimensional unsteady-flow numerical model of underground water is built and used to simulate the seepage field under different scenarios. They include even and uneven distribution of wells, excavation and dewatering by blocks, various well structures and deployment of injection wells. The research shows (1)Ultra-large pit in highly permeable aquifers has obvious multi-well effect; (2)Dense at Corner and Sparse at Center well deployment unifies water head drawdown and avoids insufficient or excessive dewatering; (3)Excavation and dewatering by blocks suppresses drawdown outside the pit; (4)Well structure with short screen pipe reduces total water yield and suppresses outside drawdown; (5)Aquifers of high permeability are highly rechargeable and recharging has fairly obvious effect on suppressing outside drawdown. Simulation results are consistent with in-situ monitoring. The research result can serve as a reference to similar underground water level control project.