深厚强透水含水层超大基坑降水群井效应研究

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

基坑减压降水的幅度与群井效应密切相关。某超大面积基坑,含水层组厚40m,中下部透水性强,采用非完整井降水。对水文地质条件概化,建立了地下水三维非稳定流数值模型,对均匀布置群井、不均匀布置群井、分块开挖降水、不同的井结构、布设回灌井等工况,进行了渗流场模拟。研究表明,强透水性含水层超大面积基坑降水的群井效应极为明显;井位角密中疏布置,可实现降深调平,避免降深不足和超降;基坑分块降水,可减少坑外降深;短滤管井结构可减少基坑总涌水量和坑外降深;强透水性含水层可灌性强,回灌对减少坑外水位下降有较明显的效果。模拟结果与现场监测较为一致。研究成果可为类似工程地下水控制设计提供参考。

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.