考虑止水帷幕的承压含水层基坑涌水量计算

Calculation of water inflow forfoundationpit withwaterproof curtain in confined aquifers

止水帷幕结合减压降水井的“墙-井”体系是深大基坑常用的降水措施之一,而实际工程中采用“墙-井”体系的基坑涌水量比按照规范公式计算的结果小。为了得到止水帷幕下的承压含水层基坑涌水量计算公式,考虑悬挂式止水帷幕阻断形成的绕流区对基坑地下水水力梯度和渗流断面的影响,本文建立计算分析模型,引入绕流区渗径影响系数,采用数值模拟确定该影响系数,得到基坑涌水量计算公式。结合工程实例验证了公式的准确性,分析了止水帷幕插入深度比和基坑尺寸比对基坑涌水量的影响,得到以下结论:基坑涌水量与止水帷幕插入深度成反比、与基坑面积成正比;当帷幕插入深度比大于0.6或基坑尺寸比小于0.4时,对基坑涌水量和降深影响较大,其他范围内影响幅度逐步减缓。本研究可为类似工程基坑涌水量计算和止水降水设施的布置提供理论依据。

The‘wall-well’system consisting of waterproof curtain combined with decompression well is one of the commonly used dewatering measures for deep foundation pits.However,the actual water inflow into the foundation pit employing this system is smaller than the calculations based on standard engineering formulas.To derive a calculation formula for the water inflow of confined aquifers in foundation pits with suspended waterproof curtains,this work considers the influence of the bypass area created by the suspended waterproof curtain on the hydraulic gradient and seepage cross-section of groundwater within the foundation pit.Introducing the impact factor on seepage path in the bypass area,its determination is accomplished by numerical simulation.Subsequently,a comprehensive calculation formula for foundation pit water inflow in confined aquifers is developed.Through analysis of engineering case studies and numerical simulations investigating the effects of waterproof curtain insertion depth ratios and pit size ratios on foundation pit water inflow,the accuracy of the formula is validated.The results show that the foundation pit water inflow is inversely proportional to the insertion depth of the waterproof curtain and directly proportional to the area of the foundation pit.Notably,when the waterproof curtain insertion depth ratio exceeds 0.6 and the foundation pit size ratio below 0.4,the impact on foundation pit water inflow and water level drawdown outside the foundation pit is more pronounced,with diminishing impact beyond these thresholds.These findings serve as a basis for similar projects in determining foundation pit water inflow and the arrangement of dewatering equipment.