基坑坑底隔渗体局部缺陷下渗流量计算及敏感性分析

Calculation of inflow at the bottom of excavation pit with defected sealing barrier and its sensitivity analysis

基坑开挖过程中采用坑底旋喷隔渗体加固是降低地下水渗流对基坑影响的重要手段。一旦隔渗体出现局部缺陷,地下水将涌入基坑,影响施工,甚至会诱发突涌事故,威胁施工安全。针对矩形基坑坑底隔渗体出现局部缺陷的情况,建立了简化的坑底隔渗体缺陷渗水量计算模型,导出了渗流量计算公式;应用GeoStudio有限元软件对坑底隔渗体局部缺陷下的基坑渗流场进行了数值模拟,并与理论计算结果进行了对比分析,探讨了公式的适用条件。结果表明:隔渗体缺陷抗渗系数δ(原状土与缺陷处的渗透系数之比)是影响公式准确性的主要因素,随着δ的增大,公式计算值与模拟值之间的相对误差呈减小趋势,当δ≥20时,计算值与模拟值基本吻合,隔渗体底部水头差异对渗流量影响较小;δ<20时公式计算值误差偏大,通过经验方法对理论公式进行修正后得到半理论半经验公式,能够较好地降低因隔渗体底部水头差异引起的渗流量计算误差。研究结果对于基坑坑底涌水量计算以及隔渗体质量分析等有一定的参考价值。

The use of the jet-grouted bottom sealing barrier reinforcement at the bottom of the pit during excavation is an efficient measure to reduce the impact of groundwater seepage on the pit.Once a local defect appears in the barrier,groundwater will pour into the pit,which will obstruct construction and even induce inrush accidents,threatening construction safety.Regarding to this problem,a simplified numerical model was established for the calculation of seepage inflow at the bottom of a rectangular pit with a defected sealing barrier,by which the formula for calculating the seepage inflow was derived.Then,GeoStudio was adopted to simulate the seepage field of the barrier with a local defect,and the results were compared with those of the previous derived formula,so as to discuss the applicable conditions of the formula.The results show that the defect impermeability coefficientδ(the ratio of the permeability coefficient of the undisturbed soil to that of the defect in the barrier)is the main factor affecting the accuracy of the formula,and the relative error between the calculated and simulated values tends to decrease with the increase ofδ,whenδ≥20,the calculated value is consistent with the simulated value,the difference in waterhead at the bottom of the seepage barrier has a small effect on the amount of seepage;whenδ<20,the relative error between the calculated and simulated values is large,a half-theoretical,half-empirical equation obtained by correcting the theoretical equation empirically can better reduce the error in the calculation of seepage volume caused by the difference in waterhead at the bottom of the sealing barrier.The results of the study have a certain referential value for the calculation of the inflow at the bottom of the pit and the analysis of barrier quality.