地下构筑物挡水效应对地表沉降参数敏感性影响分析

On the Influence of Water Retaining Effect of Underground Structures on Parameter Sensitivity for Land Subsidence Caused by Water Pumping

以比奥固结理论为基础,建立设置挡水构筑物与否的多种工况下的地面沉降有限元模型。计算分析开采不同含水层时地表沉降的特征,在此基础上设置逐渐深入地下的挡水构筑物,分析其挡水效应对抽水引起的地面沉降的影响。以最大地面沉降为指标,结合MATLAB编程计算,比较土体随机变量分布参数相对敏感性大小,并分析挡水构筑物对土体参数敏感性和结构可靠度的影响,最终加以公式推导验证参数敏感性的变化。结果表明:在边界不透水的情况下,开采含水层越深,地面沉降量越大,且挡水构筑物入深增大,最大沉降量和沉降差均增大;但是随着挡水构筑物深入地下,挡水构筑物两侧的地面沉降规律有所不同,开采井一侧为逐渐增大,另一侧足够远处为先增大后减小,沉降量变化幅值较小。影响地面沉降的土体参数按敏感性从大到小排序依次是弹性模量、渗透系数、泊松比、密度、内摩擦角,其中内聚力和孔隙比敏感性极小;分析挡水构筑物的设置对各参数敏感性的影响可知,土体渗透系数和与侧摩阻力正相关的参数(即泊松比、内摩擦角、内聚力)敏感性增大,其余参数敏感性减小,因此在分析地面沉降时,应适时考虑侧摩阻力的影响。地下挡水构筑物的设置和考虑弹性模量与渗透系数的正相关性计算得到的结构可靠度均减小。土层由侧摩阻力控制的沉降量大小取决于土层的沉降差和变形土层厚度。

Based on the Biot consolidation theory,the finite element models of land subsidence under different working conditions were established considering two cases of with and without a water retaining structure.Scenarios of land subsidence when mining different aquifers were calculated and analyzed.Water retaining structures were set up to gradually penetrate into the ground,and the influence of water retaining effect on the ground subsidence caused by water pumping were analyzed.Taking the maximum ground subsidence as the benchmark and combining MATLAB programming calculation,the relative sensitivity parameters of soil mass random variable distribution were compared,and the influences of water retaining structure on the sensitivity of soil parameters and the reliability of structure were analyzed.Finally,a formula was deduced to verify the change of parameter sensitivity.Results show that when the boundaries were not permeable,the deeper the extracted aquifer was,the greater the land subsidence was,and as the water retaining structure went deep into underground,the maximum land subsidence and the land subsidence difference increased.However,as the water retaining structure went deep into the ground,the land subsidence laws on both sides of the water retaining structure were different.The subsidence on the side of the pumping well increased gradually,while the other side far enough away from the pumping well increased first and then decreased,and the magnitude of the subsidence variation was small.The most influential parameters on the subsidence caused by water pumping were,from most to least sensitive:the elastic modulus,permeability coefficient,Poisson’s ratio,soil density,internal friction angle,and the cohesion and porosity ratio were less sensitive.By analyzing the influence of water retaining structure on the sensitivity of each parameter,it could be seen that the sensitivity of permeability coefficient and the parameters that related to lateral friction(Poisson’s ratio,internal friction angle,cohesion)increased,while the sensitivity of other parameters decreased.Therefore,the influence of lateral friction should be considered at a proper time.The structure reliability was reduced when setting up the water retaining structure or considering the positive correlation between elastic modulus and permeability coefficient.The land subsidence controlled by lateral friction depended on the land subsidence difference and the thickness of deformed soil layers.