基于变渗透系数的地下水开采-地面沉降三维模拟研究

Three dimensional simulation of groundwater exploitation and land subsidence based on variable permeability

在地面沉降过程中伴随着土体孔隙率和渗透系数的变化,但在模拟计算中为了降低计算量而忽略其变化,因而在一定程度上造成模拟结果与实际偏离。为了研究地面沉降数值模拟过程中孔隙率和渗透系数变化对模拟结果的具体影响,在Biot固结理论的基础上,耦合了Kozeny-Carman方程,建立了考虑固结过程中渗透系数变化的三维固结模型。以北京平原区的典型含水层结构为模拟对象,分别在考虑和忽略渗透系数变化的情况下进行抽水模拟,发现在考虑渗透系数变化的情况下,抽水后地层的渗透率体现了不均匀变化,在抽水井井壁附近渗透系数有所降低;考虑渗透系数变化下的地表最终形变量大于忽略渗透系数变化的情况;忽略渗透系数变化导致的模拟误差在沉降初期较小且具有继续发展的趋势,中后期较大并逐渐趋于平稳,且这一误差与抽水量正相关,与承压含水层压缩模量和渗透系数负相关,且随着承压含水层厚度的增加呈现先增大后减小的趋势。

Porosity and permeability of soil keep on changing during the process of land subsidence. However, these are often ignored in order to reduce the computation in the simulation, thus the simulation results may deviate from the actual situation. In order to examine the influence of variable porosity and permeability on the simulation results of subsidence, a 3D consolidation model considering the variation in permeability during consolidation is established based on the coupling of the Biot consolidation theory and Kozeny-Carman equation. Pumping simulations are carried out under the condition of considering and neglecting the variation of permeability in the typical aquifer structure in the Beijing plain. It is found that the change in the layer permeability after pumping is uneven, and the permeability is reduced near the well wall. Considering the change in permeability, the final deformation of the surface is larger than that of ignoring the variation in permeability. The simulation error caused by neglecting the variation in permeability is smaller and has a tendency to develop in the early stage of settlement, and it is larger and more stable in the middle and later stages. This error is positively correlated with the pumping volume and is negatively correlated with the compression modulus and permeability of confined aquifer. With the increasing thickness of the confined aquifer, the error first increases and then decreases.