基于TOUGH2-FLAC3D耦合的三维地面沉降数值模拟及控制策略研究

摘要

Land subsidence is a complex problem that involves multiple processes,displacement,and stress-strain changes.In this paper,TOUGH2 and FLAC3D are sequentially executed and linked to solve partially coupled three-dimensional land subsidence model,in which TOUGH2 solves the transport process and FLAC3D solves the deformation process.Then such a model is applied to study control strategies.Based on the idealized pumping land subsidence model,the calculations show that TOUGH2-FLAC3D is able to calculate vertical and horizontal displacements,and the horizontal deformation cannot be neglected under the condition of unlimited deformation at the top and bottom aquifer because its absolute peak value may be higher than the vertical peak.In this process,the porosity and permeability are regarded as a function of effective stress.As the effective stress decreases with time,its ability to yield water gets weak.To ensure enough water production,the area far from the well should provide more water,leading more subsidence to the aquifer.The TOUGH2-FLAC3D simulator was then applied to study land subsidence control strategies.By controlling pumping rate and time,the results show that the subsidence and subsidence area are reduced by controlling the pumping rate and time respectively.By comparing the pulsed pumping and artificial recharge strategy,the results show that subsidence and subsidence area can be controlled by proper artificial recharge,but the pulsed pumping strategy does not.The pulsed pumping strategy leads more subsidence in the distant area from the pumping well,but not much in areas around the well.%地下水开采引发的地面沉降是一种多场耦合的复杂问题,土体变形过程中渗流与应力应变相互影响.采用部分耦合原理,通过渗流和变形过程中的相关状态变量来耦合成熟的商业软件TOUGH2和FLAC3D进行三维变参数的地面沉降数值模拟研究,其中TOUGH2模拟渗流,FLAC3D模拟土体变形,并以此为工具探讨地面沉降的控制策略.基于弹性模型承压含水层抽水的理想算例进行了变参数条件下的模拟计算,发现顶底板水平变形未被约束时水平位移不可忽略,其峰值距离抽水井有一定距离,且水平位移峰值大于垂向位移峰值;此外,由于地面沉降过程中渗透系数及孔隙率减小,导致近井区域渗流量增加,变参数模型位移量大于定参数.将以上方法应用于地面沉降控制策略研究,通过控制抽水流量及抽水时间,发现限制开采速率能控制沉降量,缩短抽水时间能控制沉降范围;对比脉冲式抽水及抽水—回灌常用地面沉降控制策略,发现抽水时采取合理的回灌措施能有效控制沉降量及沉降范围,而脉冲式抽水使得近井处弹性沉降量未得到明显控制,沉降影响范围反而更大.