基于单井抽水模型试验的含水层变形特性

A study on deformation characteristics of pumped aquifer based on physical model of single well pumping test

城市地面沉降由多种因素引起,而过量抽取地下水是主要原因之一。一般认为含水砂层变形为弹性可恢复,但实际原位观测结果发现,含水砂层变形不会随水位上升而完全恢复,还存在长时间的蠕变。基于含水层系统的地下水存在形式,本研究利用室内模型模拟含水层弱透水层的交替布置方式,通过对设置在系统底部的微承压含水层非完整井进行抽水与注水回灌补给,监测含水层的水位降深与分层压缩变形随时间的变化规律。分析结果表明:无论是抽水层或是越流补给层都存在水位降深-累计压缩变形的(双)线性关系,验证了含水层存在塑性变形和与随时间发展而产生的蠕变,抽水含水层的储水系数与经验值和理论值相比较,初步验证了本试验模型的合理性;注水回灌没有使含水层变形恢复,但是减缓了沉降趋势。因此,含水层的不可恢复变形及其时间延迟性在抽水地面沉降的研究中不能忽略。本模型试验的抽水含水层变形特性研究结论可为抽水地面沉降的预测方法研究提供参考。

With the development of society and the improvement of people＇s live,the environmental problem is increasingly becoming a focus. Urban land subsidence which brings harm to normal production and life is becoming an increasing social concern,so the land subsidence control is a very essential mission to engineers and researchers. The land subsidence mechanism is very complex,but the excessive extraction of underground water is definitely considered to be one of the prime reasons,causing the water head drawdown. This is supposed to be the ultimate reason for the effective stress increasing which leads to strata compression in terms of land subsidence. Opposite to common sense,the actual observation results show that the confined aquifers have unrecoverable creep for long time due to drawdown when it is originally considered to be elastic recovery as the water level returns to its initial state. Many works on land subsidence mechanics due to groundwater withdrawal have been done,especially on investigation of in-situ field pumping data. However,the true mechanism is still indistinct. Therefore,a synthetic physical model tank was designed to study the deformation characteristics of pumped aquifers. In the model tank,an underground aquifer system consisted of two interactively layout sand layers and clay layers which was installed with pre-cast pumping and injecting well,and also with transversal arrangement of piezo meter tubes. Then the drawdown and compaction of the aquifer located at the bottom and in the middle were analyzed when the pumped layer underwent an entire process of pumping and injecting,respectively. The results indicated that there was a fantastic bilinear relationship between drawdown and compaction of the aquifers,the storage coefficient was verified to simulate the field pumping test. Also,the compaction of pumping aquifers contained plastic and creep deformation. The water recharge could only slow the subsidence trend but could not make the occurred settlement recover. The irreversible deformation and time lag of the aquifer should be paid more attention to,and conclusions of the physical model test could serve the prediction of land subsidence.