循环抽注水作用下承压含水层砂土的变形特性

为探讨人工回灌和地下水位季节性变化等因素对承压含水层砂土变形特性的影响,利用FlowTracⅡ增量固结试验系统,设计了符合承压含水层砂土应力状态、符合抽注水应力路径的单向压缩试验,研究了循环抽注水作用对砂土变形特性的影响规律及抽注水作用下砂土变形特性的影响因素。试验结果表明:抽水作用(加载)下砂土产生压缩变形,注水作用(卸载)下,砂土变形呈现压缩和回弹两种现象,且砂土孔隙比大(密度小)时易发生注水压缩现象;循环抽注水作用下砂土总体呈现压缩变形特性,随抽注水循环次数的增加和前期固结压力增大,注水作用下砂土变形逐渐由压缩向回弹转化。基于砂土结构演变,构建了以弹性理论和最小势能原理为基础的抽注水作用下砂土变形机理,解释了注水作用过程中砂土变形呈现的回弹与压缩交替波动的试验现象,用试验结果总结了注水强度、前期固结压力、注水速率等因素对砂土变形特性的影响规律,验证了抽注水作用下砂土变形机理的合理性。

Deformation characteristics of sand in confined aquifer under cyclic pumping-recharging groundwater

In order to investigate the influences of artificial recharge and seasonal changes of groundwater levels on deformation characteristics of sand in confined aquifer, using the FlowTrac II system for incremental consolidation testing, the uniaxial compression test is designed, which satisfies the sand stress states of the confined aquifer and the stress paths of pumping-recharging groundwater. Moreover, the effect of cyclic pumping-recharging groundwater on sand deformation characteristics and influencing factors of sand deformation characteristics under pumping-recharging groundwater are studied. The tests results show that the sand is compressed during pumping (loading), while both compression and rebound are observed during recharging (unloading), and compression tends to occur in the sand of large void ratio (low density). In general, the sand presents compression deformations during cyclic pumping-recharging water. However, with the increase of the number of pumping-recharging cycles and pre-consolidation pressures, the sand deforms from compression to rebound during recharging water. Considering the evolution of sand structures, the deformation mechanism of sand during pumping-recharging water is proposed using the elastic theory and the principle of the minimum potential energy. The phenomenon of alternating rebound and compression of sand during recharging water is well explained. The influences of recharging water intensity, pre-consolidation pressure and recharging water rate on the deformation characteristics of sand are summarized, and the rationality of deformation mechanism of sand during pumping-recharging water is verified by the test results.