弱透水层释水对黏性土工程特性及微观结构的影响

Influence of Aquitard Water-Releasing on the Engineering Properties and Microstructure of Clayey Soils

华北平原地下水持续超采}I起黏性土压密释水。利用天津塘沽1200m深层钻孔原状土样测试分析，探讨第四纪地层弱透水层释水对黏性土工程特性及微观结构的影响。研究发现，黏性土工程指标变化主要受压密释水的影响，释水段黏性土密度增大，孔隙度、含水量降低，渗透性减弱，固结度增高，且在厚层黏土、砂粘互层及邻近含水层处表现显著。按含水层组分析，第一含水组（0～100m）黏性土释水程度较小或以弹性变形，第二含水组（100～260m）为早期压密释水段，第三、四含水组（260～400m）为目前压密释水段并逐步增加。对比压榨前后黏性土微观结构变化发现，絮状结构黏土垂向压缩量较大，即引起水平渗透系数明显降低。

Continued overexploitation of groundwater in North China Plain has caused clayey soils compac- tion and pore water released. To investigate the influence of aquitard pore water releasing on the engineer- ing behavior and microstructure of clayey soils of the Quaternary, undisturbed soil samples of Tanggu, Tianjin collected from 1 200 m borehole were analyzed. The results reveal that engineering properties of clayey soils are mainly controlled by soil compaction, which causes density increasing, porosity and water content decreasing, permeability reducing, and consolidation increasing, especially in the thick clay layer, the interbeded sand and clay layer, or the clay layer close to the aquifer. From the aquifer analysis, we know that the first aquifer （depth 0-100 m） has smaller aquitard pore water released or has elastic clay deformation; the second aquifer （depth 100-260 m） has early stage of clayey soils compaction, as 1960s- 1980s; in the third and fourth aquifer （depth 260-400 m）, clayey soils are releasing water currently and gradually increasing. Based on the comparative analyzing the microstructure of clayey soils before and after compaction, the result also suggests that the vertical compression of loose clay is much higher, which leads to the decreasing of horizontal permeability.