基坑土体侧向卸荷真三轴试验研究

对武汉地区具有代表性的粉质粘土,用基坑开挖过程中坑周土体的应力路径在真三轴上进行模拟试验,得到平面应变条件下固结不排水卸荷试验结果,将其整理成应力-应变关系曲线、孔隙水压力-竖向应变关系曲线、中主应力系数-竖向应变关系曲线和卸荷试验应力路径图。试验结果表明,竖向(σ1)压力不变,侧向(σ3)卸荷时,其应力-应变关系随固结压力的增加,由应变硬化型向应变软化型转化;固结压力较低时,表现为剪胀,固结压力较高时,表现为先剪缩,后剪胀;当中主应力(σ2)始终大于但接近于侧向压力(σ3),按所定义的中主应力系数bd值较稳定;有效应力路径随固结压力增大产生偏转。这些结论为进一步研究粘性土中主应力的作用奠定了基础。

A study of true triaxial test on lateral unloading of soil mass of foundation pit

Taking samples of silty clay existing distinctively in Wuhan District, a simulation experiment on true triaxial test, on which the stress path around foundation pit acts is carried out in order to obtain results of consolidated undrained test under plane strain condition. What’s more, this paper turns those results into the stress-strain curves, pore water pressure-vertical strain carves, and coefficient of intermediate principal stress-vertical strain carves, as well as a graph that describes stress path in the unloading test. The conclusions are drawn based on the above mentioned experimental results as follows: the condition that vertical pressure( ) remains constant and lateral unloading( ), the stress-strain curve would change from strain hardening to strain softening with the increase of consolidation pressure. Under lower consolidation pressure the curve shows dilatation, while under higher consolidation pressure shows an initial positive dilatation and then follows with dilatation; the intermediate principal stress( ) would slightly be superior to the minor principal stress( ). By means of defining the value of bd, the coefficient of intermediate principal stress shows stabilization. The deflection of effective stress path occurs with the increase of consolidation pressure. All these would lay a foundation for a further study on the effects of intermediate principal stress that caused to clay.