真三轴加载下原状膨胀土的吸力和增湿变形特性

Suction and wetting deformation characteristics of intact expansive soils under true triaxial loading

为模拟实际工程中膨胀土的增湿膨胀变形特性,利用非饱和土湿陷真三轴仪,在测量吸力条件下对原状膨胀土进行等向固结试验、三向净主应力加载试验和增湿试验,研究净平均应力对吸力和压缩变形的影响,探讨三向净主应力加载剪切时吸力的变化规律,以及中主应力、应力比和净围压对吸力和增湿膨胀变形的影响。研究结果表明:等向压缩过程中,吸力随着净平均应力的增大而减小,较小的净平均应力(p≤100 kPa)对吸力和孔隙比的变化影响较小,而较大的净平均应力(p>100 kPa)对吸力和孔隙比的变化影响较大;由e-lnp关系曲线确定出膨胀土的屈服应力p_(y)=100 kPa,屈服吸力s_(y)=86.4 kPa;剪切时,吸力先微小降低或保持不变,q/p>1时,吸力再下降后趋于稳定,q/p≤1时,吸力再上升后趋于稳定;增湿时,吸力随着含水率、中主应力参数b值和净围压σ_(3)的增大而减小,但随着净围压和净大主应力比值k的增大而增大;原状膨胀土增湿时存在着三向变形,膨胀土的变形型态可归纳为4种形式,且与中主应力参数b值、应力比k和净围压σ_(3)密切相关。

A series of isotropic consolidation tests,three-dimensional net principal stresses loading tests and wetting tests were carried out on intact expansive soils under measuring suction by using unsaturated soil collapsible true triaxial apparatus to simulate the swelling deformation characteristics of expansive soils in practical engineering.The effects of net average stress on suction and compression deformation were studied.The variation of suction under three-dimensional net principal stresses loading,and the effects of intermediate principal stress,stress ratio and net confining pressure on suction and swelling deformation are discussed.The results show that the suction decreases with an increase in net average stress,and the smaller net average stress(p≤100 k Pa)has little effect on the variation of suction and pore ratio,while the larger net average stress(p>100 kPa)has a great influence on the change of suction and pore ratio.From the e-lnp relationship curve,it is determined that the yield stress of expansive soil is p_(y)=100 k Pa,and the yield suction is s_(y)=86.4 k Pa.When shearing,the suction decreases slightly or remains unchanged at first,q/p>1,the suction decreases again and then tends to be stable,q/p≤1,the suction increases again and then tends to be stable.When humidifying,the suction decreases with an increase in moisture content,intermediate principal stress parameter b and net confining pressure σ_(3),but increases with an increase in k value.There is a three-dimensional deformation when the intact expansive soil is humidified.In this paper,the deformation forms of expansive soils can be summarized into four forms,which is closely related to the intermediate principal stress parameter b,stress ratio k and net confining pressure σ_(3).