压缩过程中非饱和膨胀土体变特征与持水特性的水力耦合效应

土体压缩是岩土工程领域的基本问题。压缩过程中非饱和土的力学与水力学行为是同时发生且相互影响的,有必要统一考察体变特征与持水特性的水力耦合效应。为此,以荆门弱膨胀土为研究对象,开展土中水密度试验、饱和与控制吸力下的非饱和一维压缩试验,准确测量了压缩与卸荷回弹过程中孔隙比–重力含水率–吸力–竖向净应力关系,探讨了水力耦合状况下非饱和膨胀土的体变特征与持水特性规律,并建立相应本构描述。结论如下:1加载段,非饱和压缩曲线均发生明显转折,体现出屈服行为;随吸力增大,压缩曲线依次发生"穿越"现象;卸载段大体呈线性,其斜率随吸力增大而降低。提出能够描述干缩、压缩、卸荷体胀、屈服、压缩性与卸荷回弹性随吸力变化等行为的非饱和土体变方程,可直接用于分层总和法计算。2不同吸力下重力含水率变化存在较大差异;压缩至2941.8 k Pa时,不同吸力下含水率非常接近。吸力与竖向净应力对含水率变化的耦合影响可用3参数Logistic函数描述。3压缩过程中饱和度随竖向净应力增大而增大,卸荷过程中随竖向净应力降低亦增大。采用饱和度或重力含水率,对压缩过程中的水力路径会出现"湿化"与"脱湿"的不同判断,即水力耦合状况下土体表现出复杂的持水状态变化特征。

Hydro-mechanical coupling effects on volume change and water retention behaviour of unsaturated expansive soils during compression

During compression of unsaturated soils, the volume change and water content change interact simultaneously. The hydro-mechanical coupling effects on both of them are comprehensively investigated. For this purpose, tests on water density in soils and suction-controlled (0~1000 kPa) one-dimensional compression tests on saturated and unsaturated soils are carried out for Jingmen expansive soils. The conclusions are drawn as follows: (1) For the volume change behaviour, the yielding point can be observed on the load-compression curve, and the compression ones under higher suction intersect the curves under lower suction sequentially. The unloading curves appear to be linear, and the slopes of which decrease with the increasing suction. The volume change formula is presented, which is capable of predicting the shrinkage due to suction increase, volume compression/expansion due to loading/unloading, yielding, and the variety of compressibility due to suction change. (2) For the water retention behaviour during compression, the water content changes slightly under higher suction. When compressed to the net vertical pressure of 2941.8 kPa, the water contents under the four different suctions are similar. A three-parameter Logistic function is presented for simulating the coupling effects of suction and net vertical stress on water content. (3) The degree of saturation increases during both loading and unloading, both of which mean ‘wetting’. However, the water content decreases during loading, which means ‘drying’. The reason for this discrepancy is that the change of degree of saturation can be affected by change of the water content as well as that of void ratio.