非饱和黄土高吸力下的水力力学特性及微观结构分析

Hydromechanical characteristics and microstructure of unsaturated loess under high suction

联合压力板仪和蒸汽平衡法在全吸力范围内对原状与重塑黄土进行持水特性试验,使用非饱和三轴仪对高吸力下的原状与重塑黄土进行剪切试验,同时采用扫描电镜仪(scanning electron microscope,SEM)和压汞仪(mercury injection apparatus,MIP)进行微观试验,探讨了非饱和黄土结构性差异对其水力力学特性的影响。试验结果表明:随着吸力的增大,原状和重塑土的饱和度、含水率均减小,孔隙比稍有减小。由于原状及重塑黄土的初始孔隙比基本一致,因此两者压汞试验总进汞量接近。由扫描电镜和压汞试验得到的原状及重塑黄土的孔隙结构形态及优势孔径范围不一样,结构性有所差异,导致土-水特征曲线在不同吸力范围内呈现不一样的规律。原状和重塑土的应力-应变关系多呈软化现象,吸力为3.29 MPa的重塑土呈硬化现象。且随着吸力的增大,原状和重塑土的黏聚力和峰值强度均明显增加,体变由剪缩趋向剪胀现象。由于原状土具备一定结构性,胶结作用较强,其黏聚力的增幅会大于重塑土,峰值强度也高于重塑土,而两者的内摩擦角基本一致。

The water retention characteristics of intact and remolded loess in full suction range were tested by combining pressure plate apparatus and vapor equilibrium method.The shear tests of intact and remolded loess under high suction were carried out by the unsaturated triaxial apparatus.At the same time,scanning electron microscope(SEM)and mercury injection apparatus(MIP)were used to conduct microscopic tests to investigate the influence of structural differences on the hydromechanical behavior of unsaturated loess.The test results show that with the increase of suction the degree of saturation and water content of intact and remolded loess decrease,and the void ratio decreases slightly as well.Since the initial void ratio of intact and remolded loess is almost the same,the total mercury intrusion volume of their mercury intrusion tests is close.The pore structure morphology and dominant pore size range of intact and remolded loess obtained from SEM and MIP tests are different,and the structural properties vary,resulting in different soil-water characteristic curve in different suction ranges.The stress-strain relationship of intact and remolded loess mostly displays softening,and the remolded loess with a suction of 3.29 MPa shows hardening behavior.With the increase of suction,the cohesion and peak strength of both the intact and remolded loess increase significantly,and the volumetric deformation changes from shear shrinkage to dilatancy.Because the intact soil has certain structure and strong cementation,the increased magnitude of its cohesion will be greater than that of the remodeled soil,and the peak strength will be higher than that of the remodeled soil,while the internal friction angle is basically the same.