结构性对膨胀土收缩特性影响的试验研究

膨胀土的收缩性明显，容易引发边坡与地基开裂，但有关结构性对收缩特性影响的认识甚少。采用收缩自动试验装置，在恒湿恒温条件下对原状膨胀土和重塑膨胀土开展了收缩对比试验和扫描电镜（scanning electron microscope，简称SEM）测试分析，结果表明：与原状土相比，重塑土在土中水流动阶段的蒸发速率较小，蒸汽扩散阶段收缩稳定速率较慢，最终体积收缩应变量更大；重塑土体积收缩−含水率关系曲线的线性段较长，斜率较大，直线段与稳定段之间的过渡不明显，而原状土则反之；重塑土和原状土的收缩特征曲线（soil shrinkagecharacteristic curves，简称SSC）在较高含水率段基本重合，随着含水率下降，重塑土的SSC下降更快，对应的含水率范围更宽，最后进入残余−零收缩阶段时，孔隙比明显较小；Chertkov收缩模型适用于原状膨胀土，但不适用于重塑膨胀土。SEM测试结果表明，原状膨胀土较重塑膨胀土具有更强的原生结构性，初始密度与湿度相同情况下，两者颗粒排列、接触方式、胶结状态、孔隙大小与分布特征等微观结构上差异明显，导致蒸发过程中重塑土的水分迁移速率较小、基质吸力较大，是重塑土收缩更剧烈的内在原因。研究结果可为膨胀土边坡的坡面工程防护设计提供参考依据。

Experimental study of the influence of structure on the shrinkage characteristics of expansive soil

Shrinkageis inherent to expansive soil, usually resulting in slope and foundationcracking, but there is little understanding about the influence of structure onshrinkage characteristics. Using an automatic shrinkage test device, comparisontests on shrinkage and scanning electron microscope (SEM) tests for undisturbedand remolded expansive soil were carried out under the same humidity andconstant temperature. The results show that compared with undisturbed soil,remolded soil has smaller evaporation rate in the water flow stage, slowershrinkage stability rate in the vapor evaporation stage and larger volumeshrinkage strain in the end. For the remolded soil, the linear section of thecurve of volume shrinkage versus water content is longer, the slope larger, andthe transition between the linear section and the stable section not obvious,while the undisturbed soil is on the contrary. The soil shrinkagecharacteristic curves (SSC) of remolded and undisturbed soil basically coincidein the section at higher water content; with the decrease of water content, theSSC of remolded soil decreases faster and the corresponding water content rangeis wider, and when entering the residual-zero shrinkage stage, the void ratiois obviously smaller. Chertkov shrinkage model is suitable for undisturbedexpansive soil, but not for remolded one. SEM test results show that theundisturbed expansive soil has stronger primary structure than remoldedexpansive soil. Under the same initial density and humidity, there existsobvious differences in microstructure, such as particle arrangement, contactmode, cementation state, pore size and distribution characteristics between theundisturbed and remolded expansive soil, resulting in smaller water migrationrate and larger matrix suction of remolded soil during evaporation, which isthe internal reason why remolded soil shrinks more violently than undisturbedsoil. The research results can provide a reference basis for the design ofslope engineering protection for expansive soil slopes.