北疆供水一期工程膨胀土不同循环模式条件下的胀缩特性

为深入探讨北疆供水一期工程膨胀土渠坡胀缩机理，通过对膨胀土进行了3种不同循环模式条件下的无荷膨胀率、有荷膨胀率和收缩试验，从宏观角度分析了其胀缩特性规律，并采用扫描电镜试验从微观上揭示其物理机制。结果表明：膨胀土的膨胀变形随时间的延长可分为快速、匀速及稳定3个阶段，膨胀变化主要集中在快速膨胀阶段，上覆荷载越大，有荷膨胀率越小，上覆压力抑制了膨胀土的吸水膨胀作用；随着循环次数的增加，无荷膨胀率、有荷膨胀率和线缩率均呈逐渐减小的趋势，第5次循环后逐渐趋向于稳定值，其中干湿-冻融循环减小幅度最大，干湿循环次之，冻融循环最小。微观机制方面，试样经过循环后，土体孔隙和颗粒总数呈逐渐增大趋势，颗粒总面积等微观指标逐渐减小；土颗粒大小及含量是影响胀缩性的主要因素，循环作用影响黏土颗粒的大小、含量及排列等因素的变化，其中干湿-冻融循环颗粒总面积变化程度最大，膨胀土试样胀缩变化程度最大，冻融循环对微观结构影响最小，膨胀土试样胀缩变化程度最小。

Swelling-shrinkage characteristics of expansive soil under different circulation modes in first phase of Northern Xinjiang Water Supply Project

To further explore the expansion and shrinkage mechanism of expansive soil of the canal slope in the first phase of Northern Xinjiang Water Supply Project, the free expansion rate, loaded expansive soil rate and shrinkage test of the expansive soil under three different circulation modes were carried out. The law of expansion and shrinkage characteristics was analyzed from a macro perspective, and the physical mechanism was revealed from a micro perspective by scanning electron microscope test.The results show that the expansion deformation of expansive soil can be divided into three stages, including rapid, uniform and stable expansion with the time increase. The expansion change is mainly concentrated in the rapid expansion stage. The larger the overburden load, the smaller the loaded expansion rate. The overburden pressure inhibits the water absorption and expansion of expansive soil. With the increase of the cycles, the unloaded expansion rate, the loaded expansion rate and the linear shrinkage rate all show a decreasing trend, and gradually tends to a stable value after the fifth cycle. Among them, the dry-wet-freeze-thaw cycle decreases the most, followed by the dry-wet cycle, and the freeze-thaw cycle is the smallest.In terms of the microscopic mechanism, after the sample is cycled, the porosity and the total number of particles in the soil increase gradually, while micro indexes such as the total area of particles decrease gradually.The size and content of clay particles are the main factors affecting the expansion and shrinkage. The cycle effect affects the changes of the size, content and arrangement of clay particles. Among them, the total area of dry-wet-freeze-thaw cycles has the greatest change, and the expansion and shrinkage of expansive soil samples have the greatest change. The freeze-thaw cycle has the least influence on the microstructure, and the expansion and shrinkage of expansive soil samples have the least change.