降雨–蒸发条件下膨胀土裂隙演化特征试验研究

 为了解裂隙演化规律，在实验室模拟降雨–蒸发条件，开展一系列干湿循环作用下的膨胀土裂隙演化试验，记录土样干缩开裂、湿化愈合的动态演化过程。利用裂隙图像识别程序对裂隙面积率等参数进行定量分析；采用灌蜡法，观察裂隙最终形态并测量了裂隙的体积。试验结果表明：脱湿过程中裂隙发育分为缓慢→快速→缓滞增长3个阶段，其中，快速增长II阶段可完成整个裂隙发育的80%～90%；当土样基质吸力接近进气值时，土体开始出现裂隙，当含水率w接近缩限值时，裂隙发育接近停滞；干湿循环过程中，新生裂隙并不一定会在原裂隙处产生；干湿循环效应表现为：裂隙在干湿循环的作用下会逐步发育，主要体现在裂隙面积率与裂隙条数的增加，但随着裂隙发育的反复开裂、愈合使得膨胀土体结构趋于松散，拉应力势能储备逐渐降低，后期的干湿循环过程中，裂隙率、裂隙分维等形态参数会趋于稳定。灌蜡法测得裂隙体积167.8 cm3，约占试样总体积的4.8%，这一方法具有设备简单、操作性强的优势，为测量裂隙体积、观测裂隙三维形态提供了新的思路。

Experimental research of cracking process of expansive soil under rainfall infiltration and evaporation

To better understand the cracking process of expansive soil，rainfall-evaporation tests in laboratory were conducted to expansive soil. The specimen was weighed and photographed regularly during the test process in order to record the development of cracks. The image processing technique was employed to quantitatively extract the parameters of crack features，such as the crack ratio. In addition，the method of wax filling was used to observe the ultimate shape and measure the volume of cracks. It was found that the cracking process consisted of phases of slow→rapid→slow growth. 80%–90% of cracks appeared in the 2nd phase. The cracks appeared when the matric suction approached to the air-entry pressure and the development almost stopped when the water content was close to the shrinkage limit. During the drying-wetting cycles，the new cracks did not always grow along the old tracks. In the drying-wetting cycle，the cracks of expansive soil developed gradually，the crack ratio and the total number of cracks were increased. The development of cracks ceased when it reached a certain stage. The iterative presence and healing of cracks significantly weakened the soil structure that resulted in the reduction of tensile energy. The volume of the cracks is 167.8 cm3 and about 4.8% of the total volume of the sample.