干湿循环作用下云南红土裂缝发展研究

以干湿循环为控制条件,考虑初始干密度、增湿次数和脱湿次数等影响因素,采用室内试验和图像处理相结合的方法,研究云南红土裂缝的产生及其发展演化。控制初始干密度为1.20,1.30,1.40,1.50g/cm~3,通过增湿、脱湿的干湿循环及膨胀率等试验方法,观察红土样裂缝的变化,并应用Matlab图像处理技术提取红土样的裂缝特征参数。结果表明:干湿循环作用下,初始干密度越大,红土样越容易开裂,干密度较小时(1.20g/cm~3)土样始终不开裂,随干密度增大(1.30,1.40g/cm~3),红土样在第3次增湿中开裂,干密度达1.50g/cm~3时,红土样在第2次增湿中开裂,增湿过程对红土样裂缝发展的影响显著大于脱湿过程的影响;红土样的膨胀率随浸泡时间延长逐渐增大,干密度为1.20,1.30,1.40g/cm~3时约8min膨胀基本稳定,干密度为1.50g/cm~3时约36min膨胀趋于稳定;对应红土样的裂缝条数、长度、面积和宽度等特征参数随增湿次数、脱湿次数增大而增大;随干密度增大,红土样的裂缝条数、长度与面积增大,裂缝宽度在干密度约1.30g/cm~3处存在峰值。干湿循环作用引起云南红土开裂的关键因素在于增湿过程中红土样的不均匀膨胀,红土裂缝属于膨胀裂缝,其发展过程包括裂缝孕育期(0~2次)、裂缝形成发展期(2~6次)和裂缝稳定期(6~8次)3个阶段,这3个阶段综合作用的结果,最终影响了红土裂缝的发展演化趋势。

Investigation on the Development of Cracks of Laterite of Yunnan Under Wetting-drying Cycles

Under the control of drying-wetting cycle,taking the effects of initial dry density,wetting frequency and the number of drying,formation and evolution of cracks of Yunnan laterite was studied by the combination of indoor experiment and image processing in this paper.The initial dry density was set at 1.20,1.30,1.40,1.50 g/cm3,the change of crack was observed under drying-wetting cycles and expansion rate test method,characteristic parameters of cracks were extracted by Matlab image processing technology.The results showed that the laterite samples were easier to crack when the initial dry density was higher under dryingwetting cycles;the laterite samples did not crack all the time when dry density was smaller (1.20 g/cm3);the laterite samples cracked during the third wetting when the dry density increased to 1.30 or 1.40 g/cm3,the laterite samples cracked in the second wetting when the dry density reached 1.50 g/cm3;the effect of the wetting process on the development of the laterite cracks was significantly greater than that of the drying process.The expansion rate of laterite samples increased with the time of immersion.The expansion was stable at dry density of 1.20,1.30,1.40 g/cm3 for about 8 min and about 36 min at dry density of 1.50 g/cm3.The number,length,area and width of cracks of laterite samples increased with the number of wetting and drying cycles.The number,length and area of cracks increased with the increase of dry density,and the crack width reached a peak at a dry density of about 1.30 g/cm3.The key factor of the laterite cracking caused by drying-wetting cycle was the inhomogeneous expansion of the laterite samples during the process of wetting,the laterite cracks were expanding cracks.The development process included crack gestation period (0 to 2 times),crack formation and development period (2 to 6 times),and crack stabilization period (6 to 8 times),the result of these three stages finally affected the developmental trend of laterite cracks.