蒙脱土失水缩裂过程的边界摩擦与温度效应

膨胀土失水收缩产生裂隙的现象是造成其工程性质恶化的主要原因之一。现有研究成果揭示了膨胀土在失水过程中吸力增大与分布不均是造成收缩与开裂的主要原因。然而,已有关于膨胀土缩裂的试验研究很少考虑到土样边界条件对缩裂过程的影响。采用纯蒙脱土作为试验材料,设置玻璃与凡士林2种土样边界摩擦条件,测试了不同温度条件下,边界摩擦效应对土样缩裂过程与结果的影响;对产生裂隙的形态与数量进行定量化对比分析,提出了黏性土失水收缩产生裂隙的概念模型。试验结果表明:土样从饱和开始逐渐失水的过程中,低摩擦力的凡士林接触面土样开始出现裂隙的时间较晚,开裂时的临界含水量显著低于玻璃底面土样;在20,30,40℃环境温度条件下,凡士林接触面土样比玻璃接触面土样的最终裂隙量分别减少了70.3%,79.6%,77.6%;而在相同的边界摩擦条件下,温度越高则土样失水的速度越快,产生裂隙的数量也相对较高。

Effects of Boundary Friction and Temperature on the Process of Shrinking and Cracking of Pure Montmorillonite During Pore Water Evaporation

The shrinking and cracking of expansive soil during pore water evaporation is one of the main causes which greatly deteriorate its engineering properties.Latest research indicates that the increase of suction and inho-mogeneous distribution mainly lead to the shrinking and cracking of expansive soil.However,few experiments about the expansive soil shrinking consider the effect of boundary condition on the shrinking process.In this re-search,pure montmorillonite is taken as test material,and its shrinking process in the presence of glass and vaseline friction boundaries are tested at different temperatures.The computer image processing technique is employed to quantify the geometric structure and morphologic characteristics of cracks.A conceptual model of shrinking and cracking of clay is established.Test results indicate that during the process of saturation-dehydration,cracks of specimens with vaseline-surface occur late and the critical water content of cracking is obviously lower than that of glass-surface specimens.At temperatures of 20℃,30℃ and 40℃,the final amount of cracks of vaseline-surface specimen is smaller than that of glass-surface specimen by 70.3%,79.6%and 77.6%,respectively.Additional-ly,in the presence of the same boundary friction,the pore water evaporation accelerates and the final amount of cracks increases with the increasing of temperature.