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失水收缩是诱发黏性土体开裂的主要因素之一,揭示收缩开裂的内在机制对预防工程灾变具有十分重要的意义。以压实红黏土为研究对象,开展自然风干条件下4种初始干密度试样的自由收缩试验。依据试样收缩曲线的特征,确定了4个特征含水率点,包括饱和含水率、比例收缩阶段中间含水率、缩限以及残余收缩阶段中间含水率。试样从饱和含水率状态风干到上述特征含水率点后立刻用液氮冻干法干燥,并通过孔隙分析仪测定该脱湿状态下的孔隙分布特征,着重探明细观孔隙体积与宏观总体积收缩的对应过程。结果表明:失水过程的前阶段(偏湿时)团聚体间的孔隙优先收缩,表现为大孔隙体积峰值半径随着含水率的降低而减小,小孔径的孔隙体积则增多;而当达到残余阶段后团聚体内的孔隙会发生收缩,表现为小孔隙的体积峰值会减小;随着含水率进一步降低,土体进入零收缩阶段,团聚体间和团聚体内的孔隙均不会发生变化。整个失水过程中孔隙总体积明显减小,与所测得的宏观变化规律相吻合。
Loss of water shrinkage is one of the main factors that induce the cracking of cohesive soils. It is very important to reveal the intrinsic mechanism of shrinkage and cracking in preventing engineering catastrophe. Taking compacted red clay as the research object, the free shrinkage tests of four kinds of initial dry density samples under natural air drying conditions were carried out. According to the characteristics of the shrinkage curve of the sample, four characteristic moisture content points were determined, including the saturated moisture content, the water content in the middle of the proportion shrinkage phase, the shrinkage limit and the water content in the middle of the residual shrinkage phase. The sample was air-dried from the saturated water content state to the characteristic water content point immediately after drying with liquid nitrogen lyophilization, and pore size distribution characteristics of the dewetting state were measured by a pore analyzer. The mesopore volume and the macroscopic total volume Contraction of the corresponding process. The results show that the pore shrinkage of aggregates preferentially shrinks during the early stage of water loss (when wet), indicating that the peak radius of macropore volume decreases with the decrease of water cut and the pore volume of small pore increases. In the residual stage, the pores in the aggregate will shrink, showing that the peak value of the small pores will decrease. With the further reduction of the water content, the soil will enter the zero-contraction stage, and the pores in the aggregates and agglomerates will not change. During the whole water loss, the total pore volume decreased obviously, which was consistent with the measured macroscopic change rule.