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。

Desiccation shrinkage is one of the key factors which may lead to crack of clays. It’s significant to reveal the shrinkage mechanism to prevent disasters for geotechnical engineers. Free shrinkage tests have been carried out on the air-dried samples with different initial dry densities. There are four typical water content points on the shrinkage curves according to desiccation characteristic, which include saturated water content, mid water content in the scale shrinkage stage, shrinkage limited stage, mid water content in the residue stage separately. Specimens are air-dried from saturated water content to typical water content as above, and then drying up them immediately with liquid nitrogen freeze drying method, after that, the pore size distribution by the pores analyzer for acquiring relationship between micropore structure and macro volume shrinkage is determined. The results show that inter aggregate pores are prior to contract at the beginning of dehydration process, which show a large pore volume peak radius decreasing with the moisture content reduction. Meanwhile, small diameter pore volume increases. The intra aggregate pores will decrease at a residual phase showing that pore diameter of volume peak decreases. With moisture content further reducing, inter-aggregate and intra-aggregate pores will not change anymore at the zero contraction stage. The micropore structure is corresponding to macroscopic volume change during dehydration process.