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.