Abstract: 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 inhomogeneous 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 research, 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. Additionally, 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.

Key words: montmorillonite, shrinkage, crack, boundary friction effect, temperature effeect