EXPERIMENTAL STUDY ON PROPAGATION AND SELF-HEALING LAW OF DESICCATION CRACKS IN HIPPARION RED CLAY BY DIC TECHNOLOGY

The Hipparion red clay in Neogene in Northwest China has high clay content and is easy to crack due to drying. In order to study the effect of dry density on the cracking behavior of the compacted Hipparion red clay, a drying test is carried out by a self-made drying device, and the crack evolution process was analyzed by digital image correlation(DIC)method. The results show that: (1)cracking of samples with different initial dry densities occurs during drying process. The cracking process can be divided into four stages including crack initiation, crack propagation, crack self-healing and crack stabilization. The smaller the dry density, the denser and more uniform the desiccation crack network. (2)The change of strain field on the sample surface can better reflect the evolution process of desiccation crack. The blue compressive strain zone represents the shrinkage produced by water loss of sample. The red strain band represents the desiccation crack produced by tension. During drying process, the blue compressive strain area on the sample surface continues to expand and the width of the red tensile strain area decreases, indicating that the crack is pulled by the overall shrinkage of the sample and generate "self-healing" shrinkage. The smaller the dry density, the denser the tensile strain network, the higher the self-healing degree of desiccation crack. (3)The variation of the surface strain field of the sample shows that all cracks show self-healing phenomenon, but the main strain of main crack decreases the fast, and the self-healing phenomenon is the most significant, which plays a leading role in the self-healing of the crack. When the dry density of the sample is small, the larger the crack strain rate of all cracks, the higher the self-healing strain rate in the self-healing process, which indicates that the shrinkage of the sample due to water loss is more obvious.