Abstract:

Desiccation is the key factor causing the initiation and expansion of cracks in expansive soil. The evolution of cracks has an important influence on the integrity of soil structure and the long-term stability and safety of the foundation. In order to study the evolution characteristics of dry-shrinkage cracks in expansive soil, micro-CT scanning tests were carried out on undisturbed soil samples. The 2D/3D images and characteristic parameters of soil meso-cracks were obtained by using image processing technology, and the evolution of dry-shrinkage cracks was analyzed qualitatively and quantitatively. The results showed that the volume shrinkage characteristics of expansive soil in the desiccating process were restored by the 3D reconstructed digital model, which was in good agreement with the measured volume of samples. The quantitative indexes of meso-cracks, such as crack ratio, crack number, crack volume and crack structure characteristic parameters, can be extracted from micro-CT images. With the water content decreasing from 24.0% to 12.0%, the crack ratio and crack volume of expansive soil increased, while the number of cracks tended to decrease. According to the volume and geometric characteristics of cracks, cracks can be divided into connected cracks and independent cracks. During the desiccating process, the volume proportion of connected cracks increased significantly, while the number of independent cracks decreased continuously. The ‘ball-and-stick model’ effectively simulated the geometric characteristics of the cracks in expansive soil. The equivalent pore radius, throat radius, throat length and pore-throat coordination number all tended to increase during the desiccating process, and the connectivity of cracks was significantly enhanced. The SEM images showed that the connectivity of meso-cracks was closely related to the arrangement of clay particles and the development of the pores between particles.

Key words: expansive soil, desiccation and dehydration, cracks, micro-CT scanning test