Abstract:The development of crack reduces soil bearing capacity, shear strength, cohesion and other mechanical properties, promotes wall collapse. Under the condition of controlling soil thickness (0.8 cm, 1.6 cm and 2.2 cm), the indoor dehumidification test was carried out on the four layers of Benggang soil. The crack evolution characteristics of Benggang soil were analyzed by taking photos at fixed time and fixed points with a camera sand combined with digital image processing technology. The results showed that: (1) During the dehumidification process, the soil deformation first produced radial shrinkage and then the cracks developed, and the transition layer of four layers soil first produced radial shrinkage and cracks. (2) Among the four layers of soil, the degree of crack development followed the order of transition layer > laterite layer > topsoil layer > sandy layer. The large difference between transition layer and sandy layer would destroy the stability of Benggang soil and accelerate wall collapse. (3) With the increasing of soil thickness, crack development gradually weakened, and the core shrinkage phenomenon increased gradually. For the Benggang soil with a diameter of 12 cm, when the thickness was 2.2 cm, there was no crack development and only core shrinkage. The research results could provide scientific bases for studying the collapse mechanism and improving the stability of Benggang soil.