Real-time observation and analysis of fracturing process of sandstone under cyclic drying and wetting

A number of integrated and pre-existing hole sandstone specimens under cyclic drying and wetting have been prepared and tested under compression with meso-mechanical testing system. The processes of crack initiation, propagation and failure behaviors of specimens are observed by microscope. After several cyclic times of drying and wetting, the cracks initiate at lower load level, and the initial cracks generally are tensile cracks. The crack propagation in integrated specimens is three-dimensional at random, but in the specimens with pre-existing hole, the cracks start to grow at the hole wall firstly. In specimens with pre-existing hole, shearing cracks initiate from the compressive stress concentrated areas of the hole wall under natural state; on the contrary, tensile cracks may initiate at the central zone of tensile stress under cyclic drying and wetting. Moreover, the cracking progress is more complicated and its rupture form is multiple. Compared with natural specimens, the specimens under cyclic drying and wetting become more ductile, and their strength parameters are lower.