Dynamic Tensile Mechanical Properties and Fracture Characteristics of Water-Saturated Sandstone under the Freezing Effect

Dynamic tensile mechanical characteristics of coal-rock mass under the freezing effect are an important subject that is supposed to be studied during the blasting of open-pit coal mines in Northwest China. In this study, the split Hopkinson pressure bar (SHPB) test system was used to perform dynamic Brazilian disc tests on saturated sandstone at normal temperature (25 degrees C) and negative temperatures (-5 degrees C, -10 degrees C, -20 degrees C, and -30 degrees C). The high-speed failure process, macrofracture roughness and mesofracture morphologies of the samples were observed at different temperatures. The experimental results showed that the dynamic tensile strength of sandstone first increased and then decreased with the decrease of freezing temperature. In addition, a statistical model of the variation of sandstone tensile strength under the effect of temperature and loading rate was established. At different temperatures, all samples underwent the process of crack initiation from the center and then the main cracks penetrated the sample. At room temperature, a large number of secondary cracks formed at both ends of the samples and gradually merged with main cracks that do not occur at low temperatures. The fracture roughness of the sample at normal temperature was significantly greater than that at freezing temperatures, and there were no obvious rules of the roughness of fracture surfaces at different freezing temperatures. In the end, the change in the macroroughness of the fracture surface was explained by the brittle-ductile transition of the mesofracture morphologies of the sandstone samples at different temperatures.