Investigation of the Layered Effect on the Tensile Fracture Characteristics of Sandstone Using Intact and Pre-Cracked Brazilian Disk Specimens

To investigate the stratification effect on rock splitting and Mode I fracture characteristics, standard Brazilian splitting disk specimens and straight-crack disk specimens were subjected to splitting loading tests, and a high-speed camera system and acoustic emission (AE) system were used to study the rocks’ mechanical properties, fracture parameters, and AE characteristics. The results demonstrate the following: (1) The tensile strength and fracture toughness of the layered rock exhibit significant stratification effects, gradually decreasing with the increase in the number of layers and the layer angle. (2) The different angles of the stratification planes lead to the diversity of failure modes in the disk specimens. (3) The S-value and the cumulative AE count curve of specimens without prefabricated cracks show two types of pattern during loading: fluctuating increase mode, and “gentle–steep” increase mode. (4) Layered rock specimens exhibit a low ratio of rise time to voltage amplitude (RA) value and high average frequency (AF) characteristics during fracture, and the shear failure mainly occurs during the stable propagation phase after the initiation of macroscopic cracks. (5) The fracture process zone (FPZ)’s length at the peak point of the specimens decreases exponentially with the increase in the number of layers, but this reduction does not go on indefinitely, and there exists a minimum value. Within the range of 0° to 60°, the FPZ length decreases linearly with increasing stratification angle.