True-Triaxial Investigation on Failure Characteristics of Rock Mass with Varying Discontinuous Joint Occurrence: Experimental and Numerical Approaches
摘要
To investigate how discontinuous joint occurrences affect the failure characteristics of deeply buried rock, the laboratory tests and PFC3D numerical simulations were conducted under true triaxial stress conditions using rectangular sandstone specimens (70 mm × 70 mm × 70 mm) containing prefabricated discontinuous joints. The discontinuous joint dip angles (DJDAs) ranged from 0° (perpendicular to the σ1 direction) to 90° (parallel to the σ1 direction), and the discontinuous joint strikes (DJSs) were aligned either parallel to the σ2 or σ3 directions. The laboratory test results indicate that the specimen peak stress, elastic modulus, and peak strain initially decrease and subsequently increase as the DJDA increases, whereas the DJS presents minimal effect on the elastic modulus. The failure modes of the specimens with different discontinuous joint occurrences can be classified as tensile–shear mixed failure, slip-shear failure, conjugate shear failure, and external spalling with internal shear failure. The acoustic emission (AE) characteristics indicate that the duration of the AE “quiet period” and the proportion of AE high-frequency signals during the period initially decrease and subsequently increase as the DJDA increases. The simulation results indicate that the discontinuous joints promote the initiation and development of tensile microcracks, and the proportion of tensile microcracks after specimen failure initially increases and subsequently decreases as the DJDA increases. Moreover, there is a significant difference in the mechanisms by which the DJDA and DJS influence the evolution of microcracks, with DJDA mainly affecting the dip angles of microcracks and DJS primarily influencing their strike.