Macro-meso crack propagation characteristics and safety performance assessment of flawed rock mass

Abstract

The propagation of internal cracks is a common cause of instability and failure in engineering rock masses, which can pose significant risks to their safety and operational integrity. This study systematically investigated the underlying mechanisms of crack propagation in red sandstone specimens containing a single flaw under uniaxial compressive loading. The entire cracking process including initiation, propagation, and coalescence, was recorded and analyzed from macro-meso scales scale using acoustic emission (AE) technology, high-speed photography systems, and a scanning electron microscope (SEM). Furthermore, two new parameters, the weakening parameter R_c and the brittleness parameter R_i, have been proposed for the evaluation of crack sensitivity and the assessment of crack-bearing working capacity in rock masses comprising diverse lithologies (sandstone, plaster, granite, marble, and rock-like materials) and flawed inclinations (0°, 15°, 30°, 45°, 60°, 75°, and 90°). Based on the comprehensive assessment of R_c and R_i, the study proposes a new classification system that divides the safety performance of rock masses into four distinct zones: a safe zone, a flaw sensitive zone, a dangerous zone, and a brittle zone. In terms of natural rock, approximately 60–75% of sandstone and granite specimens fall within the brittle and dangerous zones, indicating a higher tendency to rockburst. In contrast, this proportion decreases to 50% for marble specimens. The dangerous zone for natural rocks is concentrated between 0° and 45°, with the most hazardous flawed inclinations ranging from 15° to 30°. Over 60% of the specimens fall within the dangerous zone at these ranges. The incorporation of fillers has been demonstrated to significantly enhance the overall load-bearing capacity of natural rock masses, notably increasing the proportion of brittle and safe zones. In comparison to natural rocks, rock-like materials have been shown to demonstrate superior safety performance, particularly in their resistance to flaw weakening and their capacity to bear initial cracks. The present study demonstrates that 75% of concrete and 54% of plaster materials are situated within the safe zone when the flawed inclination is below 75°. This research offers a novel scientific reference point for the safety performance assessment of flawed rock masses, which is advantageous for the secure construction and operation of rock mass engineering.