Influence of angles between anchor rod and cracks on the bearing mechanism of anchored rocks: Insights from the perspective of AE, DSCM and IRT

Abstract

Localized failures resulting from fractures in weakly cemented surrounding rocks can significantly contribute to overall instability in rock engineering. As the engineering geological conditions deteriorating, the mechanical behavior of these weakly cemented rocks exhibiting cracks becomes increasingly intricate. To investigate the anchoring mechanics of such rocks, particularly the impact of the angle between anchor rods and cracks on their bearing capacity, a viewable biaxial loading apparatus was developed. This apparatus was utilized in conjunction with acoustic emission (AE), digital speckle correlation methods (DSCM), and infrared thermography (IRT) to conduct biaxial loading tests on weakly cemented rocks with prefabricated cracks. The findings from these tests reveal that the stress–strain curve of anchored rocks can be categorized into distinct stages: compaction, elastic deformation, plastic deformation, and residual deformation, with the strain during the residual deformation stage comprising 46.9 % to 58.7 % of the total strain. When the angle between the anchor rod and the prefabricated cracks is ≤ 60°, significant tensile failure is observed due to the interconnection of the prefabricated cracks. Conversely, when the angle is ≥ 75°, only minor tensile failure occurs without any penetration of the cracks. As the angle increases, the number of frequency bands within the 200–300 kHz range diminishes, leading to a more uniform distribution of primary frequency signals in the 400–500 kHz range. Following the onset of unstable propagation in secondary cracks, the duration of AE events occurring near the crack tip (within a distance < 2 mm) typically exceeds 500 μs, with high-energy AE events of at least 0.1 × 10^-10 aJ being recorded at the tips of these secondary cracks.