Experimental study on the structural failure characteristics and load-bearing mechanism of anchored fractured rock mass

Bolt support is one of the primary techniques for enhancing rock mass stability, and the degree of fracturing in the rock mass significantly influences the strength and failure behavior of the anchored rock mass. To investigate the failure characteristics and load-bearing mechanisms of anchored fractured rock masses, a self-developed three-dimensional physical simulation test system was employed to conduct comparative loading tests on anchored specimens with varying fracturing degrees reinforced with prestressed bolts. The mechanical response of the anchored fractured rock mass was analyzed based on four aspects: stress-strain curves, failure modes, bolt axial forces, and acoustic emission characteristics. The failure characteristics and load-bearing mechanism were elucidated from the perspective of the evolution of load-bearing structures. The results demonstrated that in intact specimens, the free surface fractured initially upon loading, followed by the development of 40°~60° through-going shear cracks near the internal diagonal region. The peak strength of anchored specimens gradually decreased with increasing fracturing degree. Specimens with higher fracturing degrees exhibited more pronounced advancement in bolt load curves. The upper-row bolts, subjected to combined tension and shear, fractured and displayed a ">"-shaped deformation at through-going cracks. A dynamic transition law was identified between the load-bearing structure and the fracturing degree of anchored specimens. For Fracturing Degrees Ⅰ~Ⅲ, the internal load-bearing structure remained partially intact. After bolt activation, the rock mass and bolts co-bore the load until instability occurred. For Fracturing Degrees Ⅳ~Ⅴ, the inherent load-bearing structure of the rock mass was destroyed, and the bolts became the primary load-bearing component. The load on the bolts gradually increased due to rock mass bulking until instability occurred. These findings provide valuable insights for determining optimal support timing in roadway surrounding rock.