Model test on failure mechanisms of deep high-stress soft rock roadways based on excavation compensation method

Abstract

Traditional support (TS) is not sufficient to address the issue of large deformations in deep soft rock roadways with high stress. Based on model tests, this study considered the superposition effects of the evolution of tangential stress σ1 and radial stress σ3 on the crack propagation of excavated rock mass. Moreover, it explored the response characteristics and failure mechanisms of surrounding rock under different support modes. The results showed that, compared with the TS, the compensation support (CS) reduces the surrounding rock deformation, fracture and expansion area, and crack length by 73.7, 86.5, and 37.7%, respectively, while the roadway cross-sectional area increases by 36.8%. At 0.5R, σ3 of the shallow surrounding rock increases by 68.3%, and the peak value of σ1 at this location drops by 18.2%. The excavation effect causes σ3 and σ1 of the surrounding rock to decrease and increase, respectively. The decrease in σ3 leads to initiation of microcracks in the shallow surrounding rock, whereas the increase in σ1 causes the cracks to further open and propagate deeper. Finally, the dislocation, slippage and overturning of the fractured rock blocks along the structural planes result in bulking deformation of the shallow surrounding rock. The occurrence of microcracks in the deep surrounding rock leads to dilatation deformation. The CS strongly compensates for the stress of surrounding rock through negative Poisson’s ratio (NPR) cables, giving full play to the triaxial strength of the surrounding rock and mobilising the self-bearing capacity of the deep rock mass, thereby inhibiting the propagation and penetration of cracks. In contrast, the TS cables have a low prestress and weak excavation compensation effect, which makes it difficult to inhibit the evolution and coalescence of cracks, leading to large deformations in the surrounding rock.