Influences of Internal Unloading and Lateral Stress on Rockburst Behavior in Deep Hard Rock Roadways

To explore the effects of internal unloading and lateral stress on rockburst behavior in deep hard rock roadways, rockburst simulation tests were executed utilizing a self-developed internal unloading apparatus. A miniature camera was employed to monitor and record the rockburst evolution process of surrounding rock following internal unloading. Results demonstrate that the rockburst process primarily consists of four stages: the quiet stage, the buckling deformation stage, the rock fragment exfoliation stage, and the V-shaped notch formation stage. As the lateral stress increases from 15.2 MPa to 26.7 MPa, the vertical stress corresponding to the initial failure (σzi) increased from 64.00 MPa to 74.00 MPa, the fractal dimension of rock fragments decreases from 2.4033 to 2.3459, and the rockburst severity decreases. Under high lateral stress conditions, rock bearing capacity is comparatively high, making it less prone to rockbursts. However, more elastic strain energy accumulates inside the surrounding rock. Consequently, once a rockburst occurs, its intensity is notably greater than that subjected to low lateral stress. This suggests that increasing the lateral stress exerts a strengthening effect on the surrounding rock of the roadway. Numerical simulations were performed to study the crack evolution laws within the surrounding rock. Studies have revealed that internal unloading induces both shear and tensile cracks, but mainly tensile cracks. As the lateral stress increases, the number of shear and tensile cracks induced by internal unloading increases. The internal unloading triggers rock damage, leading to a strength-weakening effect. It becomes more pronounced as lateral stress increases. By comprehensively comparing the effects of internal unloading and lateral stress, the initial failure vertical stress increases with rising lateral stress, demonstrating an overall strength-strengthening effect induced by increasing lateral stress. Therefore, the strength-weakening effect resulting from internal unloading is weaker than that resulting from increasing lateral stress.