Experimental study on lateral impact resistance of the prestressed anchored rock mass

Clarifying the influences of anchorage parameters on rock mass deformation and failure under impact dynamic load is the key to the control of surrounding rock in rock burst roadways. However, the existing research mainly focuses on the influence of anchorage parameters on rock mass deformation and failure under static load. However, the research on the dynamic failure mechanism of rock mass remains insufficient. According to the deformation and failure characteristics of anchor structure in practical engineering, the dynamic response law of the anchored rock mass under lateral impact load was studied through indoor similar physical model tests. Besides, the effects of anchor material, prestress and anchorage method on crack propagation mode and dynamic mechanical characteristics of anchored rock mass were analyzed. The lateral impact mechanical model of the anchored rock mass was established. Furthermore, rational suggestions on anchorage support in deep rock burst roadways were put forward based on the impact failure mechanism of prestressed anchored rock mass. The following research results were yielded: Under impact load, the cracks of the anchored rock mass are concentrated around the impact point, and the rock sample mainly undergoes shear failure and tensile failure. The size of cracks is controlled by the anchor material, the anchoring method and the prestress level. The axial force of the bolt increases with the increase of steel strength. The axial force platform segments of HRB400, HRB500, and CRM700 bolts are 20.84kN, 20.95kN, and 45.65kN, respectively. The material of the bolt has a significant impact on the impact resistance of the rock mass. The high strength of the bolt increases the stiffness of the anchored rock mass, and the impact force and axial force of the bolt are more sensitive to the impact load. When the pre-stress of the bolt increases from 15 to 45kN, the impact force action time decreases from 47 to 16ms, and the impact force platform value increases from 24.54 to 30.60kN. The impact force change is not significant, but the impact force action time changes more significantly. High pre-stress can improve the deformation resistance of the rock mass, but it will reduce the bearing capacity and impact resistance of the anchor structure. There is also a significant difference in the axial force of the bolt between the full length anchoring and end anchoring methods. The axial force of the bolt under the full-length anchoring method shows a slow increasing trend, and the axial force of the bolt under end anchoring is similar to its static load mechanical characteristic curve. compared with end anchorage, the rock mass is of greater stiffness and deforms less severely under full-length anchorage; meanwhile, the bolt can absorb massive energy through its elongation, but it tends to break under dynamic load. For deep rock burst roadways, it is suggested to choose “three-high” bolts (cables) as the supporting material, reduce the dynamic and static loads of surrounding rock and improve the mechanical properties of surrounding rock, to weaken the influence of dynamic load on the supporting structure of the anchored surrounding rock. The research results provide some theoretical guidance for the design of anti-burst bolt support in deep rock burst roadways.