Experimental study on anchoring crack-resistance effects of prestressed anchor under impact loads

Under the action of mining stresses and impact dynamic loads, the development, expansion and instability of the primary fissures in the surrounding rock of deep roadways are an important cause for the dynamic disasters of the deep surrounding rock, and increasing the integrity of broken surrounding rock and inhibiting the re-expansion of the primary fissures by using the anchor supports are an important method to prevent the dynamic disasters in the surrounding rock. To this end, the impact dynamic load tests are performed on CCNBD specimens of prestressing anchor under different preloading moments of end anchor, and three anchoring methods of end anchor, full anchor and yield pressure + end anchor are adopted using the split Hopkinson pressure bar test system. The effects of various factors on the dynamic fracture toughness, crack initiation time and crack expansion rate of the anchored rock mass are analyzed to reveal the crack-resistance effects of the prestressed anchors under impact loads. The results show that: (1) The crack-resistance effects of the prestressed anchors improve the macro-dynamic fracture toughness of the anchored rock mass and delay the micro-crack initiation time and reduce the expansion rate. (2) Both the high preloading end anchorage and the full-length anchorage help anchors develop the crack-resistance effects. Their strengthening order is full-length anchorage > end anchorage > yield pressure + end anchorage. The third method weakens the crack-resistance effects because the yield pressure structures compensates for the crack expansion space. (3) The deformation and damage process of anchored rock mass under impact loads has three stages: crack breeding stage, crack expansion stage and anchor bearing stage. The axial stress of the anchor rod with high preloading moment and full-length anchoring has the most apparent growth rate in the crack expansion stage, and the crack-resistance effects are the most obvious. The research results have some theoretical guidance and reference significance for the anchorage support projects of deep dynamic load roadways.