Bolt Hole Drilling-reaming Mechanism And Experimental Research Of Entry In Soft Surrounding Rocks

The failure of anchoring system is a bottleneck problem of roof bolt,especially when the surrounding rock is weak and broken,and consequently,which leads to low anchorage capacity.By geological evaluation and anchorage capacity measurement the paper finds out the main factor which leads to the anchorage failure is the failure between the resin and bolt hole in terms of the failure of roof bolt in entry.According to the research result,it put forwards that the anchorage capacity may increase by reshaping the bolt hole bottom.By analyzing the anchorage system in terms of common bolt hole,cylinder reaming,positive wedge-shaped reaming and negative wedge-shaped reaming,and adopting the maximum pull-out load,the stress and displacement on the bonding interface between resin and bolt as the analyzing index,it determines that the optimum bottom shape is positive wedge-shaped reaming.Based on the stress distribution on the bonding interface between resin and bolt,it concludes the optimum wedge angle is 40°.The reaming improves the initial anchorage capacity of partially-grouted bolts and enables the bolts to bear larger pull-out load,which improves the bolt anchorage capacity significantly;when adopting extending partially-grouted bolts and fully-grouted bolts,the reaming tends to make tiny difference for improving anchorage capacity.A reaming device is developed based on the research,and the pull-out test after reaming in carried out in the laboratory,which verifies the mechanism of positive wedge-shaped reaming and indicates that it is an effective way to improve the anchorage capacity.