Abstract: This study aims to determine the reasonable anchorage length of the bolt in the roadway. Based on the slip-debonding failure mode of the interface between anchoring agent and surrounding rock, this paper deduced formulas of ultimate bearing capacity and interface shear stress distribution along the length of the bolt in the elastic stage. The safety and economy principle was also proposed for determining the reasonable anchorage length of anchors, according to the analysis of conditions of slipping and debonding at the interface between the anchors and the surrounding rock. The influencing factors on reasonable anchorage length and the design process were analysed as well. The results showed that the ultimate bearing capacity of bolts was mainly affected by the interface shear strength . Besides, the interface shear stiffness in the elastic deformation stage was the key control factor of the critical anchorage length. For different kinds of surrounding rock, the interface parameters and can be obtained through short anchor drawing test, which can provide guidance for the design of bearing capacity and reasonable anchorage length. A specific example was calculated and the obtained results agreed well with the results from practical engineering projects in coal roadway. Hence, it is proven that both the calculation method and the design process are feasible to determine reasonable anchorage length.

Key words: coal roadway bolt, non-full length anchorage, resin binding, anchoring agent-surrounding rock interface, slip debonding, reasonable anchorage length