Study on the relationship between the maximum anchoring force and anchoring length of resin-anchored bolts of hard surrounding rocks based on the main slip interface

Abstract

The critical anchoring length of the hard rock bolt anchoring system is relatively short, which is prone to problems such as the designed anchoring length being too short to achieve the expected anchoring force, or the excessive anchoring length, which causes waste of resin cartridges. Therefore, predicting the maximum anchoring force for a specific anchoring length is of substantial significance for the design of bolt support parameters design and surrounding stability control. Herein, laboratory experiments, theoretical analysis, and in-situ test are implemented to explore the relationship between the maximum anchoring force and the anchoring length for the bolt anchoring system. The achieved results reveal that the slip failure of the bolt-resin interface (B-R interface) is the main failure mode of the hard rock anchoring system. In the presence of the main slip interface condition (i.e., assuming that the anchoring system fails only at the B-R interface) and for specific values of bolt diameter and elastic modulus, the maximum anchoring force does not depend on the strength of the surrounding rock, but only the anchoring length. The proposed relational model based on the main slip interface of the maximum anchoring force and anchoring length can successfully break the strength limit or surrounding rock type to utilize more experimental data acted upon by various surrounding rock conditions. According to the relational model, the relational curve and function for the maximum anchoring force in terms of the anchoring length of the Φ20 mm rebar bolt are obtained. It is found that the obtained relational curves have high accuracy through in-situ verification and comparison with the curves proposed by other researchers. The research results could provide solid theoretical references for the maximum anchoring forces prediction and bolt support parameters design.