A novel energy-absorbing rock bolt with high constant working resistance and long elongation: principle and static pull-out test

With mining at deep levels worldwide, surrounding rocks of roadways are prone to suffer from high stress fields, large deformation, and burst-potential. Therefore, it is critical to develop high performance energy-absorbing rock bolts to carry high load, accommodate large rock deformation, and energy absorbing. In this paper, a novel energy-absorbing rock bolt with high constant working resistance and long elongation is theoretically and experimentally investigated. The new bolt is composed of three main parts: a rebar, a sleeve tube with a partial slope in the inner surface, and a circle of steel balls. The working resistance is generated by plastic flow of the sleeve tube by contact force between the steel balls and the sleeve tube. A mechanical model is established based on Contact Mechanics to better understand the factors affecting the working resistance and to guide the static pull-out tests. Two batches of the new rock bolt with constant working resistances ranging from 60 kN to 145 kN were developed by changing the number and radius of the steel balls in static pull-out experiments. The load-displacement curves of the new rock bolt indicate the performance of the new rock bolt is characterized by high stiffness, high constant working resistance and adjustable supporting length. The constant working resistance corresponds positively to the gouging depth and the radial expansion of the sleeve tube, based on theoretical analysis verified by test results. A numerical simulation of deep soft roadway is applied to investigate the performance of new energy absorbing rock bolt.