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ORIGINAL PAPER

Experimental Study on the Mechanical Behavior of Rock Bolts Subjected to Complex Static and Dynamic Loads Hongpu Kang1,2 · Jinghe Yang1,2 · Fuqiang Gao1,2 · Jianzhong Li1,2 Received: 12 August 2019 / Accepted: 15 July 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020

Abstract In underground mining practice, the rock bolt support system is the major support pattern to control the deformation and stability of openings. A rock bolt is generally subjected to complex loads including tension, torsion, bending and shear, which result from the deformation of excavations and exposure to dynamic loads that are generated by rockbursts. An understanding of the response of rock bolt under complex conditions is of great importance for rock bolt support design and practice. New sophisticated equipment has been developed for this purpose. This work involved a comprehensive experimental study on the mechanical behavior of rock bolts under complex loads. The results show that rock bolt pre-tensioning by torque application to the nut can result in decreases in tensile strength and elongation because the rock bolt is subjected to a combination of tension and distortion. When a pre-tensioned rock bolt is subjected to a shear load, the maximum shear force can reach up to 80% of the tensile capacity of the rock bolt. Higher impact energy results in a longer period of dynamic loading and a larger irreversible plastic deformation on the rock bolt, in contrast to a rock bolt that is subjected to low impact energy. The capacity and especially the deformation capacity of a rock bolt may decrease significantly after successive containment of the deformation of the surrounding rock mass from rockbursts. Keywords  Rock bolt · Mechanical behavior · Test equipment · Static–dynamic loading

1 Introduction The rock bolt support is the main support pattern for coal mine roadways in China and is important in the construction and production of safe and efficient mines. With an increase in mining depth, the number of roadways that experience high stresses and coal bursts has increased significantly. As the mining intensity increases, the influence of mininginduced stress on roadway increases greatly, resulting in a large deformation of the surrounding rock and serious dynamic disasters. New challenges occur in rock bolt supports with the most prominent being significant deformation and damage of rock bolt system accessories. Resin-anchored rock bolt are used extensively in Chinese coal mine practices. They tend to consist of rebar, bearing

* Hongpu Kang [email protected] 1



CCTEG Coal Mining Research Institute, Beijing, China



State Key Laboratory of Coal Mining and Clean Utilization (China Coal Research Institute), Beijing, China

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plates, nuts, washers, and resin cartridges. Field investigations of the failure conditions of rock bolts in more than ten mining districts in China showed four locations that are susceptible to fracture: the contact between the thread, the contact between the rebar and the boreho