Tests and analysis of mechanical behaviours of rock bolt components for China's coal mine roadways

A series of laboratory tests were performed to study the mechanical behaviours of newly developed high strength rock bolt components, including rebar, thread, plate, and domed washer. The characteristics of deformation and damage of each component were presented. The stress distribution of plate and domed washer was investigated through finite element modelling. The numerical results show that the yield and tensile strengths of the developed high strength rebar are 33.6%–58.3% and 17.2%–28.7% greater than those of the conventional rebar, respectively. The increase in yield strength was higher than that in tensile strength, suggesting an increase in yield to tensile strength ratio and a decrease in elongation. It is well-known that the thread processing may not be of high precision and accuracy as expected, which is characterised as rough thread surface, non-identical tooth height, toe stripping, and cracks in the surface. Hardening during thread processing tends to increase the thread yield and tensile strengths. In this paper, the typical deformation process of arch-shaped plate is classified into five stages. The tested plates exhibited distinct deformation characteristics and bearing capacities due to variations in shape, size, material and presence of washer. It was observed that uneven bottom surface, low bearing arch and large radius of the transitional arc connecting bearing arch and bottom surface were the major reasons accounting for low load-bearing capacity of plates. The performance of domed washer has a close relation with the shape, size, strength, and deformation compatibility with plate. Stress concentration was observed on the periphery of the contact surface between domed washer and plate, which is significantly influenced by the strength of domed washer and is considered to be 20%–30% higher than that of plate. Finally, a case study in the Datong coal mining district was presented, and the support pattern and effect of the developed rock bolt were described.