Rockburst is a form of strain energy released suddenly that is often associated with the stress concentration within a rockmass during mining excavation or blasting. In order to evaluate the shear deformation behavior of a rockbolt installed in a jointed rockmass under rockburst conditions, a series of dynamic impact load tests was undertaken involving a drop weight of 185 kg falling from a height of 2.8 m equivalent to an energy level of 5076 Joules. The test sample comprised a double shear test system, with three blocks joined together with a rockbolt at various configurations. The test sample was constrained within a steel box arrangement to provide confinement. A high-speed video camera was used to record each test with impacting, and impact displacement and acceleration recorded at the same time. By evaluating their shear load-displacement characteristic, the deformation and energy absorption characteristics of the rock support system under impact shear loading could be studied.
Dynamic loading of rock support systems arising from rockbursts can result in high stress loading in rock-bolts leading to yield of steel, loosening the rockbolt anchor, or in some cases causing complete failure of the rockbolt (Tannant et al. 1995).
Very little published data exist on the response of the rockbolt shear performance of a rockbolt in rock system under dynamic loading. The most detailed and thorough tests have mainly focused on the tensile loading either in laboratory or in-situ tests. However, a comprehensive underground support design requires understanding the deformation characteristics of support systems both in shear and tensile.
Support elements are sensitive to the rate of loading. Hence a thorough knowledge of material constitutive relationships and failure criteria is required to design an optimum support system. The drop weight test is commonly used to simulate the rockburst or blasting effect on rock and rock support systems, which give rise to a strain rate in the order of 10 s−1 equivalent to a 250 μs loading duration (Bischoff & Perry 1991). A static loading rate of 10−5s−1 is frequently used in standard uniaxial/triaxial compressive strength tests, which needs about a 200 s loading duration to failure (Bischoff & Perry 1991). The compressive strength can be 20% higher at a strain rate of 1 × 10−3s−1 compared to the compressive strength obtained at a strain rate of 1 × 10−5 s−1.