Influence of Testing Configuration on the Performance of Paddled Energy-Absorbing Rockbolts Under Impact Loading

Deep and high-stress mines are susceptible to mining induced seismicity that can challenge the installed ground support. Under these seismic conditions, conventional rockbolts such as mechanical, fully grouted rebar and frictional rockbolts are often inadequate. This has led to the development of several yielding, high energy-absorbing rockbolts that can carry large loads as well as accommodate large deformations. In this category, paddled energy-absorbing rockbolts are more widely used at seismically active mine sites. The performance of energy-absorbing rockbolts is generally determined by the impact testing method, which consists of dropping a known mass from a given height to transfer the kinetic energy of the falling mass to the rockbolt that is installed in a steel tube. All impact tests employ one of two configurations: continuous tube and split tube. The continuous tube configuration simulates an impact load directly applied onto the rockbolt plate while the split tube represents a loading condition on a rockbolt when a rock block is ejected by an impact thrust. However, the influence of the split location along the testing tube on the behaviour of energy-absorbing rockbolts had not been addressed in the past. This paper presents the results of a comprehensive testing programme whereby it was demonstrated that the location of the split within the host tube controlled both the maximum plate displacement and dissipated energy recorded prior to the rupture of the rockbolt. This has a significant influence on the performance of paddled energy-absorbing rockbolts under impact loading conditions.