Dynamic Ground Support Behaviour Assessed Through Higher Order Dynamic Parameters and Time Metrics

Abstract Laboratory-based dynamic testing of rock bolts has become a well-established practice in the ground support industry for evaluation of ground support performance under challenging seismic conditions; however, in-situ dynamic testing remains relatively limited. This study presents a detailed analysis of in-situ dynamic test data obtained from the Sandvik testing rig, encompassing two reinforcement types, MD and MDX bolts, across nine mine site locations representing diverse geomechanical environments. The investigation identifies and evaluates both conventional capacity indicators and new time-metric rate performance indicators to advance the quantitative understanding of dynamic reinforcement dynamic behaviour. Conventional capacity measures of element performance in dynamic tests, such as energy absorption, displacement, and peak load, supply data for demand-capacity evaluations. In contrast, the time-dependent rate indicators, namely power, impulse, strain-rate and the higher-order dynamic parameter jerk, supply data on how the element mechanism operated during the dynamic impact, and why it was or was not vulnerable to failure. These time-metrics capture aspects of dynamic response that have received minimal attention in prior studies yet are shown here to be highly relevant for additional information on reinforcement performance under rapid loading conditions. Results reveal that MD bolts exhibit typically up to twice the power, jerk and strain-rate values compared to MDX bolts, indicating the MD experiences more abrupt acceleration transitions, with corresponding effects on power and strain-rate. However, both element types generate comparable impulse levels during impact. Time-metric analysis was able to discriminate elements into “yielded” and “survived” response clusters, and suggest which survived elements actually might have been close to failure. Spatial variability in the time-metric parameters highlights the influence of the geomechanical environment on dynamic performance. Overall, time-metric (rate-based) parameters represent valuable complementary tools for geotechnical professionals, enhancing conventional capacity indicators rather than replacing them. Time metrics reveal the variability in element performance across different geomechanical conditions and underscore the importance of selecting appropriate reinforcement strategies based on rock mass properties. Time metrics also reveal the preferred element operating response ranges, outside of which failure is more likely. This helps the selection of element types that are more likely to perform reliably in the particular geomechanical conditions in the mine.