A new method to evaluate dynamic bolts and the development of a new dynamic rock bolt

Abstract

Until science advances our current understanding of the demands and capacity of ground support, empirical design, rather than scientific methods, must be used. When considering ground support capacity, the industry has developed a significant database of laboratory dynamic tests on rock bolts. However, a methodology has not yet been developed to translate these laboratory test results into the in situ dynamic capacity of ground support systems. Recent development and implementation of in situ testing of dynamic bolts, provides a significant improvement in evaluation and interpretation of test results. In situ testing is carried out using a portable dynamic test rig (DTR), which simulates a seismic event through a dynamic impulse applied to a test bolt. This new tool also provides an opportunity to study the effects of mining progression on bolt performance. The DTR was utilised to test the recently developed D47 MDX bolt. The 47 mm diameter MDX bolt was tested at various hard rock mines in Australia with a typical 25 kJ dynamic impulse, causing bolt displacement typically between 100mm to 150 mm.

Simulating static pull tests, shear tests and dynamic drop tests to identify basic parameters for subsequent support design

“…a dynamic test such as using the Sandvik/Epiroc method) and back-analysis or by conducting simple pull tests, which have been conducted successfully for several years. Darlington et al (2018) advised that, at one mine, the requirements were to provide an impact energy of 25 kJ and limit the displacement to 200 mm.…”

“…There have been many test facilities constructed in Australia, Canada, France, Norway, Sweden and South Africa, and field tests undertaken in Canada, Australia, the USA, Colombia, Sweden and South Africa (e.g. Dight 1982;Hyett et al 1992;Stillborg 1994;Benmokrane et al 1995;Tannant et al 1995;Ito et al 2001;Stacey & Ortlepp 2001;Aziz et al 2003;Player et al 2004;Compton & Oyler 2005;Jaramillo 1996;Varden 2005;Van Sint Jan & Palape 2007;Hadjigeorgiou & Potvin 2007;Villaescusa et al 2008;Player et al 2009;Li 2010;Blanco Martín et al 2011;Bucher et al 2013;Darlington et al 2018;Whiting 2017;Hadjigeorgiou & Tomasone 2018;Cai & Kaiser 2018;Thenevin et al 2019;Brändle & Fonseca 2019;Hagen et al 2020;Zhao et al 2021). The investigators at the facilities have looked at the load transfer capacities of bolts, mesh and plates under static and dynamic conditions.…”

“…Mine sites now specify the required energy absorption and displacement limits; if based just on laboratory results, they could be misleading, which is where in situ tests become critical (Darlington et al 2018).…”

Laboratory-based drop testing of rock reinforcement

“…During the data processing and analysis, a filter was applied to the data recorded at WASM, whereas the raw data is presented by Li & Doucet (2012). In-field testing is conducted using the Sandvik in situ rig enabling testing to be conducted at a mine site, as described by Darlington et al (2018Darlington et al ( , 2019. As the rig is privately owned, much of the data published to date is on a mechanical hybrid rockbolt, the Sandvik MDX bolt.…”

Ground support and strata monitoring: what is needed?

“…The input kinetic energy from the free falling mass is dissipated though deformation and/or displacement of the bolt (Figure 1b). In situ drop testing has been successfully carried out on mechanically anchored bolts (Darlington et al 2019) and has proven to be an efficient tool in bolt developments and to evaluate dynamic rockbolts in actual conditions as opposed to in the laboratory environment (Roach et al 2019).…”