Since the Australian mining industry's embracement of the D47 Mechanical Dynamic Extra (MDX) bolt, Sandvik has recently developed a smaller diameter version, the D39 MDX bolt. Sized for the Canadian, North American and European markets, the D39 MDX is similarly suitable for broken, very weak, strong and seismic rock conditions. The major challenge during the design phase was determining how to fit the components into the smaller envelope while maintaining the desired dynamic capacity. To test the performance of the D39 MDX bolt, the unique and well-proven Sandvik Dynamic Test Rig (DTR) was used. The DTR is a portable apparatus that simulates a seismic event by applying a dynamic impulse of up to 35 kJ. The DTR records the load and displacement of the test bolt through a series of sensors. The test bolts can be installed in any mine site using standard installation procedures and bolting machinery. Tests performed at mines showed the bolt is typically capable of absorbing an energy of 25 kJ (single impact) with displacements in the range of 120-143 mm. The tests conducted have proven that the DTR can be used efficiently in bolt development, and it opens a considerable window of opportunity for future development and evaluation of dynamic rockbolts in actual conditions as opposed to in the laboratory environment. The DTR also provides an opportunity to study the effects of mining progression on bolt performance as test bolts can be tested at any time interval after installation.
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.
With mine owners and operators continuously looking to increase development rates and reduce extraction costs, whilst maintaining safety, the need to develop new innovative products has never been in higher demand. Working with the mining industry, Sandvik has recently developed and released a mesh clamp, which is designed to work with Sandvik's MD and MDX bolt range. The mesh clamp enables the installation of mesh sheets to be quicker, safer and more cost-effective. The major challenge of designing the mesh clamp was to keep the design simple whilst still meeting the requirements of installation flexibility and remaining inobtrusive to the surrounding work area. After several design iterations were laboratory and field tested, a final concept was agreed upon. The systems performance of the mesh clamp and the mesh needed to be evaluated. This required the development of a unique laboratory test rig to simulate the relevant test environment and loading conditions. Laboratory test results proved that the mesh clamp is stronger than the 100 × 100 × 5.6 mm welded wire mesh. The mesh and mesh clamp arrangements were tested until failure occurred, at full mesh load capacity, where the mesh and mesh clamp performed well as a system to absorb a minimum of 50 kN with up to 250 mm of vertical mesh displacement.
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