Traditional support and reinforcement systems used in underground mining are limited in their capability against dynamic loads. Full-scale dynamic tests carried out by Codelco's El Teniente mine, the largest underground mine in the world, and the Swiss company Geobrugg have shown that the special design, developed by the geotechnical department of this division of Codelco, is highly suitable for protection and support in underground excavations. The design consists of high-tensile steel wire mesh, anchors and shotcrete. Because of the use of high-tensile steel wire (min. 1,770 MPa) and the flexibility of the chain-link mesh, such a support system can be applied in areas with very high static and dynamic stress. The El Teniente mine in Chile is facing significant challenges in terms of seismicity and has to adapt its ground support systems to new high demands in terms of energy absorption and the way the systems are installed inside the tunnels. This innovative ground support system of high-tensile chain-link mesh provides a solution for high energy demands up to 60 kJ. The results achieved thus far, in terms of miners' safety and production performance improvements, are very encouraging.

Ground support for dynamic conditions must be able to withstand the associated loads and deformations and the support scheme has to work as a system. In order to prove the suitability of such support systems with mesh and bolts, and to also analyse the bearing behaviour of them, a full scale test setup was commissioned in 2012 in Walenstadt, Switzerland. On this test rig it is possible to apply large energies on a ground support scheme with four dynamic bolts and a mesh panel of 2.4 × 2.4 m in a full-scale way. The test site is highly instrumented, and in this paper the analysis of the load cells, the accelerometers and the high speed video cameras is given. It can be shown that the bolts as the stiffest elements are always loaded first and then load is transferred to the surface support during the stopping process. Together with the numerical modelling and back calculation of the tests, it is possible to learn more about the stopping process of dynamic loading of ground support and consequently determine the load and energy distribution between the components. The full-scale tests show that stiff bolts and also mesh which is able to stop high loads at low deformations are required to withstand large dynamic loading without substantial deformations during a seismic event. https://papers.acg.uwa.edu.au/p/1410_08_Roth/ Analysis and numerical modelling of dynamic ground support based on instrumented A Roth et al. full-scale tests

No abstract

Rolled high tensile strength steel wire mesh for above-ground surface retention of landslides, over-steepened slopes, pit slopes and roadway exposures has been used globally for decades with high success and has become a standard of practice. Underground mining applications of the Geobrugg rolled mesh are now being used internationally in major block caving and other mining operations with good success and with well-documented performance tests. (Bucher et al. 2013) Furthermore, several other mine site-specific evaluations of cycle-time have documented efficiency improvements (Tonkin 2011).Canadian mines are seeing the need for improved surface support as mining depth increases. A working site evaluation of the rolled mesh is underway at an underground mine in Sudbury, Ontario. Here, a lighter version rolled mesh is being mechanically installed with an Epiroc Boltec boom bolter fitted with an unrolling device on the screen-handling boom.The first phase of this evaluation is intended to provide proof of concept specific to the mine. Key performance indicators are operator hazard exposure, cycle times and other efficiency measures, such as drilling time requirements, consumption of rockbolts, mesh, shotcrete and corrosion resistance, post-blast rehab requirements other effects on operations have been documented. The MINAX® 80-3 mesh used thus far is a lighter version intended for gravity conditions. A heavier version MINAX® 80-4 mesh is ideal for highstress and bursting ground conditions and will be tried later after this initial proof of concept. An additional consideration was to be able to prove that mild steel galvanised welded wire mesh (GWWM), or sheet mesh could still be installed on the blasted face with the same machine setup as for the rolled mesh.All indications thus far are that the mesh and mesh installation represent a viable alternative to current surface support processes, which can improve both safety and efficiency of operations at the minimum while providing the opportunity for improved surface support performance in high-stress ground conditions. The initial results and observations of this first Canadian evaluation of the high tensile rolled mesh will be reported when complete.