Having effective systems in place to prevent rockfalls or to ameliorate their effects is obviously one of the highest priorities for mines, given that incidents of this type pose a significant threat to the safety of workers and are usually costly – sometimes ruinuously so – in terms of lost production. A company that believes that it has some of the finest equipment and systems in the world to counter rockfalls and similar events, either in underground or open-pit environments, is Swiss safety net and mesh manufacturer, Geobrugg®.
In essence, Geobrugg develops and manufactures systems made of high-tensile steel wire that protect against natural hazards such as rockfalls, landslides, debris flow and avalanches. The company’s rockfall protection barriers are able to withstand impact energies of up to 10 000 kJ, which Geobrugg believes is unsurpassed by any other systems on the market.
MESHA® installation handler system cuts installation times.
According to Geobrugg Southern Africa’s Technical Manager, Gavin Sims, the company’s products represent the latest safety technology to improve underground and open-pit safety conditions. Geobrugg not only offers highly specialised know-how but can rely on more than 60 years of experience in steel wire processing. The office in South Africa has been in operation since 2012 and is located in Honeydew, Johannesburg.
Features of Geobrugg mesh
The Geobrugg mesh is made of high-tensile steel (1 770 N/m2) that has both static and dynamic capabilities. The rhomboidal chain-link structure combined with the knotted ends of the mesh make handling and installation easy. Less overlap is required when using Geobrugg’s mesh. Mesh panels can be connected with a T3 connection clip that Geobrugg supplies. The T3 clip has a wire diameter of 4 mm and a tensile strength of 1 770 N/m2, equivalent to the mesh itself. The coating on the mesh makes use of Geobrugg’s Ultracoating® or Supercoating® corrosion protection formulation. This coating is a 95 % Zn and 5 % Al compound.
The mesh is very light relative to its strength due to the high-tensile wire, making mechanical installation easy and safe. The mesh is characterised by high mechanical resistance, high energy absorption capability and long life.
Geobrugg systems
The company’s systems are specifically developed to resist dynamic loading and to allow for larger deformations. Geobrugg’s support system can absorb higher energies as all the company’s products are made of high-tensile steel. As such, the resulting material strength of the Geobrugg mesh is around three times stronger than the mild steel variety. Other qualities of the high-tensile steel product include the fact that the mesh is lighter than other mild steel products. The MINAX® 80/3 mesh weighs in the order of 1,45 kg/m2.
Geobrugg’s high-tensile steel mesh and systems go through a rigorous testing and certification process. Geobrugg’s mesh, in conjunction with leading yielding rock bolts, is a ground support system of choice in conditions where rock bursts are likely to occur. The company’s MINAX mesh can be used as an alternative to time-consuming mesh and lacing practice. Using the 4 mm mesh, the need for shotcreting can be eliminated. Geobrugg mesh also has a higher resistance to corrosion than mild steel products.
Full-scale dynamic tests
Rockburst damage is a risk in underground excavations due to seismicity and the blasting processes. Full-scale tests have been done in Walenstadt, Switzerland, to assess the performance of the Geobrugg mesh. These have shown that MINAX mesh provides a solution for high-energy demands, up to 60 kJ!
Recent tests developed by the geotechnical department of Chilean state-owned copper mining company, Codelco, proved that the special design of high-tensile steel mesh, anchors and shotcrete, is highly suitable for protection and support in underground excavations in areas with a high potential for extreme rock bursts. This series of large-scale tests provided the verification of the dynamic ground support system for El Teniente mine in Chile.
At one of the platinum mines in North West Province in South Africa, aerial support is required that could act as a permanent support application. A safe and feasible mining strategy was sought to eliminate the risk to people in a cost-effective way. Geobrugg’s MINAX 80/3 mesh was identified as an ideal product to meet the mine’s requirements.
The mesh, with an 8 mm cable on the leading edge facing the blasting front, was used and was secured within 0,5 m of the blast face. During installation, the blast-on mesh also doubled up as a robust safety net that would remain in place during the blast. The mesh and anchor combination has proved successful in containing hanging wall instabilities.
Mechanised mining
Deep-level mining increases exposure to rock bursts. The increased depths at which mining takes place are associated with high stresses and seismicity factors that need to be taken into consideration when choosing underground support regimes. Conventional ground support systems are designed primarily for static loads and cannot always provide safe working conditions for seismically active mines. Mechanised installations bring a significant reduction in overall installation costs and increased safety as people are removed from the drilling face.
Geobrugg’s purpose-built mechanised roll mesh handler is compatible with all standard multi-boom underground drill rigs and is operated using the hydraulic circuit normally used for the feed arrangement. Using the MESHA® installation handler system, the mesh can be installed up to 40 % faster than the standard practice of sheet meshing in the underground environment. Furthermore, miners are not exposed to the unsupported area during the installation.
Open-pit mines and quarries
In surface mining operations, Geobrugg’s range of products and systems provides rockfall mitigation solutions that are not only aesthetically more pleasing but are easier to install and more cost-effective than conventional methods. Geobrugg’s GBE rockfall barriers are installed in a number of local mines. All barriers are tested in Switzerland under the supervision of – and in cooperation with – research institutes and certification bodies. Energy categories for the GBE rockfall barrier series are approved in accordance with European Directive ETAG027 and bear the CE conformity marking. Geobrugg’s barriers have a considerably smaller carbon footprint than concrete or steel constructions.
Attenuator
The first Geobrugg attenuator system in South Africa has recently been installed in one of the diamond mines. The attenuator system combines the proven strengths of both barrier and drape systems. The barrier breaks the fall and the drape steers the rocks into a designated runout zone. Rocks and other debris accumulate at the bottom safely and can be cleared with routine periodic maintenance. Attenuators are used when the slope height is too great for a single barrier. This solution is self-cleaning and virtually maintenance-free and customers are looking at this as an alternative rockfallprotection solution.
