Company insight
Guaranteed safety in underground mines
Swiss company Geobrugg is a global leader in the supply of high-tensile steel wire safety nets and meshes to protect against natural hazards such as rockfall, landslides, debris flows, avalanches or coastal erosion. More than 300 specialists work for Geobrugg worldwide, with production facilities on all continents and a presence in 50 countries.
ining is getting deeper, and rockbursts are a growing risk in underground excavations around the world. This is especially true of mining tunnels in search of new ore horizons, which can reach depths of more than 1,000m. However, seismic events and rockbursts can occur even at lower depths. Traditional support and reinforcement systems such as shotcrete reinforced with electro-welded mesh or fibrecrete used in underground mining are limited in their capability against dynamic loads. The development of diamond- shaped lightweight MINAX steel wire meshes of very high strength in recent years has offered alternative design solutions. In order to fully understand the behaviour and capacity of various ground support systems using MINAX meshes, the Swiss company Geobrugg has carried out many full-scale dynamic tests in its own test centre in collaboration with universities and mines across the world. The need to increase the energy dissipation capacity in the support system designs of different mines has been present for many years. With this goal in
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mind, systematic studies have been carried out, aiming to improve the performance of both the single elements and the complete reinforcement systems. In addition, the development of diamond-shaped lightweight steel wire membranes of very high-tensile strength has given a great boost to this trend in recent years. These powerful, flexible solutions, combined with suitable anchors, have undoubtedly been a huge step towards solving situations where protection against dynamic loads is imperative.
Put to the test
In order to prove the suitability of such support systems with high-tensile steel mesh and bolts and analyse their bearing behaviour, a large-scale test centre was commissioned in Walenstadt, Switzerland. On a test rig it is possible to apply large energies on variable ground support systems with variable bolt patterns and meshes with a total support area of 3.6m x 3.6m in a full- scale test. The test is carried out with load cells, high-speed video analysis and accelerometers. It could be shown that a
combination of high-tensile steel mesh with a specific bolt pattern can result in high energy capacity surface support. Distribution of the impact loads during the stopping process to the different elements of the bearing support system depends on the strength and flexibility of the mesh and the bolt resistance and its pattern. Given the characteristics of a structure that attempts to reproduce the conditions of a mine, boundary conditions are generated, which do not allow a direct correlation between the results obtained in the test and those expected at the mine. However, it allows comparisons between systems/elements of fortification and helps to advance understanding of the complex problem of ground support. The new ground support designs, developed over the past few years consist of high-tensile MINAX steel wire mesh, anchors and shotcrete. Because of the use of high- tensile steel wire (at least 1,770MPa) and the flexibility of the chain-link mesh, such a support system can be used in areas with very high static and dynamic stress. In several cases around the world, it was clearly demonstrated that this type of design, with MINAX, allows high energy absorption of the dynamic loads from periodic rockbursts, depending on the magnitude of the incident, usually without requiring any maintenance. This is fundamental for both miners’ safety and essential to increasing productivity. Following this successful test series of a reinforcement system (shotcrete with mesh, bolt and a second mesh with cable bolts) under dynamic conditions, Geobrugg states: “We can add experimental antecedents to the theory and confirm that this type of support is with no doubt a huge step forward in increasing the safety in underground mining.” ●
Geobrugg’s rockburst test found that the combination of high-tensile steel mesh with a specific bolt pattern can result in high energy capacity surface support.
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www.geobrugg.com World Mining Frontiers /
www.nsenergybusiness.com
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