The MESHA wire mesh roll handler, shown here mounted on a drill jumbo, speeds installation
of the mesh and keeps operators safely away from unsupported ground.
Tools and products used for ground control in underground mines take many forms, covering a spectrum that ranges from the software needed to collect and analyze rock-stress data to the machines miners use to install hardware such as rockbolts, welded or chain-link wire mesh or shotcrete. Here’s a quick look at some novel ground-control items that have recently become available for hard rock and coal applications.
Rolling Ahead
A presentation by representatives of Swiss ground-control specialist Geobrugg AG at a major mining conference* described a method for mechanized installation of chain-link mesh rolls that was successfully tested at LKAB’s Kiruna mine in Sweden and Gold Field’s South Deep mine in South Africa. The aim was to identify a quick, efficient and effective method for installing rolls of high-tensile chain-link mesh using a mesh handler capable of being retrofitted on commonly used underground drilling equipment.
Geobrugg’s TECCO and DELTAX chain-link mesh products were used in the evaluation. They are made of high-tensile, 4- or 3-mm-diameter steel wire, respectively, and have tensile strength of 1,770 N/mm. The mesh pattern is diamond-shaped, with wires bent and double-twisted at roll edges to maintain strength in that area. Both types are available in rolls that reduce storage space requirements, and can be manufactured in widths up to 3.5 m and in specific lengths corresponding to the tunnel perimeter.
Geobrugg developed a specially designed spike plate to transfer loads from the mesh through the plate to the anchoring system. The plates are stiff and bend-resistant, made of 5-mm-thick galvanized steel in a shape that conforms to the mesh pattern-the spike plate grabs the mesh at six peripheral positions as well as the bolt in the center.
The particular machine used for mesh installation is the MESHA, available through ROCK Australia, a Perth-based company that provides specialist contracting services and products for mining and civil projects. The MESHA handler holding the mesh roll is mounted on one boom of a jumbo and the drill/bolter is mounted on another boom. MESHA, according to its supplier, fits/retrofits any multiboom underground Jumbo. With a quick release system, the jumbo can be transformed from a development drill to a full-scale ground support rig in a few minutes. During underground testing, the components were installed on a three-boom Atlas Copco Rocket Boomer.
With the MESHA handler, jumbo operators install and bolt chain-link mesh in a unified work process, are never exposed to unsupported ground in front of the machine, and can install mesh throughout the entire drive and advance length. The underlying rock remains visible for inspection by geotechnical personnel.
The underground tests, said the authors, offered strong evidence of the system’s ability to meet certain success criteria, including:
- Cost savings due to 30-50% faster installation time, compared with conventional methods.
- No unraveling of the mesh when cut.
- No failure under normal conditions.
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Geobrugg has developed a spike plate, shown here, for securing its chain-link wire mesh during installation and transferring stress loads through the plate to the anchor system.
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Cutting Hose Clutter
Another Australian company, Pempek Systems based in Castle Hill, New South Wales, has developed a unique electronic system package for the control, monitoring and semi-automation of roof drilling/bolting rigs.
Designed for easy installation on new and existing mobile mining machinery, the system comprises a drill rig-mounted, flameproof, hydraulic-electric control module (E-Box) and a companion flameproof, push button-equipped Human-Machine Interface (HMI) control station. The E-box module can be adapted to suit roof drill and miner-bolter models from several manufacturers.
Designed for easy installation on new and existing mobile mining machinery, the system comprises a drill rig-mounted, flameproof, hydraulic-electric control module (E-Box) and a companion flameproof, push button-equipped Human-Machine Interface (HMI) control station. The E-box module can be adapted to suit roof drill and miner-bolter models from several manufacturers.
Conventionally, on a miner-bolter machine a large set of hydraulic hoses is necessary between the drill rig(s) and hydraulic switching valve bank. The valves controlling flow to the drill rig functions are then either controlled by onboard hand levers or a remote control system.
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Pempek Systems’ push button interface for driller-bolter controls replaces hand levers.
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Pempek’s approach is different: The E-Box combines hydraulic valves, solenoids, sensors and electronics in a single, flameproof-certified package. The unit attaches directly to the mast of a drill rig via a hydraulic adaptor plate. This approach eliminates up to 30 hoses per machine, according to the company, depending on the make and model of the drill rig. Some hydraulic hoses are still required to provide fluid power to the E-Box module as well as connections to the drill head unit of the drill rig.
A typical miner-bolter machine, for example, is fitted with four roof drill/bolt rigs, mounted directly behind the cutter drum. Pempek said installation of the system on a machine of this type would involve fitting each rig with its own E-Box. A master processor is installed in the main enclosure and is connected to each rig’s HMI station by a power and data cable. The operator uses the HMI station to control and monitor all drilling and bolting functions for a single rig.
The system, according to Pempek, provides a number of benefits over traditional roof drill controls; including:
- Clean, simple installation.
- Smooth, electronic drilling control.
- Flameproof-certified system.
- Advanced diagnostics.
- Increased safety.
- Built-in roof mapping.
- Lower maintenance and life-cycle costs.
Easily Installed Overcasts
DSI Underground offers its EZ Overcast line, a system that can be tailored to mine-specific requirements and is designed to be deployed in often-remote mine locations where temporary aircourse routing, fall repair, or walkway protection is needed. The overcast deck and wall structures are constructed of rolled wide-flange beams in various combinations of width and height dimensions. According to the company, the overcast systems are 100% recoverable and reusable; wrenches are all that’s needed to assemble and disassemble an EZ Overcast, which breaks down to components sized for easy handling by individual workers, leaving the unit ready for reassembly, transport or storage.
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| DSI Underground’s EZ Overcast. |
Standard beam sections can be upgraded to heavier material to provide additional support in fall areas or as protection in rib-outburst conditions. They can be configured as bridge overcasts, with mine roadways passing over them, and as void filler forms, providing a uniform, yielding yet stable mine entry for long-term use when erected within and along a mine entry or through a repaired fall when backfilled with a cementitious foam concrete.
Overcasts are normally fabricated with either “inner” or “outer” applied deck material, or skins, but can be specified with both inner and outer skins for very high-pressure applications.
* J. Kalejta , E. Rorem and C. Balg, Innovative Technology System for Ground Support with a Fast, Safe and Fully Mechanized Way of Installing Wire Mesh. Paper presented at 23rd World Mining Congress, 2013, Montreal, Canada.
