Engineering & Mining Journal

DEC 2012

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GROUND CONTROL Hage went on to explain that the advent of modern admixtures applied to wet-mix sprayed concrete has reduced problems such as high rebound and dust levels, poor compaction and loss of structural performance significantly, by enabling the placed concrete to be initially plastic in nature. It has also increased output capacity considerably, he added. The introduction of alkalifree set accelerators in particular has allowed for long-term durability in both rock support and tunnel linings, as well as providing an environmentally friendly and non-caustic solution, as opposed to their predecessors, sodium silicate and aluminate. Furthermore, the addition of steel or synthetic fibers to the sprayed concrete mix has led to improved flexural and shear toughness, and resistance to impact. This is particularly the case in areas of high deformation, or where crack control is needed. New advances in spraying manipulators have made the task of setting the optimal nozzle angle and distance even easier, thanks to technology that automatically controls the spraying distance, speed and angle of the spraying jet to the surface. "The mechanization of all procedures that has taken place in the mining industry in the last 20 years has gone hand-in-hand with the development of sprayed-concrete technology, leading to higher and more efficient output," Hage said. Shotcreting technology has come a long way from its beginnings in the early years of the 20th century. TodayÕs systems and equipment are highly sophisticated, giving strong, long-life support. (Photo courtesy of BASF) From the perspective of a major international rockbolting systems supplier, with its North American headquarters in Utah, Dywidag Systems International (DSI) made reference to the U.S. hard rock market. Here, it said, major advances have included the utilization of inflatable expansion bolts and cable-bolt DSIÕs ground control product line includes a variety of roof bolts such as the Tiger Bolt System, a Òone passÓ permanent resin anchor system that can be installed with standard Jumbo drilling equipment. The companyÕs R&D; efforts also have led to the development of corrosion protection coatings for specialty roof bolts. www.e-mj.com technologies, along with coordinated FLAC and other ground control/geologic analysis methods. These have helped to improve the overall system of supports, with other ground-control stabilization technologies working as a system. With reference to Thin Spray-on Liner (TSL) technology, Rob Hawker, technology manager at Minova in Australia, told E&MJ; that no TSL has yet been successfully implemented as a mesh-replacement system for in-cycle use in hard rock mines. The company's principal product in this area, the cement modified polymer Tekflex, has been widely used in coal applications to help control rock degradation through scaling, spalling and weathering, providing a flexible, high tensile-strength lining that can accommodate stresses associated with rock movement as well as acting as a barrier to moisture degradation. Most of the development work Minova has undertaken over this period has been focused on improving its current range for special applications such as escapeshaft liners or preventing weathering, Hawker added. Looking ahead, he said the company has continued to invest in TSL research and has several new systems that it hopes to commercialize withDECEMBER 2012 • E&MJ; 49

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