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2014WinShotcreteEMag

• Extraction level: Over 5 miles (8 km) of development and has become the accepted stan- extraction drives, draw points, and access dard for underground personnel when dealing drives; and with existing and induced stresses. • Pump stations, electrical substations, The main fiber-reinforced shotcrete mixture workshops, lunch rooms, and amenities. design used at Cadia East, Type B shotcrete, is All development is excavated using drill and specified at a compressive strength (UCS) of blast with a fleet of four boring jumbo drill rigs 5800 psi (40 MPa) at 28 days and a toughness of backed up by 10 rock bolting jumbos (Fig. 2). 500 joules (ASTM C1550). Every tunnel and chamber has been supported with The fiber-reinforced shotcrete mixture design fiber-reinforced shotcrete, with a total of 150,000 yd3 has been developed over many years at CVO by (115,000 m3) sprayed as of November 2013. The Newcrest engineers with significant input from shotcrete is all supplied as fiber-reinforced wet mix the concrete supplier, additive suppliers, and the and applied in-cycle before rock bolting. shotcreting contractor. The typical development cycle at Cadia East is: The Type B shotcrete used underground at • Drill; Cadia East is reinforced with 15.2 lb/yd3 (9 kg/m3) • Charge and fire; of Barchip Shogun polyolefin fibers, supplied by • Clearance and re-entry; Elasto Plastic Concrete Pty Ltd (EPC). • Muck out; All fiber-reinforced shotcrete is batched on the • Scale/hydroscale; surface by Boral Concrete & Quarries Ltd. Boral • Shotcrete spraying; supplies all aggregates, sand, and cement and also • Rock bolt; and coordinates concrete additives. The batch plant • Survey markup for next round. operates 24 hours per day, all year. In winter, The minimum standard of ground support nighttime temperatures can reach 23°F (–5°C), consists of 2 in. (50 mm) of fiber-reinforced so heating of batch water is important. shotcrete with 8 ft (2.4 m) long resin-grouted Cadia East has the benefit of a local basalt reinforcement bar rock bolts. Many headings also quarry 12 miles (20 km) from the mine site. This have additional ground support installed according quarry is operated by Boral and supplies high- to ground conditions, longevity, and projected quality crushed basalt aggregate to the on-site stresses, such as: batch plant. • Steel mesh; All shotcrete additives are supplied through • Cable bolts; BASF Australia Ltd, including: • A second layer of fiber-reinforced shotcrete; • Hydration stabilizer; and • High-range water-reducing admixture; • Steel sets. • Liquid silica; Certain excavations have to stay safe and • Low-range water reducer; and accessible for the life of the mine; hence, the • Set accelerator. quality of substrate preparation, shotcrete batching, application of shotcrete, and integration Shotcrete Application with other ground support elements is critical to The average rate of shotcrete application has ensure a safe and low-maintenance environment. been 3800 yd3 (2900 m3) per month. This rate has been consistent and will remain so over the 4-year Mixture Design construction period of the project. This is a massive Fiber-reinforced shotcrete is an integral part amount to batch, supply, and spray each month, of ground reinforcement and support at Cadia which has presented many logistical challenges. East. It is considered essential for safe mining All fiber-reinforced shotcrete was sprayed using robotic spraying rigs by shotcreting contractor Stratacrete Pty Ltd. At the peak of project develop- Table 1: Mixture design for Type B shotcrete ment, five to six Jacon Roboshot Maxijet spray Ingredient Quantity, lb/yd3 Quantity, kg/m3 rigs were used at any one time. Stratacrete Pty Ltd River sand 1795 1065 is a mining and civil shotcrete contractor special- 10/7 mm Basalt aggregate 960 570 izing in robotic placement for both underground and surface operations throughout Australia and SL cement 675 400 selected international markets. Fly ash 95 55 All shotcrete is batched on surface by Boral Ltd High-range water-reducing 50 fl.oz/yd3 2000 mL/m3 and transported to the headings by a fleet of under- admixture ground agitator trucks via the main decline to depths Liquid silica 180 fl.oz/yd3 7000 mL/m3 of up to 4600 ft (1400 m) below surface. This can result in a one-way trip of over 6.2 miles (10 km) Low-range water reducer 30 fl.oz/yd3 1200 mL/m3 to the spraying site and can take up to 2 hours 18 Shotcrete • Winter 2014


2014WinShotcreteEMag
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