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2014WinShotcreteEMag

depending on mine traffic. Retarding of the shotcrete • Shotcrete sampling and testing of cored mixture is essential to avoid hydration, and hydra- panels for compressive strength and round tion stabilizer is added at the rate of 50 fl. oz/yd3 determinate panel to ASTM C1550 for (2 L/m3) at the batch plant. flexural strengths; Boral operated a fleet of agitator trucks, all • On-site slump testing; equipped for underground operation: • Casting of concrete cylinders; • Five CAT 730 trucks, capacity 10.4 yd3 • Concrete coring, sampling, and testing (8 m3); services; and • Four Mercedes-Benz trucks, capacity • Aggregate size, shape, and strength testing. 6.5 yd3 (5 m3); and • Two Atlas Copco 5010 trucks, 10.4 yd3 Research and Innovation (8 m3). Newcrest excavates many miles of under- Agitator truck operators carry an additional ground tunnels annually and as a result uses tens supply of hydration stabilizer and are permitted to of thousands of cubic yards of shotcrete across add a specified amount with supervisor approval its mines and development projects. Based on the in the case of excessive delays underground. significant volume of shotcrete and associated During the peak of project construction, coor- costs, Newcrest has allocated funding to research dination of traffic in the main decline was critical areas that will result in improvements in shotcrete as this was the only way in and out of the mine design, quality, and economics. for heavy vehicles. The second egress from the mine, the conveyor decline, was not available for concrete truck travel, as the 4.7 miles (7.6 km) of conveyor system with an ultimate capacity of 4850 tons per hour was being installed. The agitator trucks did not have sole access in the main decline, sharing the route with construction traffic and truck haulage of mine rock. These factors made shift-by-shift planning of shotcrete deliveries, major concrete placements, and timing of nonrevers- ible construction loads all the more important. Slickline delivery of shotcrete was trialed in a lined borehole from surface with the objective of reducing the number of concrete trucks from surface. However, the excellent coordination of Fig. 5: Nozzleman spraying heading with robotic spray rig main decline traffic and the good working rela- tionship between all parties meant that the slick- line was not required. Throughout the Cadia East Project, there were 25 to 30 headings to be sprayed each week spread over the huge extent of the mine. It has only been the well-managed daily planning and willingness of all parties involved to work together—both client and contractors—that made achievement of the high rate of shotcrete application possible. Fig. 6: Shotcreting in progress in undercut drill drive Quality Assurance Regular testing of materials and batched shot- crete is undertaken by Boral as part of their internal quality assurance standards and results are made available to CVO. Independent testing of shotcrete and concrete is carried out for CVO by K&H Geotechnical Services Pty Ltd, one of the major private testing facilities in Eastern Australia. K&H are accredited by the National Association of Testing Authorities (NATA) for Public Testing Services—Construc- tion Materials and conduct the following tests at Cadia East: Fig. 7: Agitator truck reversing up to shotcrete spray rig Shotcrete • Winter 2014 19


2014WinShotcreteEMag
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