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MINE DEVELOPMENT welded wire mesh starting 4 ft above the sill, for ground control. Shotcrete is applied only in the long-term workings. The absence of blast-related overbreak and fracturing combined with the relatively smooth, uniform profile left by the road- header allows the mine to safely reduce the number of rockbolts needed—roughly 25% fewer, on average—and to improve bolting efficiency, explained Wheeler. "Because of the longer advances we can cut with the roadheader, compared with the 8 feet or so that we're limited to with drill and blast, the overall time the bolter spends in the cut is a bit longer, but the time spent per foot of bolting is less because we need fewer of them." In addition to reduced ground control costs, the smooth profile also improves ventilation flow in the stopes. Other advan- tages include the elimination of any need for a drill jumbo, scaler or ANFO truck, and only intermittent use of a loader to clean up muck along the sides of the heading. But, the potential benefits don't end there, said Wheeler. "The safety advantages it provides for miners are tremendous, par- ticularly in the hot areas, and there also are advantages using it in other applications." These, he explained, include backfill recutting to recover "stranded" ore from areas in which a stope may have been mined out of sequence for one reason or another, as well as for mining support pillars between backfilled stopes. "The machine produces a lot less damage to adjacent backfill, compared with blasting, and we've been able to get advance rates of up to 46 feet per shift using it in backfilled areas." However, the MR360 wasn't perfect for the conditions it encountered at Rodeo. "A larger machine would be ideal," said Chacon. "One that can cut harder rock and has an enclosed cab to protect the operator from dust, along with remote-operation capability and higher spray volume on the cutterhead. It'd also be nice to have a way to move the machine under its own power when relocating it from one area to another." That wish list is soon to be fulfilled; the MR360 was scheduled to be removed from the mine at the end of May for a major rebuild, and will be replaced by a Sandvik MH620 roadheader under rental contract. Workers at Sandvik's Elko, Nevada, support facility have been busy fabricating a mockup of the MH620—essentially, a robust wire frame on wheels—that can be pulled through the mine to identify areas along the route that might hinder passage of the new machine. The MH620 is a much heavier (118-mt), longer (12.1 m) wider and more powerful model that offers the features desired by the mine, including an enclosed cab, the ability to cut rock of more than 120 MPa UCS, and an onboard diesel power pack that will enable the machine to tram without a trail- ing cable during moves. The MH620's wider cutterhead will allow the mine to return to its standard heading profile width of 25 ft (7.6 m) instead of the 20-ft single-pass maxi- mum width provided by the MR360. Other Opportunities Kirby Owens, Sandvik's product support manager–mechanical cutting, North America, believes that in locations where geological conditions are suited to the use of a roadheader, other mines also could benefit from the technology. "In addition to the advantages we've seen at Rodeo—improved safety, reduced rock bolting and shotcrete requirements and better ventilation flow, for example, there are other considerations. Mechanical cutting provides a uniform product size that can increase load capacity in batch haulage as well extend the life of compo- nents involved in transporting material. Also, with mechanical cutting, mine-devel- opment advance and production rates can be made more consistent by removal of blasting-related downtime and delays, in addition to completely eliminating explo- sives from the operating face. Closeup view of the Sandvik MH620 roadheader's cutting head. The new, larger and more powerful MH620 has replaced the Sandvik MR360 roadheader previously used by the Rodeo mine. 80 E&MJ; • JUNE 2012 "Overall, I'm excited about the advan- tages that mechanical cutting can offer compared with more conventional mining or heading development, and believe with our hardrock-class roadheaders with ICUTROC technology we can offer improvements in safety, as well as reduce mine costs while meeting or exceeding production rates pro- vided by conventional mining techniques." www.e-mj.com