Temporary support to enable simultaneous drilling and bolting
The Centre for Excellence in Mining Innovation (CEMI) wants to resurrect the idea of using a steel canopy as temporary ground support in order to speed up advance rates in underground development.
The proposed canopy, five metres wide, five metres high and 16 metres deep, would protect miners from loose rock and allow drilling or charging to proceed at the face simultaneously with the installation of screen and bolts.
“Development rates have been continually dropping,” said R&D program director Al Akerman. “It now takes one and a half to two shifts to get a 14-foot round off. Our goal is to get a round off in one shift.”
This would mean drilling, charging, blasting, mucking and installing ground support in eight or 10 hours – preferably eight.
The 16-metre deep canopy would accommodate a jumbo at the face and a bolter behind it installing ground support.
Economical
“What makes this process economical is that we’re doing two operations at the same time,” said Akerman. "Currently, in the absence of a canopy, drilling and charging can only proceed after the installation of ground support.
Screen would be draped over the top of the canopy and bolting would be done through openings or slots in the steel.
“The jumbo operator will not be under unsupported ground,” said Akerman. “Screen will go up while the jumbo is drilling or the holes are being loaded with explosives. Protecting miners from rockbursts off the face is also a concern to mining companies, so there are two options, said Akerman.
“We can screen the face (with the canopy in place), or use a temporary shield in front of the canopy similar to a chain link fence to protect miners.”
Holes would be drilled and loaded with explosives through the screen or shielding. Akerman is proposing the use of emulsion over anfo.
“We think emulsion and the use of detonator technology will give us better contour control, especially in the perimeter holes.
“Anfo tends to throw stuff 100 feet down the drift, whereas emulsion will throw it only so many feet, which means your ventilation stays in shape and you won’t be destroying the canopy.”
The steel structure will still have to be moved back from the face for blasting, but not to the same distance that would be required with anfo. The canopy can be equipped with wheels and pushed or pulled into place by a jumbo or scoop.
This isn’t the first time a canopy has been considered, acknowledged Akerman. CAMIRO did some work on it in the ’90s, but it was shelved.
The industry has been depending on technology to increase advance rates, but technology hasn’t delivered, complained Akerman. The canopy is an overlooked, low-tech solution that may be just what the industry needs.
Tunnel boring
“I know there’s been a lot of interest in tunnel boring machines, but that technology is not available to us in the Sudbury Basin. Our rock is too hard for the cutters they’re talking about at Rio Tinto or any of the work that Ashanti Gold is doing with their tunnel boring machines.
“In the last 20 years, there has been no real improvement in cutter technology,” said Akerman. “Drill and blast is one of the few options we have.”
Tunnel boring, he added, was attempted by Inco at Creighton Mine years ago, but was abandoned because of cost, cutting rate and the frequent replacement of cutters. CEMI estimates it will require $1.2 million to put the canopy idea to the test and hopes to have funding from government and industry in place before the end of 2012.
Akerman said he’d like to engage CAMIRO to manage the project and test it either at the NORCAT experimental mine in Sudbury or at a Vale or Xstrata operation.
