Engineering & Mining Journal

JUL 2017

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ROCK BOLTING JULY 2017 • E&MJ; 51 www.e-mj.com Service, the engineering affiliate of Jennmar. "We came up with some new ideas and now have several machines in op- eration. To get to that automated system, where an operator does not have to leave his station to insert a cartridge, espe- cially in the high places out West, that has been a big push for Jennmar. These self-drilling pumpable hollow-bar bolts, which are designated MPA, have multiple point-anchor loca- tions that yield under load, will work great for deep mines with high stress and squeezing ground." This injectable resin aspect of the system is really slick, Stankus explained. "The units can mount right on the bolting machines or be a stand-alone, skid-mounted unit," Stankus said. "It's all computer-controlled with a monitor in the cabin and the operator does not have to leave his station." To develop this system, a major technological hurdle had to be cleared. "The problem that everyone encountered was getting the resin and the catalyst into the hole without mixing them and getting the proper ratio," Stankus said. "We perfected a system that places both in the hole without mixing, at the right ratio, and we developed a special pump that works well." Different ground control professionals have tried to develop this system since miners started using resin and Jennmar finally solved the riddle. They developed a special manifold that allows the pump to push resin through a two-line system into the hole using an injection nozzle. Resin is relatively abrasive. Jennmar's J-Lok subsidiary developed a new resin that pumps easier and is less abrasive. Then they developed a set of special cylinders as part of the pumping system that would withstand the abrasion. Alternative Rock Bolting Technologies The MPA is a hollow core bolt with an R32 coarse thread that was developed specifically for the deep mines, which are experi- encing problems with the squeezing ground, explained Stankus. "In some cases, in the time between driling the hole and in- stalling the bolt, the hole had closed," Stankus said. "Because of the heavy pressure, they needed a self-drilling, one-pass bolt that would yield and they were asking for 6 inches of yield." That was a tough problem to solve from a technical stand- point. Jennmar decided to put the coarse threads on each end. They left a space in the middle (hollow core) and used an an- nealing process to change the properties of the center part of the bolt so that it would yield under load. The sacrificial bit on the MPA has holes that allow the use of pumpable resin. The operators drill the hole, the J Lok P sys- tem pumps the resin through the bolt, filling bolt and the void between it and the borehole. The operator loads a 45-lb bag of resin into the cylinders on the machine, which pumps the resin and catalyst in to hole. "Lots of people have tried to develop this over the years," Stankus said. "They key is to pump the resin and catalyst into the hole without mixing the two." The break- through was the manifold that Jennmar developed. The machine drills the holes with a self-drilling bolt. The op- erator pulls off the bolt, attaches the J-Lok P system and then injects the resin safely from the cab. The bolt is fully grouted and protected from corrosion. "It's actually a double-protection system because of the resin inside the hollow core and the resin that fills the space around the bolt in the drill hole," Stankus said. The corrosion the Nevada gold miners are experiencing is related to the sodium in the salt compounds found in the geo- logic formation. The salt compounds are prevalent in a horizon about 20 inches (in.) to 30 in. above the ore zone. In as little as a few months, bolts would corrode and fall out of the roof. They couldn't support themselves let alone the rock. Working with mines, Stankus and his team brought some core samples containing this salt-bearing rock back to Pennsyl- vania. They had the rock tested using their lads and labs outside the company. After three to four months, they identified the cul- prit, and developed a corrosion-resistant coating for the inflat- able bolts. Jennmar's version of the inflatable friction stabilizer is the PythonM3 with PyFlexU2 coating. The coating is corrosion resistant, so it is important that rock in the boreholes does not scrape the coating off the Python during the installation process. "We developed this coating that resisted the salt corrosion, PyFlex, but we needed to keep the coating on the inflatable bolt," Stankus said. "The solution was to develop a sacrificial urethane coating that preserves the cor- rosion-resistant coating during bolt insertion and installation." If the coating is too stiff, it would break apart when the bolt inflates. Yet, it also had to have flexural strength. "We had to find a coating that was substantial enough to resist the salt cor- rosion, but had the flexural strength to stretch and not crack during the inflation process," he said. Resin can be injected through these self-drilling, hollow-bar bolts. A cross-sectional view of the PythonM3 shows the PyFlexU2 inner and outer sacrificial coating. Resin is injected into an MPA through the orange line, which is connected to a machine-mounted unit in Nevada.

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