What makes matters worse is that many of the mines will get away with a decision to skimp here and there. Then, one day, they encounter serious problems, where tens of thousands of dollars per hour lost due to downtime from a roof fall on a conveyor wipes out all of the money saved from not installing supplemental support or having the tools on hand to avert the problem. It could also shorten one’s mining career.
“Given the current business climate, mine operators are under tremendous pressure to reduce costs, so it’s very tempting to over-economize on a roof bolt plan,” said Tony Calandra, executive vice president, Jennmar. “The less obvious value of minimized downtime can be overlooked and any perceived cost gains are quickly negated when there is a disruption due to a roof fall.”
Likening the investment in a sound roof control program to a vaccination, Alan A. Campoli, vice president of special projects, Jennmar, explained that the old hands who have suffered through the experiences of not taking these proactive measures are leaving the industry rapidly. “They know the hospital stay costs 17 times as much as the vaccination,” Campoli said. “We want to educate people about the long-term benefits of a sound roof control program. However, we have people in key positions that worry about their jobs from day-to-day and that runs counter to what we are trying to achieve.”
Many times Campoli and his Jennchem team are called upon to solve ground control problems. “It’s sometimes frustrating,” Campoli said. “We would rather not play the role of firemen; we would prefer to be constructive, building a program. For some service providers, that’s their business model — firemen selling fire hose. We would rather avoid or prevent the problems altogether.”
With this in mind, Jennmar established the Jennchem program in 2009 with the launch of its J-Crib, a pumpable crib product. Since then, Jennchem’s line of rock stabilization and water control grouts has expanded to include high strength and foaming polyurethane, silicate and phenolic grouts. Today the group, which consists of Campoli; Fred “Buster” Stafford, vice president operations, Jennchem (Pittsburgh); Ben Mirabile, technical sales and service engineer, Jennmar West Virginia; and Dakota Faulkner, manager of research and development, Keystone Mining Services (Pittsburgh), has considerable grout project design and implementation experience.
This unique combination of experience has produced novel and effective ground and water control tools. One such tool is the injectable cable bolt that has been very effective in the reinforcement of fractured and water damaged coal mine roof.
Integrating Grout With Cable Bolts
Non-tensioned and tensioned cable bolts can be used for both primary and supplemental support. They are typically installed in either 1- or 1-3/8 in. diameter drill holes and, if point anchored only, are used with 4-5 equivalent feet of resin. Cable bolts can be tensioned by various methods.
In recent years, there has been a desire to completely encapsulate the cable bolt for corrosion protection, Faulkner explained. “Fully encapsulating a cable bolt with traditional resins can be difficult,” Faulkner said. “Keystone and Jennmar have developed a new cable bolt that can be fully encapsulated during installation or post-installation with polyurethane.”
The Fully Grouted Cable Bolt (FGCB) is equipped with a special head that allows the injection of polyurethane up through the cable bolt head and cable strands, completely encapsulating the cable and filling the drill hole. “Although the FGCB was initially developed to fully encapsulate the cable for corrosion protection, it was also found that by modifying the cable bolt head and injection pressure, the polyurethane could be injected into cracks and fissures of the strata to stabilize the roof,” Faulkner said.
Cable bolts are commonly used to support outby areas, belt entries, belt rehabilitations, intersections, longwall recovery and setup entries, and longwall headgate entries. “We do a lot important work with longwall setup and recovery rooms,” Stafford said.
The use of these support systems is important to longwall miners because of the investment in the equipment and the inflexibility in using that equipment, Campoli explained. “Once those panels are developed, a mine can’t run away,” he said. “A super section can run from bad geology for a while. With a longwall you are possibly looking at stranding a $300 million investment, not to mention the investment in developing the panels.”
Increased mining activity in adverse conditions has underscored the limited effectiveness of the nontensioned, partially grouted cable supports used to supplement primary bolts, Mirabile explained. “Roof failures in conditions such as corrosive environments, highly laminated strata, low overburden depth and water intrusion have demonstrated that the need for cable technology has reached beyond the traditional nontensioned, partially grouted cable tendon,” Mirabile said. “Furthermore, declining market conditions and increased competition for coal customers has demanded that new cable bolt technology be cost-effective and readily adaptable to the mining cycle. Jennmar has developed several cable bolt technologies that can be used as stand-alone solutions or in concert with one another to mitigate adverse conditions. These technologies include rapid tensioning of cable supports, structural surface control and polyurethane injection.”
Steering Away From the Last Resort
Acknowledging that polyurethane injection is always a last resort, Campoli discussed a typical case. “A mine is developing an entry through geology that it knows is questionable. They install regular fully grouted bolts and then they have problem due to increasing horizontal stress,” Campoli said. “Now someone has to drill holes in fractured, hazardous roof to pump urethane.”
Jennchem would have suggested an injectable cable bolt that not only offer standard supplemental support, but can also be used to reinforce the ground with the polyurethane. Most mines that encounter this situation install cable bolts, Stafford explained. “So, in this situation, why not make a wise choice and install an injectable cable bolt,” Stafford said. “Only about one-third of the injectable cable bolts are used. The miners don’t inject them unless they need too.”
Campoli said injectable cable bolts function just as well as regular normal cable bolts. “It’s the same design relative to total strength,” Campoli said. “They are getting cable bolts that hold 30 to 40 tons, depending on the cable diameter. They also have the holes and the packers already drilled. All they have to do is hook the pumps up.”
Ultimately, Mirabile explained, the Jennchem team wants to be involved from the beginning and prevent those issues. “It ends up being significantly more cost effective to manage the problem from the outset than to comeback and mitigate a failure,” Mirabile said.
