Improving Roof Control Programs

New tools improve safety and reduce downtime as underground coal operators focus on achieving full capacity

by steve fiscor, editor-in-chief

Contrary to what some might believe, the coal business is experiencing a boom right now. Prices for spot sales are high for almost all regions. Many coal operators are using this swoon to reinvest in operations with an eye toward long-term performance. This includes rehabbing mainline entries and reinforcing vital areas with steel sets and secondary supports. Ideally, they would like to make these improvements without taking production offline.

The problem right now is miners and materials. The mines need to keep the miners they have healthy and train the new miners they are bringing on board. They also need to properly forecast production and estimate material needs. Similar to every other industry these days, supply lines are tight and prices for steel and special components are high — if you can find them.

The original equipment manufacturers (OEMs) and mine suppliers are well aware of the situation and, in some cases, are facing a similar set of issues when it comes to manpower and materials. Leading mining industry supplier Jennmar said keeping supply lines open is a team effort. They are also supporting and advising mines on many of these rehabbing projects as well as day-to-day mine engineering plans, such as developing roof control plans.

Safety is the highest priority underground and leading roof bolter OEM J.H. Fletcher & Co. is developing several new concepts to improve the operating conditions for roof bolting machine operators. 

Long-term Support Strategies

The coal industry is experiencing some strong demand fundaments and business is brisk for Jennmar these days. “I don’t think anyone could have predicted we would be in this situation two years ago, but business is good right now,” said Benjamin Mirabile, vice president of engineering for Jennmar. “With coal demand and prices the way they are, everyone is trying to maximize production, but a tight labor market has really limited their ability to quickly ramp up.”

Many of the requests that Jennmar has received from coal operators revolves around what they can provide that increases the efficiency of the roof bolting process, which allows them to install more bolts, more quickly, while maintaining effective support. “Many of the longwall operations have been investing in infrastructure, which includes upgrades to facilities and long-term rehabilitation of mainline infrastructure,” Mirabile said.

Demand for the Jennmar’s tensionable cable bolts remains strong. “It’s probably stronger than it’s ever been,” Mirabile said. “It’s not a new product, although we’re seeing more people adopt it. It allows the mine to combine primary and supplemental support. If the mine is already cable bolting, they can use this bolt to replace a couple of the center bolts, instead of drilling a separate hole to install the cable bolt. Miner-bolter mines have taken advantage of the technology for a while, and now we’re seeing more demand from the place-change mines. The cost ends up being about the same, but the mine will see a substantial savings in drilling. That reduced drill time equates to a more efficient process.”

Jennmar is also a major supplier of resin cartridges and polyurethane resin (PUR), which is used to consolidate broken strata. “We haven’t made any substantial changes with those products,” Mirabile said. “We are just trying to keep up with the demand. The usage for some of the chemical consolidation products is as high as ever just because more longwalls are running at capacity, which means more mines are encountering poor roof conditions more frequently.”

More smaller mines are using chemical consolidation packages for specialized applications, such as low-cover, stream crossings. “This is an area where we have gained a lot of experience in the past 10 years,” Mirabile said. “To access remote reserves, these smaller operations would rather mine under these low-cover stream valleys rather than permit a new surface installation. We have three of these projects ongoing right now, and another three or four on the horizon within the next year.”

Almost all of the major operations are currently looking at rehabbing mains and reinforcing the roof on mainline belts. “In the past quarter, we’ve had engineers underground every week for multiple days, looking at multiple mines, walking beltlines, evaluating what needs to be reinforced, and that reinforcement can go anywhere from a few roof bolts, a few props, all the way up to substantial cable bolting, consolidation with PUR, and even steel sets,” Mirabile said. “We have several mines that are investing back in themselves and steel setting mainline belts so that they don’t have to worry about it anymore.”

The projects are really based on what the mines want. Jennmar performs the evaluation and makes support recommendations. “Between JennChem and Jennmar Services, we can perform the rehabilitation all the way from clearing the beltline to erecting any steel, installing roof bolts, backfilling, etc.,” Mirabile said. “We can handle that for them and they can continue to focus on coal production.”

Pillar design and the safety factor are also a concern for older areas of the mine with wider spans. When pillar strength becomes an issue during rehab projects, Jennmar often recommends pumpable supports to reinforce the pillar.

Roof support programs required a lot of materials, especially steel. Mirabile explained Jennmar’s approach to keeping the supply lines open for the mines. “Our purchasing department, working with operations, monitors inventory daily,” Mirabile said. “Working with the mines, Jennmar field personnel provide daily reports along with forecasts for future needs. Keeping the mines supplied has been a challenge. The key to our success is communications at all levels of the organization from mines to the steel suppliers.”

From an engineering perspective, Mirabile said his team’s role is to make sure that raw material quality remains high. “That becomes more important as we pursue alternate sources for steel to keep our supply chain intact,” Mirabile said. 

Mirabile and his team have also worked on a couple of new mine development projects in Appalachia. They are currently assisting with the transition of operations from a contractor to the mine owner in West Virginia. “It’s been really rewarding for everyone to see the project investment take shape, and we got a chance to showcase our capabilities on slope construction,” Mirabile said. “The structural steel at the bottom of that slope is probably some of the best I’ve ever seen. High levels of coordination allowed the project to proceed while meeting everyone’s expectations. Supplies were delivered on time. The contractor had the skillsets in place and the steel was installed as scheduled.”

One of the concerns facing the coal business is the “brain drain,” brought about by retirement. An entire generation of highly qualified mining engineers and mine managers are approaching retirement. That’s another focus of Mirabile’s group, training the next generation. “We still have a solid shock of gray hair here at Jennmar… more added every day,” Mirabile joked. “We have the resources to help the mines with roof control plans. We recently worked with a mine to remove some incorrect information from their roof control plan, and it also allowed them to bolt more efficiently.”

Jennmar not only has the ability to design the roof support plan and the roof supports, they can also train operators. “We pride ourselves on having boots on the ground and out in the field,” Mirabile said. “When you talk about an actual ground control problem, there’s probably four or five solutions that will work if you’re talking strictly from an engineering technical standpoint, but those generally hone down into one that works with the way the mine works. It’s important to design a program that works with the way the section runs and fits into the way the mine operates. That’s where the experience pays off.”

Improving Safety for Roof Bolters

J.H. Fletcher & Co. is always looking at ways to improve safety on its equipment. “Thankfully, accidents are not that frequent,” said Ben Hardman, vice president of sales for J.H. Fletcher & Co. “But, when they occur, it tends to be either a fall of ground, which is difficult to control, or a rotational incident with the drill steel, such as a whipping drill steel or an entanglement. Fletcher has dealt with fall of ground hazards at the mine face for decades. Canopies were used first, then automated temporary roof supports, then walk through machines. All use the machine to help protect the operator. Materials handling systems make the task of installing roof skin control easier and more efficient.  Having the correct machine for the mine environment and the support being installed is critical. Keeping the operator in safe positions and in protected areas requires training by the mine.  Fletcher provides operator manuals and mine site operator orientation that must be combined with mine specific safety practices to complete task training. During machine operation, Fletcher has incorporated tram enable and two-hand fast feed into the design of the machine to help ensure the operator remains in the correct position and out of harm’s way.  More recently, we have taken steps to farther reduce the potential hazards associated with rotating drill steels and bolts.”

“We currently have several different methods to address rotation concerns,” Hardman said. “One is slowing the rotation speed on the feed retract circuit, which was first implemented a few years ago and is now integrated into every machine that Fletcher builds now. Rotation speeds vary, but they are typically in the 600-rpm range. As the operator retracts the drill steel from the hole and they are feeding it downward, the machine will automatically reduce rotation speed, providing just enough rotation to keep the steels coupled. The reduced rotation speed lowers the possibility of the drill steel whipping should the operator err and rotate without the distal end of the drill steel being constrained.”

The second method for addressing rotation concerns is the inadvertent activation circuit. The circuit uses a spool monitor system to ensure the spools are centered. The operator must hit an actuation button to activate the system. “The operator must intentionally press a button on the palm of the joystick or a palm button on the side of the machine, which allows them a few seconds to take the rotation control  joystick out of the neutral position. The two-step procedure prevents the operator from engaging the
control unintentionally.”

Similar to the two-hand fast feed, the third method under consideration is a two-hand rotation. The system has been tested at a few mines, but they really struggle with having both hands occupied for all functions, so it has not been received well, Hardman explained. Some machines used in thick seam heights with operator platforms use a foot pedal for this purpose.

Another option on the horizon, which has been used outside the United States, is the Laser Guard. The system creates a laser light curtain between the operator and the rotating drill. If a miner reaches out and breaks that beam, the system will dump stop rotation. We call it Laser Guard. “It’s used prevalently in South Africa and we’re working to offer it in the United States right now,” Hardman said. “We feel like that will be a big step forward in making sure someone doesn’t reach out and touch a rotating drill steel.”

Fletcher has also developed the indexing feed system for its bolters. The company installed its first indexing system in a South African coal mine about a month ago. “With an indexing feed mast, the operators leave the steel in the drilling head at all times,” Hardman said. “The operator drills the hole. Once that task is complete, they index that feed out of the way and the next feed inserts the resin cartridge and spins the bolt in place. It keeps the operator away from a rotating drill steel, keeps their drill steel restrained at both ends and improves ergonomics by limiting the day-to-day strain of handling drill steels. This system is only practical for high seams like those found in South Africa and some parts of Australia, where most supports can be installed utilizing single-pass drill systems.”

Another feature of that machine, which could be implemented anywhere, is a resin timer circuit, Hardman explained. “It’s hydraulically operated and doesn’t require special approval,” Hardman said. “They put the resin in the hole and the machine will automatically spin, feed and hold. Right now, spin and hold times are dependent on the operator’s judgment, which has to be repeated hundreds of times per shift.” This would be like a fail-safe that would make sure that each bolt is installed according to the resin manufacturer’s guidelines.

For existing machines, this would have to be installed during a boom exchange. “It’s a fairly extensive project,” Hardman said.