Michael K. McCarter is the professor of mining engineering at the University of Utah. He is also the chairman of the technical advisory group for the Utah Mine Safety Commission.
He recently reported to the commission on mining. McCarter said one thing he sees as a problem is the misperception people have about mining. Mining has changed a lot over the years. Mining has seen many technological advances. With these technological advances comes the need for fewer people in the industry.
Some of the challenges of mining include access, ventilation, drainage, ground control, gas control, cover; etc. Ground control and the maintenance of an equilibrium in the disturbed area is important. What are the conditions of a coal seam, before the coal is removed? The overburden places a strain on the coal seams, the removal of the coal causes the weight from the mountain above to be redistributed. When the weight can’t be supported any longer then the roof falls. These collapses can be dangerous depending on how much coal falls or in some cases the floor heaves. Sometimes a layer of coal approximately a foot deep can be left on the floor to help cut down on heaving. When the coal is not strong enough to hold then sometimes ribs burst.
McCarter explained the different types of mining including room and pillar and long wall. The amount of air to the face is regulated by law. Squares of coal are left in place. When coal is mined with a continuous miner the coal drops down and moves to the back of the machine into the shuttle car.
The shuttle car travels to a point where it dumps coal onto a conveyor belt and the coal is taken out of the mine. Roof bolts are grouted into the roof. Roof control plans are submitted to the Mine, Safety and Health Administration for approval. Fifty – seventy percent of coal is left in the pillar to hold up the roof. In retreat mining, roofs are allowed to cave as pillars are removed. “It’s an exciting process,” said McCarter. It takes the weight from the overburden and the miner operator determines when it is time to pull out. Many times mining machinery is buried. An experienced coal crew can determine how much coal can be safely removed.
The Kaiser mine in Sunnyside was the first to develop a long wall system. Mine entries are developed and there are two-three perpendicular to the main entry. With a long wall panel all the coal is completely extracted.
Hydraulic roof supports support the roof in a long wall system. The shearing machine cuts the coal and it is loaded onto the conveyor. The belt takes the coal out of the mine. The shearing machine moves forward on hydraulic power. The whole assembly moves forward. The caved area is called the gob. You can control the breakage of the roof, the workers are protected and the cave-ins managed. Ground control with long wall mining is challenging as stress is redistributed. Stress is on the sides. The stress is ahead of the face. Abutment stress can be managed. Pillars are left in the development of entries. When the pillars begin taking weight if they are weak or too small then the pillars will fail. Coal can pop off the face and can cause injury. Stress on pillars is higher after mining. Deep cover can cause problems. There is 120 psi for every 100 feet underground. In Pennsylvania mines, the stress is 900 psi. At Aberdeen the stress is 3,600 psi. before coal removal. Coal compression strength is also a cause of concern. Strong coal can cause problems. The accumulation of stress causes catastrophic failure or a seismic event. A strong roof can cause problems, rock will fail and drop during a seismic event.
Crandall Canyon mine opened in 1939 under a room and pillar operation. They operated until 1955. It reopened in 1983 with room and pillar. In 1995 the first long wall section was installed.
A long wall system is a substantial capital investment for a company. A long wall operation is a $100 million investment and it must be a big enough mine to pay for equipment.
In the Crandall mine barrier pillars were left between long wall panels. Barrier pillars are used to help combat stress. When coal is mined out the stress is high. Under deep cover there is coal stress in coal that hasn’t been mined. A barrier pillar is left that takes the load for the coal in mined panels. Barriers can be 450 feet wide. Slabs of this barrier pillar are mined out in various places along this barrier pillar.
In March of 2007, a bump occurred at Crandall and they moved out of that area.
How are barrier pillars designed and who approved the plan? There is a safety factor involved. The barriers are planned to be stronger than needed. All rock is different.
McCarter said Western mines present their own challenges. Deep long wall mining under deep cover is prone to coal bursts and the development of gases. The cost of coal development is becoming more expensive and more complex. The geology is more complex in Western mines. The coal is harder to mine. The machines are not large enough to take all the coal and some is wasted. In some places only 8 feet of a 16-20 foot seam is recovered.
The Western states depend on coal for energy. We need to understand how to mine coal and how to do it safely. The regulatory approach comes from an Eastern perspective that doesn’t apply here. Western coal is different. Better training and better technology is needed. Better trained inspectors are needed. Should Utah have its own inspectors? McCarter said MSHA would hire 150 inspectors right now if they could find them. They just aren’t available.
In Australia, the government provides 3 percent of the funding for research and the rest of the money for mining research comes from the industry.
Senator Hatch has garnered money for research into retreat mining. McCarter thinks this is a good beginning for the problems that need to be addressed. Other issues, not just retreat mining need to be addressed. It is a step in the right direction.
Matheson said he appreciated McCarter addressing the mine safety commission. He said the points Professor McCarter made remain consistent with what they have been hearing in the mine commission meetings; the need for new technology and better training. “With respect to technology and better context of research capabilities, what do we have now and what is lacking? Where is mine technology today?
McCarter said the Bureau of Mines was formed in 1912 to address coal mine safety. They made substantial progress in research regarding fires in mines and other gains. In 1994 this bureau was sacrificed. At this time you couldn’t submit a proposal for mining research. They said there was no more research to be done, all the research in mining was complete. You couldn’t get a grant for mine research. Most of the grants from the Bureau of Mines went to the Appalacian area. For years there has been no government money for research. Now some funding is becoming available. Industry is not in the habit of funding research.
Matheson questioned McCarter on the background mine inspectors need to have. McCarter said he can’t say exactly but they need mine experience, a technological degree, electrician, mechanic experience. “Someone who understands mining,” said McCarter.
McCarter says they lose a lot of would be inspectors to the private sector, for example a person could make $65,000 a year at Kennecott and only $48,000 a year at MSHA.
David Litvin, committee member wondered what role the University of Utah might play in mine safety training.
McCarter said they would be interested in participating any way they can. They can help in specialized training for specific concerns. They have two instructors who have worked with ventilation and can help in that area. Also electrical concerns can be addressed. The UofU trains mining engineers and 80 percent of those trained stay in Utah. They are very interested in making Utah mines safer. More research needs to be done into whether barrier pillars can be mined safely.
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