Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/370990
Geology and technology stabilize roof conditions OPERA T "A n underground mine is a hole in the earth where Mother Nature never intended for one to be. ere are inherent hazards in an underground stone mine — many created by grav- ity — that miners must be able to recognize and manage," says Joseph Flick, director of the Miner Training Program at Penn State University. Bill Granville, owner of J.W. Granville Consulting and acting vice president of operations at Garre Limestone, agrees, adding that without fail, foremen do pre-shi inspections to ensure the mine is safe for the miners to enter — but all underground miners must also keep a watchful eye for haz- ards throughout their shi s. "Miners must focus on the roof. Gravity is not your friend underground," he says. According to Flick, every un- derground mine has its own set of unique characteristics that can make controlling the ground around and above diffi cult. ese aspects include roof height, joints, slips, and faults. Granville says that water, fractures, shears, and karstifi cation also are geological anomalies that can aff ect an underground mine. And no miner should assume that conditions in a mine will remain static from shi to shi . "Conditions can change quickly," Granville adds. A big clue for miners that condi- tions may require closer inspection is the presence of rocks on the roadway. Rocks could have fallen from a truck, but they could have also fallen from the roof. Miners must be alert to their presence and where they came from. eir source needs to be determined and, if that source is the roof or a pillar, safety action must be taken by calling for the scaler, alerting others, and blocking off the roadway until the problem is corrected. ere are numerous things a miner must be concerned about regarding ground control. For example, miners should watch for changes to the area where pillars meet the roof; cracks, or the intersection of two or more cracks in a pillar or roof; spalling material coming from pillars, and also when pil- lars begin to take on an hourglass shape. "It's extremely hard to know how to read the signs that conditions may be changing in the mine," Granville notes. "Knowing what to look and listen for takes both the formal training mandat- ed by MSHA and on-the-job training, preferably with an experienced miner who can be a mentor." Some roof conditions in under- ground mines can be alleviated through methods such as roof bolting — a common way to improve the stability of a roof in a mine that doesn't have thick horizontal bedding planes. Craig Collins, electrical engineering manager for J.H. Fletcher and Co., says that recent developments in this arena include a roof mapping system that collects and interprets material hardness and void data, creating a col- orgraphic cross-section map for more effi cient bolting. AGGREGATES MANAGER Every mine is geologically unique, but on an underground stone mining wish list for ideal geological conditions, having a roof lie in a bedding plane is at the top. In a bedding plane that runs parallel to the ground, the roof's rock will break off in layers or slices, leaving a smooth surface. Joints, which run perpendicular to the ground, can lead to fractures and are not desirable. 1 Keep an eye above 4 Geological wish list Stone doesn't talk, so miners must learn to look for the external signals the mine emits. A foreman always conducts a pre-shift mine check using a detailed checklist, scanning the roof, fl oor, and pillars for such things as rocks on the roadway, intersecting cracks or joints in the roof, bolts on the fl oor, and color changes in the roof (water, drying, cracking, or evidence of fallen rock). Miners themselves must always be on the lookout during their shifts, watching for anomalies in the stone.