Coal Age

JUN 2018

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24 www.coalage.com June 2018 underground seals Seal Construction at the Cardinal Mine Moving from the No. 11 to the No. 9 seam, Warrior Coal reclaims assets and seals old works by steve fiscor, editor Warrior Coal, a subsidiary of Alliance Re- source Partners, operates the Cardinal mine, located near Madisonville in Hop- kins County, Kentucky. A classic room- and-pillar operation, Warrior produces ap- proximately 3.6 million tons per year (tpy) of medium/high-sulfur coal from four su- per-section continuous mining units. The Warrior complex was opened in 1985, and Alliance acquired it in 2003. In 2009, a new prep plant was constructed with a raw feed capacity of 1,200 tons per hour (tph). Once Warrior's coal is washed, it is shipped via rail or truck directly to cus- tomers or to various transloading facilities. Underground, the Cardinal mine re- cently completed a transition from the No. 11 seam to the No. 9 seam. This transition was driven by the planned depletion of the No. 11 seam and the development of the underlying No. 9 seam reserves. "We equate this process with develop- ing a new coal mine from the inside out," explained Jon Salley, engineering manag- er, Warrior Coal. The transition over the last 4 years has included the construction of nine in- ter-seam slopes, an intake shaft/hoist, and the development of a new belt corridor through two major faulted areas to the company's main belt slope. As new infra- structure was placed into service, Warrior began the process of reclaiming idle assets and preparing to seal off large portions of the old mine works. This created the next challenge for the company as adverse roof conditions existed in an area of old works at the main slope bottom. Weak shale roof and years of exposure to highly variable temperatures and moisture content had resulted in numerous rockfalls in the area that would require rehabilitation. Rehabbing the Slope Bottom The mine works at the main slope bottom due to their age and weathering required gob removal and additional support to be installed. This simple rehabilitation pro- cess was complicated, however, due to the presence of rockfalls in the old works. A final seal construction line was selected that minimized the amount of rehab work required. Unfortunately, the seal con- struction line did require one seal to be constructed where a rock fall existed. "The miners expected that the fall height would likely be as high as 25 or 30 feet," Salley said. "That was somewhat concerning." From a regulatory point of view, only a limited number of 120-psi seal options have been approved by the Mine Safety and Health Administration (MSHA) that can be constructed in heights that are ap- proximately 30 ft. After discussing plans with seal contractors and MSHA, Warrior Coal selected the Micon 120-psi Main Line Hybrid II Seal. Based upon the range of height expected, the large seal according to the Micon seal specifications would be 10 ft to 12 ft thick. Typically a rock fall is removed using a continuous miner cutting up fallen ma- terial in sections and the area is re-sup- ported. Due to the anticipated height of this fall, Warrior Coal had concerns over supporting the void cavity and keeping personnel safe from the adjacent roof fall. Warrior's management team devised a plan to backfill the cross-cut leading to the project area and develop a ramp into the mine roof to gain access to the roof overly- ing the fall. "It's ironic to think that the rock fall occurred because age and exposure had compromised the roof, yet we were going to remove the good roof to get on top of the rock," Salley said. Once on top of the fall, they would start the process of re-supporting the roof and ribs while removing the rock, bench- ing it out until they reached the mine floor. All of the excavation work was done with a Joy 14CM15 continuous miner supported by diesel scoops. The vast majority of the rock was transported by conveyor to the surface on the third shift or on the weekend and diverted off the main coal stockpile. Both roof and ribs were extensively re-supported using fully grouted rebar bolts, wire mesh, and over- sized roof pans. Miners lay a row of CMU blocks and then polyurethane glue is poured in the gap. A miner stands with construction materials inside a 30-ft tall 120-psi seal.

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