Coal Age

JUN 2018

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June 2018 25 underground seals continued Installing the Seal The Micon 120-psi Main Line Hybrid II Seal can be used in an opening up to 32.5 ft high and 28 ft wide. The construction materials include solid concrete masonry unit (CMU) blocks, prepackaged bags of pea-sized gravel and two-component liq- uid-polyurethane glue. As with any masonry project, a good foundation is important. The founda- tion for the Hybrid II seal or a portion of it could be the mine floor to which the base CMU blocks would be attached using polyurethane glue. The most com- mon foundation material is composed of pea-sized gravel saturated with polyure- thane glue. The foundation can be either flat or stepped. The first CMU wall or wythe is nor- mally constructed on the inby side of the seal. Polyurethane glue is used to grout the abutting faces of the wythes together such that the wythe thickness is a mini- mum 7-1/4 in. thick. The glue coverage of any CMU block surface should be at least 75%. The maximum, polymer-only gap between the end rows of CMU block and the rib should be 2 in. or less. The maxi- mum, polymer-only distance between the top rows of CMU block and the mine roof should be 4 in. or less. The first wythe may be constructed simultaneously with the other wythes and the miners build as many wythes as are needed to achieve the minimum seal thickness specified. The gap between ad- jacent wythes should be a minimum ¼-in. to a maximum of 2 in. and filled with poly- urethane grout. (The typical gap is about 1 in.). The gap between the two, most-outby wythes can be a minimum ¼-in. to a max- imum 4 in. and filled with grout. The CMU blocks can be cut or shaped to accommodate the sampling, water and water monitoring pipes that are cus- tomary for all seals. The Micon personnel grout the pipes and tubes to the surround- ing CMU block with polyurethane glue, as- suring that all voids are filled. When need- ed, a fibrous filler can be used for chinking the rib and roof gaps to prevent the glue from leaking when it's in a liquid state. The fibrous filler, which comes in various di- ameters, is coated with glue before being installed in the perimeter voids. Once the CMU blocks have been placed, the polyurethane grout is pumped into the gaps between the rows of blocks and each course of block gets a coat of polyurethane glue. "A row of block goes in and then polyurethane glue is poured and then another row goes on top. Be- tween each row is a 0.5-in. to 1-in. gap of polyurethane glue that holds all the rows together," Salley said. "It's essentially a big glued mass of concrete block." Innovative Solutions Building a seal this high required some prior planning and innovative thinking. As the miners benched through the gob, they treated the underground rock fall like a highwall on a road cut. "We stepped the benches down," Salley said. "We bolted chain-link fence to the roof and draped it across the benched fall so that loose ma- terial could not roll into the project area." Material handling concerns was a pri- mary driver in multiple aspects of the plan design. MSHA seal plan requirements in- clude the utilization of standing support inby and outby of constructed seals. To address this requirement, Warrior chose to install ACS Jacks; however, cavity height would make this option difficult at best to install. Warrior elected to bolt 8-in. steel I-beams to the roof and welded hinges to them. The hinges in turn were attached to four 20-ft Heintzmann ACS jacks for standing support for inby and outby the seal. "Beginning with the end in mind, we used hinges to attach the jacks to the 8-in. beams. This allowed us to install the jacks first and lower with successive lifts rather than trying to install this support later," Salley said. "A short section was added to the bottom of the ACS jacks with a screw head placed at the mine floor. This elimi- nated the hazards associated with trying to install very tall and heavy standing support and allowed for adjustment to the total height of the jack assembly." The installation of the ACS jacks complied with the MSHA requirement for standing A 3-ton hoist was attached to a trolley beam, which was bolted to the roof, and used to lift pallets of block.

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