A novel engineered crib (ATLAS Crib), developed at Southern Illinois University Carbondale (SIUC), is a composite wood element designed to achieve improved strength, stiffness, and yield properties for cribs. The element uses approximately one-third less wood, weighs about 40 percent less, and offers less ventilation resistance than a conventional crib element. Installation and manual transport times are also reduced along with the risk of physical injury to miners during these operations. This paper presents comparative results of a field demonstration of ATLAS and conventional cribs. The two different cribs were installed in adjacent areas in a headgate return air course entry. They were monitored over an extended period while the current longwall face and the adjacent longwall face mined past the demonstration area. In the latter phase the cribs on the tailgate side were subjected to the highest possible load. In addition, eight (8) ATLAS cribs in four (4) crosscuts were also installed on the headgate side of the adjacent longwall panel next to the belt entry where they were subjected to very high loads. Structurally, ATLAS cribs performed well in both areas. Crib and roof-to-floor convergence data, as a function of distance from the face, were similar for both cribs. ATLAS cribs behaved stiffer than conventional cribs. ATLAS cribs also demonstrated ventilation advantages. Based on success during this study, a field demonstration over a 600-ft (182.88 m) length of tailgate entry has been recently completed.
Coal mines typically use wooden cribs to provide standing support between roof and floor. Cribs are more extensively used in longwall mining than in room-and-pillar mining. In longwall mining, they are used primarily to support gate, setup and bleeder entries and provide temporary support during the shield removal process when moving longwall equipment from one panel to the next. Although cribs have been used since the inception of mining, current usage is subject to the following disadvantages and/or limitations:
Loading on the crib element is transverse to the wood grain resulting in low crib stiffness, which leads to low load carrying capacity and large deformations,
The cross-section of the crib element is uniform along its entire length even though most stresses are around contact areas at either end,
The uniform cross-section makes crib installation around irregular roof difficult, and
Due to weight handling crib elements for placement at heights above four (4) feet (1.2 m) requires considerable effort.
The primary author, with support from staff, developed a novel, engineered, composite wooden crib (ATLAS crib) in 2007 (see Figure 1) that overcomes most of the above disadvantages (Patent Pending). Results of preliminary testing at Illinois Coal Development Park (ICDP) and National Institute of Occupational Safety and Health (NIOSH) facilities (Gearhart, 2008) led to a field demonstration of ATLAS and conventional cribs in adjacent areas on an active longwall panel. The goal was to develop field performance data that would allow industry and regulatory agencies to make informed decisions regarding their use.
