Roof Bolting for Long–Term Entries in Underground Coal Mines

摘要

As simpler and easier reserves are exploited to depletion,underground coal mining continues in more complex geologicsettings and conditions. Roof bolting for long-term entry stabilityis always a challenge. For long-term entries of a mine such as belt,track entries and return airways, roof could be under-supportedif one uses the same bolting plan as in short-term entries or evenseem over-supported with increasing use of longer, stronger boltsalong with mesh, pans, straps or trusses. In most underground coalmines, roof deteriorates over time with cutters developing deeperin entry corners; roof sagging and popping out between bolts; entrywidth increasing due to rib sloughage; and separations developingdeeper up into the roof. In deteriorated long-term entries, roof fallscould occur at certain locations and re-bolting could be costly orsometimes unfeasible. Therefore, it is important to choose anappropriate bolting plan during development based on mining andgeologic conditions if the entries will be used for the long-term.In both short-term and long-term entries, primary roof bolting iscritical in building a strong and effective beam. But in long-termentries, supplementary bolting is necessary in certain cases toensure roof stability can still be maintained even if a roof failuredevelops beyond the primary bolted horizon. This paper deals withroof bolting for long-term entries based on studying the progressiveroof failure and roof falls under different geologic conditions. Thepaper presents bolting considerations in terms of bolt type, length,diameter and spacing as well as bolting strategy to minimize therisk of roof falls in long-term entries.