Bleeder entry evaluation using condition mapping and numerical modeling

One of the most common critical areas of longwall mining in terms of ground stability are the gateroad and bleeder entries. These critical entries provide much-needed safe access for miners and allow for adequate ventilation required for dilution of hazardous airborne contaminants and must remain open during mining of a multi-panel district. This paper is focused on the stability of the longwall entries subjected to a single abutment load such as bleeders, first tailgate, and last headgate. First tailgate and last headgate are also referred to as blind headgate and tailgate. A study of a longwall district through conditions mapping, support evaluations, and numerical modeling was conducted and evaluated by researchers from the National Institute for Occupational Safety and Health(NIOSH). The condition mapping and support evaluations were performed on entries that spanned the previous five years of mining and relied on a diverse selection of supports to maintain the functionality of the entry. Numerical modeling was also conducted to evaluate various support types with further investigation and comparison to the condition mapping.The study demonstrated the importance of the abutment load decay versus distance from the gob edge,the potential for a reduction in material handling related injuries, as well as optimal usage of secondary and standing support.