Western coal mines are operating under increasingly challenginground conditions. Researchers at the Spokane Research Laboratory of the National Institute for Occupational Safety and Health are cooperating with mines to evaluate how these conditions affect mine opening stability and related miner safety. A system was developed to monitorock and coal stresses during mining of an entire longwall panel. The system was designed to generate data in near real time to evaluate rock behavior in roof strata and the onset of hazardous conditions as overburden stress was redistributed over working entries during gob formation. Computer simulations and inmine evaluations were used to optimize instrument placement. A prototype packer assembly was designed and tested for installing sensitive instruments in a mine roof. This paper provides background information on the stress monitoring concept and focuses on the development of instrument placement techniques and the prototype packer assembly.
Stress monitoring system concept Researchers at the Spokane Research Laboratory (SRL) of the National Institute for Occupational Safety and Health (NIOSH), in cooperation with a mining company, have developed and continue to refine a stress monitoring and reporting system. The initial objective was to determine if stress monitorng instruments could gather sufficient data to recogize the conditions leading to coal bumps so these conditions could be mitigated with engineering controls before a catastrophic event. During use of the monitoring system, it became apparent that the system could also be a valuable research tool in evaluating rock behavior surrounding mine openngs. The system could also be used to study the technologies designed to maintain safe openings in more challenging ground conditions. Below is a description of the system developed to meet these objectives.
The stress monitoring system is comprised of a cluster of instruments (figure 3) placed strategically to detect changes in stress and displacement at a preselected site in the headgate of an operating longwall. These stress changes are initiated near the longwall face as load is redistributed following coal removal and gob formation. Stresses are transferred through roof strata from the area of active mining back to the instrument site. A data acquisition system retrieves data from these instruments at preselected time intervals. Raw data are then processed and reduced and used to generate graphs. These graphs illustrate trends that may be used to evaluate (1) behavior of roof strata above mine openings, (2) imminent catastrophic events, (3) effects such as typical yield pillar movement that are not a safety concern but may distort needed information, and (4) placement and type of additional support or other safety intervention.