Coal mines in southern West Virginia, south-western Virginia and eastern Kentucky have experienced coal bumps at least since 1933. Most of the bumps have occurred due to high cover, strong roof and floor strata and stress concentrations due to the mining sequence. A longwall mine in eastern Kentucky first experienced coal bumps on the tailgate side of the longwall face in 1989. The bumps continued until 1996. The bumps were the result of:
• thick overburden up to 670m.
• strong roof and floor (strata strengths up to 177 MPa UCS and elasticity modulus up to 33.1 MPa
• previous over-mining in places
• sandstone channels
Not all characteristics occurred simultaneously. The bumps produced seismic events recorded up to 4.3 (Richter scale magnitude), and damaged pillars that were up to 45 by 46 m in size. During the eight years that the bumps occurred, a large quantity of data was obtained in an effort to develop methods to predict an event, and reduce or eliminate the bumps.
• In-situ strength properties of floor, coal and roof strata
• Lab testing of floor, coal and roof samples
• Monitoring gate road pillar response with stress metres, extensometers and convergence stations
• Shield leg response
• Monitoring in an effort to determine precursors was conducted using a digital microseismic monitoring system.
• Back calculation of gate road pillar strength
A number of different remedies were trialled in an effort to eliminate or decrease the severity of the bumps.
• The gate road longwall design was varied
• Pillar size and shape
• 3 and 4 entry gate road designs
• water infusion in longwall panels,
• hydraulic induced face bumps,
• disruption of the roof strata
A yield-abutment-yield pillar design was the most effective method in reducing the affect of bumps by moving the events onto the abutment pillars, but the bumps were never eliminated and adequate precursors and advanced warnings were never achieved.