Laserfiche WebLink
App. II-B-1 <br /> Abutment zones, which are areas of high stress, surround every opening or hole in <br /> the ground, and also are found around faults and other irregularities in the earth's <br /> strata. These stresses occur regardless of the mining method. Abutment pressures <br /> are a primary cause of roof failures. <br /> Pressure and stress are dynamic in a mine, and the mining operation itself must be <br /> adapted to the manifestations of stress and pressure, which include: <br /> Bump or Bounce <br /> A failure in the coal or surrounding rock strata. <br /> Outburst <br /> Failure of the coal bed or surrounding rock strata when the <br /> compressive strength of the coal is exceeded. These are very similar <br /> to a rockburst, but usually occur when the abutment zone or zone <br /> of high stress gets so close to the face that an outburst occurs. <br /> When the coal is broken, gas is liberated which causes the coal to <br /> flow horizontally, fluidized by the rapid release of methane gas. <br /> Rockburst <br /> Failure of the coal bed or surrounding rock strata caused when the <br /> compressive forces on a pillar or block of coal or surrounding rock <br /> strata are greater than the compressive strength of the coal or <br /> surrounding rock strata. Coal and rock have the characteristic of <br /> failing suddenly when the compressive strength is exceeded rather <br /> than yielding by flexure, such as a piece of metal or steel. <br /> Bumps and bouncing, outbursts and rockbursts are very dangerous. All have great <br /> potential for damage to air courses, belt lines, escapeways, water and power lines. <br /> Bumps and bounces, characterized by a sudden upheaval of the floor, can toss <br /> men and equipment weighing several tons, and can result in the possible failure of <br /> roof and ribs. In addition, the liberation of gas through outbursting causes the coal <br /> to flow horizontally, in a fluidized manner. <br /> Safety in our mines is dependent on detection and release of stress in the coal and <br /> surrounding rock strata before the compressive strength is exceeded, causing <br /> outbursts, rockbursts and bouncing. <br /> While our instrumentation and experience afford us substantial accuracy in <br /> identifying excessive abutment pressures and stressed conditions, we cannot <br /> predict when or precisely where such conditions will develop. <br /> After a big bump which occurred in April, 1983 Mid-Continent retained a rockburst <br /> specialist, who studied the problem of stress zones and possible coal outbursts on <br /> the coal face. He outlined a two part program of detection and stress-relief. <br /> 3 <br />