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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 />BumQ 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 />~iockburst <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 />