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Pillar Design and Strength: <br />• The method of pillar strength estimation employed is based on the confined <br />core pillar design procedure (Wilson, 1972). Wilson's method considers a <br />pillar as being made up of a confined core surrounded by a distressed and <br />partially yielded outer zone, The outer exposed ribside is unconfined and <br />has a compression strength equal to the rock (coal) mass cohesion strength, <br />The concept of a pillar core and yield zone is based on evidence of an abut- <br />ment peak which is located where the stress on a pillar is at a maximum, <br />defined as o„ The stress at the outside of the pillar is low and the <br />stress increases toward the center of the pillar until an abutment peak is <br />reached at a Wilson defined depth of `~ (the distance from the outside of <br />the pillar to the point of maximum stress). <br />The design of safe pillars for 1st West Mains and West Main panels can best <br />be accanplished by comparing their strength to the observed successful pil- <br />lars in the East Mains, Calculations are also performed for comparison of <br />the safety factors from various available data, These calculations illus- <br />. trate the conservative analysis of the pillar design performed and indicate <br />that any variation in the strength of 1st West Main coal would give a higher <br />safety factor, <br />The followiny example calculation illustrates Wilson's method of pillar <br />desiyn. <br />r~ <br />