Laserfiche WebLink
December 27, 2023 Page 4-2 <br />Agapito Associates, Inc. <br />𝑇ൌ ൫௪೛ ା௪ೝ ൯൫௟೛ ା௪೤ ൯ఘ௚ு <br />௪೛ ௟೛ <br /> (Eqn. 4-2) <br /> <br /> <br />where T = pillar stress (psi) <br /> wp = pillar width (ft) <br /> lp = pillar length (ft) <br /> wr = roadway width ft) <br /> H = overburden depth (ft) <br /> = density of rock (taken as 162 pounds per cubic foot [pcf]) <br /> <br />4.4 Pillar Abutment Loading for Retreat Conditions <br />The abutment load during pillar extraction is related to the redistribution of load away from the <br />pillar extraction gob onto the neighboring pillar. For panels which behave in a critical and <br />supercritical manner (as in this case), the stress (A) resulting from the superimposed abutment load <br />can be defined as follows (see Figure 4-2): <br /> 𝐴ൌ௣௚ൣுమ ൫௟ഐ ା௪ೝ ൯୲ୟ୬⏀൧ <br />ଶ൫௪ഐ ௟ഐ ൯ (Eqn. 4-3) <br />where A = abutment stress (psi) <br /> lp = pillar length (ft) <br /> wr = roadway width (ft) <br /> H = overburden thickness (ft) <br />  = density of rock (pcf) <br />  = abutment angle (o) <br /> <br />In regard to the abutment angle used in this assessment, monitoring data collected in the United <br />States of America (USA) and Australia (CGS 1998) indicates that in supercritical panels (such as <br />this case), it is reasonable to assume an angle of 21o. In the case of the E Seam, an abutment angle <br />of 21o is regarded as a reasonably conservative “default abutment angle,” considering the amount <br />of thick sandstone units located in the overburden, which have the ability to span and redistribute <br />load away from the neighboring pillars. <br />The distance to which the resulting abutment load will be redistributed away from the failed <br />overburden onto neighboring pillars and/or barriers (D) can be estimated using the following <br />equation presented by Peng and Chiang (1984): <br /> DD = 9.3√H (Eqn. 4-4)