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<br />_ -6- <br />' <br />• PILLAR STRENGTH -PANEL "G" <br /> The design of safe pillars for the 2nd East rnd 3rd East Sections can best be <br />~ - accomplished by rnmporing their strength to the successful pillars in Panel "G" Panel <br />~ "G" is closest to the 2nd East Section test area. Therefore, the pillars in Panel "C" <br /> <br />I were analyzed using the physical properties from the Znd East Section tests and from <br />' the combined results. These results are presented on Figures 2 and 3 and in Table 2. <br />.. The method of pillar strength estimation employed was based on Wilson's (1972) <br />r <br />- <br />confined core pillar design procedure, presented in Appendix C. Wilson's method <br /> considers a pillar as being made up of a confined core surrounded by a distressed and <br /> <br />i <br />. partially yielded outer zone. The outer exposed ribside is unconfined and has a <br />. <br />•_ compression strength equal to the rock (coal) mass compression strength. As demon- <br /> ` <br /> strated by large, up to 5 ft on a side, specimen testing the strength of coal decreases <br />~-• <br />, with increasing size ((3ieniawski, 1968; Bieniawski and Van Heerden, 1975). A funds- <br /> mental strength is reached at some size, approximately 3-ft in Bieniawski's case. <br /> Pillar loading for Panel "G" pillars was estimated on the basis of full (maximum) <br /> tributary area loads, i.e, half-way to each adjacent pillar and all the way to the <br />~- surface. This conservative assumption is reasonable in view of the width of Pane! "G" <br /> in relation to measured load transfer distances, as shown in Appendix D. The majority <br /> of the pillars in Panel "G" must be subjected to full tributary area load stresses. <br /> The width of the pillars in Panel "G" ranges from 12 to over 20 ft. The 75% <br /> extraction achieved in Panel "G" (Table 3) indicates that the average pillar width was <br />~~• i6 ft. The indicated factors of safety for the pillars in Panel "G" appears to be at <br />least 1.58, and probably is in excess of 1.70. <br />The design of pillars under the Ute Water Co's. surface facilities has been based <br />• on factors of safety in excess of those that have proven stable in Pane( "G." <br />