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e <br />ESPEY, HUSTON b ASSOCIATES, INC. <br />4.0 MEASURES TO PREVENT. SUBSIDENCE ~ R~" <br />. ~:~. <br />No mining will take places undezEiCurtis Creek <br />or the Jensen 'Ranch, Whatlmining wil•~1 take place will <br />be advance room and pillar mining and under at least <br />500 feet of overburden:- As a result, subsidence is not-'' <br />an issue. 3'he remainder of part` S 6f the Permit is left <br />in for reference only and is not in'-the scope of this <br />Permit. <br />:l' i <br />p ~ i <br />Bruno Fichna and Joseph Nugent with Interplan Engineering & Appraisal <br />Company were contracted by Northern Coal to do an engineering study for pillaz <br />sizing that would protect against subsidence in the FF, .J and G seams. The, <br />following information is the result'of their study: ',, <br />Engineering Analysis: Pillar Strength Under Structures To Protect ,,L ~;, <br />kgainst Subsidence .. ... ' <br />... , . i'. _ ~ . . <br />Pillar Design <br />Pillars below the structures to be protected must be strong enough <br />to support the overburden without subsidence after mining. the FF-, J= and G <br />seams. <br />Coal samples were tested by F. M. Fox Associates, Denver, <br />Colorado. The coal hardness shows a wide vaziation, ranging from 920 to <br />4,330 PSL From this variation, a . weighted average of 2,776 PSI was <br />calculated. The cover above the uppermost seam, the FF-seam, is 500 feet <br />with seam intervals of 1,610 feet to the J-seam and 193 feet further to the G <br />seam. A column of overburden of one square inch cross section and a height of <br />500 feet weighs approximately 550 pounds and produces a pressure on the <br />virgin coal seam of 550 PSL Wlien 44'percent of the coal is extracted, the <br />remaining 56 percent of the coal is exposed to a resulting vertical pressure of <br /> <br />~p1. <br />~ ~g~ <br />5-6 <br />