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• <br />April 1989 <br />Computer_codes and_Analytical__Input <br />The geotechni.cal ciesign was based on nnmrrical analysis to <br />determine t'.lte stresses caused by longwall and room-and-pillar <br />mining. 'Clre anal.ys.is results were used itt attaining the pillar <br />sizes, itr eval.uatiitg the stresses transmitted to other seams, and <br />itt assessing general stability. <br />Two computer codes wet.•e used: F.XPAREA and MIDIAP. The first code, <br />a three-dimensional]>outtdary element program, was used to calculate <br />in-and adjacent-seam stresses and ultimately in determining pillar <br />sizes (St. .7oltrr, 1978). MII~IAP, a two-dimensional displacement <br />discotttitruity program, was used in determitrittg stresses above and <br />between the seams artd itt calculating safety factor contours <br />(Crouch, 1976) Tltese safety factor contours Helped establish the <br />offset boundary pil.l.ars needed to avoid instability caused by <br />multi-seam mining. Agapito has used these cedes in a number of <br />projects and ltas found good correlation betc~een calcLtlated and <br />measured^~tCeSSP_3 (St.. Jolty and Maleki, 1986). <br />Tables 3.4.A.14 and 3.4.A.15 show the input mechanical properties <br />• and pillar stretrgtlr data used in 'the EXPAREA analysis. Pillar <br />strengths wex•e derived based on the laboratory mechanical property <br />testing and measttretnetrts and observations in similar mines in the <br />Px•ice and t}re Paonia coalfields. In the MITIAP analysis, Mohr- <br />Coul.otnb ct.iteriotr was used in the safety factc:~r calculations with <br />a rock mass cohesion of 234 psi and an angle c+f i.nternal friction <br />of 55.5 cl~grees as input. <br />TABLE 3.4.A.14 <br />INPUT MECEEANICAL PROPERTiER <br /> <br />Specific weight. of overburden strata (lhs;'ft'i) 1491 <br />Roof and Fl~~r modulus (psi) 2.57 x 1061 <br />Roof. and fJoo.c Foisson"s ratio 0.25 <br />Coal seam modulus (psi) 0.40 x 106 <br />Gol-~ support deformation characteristics: <br />Cob deEox•ms 0.06 ft to 0.18 ft for 450 it. to <br />1,500 ft. of cover before supporting load.' <br />After this olosure, gob support .load with a 0.22 x 10 <br />psi modulus. <br /> <br />