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iii iuiiiiiiiiu iii <br />STATE OF COi,..,,<.~~ <br />MINED LAND RECLAMATION DIVISION oF.~oo <br />Department of Natural Resources ~~,-=1p--=.p9 <br />1313 Sherman St.. Room 215 „~~, , o <br />Denver, CG 80203 .+'8;i <br />303 866-3567 ~ 870 ~ <br />FHx~303 832-8106 <br />Roy Bomer, <br />Governor <br />Date: February 14 1992 Fred R. Banta, <br />, Division Duector <br />To: Christine Joh~ns7on <br />Fr: Bruce Stover /(~~.,,~. <br />Re: West Elk Stacker Tube, Permit C-80-007 Technical Revision No.61 <br />I reviewed the additional data you provided regarding geotechnical properties <br />of the gob, colluvium, and clay fill for which a stability analysis was <br />performed as part of TR No. 61. The data shows strength parameters for the gob <br />vary considerably as this material reflects a wide variety of both particle <br />sizes and mixtures of material components. The average cohesion and friction <br />angles from eight tested samples of gob were 211 PSF and 27.7 degrees, <br />respect ivly. The values chosen in performing the stability analysis for the <br />stack tube revision were 200 PSF and 28 degrees, which I believe are <br />appropriate. <br />It is important that "clay fill" and gob materials be carefully selected and/or <br />controlled so that significant zones of lower strength materials are not <br />inadvertantly incorporated into the pad foundation. The Geoweat stability <br />analysis indicates that an adequate safety factor of 1.3 can be achieved for <br />the stacker tube pad if gob and compacted clay materials having the assumed <br />properties are properly selected, placed, and compacted ae shown in the <br />submitted design. <br />