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<br />SiAlt Oi~ COI Oi: :UU ~~„~r.cn n. r,uw. r,~r•,~~~ <br />DEPARTMENT GP NATURAL RESDURCES <br />D. Monic nrsro r, Ea e[ulrv? D~rca ar <br />nt~!~Lt~ ~.n~~ tt~c.t.:~ntt~rrto~ <br />423 Centennial Budding, 1373 Sherman Street <br />Denver. Colorado 80203 Tel (303) b6Ci-3567 <br />David C. Shelton <br />Director <br />DATE: August 5, 1982 <br />-.. <br />T0: Carol Russell. ) <br />FROM: Jim Pendleton ~~ ~ ~,.=~~~'-`~T"" <br />RE: "ReconstructiQ+f Plan Storage Optimization, Dorchester Coal <br />Company, FretiR ounty, Colorado~~ <br />Pursuant to your request, I have reviewed the report referenced above. <br />This report, prepared by Rocky Mountain Geotechnical, Inc., consultant <br />to Dorchester Coal Company, presents the results of a detailed stability <br />analysis of the coal processing waste pile of the Dorchester No. 1 mine. <br />The report also contains recommended construction practices and a final <br />design configuration Lor the waste pile. <br />The consultant performed material strength testing of the processing waste, <br />in order to determine shear strength parameters Cer use in completing the <br />detailed stability analysis. The sensitivity-type analysis assumed a mired <br />processing waste, comprised of three parts coarse waste to one part fine _ <br />refuse material. The laboratory and mathematical analytical techniques _ <br />conform with tlce prudent state-of-the-art of geoteclTnica7. analysis. <br />1'he conc]usion of this report is that the approximately 2 million cubic <br />yard coal processing waste pile can be built to a maximum height of. 75 feet <br />with a maximum facial slope of 2:1 (horizontal to vertical slope). In this <br />configuration the pile has been demonstrated to exceed the required static <br />slope safety factor of 1.5, iE the following conditions are met: <br />(1) All low strength, saturated fine refuse material originally placed within <br />80 feet of the projected toe of the completed fill must be removed, mixed <br />properly and recompartecl in another area of the Eill.. <br />(2) The processing waste shall be mixed no Less than thrr_e parts course material <br />to one part of fine refuse material and placed so as to achieve 90% oC <br />this composite materials maximum standard Proctor density (ASTM standard <br />designation D698). Ala terials testing has determined that this placement <br />density can be affected if the waste is placed in lifts oC less than 3 feet <br />uncompacted thickness, at a moisture content by weight of between 12 and 22%. <br />.. ~,-- .,..K...~..- ....... - w r~~ ,.... .. <br />