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/~~ _ ~ ~ RECEIVED <br />_. ~uti Z 1997 <br /> <br />ii iii iii iii iim ii <br />sss <br />9lvlebn of Minerals & (~tlgltj~y <br />Lincoln DeVore,lnc. <br />Geotechnical Consultants • ^ <br />1441 Motor St. <br />Grand Junction, CO 81505 <br />June 18,1997 <br />Balaz & Associates <br />203 Sunset Cir. <br />Palisade. CO 81526 <br />Re: Ncw Coal Waste Pilc and Haul Road Project <br />Sanborn Creek Mine, Somerset, CO <br />TEL: (970) 242-8968 <br />FAX: (970) 242-7561 <br />We arc in receipt of a facsimile transmission of a portion of the Initial Adequacy Review Letter from the Division <br />of Minerals and Geology regarding the Sanborn Crcck Minc Project. At your request we arc addressing the <br />second paragraph oC Item 17 and all oC Items 18 & 24. Following are our findings and recommendations. <br />Item 17. Cut and Fill Slope Stability The drawings provided by Balaz & Assoc., West <br />Valley Haul Road. OXWVF-OS to OXWVF-IS have undergone several revisions based upon prcliminarv cut <br />and fill sections provided by Lincoln DcVore. The recommended sections from Lincoln DeVore were based <br />upon the bottom bench and toe oC the major earth fills to be Counded upon the more competent rocks of the <br />Bowie Member of the Mesa Verde Fonnation. The original road conswction/cut fill section provided by <br />Lincoln DcVorc in our 2-20-97 report oCthc Haul Road Slope Stability assumed the existing bedrock might not <br />be utilized Cor fill support and the tce area would be founded on the colluvial soils on the slopes. During the <br />analysis for the 2-20-97 report, the maximum fill slope height vas computed to be 20 feet, with the strength of <br />the foundation colluvium governing the slope configuration. <br />Careful analysis vas made of the higlrcr earth fills proposed for this silt. with adjustments in the road alignments <br />made to place the bast of the earth CII on the relatively more competent rocks of the Bowie Member. With these <br />adjustments in the road alignment, the f II slopes could be steepened to as much as I : I (horizontal:vertical)ernd <br />the computed slope stabilih• could be governed by the design and construction techniques of the earthen fill <br />itself. rather than the foundation soils. The construction techniques would include, fill soil selection, appropriate <br />slope benching. proper fill placement and compaction and use of a mechanical soil stabilization with <br />Gcotcchnical Fabric or Gcogrid, as required. In general, the same slope materials utilized for the 2-20-97 <br />Lincoln DcVorc report arc utilized for this study. <br />The appendices of this report contain the printouts of the Slope S[abililq Study. The computer program <br />GEOSLOPE. Version 4.10, supplied by GEOCOMP Corp., vas used. The GEOSLOPE program is based upon <br />the program STABL3, dccelopcd at Purdue University. External loads. 2-16,000 Ibs for a single axle, were <br />applied in tlrc 'outside lane of the haul road to model truck traffic. <br />For computational purposes the sccuon along the haul road at station 8+00 vas dclennincd to probable be the <br />~vorsc cast on the south facing slopes and yeas studied for global stability, stabilih• of the fill portion and stability <br />of the cut section. assuming the Boccie shale is present in the majorih of the cut, with several significant <br />sandstone beds ~~hich arc evident in surface exposures. <br />