Laserfiche WebLink
• Balaz & Associates <br />New Coal Waste Pile and Haul Read Project, Sanborn Creek Mine, Somerset, CO <br />June l8, 1997 Page 2 <br />It must be noted the geologic section in this area could only be approximated From existing road cuts and surface <br />outcrops oC the Bowie Member. For the most critical trial failure surfaces, the safety factor calculated by the <br />Modified Bishop Method for global stability (fill height increased to 52') waz found to be approximately 1.8. <br />The most critical trial failure surfates safety factor calculated by the Modified Bishop Method for the 611 portion <br />.vas found to be approximately 1.7. The most critical trial failure surface, az calculated by the Modified Bishop <br />Method for the cut section, above the proposed road waz found to, have a safety factor of approximately 2.4. <br />It should be noted the fill section was placed at a slope of 1: I (H:V), with the toe of this slope placed on the <br />existing brnch, knot~n as the Wcs- Yard. An additional rcquircmrnt on this 611 is that a minimum distance of <br />25 feet from the toe oC the new haul road 611 to the edge of the existing West Yard brnch crest must be <br />maintained This particular requittartrnt is for slope stability wncems for the upper fill, to allow sufficient room <br />to construM the sodimrnt pond road and to minimize the amount of fill used to construct the sedimrnt pond road <br />which may adversely affect the global stability of the entire slope section. <br />The most recent road alignment and sections observed by personnel of Linwln DeVorc on 6-2-97 indicate that <br />the fdl at station 27+00 will be the most critical in this portion of the haul road, due to fill height and possible <br />colluvium supporting the 611 base and tae. The base of the fill at 27+00 will require a bench to be cut into the <br />existing slopes through the assumed colluvium and into the Bowie Membtt. It should be noted the highest <br />portion of this fill should be founded on the existing road section, which will require additional excavation prior <br />to beginning the earthen fill for the haul road. The toe of this slope is to be set back 7 fat from the txisting <br />outside shouldttlfill crest. The fill slope in this area will be at approximately 1.7:1 (H:V). It must be noted the <br />geologic section in this area was approximated from existing road cuts and surface outcrops of the Bowie <br />Member. For the most critical trial failure surfaces, the safety factor calculated by the Modified Bishop Method <br />for global stability tvaz found to be approximately 1.7. `Select' colluvial fill was used, due to hightt unit weight <br />to be consen•ativc. Thc most critical trial Cailurc surfaces safety factor calculated by the Modified Bishop <br />Method for the fill portion was found to be approximately I.S. The most critical trial failure surface. as <br />calculated b.• the Modified Bishop Method for the cut section, above the proposed road was found to have a <br />safety factor oC approximately 6, which is very high, but natural Gacture patterns will probably decrease the <br />safety factor to less than 2. <br />If these road sections can be constructed with the silty, sandy gravel colluvium and alluvium, N theory, little or <br />no soil reinforcerttettl (mechanically stabilized earth) will be required. In reality, it is anticipated that, even with <br />selective usage of on site materials, that the clayry colluvium and "rocky" portions of excavations from the <br />Bowie Membtt will undoubtably be utilized in the earth fills. Unfortunately, the amount of clayey materials <br />and the qualin• oC the actual fill cannot be readily assessed without a significant number of exploration pits. <br />It is recottmtrnded that the higher fills placed in the vicinity of station 8+00 be mechanically stabilized for at least <br />the bottom 20 fact. For preliminary design purposes, it is assumed that the mechanical reinforcing can be <br />aceomplishcd using a gcotcxtile, non-woven needle punched fabric with a minimum wide strip tensile strength <br />of GS pounds per inch in the weakest direction. Thc fabric is to extend into the 611 a minimum oC 12 Cect and <br />is to be placed in the fill, ecerv 3 feet oC vertical height. For ease of constroction and to help convol the slope <br />. face during construction, fabric in access of 12 Ceet could be wrapped up and around to partially rnclose the fill <br />face. Thc fill face and fabric must be wvered with a rocky soil, which could be revegetated. <br />