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~i'3 Ur,awNp Owrry <br />April 17, 2001 <br />' ¢tG Jo0 Na 793 <br />! !~ P~ 3 <br />,~ <br />Stability of the 3-inch Minus Stockpile <br />Slope stability analysis reported by Geotechnicai Engineering Group was also a <br />topic of the DMG memo. The memo makes mention of the angle of intemai friction <br />-!~ value range used in calculations of 35 to 45 degrees as representative of a fairly strong <br />,y granular material. We believe engineering properties disclosed by the limited laboratory <br />-= testing program performed on embankment materials justifies the range of intemai <br />~=i angle of friction used in calculations. Samples of the embankment material tested <br />exhibited non liquid and non plastic characteristics, 53 and 61 percent retained on the <br />No. 4 sieve, 41 and 7 percent passing the Na. 200 sieve and 100 percent 2 or more <br />fractured faces. This is the justification presented for the intemai angle of friction values <br />used in our glculaifons. <br />The pMG memo states 'Rhino apparently based it's assumption of dry conditions <br />1i on the five test pits it dug surrounding the pile in October of 2000.' This is incorrect. <br />The GEG report states that groundwater was not encountered at the site and the <br />°H embankment material encountered was virtually free draining. These observations, the <br />~~ configuration of the site and surrounding area and the drainage improvements proposed <br />ware considered to model the embankment pile as a dry condition. We did not identify <br />aquicludes at the embankment area. The foundation soils also appeared to have <br />drained characteristics. <br />The embankment foundation soils observed consisted of silty to clayey, gravelly <br />~, cobbles and boulders, lightly to moderately cemented, dry and red. Backhoe refusal <br />was reached in the two cower test pits (TP-4 and TP-5) in the natural strata at depths of <br />~'" 3 to 4 feet below the ground surface. We observed similar oversized pieces and <br />cementation in the natural slope above the stockpile. We identified that as depth in the <br />natural strata increased, cementation and particle size increased. The native soils <br />T appeared to be weathered natural formation. In comparison, the embankment material <br />was man placed fill, had particle size less than 3 inches and generally no cohesion. For <br />these reasons (and not arbitrarily}, we controlled the failure surfaces to occur within the <br />embankment material. For these reasons, we believe this assumption was reasonable. <br />The DMG memo requests additional information regarding the stability analysis <br />e performed. Factor of safety values reported resulted from a circular radius of 380 feet, <br />~ arc length of 83 feet, soil moist density of 126 pci, cohesion value of 0 and intemai <br />angle of friction of 35 and 45 degrees. These data resulted in calculated factor of safety <br />~ against movement of 1.4 and 2.1, respectively. <br />i <br />The DMG memo indicates actual operational stability of the reclaimed 3-inch <br />minus pile can be observed and documented by installing and periodic surveying of <br />inexpensive survey monument hubs. We agree this could be demonstrated relatively <br /> <br />