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<br />~ IIiI'WOIa ll-1'/U4'LAI< L~CO'fliCi;i\ICi~I., iNC. <br />December 2, 1994 <br />NCIG Financial, Inc. <br />Attu: Peter Maltheis <br />~U2111:ndJ 15~i <br />t ::cmvuoJ tit Sri ngti, CO ~ I oU I <br />I•,i~:10:49~161015.1 <br />I'Lunc ::11.1 945"71Wa <br />0304 Stone ping Road <br />New Casllc, Colorado S 1647 .lob No. 194 ~4S <br />Su~jcct: Comments Regarding Stability of Graded Cut Ind Pill Slopes, New Castle <br />Energy Mine Facilities, County Road 33~, Garlicld County, Colot'ado. <br />Gentlemen: <br />As requested, we have reviewed the gcotcchnical reports and grading plan prcparcd lot' the <br />subject site and made s cut'sory t'evicw of !hc constructed grading conditions. The <br />purpose of ow' wort: was to develop opinions on the overall stability oC lltc graded slopes. <br />Our review does not include the portal slopes. <br />Previous Studies: We wuc provided a gcotcchnical report prcparcd for grading design <br />and processing f:rcilitics by Chen K f\ssociates (Chen, 1955). Tire grading plan was <br />prcparcd by Schnnlescr cC Associates. A reproduction of the grading plan presented in <br />Chcn's report is attached. <br />Subsoil Conditions: The subsoils encountered in the development area by Chcn's borings <br />consist mainly of gravelly sand and clay. Soils oC higher gravel content and Icss clay wcrc <br />:dso found. No free wafer' was cncomitcrcd to the drilled depths of 1~ to 70 feet and the <br />natural moisture was relatively low. <br />Site Grading: We have not been provided an as-build grading plan. It appears ii•om our <br />cursory observations of the site that the ~~rnding was generally conducted according to <br />Schnulescr's gl'adlllg CICSIgn. IhC dcslg^ Cnt an<I IIII SIOpeS 1'angc LO a IllaSllllu111 helghl Of <br />2J Icct and maximum grade of l 3/4: l (horizontal to vertical) according to the Chen <br />report. "I'he on-site soils wcrc used to construct die 1711 embankments. <br />Slope Stability: We did not observe indications of overall instability ol~ the consu'ucted <br />slopes. The soil conditions idcntilicd by Chen & Associates appear appropriate for the <br />stability analysis. Accordingly, we h:n~c assumed the following parameters: <br />Internal Friction: <br />3~° <br />Cohesion: 200 psf <br />Moist Unit Weight: 125 pct <br />Maximum Slope ] Icight: 25 feet <br />Maximum Slope Grade: 30° (1 3/4:1) <br />fully drained cntbankmcnt and foundation <br />We understand that graded slopes steeper than 2:1 require a safety Factor of at least 1.3. <br />Based on the assigned subsoil and grading parameters, the calculated saicty factor against <br />