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• <br />U <br /> <br />1-I lil'wUI: I'1 l-~~AIVLAIi i'I <br />~GO'r1iCl;i~fICAL, I,C_. :10^_II Ri~,id lSl <br />Glyn wood til~ri u;•,:, CU 5IId1l <br />Dcccmbcr2, 1994 I.i.`,u:4o.15-rlsl <br />I ~I~,n,~• is}'t.lsa~cla <br />NCIG Financial, lnc. <br />Attn: Peter Matthcis <br />0364 Stone King Road <br />Ncw Castle, Colorado S 1647 Job No. 194 545 <br />Subject: Connncnts Regarding Stability of Graded Cut and Pill Slopes, New Castlc <br />Energy Minc Facilities, County Road 335, Garlicld County, Colorado. <br />Gentlemen: <br />As requested, we have reviewed the gcotcchnical reports and grading plan prcparcd for the <br />subject site and made a cursory review of the constructed grading conditions. The <br />purpose of our work was to develop opinions on the overall stability of the graded slopes. <br />Our review does not include the portal slopes. <br />Previous Studies: We were provided a gcotcchnical report prcparcd for grading design <br />and processing facilities by Chcn ~~: Associates (Chen, 1955). The grading plan was <br />prcparcd by Schnwcscr K Associates. f\ reproduction of the g1,lding plan proscnted in <br />Chcli s report is attached. <br />Subsoil Conditions; The subsoils encountered in the development area by Chen's boriltgs <br />consist mainly of gravelly sand and clay. Soils of higher gravel content and Icss clay were <br />also toned. No tree water was encountcrd to dtc drilled depths of 15 to 70 fccc and the <br />natural mois[uro was relatively law. <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 grading was generally conducted according to <br />Sclunuescr's grading design. 'fhe design cut and fill slopes t,~nge to a maximum height of <br />ZS feel and maximum grade of 13/4:1 (horizontal to vertical) according to the Chcn <br />report. The on-site soils were used to construct the fill cmbanluncnts. <br />Slope Stability: \Vc did not observe indications of overall instability of the constructed <br />slopes. 1'he soil conditions idcntiGed by Chcn S; Associates appear appropriate for the <br />stability analysis. Accordingly, we have assumed the following par.vnctcrs: <br />tntcrnal Friction: <br />32° <br />Cohesion: 200 psi <br />Moist Unit Weight: 12~ pcf <br />Ntaxinnun Slope 1leight: 25 feet <br />Maximum Slope Grade: 30° (1 3/4:1) <br />Dully drained embanl:mcnt and foundation <br />WC Un(ICrsfalld Iltat gra(ICCI SIOpCS steeper than 2: I require a safety factor of at least I.3. <br />[3ased on the assigned subsoil and grading parameters, the calculated safety factor against <br />