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^ r <br /> -- ---- <br /> � ������ � <br /> ' " �� <br /> ==���� | <br /> Civil, Structural & Geotechnical Engineers <br /> . <br /> July 29, 2013 <br /> Ta0n0eB|xh0p, PE <br /> ]E Stover&Associates <br /> 23533 North 7"' 9T., Unit B <br /> Grand Junction, C{} 815U1 <br /> RE: 8OVVlE# 2 MINE, CWOA PILE #2EXPANSION <br /> SU8J: EJABILTY ANALYSIS DF PROPOSED SLOPES DF2.5M:1\i5ECT7ONSA'A'ANOF-P <br /> DearTamme: <br /> Per your recent request, we have analyzed the proposed expansion of the B0Vvi8 Mine [Val Waste <br /> Disposal Area (CVVDA) #3 for slope stability based on the AUtO[AO topography for cross-sections ArA' <br /> and F-F'that you provided dated July 24, 2013. ltiSour understanding that some areas of Pile #2 are <br /> proposed to have slopes 0[2.5:l as detailed in that July Z4mdrawing. Based on the recent topographic <br /> survey, the proposed revised slope configuration and the rDahSri8| properties from the stability analysis <br /> presented in our December 2008 report for both the native and waste materials, we performed <br /> aD8|ySe5 in SLIDE (version 5.0) to cVDhrD the factor ofsafety for the proposed expansion. <br /> Assumptions for CWDA #2 Expansion Stability Analysis <br /> * Depth t0 native SO||S was modeled as actual depth of gob t0 native surface based on <br /> comparative site surveys performed by Steve Cragg and shOvvO in profile on your July 24, 2013 <br /> AULoCAD drawing file. <br /> * Material properties are the Sa[OH as originally modeled in 0U[ 2008 Gob P||8 #2 stability analysis: <br /> Gob has an average internal angle of friction, ph|,(4/) of 34 degrees and an average unit weight of 110 <br /> p[f, and an average COh8s(Vg strength o[0 psf; Native 60i| has a cP of 34 degrees, an average unit <br /> weight of 125 pcf8Md a cohesive strength of psf. <br /> * No phreatiC surface was DlOdg|ed iD our analysis since the geOL8Chnicn| investigation, performed <br /> in our December 2O08CVVOApile #Z report, encountered nU groundwater iMthe native soils and the <br /> ultimate pile stability assumes deVvatering which is r8aS0Dab/9 given the decreasing pore pressures in <br /> the vibrating wire piezonnetpr [esu|tS over the past years. <br /> The minimum global factor of safety (F.S.) for the proposed configuration of the expanded CVVDA #2 at <br /> the BOVvi8 #3 Mine was determined to be 1.533 for section A-A' (Revised) and 1.562 for section F-F' <br /> Using the siD1p|ified]anbU method used for analysis. To confirm this calculation, the 3|Vp8 was also <br /> analyzed using three other methods: Spencer, Bishop simplified and GLF/M0rgenSLer0-Price with the <br /> global Uo|Di[OurD for each method shown in Figures 1 and 2 [eSpeCt|Vo|y for sections A-A'and F-F'. <br /> Bowie—CVVDA #2 PNOS-126-GEO <br /> July 29, 2013 Slope Analysis <br /> Page 1of4 <br />