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The following discussion is taken from Call and Nicholas, Inc. Executive Summary: <br /> Analytical stability analyses included.- (1) bench-scale back break analysis from which <br /> the expected distribution of bench face angles (BFA) and reliability schedules were developed, <br /> and(2) global wall stability associated with long release structures and weak rock mass. The <br /> back break analysis relied on cell-mapping conducted along existing mine benches in the Wild <br /> Horse Extension (WHEA)portion of the North Cresson mining areas. The global stability <br /> analyses were performed using rock strength data and drilling data to characterize the rock <br /> mass and to estimate the shear strength of the rock mass in relation to the excavation induced <br /> stresses. <br /> The CNI investigation consisted of <br /> 1. Determining geotechnically justifiable slope design angles for the NA mining areas <br /> including the Wild Horse Extension (WHEA), Globe Hill, and Schist Island areas. <br /> 2. Testing strength samples collected from geotechnical core holes. Data were lacking <br /> in the Globe Hill pipe zone before this study. <br /> 3. Projecting the known geology on cross sections used in the overall slope analysis. <br /> 4. Generating a geotechnical block model based on the most recent drilling database. <br /> S. Analyzing bench-scale stability based on cell mapping data collected in the WHEX <br /> mine. <br /> 6. Analyzing global slope stability for critical walls. <br /> 7. Providing recommendations for slope management over the life of the project. <br /> 8. Preparing a report to summarize the analyses and recommendations. <br /> Previous studies conducted by CNI included the following: <br /> • Geotechnical Review of the 2006 Pit Designs. The purpose of this <br /> review was to evaluate the existing geotechnical criteria used by CC&V to select slope <br /> angles. Mines evaluated included Main Cresson, Altman, Wildhorse, South Cresson, <br /> and Schist Island. <br /> • (May 2009) Cripple Creek and Victor Mine November 2008 Deep Cresson Pit Design <br /> Slope Recommendations. This report investigated the stability of the November 2008 <br /> Deep Cresson Pit Design. The investigation included a site visit and laboratory <br /> testing program. <br /> • (July 2010) East Wall Deep Cresson Slope Stability Design Options. This study <br /> reviewed the stability design criteria for the east wall of the Deep Cresson layback. <br /> The work was performed to determine if there was any upside potential for <br /> steepening the interramp angle on the east wall. <br /> • (April 2011) Cripple Creek and Victor Mine Wild Horse Extension Pit Design Slope <br /> Recommendations. This was the first geotechnical evaluation of the July 2010 Wild <br /> Horse Extension (WHEA) mine design. <br /> • (October 2011) Geotechnical Slope Design Recommendations for the MLE2 Mining <br /> Areas. This report presented the geotechnical slope evaluation of the mining areas <br /> associated with the Mine Life Extension 2 Project (MLE2). <br /> • (June 2012) Analysis of West Cresson Slope Stability when Mining Exposes Stopes at <br /> 4 <br />