2009-12-04_REPORT - M2007014 - Laserfiche WebLink

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C: 3 :: I1 ::::C COG uu■■u iii , R ASSOCIATES, AND December 2, 2009 High Country Pipeline P.O. Box 670 Penrose, Colorado 81240 Subject: Byzantine Quarry Slope Assessment 112c Mining Permit Application File No. M- 2007 -014 Project No. D09.210 To Whom It May Concern: On November 17, 2009 Joseph A. Cesare and Associates, Inc. /Construction Technical Services (JAC /CTS) visited the Byzantine Quarry site in Fremont County, Colorado in order to observe the quarry development to date for general conformance with the following references: 1. Report titled "GEOTECHNICAL STABILITY EXHIBIT, Byzantine Quarries, Fremont County, Colorado," JAC /CTS, revised December 20, 2006, Project No. D06.287.A. 2. Letter titled "Review of Plans for 112 Permit, Byzantine Quarries, Fremont County, Colorado," JAC /CTS, January 17, 2007, Project No. D06.287. In Reference 1, JAC /CTS identified planar failure along bedding planes to be the governing mode of failure. The presence of clay seams along the bedding planes will likely be the critical factor in long term stability of highwall configurations. Measurements indicated bedding generally strikes between N10V and N30 with dips ranging from 20 to 34 degrees. In the references, JAC /CTS recommends that pit walls that are oriented within 20 degrees of strike of bedding will need to have an overall slope of 30 degrees (1.6H:1.OV) or shallower. This configuration applies for the west pit wall which comprises the majority of the cut face. Walls at other orientations will be stable at slopes of 63 degrees (0.51-1:1V). In Reference 2 we indicate that the surveying plans call for 40 -foot wide benches with near vertical (0.06H:1 V) bench face of 30 -feet high. We go on to recommend 48 feet wide benches in order to maintain an overall slope of 1.6HAV. 7108 South Alton Way, Building B * Centennial, Colorado 80112-2109 • www.jacesare.com Phone (303) 220 -0300 • Fax (303) 220 -0442