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~~ttm~Fr~ ~tn~ 1~l~suria~PS ~~~~~~~~~~~~~~~~~~~ - CONSULTING GEOTECHN ICAL ENGINEERS AND ~~L-+.TE2IAL TESTING ' December 21, 1995 %j ' Goff Engineering ' 555 South Camino del Rio Durango, Colorado 81301 Attention: Mr. Harry Goff, P.E. ~ PN: D95263MT ' Subject: Oak Ridge Energy Crushing By-Product Deposition Pile ' Durango, Colorado, Mr. Goff, ' This letter presents the results of our simplified Bishops method of slices slope stability analysis. The critical potential failure surface is presented on Figure 1. The daily field reports 1 and field density test results which were previously sent to you during the monitoring of the material placement are presented in Appendix A. The laboratory moisture content-dry density ' relationship (Proctor), and direct shear test results are presented in Appendix B. We began our materials testing services for this project on ' November 15, 1995 as you requested. The material placed consists of a by-product of the crushing operations at she Durango Construction Ewing Mesa gravel pit mining operati.or.. Durango ' construction produces several road base and aggregate products at the Ewing Mesa pit. We understand that asphalt concrete aggregate is the primary material being produced which results in the by- ' product used. The by-product consists of a silty clay with some sand and small gravel. All of the material tested has a nominal dimension of less than three-quarter (3/4) inch. ' we performed a standard moisture content-dry density relationship (Proctor), American Association of State Highway and Transportation Officials (RASHTO) Test Method T-99, test on the ' material being placed as requested. During our November 15, 1995 telephone conversation with you and Mr. Harry Reany, Colorado Division of Mining and Geology, we discussed the compaction ' requirements and the required theoretical slope stability factor of safety of the material being placed. We understand that the material must be compacted to a minimum relative compaction of ninety (90) percent of maximum dry density as determined by AASHTO ' T-99, Standard Proctor Test. The required theoretical slope stability factor of safety is 1.3 when using the simplified Bishops Method of slices analysis. 1 ' P.G. BOR 7935 P.J. BO.~ 0045 y= 1: 9o3o`O:-:~ie GP.a:~O .TUNCPI OPI, CO MOLR'aZOS E. CO. 31402 :GJ, 3.30: 307) 245-4605 1307) 249-.154 i]031 =53-i.J96