2016-12-19_REVISION - M1980244 (2)

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Technical Memorandum Newmont CC&V Gold Mine East Cresson Overburden Storage Area Stability Review/Update NewFields Job No. 475.0106.005 9 December 2016 Page 5  Overburden: Overburden material in the ECOSA is essentially rockfill from the pits with no economic value. As such, the engineering properties are similar to that of the ore that has been studied throughout the project history and modeled with a 39 or 40 degree friction angle. In agreement with older designs, the initial evaluation of the ECOSA considered a friction angle of 39 degrees (Adrian Brown, 2012). Based on the project history and new laboratory test data (measured friction angle of 41 degrees), the continued use of a 39 degree friction angle to represent the strength of the overburden was deemed reasonable and applied in the current evaluation.  Colluvium: Strength parameters for the colluvium foundation was based on the recent laboratory test data and existing data from around the site for unconsolidated foundation materials. Adrian Brown (2012) characterized the strength of the colluvium under the ECOSA using an empirical relationship between shear strength, liquid limit and clay fraction of the material. Based on visual observation of colluvium and recent test data, this value is too conservative for a coarse‐gravel with minimal fines. The current evaluation uses an average value between the recent laboratory data and that utilized by Adrian Brown (35 degree and no cohesion). As some of the fines within the colluvium are fine‐grained, the strength was reduced by 20 percent for the pseudostatic evaluation to account for development of excess pore pressure.  Bedrock: The dominant rock type underlying the facility is Tertiary phonolites. The unit weight and strength for bedrock was developed from data presented by Call & Nicholas (2015) for this material type and a poor to fair rock quality designation (40 – 60%). The associated unit weight, φ and cohesion values are 153 pcf, 34.5 degrees and 20,000 psf, respectively. Stability Evaluation Results 3.4 The stability analyses resulted in acceptable minimum FOS values for both static and pseudo‐ static conditions, as show in Table 2.2. The output graphics from the stability models are included as Attachment C.