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 2 2.0 SAMPLING AND MATERIAL CHARACTERIZATION A representative sample of colluvium was obtained from an exposed cut bank located southwest of the ECOSA facility for laboratory testing, and the sample location is shown on Figure 1. In addition, a sample of the overburden material was obtained from within the active portions of the facility. The particle size distribution and shear strength was measured in the laboratory for each sample, and laboratory data sheets are included as Attachment A. Based on the laboratory data, both the colluvium and overburden are 6‐inch minus material, with a dominant portion of gravel‐sized particles and minimal fines. Both samples are considered non‐plastic. Direct shear tests were run in an 8‐inch square shear box under saturated conditions. To comply with ASTM D3080 test standards that provide guidance on maximum particle size as a function of the shear box size, only minus ¾‐inch material was used for the test. Results of the laboratory tests are summarized in Table 1.1. Table 1.1 Summary of Material Properties Sample ID % Gravel % Sand % Fines USCS Group Symbol Friction Angle (deg) Cohesion (psf) Overburden 58.8 33.9 7.3 GP‐GM 41.4 361 Colluvium 67.6 23.7 8.7 GP‐GM 40.1 0 As a significant portion of the larger, gravel‐sized particles are removed from the test specimens, the reported shear strengths are considered a conservative estimate and in‐place materials at the ECOSA are likely more competent. 3.0 OVERBURDEN STORAGE AREA STABILITY EVALUATION Stability analyses were performed using the computer program SLIDE 6 by Rocscience for static and pseudo‐static conditions. SLIDE is a two‐dimensional slope stability program for evaluating circular or noncircular failure surfaces in soil or rock slopes using limit equilibrium methods. Spencer’s procedure, which is applicable for all slope geometries and soil profiles, was utilized within the stability model and assumes all inter‐slice forces are parallel and have the same inclination. Minimum acceptable factors of safety (FOS) for static and pseudo‐static conditions were based on criteria established by the Colorado Department of Reclamation, Mining, and Safety (DRMS), as follows: