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3. Changes in soil properties due to mine operations and variability in subsurface <br /> material, <br /> 4. Accuracy (or approximations used) in developing design/ analysis methods, <br /> 5. Additional considerations if relevant: Construction tolerances, Relative change in <br /> probability of failure by changing the factor of safety, and Relative cost of <br /> increasing or decreasing the factor of safety. <br /> The Division engineering staff has researched the standard of care for factors of safety <br /> accepted by the industry, including literature searches, regulatory agency <br /> requirements/guidelines, and departments of transportation standards. In order to be <br /> consistent with other Colorado State agencies, we also considered FS standards used <br /> by the Colorado Department of Transportation (CDOT) and the Colorado Geological <br /> Survey (CGS). CDOT uses the AASHTO minimum FS of 1 .3 for construction slopes <br /> near roadways and utilities. CGS uses a minimum FS of 1 .5 for residential areas when <br /> using "generalized" strength values, or 1 .3 for analyses when good quality site-specific <br /> soil parameters are known. It should be noted that most industry standards assume a <br /> permanent slope configuration, ignoring the temporary conditions that are frequently <br /> observed in the mining industry. <br /> 30.4 — Guidance for Stability Criteria and Use of Minimum Factors of Safety <br /> The permittee should either follow the criteria in Table 1 for all stability analyses <br /> submitted to the Division; or, alternatively, the permittee may submit stability analyses <br /> based on site-specific engineering analysis performed in consideration of good <br /> practices as specified in relevant industry guidelines and/or professional standards and <br /> reviewed by the Division on a case-by-case basis. <br /> Slope stability analyses for existing facilities may also be reviewed on a case-by-case <br /> basis, subject to the criteria described herein. <br /> Table 1. Recommended Minimum Factors of Safety for Slope Stability Analyses for <br /> Operations and Reclamation <br /> Generalized, Strength <br /> Assumed, or Single Measurements <br /> Type of Structure/Consequence of Failure Test Strength Resulting from <br /> Measurements Multiple Tests0) <br /> Non-Critical Structures (e.g., fences) 1 .3 1 .25 <br /> No imminent danger to human life, minor (1.15)(2) (1.1)(2) <br /> repair costs, and minor environmental <br /> impact if slope fails <br /> Effective May 16,2018 MLRB Policies Page 12 <br />