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Hitch Rack Ranch Quarry Waste Stockpile Stability Analyses/591-6 <br /> NORWEST March 13,2018 <br /> 2 2 <br /> COR PORAT ION <br /> addition,the overburden is relatively thin on site at around 4 ft(1.2 m)which would limit the variability in <br /> stratigraphy. Details of the overburden soil materials are discussed in Section 4. <br /> 3. DESIGN CRITERIA <br /> The project design criteria are outlined in Table 3.1 to provide a basis for the stability evaluation. <br /> Table 3.1 <br /> Design Criteria for Waste Stockpile Stability <br /> — . th'�e� il►a�ue <br /> Operation Inter-bench Slope Factor of Safety(FoS)—Static 1.0 <br /> Operation Global Slope FoS—Static 1.5 <br /> Operation Global Slope FoS—Pseudo-static 1.3 <br /> Operation Seismic Coefficient 0.014 g(1:475 yr) <br /> Closure Global Slope FoS—Static 1.5 <br /> Closure Global Slope FoS—Pseudo-static 1.3 <br /> Closure Seismic Coefficient 0.036 g(1:2,475 yr) <br /> Operation Inter-bench Slope Angle 1.7H:1V(30 degrees) <br /> Closure Slope Angle 3H:1V(18 degrees) <br /> The stockpiles will be constructed in five (5) to 10 ft (1.5 to 3 m) lifts based on the proposed equipment <br /> sizes, and the edges of the stockpiles will be dumped or pushed to form angle of repose slopes. Several <br /> lifts will be placed before a bench is established.The bench heights at the HRRQ are less than 160 ft(50 m) <br /> which are well within general mining practice. The inter-bench slope will be monitored during mining <br /> operation where bench clean up and maintenance are expected to occur. Due to both of these factors,the <br /> FoS for inter-bench slope stability is accepted to be 1.0 where minor sloughing is expected and impact of <br /> the sloughing is deemed low. It is assumed that benches will be constructed as designed and maintained <br /> during operation. <br /> The FoS of the operational global slope stability under static conditions is conservatively set to 1.5 and the <br /> pseudo-static FoS is 1.3. These FoS are deemed appropriate to accommodate the assumptions made for <br /> the material properties and ground conditions according to the Interim Guidelines for Mined Rock and <br /> Overburden Piles Investigation and Design Manual (BCMWRPRC 1991). Details for the material <br /> assumptions are discussed in Section 4. The seismic coefficient for the pseudo-static analyses is set to <br /> 0.014g, which correspond to one half of the value Sl value representing the 10% chance to exceed a 1 in <br /> 50-year event, equivalent to a 1 in 475-year recurrence. The seismic coefficients are provided by United <br /> States Geological Survey(USGS) and the seismic output reports are provided in Appendix B. <br /> The FoS of the closure global slope stability for static and pseudo-static are 1.5 and 1.3, respectively.They <br /> are appropriate according to standard practice. The seismic coefficient for the pseudo-static analyses is <br /> set to 0.036g, which correspond to one half of the S1 value representing the 2% chance to exceed a 1 in <br />