Laserfiche WebLink
presented. We strongly recommend following the Urban Drainage and Flood Control District's <br /> updated designs for grade control structures, which have been revised since 1983. <br /> Response: Check Structures have not been previously installed in the Ralston Creek, and <br /> based on guidance from USACE during an inspection of the Schwartzwalder site in early <br /> 2016, USACE stated check structures may be needed if Ralston Creek was rerouted from <br /> its current path. Cotter does not intend to reroute Ralston Creek and therefore check <br /> structures will not be necessary <br /> Comment No. 6 - The Division views the waste rock piles as critical structures as they are <br /> designed to keep waste rock out of Ralston Creek. Plates 12 and 13 prepared by McDermid <br /> Engr.Assoc.Inc.in February 1983 summarize slope stability analyses results. It appears only the <br /> cover stability and the contact with the native ground were analyzed as potential failure <br /> surfaces. The various strength parameters used for bedrock, alluvial soils and colluvial soils <br /> were obtained from simple soil testing and/or literature data. It does not appear that slope <br /> failure surfaces thought the waste rock itself were considered as is the current general practice <br /> for slope stability. As such it does not appear any strength parameters of the waste rock itself <br /> are discussed. Please revisit the slope stability of the waste rock piles and consider potential <br /> circular failures that may extend through the waste rock, using the Division's factors of safety <br /> in Table 1. <br /> DRMS Table 1. Minimum Factors of Safety for Slope Stability Analyses <br /> Type of Structure/Consequence Generaiixed,Assumed,orSinjle Strength Measurements <br /> of Failure TestStren Meas_u_rement_s Resulting from Multiple Tests(') <br /> Non Critical Structures(e.g., 1.3 1.25 <br /> fences)/No imminent danger to (1.15)(2) (1.1)(2) <br /> human life,minor environmental <br /> impact,and minor repair costs if <br /> slope fails <br /> Critical Structures(e.g., 1.5 1.3 <br /> residences,utilities)/Potential <br /> human safety risk,major <br /> environmental impact,and <br /> major repair costs if slope fails <br /> (1) The number of tests required to provide a high degree of confidence in the strength parameters used <br /> depends on the variability of the material being tested and the extent of the highwall disturbance. <br /> (2) Numbers without parentheses apply for analyses using static conditions and those within <br /> parentheses apply to analyses using seismic acceleration conditions <br /> Response: Refer to Attachment D, Engineering Analytics letter and report dated October <br /> 26, 2016 <br /> 2016-11-07 Response to TR23 Adequacy Review 11 <br />