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Technical Memorandum <br /> Date: August 31, 2023 <br /> Project: Holcim, WCR Inc. — Morrison Quarry Drainage Design <br /> To: Kate Garufi <br /> From: Caleb Stock, PE <br /> Subject: Highwall Reclamation Diversion Channel Slope Stability Analysis <br /> Attachments A — Stability Analysis Results <br /> Introduction and Background <br /> Holcim-WCR, Inc. (Holcim) retained HDR Engineering Inc. (HDR) to design a stormwater <br /> diversion channel as part of highwall reclamation at the Morrison Quarry. The diversion channel <br /> is being constructed on a reclaimed slope; the reclaimed slope is a 60 horizontal:40 vertical <br /> (60H:40V) bench buried with mine spoils. Reclamation of the highwall has been self-performed <br /> by Holcim and construction of the diversion channel is anticipated to be self-performed by <br /> Holcim. A geotechnical investigation of the 60H:40V benches or mine spoils has not been <br /> performed to determine subsurface material properties or presence of groundwater. <br /> The proposed diversion channel is a trapezoidal channel that will be lined with a geosynthetic <br /> and covered with riprap. The channel is designed to be 14 feet wide at the banks, with a depth <br /> of 2 feet deep with side slopes of 2H:1V down to a bottom width of 2 feet. <br /> Figure 1 shows the location of the proposed channel alignment as well as the stationing where <br /> model cross-sections are identified. This Technical Memorandum presents the methodology, <br /> assumptions, and results of the stability analysis. <br /> Design Criteria <br /> The Morrison Quarry is regulated by the Colorado Division of Reclamation, Mining, and Safety <br /> (DRMS). DRMS criteria (2018) indicate a required factor of safety of 1.3 for reclamation slopes <br /> of non-critical structures when generalized, assumed, or single test strength measurements are <br /> applicable such as this circumstance. <br /> Model Inputs <br /> Slope stability was evaluated using the finite element program SLOPE/W in GeoStudio 2023.1 <br /> software [1]. Slope stability was analyzed using limit equilibrium principles. Potential failure <br /> surfaces were analyzed using the Spencer method, which satisfies both force and moment <br /> equilibrium. The SLOPE/W program incorporates a search routine to locate those failure <br /> surfaces with the lowest factor of safety within user-defined search limits. Trial failure surfaces <br /> were defined with "entry and exit" parameters, resulting in a range of possible locations to <br /> search for the critical potential failure surface (lowest factor of safety). A minimum slip surface <br /> hdrinc.com 1670 Broadway, Suite 3400, Denver, CO 80202 <br /> (303)764-1520 <br />