2023-10-31_REVISION - M1973021 ‎(4)‎

• Permit No: M1973021
• IBM Index Class Name: Revision
• Doc Date: 10/31/2023
• Doc Name Note: Attachment B - Appendix G - Diversion Channel Slope Stability Analysis
• Doc Name: Request for Technical Revision
• From: Holcim - WCR, Inc.
• To: DRMS
• Type & Sequence: TR9
• Media Type: D
• Archive: No

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