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Geosyntecc� <br /> consultants Page 3 of 12 <br /> Client: Arcosa LWB Project: Permit Amendment Project No.: DE0374 Task: Exhibit S—Structures Evaluation <br /> Written by: Jonathan Gillen Date: 7/8/2019 Reviewed by: Youngmin Cho Date: 7/9/2019 <br /> Approved by: Poppy Staub Date: 7/15/2019 <br /> Highway 93 and the features contained within the Right of Way (ROW) consist of the roadway <br /> surface,the roadway embankment,a surface water drainage Swale located west of the road surface. <br /> Other structures such as overhead utility/power lines owned by Excel Energy, and a wood and <br /> barbed-wire fence owned by Arcosa periodically traverse within the Highway 93 ROW in different <br /> places. Collectively,these structures are within approximately 78 ft of the eastern excavation limit <br /> of the current quarry configuration at their closest point. <br /> Cross section line A-A' is shown on Figure S-2. The topography and location of the mine and the <br /> Highway 93 ROW shown along Section A-A'were used to develop a 2-dimensional slope stability <br /> model. The 2-dimentional model (i.e., slope stability model) geometry of Cross section A-A' is <br /> shown as Figure S-4.This model utilizes a depth to shallow groundwater equal to 5 feet bgs within <br /> the Slocum Alluvium though groundwater at this Site is often perched or dry. A live load equal to <br /> 240 pounds per square foot (lb/ft2) representing heavy traffic loading was applied to the location <br /> representing the road surface along Highway 93. <br /> The slope stability model was generated using the SLIDE' 7.0 slope stability software <br /> (RocScience,Inc.2018),and analyses were performed to evaluate non-circular failure and circular <br /> rotational failure modes. The Spencer method was used for non-circular analyses since it satisfies <br /> horizontal and moment equilibrium. The Bishop Simplified method was used for the circular <br /> analysis. The method of analysis also utilizes the Mohr-Coulomb strength criteria for materials <br /> used in the analysis. <br /> A pseudo-static seismic analysis was performed using peak ground acceleration (PGA), the non- <br /> circular analysis and the Spencer method. The pseudo-static analysis references the United States <br /> Geological Survey (USGS)published values for peak ground acceleration for a given region. The <br /> PGA used in this analysis is the published value corresponding to a probability of exceedance <br /> equal to 2% in a 50-year period. The USGS PGA map is provided in Attachment A. <br /> A target minimum factor of safety (FS) of 1.5 was chosen for static slope stability, and a target <br /> minimum FS of 1.3 was chosen for seismic slope stability based on Table 2 from the Policies of <br /> the Mined Land Reclamation Board(DBMS Policies), issued in 2018 by the Colorado Department <br /> of Natural Resources (DNR) DRMS. These values were selected because this analysis utilizes <br /> what the DRMS would consider"Generalized, Assumed, or Single Test Strength Measurements" <br /> for soil and rock properties. This model also considers Highway 93 ROW and utilities to be <br /> "Critical Structures" as defined by DRMS in the policy document referenced above. <br /> MATERIAL PROPERTIES <br /> Material properties used in the analyses are based on the results of a literature review performed <br /> to obtain general, or "preliminary", physical-mechanical properties in lieu of site-specific <br /> measured values (i.e., in lieu of values from laboratory or in-situ testing). The appropriate FS <br /> Structures Evaluation <br /> Arcosa LWB Plan—Permit Amendment 2019-07-16 <br />