2024-02-01_REVISION - M1973021 (2)

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Geotechnical Stability Exhibit Engineering Evaluation of Highwall Design for the South Quarry of the Morrison Quarry January 2024 | 18 5 Design Methodology 5.1 3-D Geologic Model A three-dimensional (3-D) geologic model was prepared and submitted to Aggregate Industries by GEI in 2018, as an update to the 2017 version, and was included in the Permit M-1973-021 AM-07 Geotechnical Stability Exhibit. As part of this task order, HDR prepared a separate model incorporating historic data, as well as the recent drilling effort, to better define the geologic structural conditions of the site. Reserve calculations were not part of this effort. The HDR geologic model was prepared to visualize the areas of competent bedrock in relation to areas in which the bedrock was considered lesser strength, and thusly modeled in the stability calculations as weaker material. In general, based on the results of the petrographic analyses, the weaker rock is described as Talc-Gneiss; however, the exact mineralogic composition of the rock in this area is variable and may consist of a percentage of clay mineral assemblages. Development of the geologic model was performed using LeapFrog Works, version 2022.1.1, and includes boring data from the previous drilling efforts as well as the recent 2022 HDR field event. The proposed geometry linework was downloaded from the Propellor site, maintained by Holcim, and includes mapping of 40/40 benches below El. 6600. File was dated December 21st, 2022. Lithologic mapping included simplifying the boring data by competent material, including biotite gneiss, granitic gneiss, quartz, etc., as compared to less competent including the previously described sillimanitic gneiss, talc-gneiss, or gneiss with a combination of intermixed sedimentary material. Upon simplifying the lithologies, HDR correlated the materials to estimate the lithologic bounds, and included existing mapped exposures to better refine the model. The resulting model is included in Appendix B, Geologic Model, along with cross sections cut to show the subsurface conditions at pre-determined station intervals. The model is estimated based on currently available information and could be refined with additional drilling information. 5.2 Bench Stability The simplified geologic model with anticipated 60/40 bench configurations above El. 6,600 and 40/40 bench configurations from El. 6,600 to current permitted El 6,500, was utilized to evaluate the current and future stability of the Morrison Quarry as mining proceeds in the South Quarry below El. 6600’. Evaluations of stability include global and local factors of safety with RocScience SLIDE2 and FLAC/Slope, as well as kinematic analysis using RocScience DIPS of planar, toppling and wedge failures based on discontinuity data collected via field visits, high- density orthoimagery, and downhole geophysics. 5.2.1 Hoek-Brown Parameters The 3-D geologic model provides a spatial representation of competent biotite/granitic gneiss and less competent talc-gneiss. In order to evaluate the stability of the proposed bench configurations, generalized Hoek-Brown strength parameters were defined based on recent field