2024-02-02_REVISION - M1982121 (6)

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K jL U UFF � RM R Aggregates, Inc. u N D E R G R O U N i Rock Failure Analyses and Stabilization Report E N GI N E ER I N G. IN C Mid Continent Limestone Quarry Colorado DRMS7 are scaled based on the robustness of input parameters and analyses weighted by the consequence of failure. The Colorado DRMS recommended FOS values, captured again in the 2018 Policies of the Mined Land Reclamation Board report', are reproduced in Table 4 below. Table 4. Slope Stability Design Standard Minimum Factor of Safety Consequence of Failure/ Generalized,Assumed, Strength Measurements Analyses or Single Test Strength Resulting from Multiple Measurements Tests Non-Critical Structures- Static 1.3 1.25 Non-Critical Structures— Pseudostatic 1.15 1.1 Critical Structures - Static 1.5 1.3 Critical Structures— 1.3 1.15 Pseudostatic For the RMR Aggregate site, the failure path of the slope could impact quarry facilities on the bench, and potentially impact life safety,therefore the structures were considered Critical. Static analyses were performed, together classified in Table 4 as "Critical structures—static". The slope stability analyses were performed using some historic data provided by the client, but the model input parameters were largely informed by empirical values that were confirmed through our backanalysis, classified as "Generalized, assumed, or single test strength measurements" in Table 4.Therefore, a FOS of 1.5 was considered as the minimum acceptable FOS for static analyses on the project. Seismic analyses was also performed, classified in Table 4 as "Critical structures— Pseudostatic", where MLRB dictates the minimum acceptable FOS of 1.3 for pseudostatic analyses on the project. As a cross check, other mine-industry references commonly used for recommendation of an acceptable minimum value for FOS include a table of minimum FOS for slope scale vs. consequence of failure from the Acceptance Criteria chapter in the Guidelines for Open Pit Slope Design manual, reproduced here as Table 5. Colorado Division of Reclamation, Mining and Safety,2016, Design Standard of Care for Slope Stability/Geotechnical Analyses. 8 Colorado Department of Reclamation, Mining and Safety,2018,Policies of the Mined Land Reclamation Board,dated May 16,2018, 14pp; https:Hdrms.colorado.gov/rules-and-regulations Page 11 535 16t'STREET,SUITE 620 1 DENVER,Co 80202 1 (303)732-3692 1 WWW.KILDUFFUNDERGROUND.COM