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Geotechnical Stability Exhibit <br /> Engineering Evaluation of Highwall Design for the South Quarry of the Morrison Quarry <br /> <br /> January 2024 | 21 <br /> <br />Figure 6: Geologic Strength Index for Jointed Rocks <br />Selected Hoek-Brown parameters for stability evaluation of the existing and proposed bench <br />configurations are summarized in Table 9 below. <br />Table 9 – Selected Hoek-Brown Design Parameters <br />Material UCS <br />(psi) GSI mi D <br />Competent <br />Material 10180 45 28 1 <br />Talc-Gneiss 7117 35 23 1 <br /> <br />5.2.1.1 Design UCS Value <br />Due to the significant heterogeneity of the rock mass in the project area, the overall average of <br />the recent and historic UCS laboratory testing values were utilized for the competent material, <br />with the understanding that including talc-gneiss UCS values will conservatively reduce the <br />weight of the upper outliers (greater than 14 ksi) which are most likely caused by the abundance <br />of very hard quartz and quartz pegmatite material within the quarry. This approach is visualized <br />on Figure 7, wherein a scatter plot of the UCS laboratory testing results is presented and the <br />green box indicates samples included for determination of the talc-gneiss design UCS value, <br />and the red box encompasses samples included for determination of the competent material <br />design UCS value. With the addition of the recent UCS testing, the recommended design