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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 | 19 <br />observations of the quarry by HDR geologists, subsurface exploration parameters such as <br />recovery, RQD, and drill rate, and a comprehensive laboratory testing program. <br />The Hoek-Brown model is a non-linear shear strength model for rock that is well known in the <br />geotechnical engineering industry for quantifying the factor of safety of simplistic stress-strain <br />models of rock cuts. The generalized Hoek-Brown model relies on the Geologic Strength Index <br />(GSI), intact UCS (σci), disturbance factor (D), and the material constants mb, a, and s, where mb <br />is reliant on the material constant for intact rock mi modified for GSI. The major and minor <br />principal stresses (σ1 and σ3) are formulated within the Hoek-Brown (Hoek, et. al. 2002) model <br />via Equation 1, below. <br /> <br />σ = σ + σ (m <br />σ <br />σ + ) <br />Eq. ( 1) <br />Where the rock mass material constants mb, s, and a are given by Equations 2, 3 and 4, below. <br />m = m exp <br />− 100 <br />28 − 14 <br /> <br />Eq. ( 2) <br />= <br />1 <br />2 + <br />1 <br />6 ( <br /> ! <br />"− <br />#$ <br />) <br />Eq. ( 3) <br />= exp <br />− 100 <br />9 − 3 <br /> <br />Eq. ( 4) <br />And the disturbance factor D, constant mi for intact rock by rock group, and Geologic Strength <br />Index are found by interpretation of Figure 4, Figure 5, and Figure 6, below.