WKP PFS – Geotechnical Section Approved by: Approval Date: TBA OceanaGold PEX-000-PLN-046-A Page 10 of 22 1.5.4 Young’s Modulus and Poisson’s Ratio Table 9 shows the Young’s modulus and Poisson’s ratio for 10 lab samples taken from WKP core. The results show a strong correlation between the UCS and Young’s modulus. More lab testing would be required to understand the variations. However, the main use for the Young’s modulus is for numerical stress modelling. For numerical models the elastic modulus is derived from the Geological Strength Index (GSI) that comes from rock mass classification. The numerical models use the derived elastic modulus for the overall rock mass (the rock mass elastic modulus). This numerical model uses the rock mass elastic modulus to calculate elastic convergence of stopes, and the stress regeneration on the backfill material. Additional lab testing for Young’s modulus is not as critical as additional lab testing for UCS. Table 9: Young’s modulus and Poisson’s ratio for WKP lab samples 1.5.5 Triaxial Strength In the Scoping Study (SRK, 2019) triaxial testing was performed on Northern Rhyolite samples taken fromWKP68. The results are shown below in Figure 7. The mi value of 25 is used in numerical stress modelling for the Hoek-Brown failure criterion for the rock mass. Figure 7: Triaxial testing results from Northern Rhyolite samples taken from WKP68
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