June 2022 G-14642.71-006-R-Rev0_FINAL 29 A total of 22 core samples were sent to EPrecision geotechnical laboratory in Perth for a range of tests to characterise some of the geomechanical properties of the rock encountered by WKP-P05D. Test results are summarised in Table 10. Table 10: Summary of laboratory testing carried out on samples from WKP-P05D. Rock type Bulk Density* (t/m³) UCS* (MPa) Young’s modulus* (GPa) Poisson’s ratio* Cerchar Abrasivity Index Porphyritic Andesite 2.60 95 [60 to 127] 52.0 0.27 2.21 Epiclastic Andesite / Rhyolite 2.00 7 [3 to 15] 3.0 0.32 Flow banded Rhyolite 2.40 63 [2 to 98] 34.0 0.27 0.76 Notes: *denotes mean values with range in parentheses. The results corroborate with the descriptions in the bore hole log and describe strong porphyritic andesite, underlain by weak epiclastic units, which in turn are underlain by the moderately strong rhyolite host material. The Cerchar Abrasivity Index test results imply that the porphyritic andesite is ‘very abrasive’ and the rhyolite is ‘slightly abrasive’. 7.1.3 Key geotechnical issues The following outlines key geotechnical issues that affect the design and construction of the Main Access Tunnel. 7.1.3.1 Tunnel geology The geological information that is currently available indicates that the tunnel alignment will encounter a suite of volcanic rocks including flows, tuffs, breccias or pyroclastic materials and potentially minor sedimentary deposits. Based on the available drill core reviewed as part of this assessment, the layers appear to be in the order of tens to hundreds of metres in thickness and oriented sub-horizontal or gently inclined. The materials are typically strong rock or weak altered rock based on available drill core; however, very weak materials are anticipated within fault zones. Mapped faults and lineaments, inferred to be faults, cross the tunnel alignment at various locations. The faults are likely to be normal (extensional) faults associated with the local tectonic setting. Ground conditions in these zones are likely to include brecciated zones tens to hundreds of metres in width with local highly sheared clay gouge zones. A fault has been inferred to cross the tunnel alignment near to Ventilation Shaft 1 based on geophysical investigations by OGNZL. This fault was not identified during logging of boreholes in the vicinity.
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