June 2022 G-14642.71-006-R-Rev0_FINAL 15 Table 3: Summary of rock sample test results. Bulk Density (t/m3) Dry Density (t/m3) Water content (%) UCS (MPa) Waipupu Formation (13 samples from WNDD007) Mean 2.50 2.36 5.98 19.9 Minimum 2.43 2.25 2.70 11.0 Maximum 2.59 2.50 8.10 49.0 Whitiroa Andesite (23 samples from WNDD008) Mean 2.12 1.83 16.74 14.3 Minimum 1.91 1.45 3.00 2.6 Maximum 2.48 2.40 31.50 61.0 6.1.4 Summary of geotechnical characteristics of Willows Road farm Logs from test pits and boreholes undertaken on the Willows Road farm site describe fine grained soils up to several metres thick overlying highly weathered volcanic rock. Volcanic rock comprises andesite flows, tuffs and breccias of the Whitiroa Andesite and Waipupu Formation ranging from very weak rock to strong rock. The overlying fine grained soils comprise weathered volcanic ash, residual weathered volcanic rock and associated colluvium. Alluvial soils were encountered beneath the terraces adjacent to Mataura Stream and these included gravels sands and silts, often containing boulders of volcanic rock. 6.2 Tunnel Portal 6.2.1 Ground conditions The proposed tunnel portal site is located on the east side of the proposed Willows Rock Stack (WRS) footprint. The portal site is located on the west side of a narrow ridge. The surrounding slopes are relatively steep (approximately 30°) and hummocky ground is indicative of shallow instability. Scattered outcrops of weak, weathered andesite are evident and are overlain by fine grained volcanic ash and colluvial/regolith soils. No drillholes have been targeted at the portal site to date. However, ground conditions encountered in test pits, boreholes and outcrops in the vicinity are summarised as follows: 0.0 m to 1.0 m below ground level (BGL): fine grained cohesive soils derived from highly weathered volcanic ash. 1.0 m to 5.0 m BGL: highly weathered andesite. More than 5.0 m BGL: moderately weathered, moderately strong andesite, lapilli tuff and tuff breccia.
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