June 2022 G-14642.71-006-R-Rev0_FINAL 8 Table 1: Summary of in situ stress measurements at Trio Underground Mine at Waihi (provided to WSP by OGNZL). Vertical depth (m) Sample location Rock type Stress component Magnitude (MPa) Bearing (degrees) Plunge (degrees) 174 FU 163 Feldspar Andesite σ1 12 018 03 σ2 8 287 07 σ3 5 133 82 420 FU 178 Quartz Andesite σ1 23 019 00 σ2 15 109 05 σ3 11 285 85 The results in Table 1 are reported in mine grid north and their poles are plotted in Figure 4 and stress gradients are plotted in Figure 5. The results from the measurements of in situ stress at Waihi are useful for preliminary design of the proposed tunnels. The results appear to be consistent with the regional tectonic setting on the western margin of the Taupo Volcanic Zone and with the world stress map (www.worldstressmap.org). Further investigation of in situ stress would be advisable as part of detailed design of the tunnels.
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