June 2022 G-01483.84-017-R-Rev0 Because the 32 river terraces, comprising both fine grained soils and boulder gravel deposits. On the sloping ground on the west side of the impoundment the site investigations indicate up to about 4 m of stiff to very stiff clay, interpreted to be volcanic ash, colluvium or residual soil derived from the underlying volcanics. Cross sections A-C (Figure 12) show the inferred distribution of materials across the impoundment. Figure 10: WCP Overview. Figure 11: WCP embankment cut and fill areas (Cyan blue fill above current ground level). 7.3.1 Excavation and Cut Slopes The area of proposed excavation is inferred to comprise boulder gravel alluvium, fine grained alluvial soils, stiff to very stiff clays and overlying topsoils. All is inferred to be readily excavatable with plant that will be present on site. It is not expected that the excavation will encounter Whitiroa Andesite, but if present, this is expected to be excavatable by ripping. Cut and fill slopes shown in Figure 11 and sections (Figure 12) are formed at 1.5H:1V, which is believed to be appropriate for preliminary design given the combination of materials that are present (mainly gravelly alluvium and stiff to very stiff clays). Steeper cuts may be possible given further geotechnical information during detailed design. We have assumed that all excavated materials will be cut to waste. 7.3.2 Embankment Design An embankment will be constructed around the eastern margin of the impoundment. The embankment will not exceed a maximum height of 4 m and will have a minimum crest width of 5 m. Embankment slopes have been assumed to be constructed at 1.5H:1V, which is believed to be adequate if constructed from suitable well graded fill. Foundation soils will be stripped in the embankment footprint, removing topsoil and any weak or compressible materials. The site investigation data suggests that bouldery gravel alluvium will underlie the stripped footprint. The embankment ends will abut against insitu ground that will be stripped of any weak
RkJQdWJsaXNoZXIy MjE2NDg3