B-1 - Area 1, Coromandel Forest Park – Assessment of Environmental Effects 43 Figure 24: Typical Drilling Platform Layout 3.2.3.2 Vent Shaft Construction Construction of Vent Shafts 2 – 5 will be carried out mostly from underground using a bottom-up method( (refer Figure 25). Depending on the geotechnical conditions encountered at the surface, some concreting and/or reinforcing of the site may be required to support the surface break through. This could include drilling a circle of interconnecting vertical holes Completion of shaft construction will depend upon the prevailing geotechnical conditions. Methods for addressing weak surface soils could include drilling of a circle of interconnecting holes, filled with concrete until competent rock is reached, to form a cage. Blasting from underground inside the constructed cage structure or excavation with a small machine from above until competent rock is reached. In the latter case, spoil management is a key consideration with the option of removal by helicopter and/or temporary surface storage and return to underground once the shaft surface connection is created. Should ground conditions require, a concrete slab will be formed, reinforced and poured from the surface to form the shaft surface collar onto which the required surface infrastructure can be placed. It is possible that concrete will need to be pumped from
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