June 2022 G-01483.84-017-R-Rev0 Because the 48 of the native soils is anticipated during detailed design stage which may include trial fills to evaluate the properties of the materials when placed and compacted. If some of the soil material proves to be difficult to place and compact some options that could be considered include: ▪ Cutting those materials to waste. ▪ Encapsulating the poorer soils as a bulk fill surrounded by better material. ▪ Stabilisation of the soils with cement or lime. It is anticipated that any fills comprising the native volcanic soils will require addition of a granular aggregate running surface as described above. Cut slopes on the southwestern margin of the SFA are currently designed at 1.5H:1V in the stiff to very stiff clays encountered in the site investigations. This is believed an appropriately conservative configuration; however, partial or complete support of the slopes could achieve steeper slope configurations using various possible retaining wall or reinforced earth options. If unsupported slopes are considered, the erodibility of the exposed soils will need to be evaluated as flatter slopes can be prone to erosion. The northeastern margin of the SFA closest to the Mataura Stream will need to incorporate engineered support to achieve the planned SFA footprint without incursion into the environmental footprint of the stream. A range of slope support methods could be adopted, including retaining walls, gabion walls or reinforced earth slopes. It is anticipated that a vegetated, reinforced soil slope will be the preferred option; however, consideration of the foundation conditions, available soil types, aesthetics and surcharge requirements will need to be given during detailed design. Reinforced earth slopes can be constructed at slopes exceeding 1H:1V to and exceeding the required height of 5 m.
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