Reference Documents

                                           PROPOSED SUBDIVISION
                                           41 TALLOWWOOD PLACE, BLACK MOUNTAIN

            6.3         Building Foundations
            6.3.1           Site Classification
            Based on the results of the investigation, preliminary characteristic surface movements (‘ys’) for the natural
            soil profile are estimated to range up to 40 mm, equivalent to Class H1 in accordance with AS 2870-2011
            Residential Slabs and Footings. As mentioned previously, surface cracking was noted across the proposed
            new building area which appeared to be related to soil shrinkage due to drying.

            It should be noted that the predicted order of movement is based on the existing natural soil profiles (i.e. no
            additional cutting or filling), and moisture content changes within soils due to normal seasonal moisture
            variations only.

            Reactive soil movements and site classification should be assessed by the footing design engineer at
            building stage to consider the extent of earthworks across the proposed new building area, together with any
            retained trees (trees located near footings can influence the potential ground movement, and result in more
            severe site classifications). A site classification ‘soil test’ may be required prior to building works to confirm
            the site classification and footing design parameters.

            It should be noted that the placement of highly reactive clay fill may have an adverse impact on the site
            classifications.

            Due to the clayey nature of the site soils, it would be prudent to implement the following practices to prevent
            changes in soil moisture:
                     Prevent drying of the clay soils during construction by minimizing exposure. This may be achieved
                      by measures such as covering subgrades with HDPE (‘black builders plastic’) or ‘Bidim’, and
                      placement of ‘blinding’ layers across the excavation subgrade and footing bases.
                     Install and maintain temporary drainage to prevent saturation of the site during construction.
                     Seal the ground surface around the building perimeter (e.g. concrete or paved pathway).
                     Plant shrubs/trees at least a distance from the building equal to the mature height of the shrub/tree.
                     Maintain stormwater drains to prevent overflow into soils and repair any damaged drains
                      immediately.

            6.3.2           Footing Design
            All footings supporting the proposed new residence and ancillary structures (including all retaining walls) must
            penetrate any fill and natural soil to found at least 0.3 m into very low strength (or stronger) phyllite. Based on
            the test pits, footing depths are anticipated to range between about 1.5 m and 2 m BGL (below existing
            ground levels), however, depths are likely to be shallower in areas of future cut and deeper in areas of future
            fill.

            The subsurface conditions encountered indicate that steel reinforced concrete bored piles or ‘bucket piers’ will
            generally be required unless excavations expose the required foundation materials at or near the subgrade.
            High-level footings and steel reinforced concrete bored piles (or similar) founded at least 0.3 m into very low
            strength (or stronger) weathered andesite may be designed using an allowable bearing pressure 400 kPa
            (footings) and 600 kPa (piles), respectively.

            It is recommended that the bases of all footings should be formed level/horizontal to ensure loads are well
            keyed into the slope. Footing design should also account for potential soil reactivity. A suitably qualified and
            experienced geotechnical RPEQ should inspect the footing excavations to confirm appropriate foundation
            materials and cleanliness prior to pouring concrete.

            All footings should found such that they are not adversely affected by any adjacent excavations, trenches, or
            retaining walls that are not designed to support building loads. Where footings are located within a horizontal
            distance of 1.5H (H being the batter height) of any cut or fill batter crest, these footings must be founded at a
            depth level with the toe of the batter. Footings should found at least below a plane extending 1 m horizontally
            from the base of trenches/excavations/retaining walls, then rising up at 1V:1H, as illustrated in Text Figure 14
            overleaf.


             22 May 2023
             Report No. 23099-001-Rev0                              16

Document Set ID: 22826802
Version: 1, Version Date: 23/02/2024