Reference document Geotech Investigation · MCU22/0087.01

                                          PROPOSED UNIT DEVELOPMENT
                                          37 BOTTLEBRUSH AVENUE, NOOSA HEADS

            6.3         Building Foundations
            6.3.1         Indicative Site Classification
            Site classifications for footing design are determined in accordance with AS 2870-2011 Residential Slabs and
            Footings, and depend on the depth of cut / fill undertaken at a site, variations in the natural soil/rock depths,
            and the reactivity of the in situ soil / rock and any imported fill materials. It should be noted that the proposed
            works are outside of the scope of AS2870.

            Based on the results of the investigation, the site is classified as Class P in accordance with AS 2870-2011
            Residential Slabs and Footings, due to the presence of uncontrolled fill and poor bearing capacity soils at
            shallow depths. However, if not for these factors, the site would have the characteristics of Class S, with the
            estimated characteristic surface movements (‘ys’) ranging up to about 20 mm. Due to the potential variability
            in subgrade density a site classification of Class M is recommended in relation to assessment of flexibility
            requirements for ground slab, footing and plumbing design.

            6.3.2         Footing Design
            No design loadings were available at the time of reporting. Footings for the proposed development and any
            ancillary structures (e.g. retaining walls, etc.) must penetrate through any fill materials and unsuitable natural
            soils (i.e. very loose to loose sands) to found at least 0.5 m into medium dense (or denser) natural sands.
            Such materials were encountered in the boreholes below depths of about 1 m to 2.5 m BGL (existing ground
            levels) and somewhat shallower in the area of BH1 where it is assumed the site had previously been cut down
            to form the driveway. Thus, piled footings will be required unless excavations expose such materials at or
            near foundation subgrade level.

            Piles so founded may be designed using an allowable end bearing pressure (EBP) of 500 kPa. Piles founded
            in dense sand may adopt an allowable EBP of 1 MPa. High level footings, where achievable in deeper cut
            areas, may be designed using an allowable bearing pressure of 100 kPa provided that they are founded in the
            natural medium dense (or denser) sands. Settlement under such loads is expected to be in the order of up to
            20 mm or 1% of footing width.

            Given the sandy soil profile and depths of footings required, steel screw piles are considered to be a suitable
            foundation type for the proposed unit development generally. However, in areas of cut exposing medium
            dense (or denser) sands at the subgrade level conventional high-level footings may be adopted. It should be
            noted that excavation for concrete strip footings (or similar) may loosen the base. Therefore, the use of a
            vibrating plate and ample water would be required to densify any high-level footing bases prior to the
            placement of reinforcing steel.

            Due to the presence of loose sands, open bored piers or driven piles are not considered to be suitable for
            this site. Steel reinforced concrete bore piles may be possible; however, the use of sacrificial liners (e.g.
            formatube etc.) would be required. The advice of a specialist piling contractor must be sought regarding
            feasibility, design and installation of the piling system for this site, including an assessment of potential
            vibration effects on nearby structures, and monitoring requirements.

            If steel screw piles are adopted, it will be important to ensure close supervision of installation, as piling may
            not encounter sufficient drilling resistance (from torque measurement) in sands at the suggested founding
            depth, and piles could extend to much greater depth than necessary.
            It is therefore recommended that site specific static load testing be conducted from screw piles, if adopted, at
            a minimum. Where tension or compression capacity developed in the footings is critical for the future
            structure (e.g. resistance to uplift forces from high winds), then cyclic load tests (including measurement of
            deflections under tension and compression cycles) should also be undertaken prior to construction.
            Kentledge for static testing, or simulated cyclic loads, should prove the piles to a minimum of two times the
            expected working load within tolerable deflections.

            Footing design should also account for potential soil reactivity to be equivalent to Class M. It should be noted
            that placement of reactive clay (which is not recommended) may result in a more severe equivalent site
            classification, such as H1 or greater.




             13 May 2022
             Report No. 22151-001-Rev0                              12
Document Set ID: 22198682
Version: 1, Version Date: 05/12/2022