Attachment F - Geotechnical Report

                              PROPOSED COMMERCIAL & RESIDENTIAL DEVELOPMENT
                              30-32 DOONELLA ST, TEWANTIN



Executive Summary
This report details the results of a geotechnical investigation undertaken for a proposed commercial and
residential development at 30-32 Doonella St, Tewantin. The investigation was performed by Tectonic for
Doonella Street Unit Trust.

The investigation comprised drilling of boreholes at five locations, together with in situ strength testing and
geotechnical laboratory analyses. This report summarises the results of the investigation and provides
geotechnical recommendations regarding the design of earthworks, footings, site classification, retaining
walls, and pavements.

Design drawings prepared by Archicology indicate that the proposed development will comprise two to three
storey commercial and residential buildings, incorporating a partially in-ground basement for carparking.
Excavations for the basement will range up to about 3 m deep, with retaining walls proposed to support cut
batters.
Boreholes generally encountered consistent subsurface profiles which can be summarised as follows:

        Loose to medium dense silty/clayey sands and gravels together with firm to stiff sandy/silty clays
         (fill and natural materials) to depths of between 0.75 m and 1.5 m BGL; overlying
        Mostly very stiff, medium to high plasticity natural silty clays to borehole termination at depths of 3 m
         to 6 m BGL.
Groundwater seepage was not encountered in any of the boreholes at the time of investigation, with soils
being moist. However, it should be noted that groundwater seepage may develop at shallow depths within
permeable horizons, particularly following periods of heavy or prolonged rainfall.
A summary of our geotechnical recommendations is as follows:

       Stripping depths to remove existing topsoil are likely to range up to about 300 mm.
       Excavation to the design levels should be achievable using conventional earthmoving equipment
        such as excavators with toothed buckets and small dozers with blades.
       The proposed basement excavation extends to within 2 m to 5 m of the property boundaries.
        Temporary batters within the existing fill materials may be formed at 1V:1H, say by ‘stepped’
        battering and benching, provided that groundwater is not encountered.
       Subject to detailed assessment of proposed excavation depths and existing site conditions (e.g.
        proximity of existing structures such as buildings and services), it is anticipated that temporary
        shoring should not be required.
       Excavated materials should comprise mostly silty clays of high plasticity, which would be suitable
        for re-use as structural fill subject to appropriate moisture control.
       Conventional high level strip and pad footings founded within the very stiff (or stiffer) natural clays
        may be designed to support the proposed building walls and columns, adopting an allowable
        bearing capacity of 250 kPa.
       Footing design may assume an equivalent site classification of Class M (AS2870:2011) based on
        the natural soil profiles encountered.
       Design of the basement level pavement may be based upon a CBR value of 3%, subject to
        excavation and replacement of the natural silty clay subgrade with select granular fill (e.g. minimum
        CBR 15% ‘roadbase’) to a minimum depth of 200 mm.

As the proposed basement excavation will not extend below RL 5 m AHD, an acid sulfate soil investigation
is not warranted for this project.




22 June 2018
Report No. 18151-001-Rev0                               ii