Geotechnical Investigation Report

J001369-001-R-Rev0                                                                                     August 2021



Executive Summary
Core Consultants Pty Ltd (Core) has carried out a geotechnical investigation for a proposed development at
23 Bottlebrush Avenue, Noosa Heads.
The proposed development comprises a three-level apartment with a single-level basement and associated
driveway, visitor carparking, courtyard and pool. It is anticipated that earthworks for the project will generally
include cuts of between 2 m to 5 m depths, with minor filling to form finished surface levels.
The fieldwork comprised a walk-over survey and the drilling of two boreholes (designated HA1 and HA2) to
4 m below ground level (BGL).
The subsurface profile encountered in the boreholes generally comprised sand topsoil of between 0.1 m to
0.18 m thickness, overlying sand fill up to 1 m depth (HA1) over natural aeolian sand. The sand is generally
loose to medium dense, becoming dense from about 1.5 m depth. The fill encountered in HA1 is assumed to
be uncontrolled.
Groundwater was not encountered in the boreholes during the investigation. Due to the relatively permeable
nature of the sand, prolonged periods of high groundwater or saturated soils are not anticipated except
following periods of high rainfall.
The site is classified as ‘Class ‘P’ due to the presence of uncontrolled fill. However, the natural soils on site
may be classed as equivalent ‘Class ‘S’ in accordance with AS 2870-2011. The estimated characteristic
ground surface movement due to seasonal moisture variation (‘y s’ value) for this site is less than 20 mm.
Due to space constraints preventing trimming of batters to safe slopes, positive support by engineer-
designed retaining structures will be required for excavation of the basement. Possible retention systems
could include sheet pile walls.
High level footings may be designed for the basement using an allowable bearing capacity of 200 kPa in the
dense natural sand.
A qualitative slope stability risk assessment for this project has been carried out following the Australian
Geomechanics Society (AGS) Guidelines for Landslide Risk Management (March 2007). The assessed risk
is Low for the proposed development. This level of risk is normally acceptable to regulators.
Comments and recommendations regarding site preparation and trafficability, filling and compaction,
excavatability, retaining wall design parameters, drainage and general foundation maintenance are provided
in this report.
From a geotechnical viewpoint, our assessment is that the site is suitable for the proposed development
subject to the implementation of the recommendations in this report.




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