20220109 - Geotech · OPW23/0182

                             PROPOSED RESIDENCE
                             21 MAHER TERRACE, SUNSHINE BEACH

3.0      METHOD OF INVESTIGATION
As part of our assessment, a desk-top study was carried out comprising a review of published geological
maps, slope stability studies as well as Noosa Shire Council (NSC) planning overlays and site information.

An experienced geotechnical engineer from Tectonic undertook a site walk-over on 22 June 2021 to visually
assess any indicators of past slope instability. The walk-over included assessment of soil exposures,
surface drainage conditions, topography, evidence of erosion or past instability, and vegetation
coverage/condition.

This was incorporated with a subsurface investigation comprising the drilling of two boreholes (designated
BH1 and BH2) in accessible areas across the site. Borehole BH1 was drilled in the northern corner of the
site using a 4WD mounted solid flight auger rig, owned and operated by Contract Drilling, to 5.4 m below
ground level (BGL). Due to access restrictions borehole BH2 was drilled to the front of the existing
residence to 2.5 m BGL using hand augering techniques.

In-situ testing, using the dynamic cone penetrometer (DCP) method, was carried out from the ground surface
and within each borehole. DCP testing was extended below the base of the hand augered borehole (BH2) to
4.3 m BGL. Boreholes were backfilled on completion with spoil arising during drilling, with excess material
slightly mounded at surface. Due to access restrictions (e.g. existing pool, gardens etc.) one additional
standalone DCP (denoted DCP3) was undertaken to the rear of the residence, which was continued to
practical refusal at 5.7 m BGL.

One selected soil sample was dispatched to a NATA accredited laboratory for geotechnical testing.
Laboratory testing was undertaken in accordance with Australian Standard AS1289 Method for Testing Soils
for Engineering Purposes and comprised Atterberg limits and particle size distribution (PSD) analyses to
assess material properties.

Borehole and DCP locations are shown in Figure 1 attached at the end of this report, with borehole and
DCP logs presented in Appendix A, together with explanatory notes. Borehole coordinates were recorded
using a handheld global positioning system (GPS).

The results of the desk-top study and walk-over survey are included in Section 4 below.


4.0      RESULTS OF INVESTIGATION
4.1      Site Description
The site is formally described as Lot 747 on RP481111, covering an area of about 550 m2, with frontage to
Maher Terrace along the north-eastern boundary. At the time of the investigation a single to double storey
residential building occupied most of the central part of the site, with access provided via a concrete
driveway directly off Maher Terrace. A pool was located in the southern corner of the site, with blockwork
retaining walls about 1 m high tracing surrounding garden beds. A timber sleeper wall about 1 m high
supported a level area adjacent to the south-eastern corner of the site, with a 1.6 m high timber sleeper wall
supporting an inferred cut beneath the northern part of the residence.

Based on a visual assessment the existing building, driveway, rear retaining walls and pool were noted to be
in good structural condition exhibiting no obvious signs of distress (e.g. cracking, misalignment, etc.) that
could be attributed to slope instability. Dilapidation was evident within the existing timber sleeper wall to the
south-east of the residence, which appeared to be related to age and poor construction as opposed to
ground movements.
Similar residential allotments with houses occupied properties to the north, south and west of the site, with
relatively dense vegetation on the opposing side of Maher Terrace to the east/north-east. Observable walls
in neighbouring residences appeared to be in relatively good structural condition, based on an external
assessment. It was noted that longitudinal cracking was evident within the asphalt seal of Maher Terrace
downslope (north) of the subject site. This cracking is consistent with creep movement in the road
embankment and/or upper natural soils. Generally, the surrounding road surface was noted to be in
relatively good condition.


16 July 2021
Report No. 21236-001-Rev0                               2