Council archive · source document
Reference Document - Geotech Report - MCU24 0094 · MCU24/0094
Very large file (11.3 MB): the original may take a few minutes to open or download. The page text below is quick to read.
REFERENCE DOCUMENT
MCU24/0094
NOOSA COUNCIL
8 APRIL 2025
GEOTECHNICAL INVESTIGATION
Proposed Residence
33 Ross Crescent
Sunshine Beach
Report for: 33 Ross Crescent Pty Ltd
24096-001-Rev0
18 June 2024
Tectonic Geotechnical Pty Ltd
PO Box 899, Buderim QLD 4556
Office: 07 5478 9016
Email: [email protected]
www.tectonicgeo.com.au
A.B.N. 83 165 727 828
See the original
The page text is free to read. Viewing or downloading an original file needs an account.
Log in to see the originalFull text of the other 47 pages
Page 2
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Document Review
Document No. Revision Prepared By Reviewed By Date Issued
001 Draft Jarrad McVey Ashley Davey 16 May 2024
001 0 Jarrad McVey Ashley Davey 18 June 2024
Report Distribution
Document Revision Method of Delivery Issued To
33 Ross Crescent Pty Ltd
001 0 Electronic
C/- Shaun Lockyer Architects
Nic Milloy
001 0 Electronic Shaun Lockyer Architects
([email protected])
Prepared By: Reviewed By:
Jarrad McVey BEng Ashley Davey RPEQ 8159
Geotechnical Engineer Principal Geotechnical Engineer
18 June 2024
Report No. 24096-001-Rev0 i
Page 3
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Executive Summary
This report details the results of a geotechnical investigation undertaken for a proposed residential
development at 33 Ross Crescent, Sunshine Beach; carried out by Tectonic for 33 Ross Crescent Pty Ltd.
The results contained herein represent the first stage (Stage 1) of investigation, and further investigation is
recommended comprising deep borehole drilling to depths in the order of 20 m to 25 m below ground level
(BGL) to confirm the findings of this report.
Preliminary architectural drawings indicate that the development will consist of the construction of a three
storey building terraced into the slope. Terraced landscaping and an above ground pool will extend towards
the eastern boundary of the site (which is situated along a moderately steep dune crest, dipping down to
Sunshine Beach).
The boreholes and in situ test results indicate a subsurface profile of poorly graded dune sands to the
maximum investigation depth of the borehole drilling and testing (which ranged up to 5.6 m BGL). Very
loose and loose sands were deepest in boreholes BH2 and BH3, extending to about 2.7 m BGL.
Slope stability modelling was carried out considering short-term erosion from a 100 year average recurrence
interval extreme storm event (as nominated by the appointed coastal engineering experts, Haskoning
Australia); and estimated retrogression of the dune over time. It was indicated in the Haskoning Australia
assessment that virtually the entirety of the dune face would be affected by such a future erosion event,
extending approximately 5 m to 10 m laterally into the dune. The storm erosion cut alone would be of
sufficient magnitude to affect the proposed building footprint without engineered protection.
It is recommended that the eastern property boundary be protected by a shear pile structure. Given our
understanding of the ground conditions and the predicted future dune morphology, this would be founded
into the underlying dense (or denser) sands. Subject to detailed design, relatively ‘heavy’ construction (e.g.
secant or contiguous piles), with additional structural support (e.g. ground anchors) is likely to be required.
This would be in order to allow the anticipated ‘wall upstand’ of about 6.6 m height indicated by the stability
analyses to be achieved. The boundary piles may need a minimum installation length of about 12.5 m
depth. Protection against erosion and adverse interaction with adjacent properties shall also be installed.
This should consist of a grout curtain extending from the shear pile wall to an equivalent distance of 23 m
from the rear (eastern) boundary, and along the northern and southern boundaries, tapering from 8.5 m
depth in the east. Structural designers must undertake finite element analysis to assess soil/structure
interactions and calculate both bending and shear stresses in the piles. Retaining structures should also
undergo rigorous design checks of global and internal stability.
The following additional recommendations are provided for the proposed development:
The proposed residence and any ancillary structures (including retaining walls and pools) must be
supported by footings founded at least 1 m into natural medium dense (or denser) sands. In some
areas of deeper cut, high level footings may be adopted. Elsewhere, piles will be required.
Excavations close to site boundaries may necessitate the installation of temporary shoring.
Ground vibrations during construction must be minimised and monitored. Where excessive
vibrations occur, alterations to construction techniques may be required. It is recommended that a
dilapidation survey of adjoining structures be completed prior to construction.
Revegetation of bare slopes around the development area should be undertaken as soon as
possible following construction. Similarly, improvements to the vegetation (i.e. with site appropriate
natural species) on the natural dune face downslope of the residence would also aid in restricting the
development of slope instability.
Collected roof water should be directed by pipes to the council stormwater system along Ross
Crescent (possibly through the use of a ‘wet’ or ‘charged’ drainage system) or; where not physically
possible, surface water should be directed to infiltrate into the ground around the edges of hard
surfaces, with infiltration areas set back as far as possible from the rear boundary. Hydraulic design
should be such that under no circumstances are uncontrolled stormwater flows permitted over the
dune face; where channelised erosion and scour features could develop.
18 June 2024
Report No. 24096-001-Rev0 ii
Page 4
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Table of Contents
1.0 INTRODUCTION ........................................................................................................................................................ 1
2.0 PROPOSED DEVELOPMENT ................................................................................................................................... 1
3.0 METHOD OF INVESTIGATION ................................................................................................................................. 3
3.1 Fieldwork ...................................................................................................................................................... 3
3.2 Geotechnical Laboratory Testing .................................................................................................................. 3
4.0 RESULTS OF INVESTIGATION ................................................................................................................................ 4
4.1 Site Description............................................................................................................................................. 4
4.2 Topography................................................................................................................................................... 6
4.3 Geology ........................................................................................................................................................ 7
4.4 Subsurface Conditions.................................................................................................................................. 8
4.5 Groundwater ................................................................................................................................................. 8
4.6 Geotechnical Laboratory Test Results .......................................................................................................... 8
4.7 Surface Drainage .......................................................................................................................................... 8
5.0 SLOPE STABILITY ASSESSMENT .......................................................................................................................... 9
5.1 Existing Conditions ....................................................................................................................................... 9
5.2 Stability Assessment..................................................................................................................................... 9
5.2.1 Quantitative Assessment ...................................................................................................................... 11
6.0 GEOTECHNICAL RECOMMENDATIONS .............................................................................................................. 13
6.1 Earthworks .................................................................................................................................................. 14
6.1.1 Site Preparation and Trafficability ......................................................................................................... 14
6.1.2 Excavations ........................................................................................................................................... 14
6.1.3 Filling..................................................................................................................................................... 15
6.2 Building Foundations .................................................................................................................................. 15
6.2.1 Indicative Site Classification.................................................................................................................. 15
6.2.2 Footing Design ...................................................................................................................................... 16
6.3 Temporary and Permanent Retention......................................................................................................... 17
6.4 Drainage ..................................................................................................................................................... 18
7.0 CONCLUSION ......................................................................................................................................................... 19
8.0 LIMITATIONS .......................................................................................................................................................... 19
18 June 2024
Report No. 24096-001-Rev0 iii
Page 5
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
TABLES
Table 1: Summary of Subsurface Profiles ........................................................................................................................... 8
Table 2: Stability Risk Levels .............................................................................................................................................. 9
Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007) ....................................................................... 10
Table 4: Soil Parameters Adopted for Slope/W Analyses ................................................................................................. 12
Table 5: Slope/W Analysis Results ................................................................................................................................... 12
Table 6: Retaining Structure Design Parameters .............................................................................................................. 18
TEXT FIGURES
Text Figure 1: Architectural rendering of the proposed development looking west (courtesy SLA)..................................... 1
Text Figure 2: Preliminary building layout plan (courtesy SLA) .......................................................................................... 2
Text Figure 3: Preliminary cross sections (courtesy SLA), looking north (upper), looking south (lower) ............................. 2
Text Figure 4: Recent aerial image of the site and immediate surrounds (courtesy Nearmap, 10 April 2024) .................... 4
Text Figure 5: Oblique drone image of the site and surrounds, looking south..................................................................... 5
Text Figure 6: Drone image looking west towards the subject site...................................................................................... 5
Text Figure 7: Looking north along the coastline, oblique drone image .............................................................................. 6
Text Figure 8: Site plan showing ground surface contours (courtesy Noosa Council [NC] ‘Intramaps’) ............................. 7
Text Figure 9: Extract of Laguna Bay 1:100,000 Scale Surface Geology Map.................................................................... 7
Text Figure 10: Extract from NC landslide hazard overlay mapping ................................................................................... 9
Text Figure 11: Footing depth required to mimimise risk of undermining .......................................................................... 17
FIGURES
Figure 1: Site Plan
Figure 2: Subsurface Section A-A'
Figures 3 to 7: Slope/W Outputs
APPENDICES
APPENDIX A
Borehole & DCP Reports and Explanatory Notes
APPENDIX B
Geotechnical Laboratory Test Certificates
APPENDIX C
AGS Guidelines – Qualitative Terminology for Use in Assessing Risk to Property
Some Guidelines for Hillside Construction
APPENDIX D
Limitations
18 June 2024
Report No. 24096-001-Rev0 iv
Page 6
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
1.0 INTRODUCTION
This report details results of a geotechnical investigation undertaken for a proposed residential development
at 33 Ross Crescent, Sunshine Beach. The investigation was carried out by Tectonic for 33 Ross Crescent
Pty Ltd, in accordance with our Proposal P24147-Rev0 dated 6 March 2024. Shaun Lockyer Architects
(SLA) are the architects and project managers for the development.
Haskoning Australia (RHDHV) are the coastal engineers for the project and have provided a coastal
engineering erosion cut profile, detailing the Erosion Prone Area associated with the coastal building line at
the subject site.
The geotechnical investigation comprised the drilling of three boreholes using a hand auger. Two boreholes
were advanced around an existing residence on site, with a third borehole at the toe of the high dune on the
seaward side of the site. In situ dynamic cone penetrometer (DCP) testing was also conducted adjacent and
within the boreholes and at three additional stand-alone locations. Geotechnical laboratory testing was
undertaken on selected soil samples.
This report presents the results of the geotechnical investigation and slope stability modelling to address
possible slope failure following a hypothetical future sea surge/storm event nominated by RHDHV, along with
geotechnical recommendations and comments for the proposed development in general.
2.0 PROPOSED DEVELOPMENT
Preliminary architectural drawings (Ref. Shaun Lockyer Architects, Job No. 0427, Dwg. No. 000.00 to
400.05 [not inclusive], revisions A to C, dated 17 June 2024) indicate that the existing residence would be
demolished and replaced with a multi storey residence over an expanded footprint. The upper levels will be
terraced down into the natural slope to the west, being taken to daylight in the east. The lower level and pool
will form a jutting terrace further to the east over a lesser footprint than the upper levels.
The swimming pool is indicated to mostly be above ground with the eastern end expected to be cantilevered.
Building construction is shown to consist of suspended concrete floors, concrete and masonry walls, full
height glazed facades and some timber cladding applied in select locations.
In order to construct the terraced residence, earthworks will be required comprising excavations of about
3.5 m depth for both the upper ground level and the lower level together with filling up to about 1.5 m high to
form platforms for slab edges and general landscaping. Deeper excavations may be required elsewhere as
part of the development (e.g. for underground services, lift pit and footings).
The proposed development is illustrated in Text Figures 1 to 3 below and overleaf.
Text Figure 1: Architectural rendering of the proposed development looking west (courtesy SLA)
18 June 2024
Report No. 24096-001-Rev0 1
Page 7
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Text Figure 2: Preliminary building layout plan (courtesy SLA)
Text Figure 3: Preliminary cross sections (courtesy SLA), looking north (upper), looking south (lower)
18 June 2024
Report No. 24096-001-Rev0 2
Page 8
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
3.0 METHOD OF INVESTIGATION
3.1 Fieldwork
An experienced geotechnical engineer from Tectonic undertook a site walk-over on 3 April 2024 to visually
assess 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.
In conjunction with the walk-over three hand auger boreholes (designated BH1 to BH3) were drilled.
Boreholes BH1 and BH2 were drilled within the proposed building footprint, and BH3 further downslope
towards the toe of the main high dune. In situ testing utilising the dynamic cone penetrometer (DCP) method
was completed from surface adjacent to each borehole, and at selected depths downhole. In addition, three
standalone DCP tests were also conducted at northern and southern points along the eastern boundary, and
around half-way down the dune face. Hand augers were taken to slow progress at depths of between 3 m
and 4 m below ground level (BGL) due to collapsing sands, with DCP testing extending below the base of
the boreholes to depths of up to 5.5 m BGL.
Boreholes were backfilled with drilling spoil and left slightly mounded at the ground surface. Disturbed soil
samples were recovered from the auger cuttings. The engineer was responsible for logging soil profiles and
maintaining investigation practices in accordance with AS1726 Geotechnical site investigations, supervising
in situ testing, and recovering samples.
Borehole and DCP reports are attached in Appendix A, together with explanatory notes. Test locations are
shown in Figure 1 and subsurface conditions are discussed in Section 4.4.
3.2 Geotechnical Laboratory Testing
Two selected disturbed soil sample were dispatched to Construction Sciences, a NATA accredited laboratory
located in Kunda Park, for geotechnical testing. Testing comprised two particle size distribution (PSD) tests
for soil classification purposes. Geotechnical laboratory testing was undertaken in accordance with
Australian Standard AS1289 Method for Testing Soils for Engineering Purposes.
Laboratory test results are summarised in Section 4.6, and the test certificates are attached in Appendix B.
18 June 2024
Report No. 24096-001-Rev0 3
Page 9
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
4.0 RESULTS OF INVESTIGATION
4.1 Site Description
The site is formally described as Lot 6 on RP216711, covering an area of 3517 m2, with a curving frontage to
Ross Crescent along the western boundary. At the time of the investigation, an existing residence was
located in the north-eastern corner of the site. The remainder of the site was a combination of sloping
grassed areas and a swimming pool to the north. Denser coastal vegetation including relatively large mature
trees and smaller shrubs was present to the south of the block.
The site was accessed via a concrete driveway sloping from Ross Crescent to a rendered blockwork garage
terraced into the slope. The existing residence (to be demolished) was a two-storey rendered blockwork
structure, terraced into the slope with a large timber deck extending out towards the east. The provided
survey plan indicates that sewer and stormwater mains run under the pavement along Ross Crescent.
In the northern half of the site a small relatively level grassed area was observed directly to the east of the
existing residence near the partially in-ground swimming pool. Some cut and fill earthworks may have been
undertaken to achieve this, however the remnant of a natural, retreating paleo dune crest may also have
been exploited. The southern half of the site sloped moderately down from Ross Crescent at what appeared
to be the natural slope. At approximately the eastern boundary and beyond the main dune fell towards the
beach at about 17°, with a small foredune observed at the toe.
The residence and other structures around the garden areas appeared to be in relatively good condition,
based on a visual exterior assessment, with no signs of structural distress which could be attributed to global
instability.
A recent aerial image of the site and surrounds is shown in Text Figure 4.
Subject site
Sunshine Beach
Text Figure 4: Recent aerial image of the site and immediate surrounds (courtesy Nearmap, 10 April 2024)
Site conditions at the time of our investigation are shown in Text Figures 5 to 7 on the following pages.
18 June 2024
Report No. 24096-001-Rev0 4
Page 10
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Residence on subject site
Pool on subject site
Dune slack
Smaller frontal
dune
Main dune
Text Figure 5: Oblique drone image of the site and surrounds, looking south
Residence on subject site
Historical earthworks batter
Approx. lot boundary
Text Figure 6: Drone image looking west towards the subject site
18 June 2024
Report No. 24096-001-Rev0 5
Page 11
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Subject site
Text Figure 7: Looking north along the coastline, oblique drone image
4.2 Topography
During our site walk-over, topographic features specific to the site were noted, and ground slopes were
recorded using a hand-held clinometer. As illustrated in Text Figure 8 overleaf, the site is located just
beyond the initial crest of a high dune at Sunshine Beach. The stoss face of the dune is generally eastward
facing at the site location.
Ground around the existing residence was terraced with generally relatively level benches supported by
blockwork walls up to about 3 m height that were incorporated within the existing residence and garage.
Beyond the residence, in the northern half of the site, a small relatively level grassed area had been created
by historic cut to fill earthworks with a downslope batter of up to 35°. The southern half of the site naturally
sloped to the east at about 22°. At approximately the eastern boundary and beyond the dune fell towards
the beach at about 17°. At the toe of the high dune a shallow dune slack was noted before the small frontal
dune of about 1 m height. The beach dropped down from about RL 4 m AHD at the toe of the frontal dune to
the shoreline (around RL 0 m AHD).
Around 200 m south of the subject site a creek line joins the beach from the west. The creek had a
consistent, but relatively small flow at the time of our fieldwork; discharging directly into the ocean.
A selection of the geomorphological features described above are denoted on Text Figures 4 to 7 on the
preceding pages.
18 June 2024
Report No. 24096-001-Rev0 6
Page 12
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Subject site
Text Figure 8: Site plan showing ground surface contours (courtesy Noosa Council [NC] ‘Intramaps’)
4.3 Geology
Available geological information 1 indicates that the site is underlain by Holocene and Pleistocene age quartz
dune sand (described as “parabolic dunes” and “blowout dunes’; Ref. extract in Text Figure 9 below).
Approx. site location
Text Figure 9: Extract of Laguna Bay 1:100,000 Scale Surface Geology Map
1
Queensland Government, Dept. of Natural Resources, Mines and Energy, 1:100,000 Laguna Bay Surface Geology, Sheet 9545, 2018
18 June 2024
Report No. 24096-001-Rev0 7
Page 13
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
4.4 Subsurface Conditions
Detailed descriptions of the subsurface conditions encountered in the boreholes are provided in the
borehole reports attached in Appendix A, along with definition sheets which describe terms and
abbreviations used on the reports. Subsurface conditions encountered in the boreholes are summarised
as below and are illustrated as a cross-section in Figure 2.
The boreholes and in situ test results indicate a subsurface profile of relatively poorly graded dune sands to
the maximum investigation depth of the borehole drilling and testing. Very loose and loose sands were
deepest in boreholes BH2 and BH3, at the dune crest, extending to about 2.7 m BGL.
Table 1 below provides a more detailed summary the subsurface profile encountered in each borehole
(noted in a west to east direction, Ross Crescent to high foredune toe).
Table 1: Summary of Subsurface Profiles
Material / Test
BH1 BH2 BH3 DCP4 DCP5 DCP6
Location
Very Loose to Loose *0.0 – 1.9
0.0 – 1.2 0.0 – 2.7 0.0 – 2.5 *0.0 – 2.4 *0.0 – 2.3
Sands *2.4 – 3.0
1.2 – 1.5
Medium Dense 2.7 – 4.0 2.5 – 3.0 *1.9 – 2.4
2.0 – 4.0 *2.4 – 2.7 *2.3 – 3.8
Sands *4.0 – 4.6 *3.0 – 3.4 *3.0 – 3.4
*4.0 - 4.8
Dense (or denser) 1.5 – 2.0
*4.6 – 5.1 TD *3.4 – 4.4TD *2.7 – 2.8TD *3.4 – 3.9TD *3.8 – 3.9TD
Sands *4.8 – 5.5 TD
Notes: 1. Depths noted in m BGL at time of investigation (3 April 2024)
2. TD denotes DCP test termination depth
3. * denotes materials inferred from DCP results
4.5 Groundwater
No signs of groundwater seepage (‘springs’) were observed at the ground surface during our walk-over. It is
expected that an unconfined groundwater table would exist at the toe of the dune, close to sea level, and
fluctuate with tidal and weather conditions.
Groundwater seepage may develop, particularly following periods of prolonged or heavy rainfall at various
levels through the dune profile. Based upon experience at other similar sites in the area, such seepage
would be expected to be transient and of relatively minor lateral extent.
4.6 Geotechnical Laboratory Test Results
PSD analysis on two sand samples selected from boreholes BH1 and BH2 indicates that the soils generally
comprise poorly graded, fine to medium grained sand (predominantly medium grained). The samples tested
had a very low proportion of silt fines at 4 % and 3%, respectively (i.e. the dune sands are relatively ‘clean’).
Full test results (laboratory certificates) are presented in Appendix B.
4.7 Surface Drainage
Surface drainage would be expected to follow natural surface contours to the east towards the beach. The
site has a relatively small catchment, with the majority of upslope run-off expected to be intercepted by the
kerb and channel drainage along Ross Crescent.
Given the sandy nature of the site, rainfall would normally be anticipated to infiltrate the ground surface
relatively quickly. However, as the proposed development will occupy a large part of the block, significant
run-off from hard surfaces will likely occur. Nevertheless, where directed into swales rather than pipes,
such run-off would be expected to infiltrate into the natural sands relatively rapidly. No significant surface
run-off features were noted across the allotment during our assessment (e.g. deep rilling or scour/wash out
scars).
18 June 2024
Report No. 24096-001-Rev0 8
Page 14
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
5.0 SLOPE STABILITY ASSESSMENT
5.1 Existing Conditions
The Noosa Planning Scheme 2020 includes a landslide hazard overlay map (Ref. Text Figure 10) which
indicates that the site, and most of the main dune below, have Moderate and High Hazard Areas.
Subject site
Text Figure 10: Extract from NC landslide hazard overlay mapping
It should be noted that the NC landslide hazard mapping is a broad-scale indication of the potential
landslide susceptibility and is superseded by this site-specific assessment. The allotment did not exhibit
any visible surface features which would indicate larger scale significant global slope instability during our
walkover within proposed building areas. No landslide back scarps, noteworthy groundwater seepage or
areas of naturally ‘hummocky’ ground were observed. Medium dense sands were encountered at relatively
shallow depths below surface, with the main dune standing at between 17° and 22°.
Given the presence of very loose to loose sands to depths of in the order of 1.2 m to 2.7 m BGL in slopes
within the site and beyond in the high dune, the sand slopes would be close to the ‘limit of equilibrium’. The
limit of equilibrium is the ‘tipping point’ to instability, where the factor of safety (FOS) of the slope is
approximately 1.0. The FOS of a slope is the balance (ratio) between the forces driving instability (e.g. soil
weight, groundwater pressure) and the resisting forces (e.g. soil friction and cohesion).
5.2 Stability Assessment
The risk assessment for this project has been carried out following AGS 2007 Practice Note Guidelines for
Landslide Risk Management. Relative levels of risk and their implications are given in Table 2.
Table 2: Stability Risk Levels
Risk Level Example Implications(1)
Unacceptable without treatment. Extensive detailed investigation and research, planning and
Very High
VH implementation of treatment options essential to reduce risk to Low; may be too expensive and not
Risk
practical. Work likely to cost more than value of property.
Unacceptable without treatment. Detailed investigation, planning and implementation of treatment
H High Risk options required to reduce risk to Low. Work would cost a substantial sum in relation to the value of
the property.
May be tolerated in certain circumstances (subject to regulators’ approval) but requires investigation,
Moderate
M planning and implementation of treatment options to reduce risk to Low. Treatment options to reduce
Risk
to Low risk should be implemented as soon as practicable.
Usually acceptable to regulators. Where treatment has been required to reduce the risk to this
L Low Risk
level, ongoing maintenance required.
Very Low
VL Acceptable. Manage by normal slope maintenance procedures.
Risk
Note: (1) The implications for a particular situation are to be determined by all parties to the risk assessment and may
depend on the nature of the property at risk; these are only given as a general guide.
18 June 2024
Report No. 24096-001-Rev0 9
Page 15
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Considering the existing site conditions (Ref. Section 2), and subject to the implementation of
recommendations given below, it is assessed that there would be a Low (L) Risk of global slope instability
affecting the proposed development. Regulators (NC) normally require that a Very Low or Low Risk of
landslide affecting the property must be demonstrated to enable development approval. Summarised in
Table 3 is our qualitative assessment of landslide risk for the development site. A summary of qualitative
terminology for use in assessing risk to property is attached (taken from AGS 2007).
Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007)
Assessed
Hazard Likelihood Consequence Risk Comments
Given the low to moderate natural gradients
through the proposed building areas,
retention system proposed and proposed
1: Failure through very loose to protection of the eastern side of site using a
loose natural sands and sand fill shear pile wall, it is considered Unlikely
Unlikely Medium Low
above the foundation depth in that a landslide in these materials would
future building areas affect the proposed development. Given a
potential Medium impact from such
instability the resultant risk would be Low
as per AGS 2007.
The likelihood of a deep failure through the
medium dense (or denser) natural sand below
the proposed foundation depth is assessed as
2: Deep failure through the Rare due to the lack of precedence of such
medium dense (or denser) sands Rare Major Low movements locally, no signs of any existing
below the foundation depth slope instability and a lack of groundwater.
Although the consequence of such a failure
would be Major, the resultant risk is Low as
per AGS 2007.
The likelihood of failure of a temporary
retention system, if required (sheet pile wall, or
similar) as outlined in Section 6.3, is assessed
as Unlikely, subject to detailed design by a
3: Instability of temporary sheet
suitably qualified RPEQ engineer, which
pile retention system (if required),
Unlikely Medium Low accounts for the required factors of safety
or similar, as discussed in
against slope instability, and construction by a
Section 6.3.
specialist contractor. Although the
consequence of such a failure could be
Medium, the resultant risk is Low as per
AGS2007.
While the modelling indicates it is Possible that
an extreme erosion event will occur at the site,
the likelihood of a landslide extending through
the future piled wall system along the eastern
edge of the building or site boundary as
4: Retrogressive failure of the
outlined in Section 6.0 is assessed as Rare,
high foredune face considering a
subject to detailed design by a suitably
hypothetical storm and wave Rare Major Low
qualified RPEQ engineer, construction by a
scenario, impacting the subject
specialist contractor, and considering the
site.
results of our quantitative slope stability
analysis outlined in Section 5.2.1. Although
the consequence of such a failure would be
Major, the resultant risk is Low as per
AGS2007.
The potential impacts on slope stability of the development components have been assessed, and the
measures recommended below in Section 6 have been designed to mitigate those impacts.
18 June 2024
Report No. 24096-001-Rev0 10
Page 16
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
5.2.1 Quantitative Assessment
In order to estimate the factor of safety (FOS) against slope instability for the proposed development,
numerical analysis has been conducted using Slope/W. The ground surface profile has been modelled
using a combination of architectural layout drawings and slope angles measured in the field by Tectonic.
The analysed subsurface profile was compiled based on the results of our subsurface investigation. Some
inferences regarding subsurface conditions were made between test locations. A minimum FOS value of 1.5
is the commonly adopted industry standard for long term conditions.
Although the existing sand dune slope would be considered relatively stable in the short term, it is
acknowledged that there were positive gradients dipping down and away from the eastern edge of the likely
building area, and very loose/loose sands were present in the near surface profile. The longer term stability
of the site could in addition be affected by other factors such as erosion by storm tides, which could
theoretically lead to larger scale failures.
Modelling has therefore been carried out considering a hypothetical storm and wave scenario nominated by
coastal engineering experts (RHDHV), and taking into account subsequent retrogression of the dune over
time. Each of the cases analysed are summarised as follows:
Case 1 – Reprofiling of slope due to storm erosion profile (piled wall protecting eastern edge of
building indicative only).
Case 2 – Lower slope failure due to the regression from Case 1.
Case 3 – Retrogressive upper slope failure following the Case 2 failure.
Case 4 – Slope stability analysis following regressive failure of the slope from Case 1 to Case 3, with
the high dune ultimately assuming an inclination of 28° (eastern property boundary and ground
above protected by a shear pile wall). Case 4a illustrates shear wall protection along the eastern
edge of the building area, and Case 4b demonstrates the feasibility of the pile wall approximately
along the eastern site boundary.
The modelled ground surface profile for the initial Case 1 was based on provided survey information across
the subject site (Ref. AJS Surveys, Plan Ref. 23311-D1-A, dated 6 November 2023) with surface profiles
beyond the eastern property boundary estimated from slope angles and measurements in the field by
Tectonic. The horizontal extent of erosion adopted in Case 1 was based on information provided in the
referenced RHDHV report (Ref. Section 1.0), which included a combination of short-term erosion from a
100 year average recurrence interval (ARI) storm event. It was indicated in the RHDHV assessment, that
virtually the entirety of the high dune face would be affected by a future erosion cut, extending approximately
5 m to 10 m laterally into the dune face; with a localised scarp crest at around RL 13 m AHD. In addition, the
erosion cut is shown to extend into the subject site, within the proposed building envelope. A toe level of
around RL 2.4 m AHD was adopted for all cases; generally consistent with the larger scale erosion cut given
by RHDHV in their modelling.
Subsurface conditions for Cases 1 to 4 were developed using the borehole and DCP information collected
during the investigation.
Based on the subsurface conditions at the site, and the extent of earthworks, it is anticipated that building
loads for the proposed residence and ancillary structures will be transferred by a mixture of high-level and
piled footings into the natural medium dense (or denser) sands underlying the site. A surcharge load of
5 kPa was modelled in areas where the building loads are to be transferred via piled foundations to the
underlying soils and in landscaped areas and 30 kPa was applied across the proposed building area were
medium dense (or denser) sands are expected at bulk earthworks levels to represent the distributed load
from the lower level and two full floors above.
The soil parameters adopted for the analyses are summarised in Table 4 on the following page and are
based on interpretation of the site investigation, in situ testing and laboratory test results. The parameters
are consistent with the low to mid range values recommended for similar materials in Appendix D of
Australian Standard AS4678-2002 Earth Retaining Structures. Due to the dune slopes and high
permeability soils, a groundwater table is not anticipated in the slope and therefore, was not modelled.
18 June 2024
Report No. 24096-001-Rev0 11
Page 17
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Table 4: Soil Parameters Adopted for Slope/W Analyses
Friction Angle, ɸ
Material Description Unit Weight (kN/m3) Cohesion, c (kPa)
(degrees)
Very Loose/Loose
17 0 27
Sands
Medium Dense Sands 18 0 34
Dense (or denser) Sand 19 0 36
Future Granular Fill 18* 0* 33*
* Depends on type of fill used and compaction achieved
Commonly adopted industry standards generally require minimum FOS values against slope instability of 1.3
and 1.5 for short-term and long-term conditions, respectively. Administering authorities such as Noosa
Council normally require a minimum FOS of 1.5 or greater for long-term conditions. Results of the stability
analyses are presented in Table 5, with the Slope/W outputs attached in Figures 3 to 7.
Table 5: Slope/W Analysis Results
Analysis Description Factor of Safety
Lateral dune failure caused by storm erosion event
Case 1b 1.7
(Site protected by shear pile wall)
Case 2 Lower slope failure due to regression from Case 1 1.0
Case 3 Retrogressive upper slope failure following the Case 2 failure 0.8
Slope stability analysis following regression of the slope from
Case 4a Case 1 to Case 3, with the eastern edge of the building area 1.6
protected by a shear pile wall
Slope stability analysis following regression of the slope from
Case 4b Case 1 to Case 3, with the eastern property boundary protected 1.5
by a shear pile wall
Results of the analyses indicates the following:
Case 1 – It was noted that the storm erosion cut would affect the eastern part of the site (including
impacting the proposed main residential building). A residual FOS of less than 1.0 was shown in that
scenario, and as such the model for Case 1 includes protection of the eastern edge of the building
with a piled wall, a FOS of 1.7 is assessed following this type of event.
Case 2 – The over steep face of the dune would lead to retrogressive failures progressively moving
up slope. The nature of the failures will be dependent on numerous factors such as surface soil
stabilisation provided by vegetation and local variations in subsurface conditions (e.g. indurated sand
or dense sand zones), however the modelled slip surface is consistent with previous experience in
similar conditions. The FOS of 1.0 indicates that the slope would be in a marginal state of stability
following Case 1.
Case 3 – Following retrogressive translational failure(s), further instability of the slope extending up to
the eastern property boundary would occur based on the minimum calculated FOS of 0.8.
Case 4 – If the eastern edge of the proposed building (Case 4a) or property boundary (Case 4b) is
protected by an engineer designed and certified shear pile structure the potential critical slip surface
takes the form of a deep-seated failure into the underlying dense (or denser) sands. Such a slip
surface results in a FOS above 1.5, allowing for retrogression of the slope from Cases 1 to 3
(including a slight landward migration of the dune toe). It is noted that the position of the shear pile
wall would be dependent on the future maintenance and expectation of land use to the east of the
property. The pile wall structure would be significant, with deep piles (up to 12.5 m BGL) and a
concrete capping beam.
18 June 2024
Report No. 24096-001-Rev0 12
Page 18
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
6.0 GEOTECHNICAL RECOMMENDATIONS
It is recommended that the eastern property boundary be protected by a shear pile structure. Alternatively,
depending on access for the shear pile installation, the wall may be brought back to protect the structure
alone, depending on the expectation of future maintenance and serviceability of the back garden area to the
east of the proposed building and pool. Given our understanding of the ground conditions and the predicted
future slope geomorphology, the shear pile wall would be founded into the underlying dense (or denser)
sands. Subject to detailed design, such a structure could comprise cased micro-piles, secant, or contiguous
piles.
The adopted structure should comprise piles structurally tied together at the surface using a steel-reinforced
concrete capping beam. An ‘A-frame’ structure may ultimately be required (i.e. vertical and raked piles) to
achieve the required shear force resistance, at least if micro-piles are adopted, especially where allowance is
given for the anticipated ‘upstand’ ranging up to about 6.6 m high indicated by the stability analyses.
A summary of the minimum piling requirements for the shear pile wall is given as follows:
Case 4a: Shear pile wall along eastern edge of building area
Minimum Pile Length: 10 m
‘Upstand’ Height: 3.7 m
Unfactored resistance to normal shear forces: 200 kN/m*
Case 4b: Shear pile wall along eastern property boundary
Minimum Pile Length: 12.5 m
‘Upstand’ Height: 6.6 m
Unfactored resistance to normal shear forces: 250 kN/m*
*The quoted resistance to normal shear forces is as utilised within the scope of the program Slope/W. It is
noted that this does not necessarily relate to actual design parameters, and designers must undertake finite
element analysis to assess soil/structure interactions and calculate both bending and shear stresses in the
piles. Retaining structures should also undergo rigorous checks of global and internal stability. The designer
must be satisfied that the geotechnical data presented is adequate to allow the analyses to be undertaken
with a high degree of confidence.
For a non-contiguous pile wall system such as micro-piles, a grout ‘curtain’ would need to be installed along
the length of the wall to prevent the flow of sand between the piles. Based on the highest modelled vertical
face of about 6.6 m height along the eastern boundary, such a grout ‘curtain’ should be installed down to at
least 8.5 m below the ground surface (existing). Where the pile wall was constructed along the eastern edge
of the building, this would be reduced slightly to about 5.5 m depth.
Whilst the proposed structure will prevent erosion along the eastern (rear) boundary of the property, there is
potential for the design erosion event to remove sand from the neighbouring properties to the north and
south exposing the side boundaries of the subject property to instability and erosion. The extent of the side
boundary erosion protection required has been determined by a line drawn at 28° extending upwards from
the estimated dune toe, following extreme storm erosion, and subsequent retrogressive failures. Erosion
protection is required to extend from the shear pile wall to an equivalent distance of 23 m from the eastern
property boundary, along the north and south boundaries, tapering from ground level to a depth to tie into the
shear pile wall along the eastern edge.
Whether the pile wall will also need to extend around the side boundaries will depend on the dimensions and
strength of the grout curtain installed and its ability to provide at least emergency support to the retained
sand. This should be considered as part of the detailed design.
General geotechnical recommendations for site development are provided in the following sections.
18 June 2024
Report No. 24096-001-Rev0 13
Page 19
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
6.1 Earthworks
Bulk excavations in the order of up to 3.5 m depth/height are anticipated for the terraced construction.
Isolated deeper excavations may be required for underground services and footings. The pool is shown to
be mostly above ground on the drawings, with filling required to create the building terraces (supported by an
RPEQ designed retaining walls). Filling elsewhere is anticipated to be for landscaping only, should be less
than 0.5 m high.
The advice give herein should be treated as preliminary to aid in project planning, and Tectonic must review
detailed design drawings for the residence prior to construction.
6.1.1 Site Preparation and Trafficability
Following clearing of existing vegetation, any tree stumps and large roots should be ‘grubbed out’. Any
organic rich topsoil should then be stripped and set aside. Similarly, all foundations and remaining structural
elements from the existing residence should be removed and ‘grubbed out.’ Based on the boreholes and site
observations, stripping depths to remove existing unsuitable upper soils should be relatively shallow
however, deeper areas of unsuitable materials may be present across the site, particularly related to the
existing structure (e.g. retaining wall backfill, service trenches, footing excavations). Topsoil materials must
not be used in structural fill; however, may be placed across landscaping areas.
It should be noted that compaction of such relatively ‘clean’ sands as structural fill requires the addition of
substantial volumes of water (‘flooding’) combined with the use of vibratory compaction equipment (typically
a vibrating plate). Care must be taken with the use of vibratory equipment (e.g. compactors or sheet piling)
to ensure that there are no adverse impacts on surrounding structures. The impacts from ground vibration
must be closely monitored and managed during construction. It would be prudent to conduct a dilapidation
survey of neighbouring structures prior to commencement of construction; and furthermore it is
recommended that a suitably qualified and experienced civil/structural RPEQ is engaged to provide a
vibration management plan for the proposed construction works.
The exposed natural subgrade following excavations will likely be in a loose condition and must be
compacted by several passes of a vibrating plate or minimum 4 tonne vibrating smooth drum roller, in
conjunction with surface application of ample water, to achieve the required compaction.
Due to the potential for development of poor trafficability during construction, placement of a minimum
150 mm thick granular working platform may be required across laydown areas. Specific platform design
would be required prior to mobilisation and trafficking of any heavy mobile plant on the site (e.g. mobile
cranes, concrete pumps or piling rigs).
Due to the highly permeable nature of the sands at this site, stormwater is expected to rapidly infiltrate the
ground, making un-sealed surface drainage ineffective for the control of flows. Any sealed areas should be
graded to ensure free drainage of stormwater away from construction areas, and to a control point(s).
6.1.2 Excavations
Excavations through the soils should be achievable using conventional earthmoving plant (e.g. small or
larger excavators with toothed buckets). Temporary, unsurcharged cuts in the very loose to loose sand
could be formed at 1V:2H, and at 1V:1.5H in medium dense (or denser) sand, for batters up to 3.5 m in
height. Flatter batters or temporary retention may be required if groundwater seepage is encountered or if
sloughing of dry sand occurs at the batter surface. Deeper cuts, if required, may require temporary shoring,
unless assessed and approved by Tectonic during construction.
Permanent cuts or fills greater than 1 m must be retained. Permanent cut and fill batters up to 1 m high shall
not exceed 1V:2.5H. Any permanent soil and fill batters will require erosion protection (e.g. revegetation or
surface protection). Similarly, improvements to the vegetation (i.e. with site appropriate natural species) on
the natural high dune face downslope of the residence would aid in restricting the development initial surficial
failures.
Based on the preliminary design details provided, the above temporary batter slopes may be achievable due
to the favourable proposed positioning of the new structure. However, if spatial or other constraints (e.g.
undermining of sewer and stormwater services under Ross Crescent) do not allow this, temporary shoring
18 June 2024
Report No. 24096-001-Rev0 14
Page 20
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
(e.g. sheet piles) or propping will be required as per the recommendations in Section 6.3 below.
Excavations in close proximity to existing structures and infrastructure, including on neighbouring properties
and the road corridor, will need to be specifically designed to prevent undermining. If undermining is a
potential issue the existing structures may need to be underpinned or excavations may require temporary
shoring.
The advice of a suitably qualified and experienced structural RPEQ must be sought regarding any potential
undermining and design and construction of any underpins/temporary shoring (if required).
The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations (e.g. limits on personnel entry into trenches).
6.1.3 Filling
The natural sandy soils where free of deleterious materials (e.g. vegetation, organics etc.) may be reused as
structural fill (retained under the building), subject to appropriate moisture adjustment. It should be noted
that compaction of such relatively ‘clean’ sands as structural fill requires the addition of substantial volumes
of water (‘flooding’) combined with the use of vibratory compaction equipment (typically a smooth drum roller
or heavy vibrating plate). Should importation of fill be required, it is recommended that such fill should
comply with the following:
Minimum CBR of 10 %
Maximum plasticity index of 15 %
Shrink-swell index ≤ 1 %
Maximum particle size of 100 mm
The primary recommendation would be to re-use site won material, or use a similar granular soil where
import is required. In compliance with above, cohesive soils may be tolerated, however their use should be
limited to lower layers in fill (at least 1 m below surface) and impacts on site classification (Ref. Section
6.2.1) must be assessed by designers.
Any fill should be compacted at moisture contents within the range of ±2 % of optimum moisture content for
Standard Compaction. Fill material should be placed in 250 mm thick (loose thickness) layers and be
compacted by repeated rolling using a minimum 4 tonne smooth drum roller (or equivalent, with vibration on
if safe to do so) to achieve a dry density ratio of at least 95 % of the maximum Dry Density Ratio (DDR),
based upon the Standard Compaction method, or a Dry Density Index of at least 70 %.
Confirmatory compaction testing must be carried out at regular intervals. A minimum of two tests per
vertical lift is recommended where structural fill heights are to exceed 300 mm. Further details for control
and testing of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for Commercial
and Residential Developments.
6.2 Building Foundations
6.2.1 Indicative Site Classification
Site classification for footing design is 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 profile, and the
reactivity of the in situ soil and any imported fill materials.
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 poor bearing capacity soils at shallow depths, and
trees. 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. However, 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 slabs, footing and plumbing design.
18 June 2024
Report No. 24096-001-Rev0 15
Page 21
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
6.2.2 Footing Design
No design loadings were available at the time of reporting. Footings for the proposed residence and any
ancillary structures (e.g. retaining walls, pool etc.) must penetrate through any fill materials and unsuitable
natural soils (i.e. very loose to loose sands) to found at least 1 m into medium dense (or denser) natural
sands. High-level footings may be possible in areas of deeper excavation where medium dense to dense (or
denser) sands are exposed at or near the subgrade. This would be subject to an assessment by a suitably
qualified and experienced geotechnical RPEQ (including verification testing). High-level footings, so founded,
could be designed using a maximum allowable bearing pressure of 100 kPa.
Elsewhere (excluding the shear pile wall), based on the results of the investigation, pile founding depths of
about 1.5 m to 4 m BGL (existing ground levels) are anticipated. Deeper pile depths may be necessary
subject to an assessment of building loads at the detailed design stage.
Excluding the shear pile wall, steel screw piles would be an appropriate footing option for the residence. Piles
may be designed using a maximum allowable end bearing pressure of 600 kPa in medium dense sands, or
at least 1 MPa in the deeper dense sands. Due to the presence of very loose to loose upper sands, together
with the restricted site conditions and close proximity of adjacent houses, open bored piers or driven piles
are not recommended for this site. A possible alternative to screw piles could be grout-injected, CFA piles,
provided that construction water loss is carefully monitored and controlled. Steel reinforced concrete bored
piles may be possible; however, the use of sacrificial liners (e.g. Formatube) would be required.
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.
Ultimately, the advice of a specialist piling contractor should be sought regarding pile design and
construction. However, where steel screw piles are adopted site specific load testing and the results of this
geotechnical investigation should be considered by the structural engineers in validating any generic torque
to capacity ratios provided as part of the proposed design. An assessment of potential vibration effects on
nearby structures and monitoring requirements should also be included.
Footing design should also account for potential soil reactivity to be equivalent to Class M. It should be noted
that the placement of reactive clay may result in a more significant equivalent site classification, such as Class
H1 (or higher).
All footings should found such that they are not adversely affected by any adjacent excavations, trenches,
retaining walls, or in ground structures that are not designed to support building loads. Footings should
found at least below a plane extending 1 m horizontally from the base of trenches/excavations/swimming
pool, then rising up at 1V:1H, as illustrated in Text Figure 11 overleaf. Where consideration is given to the
use of high level footings to the eastern side of the residence, structural designers should allow for the
deepest founding depth of either:
taking footings below the zone of active earth pressure (within this zone reduced foundation capacity
and adverse interaction with the seaward retention system are anticipated); or
the arrangement should comply with Text Figure 11 overleaf, with the relevant plane taken from the
equivalent ground level at the front of the exposed piled wall following the most onerous erosion
case in the stability modelling (Ref. Section 5.2.1).
18 June 2024
Report No. 24096-001-Rev0 16
Page 22
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Text Figure 11: Footing depth required to mimimise risk of undermining
It is recommended that footings be inspected by a suitably qualified and experienced engineer prior to
placement of steel reinforcement and pouring of concrete to confirm allowable bearing pressures and
cleanliness of excavations.
If any soil conditions encountered during construction are found to differ from those noted in the geotechnical
investigation, Tectonic should be notified immediately and an inspection carried out to determine if changes
to footing design are required.
6.3 Temporary and Permanent Retention
Excavations are expected to range up to around 3.5 m BGL (existing ground levels). Preliminary design and
layout information indicates that construction utilising temporary battering should generally be achievable,
however if spatial constraints do not allow this (possibly along the western boundary adjacent Ross
Crescent), some form of temporary shoring may be required.
Based upon our experience with similar sites, we anticipate that temporary shoring may be achieved by use
of sheet piles, however Unitywater requirements for their infrastructure may restrict the use of sheet piles.
Shoring of deeper cuts would likely require lateral restraint, and this is conventionally achieved by helical
steel anchors (similar to screw piles); and the proximity to the road corridor would require permissions to be
obtained for subterranean access. Therefore, where lateral support by cantilever only is not feasible, it is
suggested that internal struts/propping be considered to provide lateral restraint for the shoring system.
Anchored or propped sheet piles may require pre-drilling to prevent adverse vibrations during sheet pile
installation (where penetration of the deeper dense sands is required).
Other shoring methods that could be considered include bored contiguous or secant piles. Conventional
non-contiguous or soldier pile walls are not feasible for the proposed development due to the likelihood that
loose sands would ‘flow’ through gaps between the piles. Their use may however be possible where
additional grout panels are included in the design.
An advantage of contiguous or secant pile wall retention systems is that they are ultimately used for the
permanent walls, whereas sheet piles would be temporary to provide retention during construction only,
therefore requiring a permanent structural wall to be constructed. Bored pile walls generally require greater
width (horizontally) for installation as compared to sheet piles and are often more expensive.
The advice of a specialist shoring contractor must be sought regarding feasibility, design and installation of
the proposed retention system. It will be necessary to conduct numerical analysis to optimise the retention
system. Detailed design will also need to account for relevant factors of safety to maintain the temporary
and long-term stability of the retention system.
18 June 2024
Report No. 24096-001-Rev0 17
Page 23
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
Retaining structures greater than 1 m high, or those required to support surcharge loads or sloping backfill,
will require engineer design and certification of construction. Retaining wall design should be carried out in
accordance with AS4678-2002 Earth retaining structures.
Design for temporary and permanent retaining structures could be carried out using a pressure distribution
applicable to the wall type and based on the parameters listed in Table 6. These values do not include
allowance for hydrostatic pressures, backslopes (assumed to be horizontal), nor transient (e.g. construction)
or adjacent footing loadings.
Table 6: Retaining Structure Design Parameters
Lateral earth pressure coefficients
Unit
Friction
Retained material weight
angle (°) Ka Ko
(kN/m3) Kp
(Cantilever wall) (Non-yielding wall)
Very Loose/ Loose
17 27 0.38 0.55 2.66
Sands
Medium Dense Sands 18 34 0.28 0.44 3.54
Dense (or Denser)
19 36 0.26 0.41 3.85
Sands
Future Controlled Fill* * * * * *
Note: * Depends on fill material type and level of compaction.
Retaining structures must be founded as per the recommendations in Section 6.2.2 above with the footings
also designed to account for lateral loads imposed by the retaining wall. Detailed design must include an
assessment of internal and global stability. A solution using screw piles to support retaining walls, possibly
including raked piles, may be feasible although bending and shear capacities would need to be carefully
checked in design from a soil-structure interaction viewpoint. Additional lateral capacity may be achieved by
incorporating a deeper pile cap that also acts as a shear key attracting passive resistance from the sands in
front of the wall.
6.4 Drainage
Surface diversion drainage should be constructed above the crest of any new cut or fill embankment or
retaining walls (e.g. grassed or landscaped swales or diversion mounds). Adequate site drainage must be
installed to ensure that stormwater runoff is directed away from building walls, footings, batters and retaining
walls.
Although unlikely, if groundwater seepage is encountered during excavations, Tectonic must be notified to
assess the impact on stability.
Subsurface drainage must be installed behind any retaining walls (e.g. slotted ‘aggi’ pipe wrapped in filter
‘sock’ placed in gravel backfill). Depending on matters such as the extent of drainage installed and site-
specific groundwater conditions, the designer must make an assessment of hydrostatic pressure to be
accounted for in the design of the retaining structure.
It is assumed that the pool floor will include a hydrostatic pressure relief valve. The outlet pipe from this
valve must be taken to ‘daylight’ at the ground surface.
Collected roof water should be directed by pipes to the council stormwater system along Ross Crescent
(e.g. through the use of a ‘wet’ or ‘charged’ drainage system) or; where not physically possible, surface
water should be directed to infiltrate into the ground around the edges of hard surfaces, with infiltration
areas at least 10 m upslope of the rear boundary. Hydraulic design should be such that under no
circumstances are uncontrolled stormwater flows permitted over the dune face; where channelised erosion
and scour features could be allowed to develop.
Design of the stormwater system should be undertaken by a suitably qualified and experienced RPEQ.
18 June 2024
Report No. 24096-001-Rev0 18
Page 24
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
7.0 CONCLUSION
Based on the findings of our assessment it is concluded that a Low Risk of slope instability could be
achieved for the proposed development, subject to the following:
Implementation of the recommendations given in this report in formulating the feasibility of the
development, and preparing the preliminary design;
Review of the detailed design by Tectonic to confirm compliance with the recommendations herein;
and
Confirmation of the deeper subsurface profile present below the building envelope for the detailed
design stage, via further ground investigation following access being facilitated by the demolition of
the existing residence. This should comprise a borehole taken to depths in the order of 20 m to
25 m BGL, using a rotary drill rig capable of solid flight augering and deep cased wash boring, with
standard penetration tests (SPTs).
8.0 LIMITATIONS
Your attention is drawn to the document Limitations, which is included in Appendix D of this report. The
statements presented in this document are intended to advise you of what your realistic expectations of this
report should be, and to present you with recommendations on how to minimise the risks associated with the
services provided by Tectonic for this project.
18 June 2024
Report No. 24096-001-Rev0 19
Page 25
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Ph: 07 5478 9016
PROJECT:
PROPOSED RESIDENCE
33 ROSS CRESCENT,
SUNSHINE BEACH
TITLE:
BH1 DCP4 SITE PLAN
A
CLIENT:
BH2
BH3 33 ROSS CRESCENT PTY LTD
DCP6
DRAWN: DATE:
A’
DCP5 BC 04/04/2024
CHECKED: DATE:
JM 13/05/2024
SCALE:
AS SHOWN
LEGEND:
Approx. Borehole Locations
Approx. Standalone DCP
Locations
A A’ Section Line A-A’
(Refer Figure 2)
Notes:
FIGURE:
Aerial imagery courtesy of NearMap (22 January 2024) PROJECT NO.: REV:
0m 20 40 60 80m 24096-001 1 0
Page 26
0 10 20 30 40 50 60 70 80 90
45 45
40 40
35 35
30 30
25 Ross Crescent 25
Sunshine Beach
ELEVATION (m AHD)
20 20
BH1
DCP9
Blows/100 mm
(3 m) 15 30
DCP5
15 15
DCP4
BH2
DCP9
Approx. ground surface
DCP9 Blows/100 mm
DCP9 Blows/100 mm (-26 m)15 30
(-4 m) 15 mm
Blows/100 30
4.0 (15 m)15 30
10 10
2.8
DCP6
3.9
4.0
TECTONIC 3.00.2 LIB.GLB Fence FENCE A3L 24096.GPJ 24096 SEC2.GDW 13/5/2024 10:49 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 3.00.2 2021-03-30
BH3
DCP9
Blows/100 mm
(1 m) 15 30 DCP9
5 (12 m)
Blows/100 mm
15 30
5
3.9 3.0
0 0
-5 -5
-10 -10
0 10 20 30 40 50 60 70 80 90
DISTANCE (m)
POST LEGEND MATERIAL GRAPHIC
BH #
Baseline Offset TOPSOIL
(0 m)
DCP Blows/100 mm
15 30
DCP or PSP FILL
SAND
TITLE DRAWN DATE
H 1:300 JM 13/05/2024
33 Ross Crescent Pty Ltd CHECKED DATE
0 2 4 6 8 10m
33 Ross Crescent, Sunshine Beach RG 13/05/2024
V 1:300
SCALE
Proposed Residence H 1:300 V 1:300 A3
0 2 4 6 8 10m
Coord.System: MGA2020 Zone 56 Height Datum: AHD Subsurface Section (Section A-A') PROJECT No FIGURE No
Depth at EOH
24096 2
Page 27
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
33 ROSS CRESCENT,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 1
CLIENT:
33 ROSS CRESCENT PTY LTD
DRAWN: DATE:
Indicative Building Piles Shear Pile Wall
JPM 15/05/2024
CHECKED: DATE:
RG 15/05/2024
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
24096 3 0
Page 28
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
33 ROSS CRESCENT,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 2
CLIENT:
33 ROSS CRESCENT PTY LTD
DRAWN: DATE:
JPM 15/05/2024
Shear Pile Wall
Indicative Building Piles CHECKED: DATE:
RG 15/05/2024
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
24096 4 0
Page 29
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
33 ROSS CRESCENT,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 3
CLIENT:
33 ROSS CRESCENT PTY LTD
DRAWN: DATE:
JPM 15/05/2024
Indicative Building Piles Shear Pile Wall CHECKED: DATE:
RG 15/05/2024
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
24096 5 0
Page 30
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
33 ROSS CRESCENT,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 4a
CLIENT:
33 ROSS CRESCENT PTY LTD
DRAWN: DATE:
JPM 15/05/2024
Indicative Building Piles Shear Pile Wall CHECKED: DATE:
RG 15/05/2024
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
24096 6 0
Page 31
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
33 ROSS CRESCENT,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 4b
CLIENT:
33 ROSS CRESCENT PTY LTD
DRAWN: DATE:
JPM 15/05/2024
Indicative Building Piles Shear Pile Wall CHECKED: DATE:
RG 15/05/2024
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
24096 7 0
Page 32
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
APPENDIX A
Borehole & DCP Reports and Explanatory Notes
18 June 2024
Report No. 24096-001-Rev0
Page 33
Borehole No.
BH1
Page 1 of 1
Engineering Log - Borehole Project No.: 24096
Client: 33 Ross Crescent Pty Ltd Commenced: 3/4/2024
Project Name: Proposed Residence Completed: 3/4/2024
Hole Location: 33 Ross Crescent, Sunshine Beach Logged By: BC
Hole Position: 511060.0 m E 7078776.6 m N MGA2020 Zone 56 Checked By: JPM
Drill Model and Mounting: Hand Auger Inclination: -90° RL Surface: 17.00 m
Hole Diameter: 65 mm Bearing: 360° Datum: AHD Operator: Tectonic
Drilling Information Material Description and Observations
Relative Density
Classification
Pocket DCP TEST
Penetration
Consistency
Graphic Log
Samples Material Description
Penetrometer
Recovery
Condition
Tests soil type: plasticity or particle characteristics,
Moisture
UCS Blows per 100 mm
Symbol
Method
Remarks secondary and minor components, colour
Water
RL Depth (kPa)
(m) (m) 0 5 10 15 20 25
100
200
300
400
500
Silty SAND, (TOPSOIL/FILL), fine to medium
grained, brown, with rootlets
Silty SAND, (FILL), fine to coarse grained, brown,
low liquid limit
SAND, fine to medium grained, pale grey, trace L
silt (AEOLIAN)
16.0
1
MD
DS1.5-1.9m
Not Encountered
D
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24096.GPJ <<DrawingFile>> 13/5/2024 10:29 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 3.00.2 2021-03-30
15.0
2 M
HA
becoming yellow brown
14.0
3 MD
becoming pale grey
13.0
4
Hole Terminated at 4.00 m
Slow progress due to collapsing sands
12.0
5
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
AD/T-Auger Drilling TC Bit VE - Very Easy Level (Date) U## - Undisturbed Sample (## mm) D - Dry VS - Very Soft
AD/V-Auger Drilling V Bit E - Easy DS - Disturbed Sample M - Moist S - Soft
RT - Rotary Tri-cone Bit Inflow BDS - Bulk Disturbed Sample W - Wet F - Firm
RD - Rotary Drilling F - Firm SPT - Standard Penetration Test VSt - Very Stiff
Partial Loss
NMLC -Rock Core H - Hard H - Hard
VH - Very hard Complete Loss
HA - Hand Auger Plastic Limit VL - Very Loose
Graphic Log/Core Loss L - Loose
Classification Symbols and < PL MD - Medium Dense
Core recovered (hatching Soil Descriptions
indicates material) = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Core loss Fr - Friable
Classification System
Page 34
Borehole No.
BH2
Page 1 of 1
Engineering Log - Borehole Project No.: 24096
Client: 33 Ross Crescent Pty Ltd Commenced: 3/4/2024
Project Name: Proposed Residence Completed: 3/4/2024
Hole Location: 33 Ross Crescent, Sunshine Beach Logged By: BC
Hole Position: 511087.5 m E 7078757.8 m N MGA2020 Zone 56 Checked By: JPM
Drill Model and Mounting: Hand Auger Inclination: -90° RL Surface: 12.40 m
Hole Diameter: 65 mm Bearing: 360° Datum: AHD Operator: Tectonic
Drilling Information Material Description and Observations
Relative Density
Classification
Pocket DCP TEST
Penetration
Consistency
Graphic Log
Samples Material Description
Penetrometer
Recovery
Condition
Tests soil type: plasticity or particle characteristics,
Moisture
UCS Blows per 100 mm
Symbol
Method
Remarks secondary and minor components, colour
Water
RL Depth (kPa)
(m) (m) 0 5 10 15 20 25
100
200
300
400
500
Silty SAND, (TOPSOIL), fine to medium grained,
SP brown, with rootlets
SAND, fine to medium grained, brown grey, trace
DS0.3-0.7m VL
silt, (AEOLIAN)
11.4
1 becoming pale yellow, pale brown
HA
Not Encountered
L
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24096.GPJ <<DrawingFile>> 13/5/2024 10:29 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 3.00.2 2021-03-30
10.4
2 M
9.4
3
becoming brown grey
MD
becoming pale grey
8.4
4
Hole Terminated at 4.00 m
Slow progress due to collapsing sands
7.4
5 15/85mm
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
AD/T-Auger Drilling TC Bit VE - Very Easy Level (Date) U## - Undisturbed Sample (## mm) D - Dry VS - Very Soft
AD/V-Auger Drilling V Bit E - Easy DS - Disturbed Sample M - Moist S - Soft
RT - Rotary Tri-cone Bit Inflow BDS - Bulk Disturbed Sample W - Wet F - Firm
RD - Rotary Drilling F - Firm SPT - Standard Penetration Test VSt - Very Stiff
Partial Loss
NMLC -Rock Core H - Hard H - Hard
VH - Very hard Complete Loss
HA - Hand Auger Plastic Limit VL - Very Loose
Graphic Log/Core Loss L - Loose
Classification Symbols and < PL MD - Medium Dense
Core recovered (hatching Soil Descriptions
indicates material) = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Core loss Fr - Friable
Classification System
Page 35
Borehole No.
BH3
Page 1 of 1
Engineering Log - Borehole Project No.: 24096
Client: 33 Ross Crescent Pty Ltd Commenced: 3/4/2024
Project Name: Proposed Residence Completed: 3/4/2024
Hole Location: 33 Ross Crescent, Sunshine Beach Logged By: BC
Hole Position: 511145.3 m E 7078752.5 m N MGA2020 Zone 56 Checked By: JPM
Drill Model and Mounting: Hand Auger Inclination: -90° RL Surface: 4.30 m
Hole Diameter: 65 mm Bearing: 360° Datum: AHD Operator: Tectonic
Drilling Information Material Description and Observations
Relative Density
Classification
Pocket DCP TEST
Penetration
Consistency
Graphic Log
Samples Material Description
Penetrometer
Recovery
Condition
Tests soil type: plasticity or particle characteristics,
Moisture
UCS Blows per 100 mm
Symbol
Method
Remarks secondary and minor components, colour
Water
RL Depth (kPa)
(m) (m) 0 5 10 15 20 25
100
200
300
400
500
SP SAND, fine to medium grained, pale yellow, pale HW
brown, trace silt (AEOLIAN)
3.3
1 VL
DS1.0-1.5m
Not Encountered
M
HA
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24096.GPJ <<DrawingFile>> 13/5/2024 10:29 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 3.00.2 2021-03-30
2.3
2
L
MD
1.3
3
Hole Terminated at 3.00 m
Slow progress due to collapsing sands
0.3
4
15/50mm
-0.7
5
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
AD/T-Auger Drilling TC Bit VE - Very Easy Level (Date) U## - Undisturbed Sample (## mm) D - Dry VS - Very Soft
AD/V-Auger Drilling V Bit E - Easy DS - Disturbed Sample M - Moist S - Soft
RT - Rotary Tri-cone Bit Inflow BDS - Bulk Disturbed Sample W - Wet F - Firm
RD - Rotary Drilling F - Firm SPT - Standard Penetration Test VSt - Very Stiff
Partial Loss
NMLC -Rock Core H - Hard H - Hard
VH - Very hard Complete Loss
HA - Hand Auger Plastic Limit VL - Very Loose
Graphic Log/Core Loss L - Loose
Classification Symbols and < PL MD - Medium Dense
Core recovered (hatching Soil Descriptions
indicates material) = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Core loss Fr - Friable
Classification System
Page 36
CLIENT : 33 ROSS CRESCENT PTY LTD SHEET : 1 OF 1
CONTRACTOR : Tectonic
PROJECT : Proposed Residence
LOCATION : 33 Ross Crescent, Sunshine Beach
PROJECT No. : 24096
TEST: DCP4 TEST: DCP5 TEST: DCP6
LOGGED: BC 3/4/2024 CHECKED: JPM LOGGED: BC 3/4/2024 CHECKED: JPM LOGGED: BC 3/4/2024 CHECKED: JPM
EASTING: 511093.9 m NORTHING: 7078775.8 m EASTING: 511083.8 m NORTHING: 7078735.4 m EASTING: 511117.9 m NORTHING: 7078751.3 m
MGA2020 Zone 56 MGA2020 Zone 56 MGA2020 Zone 56
Depth (m)
Depth (m)
Depth (m)
GROUND RL: 12.00 m AHD GROUND RL: 12.70 m AHD GROUND RL: 5.20 m AHD
Blows per 100 mm Blows per 100 mm Blows per 100 mm
0 5 10 15 20 25 0 5 10 15 20 25 0 5 10 15 20 25
HW
1 1 1
2 2 2
TECTONIC 3.00.2 LIB.GLB Log IS DCP 3 PER PAGE 24096.GPJ <<DrawingFile>> 13/5/2024 10:30 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 3.00.2 2021-03-30
15/50mm
3 3 3
15/80mm
4 4 4
5 5 5
Comments Comments Comments
Page 37
TERMS USED ON LOGS
DRILLING/EXCAVATION METHOD
AD* Auger Drilling RA Rotary Air BH Tractor Mounted Backhoe
ADH Hollow Auger RD Rotary Blade or Drag bit EX Tracked Hydraulic Excavator
HA Hand Auger RT Rotary Tri-cone bit HMLC Core – 63mm
*T TC-Bit HQ Core – 63mm
*V V-Bit NMLC Core – 47mm
NQ Core – 52mm
R Ripper
RH Rock Hammer
WATER
GROUNDWATER NOT The observation of groundwater, whether present or not, was not possible due to drilling water,
OBSERVED surface seepage or cave in of the borehole/test pit.
GROUNDWATER NOT The borehole/test pit was dry soon after excavation. However, groundwater could be present in
ENCOUNTERED less permeable strata. Inflow may have been observed had the borehole/test pit been left open
for a longer period.
SAMPLING AND TESTING
SPT Standard Penetration Test to AS1289.6.3.1-2004
5,4,10 N=14 5,4,10 = Blows per 150mm. N = Blows per 300mm penetration following 150mm seating
30/65mm Where practical refusal occurs, the blows and penetration for that interval are reported
RW Penetration occurred under the rod weight only
HW Penetration occurred under the hammer and rod weight only
HB Hammer double bouncing on anvil
DS Disturbed sample
BDS Bulk disturbed sample
SV Field shear vane test expressed as uncorrected shear strength (sv = peak value, sr = residual value)
PP Pocket penetrometer test expressed as instrument reading in kPa
U50 Thin walled tube sample - number indicates nominal sample diameter in millimetres
DCP Dynamic cone penetration test
CPT Electronic cone penetration test
CPTu Electronic cone penetration test with pore pressure (u) measurement
Rev1
February 2021
Page 38
METHOD OF SOIL DESCRIPTION
USED ON LOGS
CLASSIFICATION AND INFERRED STRATIGRAPHY
Soil is classified and described in borehole and test pit logs using the preferred method given in AS1726 – 2017.
The material properties are assessed in the field by visual/tactile methods.
Particle Size Plasticity Properties
Major Sub Division Particle Size
Division
BOULDERS > 200 mm
COBBLES 63 to 200 mm
Coarse 19 to 63 mm
GRAVEL Medium 6.7 to 19 mm
Fine 2.36 to 6.7 mm
Coarse 0.6 to 2.36 mm
SAND Medium 0.21 to 0.6 mm
Fine 0.075 to 0.21
SILT 0.002 to 0.075
CLAY < 0.002 mm
NOTE: The U line is an approximate upper bound for most materials.
Data which plot above the U line may represent unusual/problem soil
behavior, or unreliable data and should be considered carefully.
MOISTURE CONDITION AS1726 - 2017
Symbol Term Description
D Dry Sands and gravels are free flowing. Clays & Silts may be brittle or friable and powdery.
M Moist Soils are darker than in the dry condition & may feel cool. Sands and gravels tend to cohere.
W Wet Soils exude free water. Sands and gravels tend to cohere.
CONSISTENCY AND DENSITY AS1726 - 2017
Symbol Term Undrained Shear Symbol Term Density Index % SPT “N” #
Strength
VS Very Soft 0 to 12 kPa VL Very Loose Less than 15 0 to 4
S Soft 12 to 25 kPa L Loose 15 to 35 4 to 10
F Firm 25 to 50 kPa MD Medium Dense 35 to 65 10 to 30
St Stiff 50 to 100 kPa D Dense 65 to 85 30 to 50
VSt Very Stiff 100 to 200 kPa VD Very Dense Above 85 Above 50
H Hard Above 200 kPa
In the absence of test results, consistency and density may be assessed from correlations with the observed behaviour of
the material.
# SPT correlations are not stated in AS1726 – 2017, and may be subject to corrections for overburden pressure and
equipment type.
Rev1
October 2017
Page 39
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
APPENDIX B
Geotechnical Laboratory Test Certificates
18 June 2024
Report No. 24096-001-Rev0
Page 40
Construction Sciences Pty Ltd Laboratory: Sunshine Coast Laboratory
ABN: 74 128 806 735 Phone: 07 5452 0100
Fax: 07 5452 0133
Address: Email: [email protected]
32 Hi-Tech Drive,
Kunda Park QLD 4556
PARTICLE SIZE DISTRIBUTION REPORT
Client: Tectonic Geotechnical Pty Ltd Report Number: 3740/R/64536-2
Client Address: 924 David Low Way, Marcoola Project Number: 3740/P/2437
Project: 33 Ross Crescent, Sunshine Beach Lot Number:
Location: Various Internal Test Request: 3740/T/48811
Supplied To: Tectonic Geotechnical Pty Ltd Client Reference/s: O/N 22182
Area Description: Report Date / Page: 8/04/2024 Page 1 of 2
Test Procedures: AS1289.3.6.1
Sample Number 3740/S/254238 Borehole name BH1
Sampling Method Tested As Received Start Sample Depth (m) 1.5
Date Sampled 3/04/2024 End Sample Depth (m) 1.9
Sampled By Client Sampled (m)
Date Tested 8/04/2024 Material Source 32/20/80
Prep / Drying Method n/a Material Type -
Prep > 53mm (%) - Specification -
Specification Percent Specification PARTICLE SIZE DISTRIBUTION GRAPH
AS Sieve (mm)
Minimum (%) Passing (%) Maximum (%)
9.5 100 100
6.7 100
90
4.75 100
2.36 100
80
1.18 99
0.600 99
70
0.425 96
Percent Passing (%)
0.300 78
60
0.150 7
0.075 4 50
40
30
20
10
0
6.7
9.5
1.18
2.36
4.75
0.075
0.150
0.300
0.425
0.600
AS Sieve Size (mm)
Remarks Re-Issued Report Replaces Report No 3740/R/64536-1 (reason: Incorrect address reported initially.)
Accredited for compliance with ISO/IEC 17025 – Testing
Accreditation Number: 1986
Corporate Site Number: 3740
Approved Signatory: Thomas Hewitt
Form ID: W9Rep Rev 3
Page 41
Construction Sciences Pty Ltd Laboratory: Sunshine Coast Laboratory
ABN: 74 128 806 735 Phone: 07 5452 0100
Fax: 07 5452 0133
Address: Email: [email protected]
32 Hi-Tech Drive,
Kunda Park QLD 4556
PARTICLE SIZE DISTRIBUTION REPORT
Client: Tectonic Geotechnical Pty Ltd Report Number: 3740/R/64536-2
Client Address: 924 David Low Way, Marcoola Project Number: 3740/P/2437
Project: 33 Ross Crescent, Sunshine Beach Lot Number:
Location: Various Internal Test Request: 3740/T/48811
Supplied To: Tectonic Geotechnical Pty Ltd Client Reference/s: O/N 22182
Area Description: Report Date / Page: 8/04/2024 Page 2 of 2
Test Procedures: AS1289.3.6.1
Sample Number 3740/S/254239 Borehole name BH2
Sampling Method Tested As Received Start Sample Depth (m) 0.3
Date Sampled 3/04/2024 End Sample Depth (m) 0.7
Sampled By Client Sampled (m)
Date Tested 8/04/2024 Material Source 32/20/80
Prep / Drying Method n/a Material Type -
Prep > 53mm (%) - Specification -
Specification Percent Specification PARTICLE SIZE DISTRIBUTION GRAPH
AS Sieve (mm)
Minimum (%) Passing (%) Maximum (%)
9.5 100 100
6.7 100
90
4.75 100
2.36 99
80
1.18 99
0.600 98
70
0.425 96
Percent Passing (%)
0.300 75
60
0.150 6
0.075 3 50
40
30
20
10
0
6.7
9.5
1.18
2.36
4.75
0.075
0.150
0.300
0.425
0.600
AS Sieve Size (mm)
Remarks Re-Issued Report Replaces Report No 3740/R/64536-1 (reason: Incorrect address reported initially.)
Accredited for compliance with ISO/IEC 17025 – Testing
Accreditation Number: 1986
Corporate Site Number: 3740
Approved Signatory: Thomas Hewitt
Form ID: W9Rep Rev 3
Page 42
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
APPENDIX C
AGS Guidelines - Qualitative Terminology for Use in
Assessing Risk to Property
Some Guidelines for Hillside Construction
18 June 2024
Report No. 24096-001-Rev0
Page 43
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX C: LANDSLIDE RISK ASSESSMENT
QUALITATIVE TERMINOLOGY FOR USE IN ASSESSING RISK TO PROPERTY
QUALITATIVE MEASURES OF LIKELIHOOD
Approximate Annual Probability
Implied Indicative Landslide
Description Descriptor Level
Indicative Notional Recurrence Interval
Value Boundary
10-1 5x10-2
10 years The event is expected to occur over the design life. ALMOST CERTAIN A
20 years The event will probably occur under adverse conditions over the
-2
10 100 years
design life.
LIKELY B
-3
-3 5x10 200 years
10 1000 years The event could occur under adverse conditions over the design life. POSSIBLE C
5x10-4 2000 years
The event might occur under very adverse circumstances over the
10-4 10,000 years
design life.
UNLIKELY D
-5 5x10-5 20,000 years
10 The event is conceivable but only under exceptional circumstances
100,000 years RARE E
over the design life.
-6 5x10-6 200,000 years
10 1,000,000 years The event is inconceivable or fanciful over the design life. BARELY CREDIBLE F
Note: (1) The table should be used from left to right; use Approximate Annual Probability or Description to assign Descriptor, not vice versa.
QUALITATIVE MEASURES OF CONSEQUENCES TO PROPERTY
Approximate Cost of Damage
Description Descriptor Level
Indicative Notional
Value Boundary
Structure(s) completely destroyed and/or large scale damage requiring major engineering works for
200% CATASTROPHIC 1
stabilisation. Could cause at least one adjacent property major consequence damage.
100%
Extensive damage to most of structure, and/or extending beyond site boundaries requiring significant
60% MAJOR 2
stabilisation works. Could cause at least one adjacent property medium consequence damage.
40%
Moderate damage to some of structure, and/or significant part of site requiring large stabilisation works.
20% MEDIUM 3
Could cause at least one adjacent property minor consequence damage.
10%
5% 1% Limited damage to part of structure, and/or part of site requiring some reinstatement stabilisation works. MINOR 4
Little damage. (Note for high probability event (Almost Certain), this category may be subdivided at a
0.5% INSIGNIFICANT 5
notional boundary of 0.1%. See Risk Matrix.)
Notes: (2) The Approximate Cost of Damage is expressed as a percentage of market value, being the cost of the improved value of the unaffected property which includes the land plus the
unaffected structures.
(3) The Approximate Cost is to be an estimate of the direct cost of the damage, such as the cost of reinstatement of the damaged portion of the property (land plus structures), stabilisation
works required to render the site to tolerable risk level for the landslide which has occurred and professional design fees, and consequential costs such as legal fees, temporary
accommodation. It does not include additional stabilisation works to address other landslides which may affect the property.
(4) The table should be used from left to right; use Approximate Cost of Damage or Description to assign Descriptor, not vice versa
Australian Geomechanics Vol 42 No 1 March 2007
68039 Landslide Risk Management Issued 10/7/07
Page 44
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX C: – QUALITATIVE TERMINOLOGY FOR USE IN ASSESSING RISK TO PROPERTY (CONTINUED)
QUALITATIVE RISK ANALYSIS MATRIX – LEVEL OF RISK TO PROPERTY
LIKELIHOOD CONSEQUENCES TO PROPERTY (With Indicative Approximate Cost of Damage)
Indicative Value of 1: CATASTROPHIC 2: MAJOR 3: MEDIUM 4: MINOR 5:
Approximate Annual 200% 60% 20% 5% INSIGNIFICANT
Probability 0.5%
A – ALMOST CERTAIN 10-1 VH VH VH H M or L (5)
-2
B - LIKELY 10 VH VH H M L
C - POSSIBLE 10-3 VH H M M VL
D - UNLIKELY 10-4 H M L L VL
-5
E - RARE 10 M L L VL VL
-6
F - BARELY CREDIBLE 10 L VL VL VL VL
Notes: (5) For Cell A5, may be subdivided such that a consequence of less than 0.1% is Low Risk.
(6) When considering a risk assessment it must be clearly stated whether it is for existing conditions or with risk control measures which may not be implemented at the current
time.
RISK LEVEL IMPLICATIONS
Risk Level Example Implications (7)
Unacceptable without treatment. Extensive detailed investigation and research, planning and implementation of treatment
VH VERY HIGH RISK options essential to reduce risk to Low; may be too expensive and not practical. Work likely to cost more than value of the
property.
Unacceptable without treatment. Detailed investigation, planning and implementation of treatment options required to reduce
H HIGH RISK
risk to Low. Work would cost a substantial sum in relation to the value of the property.
May be tolerated in certain circumstances (subject to regulator’s approval) but requires investigation, planning and
M MODERATE RISK implementation of treatment options to reduce the risk to Low. Treatment options to reduce to Low risk should be
implemented as soon as practicable.
Usually acceptable to regulators. Where treatment has been required to reduce the risk to this level, ongoing maintenance is
L LOW RISK
required.
Acceptable. Manage by normal slope maintenance procedures.
VL VERY LOW RISK
Note: (7) The implications for a particular situation are to be determined by all parties to the risk assessment and may depend on the nature of the property at risk; these are only
given as a general guide.
Australian Geomechanics Vol 42 No 1 March 2007
68039 Landslide Risk Management Issued 10/7/07
Page 45
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX G - SOME GUIDELINES FOR HILLSIDE CONSTRUCTION
GOOD ENGINEERING PRACTICE POOR ENGINEERING PRACTICE
ADVICE
GEOTECHNICAL Obtain advice from a qualified, experienced geotechnical practitioner at early Prepare detailed plan and start site works before
ASSESSMENT stage of planning and before site works. geotechnical advice.
PLANNING
SITE PLANNING Having obtained geotechnical advice, plan the development with the risk Plan development without regard for the Risk.
arising from the identified hazards and consequences in mind.
DESIGN AND CONSTRUCTION
Use flexible structures which incorporate properly designed brickwork, timber Floor plans which require extensive cutting and
or steel frames, timber or panel cladding. filling.
HOUSE DESIGN
Consider use of split levels. Movement intolerant structures.
Use decks for recreational areas where appropriate.
SITE CLEARING Retain natural vegetation wherever practicable. Indiscriminately clear the site.
ACCESS & Satisfy requirements below for cuts, fills, retaining walls and drainage. Excavate and fill for site access before
DRIVEWAYS Council specifications for grades may need to be modified. geotechnical advice.
Driveways and parking areas may need to be fully supported on piers.
EARTHWORKS Retain natural contours wherever possible. Indiscriminatory bulk earthworks.
Minimise depth. Large scale cuts and benching.
CUTS Support with engineered retaining walls or batter to appropriate slope. Unsupported cuts.
Provide drainage measures and erosion control. Ignore drainage requirements
Minimise height. Loose or poorly compacted fill, which if it fails,
Strip vegetation and topsoil and key into natural slopes prior to filling. may flow a considerable distance including
Use clean fill materials and compact to engineering standards. onto property below.
FILLS Batter to appropriate slope or support with engineered retaining wall. Block natural drainage lines.
Provide surface drainage and appropriate subsurface drainage. Fill over existing vegetation and topsoil.
Include stumps, trees, vegetation, topsoil,
boulders, building rubble etc in fill.
ROCK OUTCROPS Remove or stabilise boulders which may have unacceptable risk. Disturb or undercut detached blocks or
& BOULDERS Support rock faces where necessary. boulders.
Engineer design to resist applied soil and water forces. Construct a structurally inadequate wall such as
Found on rock where practicable. sandstone flagging, brick or unreinforced
RETAINING
Provide subsurface drainage within wall backfill and surface drainage on slope blockwork.
WALLS
above. Lack of subsurface drains and weepholes.
Construct wall as soon as possible after cut/fill operation.
Found within rock where practicable. Found on topsoil, loose fill, detached boulders
Use rows of piers or strip footings oriented up and down slope. or undercut cliffs.
FOOTINGS
Design for lateral creep pressures if necessary.
Backfill footing excavations to exclude ingress of surface water.
Engineer designed.
Support on piers to rock where practicable.
SWIMMING POOLS Provide with under-drainage and gravity drain outlet where practicable.
Design for high soil pressures which may develop on uphill side whilst there
may be little or no lateral support on downhill side.
DRAINAGE
Provide at tops of cut and fill slopes. Discharge at top of fills and cuts.
Discharge to street drainage or natural water courses. Allow water to pond on bench areas.
SURFACE Provide general falls to prevent blockage by siltation and incorporate silt traps.
Line to minimise infiltration and make flexible where possible.
Special structures to dissipate energy at changes of slope and/or direction.
Provide filter around subsurface drain. Discharge roof runoff into absorption trenches.
Provide drain behind retaining walls.
SUBSURFACE
Use flexible pipelines with access for maintenance.
Prevent inflow of surface water.
Usually requires pump-out or mains sewer systems; absorption trenches may Discharge sullage directly onto and into slopes.
SEPTIC &
be possible in some areas if risk is acceptable. Use absorption trenches without consideration
SULLAGE
Storage tanks should be water-tight and adequately founded. of landslide risk.
EROSION Control erosion as this may lead to instability. Failure to observe earthworks and drainage
CONTROL & Revegetate cleared area. recommendations when landscaping.
LANDSCAPING
DRAWINGS AND SITE VISITS DURING CONSTRUCTION
DRAWINGS Building Application drawings should be viewed by geotechnical consultant
SITE VISITS Site Visits by consultant may be appropriate during construction/
INSPECTION AND MAINTENANCE BY OWNER
OWNER’S Clean drainage systems; repair broken joints in drains and leaks in supply
RESPONSIBILITY pipes.
Where structural distress is evident see advice.
If seepage observed, determine causes or seek advice on consequences.
Australian Geomechanics Vol 42 No 1 March 2007 113
Page 46
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007 114 Australian Geomechanics Vol 42 No 1 March 2007
Page 47
PROPOSED RESIDENCE
33 ROSS CRESCENT, SUNSHINE BEACH
APPENDIX D
Limitations
18 June 2024
Report No. 24096-001-Rev0
Page 48
LIMITATIONS This document has been prepared for the purpose outlined in Tectonic’s proposal and no responsibility is accepted for the use of this document, in whole or in part, for any other purpose. The scope of Tectonic’s Services are as described in Tectonic’s proposal, and are subject to restrictions and limitations. Tectonic did not perform a complete assessment of all possible conditions or circumstances that may exist at the site referenced in the report. If a service is not expressly indicated, do not assume it has been provided. If a matter is not addressed, do not assume that any determination has been made by Tectonic in regards to it. Conditions may exist which were undetectable given that economic and time constraints limit the practical extent of geotechnical investigation. Variations in conditions may occur between investigation locations, and there may be special conditions pertaining to the site which have not been revealed by the investigation and which have not therefore been taken into account in the document. Where variations exist on site, additional studies and actions may be required. Tectonic’s opinions are based upon information that existed at the time that the work was performed. The passage of time, man-made or natural events, may alter the site conditions. It is understood that the Services undertaken allowed Tectonic to form an opinion of the actual conditions of the site at the time the site was visited and cannot be used to assess the effect of any subsequent changes in the quality of the site, or its surroundings, or any laws or regulations. Any assessments made in the preparation of this document are based on the conditions indicated from published sources and the findings of the investigation described. Actual subsurface conditions may differ from those indicated in the document (e.g. between boreholes or test pits). No warranty is included, either express or implied, that the actual conditions will conform exactly to the assessments contained in this document. Where data supplied by the client or other external sources, including previous site investigation data, have been used, it has been assumed that the information is correct unless otherwise stated. No responsibility is accepted by Tectonic for incomplete or inaccurate data supplied by others. This document is provided for the sole use by the Client and its professional advisers. No responsibility whatsoever for the contents of this document will be accepted to any person other than the Client. Any use which a third party makes of this document, or any reliance on or decisions to be made based on it, is the responsibility of such third parties. Tectonic accepts no responsibility for damages, if any, suffered by any third party as a result of decisions made or actions based on this document. Rev 1 (March 2016)
Used in these records
Reference Document - Geotech Report - MCU24 0094Related documentApplication case desk ↗
About this file
- File size
- 11.3 MB (very large file)
- File type
No other editions are linked here.
Original file
Log in to download the original file
The download may take a few minutes. On mobile data, it is best to wait for Wi-Fi.