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RFI - 21370-001-Rev1 66 Seaview Tce
GEOTECHNICAL INVESTIGATION
Proposed Residence
66 Seaview Terrace
Sunshine Beach
Report for: Catherine & Gavin Deane
21370-001-Rev1
28 April 2022
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
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Page 2
PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
Document Review
Document No. Revision Prepared By Reviewed By Date Issued
Draft Robert Gibb Ashley Davey 10 November 2021
001 0 Robert Gibb Ashley Davey 23 November 2021
001 1 Robert Gibb Ashley Davey 28 April 2022
Report Distribution
Document Revision Method of Delivery Issued To
Gavin Deane
001 1 Electronic
([email protected])
Catherine Deane
001 1 Electronic
([email protected])
Jack Lewis
001 1 Electronic Pivotal Perspective
([email protected])
Prepared By: Reviewed By:
Robert Gibb BSc (Hons) Ashley Davey BE (Geol.) RPEQ 8159
Engineering Geologist Managing Director
28 April 2022
Report No. 21370-001-Rev1 i
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PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
Executive Summary
This report details the results of a geotechnical investigation undertaken for a proposed residential
development at 66 Seaview Terrace, Sunshine Beach (‘the subject site’). The investigation was carried out
by Tectonic for Catherine and Gavin Deane.
Haskoning Australia (RHDHV) has provided a coastal engineering report, detailing a review of the Erosion
Prone Area at the site (Ref. PA2906-RHD-ZZ-XX-RP-Z-0001, Status P01.01/S0, dated 12 April 2022).
The geotechnical investigation comprised drilling of boreholes at three locations; one using a tracked vehicle
mounted rotary rig; the other two by hand auger methods on the face and crest of the dune. Dynamic cone
penetrometer (DCP) testing was also conducted along with geotechnical laboratory testing of 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 associated geotechnical recommendations and comments.
Preliminary architectural drawings supplied to us indicate that it is proposed to construct a building of three
storeys. The lowest storey would be completely in-ground to the western side of the structure, and the
uppermost level would be only partially enclosed. The centre storey would have a cantilevered frontage
extending around 3 m from the eastern edge of the building, mimicked above by the third storey. To
accommodate the lower level being ‘dug in’ to the dune, on the upslope side, bulk excavations against the
western boundary with Seaview Terrace are expected to reach around 3.5 m below ground level (BGL).
Excavations will extend close to some of the site boundaries, and temporary retention will thus be required.
Borehole BH3 was drilled within the proposed building envelope using a rotary drill rig and encountered:
Natural Sands – comprising loose, dry to moist, fine to medium grained sands to 1.25 m BGL;
then becoming medium dense to 4.2 m BGL; followed by
Interlayered Indurated Sand & Sands – comprising dense materials to 9.3 m BGL, then
becoming very dense 29.6 m BGL; and consisting of sands, occasionally being weakly cemented
indurated sand (‘coffee rock’); underlain by
Residual Soils and Extremely Weathered (XW) Material – comprising, hard, medium to high
plasticity, sandy clays to the borehole termination depth of 31.45 m BGL.
Boreholes BH1 and BH2 were drilled using hand augering equipment at the eastern edge of the
development area, and at the toe of the dune, respectively. DCP4 was undertaken around the centre of the
main high dune face. These locations encountered/indicated a similar subsurface profile as follows:
Natural Sands – comprising loose sand (occasionally silty) to between 1.1 m and 1.6 m BGL, then
becoming medium dense to depths of between 2.3 m and 4.8 m BGL, and dense thereafter to the
maximum depth of investigation (Ref. attached borehole logs and in situ test results). Borehole
BH2 at the toe of the high dune encountered the deepest depth to dense (or denser) materials.
DCP3 was undertaken through a fill embankment to the western side boundary and indicated that the
materials are variable in density, from very loose to medium dense.
No signs of groundwater seepage (‘springs’) were observed at the ground surface during our walk-over.
Groundwater seepage was encountered in borehole BH2 (located at the toe of the high dune) at about 1.9 m
BGL, which is inferred to represent a ‘perched’, unconfined groundwater table that builds up and diminishes
in the sands above the denser materials below, in response to prevailing weather conditions. No
groundwater was present in the standpipe installed in borehole BH3 to 6 m BGL following completion of
drilling on 8 October 2021. Groundwater conditions are expected to be reflective of prevailing weather
conditions and seepage may develop, particularly following periods of prolonged or heavy rainfall.
Modelling has been carried out using Slope/W to assess the factor of safety (FOS) against instability of the
sand dune slope considering a hypothetical storm and wave scenario assessed by RHDHV. Each of the
cases analysed are summarised as given overleaf:
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PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
Case 1 – Vertical cut into the toe of the sand dune slope caused by erosion scouring, and allowing
for a 500 year average recurrence interval (ARI) storm event.
Case 2 – Slope failure following reprofiling of the slope due to the failure/erosion from Case 1.
Case 3 – Retrogressive upper slope failure following reprofiling of the slope due to the Case 2
failure.
Case 4 (along the eastern boundary) – piles should be at least 6 m long, with a 120 kN shear force
resistance and horizontal pile to pile spacing of 1 m. A minimum embedment of 1 m is also
recommended in to dense (or denser) sand.
Case 5 (along the eastern edge of the residence) – piles should be at least 6 m long, with a
100 kN shear force resistance and horizontal pile to pile spacing of 1 m. A minimum embedment of
1 m is also recommended in to dense (or denser) sand.
The modelled ground surface profile for the initial Case 1 was based on provided survey information across
the subject site, with surface profiles beyond the eastern property boundary augmented with 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, which included a combination of short-term erosion
from a 500 year (ARI) storm event and shoreline recession due to sea level rise for the 2100 climate extreme
event scenario.
Whilst the proposed micro-pile (or similar) structure would prevent erosion along the eastern (rear) boundary
of the property or residence, there is potential for the design erosion event to remove sand from the
neighbouring properties to the north and south, therefore 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 to the west from the base of the rear point of the
erosion event. Grout curtain erosion protection is required to extend from the rear boundary at least 10 m
westward along the north and south boundaries, tapering from 3 m deep at the eastern end.
It should be noted that this report gives advice on the use of a piled wall, based on slope stabilisation factors
only, and detailed design will be required by the piling contractor.
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 to dense (or denser) sands.
Based on the results of the investigation founding depths (excluding the proposed pile wall) are
anticipated to range up to about 3 m BGL (existing ground levels). In some areas of deeper cut, high
level footings may be adopted. Elsewhere, piles would be required.
Cutting for the lower level up to about 3.5 m BGL along the western site boundary will necessitate
the installation of temporary shoring prior to excavation. Based upon our experience with similar
projects in proximity, shoring could comprise sheet piles or contiguous piles.
Landscaping fill to the rear of the property should be limited to 0.5 m high.
Ground vibrations during construction should 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 high dune face downslope of the residence would also aid in
restricting the development of initial surficial failures.
All collected roof water should be directed by pipes to the council stormwater system along Seaview
Terrace (such as via the use of ‘charged’ or ‘wet’ systems) or, where not possible, surface water
should be directed to infiltrate into the ground around the edges of hard surfaces, with infiltration
areas setback as far as possible from the rear boundary.
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Report No. 21370-001-Rev1 iii
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PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
Table of Contents
1.0 INTRODUCTION ........................................................................................................................................................ 1
2.0 PROPOSED DEVELOPMENT ................................................................................................................................... 1
3.0 METHOD OF INVESTIGATION ................................................................................................................................. 2
3.1 Fieldwork ...................................................................................................................................................... 2
3.2 Geotechnical Laboratory Testing .................................................................................................................. 2
4.0 RESULTS OF INVESTIGATION ................................................................................................................................ 3
4.1 Site Description............................................................................................................................................. 3
4.2 Topography................................................................................................................................................... 6
4.3 Geology ........................................................................................................................................................ 8
4.4 Subsurface Conditions.................................................................................................................................. 8
4.5 Groundwater ................................................................................................................................................. 9
4.6 Geotechnical Laboratory Test Results .......................................................................................................... 9
4.7 Surface Drainage ........................................................................................................................................ 10
5.0 SLOPE STABILITY ASSESSMENT ........................................................................................................................ 10
5.1 Existing Conditions ..................................................................................................................................... 10
5.2 Stability Assessment................................................................................................................................... 11
5.2.1 Quantitative Assessment ...................................................................................................................... 12
6.0 GEOTECHNICAL RECOMMENDATIONS .............................................................................................................. 15
6.1 Earthworks .................................................................................................................................................. 15
6.1.1 Site Preparation and Trafficability ......................................................................................................... 15
6.1.2 Excavations ........................................................................................................................................... 16
6.1.3 Filling..................................................................................................................................................... 17
6.2 Building Foundations .................................................................................................................................. 17
6.2.1 Indicative Site Classification.................................................................................................................. 17
6.2.2 Footing Design ...................................................................................................................................... 17
6.3 Temporary and Permanent Retention......................................................................................................... 19
6.4 Drainage ..................................................................................................................................................... 20
7.0 CONCLUSION ......................................................................................................................................................... 21
8.0 LIMITATIONS .......................................................................................................................................................... 21
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66 SEAVIEW TERRACE, SUNSHINE BEACH
TABLES
Table 1: Summary of Subsurface Profiles ........................................................................................................................... 9
Table 2: Stability Risk Levels ............................................................................................................................................ 11
Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007) ....................................................................... 12
Table 4: Soil Parameters Adopted for Slope/W Analyses ................................................................................................. 13
Table 5: Slope/W Analysis Results ................................................................................................................................... 14
Table 6: Retaining Structure Design Parameters .............................................................................................................. 20
TEXT FIGURES
Text Figure 1: Section through proposed residence, looking north (courtesy Shaun Lockyer Architects) ........................... 1
Text Figure 2: Recent aerial image of the site and immediate surrounds (courtesy Nearmap, 10 September 2021).......... 3
Text Figure 3: Oblique drone image of the site, looking north-west .................................................................................... 4
Text Figure 4: Looking due west over dune in vicinity of site .............................................................................................. 4
Text Figure 5: Looking north-east over site frontage to Seaview Terrace ........................................................................... 5
Text Figure 6: Looking south along frontage showing road embankment along western site boundary ............................. 5
Text Figure 7: Looking east over proposed building area, drill rig at borehole BH3 ............................................................ 6
Text Figure 8: Site plan showing ground surface contours (courtesy Noosa Council ‘Intramaps’) ..................................... 6
Text Figure 9: Drone image of the dune face and main beach looking north ...................................................................... 7
Text Figure 10: Extract of Gympie Special 1:100,000 Geology Map ................................................................................... 8
Text Figure 11: Extract from Noosa Council landslide hazard overlay mapping ............................................................... 10
Text Figure 12: Footing depth required to prevent undermining........................................................................................ 18
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 Construciton
APPENDIX D
Limitations
28 April 2022
Report No. 21370-001-Rev1 v
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PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
1.0 INTRODUCTION
This report details the results of a geotechnical investigation undertaken for a proposed residential
development at 66 Seaview Terrace, Sunshine Beach (‘the subject site’). The investigation was carried out
by Tectonic for Catherine and Gavin Deane, in accordance with Proposal P21519-Rev0 dated 8 September
2021. Pivotal Perspective are the consulting town planners and project managers for the development.
Haskoning Australia (RHDHV) has provided a coastal engineering report, detailing a review of the Erosion
Prone Area associated with the coastal building line at the subject site (Ref. PA2906-RHD-ZZ-XX-RP-Z-
0001, Status P01.01/S0, dated 12 April 2022).
The geotechnical investigation comprised drilling of boreholes at three locations; one using a tracked vehicle
mounted rotary rig; the other two by hand auger methods at the toe and crest of the dune. Dynamic cone
penetrometer (DCP) testing was also conducted along with geotechnical laboratory testing of 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
associated geotechnical recommendations and comments.
2.0 PROPOSED DEVELOPMENT
Preliminary architectural drawings were supplied to us (Ref. Shaun Lockyer Architects, Project No. 0375,
Dwg. No. 000.00 to 400.02, Rev C, dated 20 October 2021).
The drawings indicate that it is proposed to construct a building of three storeys. The lowest storey would be
completely in-ground to the western side of the structure, and the uppermost level would be only partially
enclosed. The centre storey would have a cantilevered frontage extending around 3 m from the eastern edge
of the building, mimicked above by the third storey. A mixture of masonry, stonework, brickwork and concrete
walls; with complimentary wooden cladding and shutters also spread across the exterior.
A swimming pool would occupy the strip between the northern side of the residence, being mostly above
ground to the east; with a small section expected to be in-ground to the west. A concrete shell is indicated for
the pool, with a glass eastward facing front towards the beach.
To accommodate the lower level being ‘dug in’ to the dune, on the upslope side, bulk excavations against
the western boundary with Seaview Terrace are expected to reach around 3.5 m below ground level (BGL).
Excavations will therefore extend close to some of the site boundaries and, therefore, temporary retention
will be required. Isolated deeper excavations may be required for underground services and footings or
other specific elements.
Text Figure 1 below presents a cross sectional view of the proposed development.
Text Figure 1: Section through proposed residence, looking north (courtesy Shaun Lockyer Architects)
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66 SEAVIEW TERRACE, SUNSHINE BEACH
3.0 METHOD OF INVESTIGATION
3.1 Fieldwork
An experienced engineering geologist from Tectonic undertook a site walk-over on 15 September 2021 to
visually assess any indicators of past slope instability. The walk-over included assessment of soil
exposures, surface drainage conditions, topography, evidence of erosion or past instability, and vegetation
coverage/condition.
At the time of the walkover two boreholes (designated BH1 and BH2) were undertaken at the main break in
slope from the site to the dune face (approximate to the eastern site boundary), and towards the toe of the
dune, respectively. In situ testing utilising the DCP method was completed from surface adjacent to each
borehole, and at selected depths downhole. In addition, standalone DCP testing was also conducted through
inferred fill embankment materials off Seaview Terrace to the western boundary of the site, and at an
intermediate point, around half-way down the dune face. Hand augers were taken to depths of between 3 m
and 6 m BGL.
A separate phase of investigation was completed on 8 October 2021. A small excavator owned and
operated by Bebrok was utilised to temporarily remove and replace boulders to the site frontage, and
undertake minor vegetation clearing and earthworks to create a relatively level drilling platform within the
proposed building envelope. One borehole (designated BH3) was drilled to 31.45 m BGL. This borehole
was drilled using a tracked vehicle mounted Hydrapower Scout rotary drill rig, owned and operated by
Drillsure Geotechnical Pty Ltd. This drill rig was equipped with solid flight augering and rotary wash boring
capabilities, allowing deep penetration through the sand dune profile.
In situ testing in borehole BH3 comprised standard penetration tests (SPT) generally at 1.5 m intervals.
Boreholes BH1 and BH2 were backfilled with drilling spoil and left slightly mounded at the ground surface. A
standpipe was installed in borehole BH3, to a depth of 6 m BGL for groundwater monitoring. Disturbed soil
samples were recovered from SPT spoon, and auger cuttings at shallower depth.
The engineering geologist 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. Borehole locations
are shown in Figure 1.
3.2 Geotechnical Laboratory Testing
Select disturbed soil samples were dispatched to the NATA accredited laboratory of QC Testing, located in
Yandina, for geotechnical testing and 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 test certificates are attached in Appendix B.
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4.0 RESULTS OF INVESTIGATION
4.1 Site Description
The site is formally described as Lot 69 on RP81810, covering an area of about 576 m2, with frontage to
Seaview Terrace along the western boundary. At the time of the investigation the site was vacant of any
structures, with a variably dense vegetation cover comprising bushes and scattered small to medium size
trees. Denser vegetation was present further down the dune face (east) which primarily comprised low
ground coverage and a small number of trees, such as Banksia and She-Oak.
Two to three storey houses were generally present in the vicinity of the site, of varying age and construction
methodology. The closest residence was 64 Seaview Terrace adjoining the subject allotment to the south.
The structure consisted of a masonry brick dwelling, over a split level type construction, being one storey just
off Seaview Terrace, and extending to two storeys, with a suspended verandah on the seaward side.
The asphalt seal along Seaview Terrace in the vicinity of the site was in relatively good condition overall, with
several patches and reseals evident, which we understand was due to the relatively recent installation of
underground services. No kerb was present along the eastern edge of Seaview Terrace above the site.
A 2021 aerial image of the site and surrounds is shown in Text Figure 2 below.
Subject site
Sunshine Beach
Text Figure 2: Recent aerial image of the site and immediate surrounds (courtesy Nearmap, 10 September 2021)
Site conditions at the time of our investigations are shown in Text Figures 3 to 7 on the following pages.
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Subject site
Text Figure 3: Oblique drone image of the site, looking north-west
Subject site
Text Figure 4: Looking due west over dune in vicinity of site
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PROPOSED RESIDENCE
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Text Figure 5: Looking north-east over site frontage to Seaview Terrace
Boundary peg
Road embankment at ~30°
Text Figure 6: Looking south along frontage showing road embankment along western site boundary
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PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
Text Figure 7: Looking east over proposed building area, drill rig at borehole BH3
4.2 Topography
During the 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 below, the site is located at a
beachward break in slope, on the easterly facing flank of a high sand dune slope; which eventually crests
about 190 m to the west/north-west.
Subject site
Text Figure 8: Site plan showing ground surface contours (courtesy Noosa Council ‘Intramaps’)
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Locally, Seaview Terrace had been constructed on a cut and fill earthworks feature, sidelong to the slope. A
small cut was estimated (<1 m depth), with filling on the downslope side resulting in an embankment
estimated to contain about 1 m height of material, battered at around 30°. The batter was present with the
site, just over the western boundary (Ref. Text Figure 6 on the preceding pages). A more gently sloping area
was present through the majority of the site area, and building envelope, being around 8°, sloping to the
east. An area to the south-east corner of the lot, and beyond the eastern boundary sloped at around 18° to
22°. Beyond this, the main high dune face then dropped down to Sunshine Beach at between 29° and 33°.
The face of the dune was relatively consistent and linear, steepening to 40° around 2 m to 3 m up from the
toe.
Beyond the toe of the main high dune, a trough was present of about 10 m width; then a small foredune
around 1.5 m height, with sidelopes of around 10° to 11°. A shorter trough of about 5 m width was then
present to an incipient dune, around 1.5 m to 2 m height; with sideslopes of up to 15°. The beach extended
thereafter, dropping down from about RL 2 m AHD to the shoreline (around RL 0 m AHD).
The abovementioned geomorphological features are illustrated below in Text Figure 9.
Dune continues well off site
to west
High dune
Foredune
Incipient dune
Subject site
Troughs
Text Figure 9: Drone image of the dune face and main beach looking north
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PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
4.3 Geology
Available geological information 1 indicates that the site is underlain by Pleistocene age quartz dune sand
(Ref. extract of published mapping in Text Figure 10 below). The headlands to the north/north-east of the site
are indicated to consist of materials derived of the Tiaro Coal Measures, a late Triassic to Jurassic age
sedimentary deposit. These materials are expected to underly the dune sands proximal to the site.
Approx. site location
Text Figure 10: Extract of Gympie Special 1:100,000 Geology Map
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 (attached at end of text).
Borehole BH3 was drilled within the proposed building envelope using a rotary drill rig and encountered:
Natural Sands – comprising loose, dry to moist, fine to medium grained sands to 1.25 m BGL;
then becoming medium dense to 4.2 m BGL; followed by
Interlayered Indurated Sand & Sands – comprising dense materials to 9.3 m BGL, then
becoming very dense 29.6 m BGL; and consisting of sands, occasionally being weakly cemented
indurated sand (‘coffee rock’); underlain by
Residual Soils and Extremely Weathered (XW) Material – comprising, hard, medium to high
plasticity, sandy clays to the borehole termination depth of 31.45 m BGL.
Boreholes BH1 and BH2 were drilled using hand augering equipment at the eastern edge of the
development area, and at the toe of the dune, respectively. DCP4 was undertaken around the centre of the
main high dune face. These locations encountered/indicated a similar subsurface profile as follows:
Natural Sands – comprising loose sand (occasionally silty) to between 1.1 m and 1.6 m BGL, then
becoming medium dense to depths of between 2.3 m and 4.8 m BGL, and dense thereafter to the
maximum depth of investigation (Ref. attached borehole logs and in situ test results). Borehole
BH2 at the toe of the high dune encountered the deepest depth to dense (or denser) materials.
1
Queensland Government, Department of Mines and Energy, 1:100,000 Gympie Special Geology Map, Sheet 9445 & Part 9545, 1999
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DCP3 undertaken through the inferred fill embankment to the western side boundary indicates that the
materials are variable in density, from very loose to medium dense.
Table 1 below summarises the subsurface profile encountered at each test location (noted in a west to east
direction, Seaview Terrace to high dune toe).
Table 1: Summary of Subsurface Profiles
Very Dense Hard Sandy
Very Loose Loose Sands Dense (or Indurated Clay
Investigation Medium
to Medium (Natural denser) Sand (‘Coffee (Residual/
Location Dense Sands
Dense (Fill) Dune Sands) Sands Rock’) and XW Material)
Sand
DCP3 0.0 – 1.0 1.0 – 1.9TD - - - -
BH3 - 0.0 – 1.25 1.25 – 4.2 4.2 – 9.3 9.3 – 29.6 29.6 – 31.45TD
BH1 - 0.0 – 1.5 1.5 – 3.2 3.2 – 6.0TD - -
DCP4 - 0.0 – 1.1 1.1 – 2.3 2.3 – 2.69TD - -
BH2 - 0.0 – 1.6 1.6 – 4.8 4.8 – 5.9TD - -
Notes: 1. Depths noted in m BGL at time of investigation (15 September & 8 October 2021)
2. NE denotes not encountered
3. TD denotes borehole terminated at target depth
4.5 Groundwater
No signs of groundwater seepage (‘springs’) were observed at the ground surface during our walk-over.
Groundwater seepage was encountered in borehole BH2 (located at the toe of the high dune) at about 1.9 m
BGL, which is inferred to represent a ‘perched’, unconfined groundwater table that builds up and diminishes
in the sands above the denser materials below, in response to prevailing weather conditions. Groundwater
was not encountered to 6 m BGL in borehole BH1, with groundwater not observed due to the introduction of
drilling fluid below 2.5 m BGL in borehole BH3.
No groundwater was present in the standpipe installed in borehole BH3 to 6 m BGL following completion of
drilling on 8 October 2021.
Groundwater conditions are expected to be reflective of prevailing weather conditions and seepage may
develop, particularly following periods of prolonged or heavy rainfall.
4.6 Geotechnical Laboratory Test Results
PSD analyses on two sand samples from boreholes BH1 and BH2 indicate that the soils generally comprise
fine and fine to medium grained sands with <1% silt fines (i.e. relatively ‘clean’). Full test results (laboratory
certificates) are presented in Appendix B.
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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 some run-off expected to enter the site from the cul-de-sac head
due to the open unedged frontage to Seaview Terrace. It is anticipated that this would be intercepted by
upgraded verge landscaping, and kerbage along Seaview Terrace as part of the residential development.
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).
5.0 SLOPE STABILITY ASSESSMENT
5.1 Existing Conditions
The Noosa Planning Scheme 2020 includes a landslide hazard overlay map (Ref. extract in Text Figure 11
below) which indicates that the site is within a Moderate Hazard Area.
Subject site
Text Figure 11: Extract from Noosa Council landslide hazard overlay mapping
It should be noted that the Noosa Council landslide hazard map 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: 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 high dune standing at between 29° to 33°.
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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
Very High
VH and implementation of treatment options essential to reduce risk to Low; may be too
Risk
expensive and not practical. Work likely to cost more than value of property.
Unacceptable without treatment. Detailed investigation, planning and implementation of
H High Risk treatment 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
Moderate
M investigation, planning and implementation of treatment options to reduce risk to Low.
Risk
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
L Low Risk
this 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.
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 (NSC) 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 in Appendix C (taken from AGS 2007).
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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 area (8° across majority of
building area, 18° to 22° towards eastern boundary),
1: Failure through very loose to
retention system proposed and protection of eastern
loose natural sands above the
Unlikely Medium Low side of site using a shear pile wall it is considered
foundation depth across the
Unlikely that a landslip in these materials would affect
building area
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 Rare due to the lack of
2: Deep failure through the precedence of such movements locally, no signs of any
medium dense (or denser) sands Rare Major Low existing slope instability, apparent lack of groundwater,
below the foundation depth and relatively shallow depth to dense (or denser) sands
below this intermediate unit. Although the consequence of
such a failure would be Major, the resultant risk is Low as
per AGS 2007.
The likelihood of a slip/failure of a temporary retention
system (sheet pile wall, or similar) as outlined in Section
6.3, is assessed as Rare, subject to detailed design by a
3: Instability of temporary sheet
suitably qualified RPEQ engineer, which accounts for the
pile retention system, or similar, Rare Major Low
road embankment fill, required factors of safety against
as discussed in Section 6.4.
slope instability, and construction by a specialist
contractor. Although the consequence of such a failure
could be Major, the resultant risk is Low as per AGS2007.
The likelihood of a slip/failure through the future micro-pile
wall system along the eastern boundary as outlined in
Section 6.0, and advised by the coastal erosion specialists
4: Retrogressive failure of the
(RHDHV); is thus assessed as Barely Credible, subject to
high dune face considering a
Barely detailed design by a suitably qualified RPEQ engineer,
hypothetical storm and wave Major Very Low
Credible construction by a specialist contractor, and considering the
scenario, impacting the subject
results of our quantitative slope stability analysis outlined
site.
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 4 have been designed to mitigate those impacts.
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 preliminary design drawings, site survey information and slope angles measured local to
the site 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.
Considering the moderate gradients recorded in the eastern part of the site, progressing closeby to the main
steep dune face, and the presence of loose sands, the stability of the lower part of the existing high dune
slope is considered marginal. The slope is probably held in place by the stabilising effects of negative soil
pore pressures and shallow root systems. Any disturbance to the lower part of the dune slope, such as from
erosion by high seas, could lead to large scale instability.
Modelling has therefore been carried out considering a hypothetical storm and wave scenario nominated by
coastal engineering experts (RHDHV) in their report (Ref. Section 1.0). Each of the cases analysed are
summarised on the following page:
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Case 1 – Vertical cut into the toe of the sand dune slope caused by erosion scouring, and allowing
for a 500 year average recurrence interval (ARI) storm event.
Case 2 – Slope failure following reprofiling of the slope due to the failure/erosion from Case 1.
Case 3 – Retrogressive upper slope failure following reprofiling of the slope due to the Case 2
failure.
Case 4 – Slope stability analysis following reprofiling of the slope from Case 1 to Case 3, with the
eastern property boundary protected by a micro-pile (or similar) structure (piles min 7 m in length
and with 120 kN shear force resistance).
Case 5 – Slope stability analysis following reprofiling of the slope from Case 1 to Case 3, with the
eastern edge of the residence protected by a micro-pile (or similar) structure (piles min 6 m in length
and with 120 kN shear force resistance).
The modelled ground surface profile for the initial Case 1 was based on provided survey information across
the subject site (Ref. Minstaff Survey, Dwg. No. M3973 3003 2, Rev B; dated 19 October 2021) 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 500
year average recurrence interval (ARI) storm event. It was indicated in the RHDHV assessment, that while
the foredune and incipient dunes may be affected, significant erosion at the toe of the high dune face would
not occur. During our walk-over assessment at the site, it was noted that a steepening at the toe of the dune
was present. This was taken in to account as part of the development of the modelled ground profile. It is
noted that this resulted in a slightly more conservative, higher dune slope (following the retrogressive
failures); than would be proposed where considering coastal erosion only. An eventual toe level in the order
of RL 2.6 m AHD resulted, in line with the most onerous erosion case outlined by in the RHDHV modelling
(i.e. 500 year ARI event).
Subsurface conditions for Cases 1 to 5 were developed using the borehole and DCP information collected
during the investigation.
A surcharge load of 5 kPa was applied across crest of the dune to the eastern boundary to replicate future
landscaping fill. Building loads for the proposed residence and ancillary structures were included in the
modelling, given the height of the structure proposed (three full storeys above ground to the seaward side),
but will largely be transferred by a piled footing system into the natural medium dense (or denser) sands at
depth and would be anticipated to have a partial surcharge effect on the ground surface.
The soil parameters adopted for the analyses are summarised in Table 4 and are based on interpretation of
the site investigation, in situ testing and laboratory test results. The parameters are consistent with the
range of values recommended for similar materials in Appendix D of Australian Standard AS4678-2002
Earth Retaining Structures. Due to the relatively steep slopes and high permeability soils, a groundwater
table is not anticipated in the slope and therefore, was not modelled.
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
Hard Clays (Residual) 19 7 30
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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 overleaf, with the Slope/W outputs attached in Figures 3 to 7 at the end of
the report.
Table 5: Slope/W Analysis Results
Analysis Description Factor of Safety
Vertical cut into the toe of the dune caused by erosion scouring
Case 1 0.7
during a high sea event.
Lower slope failure following reprofiling of the slope due to
Case 2 0.9
failure/erosion from Case 1.
Retrogressive upper slope failure following reprofiling of the slope
Case 3 1.2
due to the Case 2 failure
Slope stability analysis following reprofiling of the slope from
Case 4 Case 1 to Case 3, with the eastern property boundary protected 1.5
by a micro-piled (or similar) wall.
Slope stability analysis following reprofiling of the slope from Case
Case 5 1 to Case 3, with the eastern edge of the residence protected by a 1.5
micro-piled (or similar) wall.
Results of the analyses indicates the following:
Case 1 – The assessed FOS of 0.7, being much less than 1.0, indicates a slope failure. A vertical
erosion cut would lead to retrogressive failures moving up slope, primarily within the very loose to
medium dense sands. 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 zones), however the modelled slip surface is consistent with previous experience in
similar conditions.
Case 2 – The FOS of 0.9 indicates that further slope failure is likely following reprofiling of the slope
due to erosion/failure from Case 1.
Case 3 – Following reprofiling of the slope from retrogressive translational failure(s), further instability
of the slope extending under the eastern property boundary is at high risk of occurring based on the
calculated FOS of about 1.2.
Case 4 – If the eastern boundary is protected by an engineer designed and certified micro-pile (or
similar) structure the potential critical slip surface takes the form of a deep-seated failure into the
underlying medium dense (or denser) sands. Such a failure results in a FOS of 1.5 or greater, even
following a vertical erosion cut and reprofiled slope from Cases 1 to 3.
Case 5 – If the eastern edge of the proposed residence is protected by an engineer designed and
certified micro-piled (or similar) wall structure the potential critical slip surface also takes the form of a
deep-seated failure into the underlying medium dense and/or dense (or denser) sands. Such a failure
also results in a FOS of 1.5 or greater, including allowance for a vertical erosion cut and reprofiled
slope from Cases 1 to 3.
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6.0 GEOTECHNICAL RECOMMENDATIONS
It is recommended that the eastern property boundary be protected by a micro-pile structure (or similar)
founded into the underlying natural medium dense (or denser) sands. An alternative option to a micro-pile
wall could be a relatively slender continuous flight auger (CFA) pile system. The adopted structure should
comprise piles structurally tied together at the surface using a steel-reinforced concrete capping beam. An
‘A-frame’ structure may be required (i.e. vertical and raked piles) to achieve the required shear force
resistance, should micro-piles be adopted.
It is noted that due to the relatively steep nature of the existing sand dune, access for construction plant
along the eastern boundary may be difficult; however the moderately sloping natural area across much of the
actual lot may provide an opportunity for progressive construction staging. An alternative option could be to
support the eastern edge of the proposed residence via a similar structure as illustrated in Case 5, shown in
Figure 7 (attached at the end of the report). A disadvantage of constructing the shear wall structure along
the eastern edge of the residence would be the loss of ground below the wall (east) following possible future
erosion events and retrogressive slope failure(s). Slightly longer piles would be required along the eastern
boundary compared to the eastern edge of the residence.
Based on the slope stability analyses the micro-piles (or similar) would need to be constructed as follows:
Case 4 (along the eastern boundary) – piles should be at least 6 m long, with a 120 kN shear force
resistance and horizontal pile to pile spacing of 1 m. A minimum embedment of 1 m is also
recommended in to dense (or denser) sand.
Case 5 (along the eastern edge of the residence) – piles should be at least 6 m long, with a
100 kN shear force resistance and horizontalpile to pile spacing of 1 m. A minimum embedment of
1 m is also recommended in to dense (or denser) sand.
A grout ‘curtain’ must be installed along the length of the wall to prevent the flow of sand between the piles.
Based on an anticipated highest modelled vertical face of about 1.5 m to 2 m high along the eastern
boundary or eastern edge of the residence, the grout ‘curtain’ should be installed down to at least
3 m below the ground surface.
Whilst the proposed micro-pile (or similar) structure will prevent erosion along the eastern (downslope)
boundary of the property, there is potential for the design erosion event to remove sand from the
neighbouring property to the south, and the vicinity of the public access stairs to the north; 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 to the west from the base
of the rear point of the erosion event. Erosion protection is required to extend from the rear boundary, or
rear of the residence, at least 10 m westward along the north and south boundaries, tapering from 3 m deep
at the eastern side.
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.
It should be noted that the above specifications are indicative of similar micro-pile and grout curtain designs
used for slope stabilisation projects and detailed design will be required by the piling contractor.
General geotechnical recommendations for site development are provided in the following sections.
6.1 Earthworks
Provided drawings indicate that excavations in the order of about 3.5 m deep (to the western boundary) will
be required, with filling anticipated to be for landscaping only less than 0.5 m high. Should proposed
cuts/fills exceed these quantities, Tectonic must assess the impacts on slope stability before construction.
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 or uncontrolled fill should then be stripped and set aside. Based on the boreholes and
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site observations, stripping depths to remove existing root affected soils and uncontrolled fill (e.g. where the
road embankment impacts the building envelope to the western boundary) should generally range between
about 0.2 m and 0.5 m deep; however, deeper areas of unsuitable materials may be present across the site.
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, such as underground services, or the
stairs along the northern boundary. 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. Our preliminary recommendation would be that allowance is made for
equipment and works such that the peak particle velocity does not exceed 10 mm/s, where measured at the
property boundary.
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, will 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 (as was the maximum natural slope present above the main high dune face, around 22°).
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.
It is likely that the above temporary batter slopes will not be able to be achieved at least along the western
boundary, due to spatial restraints, and so temporary shoring may be required (e.g. sheet piles) as per the
recommendations in Section 6.3 below. Excavations in close proximity to existing structures and
infrastructure (e.g. sewer main along the western boundary), including on neighbouring properties, will need
to be specifically designed to prevent undermining. It is recommended that footing exposures or
confirmation of existing foundations via certified building plans be undertaken to assess the possibility of
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).
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6.1.3 Filling
The natural sandy soils where free of deleterious materials (e.g. vegetation, excessive rootlets/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 classifications for footing design are determined in accordance with AS 2870-2011 Residential Slabs and
Footings, and depend on the depth of cut / fill undertaken at a site, variations in the natural soil/rock depths,
and the reactivity of the in situ soil / rock and any imported fill materials.
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,
uncontrolled fill 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.
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 to 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 RPEQ geotechnical engineer. High-level footings, so founded, could be
designed using a maximum allowable bearing pressure of 100 kPa.
Elsewhere (excluding pile wall), based on the results of the investigation, pile founding depths of about 2.5 m
to 3 m BGL (existing ground levels) are anticipated. Deeper pile depths may be necessary subject to
assessment of building loads at the detailed design stage.
Steel screw piles are considered to be a suitable foundation option. Piles so founded may be designed using
an allowable end bearing pressure of 1 MPa. 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
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piles are not anticipated to be suitable for this site. A suitable alternative to screw piles could be grout-
injected, CFA piles, provided that construction water loss is carefully monitored and controlled. Steel
reinforced concrete bore 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 12. 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 12, with the relevant plane taken from the
equivalent ground level at the front of the exposed micropiled wall following the most onerous
erosion case in the stability modelling (Ref. Section 5.2.1).
Text Figure 12: Footing depth required to prevent undermining
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Site drainage should be designed to readily remove surface water and to prevent ponding of water on
subgrade areas during construction and also adjacent to foundations and perimeter slabs once construction
is completed.
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 (depending on foundation methodologies).
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) and, given that the
planned excavation extends close to some of the site boundaries and underground infrastructure (e.g.
underground services), and will interact with the existing road embankment alongside Seaview Terrace,
some form of temporary shoring will likely 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). However, the proximity to neighbouring properties and 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.
Other shoring methods that could be considered include bored contiguous or secant piles. 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.
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.
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 overleaf. These values do not
include allowance for hydrostatic pressures, backslopes (assumed to be horizontal), nor transient (e.g.
construction) or adjacent footing loadings.
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Table 6: Retaining Structure Design Parameters
Lateral earth pressure coefficients
Unit
Friction
Retained material weight
angle (°) Ka Ko
(t/m3) Kp
(Cantilever wall) (Non-yielding wall)
Very Loose/ Loose
1.8 27 0.36 0.53 2.77
Sands
Medium Dense Sands 1.9 34 0.28 0.44 3.54
Dense (or Denser)
1.9 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.
All collected roof water should be directed by pipes to the council stormwater system along Seaview
Terrace (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 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 be allowed to develop.
Design of the stormwater system should be undertaken by a suitably qualified and experienced RPEQ.
28 April 2022
Report No. 21370-001-Rev1 20
Page 27
PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
7.0 CONCLUSION
Based on the findings of our assessment it is assessed that there would be a Low Risk of slope instability
affecting the proposed development subject to implementation of the recommendations given in this report.
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.
28 April 2022
Report No. 21370-001-Rev1 21
Page 28
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
Subject site 66 SEAVIEW TERRACE,
SUNSHINE BEACH
DCP3
A BH3
TITLE:
SITE PLAN
BH1 DCP4
BH2
CLIENT:
CATHERINE & GAVIN DEANE
A’
DRAWN: DATE:
RKG 5/11/2021
CHECKED: DATE:
ACD 9/11/2021
SCALE:
AS SHOWN
Sunshine Beach
LEGEND:
APPROX. MACHINE BOREHOLE
LOCATION
APPROX. HAND AUGER
LOCATION
APPROX. STAND-ALONE DCP
0 20 40 m LOCATION
SECTION A-A’ (REF. FIGURE 2)
PROJECT NO.: FIGURE: REV:
Notes
1. Base image courtesy Near Map (10 September 2021) 21370 1 0
Page 29
TECTONIC 3.00.2 LIB.GLB Fence FENCE A4L 21370.GPJ 21370 FIGURE 2.GDW 5/11/2021 11:58 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
0 10 20 30 40 50 60 70 80
Seaview Terrace Approx. Proposed Building Area
DCP3
BH3
(-2 m)
(4 m)
L
1.9 N=12
BH1
N=18
30 MD
30
N=35
(-4 m)
N=44 L
D
N=45 MD
25 N=54
25
D
DCP4
N=R
N=54 6.0
20 N=R
(5 m) 20
ELEVATION (m AHD)
N=R
Indicative Ground Surface
N=53
N=52 2.7
15 15
N=R VD
N=R
10 N=R 10
BH2
Sunshine Beach
(-3 m)
5 VL to L 5
L
H MD
N=49
3.0
31.5
0 0
-5 -5
-10 -10
0 10 20 30 40 50 60 70 80
DISTANCE (m)
MATERIAL GRAPHIC TITLE DRAWN DATE
SAND RG 5/11/2021
Catherine & Gavin Deane C/- Pivotal Perspective CHECKED DATE
Silty SAND
66 Seaview Terrace, Sunshine Beach ACD 5/11/2021
SCALE
Indurated Sand
Proposed Residence H 1:400 V 1:400 A4
Sandy CLAY Subsurface Section A-A' PROJECT No FIGURE No
21370 2
Page 30
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
66 SEAVIEW TERRACE,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 1
CLIENT:
CATHERINE & GAVIN DEANE
DRAWN: DATE:
RKG 28/04/2022
CHECKED: DATE:
ACD 28/04/2022
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
Notes
1. For soil parameters Ref. Table 4 in report 21370 3 1
Page 31
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
66 SEAVIEW TERRACE,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 2
CLIENT:
CATHERINE & GAVIN DEANE
DRAWN: DATE:
RKG 28/04/2022
CHECKED: DATE:
ACD 28/04/2022
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
Notes
1. For soil parameters Ref. Table 4 in report 21370 4 1
Page 32
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
66 SEAVIEW TERRACE,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 3
CLIENT:
CATHERINE & GAVIN DEANE
DRAWN: DATE:
RKG 28/04/2022
CHECKED: DATE:
ACD 28/04/2022
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
Notes
1. For soil parameters Ref. Table 4 in report 21370 5 1
Page 33
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
66 SEAVIEW TERRACE,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 4
CLIENT:
CATHERINE & GAVIN DEANE
Reprofiled slope to 28°
DRAWN: DATE:
RKG 28/04/2022
CHECKED: DATE:
ACD 28/04/2022
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
Notes
1. For soil parameters Ref. Table 4 in report 21370 6 1
Page 34
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Office: 07 5478 9016
Email: [email protected]
PROJECT:
GEOTECHNICAL INVESTIGATION
66 SEAVIEW TERRACE,
SUNSHINE BEACH
TITLE:
SLOPE/W OUTPUT – CASE 5
CLIENT:
CATHERINE & GAVIN DEANE
Reprofiled slope to 28°
DRAWN: DATE:
RKG 28/04/2022
CHECKED: DATE:
ACD 28/04/2022
SCALE:
AS SHOWN
LEGEND:
PROJECT NO.: FIGURE: REV:
Notes
1. For soil parameters Ref. Table 4 in report 21370 7 1
Page 35
PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
APPENDIX A
Borehole & DCP Reports and Explanatory Notes
28 April 2022
Report No. 21370-001-Rev1
Page 36
Borehole No.
BH1
Page 1 of 1
Engineering Log - Borehole Project No.: 21370
Client: Catherine & Gavin Deane C/- Pivotal Perspective Commenced: 15/9/2021
Project Name: Proposed Residence Completed: 15/9/2021
Hole Location: 66 Seaview Terrace, Sunshine Beach Logged By: RKG
Hole Position: 511363.0 m E 7080300.0 m N MGA2020 Zone 56 Checked By: ACD
Drill Model and Mounting: Hand Auger Inclination: -90° RL Surface: 28.00 m
Hole Diameter: 100 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 (AS 1289.6.3.2-1997)
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 grained, brown grey, trace of rootlets
DS (DUNE SANDS)
0.2-1.0m SW
SAND, fine to medium grained, grey D L
26.0
Not Encountered
2
MD
becoming brown grey and pale brown grey
HA
M
24.0
4
D
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 21370.GPJ <<DrawingFile>> 5/11/2021 11:26 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
22.0
6
Hole Terminated at 6.00 m
Target depth
20.0
8
18.0
10
16.0
12
14.0
14
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 37
Borehole No.
BH2
Page 1 of 1
Engineering Log - Borehole Project No.: 21370
Client: Catherine & Gavin Deane C/- Pivotal Perspective Commenced: 15/9/2021
Project Name: Proposed Residence Completed: 15/9/2021
Hole Location: 66 Seaview Terrace, Sunshine Beach Logged By: RKG
Hole Position: 511410.0 m E 7080282.0 m N MGA2020 Zone 56 Checked By: ACD
Drill Model and Mounting: Hand Auger Inclination: -90° RL Surface: 5.00 m
Hole Diameter: 100 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 (AS 1289.6.3.2-1997)
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
HW
SM Silty SAND, fine grained, brown (DUNE SANDS) D to VL to HW
SP SAND, fine grained, brown grey and pale brown M L HW
DS grey
0.7-1.5m becoming brown grey and black, with micaceous M L
grains
HA
3.0
2 becoming fine to medium grained, orange brown
Seepage at 1.95 m during drilling
SM and pale orange brown MD
W
Silty SAND, fine to medium grained, orange
brown and pale orange brown Augered to 3.0m
Hole Terminated at 3.00 m
Target depth
1.0
4
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 21370.GPJ <<DrawingFile>> 5/11/2021 11:27 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
-1.0
6
-3.0
8
-5.0
10
-7.0
12
-9.0
14
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 38
Borehole No.
BH3
Page 1 of 2
Engineering Log - Borehole Project No.: 21370
Client: Catherine & Gavin Deane C/- Pivotal Perspective Commenced: 8/10/2021
Project Name: Proposed Residence Completed: 8/10/2021
Hole Location: 66 Seaview Terrace, Sunshine Beach Logged By: RKG
Hole Position: 511351.0 m E 7080314.0 m N MGA2020 Zone 56 Checked By: ACD
Drill Model and Mounting: Hydrapower scout Inclination: -90° RL Surface: 33.00 m
Hole Diameter: 100 mm Bearing: 360° Datum: AHD Operator: Drillsure
Drilling Information Material Description and Observations
Relative Density
Classification
Pocket Shear
Penetration
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Recovery
Condition
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
Remarks secondary and minor components, colour Observations
Water
RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100 150200
SM Silty SAND, fine grained, pale brown grey 0.00: DUNE SANDS
D to
L
M
SPT
AD/T
4,5,7 SP SAND, fine grained, pale grey, trace of silt
N=12
31.0
2
SPT becoming fine to medium grained sand MD
5,7,11
N=18
29.0
4
SPT
9,15,20 SP SAND, fine to medium grained, pale grey, with
N=35 minor grey mottling, poorly graded (fine <
medium)
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 21370.GPJ <<DrawingFile>> 5/11/2021 11:27 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
SPT
8,17,27
27.0
6
N=44
D
Not Observed
SPT occasionally tending to pale brown grey
10,19,26
N=45
25.0
8
SPT M
10,25,29
N=54
RD
SP SAND, fine to medium grained, pale orange
brown, trace of silt, poorly graded (fine >
23.0
10 medium), with occasional weakly cemented, very
SPT thin dark orange brown indurated lenses
15,24,30/100mm
N*>60
SP SAND, fine grained, orange brown, with silt,
occasional dark orange brown, very thin lenses
SPT
13,24,30
21.0
12
N=54 SM Silty SAND, fine grained, dark orange brown,
indurated, very weakly cemented to no
cementation VD
SPT
13,30/150mm
N*>60
19.0
14
SPT
19,30/100mm
N*>60
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 39
Borehole No.
BH3
Page 2 of 2
Engineering Log - Borehole Project No.: 21370
Client: Catherine & Gavin Deane C/- Pivotal Perspective Commenced: 8/10/2021
Project Name: Proposed Residence Completed: 8/10/2021
Hole Location: 66 Seaview Terrace, Sunshine Beach Logged By: RKG
Hole Position: 511351.0 m E 7080314.0 m N MGA2020 Zone 56 Checked By: ACD
Drill Model and Mounting: Hydrapower scout Inclination: -90° RL Surface: 33.00 m
Hole Diameter: 100 mm Bearing: 360° Datum: AHD Operator: Drillsure
Drilling Information Material Description and Observations
Relative Density
Classification
Pocket Shear
Penetration
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Recovery
Condition
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
Remarks secondary and minor components, colour Observations
Water
RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100 150200
SPT SP SAND, fine grained, pale brown, with silt
13,23,30
N=53
SPT
11,22,30
15.0
18
N=52
SPT SP SAND, fine to medium grained, yellow brown,
13,30 poorly graded (fine > medium)
N=R
13.0
20
becoming pale orange brown, with occasional
very thin, brown lenses
SPT
13,25,30/130mm
N*>60
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 21370.GPJ <<DrawingFile>> 5/11/2021 11:27 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
11.0
22
VD
Not Observed
SPT SM Silty SAND, fine to medium grained, dark grey to
13,21,30/130mm dark grey brown, partially indurated, very weakly
N*>60 cemented M
RD
9.0
24
7.0
26
5.0
28
CI to Sandy CLAY, medium to high plasticity, pale grey 29.60: RESIDUAL
3.0
30 CH mottled yellow brown and orange brown, fine to
medium grained sand
H
SPT remnant rock texture visible 31.00: Grading to
450
12,22,27 EXTREMELY
N=49 Hole Terminated at 31.45 m 590 WEATHERED MATERIAL
Target depth
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 40
CLIENT : Catherine & Gavin Deane C/- Pivotal Perspective SHEET : 1 OF 1
CONTRACTOR : Tectonic
PROJECT : Proposed Residence
LOCATION : 66 Seaview Terrace, Sunshine Beach
PROJECT No. : 21370
TEST: DCP3 TEST: DCP4
LOGGED: RKG 15/9/2021 CHECKED: ACD LOGGED: RKG 15/9/2021 CHECKED: ACD
22/9/2021 22/9/2021
EASTING: 511344.0 m NORTHING: 7080311.0 m EASTING: 511390.0 m NORTHING: 7080299.0 m
Depth (m)
Depth (m)
MGA2020 Zone 56 MGA2020 Zone 56
GROUND
BlowsRL:
per19.00 m AHD
100 mm (AS 1289.6.3.2-1997) GROUND
BlowsRL:
per34.50 m AHD
100 mm (AS 1289.6.3.2-1997)
0 5 10 15 20 25 0 5 10 15 20 25
HW HW
HW HW
HW HW
HW
1 1
2 2
20/90mm
Refusal
TECTONIC 3.00.2 LIB.GLB Log IS DCP 3 PER PAGE 21370.GPJ <<DrawingFile>> 5/11/2021 11:21 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
3 3
4 4
5 5
6 6
Comments Comments
Page 41
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 42
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 43
PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
APPENDIX B
Geotechnical Laboratory Test Certificates
28 April 2022
Report No. 21370-001-Rev1
Page 44
Particle Size Distribution Report
Client : Tectonic Geotechnical Report Number: YA-873 - 1/1
Address : PO Box 899 Buderim, Buderim , QLD, 4556 Report Date : 24/09/2021
Project Name : 66 Seaview Tce Order Number :
Project Number : YA-873 Test Method : AS1289.3.6.1
Location: Seaview Tce Page 1 of 1
Sample Number : S21-2749 SAMPLE LOCATION
Sampling Method : AS1289.1.2.1 Clause 6.5.3 BH1
Sampled By : Client 0.2 - 1.0m
Date Sampled : 15/09/2021 DS
Date Tested : 23/09/2021 Sample Description
Material Type : Existing Material Test Number : BH1
Material Source : Insitu Lot Number :
Remarks : Specification Number :
AS Sieve Percent Specification
Size(mm) Passing Limits
100
75
63
53
37.5
26.5
19.0
16.0
13.2
9.5
6.7
4.75
2.36
1.18 100
0.600 100
0.425 95
0.300 67
0.150 5
0.075 3
APPROVED SIGNATORY
Accredited for compliance with ISO/IEC 17025 - Testing
The results of the tests, calibrations and / or measurements
included in this document are traceable to Australian / National
Standards.
Chris Davidson - Laboratory Coordinator
This report shall not be reproduced except in full without
NATA Accreditation Number
approval of the laboratory providing assurance that parts of a
report are not taken out of context. 19751
Document Code RF141-6
Page 45
Particle Size Distribution Report
Client : Tectonic Geotechnical Report Number: YA-873 - 2/1
Address : PO Box 899 Buderim, Buderim , QLD, 4556 Report Date : 24/09/2021
Project Name : 66 Seaview Tce Order Number :
Project Number : YA-873 Test Method : AS1289.3.6.1
Location: Seaview Tce Page 1 of 1
Sample Number : S21-2750 SAMPLE LOCATION
Sampling Method : AS1289.1.2.1 Clause 6.5.3 BH2
Sampled By : Client 0.7 - 1.5m
Date Sampled : 15/09/2021 DS
Date Tested : 23/09/2021 Sample Description
Material Type : Existing Material Test Number : BH2
Material Source : Insitu Lot Number :
Remarks : Specification Number :
AS Sieve Percent Specification
Size(mm) Passing Limits
100
75
63
53
37.5
26.5
19.0
16.0
13.2
9.5
6.7
4.75
2.36 100
1.18 100
0.600 99
0.425 96
0.300 84
0.150 12
0.075 1
APPROVED SIGNATORY
Accredited for compliance with ISO/IEC 17025 - Testing
The results of the tests, calibrations and / or measurements
included in this document are traceable to Australian / National
Standards.
Chris Davidson - Laboratory Coordinator
This report shall not be reproduced except in full without
NATA Accreditation Number
approval of the laboratory providing assurance that parts of a
report are not taken out of context. 19751
Document Code RF141-6
Page 46
PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
APPENDIX C
AGS Guidelines - Qualitative Terminology for Use in
Assessing Risk to Property
Some Guidelines for Hillside Construction
28 April 2022
Report No. 21370-001-Rev1
Page 47
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
Form No. 68039
68039 RL2Risk
Landslide August 2010
Management Issued 10/7/07
Page 48
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
Form No. Landslide
68039 68039 RL2Risk
August 2010
Management Issued 10/7/07
Page 49
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
Form No. 68029 RL2 August 2010
Page 50
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
114 Australian Geomechanics Vol 42 No 1 March 2007
Form No. 68029 RL2 August 2010
Page 51
PROPOSED RESIDENCE
66 SEAVIEW TERRACE, SUNSHINE BEACH
APPENDIX D
Limitations
28 April 2022
Report No. 21370-001-Rev1
Page 52
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)