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REFERENCE DOCUMENTS
MCU24/0153 & OPW24/0202
NOOSA COUNCIL
15 DECEMBER 2025
Proposed Unit Development
51 Elanda Street, Sunshine Beach
Proposed Unit Development 30 September 2024 | Ref. 24265-001-Rev0
30 September 2024 | 24265-001-Rev0 i
Document Set ID: 23376055
Version: 1, Version Date: 28/11/2024
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Full text of pages 2 to 48 (of 57)
Page 2
Document Review
Doc No. Revision Prepared By Reviewed By Date Issued
001 0 Ben Cole Geoff Hurley 30 September 2024
Doc No. Revision Method of Delivery Issued To
001 0 Electronic Martin Smith ([email protected])
Prepared By Reviewed By
Ben Cole Geoff Hurley BSc (Hons) MSc DIC C.Geol RPEQ 5716
Undergraduate Geotechnical Engineer Senior Consultant
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Executive Summary
This report details the results of a geotechnical investigation undertaken for a proposed unit
development at 51 Elanda Street, Sunshine Beach. The investigation comprised drilling of boreholes at
four locations across accessible areas of the development footprint. This report summarises the results
of the investigation and provides geotechnical recommendations regarding earthworks and footings,
together with temporary and permanent basement retention.
Architectural design drawings provided indicate that the development will comprise a three-storey
building, over a single level basement carpark. Excavations will be in the order of up to 7 m deep and
localised filling less than 1 m high is anticipated. Excavations are expected to extend close to the site
boundaries and therefore, some form of temporary retention will be required.
The subsurface conditions encountered in the boreholes are summarised as follows:
▪ Topsoil – comprising loose silty sand to depths of 0.1 m to 0.2 m below ground level (BGL); then
▪ Fill – comprising loose silty sand to depths of between 0.4 m and 1.3 m BGL; then
▪ Natural Sands – comprising poorly graded sands mostly being loose to depths of between 1.4 m
and 2.6 m BGL; then becoming medium dense and increasing to dense below depths of about
2.8 to 3.8 m BGL.
No signs of groundwater seepage (‘springs’) were observed during our walk-over. Groundwater was not
encountered in the boreholes at the time of investigation.
Provided the recommendations within this report are adhered to, and subject to detailed design and
construction of the footing and retention system by a suitably qualified and experienced RPEQ structural
engineer, there should be a Low Risk to property from slope instability.
Excavations through the existing soils should be achievable using conventional earthmoving plant (e.g.
small or larger excavators with toothed buckets). Temporary unsurcharged cuts could be formed at
1V:2H in the very loose to loose sands, and at 1V:1H in medium dense (or denser) sand, for batters up to
3 m in height, provided groundwater seepage is not encountered and sands do not slough from the
batter face as they dry out. It is expected that space restrictions will limit battering of temporary cuts on
the site and so some form of temporary retention system, such as sheet piles or contiguous reinforced
concrete piles, will be required. These retention systems, which may have to be temporarily braced during
construction, may also be designed to form the permanent basement walls.
Footings for the proposed development and any ancillary structures (e.g. retaining walls) must penetrate
through any fill materials and unsuitable natural soils (i.e. very loose to loose sands) to found at least
0.5 m into medium dense (or denser) natural sands. Such materials were encountered in the boreholes
below depths of between about 1.4 m and 2.6 m BGL (existing ground levels). High-level footings would
be suitable in excavation areas where medium dense (or denser) natural sands are exposed at the
subgrade level. Piled footings would be required unless excavations expose such materials at or near
foundation subgrade level. Given the sandy soil profile, where deepened footings are required, steel
screw piles are considered to be a suitable foundation type. Due to the presence of loose sands,
together with the close proximity of adjacent buildings, open bored piers or driven piles are not
considered to be suitable for this site. Cast in place continuous flight auger (CFA) piles may also be
suitable for both foundation and shoring piles provided a small rig capable of traversing the site can be
sourced.
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Contents
Executive Summary.........................................................................................................................................................iii
1. Introduction ............................................................................................................................................................ 1
2. Proposed Development ....................................................................................................................................... 1
3. Method of Investigation ......................................................................................................................................2
4. Results of Investigation .......................................................................................................................................2
4.1 Site Description ......................................................................................................................................................... 2
4.2 Topography................................................................................................................................................................. 4
4.3 Geology ........................................................................................................................................................................ 5
4.4 Subsurface Conditions ............................................................................................................................................ 6
4.5 Groundwater............................................................................................................................................................... 7
4.6 Surface Drainage....................................................................................................................................................... 7
5. Slope Stability Assessment .................................................................................................................................8
5.1 Existing Conditions................................................................................................................................................... 8
5.2 Stability Assessment ................................................................................................................................................ 9
6. Geotechnical Recommendations ..................................................................................................................... 11
6.1 Development Limitations..................................................................................................................................... 11
6.2 Earthworks ................................................................................................................................................................. 11
6.2.1 Site Preparation and Trafficability................................................................................................... 11
6.2.2 Excavations .............................................................................................................................................. 12
6.2.3 Filling ......................................................................................................................................................... 12
6.3 Building Foundations ............................................................................................................................................ 13
6.3.1 Indicative Site Classification .............................................................................................................. 13
6.3.2 Footing Design....................................................................................................................................... 13
6.4 Temporary and Permanent Retention ............................................................................................................ 15
6.5 Drainage ..................................................................................................................................................................... 16
7. Conclusion ............................................................................................................................................................. 17
8. limitations .............................................................................................................................................................. 17
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Appendices
Appendix A Borehole Reports and Explanatory Notes
Appendix B AGS Guidlines - Qualitative Terminology for Use in Assesing the Risk to Property Some
Guidelines for Hillside Construction
Appendix C Limitations
Text Figures
Text Figure 1: South elevation plan (courtesy Archend).................................................................................................... 1
Text Figure 2: 2023 aerial image of the site and immediate surrounds (courtesy Nearmap imagery) ........... 3
Text Figure 3: Easterly facing view of the site driveway and adjacent alleyway from Elanda Street ................ 3
Text Figure 4: Concrete block retaining wall (LHS) and beam cracking (RHS) at north of site ........................... 4
Text Figure 5: Concrete block wall supporting internal basement undercroft (LHS) and cracking
observed in retaining wall (RHS) along southern boundary ................................................................................ 4
Text Figure 6: Plan showing ground surface contours (courtesy Noosa Council ‘Intramaps’) ........................... 5
Text Figure 7: Extract of 1:100,000 Laguna Bay Surface Geology Map ........................................................................ 5
Text Figure 8: Extract from NC landslide hazard overlay mapping ............................................................................... 8
Text Figure 9: Footing depth required to prevent undermining ................................................................................. 15
Figures
Figure 1: Site Plan
Tables
Table 1: Summary of Subsurface Conditions........................................................................................................................ 6
Table 2: Stability Risk Levels ........................................................................................................................................................ 9
Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007) ............................................................... 10
Table 4: Retaining Structure Design Parameters............................................................................................................... 16
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1. Introduction
This report details the results of a geotechnical investigation undertaken for a proposed unit
development at 51 Elanda Street, Sunshine Beach. The investigation was performed by Tectonic for
Archend, generally in accordance with Proposal P24478-Rev0, dated 9 August 2024.
The investigation comprised drilling of boreholes at four locations across accessible areas of the
development footprint. This report summarises the results of the investigation and provides
geotechnical recommendations regarding earthworks and footings, together with advice for temporary
and permanent basement retention.
In summary, subject to the implementation of the recommendations made herein, it is assessed that
there would be a Low Risk of slope instability affecting the proposed development in accordance with
the Australian Geomechanics Society Guidelines for Landslide Risk Management, dated March 2007 (AGS
2007).
2. Proposed Development
Design details provided to us indicate that the development will comprise a three-storey building, over a
basement carpark covering most of the site. The construction will include a combination of masonry
walls and reinforced concrete floors with various architectural finishes to the walls. Excavations for the
development will be in the order of up to 7 m deep in the upslope area adjacent to Elanda Street with
the basement level shallowing to about 2 m to 3 m deep downslope to the east. Localised filling less
than 1 m high is anticipated. Excavations are expected to extend close to the site boundaries and
therefore, some form of temporary retention will be required. Isolated deeper excavations may be
required for the lift overrun pit and other elements.
Extract from the design drawings provided by Archend are provided below in Text Figure 1.
Text Figure 1: South elevation plan (courtesy Archend)
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3. Method of Investigation
As part of our assessment, a desk-top study was carried out comprising a review of published geological
maps, slope stability studies as well as Noosa Council (NC) planning overlays and site information.
An experienced geotechnical engineer from Tectonic undertook a site walk-over on 6 September 2024 to
visually assess any indicators of past slope instability. The walk-over included assessment of soil
exposures, surface drainage conditions, topography, evidence of erosion or past instability, and
vegetation coverage/condition.
This was followed by a subsurface investigation comprising the drilling of four boreholes (designated
BH1 to BH4) in accessible areas across the site. Borehole BH1 was drilled on the existing driveway
toward the western boundary of the site using Tectonic’s 4WD mounted solid flight auger rig to a depth
of 8 m below ground level (BGL). Due to access restrictions boreholes BH2 to BH4 were drilled using
hand augering techniques to 3 m BGL to the north, east and south of the site. A further two boreholes,
designated BH2A and BH2B were drilled to a depth of 1 m BGL to attempt to delineate rubbish
encountered in the area during a previous soil test by another firm.
In-situ testing, using the dynamic cone penetrometer (DCP) method, was carried out from the ground
surface and within each borehole. DCP testing was extended below the base of the hand augered
boreholes to depths between 4.5 m and 6.0 m BGL. Boreholes were backfilled on completion with
drilling spoil, with excess material slightly mounded at surface.
Laboratory classification testing was not warranted due to the sandy nature of the subsurface conditions
encountered.
Borehole locations are shown in Figure 1 attached at the end of this report, with borehole and DCP logs
presented in Appendix A, together with explanatory notes. Subsurface conditions are discussed in
Section 4.4. Borehole coordinates were recorded using a handheld global positioning system (GPS).
The results of the desk-top study and walk-over survey are included in Section 4 below.
4. Results of Investigation
4.1 Site Description
The site is formally described as Lot 403 RP48112, covering an area of 755 m2, with frontage to Elanda
Street to the west. At the time of the investigation a two-storey residential building occupied most of
the western part of the site. The building was surrounded by at-grade concrete pathways and slabs with
some garden spaces. Neighbouring properties consisted of two to three storey residential unit buildings
to the north, east and south. An alleyway and drainage easement along the southern boundary provided
pedestrian access between Elanda Street and Henderson Street to the east and also accommodated
hydraulic services including stormwater and sewer mains.
Inferred cut and fill earthworks had taken place across the site and adjacent areas. The site had been
levelled with cut to fill earthworks up to about 2 m high supported by retaining walls along the northern
and southern boundaries. Cut to fill estimated to be up to about 1 m was observed to form retained
garden terraces.
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Cut and fill embankments were retained by the existing building as well as concrete block retaining walls
ranging in heights of less than 0.5 m to 2.1 m high. Cracking was observed in some retaining walls on the
property, appearing to likely be related to age and poor construction. A rendered concrete block
retaining wall was observed on the northern neighbouring property, increasing up to 2.2 m to form the
entrance of a basement carpark below that building. Other observable walls of neighbouring properties
appeared to be in relatively good structural condition, based on an external assessment.
Significant cracking was observed on a concrete beam at the north-eastern corner of the residence.
Minor cracking was observed in the concrete slab surrounding the building which appeared to be related
to age, poor construction and possibly consolidation of the upper loose sands.
A 2021 aerial image of the site and surrounds is shown in Text Figure 2 overleaf.
Subject Site
Text Figure 2: 2023 aerial image of the site and immediate surrounds (courtesy Nearmap imagery)
Site conditions at the time of our investigation are shown below and overleaf in Text Figures 3 to 5.
3°
Text Figure 3: Easterly facing view of the site driveway and adjacent alleyway from Elanda Street
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Cracking in beam
Text Figure 4: Concrete block retaining wall (LHS) and beam cracking (RHS) at north of site
Cracking in retaining wall
2.1 m
Text Figure 5: Concrete block wall supporting internal basement undercroft (LHS) and cracking
observed in retaining wall (RHS) along southern boundary
4.2 Topography
As illustrated in Text Figure 6 overleaf, the site is located on the easterly facing flank of an ancient sand
dune which crests about 120 m to the north-west. During the site walk-over, topographic features
specific to the site were noted, and ground slopes were recorded using a hand-held clinometer.
The natural surface profile had been interrupted by historic landscaping and residential construction;
with inferred less altered ground slopes along the alleyway bordering the southern site boundary from
Elanda Street to Henderson Street. Much of the eastern part of the site appeared to be uninterrupted by
historic landscaping. The inferred natural slopes in the area measured at the time of our assessment
ranged from about 3° to the west, up to about 15° to the east. Based on our observations it appeared
that cut and fill earthworks had been undertaken across the site, resulting in a generally flat building
platform and a terraced lawn and garden areas supported by various retaining walls, as discussed in
above in Section 4.1.
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Generally, no irregular surface features were noted which would indicate global slope instability.
Subject Site
Text Figure 6: Plan showing ground surface contours (courtesy Noosa Council ‘Intramaps’)
4.3 Geology
Available geological information1 indicates that the site is underlain by Pleistocene age parabolic sand
dunes comprising “quartz sand” (Ref: Text Figure 7).
Approx. Site Location
Text Figure 7: Extract of 1:100,000 Laguna Bay Surface Geology Map
1
Queensland Government, Department of Mines and Energy, 1:100,000 Laguna Bay Surface Geology Map, Sheet 9545, 11 July 2018
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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. The subsurface conditions encountered in the boreholes are
summarised as follows:
▪ Topsoil – comprising loose silty sand to depths of 0.1 m to 0.2 m below ground level (BGL); then
▪ Fill – comprising loose silty sand to depths of between 0.4 m and 0.1.3 m BGL; then
▪ Natural Sands – comprising poorly graded sands mostly being loose to depths of between 1.4 m
and 2.6 m BGL; then becoming medium dense and increasing to dense below depths of about
2.8 to 3.8 m BGL.
Table 1 below summarises the subsurface profile in each borehole.
Table 1: Summary of Subsurface Conditions
Medium Dense (or
Borehole No. Topsoil Fill Loose Sands
Dense Sands denser) Sands
0.0 – 0.2 0.2 – 0.4 0.4 – 1.5 1.5 – 2.8 2.8 – 8.0TD
BH1
0.0 – 0.1 0.1 – 0.4 0.4 – 1.4 1.4 – 3.0TD 3.3* – 4.7DCP
BH2
0.0 – 0.1 0.1 – 1.3 1.3 – 2.6 2.6 – 3.0 TD 3.7* – 4.8DCP
BH3
BH4 0.0 – 0.1 - 0.1 – 1.7 1.7 – 3.0TD 3.8 – 4.8TD
Notes: 1. Depths noted in m BGL at time of investigation (22 February 2022)
2. NE denotes not encountered
3. TD denotes borehole terminated at target depth
4. * inferred from DCP testing
5. DCP denotes DCP termination depth
A site classification ‘soil test’ report by Australian Soil Investigations (ASI) (Ref. Report No. 230154(S),
dated 12 June 2023) comprised the drilling of two boreholes (designated BH1 and BH2) in accessible
locations to the east of the property. Rubbish was noted by ASI in BH2 at a depth of 0.7 m BGL. Three
boreholes (designated BH2, BH2A and BH2B) were drilled by Tectonic in this area to delineate the extent
of this rubbish, however, no deleterious material was encountered at those locations.
ASI has classified the site as Class P, as per AS2870, due to poor bearing capacity and fill; however, has
stated that the site would have the shrink-swell characteristics of a Class S site.
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4.5 Groundwater
No signs of groundwater seepage (‘springs’) were observed during our walk-over. Groundwater was not
encountered in the boreholes at the time of investigation.
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 Surface Drainage
Surface drainage would be expected to follow natural surface contours to the east, draining into
stormwater infrastructure at the east of the property and towards the Henderson Street roadside
drainage system. It is noted that the site has a relatively large catchment; however, most runoff from
upslope of the property is anticipated to be intercepted by the existing stormwater infrastructure
associated with the neighbouring structures and roadside drainage systems along Elanda Street.
Given the sandy nature of the site, rainfall would normally be anticipated to infiltrate the ground surface.
However, as the proposed development will occupy a large part of the block, significant run-off from
hard surfaces will 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 during our assessment (e.g. deep rilling or scour/wash
out scars). This indicates that significant overland flow is generally absent during rainfall events.
Recommendations to improve surface drainage as part of the development works are provided in
Section 6.5.
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5. Slope Stability Assessment
5.1 Existing Conditions
The Noosa Planning Scheme 2020 includes a landslide hazard overlay map (Ref. extract in Text Figure 8).
Mapping indicates that part of the site is within a Moderate (pale yellow shading) Landslide Hazard Area.
Lot boundary
Text Figure 8: Extract from NC landslide hazard overlay mapping
It should be noted that the Noosa landslide hazard map is a broad-scale indication of the potential
landslide susceptibility and is superseded by this site-specific assessment. Our observations of surface
features relevant to this slope stability assessment are summarised as follows:
The existing residence and some retaining walls were noted to be cracked in some places however this
distress was inferred to be associated with poor construction or consolidation of upper loose sands as
opposed to global instability.
No indicators of recent global slope instability were observed, i.e. no landslide scarps or ‘hummocky’
ground was evident across the proposed building area.
No signs of groundwater seepage ‘springs’ were observed across the proposed development area.
Overall inferred natural ground slopes were relatively moderate.
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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 and the
Qualitative Terminology for Use in Assessing Risk to Property is also attached in Appendix B.
Table 2: Stability Risk Levels
Risk Level Example Implications(1)
V Very High Unacceptable without treatment. Extensive detailed investigation and research,
H Risk planning and implementation of treatment options essential to reduce risk to Low;
may be too expensive and not practical. Work likely to cost more than value of
property.
H High Risk Unacceptable without treatment. Detailed investigation, planning and
implementation of treatment options required to reduce risk to Low. Work would
cost a substantial sum in relation to the value of the property.
M Moderate May be tolerated in certain circumstances (subject to regulators’ approval) but
Risk requires investigation, planning and implementation of treatment options to reduce
risk to Low. Treatment options to reduce to Low risk should be implemented as soon
as practicable.
L Low Risk Usually acceptable to regulators. Where treatment has been required to reduce the
risk to this level, ongoing maintenance required.
VL Very Low 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.
Given the geology, topography and particularly the relatively moderately sloping terrain across the
proposed development area, it is considered rare that a landslide could affect the proposed development.
Sand dune slopes are generally close to the ‘limit of equilibrium’ where the surface gradient is about 30°,
although possibly lower in the order of 26˚ to 28˚ for very loose sands. The limit of equilibrium is the
‘tipping point’ to instability, where the factor of safety (FOS) of the slope is approximately 1.0. The FOS of
a slope is the balance (ratio) between the forces driving instability (e.g. soil weight, groundwater pressure)
and the resisting forces (e.g. soil friction and cohesion). Inferred natural slopes around this site are
between 3° and 15°.
Considering the existing site conditions (Ref. Section 2), and subject to the implementation of
recommendations given below, it is assessed that there would be a Low (L) Risk of global slope instability
affecting the proposed development. Regulators (NC) normally require that a Very Low or Low Risk of
landslide affecting the property must be demonstrated to enable development approval. Summarised in
Table 3 overleaf is our qualitative assessment of landslide risk for the development site. A summary of
qualitative terminology for use in assessing risk to property is attached (taken from AGS 2007).
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Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007)
Assessed
Hazard Likelihood Consequence
Risk
Comments
Failure through very loose to Unlikely Medium Low Given the low to moderate natural gradients through the
loose natural sands above the proposed building area, it is considered Unlikely that a
foundation depth landslip would develop in these materials, subject to
implementation of the recommendations in Section 4.
Given a potential Medium impact from such instability
the resultant risk would be Low as per AGS 2007.
Deep failure through the Rare Major Low The likelihood of a deep failure through the medium
medium dense (or denser) dense (or denser) natural sand below the proposed
sands below the foundation foundation depth is assessed as Rare due to the lack of
depth precedence of such movements locally, no signs of any
existing slope instability and a lack of groundwater.
Although the consequence of such a failure would be
Major, the resultant risk is Low as per AGS 2007.
Temporary instability through Rare Major Low The likelihood of a slip/failure through any temporary
temporary retention system, as retention system (sheet pile wall, contiguous pile wall or
discussed in Section 6.4. similar) as outlined in Section 6.4, is assessed as Rare,
subject to detailed design by a suitable qualified RPEQ
engineer and construction by a specialist contractor
which accounts for the required factors of safety against
slope instability. 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.
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6. Geotechnical Recommendations
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached.
6.1 Development Limitations
It is anticipated earthworks may include cuts for the basement level of up to about 7 m deep with only
minor filling expected to be required up to about 1 m in height to form finished surface levels. Should
proposed cuts/fills exceed this quantity, Tectonic must assess the impacts on slope stability before
construction.
6.2 Earthworks
6.2.1 Site Preparation and Trafficability
Following removal of the existing buildings and associated construction elements (e.g. footings, services,
etc.), any tree stumps and large roots should be ‘grubbed out’. Any organic rich topsoil and uncontrolled
fill should then be stripped and set aside. Based on site observations and boreholes, topsoil (where
present) stripping depths should generally range between 0.1 m and 0.2 m BGL, with uncontrolled fill
encountered to depths of between 0.4 m to 0.6 m BGL. It is noted that deeper pockets of topsoil or
uncontrolled fill may exist and deeper, localised grubbing out of tree roots may be required.
Rubbish was noted during soil testing by ASI at a depth of 0.7 m BGL. Three boreholes (designated BH2,
BH2A and BH2B) were drilled by Tectonic in this area to delineate the extent of this rubbish, however, no
deleterious material was encountered at those locations. It would be prudent to allow to investigate this
area further by excavation of test pits prior to construction commencing to assess if rubbish is present
and to what extent.
Topsoil materials must not be used in structural fill; however, may be placed across landscaping areas.
Unsuitable natural material such as any saturated, loose or soft materials encountered should also be
removed during subgrade preparation for bulk earthworks.
It should be noted that compaction of such relatively ‘clean’ sands as structural fill requires the addition
of substantial volumes of water (‘flooding’) combined with the use of vibratory compaction equipment
(typically a vibrating plate). Care must be taken with the use of vibratory equipment (e.g. compactors or
sheet piling) to ensure that there are no adverse impacts on surrounding structures. The impacts from
ground vibration must be closely monitored and managed during construction. It would be prudent to
conduct a dilapidation survey of neighbouring structures prior to commencement of construction.
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 poor trafficability during placement of a minimum 150 mm thick granular
working platform may be required on soil subgrades along haul roads and across laydown areas.
Specific platform design would be required prior to mobilisation and trafficking of any heavy mobile
plant on the site (e.g. cranes, concrete pumps or piling rigs).
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Construction areas and surrounds should be graded to shed surface water runoff. Swale drains should
be constructed along the crest and toe of any cuts, and above fill batters, where possible. Drains are to
be graded to discharge collected waters to a control point(s) before release into existing stormwater
infrastructure.
It should be noted that during wet weather, the natural soils may cause sediment run-off. Appropriate
erosion and sediment control measures must be installed prior to commencement of earthworks at this
site.
6.2.2 Excavations
Excavations through the existing 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:1H in medium dense (or denser) sand for batters up to
3 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, should be
specifically assessed by Tectonic.
If filling or permanent cuts exceed 1 m, then these must be retained. Permanent cut and fill batters up to
1 m high shall not exceed 1V:2.5H. Any permanent soil and fill batters will require erosion protection (e.g.
revegetation or surface protection).
Temporary batter slopes would not be able to be achieved in places, due to spatial restraints, and so
temporary shoring will be required (e.g. sheet piles or contiguous piles) as per the recommendations in
Section 6.4 below. Excavations in close proximity to existing structures, including on neighbouring
properties, will need to be specifically designed to prevent undermining. It is recommended that footing
exposures or confirmation of 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 RPEQ structural engineer must be sought regarding
any potential undermining as well as 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).
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).
6.2.3 Filling
The existing sandy soils (fill and natural) where free of deleterious materials (e.g. vegetation, building
debris etc.) may be reused as structural fill, 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).
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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
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 98% of the maximum Dry Density
Ratio (DDR), based upon the Standard Compaction method, or a Dry Density Index of at least 75%.
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.
Fill embankment edges must be over-filled by 0.5 m (horizontally) and then trimmed back to well
compacted material.
6.3 Building Foundations
6.3.1 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. It should be noted that
the proposed works are outside of the scope of AS2870.
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 uncontrolled fill and poor bearing capacity soils at
shallow depths. However, 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. 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 slab, footing and plumbing design.
6.3.2 Footing Design
No design loadings were available at the time of reporting. Footings for the proposed development and
any ancillary structures (e.g. retaining walls, etc.) must penetrate through any fill materials and unsuitable
natural soils (i.e. very loose to loose sands) to found at least 0.5 m into medium dense (or denser) natural
sands. Such materials were encountered below depths between about 1.4 m and 2.6 m BGL (existing
ground levels) in the boreholes. Thus, piled footings will be required unless excavations expose such
materials at or near foundation subgrade level (e.g. as anticipated in deeper basement cut areas).
Piles so founded may be designed using an allowable end bearing pressure of 500 kPa. High level
footings, where achievable in deeper cut areas, may be designed using an allowable bearing pressure of
100 kPa provided that they are founded in the natural medium dense (or denser) sands. Settlement under
such loads is expected to be in the order of up to 20 mm or 1% of footing width.
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Given the sandy soil profile and depths of footings required, steel screw piles are considered to be a
suitable foundation type for the proposed unit development generally. However, in areas of cut
exposing medium dense (or denser) sands at the subgrade level conventional high-level footings may be
adopted. It should be noted that excavation for concrete strip footings (or similar) may loosen the base.
Therefore, the use of a vibrating plate and ample water would be required to densify any high-level
footing bases prior to the placement of reinforcing steel.
Due to the presence of loose sands, open bored piers or driven piles are not considered to be suitable
for this site. Steel reinforced concrete bore piles may be possible; however, the use of casings or
sacrificial liners (e.g. formatube etc.) would be required. Cast in place continuous flight auger (CFA) piles
may also be suitable for foundation piles (and shoring piles) provided a small rig capable of traversing
the site can be sourced.
The advice of a specialist piling contractor must be sought regarding feasibility, design and installation of
the piling system for this site, including an assessment of potential vibration effects on nearby structures,
and monitoring requirements.
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.
Footing design should also account for potential soil reactivity to be equivalent to Class M. It should be
noted that placement of reactive clay (which is not recommended) may result in a more severe equivalent
site classification, such as H1 or greater.
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/retaining
walls/swimming pool, then rising up at 1V:1H, as illustrated in Text Figure 10 overleaf.
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Text Figure 9: Footing depth required to prevent undermining
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.
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.
6.4 Temporary and Permanent Retention
Excavations for the basement level may extend to depths of around 7 m BGL (existing ground levels) and
the basement footprint will extend close to some of the site boundaries, so some form of temporary
shoring will be required to support the basement excavation.
Based upon our experience with similar sites, we anticipate that temporary shoring may be achieved by
use of reinforced concrete contiguous pile wall. Sheet piling is not considered suitable for this site due
to the depth of the excavation, the risk of consolidation of loose sands from vibratory effects and the
potential for lateral movements to result in distress to existing structures or underground services behind
the boundary walls. An alternative a secant pile wall configuration could be considered along with
propping of the shoring wall with the use of internal struts. The temporary wall can also act as the
permanent basement wall if appropriately designed.
Installation of such piles in this setting would require the use of cast in place CFA piles. We understand
that the client has been in consultation with a specialist contractor who has a small specialised rig that
would be capable of installing such piles on this terrain. The advice of a specialist shoring contractor
must be sought regarding feasibility, design and installation of the proposed retention and subsurface
drainage system. It will be necessary to conduct numerical analysis to optimise the retention system.
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Detailed design will also need to account for relevant factors of safety to maintain the temporary and
long-term stability of the retention system and control deflections so as not to put neighbouring
structures or underground services at risk or distress.
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 trapezoidal (for
propped or anchored walls) pressure distribution applicable to the wall type and based on the
parameters listed in Table 4. These values do not include allowance for hydrostatic pressures nor
transient (e.g. construction) or adjacent footing loadings.
Table 4: Retaining Structure Design Parameters
Unit Lateral earth pressure coefficients
Friction
Retained material weight Ka Ko Kp
angle (°)
(kN/m3) (Cantilever wall) (Non-yielding wall)
18 28 0.36 0.53 2.77
Very Loose/ Loose
Sands
19 34 0.28 0.44 3.54
Medium Dense (or
Denser) 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 6.3.2 above with the piled
footings, if required, also designed to resist lateral loads imposed by the retaining wall. Detailed design
must include an assessment of stability.
6.5 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.
All excess stormwater collected around the residence (including overflow from rainwater tanks etc.) must
be directed by pipes or lined channels to discharge into the existing stormwater infrastructure along
Bottlebrush Avenue or Noosa Drive. Subsurface disposal of stormwater must not be undertaken.
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7. 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. Limitations
Your attention is drawn to the document Limitations, which is included in Appendix C 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.
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0 5 10 15 20m LEGEND CHEN, DRC IE CT Ae APPROXIMATE BOREHOLE LOCATIONS ARCHEND GEOTECHNICAL INVESTIGATION FOR PROPOSED UNIT DEVELOPMENT DRAWN BY DATE 3 51 ELANDA STREET, SUNSHINE BEACH CI SITE BOUNDARY BC 24/09/2024 " DRAWING TITLE NOTES CHECKED BY DATE SITE PLAN BASEMAP COURTESY OF NEARMAP, DATED 15 NOVEMBER 2023 DP 24/09/2024 PROJECT NO. DOC NO. FIGURE NO. REVISION SCALE SHEET SIZE AS SHOWN AB 24265 001 1 0 Document Set ID: 23376055 Version: 1, Version Date: 28/11/2024
Page 24
Appendix A
Borehole Reports and Explanatory Notes
Proposed Unit Development
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Page 25
Borehole No.
BH1
Page 1 of 1
Engineering Log - Borehole Project No.: 24265
Client: Archend Commenced: 6/9/2024
Project Name: Proposed Unit Development Completed: 6/9/2024
Hole Location: 51 Elanda Street, Sunshine Beach Logged By: BC
Hole Position: 510867.0 m E 7079242.0 m N MGA2020 Zone 56 Checked By: DP
Drill Model and Mounting: 4WD Auger Inclination: -90° RL Surface: No survey
Hole Diameter: 100 mm Bearing: 360° Datum: AHD Operator: WD
Drilling Information Material Description and Observations
Relative Density
Classification DCP TEST
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description
Penetrometer
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
UCS Blows per 100 mm
Symbol
Method
secondary and minor components, colour
Water
Remarks RL Depth (kPa)
(m) (m) 0 5 10 15 20 25
100
200
300
400
500
Silty SAND (TOPSOIL), fine to coarse
grained, brown, with organics
Silty SAND (FILL), fine to coarse grained,
SP
HA
orange brown, with fine to medium sized
subrounded gravel, with clay pockets L
SAND, fine to medium grained, grey, with silt, Augered to 0.9m
1 (AEOLIAN)
becoming pale grey, without silt
2
DS_2.0-2.5m
MD
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24265.GPJ <<DrawingFile>> 24/9/2024 13:59 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
Not Encountered
D
4 M
Augered to 4.4m
AD/T
5
Augered to 5.9m
6 20/70
VD
7
8
Hole Terminated at 8.00 m
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 < PL MD - Medium Dense
Core recovered (hatching and Soil Descriptions D - Dense
indicates material) = PL
Based on Unified Soil < PL VD - Very Dense
Core loss Classification System Fr - Friable
Document Set ID: 23376055
Version: 1, Version Date: 28/11/2024
Page 26
Borehole No.
BH2
Page 1 of 1
Engineering Log - Borehole Project No.: 24265
Client: Archend Commenced: 6/9/2024
Project Name: Proposed Unit Development Completed: 6/9/2024
Hole Location: 51 Elanda Street, Sunshine Beach Logged By: BC
Hole Position: 510885.0 m E 7079262.0 m N MGA2020 Zone 56 Checked By: DP
Drill Model and Mounting: 4WD Auger Inclination: -90° RL Surface: No survey
Hole Diameter: 100 mm Bearing: 360° Datum: AHD Operator: WD
Drilling Information Material Description and Observations
Relative Density
Classification DCP TEST
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description
Penetrometer
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
UCS Blows per 100 mm
Symbol
Method
secondary and minor components, colour
Water
Remarks RL Depth (kPa)
(m) (m) 0 5 10 15 20 25
100
200
300
400
500
Silty SAND (TOPSOIL), fine to coarse
grained, brown, with organics
Silty SAND (FILL), fine to coarse grained,
SP brown
SAND, fine to medium grained, grey, L
(AEOLIAN)
Not Encountered
Augered to 1.0m
1
becoming pale grey
M
HA
MD
Augered to 2.0m
2
D
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24265.GPJ <<DrawingFile>> 24/9/2024 13:59 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
Hole Terminated at 3.00 m
Target depth
4
5
6
7
8
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 < PL MD - Medium Dense
Core recovered (hatching and Soil Descriptions D - Dense
indicates material) = PL
Based on Unified Soil < PL VD - Very Dense
Core loss Classification System Fr - Friable
Document Set ID: 23376055
Version: 1, Version Date: 28/11/2024
Page 27
Borehole No.
BH2A
Page 1 of 1
Engineering Log - Borehole Project No.: 24265
Client: Archend Commenced: 6/9/2024
Project Name: Proposed Unit Development Completed: 6/9/2024
Hole Location: 51 Elanda Street, Sunshine Beach Logged By: BC
Hole Position: 510882.0 m E 7079259.0 m N MGA2020 Zone 56 Checked By: DP
Drill Model and Mounting: 4WD Auger Inclination: -90° RL Surface: No survey
Hole Diameter: 100 mm Bearing: 360° Datum: AHD Operator: WD
Drilling Information Material Description and Observations
Relative Density
Classification
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description
Penetrometer
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
UCS
Symbol
Method
secondary and minor components, colour
Not Encountered Water
Remarks RL Depth (kPa)
(m) (m) 0 5 10 15 20 25
100
200
300
400
500
Silty SAND (TOPSOIL), fine to coarse
grained, brown, with organics
Silty SAND (FILL), fine to coarse grained,
SP M L
HA
brown
SAND, fine to medium grained, grey,
(AEOLIAN)
1
becoming pale grey
Hole Terminated at 1.00 m
Target depth
2
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24265.GPJ <<DrawingFile>> 24/9/2024 13:59 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
4
5
6
7
8
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 < PL MD - Medium Dense
Core recovered (hatching and Soil Descriptions D - Dense
indicates material) = PL
Based on Unified Soil < PL VD - Very Dense
Core loss Classification System Fr - Friable
Document Set ID: 23376055
Version: 1, Version Date: 28/11/2024
Page 28
Borehole No.
BH2B
Page 1 of 1
Engineering Log - Borehole Project No.: 24265
Client: Archend Commenced: 6/9/2024
Project Name: Proposed Unit Development Completed: 6/9/2024
Hole Location: 51 Elanda Street, Sunshine Beach Logged By: BC
Hole Position: 510884.0 m E 7079258.0 m N MGA2020 Zone 56 Checked By: DP
Drill Model and Mounting: 4WD Auger Inclination: -90° RL Surface: No survey
Hole Diameter: 100 mm Bearing: 360° Datum: AHD Operator: WD
Drilling Information Material Description and Observations
Relative Density
Classification
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description
Penetrometer
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
UCS
Symbol
Method
secondary and minor components, colour
Not Encountered Water
Remarks RL Depth (kPa)
(m) (m) 0 5 10 15 20 25
100
200
300
400
500
Silty SAND (TOPSOIL), fine to coarse
grained, brown, with organics
Silty SAND (FILL), fine to coarse grained,
SP M L
HA
brown
SAND, fine to medium grained, grey,
(AEOLIAN)
1
becoming pale grey
Hole Terminated at 1.00 m
Target depth
2
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24265.GPJ <<DrawingFile>> 24/9/2024 13:59 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
4
5
6
7
8
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 < PL MD - Medium Dense
Core recovered (hatching and Soil Descriptions D - Dense
indicates material) = PL
Based on Unified Soil < PL VD - Very Dense
Core loss Classification System Fr - Friable
Document Set ID: 23376055
Version: 1, Version Date: 28/11/2024
Page 29
Borehole No.
BH3
Page 1 of 1
Engineering Log - Borehole Project No.: 24265
Client: Archend Commenced: 6/9/2024
Project Name: Proposed Unit Development Completed: 6/9/2024
Hole Location: 51 Elanda Street, Sunshine Beach Logged By: BC
Hole Position: 510899.0 m E 7079247.0 m N MGA2020 Zone 56 Checked By: DP
Drill Model and Mounting: 4WD Auger Inclination: -90° RL Surface: No survey
Hole Diameter: 100 mm Bearing: 360° Datum: AHD Operator: WD
Drilling Information Material Description and Observations
Relative Density
Classification DCP TEST
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description
Penetrometer
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
UCS Blows per 100 mm
Symbol
Method
secondary and minor components, colour
Water
Remarks RL Depth (kPa)
(m) (m) 0 5 10 15 20 25
100
200
300
400
500
Silty SAND (TOPSOIL), fine to coarse
grained, brown, with organics D to
Silty SAND (FILL), fine to coarse grained, M
brown
Not Encountered
Augered to 1.0m
1
L
SP SAND, fine to medium grained, pale grey,
HA
(AEOLIAN)
M
Augered to 2.0m
2
MD
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24265.GPJ <<DrawingFile>> 24/9/2024 14:00 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
Augered to 3.0m
3
Hole Terminated at 3.00 m
Target depth
4
5
6
7
8
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 < PL MD - Medium Dense
Core recovered (hatching and Soil Descriptions D - Dense
indicates material) = PL
Based on Unified Soil < PL VD - Very Dense
Core loss Classification System Fr - Friable
Document Set ID: 23376055
Version: 1, Version Date: 28/11/2024
Page 30
Borehole No.
BH4
Page 1 of 1
Engineering Log - Borehole Project No.: 24265
Client: Archend Commenced: 6/9/2024
Project Name: Proposed Unit Development Completed: 6/9/2024
Hole Location: 51 Elanda Street, Sunshine Beach Logged By: BC
Hole Position: 510912.0 m E 7079249.0 m N MGA2020 Zone 56 Checked By: DP
Drill Model and Mounting: 4WD Auger Inclination: -90° RL Surface: No survey
Hole Diameter: 100 mm Bearing: 360° Datum: AHD Operator: WD
Drilling Information Material Description and Observations
Relative Density
Classification DCP TEST
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description
Penetrometer
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
UCS Blows per 100 mm
Symbol
Method
secondary and minor components, colour
Water
Remarks RL Depth (kPa)
(m) (m) 0 5 10 15 20 25
100
200
300
400
500
Silty SAND (TOPSOIL), fine to medium
SP grained, brown, with organics
SAND, fine to medium grained, pale grey,
(AEOLIAN)
L
Not Encountered
Augered to 1.0m
1
M
HA
Augered to 2.0m
2
MD
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24265.GPJ <<DrawingFile>> 24/9/2024 14:00 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
Augered to 3.0m
3
Hole Terminated at 3.00 m
Target depth
4
5
6
7
8
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 < PL MD - Medium Dense
Core recovered (hatching and Soil Descriptions D - Dense
indicates material) = PL
Based on Unified Soil < PL VD - Very Dense
Core loss Classification System Fr - Friable
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TERMS USED ON LOGS
DRILLING/EXCAVATION METHOD
AD* Auger Drilling RD Rotary Blade or Drag bit NQ Diamond Core - 47 mm
*V V-Bit RT Rotary Tri-cone bit NMLC Diamond Core - 52 mm
*T TC-Bit RA Rotary Air HQ Diamond Core - 63 mm
HA Hand Auger HMLC Diamond Core – 63mm
ADH Hollow Auger BH Tractor Mounted Backhoe
EX Tracked Hydraulic Excavator
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
FV Field vane shear 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
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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.
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Appendix B
AGS Guidlines - Qualitative Terminology for Use
in Assesing the Risk to Property
Some Guidelines for Hillside Construction
Proposed Unit Development
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PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX C: LANDSLIDE RISK ASSESSMENT
QUALITATIVE TERMINOLOGY FOR USE IN ASSESSING RISK TO PROPERTY
QUALITATIVE MEASURES OF LIKELIHOOD
Approximate Annual Probability
Implied Indicative Landslide
Description Descriptor Level
Indicative Notional Recurrence Interval
Value Boundary
10-1 5x10-2
10 years The event is expected to occur over the design life. ALMOST CERTAIN A
20 years The event will probably occur under adverse conditions over the
-2
10 100 years
design life.
LIKELY B
-3
-3 5x10 200 years
10 1000 years The event could occur under adverse conditions over the design life. POSSIBLE C
5x10-4 2000 years
The event might occur under very adverse circumstances over the
10-4 10,000 years
design life.
UNLIKELY D
-5 5x10-5 20,000 years
10 The event is conceivable but only under exceptional circumstances
100,000 years RARE E
over the design life.
-6 5x10-6 200,000 years
10 1,000,000 years The event is inconceivable or fanciful over the design life. BARELY CREDIBLE F
Note: (1) The table should be used from left to right; use Approximate Annual Probability or Description to assign Descriptor, not vice versa.
QUALITATIVE MEASURES OF CONSEQUENCES TO PROPERTY
Approximate Cost of Damage
Description Descriptor Level
Indicative Notional
Value Boundary
Structure(s) completely destroyed and/or large scale damage requiring major engineering works for
200% CATASTROPHIC 1
stabilisation. Could cause at least one adjacent property major consequence damage.
100%
Extensive damage to most of structure, and/or extending beyond site boundaries requiring significant
60% MAJOR 2
stabilisation works. Could cause at least one adjacent property medium consequence damage.
40%
Moderate damage to some of structure, and/or significant part of site requiring large stabilisation works.
20% MEDIUM 3
Could cause at least one adjacent property minor consequence damage.
10%
5% 1% Limited damage to part of structure, and/or part of site requiring some reinstatement stabilisation works. MINOR 4
Little damage. (Note for high probability event (Almost Certain), this category may be subdivided at a
0.5% INSIGNIFICANT 5
notional boundary of 0.1%. See Risk Matrix.)
Notes: (2) The Approximate Cost of Damage is expressed as a percentage of market value, being the cost of the improved value of the unaffected property which includes the land plus the
unaffected structures.
(3) The Approximate Cost is to be an estimate of the direct cost of the damage, such as the cost of reinstatement of the damaged portion of the property (land plus structures), stabilisation
works required to render the site to tolerable risk level for the landslide which has occurred and professional design fees, and consequential costs such as legal fees, temporary
accommodation. It does not include additional stabilisation works to address other landslides which may affect the property.
(4) The table should be used from left to right; use Approximate Cost of Damage or Description to assign Descriptor, not vice versa
Australian Geomechanics Vol 42 No 1 March 2007
68039 Landslide Risk Management Issued 10/7/07
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PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX C: – QUALITATIVE TERMINOLOGY FOR USE IN ASSESSING RISK TO PROPERTY (CONTINUED)
QUALITATIVE RISK ANALYSIS MATRIX – LEVEL OF RISK TO PROPERTY
LIKELIHOOD CONSEQUENCES TO PROPERTY (With Indicative Approximate Cost of Damage)
Indicative Value of 1: CATASTROPHIC 2: MAJOR 3: MEDIUM 4: MINOR 5:
Approximate Annual 200% 60% 20% 5% INSIGNIFICANT
Probability 0.5%
A – ALMOST CERTAIN 10-1 VH VH VH H M or L (5)
-2
B - LIKELY 10 VH VH H M L
C - POSSIBLE 10-3 VH H M M VL
D - UNLIKELY 10-4 H M L L VL
-5
E - RARE 10 M L L VL VL
-6
F - BARELY CREDIBLE 10 L VL VL VL VL
Notes: (5) For Cell A5, may be subdivided such that a consequence of less than 0.1% is Low Risk.
(6) When considering a risk assessment it must be clearly stated whether it is for existing conditions or with risk control measures which may not be implemented at the current
time.
RISK LEVEL IMPLICATIONS
Risk Level Example Implications (7)
Unacceptable without treatment. Extensive detailed investigation and research, planning and implementation of treatment
VH VERY HIGH RISK options essential to reduce risk to Low; may be too expensive and not practical. Work likely to cost more than value of the
property.
Unacceptable without treatment. Detailed investigation, planning and implementation of treatment options required to reduce
H HIGH RISK
risk to Low. Work would cost a substantial sum in relation to the value of the property.
May be tolerated in certain circumstances (subject to regulator’s approval) but requires investigation, planning and
M MODERATE RISK implementation of treatment options to reduce the risk to Low. Treatment options to reduce to Low risk should be
implemented as soon as practicable.
Usually acceptable to regulators. Where treatment has been required to reduce the risk to this level, ongoing maintenance is
L LOW RISK
required.
Acceptable. Manage by normal slope maintenance procedures.
VL VERY LOW RISK
Note: (7) The implications for a particular situation are to be determined by all parties to the risk assessment and may depend on the nature of the property at risk; these are only
given as a general guide.
Australian Geomechanics Vol 42 No 1 March 2007
68039 Landslide Risk Management Issued 10/7/07
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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
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Appendix C
Limitations
Proposed Unit Development
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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.
Limitations
August 2024 | Rev2
Document Set ID: 23376055
Version: 1, Version Date: 28/11/2024
Page 40
PO Box 899 tectonicgeo.com.au [email protected]
Buderim
Proposed Unit QLD 4555
Development
30 September 2024 | 24265-001-Rev0 4
Document Set ID: 23376055
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Page 41
Technical Memorandum
51 Elanda Street Stormwater Management Plan Addendum
Client: Archend
Council: Noosa Shire Council
Document reference: 51 Elanda Street- Response to Council information request
Prepared By: Adam Young
Signed: Eoin Whitmore RPEQ: 31423
Date: 26/09/2025
Purpose
This technical memorandum has been prepared in response to Council’s Further Advice Request for
application MCU24/0153, OPW24/0202, and PLM24/0024 at 51 Elanda Street, Sunshine Beach. The
purpose of this memo is to address the issues raised by Council and provide a detailed response to
ensure the resolution of outstanding matters related to the civil scope of works.
As part of this submission, amended Operational Works plans have been attached. These plans have
been updated to reflect the responses outlined in this memorandum and demonstrate compliance
with the relevant requirements.
Issue – Updated Stormwater Engineering Drawings and Report
Amended plans and associated reports must be submitted to Council prior to any further
development applications being made and must include the following to the reasonable
satisfaction of the Manager, Development Assessment:
1.1. Provide updated stormwater and engineering drawings including:
a. Additional detail demonstrating that the post-development peak flow rate
discharging to structure “7/1” does not exceed the pre-development peak flow
rate. The detail must clearly demonstrate that the development and calculations
incorporate appropriate climate change allowances in accordance with AO2.4 of
the Water Quality and Drainage Code.
b. Additional detail confirming an appropriate climate change allowance has been
T 1300 469 707 U WWW.RECOR.AU
PAGE 1 OF 7
Page 42
applied to the sizing of all detention tanks.
c. A stormwater design calculation table.
d. Details of detention outlet orifices / controls.
f. Prepared by a suitably qualified person (RPEQ)
RECOR RESPONSE:
A 12d Model drainage analysis was conducted for the entire site. The 1% AEP (Q100) and 10% AEP
(Q10) hydraulic grade lines (HGLs) are presented in the stormwater long section plans for reference.
The site drainage and detention/ rainwater harvesting tanks have been modelled in 12d using the
ILSAX method of dynamic drainage analysis. All rainfall data was obtained from the Bureau of
Meteorology (BOM) Intensity-Frequency-Duration (IFD) data website and is based on the latest 2019
data. The rainfall data obtained was then multiplied by a factor of 1.2 to simulate an increase of 20%.
Refer tables 1 and 2 below for the original and climate change adjusted rainfall data.
Table 1: IFD Table
Annual Exceedance Probability (AEP)
Duration 63.2% 50%# 20%* 10% 5% 2% 1%
1 min 173 195 263 308 351 405 446
2 min 147 167 230 273 316 375 420
3 min 138 157 215 254 293 346 386
4 min 131 149 203 239 275 321 357
5 min 125 142 193 227 259 301 333
10 min 103 116 155 181 205 236 259
15 min 87.0 98.1 132 153 174 199 218
20 min 76.0 85.7 115 134 152 175 192
25 min 67.8 76.5 103 120 137 158 173
30 min 61.4 69.3 93.5 109 125 144 159
45 min 48.6 55.0 74.9 88.2 101 118 131
1 hour 40.8 46.3 63.5 75.2 86.5 102 113
1.5 hour 31.7 36.1 50.2 59.8 69.4 82.2 92.2
2 hour 26.5 30.3 42.4 50.8 59.2 70.6 79.5
3 hour 20.5 23.6 33.5 40.4 47.4 56.9 64.4
4.5 hour 16.0 18.4 26.5 32.2 37.9 45.8 52.0
6 hour 13.4 15.5 22.5 27.4 32.4 39.2 44.6
2
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9 hour 10.5 12.2 17.8 21.8 25.9 31.5 35.9 12 hour 8.78 10.3 15.1 18.6 22.1 26.9 30.7 18 hour 6.85 8.02 11.9 14.7 17.5 21.4 24.6 24 hour 5.71 6.70 9.96 12.3 14.8 18.2 20.9 30 hour 4.95 5.80 8.65 10.7 12.9 15.9 18.3 36 hour 4.38 5.14 7.68 9.54 11.5 14.2 16.4 48 hour 3.60 4.22 6.31 7.87 9.50 11.8 13.7 72 hour 2.68 3.14 471 5.89 7.14 8.98 10.5 96 hour 2.16 2.52 3.78 4.73 5.76 7.26 8.52 120 hour 1.81 2.12 3.17 3.97 4.83 6.10 7.16 144 hour 1.57 1.83 ae) 3.42 4.16 5.24 6.15 168 hour 1.39 1.62 2.41 3.01 3.65 4.59 5.37 Table 2: IFD Table - Rainfall intensities with 20% increase Annual Exceedance Probability (AEP) Duration 63.2% 50%# 20%* 10% 5% 2% 1% 1min 207.6 234 315.6 369.6 421.2 486 535.2 2 min 176.4 200.4 276 327.6 379.2 450 504 3 min 165.6 188.4 258 304.8 351.6 415.2 463.2 4min aia 178.8 243.6 286.8 330 385.2 428.4 Smin 150 170.4 231.6 272.4 310.8 361.2 399.6 10 min 123.6 139.2 186 217.2 246 283.2 310.8 15 min 104.4 117.72 158.4 183.6 208.8 238.8 261.6 20 min 91.2 102.84 138 160.8 182.4 210 230.4 25 min 81.36 91.8 123.6 144 164.4 189.6 207.6 30 min 73.68 83.16 112.2 130.8 150 172.8 190.8 45 min 58.32 66 89.88 105.84 121.2 141.6 157.2 1 hour 48.96 55.56 76.2 90.24 103.8 122.4 135.6 1.5 hour 38.04 43.32 60.24 71.76 83.28 98.64 110.64 2 hour 31.8 36.36 50.88 60.96 71.04 84.72 95.4 3 hour 24.6 28.32 40.2 48.48 56.88 68.28 77.28 4.5 hour 19.2 22.08 31.8 38.64 45.48 54.96 62.4 6 hour 16.08 18.6 27 32.88 38.88 47.04 53.52
Page 44
9 hour 12.6 14.64 21.36 26.16 31.08 37.8 43.08
12 hour 10.536 12.36 18.12 22.32 26.52 32.28 36.84
18 hour 8.22 9.624 14.28 17.64 21 25.68 29.52
24 hour 6.852 8.04 11.952 14.76 17.76 21.84 25.08
30 hour 5.94 6.96 10.38 12.84 15.48 19.08 21.96
36 hour 5.256 6.168 9.216 11.448 13.8 17.04 19.68
48 hour 4.32 5.064 7.572 9.444 11.4 14.16 16.44
72 hour 3.216 3.768 5.652 7.068 8.568 10.776 12.6
96 hour 2.592 3.024 4.536 5.676 6.912 8.712 10.224
120 hour 2.172 2.544 3.804 4.764 5.796 7.32 8.592
144 hour 1.884 2.196 3.276 4.104 4.992 6.288 7.38
168 hour 1.668 1.944 2.892 3.612 4.38 5.508 6.444
The below table shows the climate change adjusted Pre-Development Catchment Runoff estimations
provided in the original SCCE SMP prepared in November 2024.
Table 3: Predevelopment site discharge (m3/s)
Flow Event Existing Scenario(m³/s)
Q10 (10% AEP) 0.040
Q1 (1% AEP) 0.062
The following unmitigated post-development flow results were derived from the 12d model which
was run with the climate change adjusted rainfall data in Table 2 Above.
Table 4: Unmitigated post-development site discharge – adjusted for climate change (m3/s)
Flow Event Climate Change Incl. (m³/s)
Q10 (10% AEP) 0.050
Q1 (1% AEP) 0.084
The following mitigated post-development flow results were achieved with the use of an onsite
detention tank
Table 5: Mitigated post-development site discharge -adjusted for climate change (m3/s)
Flow Event Climate Change Incl. (m³/s)
Q10 (10% AEP) 0.035
Q1 (1% AEP) 0.057
4
Page 45
Table 6: Detention Tank Parameters
Detention Tank Parameters
Tank Volume 5.0m³
Storage Volume 4.8m³
Area 5.0m²
Base RL 42.849m
AEP1% max. water level RL 43.807m
AEP1% max. water level depth 0.958m
Orifice plate outlet diameter 150mm
Outlet pipe diameter 225mm
Orifice plate outlet control RL (middle of pipe) 42.924m
The 12d dynamic inflow and outflow outputs for the rainwater harvesting tank (structure 213) and
the detention tank (structure 6-1) are below:
AEP10%
Table 7: Structure 2-3 AEP10% inflows and outflows
5
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Table 8: Structure 6-1 AEP10% inflows and outflows AEP1% Table 9: Structure 2-3 AEP1% inflows and outflows 6
Page 47
Table 10: Structure 6-1 AEP1% inflows and outflows
In both the major and minor events, the climate change adjusted post development flows have been
effectively mitigated such that the outflows to the existing stormwater network are lower than the
predevelopment flow. It is therefore confirmed that Acceptable Outcome 2.4 of the water quality
and drainage code has been achieved.
The model also confirms that there is sufficient capacity in the external pit to take all flows from the
development. We trust that this Technical Memorandum, in conjunction with the amended civil
drawings, is sufficient to evidence to council that the stormwater quantity measures have been
designed to mitigate the 20% increase in rainfall allowing for climate change.
All other engineering items within the Decision Notice for application OPW24-0202 dated the 11th of
August 2025, have been addressed within the engineering drawings.
Please contact the undersigned for any further clarifications:
➢ Email- [email protected]
➢ Phone- 0451453640.
Eoin Whitmore, Associate Engineer
RPEQ Number: 31423
Date: 26/09/2025
7
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-
REFERENCE DOCUMENT
51 Elanda St, Sunshine Beach
MCU24/0153 & OPW24/0202
NOOSA COUNCIL
15 DECEMBER 2025
Landscape Operational Works Plan
The landscape operational works plan package consists of the following schedule of drawings;
LD1 General Notes, Sheet Layout & Site Location
LD2 Project Specifications
LD3 Project Specifications, Annual Maintenance & Finishes Schedule
LP1 & 2 = Ground Floor / Basement LD4
LD5
Plant Schedules
Typical Details
T
LP1 Landscape Plan (Ground 1/2)
LP3 = First level LP2
LP3
LP4
Landscape Plan (Ground 2/2)
Landscape Plan (First Level)
Landscape Plan (Second Level)
LP5 Landscape Plan (Roof)
LP4 = Second level BUP102822 BUP106270
This package has been developed to comply with;
T
·
LP5 = Roof ·
Noosa Plan 2020
Bioretention Technical Design Guidelines Version 1, October 2012 (Water by Design)
Sources;
- Architects: Archend
- Civil: Recor | Project Management & Technical Services
LP1 LP3-5 LP2
Sample Approvals;
· Landscape Installer is to provide LA with following samples for LA approval prior to construction;
T
- Composted Forest Litter
Certifications;
· Landscape Installer is to provide LA with following certifications prior to on-maintenance inspection;
ELANDA STREET
1:4
- AS 2303:2015
- AS4419 Soil Certification
1:8
- Mulch - Weed free / Pest Free
1:20
T
1:20
1:40
1:8
GTP689
TE
T
SW 51 Elanda St, Sunshine Beach
SW
SP193676 BUP9277
SW
SHEET KEY LAYOUT N.T.S SITE LOCATION N.T.S
LOT 2 SP164980
anembo consultants
Client: Location: Project Description: Drawing Title: JOB No.: S24111298
FILE: 250321 D 21.03.25 ARCH BASE UPDATE CK TH
ArchEnd 51 Elanda St, Sunshine Beach Landscape Works DWG. No. LD1 C 27.11.24 COUNCIL SUBMISSION CK TH
anembo consultants pty.ltd. A.B.N. 75 089 473 156
SHEET 1 OF 10 B 21.11.24 FOR REVIEW CK TH This document is the copyright of anembo consultants & shall PO Box 24 Moffat Beach Q 4551 Landscape Architects
GENERAL NOTES,
Development: Lot on Plan: Project Status: SHEET LAYOUT & SITE
APPROVED:
A 11.11.24 FOR REVIEW CK TH
not be copied without written approval, nor shall it be used Ph: 07 5437 0000 Project Management
T Hindley AILA 713 except for the development and the site specified. Scale can email: [email protected] Environmental
Development Lot 403 on RP 48112 Landscape Operational Works LOCATION CATEGORY: MHD ISSUE DATE DESCRIPTION DWN CKD ISSUE DATE DESCRIPTION DWN CKD
not be guaranteed when printing from PDF files. www.anembo.com Arboriculture
The text continues on page 49.