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Geotechnical Report
GEOTECHNICAL INVESTIGATION
Proposed Unit Development
31 Bottlebrush Avenue, Noosa Heads
Report for: Camtegan Pty Ltd
20370-001-Rev0
17 December 2020
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 UNIT DEVELOPMENT
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Document Review
Document No. Revision Prepared By Reviewed By Date Issued
Bennett Hume
001 0 David Pollock 17 December 2020
aeolian
Report Distribution
Document Revision Method of Delivery Issued To
Camtegan Pty ltd c/-Cole Projects QLD Pty Ltd
001 0 Electronic
Mr Cam Cole ([email protected])
Prepared by: Reviewed By:
Bennett Hume BEng Civil (Hon) BEnvSci David Pollock BE(Civil) RPEQ 14121
Graduate Geotechnical Engineer Senior Geotechnical Engineer
17 December 2020
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Executive Summary
This report details a geotechnical investigation undertaken for a proposed unit development at 31
Bottlebrush Avenue, Noosa Heads. The investigation was carried out by Tectonic for Camtegan Pty Ltd.
This report presents the results of our geotechnical investigation, incorporating a slope stability
assessment, together with geotechnical advice for the project.
The proposed development comprises a three storey unit block constructed with masonry blockwork, and a
partially inground semi-basement level for carparking and storage. No earthworks plans were provided but
based on the layout details provided it is anticipated earthworks will include cuts for the basement level of up
to about 3 m deep in in the rear, northern part with the excavation daylighting in the central/southern part.
Only minor filling is expected to be required up to say 1 m in height to form finished surface levels.
Site investigation works comprised desktop review, a walk-over survey combined with drilling of two
boreholes to depths of 3 m and 5 m below ground level (BGL) with insitu strength testing.
The site presents as a south-west facing sand dune slope dipping at an overall angle of about 10° to 12°.
Subsurface conditions encountered in the boreholes comprised, very loose to loose silty sand fill to 0.6 m
BGL (in borehole BH1 only), overlying natural loose sand becoming medium dense below depths of 1.2 m
to 1.4 m BGL and grading to dense below 3.6 m to 4.3 m BGL.
Groundwater was not encountered in any test pits at the time of investigation.
Based upon the existing site conditions, and subject to the implementation of recommendations given within
this report, it is our assessment that there would be a Low (L) Risk of global slope instability affecting the
proposed unit development.
Excavations through the existing soils should be achievable using conventional earthmoving plant (e.g. small
or larger excavators with toothed buckets). Temporary cuts in the very loose to loose sands could be formed
at 1V:2H and at 1V:1 in medium dense or dense 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. If space
restrictions limit battering of temporary cuts on the site, some form of retention will be required such as sheet
piles.
Based on the results of the investigation, the natural soil profile is non-reactive and so would be estimated to
have characteristic surface movements (‘ys’) of less than 20 mm (equivalent to Class S based on the reactivity
of the foundations assessed in accordance with AS 2870-2011 Residential Slabs and Footings). It should be
noted that the predicted order of movement is based on the existing soil profiles (i.e. no additional cutting or
filling), and moisture content changes within soils due to normal seasonal moisture variations only.
Footings for the proposed development 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 0.5 m into medium dense (or denser) natural sands. Such materials were encountered below depths of
1.2 m to 1.4 m BGL. Thus, piled footings will be required unless excavations expose such materials at or near
foundation subgrade level. Given the sandy soil profile and depths of footings 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 residences, open bored piers or driven piles are not considered to be suitable for this
site.
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Table of Contents
1.0 INTRODUCTION ........................................................................................................................................................ 1
2.0 PROPOSED DEVELOPMENT ................................................................................................................................... 1
3.0 METHOD OF INVESTIGATION ................................................................................................................................. 2
4.0 RESULTS OF INVESTIGATION ................................................................................................................................ 2
4.1 Site Description............................................................................................................................................. 2
4.2 Topography................................................................................................................................................... 4
4.3 Geology ........................................................................................................................................................ 5
4.4 Subsurface Conditions.................................................................................................................................. 5
4.5 Groundwater ................................................................................................................................................. 7
4.6 Surface Drainage .......................................................................................................................................... 7
4.7 Existing Structures ........................................................................................................................................ 7
5.0 SLOPE STABILITY ASSESSMENT .......................................................................................................................... 8
5.1 Existing Conditions ....................................................................................................................................... 8
5.2 Stability Assessment..................................................................................................................................... 8
6.0 GEOTECHNICAL RECOMMENDATIONS .............................................................................................................. 10
6.1 Development Limitations ............................................................................................................................ 10
6.2 Earthworks – General ................................................................................................................................. 10
6.2.1 Site Preparation and Trafficability ......................................................................................................... 10
6.2.2 Excavations ........................................................................................................................................... 10
6.2.3 Filling..................................................................................................................................................... 11
6.3 Building Foundations .................................................................................................................................. 11
6.3.1 Indicative Site Classification.................................................................................................................. 11
6.3.2 Footing Design ...................................................................................................................................... 11
6.4 Retaining Structures ................................................................................................................................... 13
6.5 Drainage ..................................................................................................................................................... 13
7.0 SUMMARY & CONCLUSIONS................................................................................................................................ 13
8.0 LIMITATIONS .......................................................................................................................................................... 14
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TABLES
Table 1: Summary of Subsurface Conditions ...................................................................................................................... 7
Table 2: Stability Risk Levels .............................................................................................................................................. 8
Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007) ......................................................................... 9
Table 4: Retaining Structure Design Parameters .............................................................................................................. 13
TEXT FIGURES
Text Figure 1: Extract of K Architects’ site layout plans for semi basement and ground floor levels ................................... 1
Text Figure 2: Recent aerial image of the site (courtesy Nearmap © ™, image dated 29 October 2020) ........................... 3
Text Figure 3: View from Bottlebrush Avenue looking north-east at front of site ................................................................. 3
Text Figure 4: View of eastern side of residence looking north east. .................................................................................. 3
Text Figure 5: View of rear of property looking north-west .................................................................................................. 4
Text Figure 6: Site plan showing ground surface contours (courtesy SCC My Maps website)............................................ 4
Text Figure 7: Extract of Gympie Special 1:100,000 Geology Map ..................................................................................... 5
Text Figure 8: Location and soil profile at borehole BH1 ..................................................................................................... 6
Text Figure 9: Location and soil profile at borehole BH2 ..................................................................................................... 6
Text Figure 10: Footing depth required to prevent undermining....................................................................................... 12
FIGURES
Figure 1: Site Plan
APPENDICES
APPENDIX A
Test Pit Reports & Explanatory Notes
APPENDIX B
AGS Guidelines - Qualitative Terminology for Use in Assessing Risk to Property
Some Guidelines for Hillside Construction
APPENDIX C
Limitations
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1.0 INTRODUCTION
This report details a geotechnical investigation undertaken for a proposed unit development at 31
Bottlebrush Avenue, Noosa Heads. The investigation was carried out by Tectonic for Camtegan Pty Ltd..
This report presents the results of our geotechnical investigation, incorporating a slope stability
assessment, together with geotechnical advice for the project. 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 extension in accordance with the Australian Geomechanics Society “Guidelines for
Landslide Risk Management”, dated March 2007 (AGS 2007).
2.0 PROPOSED DEVELOPMENT
Architectural drawings were supplied to us with the project brief (K Architecture, Dwg. No. SK01 to SK04 [not
inclusive], Issue P1, dated 12 November 2020). We understand that the proposed development comprises a
three storey unit block constructed with masonry blockwork, with a partial inground semi-basement for
carparking and storage. No earthworks plans were provided but based on the layout details provided it is
anticipated earthworks will include cuts for the basement level of up to about 3 m deep in in the rear,
northern part with the excavation daylighting in the central/southern part. Only minor filling is expected to be
required up to say 1 m in height to form finished surface levels.
The property has existing connections to town water supply and sewerage. Extracts from the proposed
layout drawings are shown in Text Figure 1 below.
Seim-Basement Level Plan Level 1 Floor Plan
Text Figure 1: Extract of K Architects’ site layout plans for semi basement and ground floor levels
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3.0 METHOD OF INVESTIGATION
As part of our assessment, a desk-top study was carried out comprising a review of published geological
maps, slope stability studies as well as Noosa Shire Council (NSC) planning overlays and site information.
An experienced geotechnical engineer from Tectonic undertook a site walk-over on 2 December 2020 to
visually assess any indicators of past slope instability. The walk-over included assessment of soil
exposures, surface drainage conditions, topography, evidence of erosion or past instability, and vegetation
coverage/condition.
This was incorporated with a subsurface investigation comprising the drilling of boreholes at two locations.
The boreholes, designated BH1 and BH2, were hand augured at the front and rear of the property to depths
of 3 m and 5 m below ground (BGL), respectively. In-situ testing, using the dynamic cone penetrometer
(DCP) method, was carried out from the ground surface adjacent to and within each borehole with the testing
extended below the base of the boreholes to depths of 3.8 m and 5.4 m BGL in boreholes BH1 and BH2
respectively. The boreholes were backfilled on completion with spoil arising during drilling, with excess
material slightly mounded at surface.
Laboratory testing was not warranted due to the sandy nature of the subsurface conditions encountered.
Reports of the boreholes and explanatory notes are attached. Test locations are shown in Text Figure 1
above. The results of the desk-top study and walk-over survey are included in Section 4 below.
4.0 RESULTS OF INVESTIGATION
4.1 Site Description
The subject site comprised an allotment described as Lot 136 on RP88934, covering an area of 506 m2 (Ref.
Text Figure 2 below). The site had frontage to Bottlebrush Avenue to the south west with access via a
concrete driveway crossover. Surrounding properties comprised residential housing to the north, east and
west with a shopping complex situated south east of the property.
At the time of the investigation there was an existing two-story residence situated in the central part of the
allotment. The existing dwelling was built into the slope with construction comprising masonry blockwork with
a lightweight roof. There was existing masonry blockwork retaining walls at the front and rear of the
property. Wall heights varied from about 1 m up to a maximum of 3 m high (adjacent to the driveway entry in
the south-western part).
Approx. lot boundary
BH2
Existing residence
BH1
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Text Figure 2: Recent aerial image of the site (courtesy Nearmap © ™, image dated 29 October 2020)
Site conditions at the time of our investigation are shown below and overleaf in Text Figures 3 to 5 overleaf.
Text Figure 3: View from Bottlebrush Avenue looking north-east at front of site
Text Figure 4: View of eastern side of residence looking north east.
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Text Figure 5: View of rear of property looking north-west
4.2 Topography
The site was located on sand dune with an overall slope of about 10° to 12° dipping to the southwest (as
illustrated in Text Figure 6 below).
Lot boundary
Text Figure 6: Site plan showing ground surface contours (courtesy SCC My Maps website)
The existing residence was sited on a levelled building pad with cut and fill estimated, by visual appraisal, to
be up to about 1.5 m deep/high.
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4.3 Geology
Available geological information 1 indicates that the site is underlain by Pleistocene age dune sand (Ref. Text
Figure 7).
Approx. site location
Text Figure 7: Extract of Gympie Special 1:100,000 Geology Map
4.4 Subsurface Conditions
Subsurface conditions encountered in the boreholes are summarised below, with borehole reports providing
detailed descriptions given in Appendix A.
Subsurface conditions encountered in the boreholes comprised, very loose to loose silty sand fill to 0.6 m
BGL (in borehole BH1 only), overlying natural loose sand becoming medium dense below depths of 1.2 m
to 1.4 m BGL and grading to dense below 3.6 m to 4.3 m BGL.
Photographs showing cuttings from the boreholes which illustrate the typical subsurface conditions
encountered are given in Text Figure 8 and 9 below and overleaf
A tabulated summary of the encountered subsurface conditions is also presented in Table 1 on the following
page.
1
Queensland Government, Department of Mines and Energy, 1:100,000 Gympie Special Geology Map, Sheet 9445 & Part 9545, 1999
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BH1
0m
1m
2m
1m
2m 3m
Text Figure 8: Location and soil profile at borehole BH1
BH2
0m 1m
1m 2m
2m 3m
3m 4m
4m 5m
Text Figure 9: Location and soil profile at borehole BH2
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Table 1: Summary of Subsurface Conditions
Very Loose to Loose Medium Dense Dense Sand
BH Topsoil Fill
Silty Sand/Sand Sand
No.
Depth in metres below ground
BH1 NE 0.0 - 0.6 0.6 - 1.2 1.2 - 3.6 3.6 – 3.8 (TD)
BH2 0 - 0.05 NE 0.05 – 1.4 1.4 – 4.3 4.3 – 5.4 (TD)
Notes:
1) TD – denotes borehole ‘Termination Depth’ of DCP testing.
More detailed descriptions of the subsurface conditions are provided in the borehole reports attached in
Appendix A.
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
occur at shallower depths, and at locations not previously observed, particularly following periods of
prolonged or heavy rainfall.
4.6 Surface Drainage
Surface drainage would be expected to follow natural surface contours to the south west with flows directed
into the kerbside drainage on Bottlebrush Avenue, thus draining into the road side drainage system. Run-off
would likely currently be of relatively low volume due to the sandy nature of the exposed soils at the site,
and is currently interrupted by terracing, retaining walls and landscaping features.
It is acknowledged that a catchment for the site exists to the north east, extending to the crest of the dune
(Ref. Section 4.2 above). However, 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.
4.7 Existing Structures
The exiting residence comprised a two storey masonry brick structure sited on a levelled building pad with
concrete block walls supporting cut and fill in various locations around the perimeter ranging in height from
about 1 m up to a maximum of 3 m high. The structures did not exhibit any signs of distress that could be
attributed to slope instability however the retaining wall at the front of the stie alongside the driveway was
cracked. The distress to this wall appeared likely to be a result of subsidence due to consolidation
settlement of the loose sand (both fill and upper natural foundation materials) under the wall and
embankment loading.
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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 9).
Mapping indicates that the site is within a Moderate Landslide Hazard Area.
Lot boundary
Text Figure 1: Extract from NSC 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. No visual signs of global slope
instability were observed across the site. No landslide back scarps or areas of naturally ‘hummocky’
ground were observed.
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)
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
L Low Risk
to 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.
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Given the geology, topography and particularly the relatively gently sloping terrain of the sand dune 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).
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 below is our qualitative assessment of landslide risk for the development site. A summary of qualitative
terminology for use in assessing risk to property is attached (taken from AGS 2007).
Table 3: Details of Qualitative Risk Assessment for Property (AGS 2007)
Assessed
Hazard Likelihood Consequence
Risk
Comments
Given the low to moderate natural gradients through
the proposed building areas, and scope of the
Failure through very loose to proposed site works, it is considered Unlikely that a
loose fill and loose natural soils Unlikely Medium Low landslide would develop in these materials, subject
above the foundation depth 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.
The likelihood of a deep failure through the medium
Deep failure through the natural dense or denser natural sand is assessed as Rare due
medium dense or denser sand Rare Major Low to the gentle to moderate overall ground slopes through
below the foundation depth the building areas and no signs of any existing slope
instability. Although the consequence of such a failure
would be Major, the resultant risk is Low as per AGS
2007.
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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6.0 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 will include cuts for the basement level of up to about 3 m deep in in the rear 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 – General
6.2.1 Site Preparation and Trafficability
Any uncontrolled fill, existing mulch, and organic rich topsoil must be stripped from the development areas,
whilst vegetation, tree stumps and large roots must be ‘grubbed out’. Based on the boreholes, mulch and
topsoil stripping depths should generally range between 0.1 m and 0.2 m BGL, however deeper pockets of
mulch/topsoil or uncontrolled fill may exist and deeper, localised grubbing out of tree roots may be required.
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 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.
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 watercourses.
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 cuts in the very loose to loose sands could be formed
at 1V:2H and at 1V:1H in medium dense 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).
If the above temporary batter slopes cannot be achieved, due to spatial restraints, temporary shoring will be
required (e.g. sheet piles). 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
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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 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).
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).
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 95% 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
Based on the results of the investigation, the natural soil profile is non-reactive and so would be estimated to
have characteristic surface movements (‘ys’) of less than 20 mm (equivalent to Class S based on the reactivity
of the foundations assessed in accordance with AS 2870-2011 Residential Slabs and Footings).
It should be noted that the predicted order of movement is based on the existing soil profiles (i.e. no additional
cutting or filling), and moisture content changes within soils due to normal seasonal moisture variations only.
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, pool, 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 of 1.2 m to 1.4 m BGL in the boreholes. Thus, piled
footings will be required unless excavations expose such materials at or near foundation subgrade level.
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Piles so founded may be designed using an allowable end bearing capacity of 300 kPa. High level footings,
where achievable in deeper cut areas, may be designed using an allowable bearing capacity of 100 kPa
provided that they are founded in the natural medium dense (or denser) sands.
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 would be required to densify any high level footing bases prior to the placement of reinforcing
steel.
Due to the presence of loose sands, together with the close proximity of adjacent residences, open bored
piers or driven piles are not considered to be suitable for this site. 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.
Footing design should also account for potential soil reactivity to be equivalent to Class S. It should be noted
that placement of reactive clay may result in a more severe equivalent site classification, such as M or greater.
All footings should found such that they are not adversely affected by any adjacent excavations, batter
slopes, trenches, retaining walls, or in ground structures (e.g. swimming pool) 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.
Text Figure 10: Footing depth required to prevent undermining
It will be important to ensure close supervision of screw pile installation, as piling will not encounter drilling
refusal at the recommended founding depth, and piles could extend to much greater depth than necessary.
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.
17 December 2020
Report No. 20370-001-Rev0 12
Page 18
PROPOSED UNIT DEVELOPMENT
31 BOTTLEBRUSH AVENUE, NOOSA HEADS
6.4 Retaining Structures
Retaining structures must be founded as per the recommendations in Section 4.2 above. 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.
Retaining structures must be founded as per the recommendations in Section 4.2 above with the piled
footings, if required, also designed to resist lateral loads imposed by the retaining wall. 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 in the sands in front of the wall.
We suggest the parameters outlined in Table 4 may be adopted for retaining wall design: The values in
Table 4 assume that the walls are fully drained and no allowance is included for hydrostatic pressures,
construction loading, up-slope footing loadings, the effects of sloping ground and backfill compaction
stresses.
Table 4: 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 28 0.36 0.53 2.77
Sands
Medium Dense (or
1.9 34 0.28 0.44 3.54
Denser) Sands
Future Controlled Fill* * * * * *
Note: * Depends on fill material type and level of compaction.
6.5 Drainage
Surface diversion drainage should be constructed above the crest of any new cut or fill embankment (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 retaining walls in order to prevent the development of
hydrostatic pressure (e.g. slotted ‘aggi’ pipe wrapped in filter ‘sock’ placed in gravel backfill).
All collected surface water, roof water, and overflow from any tanks/pools should be directed by pipes or
surface channels (with erosion protection) to the kerbside drainage alongside Bottlebruch Avenue. Due to
potential for stormwater infiltration, any permeable surface channels must be located a minimum of 5 m from
any future structures or batters.
7.0 SUMMARY & CONCLUSIONS
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.
17 December 2020
Report No. 20370-001-Rev0 13
Page 19
PROPOSED UNIT DEVELOPMENT
31 BOTTLEBRUSH AVENUE, NOOSA HEADS
8.0 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.
17 December 2020
Report No. 20370-001-Rev0 14
Page 20
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Ph: 07 5478 9016
PROJECT:
PROPOSED UNIT DEVELOPMENT
31 BOTTLEBRUSH AVENUE
NOOSA HEADS
BH2 TITLE:
Site boundary
SITE PLAN
CLIENT:
CAMTEGAN PTY LTD
DRAWN: DATE:
BH1 BNH 16/12/2020
CHECKED: DATE:
DJP 17/12/2020
SCALE:
AS SHOWN
LEGEND:
Borehole Location
0 10m 20m
Scale (Approximate Only)
PROJECT NO.: FIGURE: REV:
Notes:
20370-001 1 0
Base plan courtesy NearMap © ™
Page 21
PROPOSED UNIT DEVELOPMENT
31 BOTTLEBRUSH AVENUE, NOOSA HEADS
APPENDIX A
Borehole Reports & Explanatory Notes
17 December 2020
Report No. 20370-001-Rev0
Page 22
Cored Borehole No.
BH1
Page 1 of 1
Engineering Log - Cored Borehole Project No.: 20370
Client: Camtegan Pty Ltd Commenced: 02/12/2020
Project Name: Proposed Unit Development Completed: 02/12/2020
Hole Location: 31 Bottlebrush Ave, Noosa Heads Logged By: BH
Hole Position: 509147.0 m E 7050356.0 m N MGA94 Zone 56 Checked By: DJP
Drill Model and Mounting: Hand Auger Inclination: -90° RL Surface: No survey
Barrel Type and Length: Bearing: 360° Datum: AHD Operator: MS/BH
Drilling Information Rock Substance Rock Mass Defects
Strength
Graphic Log
Weathering
Material Description Is(50) Defect Defect Description
RQD (%)
SCR (%)
rock type: grain characteristics, colour, Spacing thickness, type, inclination, planarity,
TCR (%)
Support
Method
structure, minor components - Axial (mm) roughness, coating/infilling
Water
RL Depth - Diametral
1000
3000
(m) (m)
100
300
Particular General
VH
EH
EL
VL
30
M
H
L
Silty SAND (FILL), fine to medium grained, brown
grey, trace of organics
Silty SAND, fine to medium grained, grey
(AEOLIAN)
1
Not Encountered
SAND, fine to medium grained, pale grey
(AEOLIAN)
HA
TECTONIC 2.00.2 LIB-GINT.GLB Log 1 TECTONIC CORED BOREHOLE 20370.GPJ <<DrawingFile>> 17/12/2020 14:47 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 2.00.2 2016-10-13 Prj: Tectonic 2.00 2016-02-16
2
3
Hole Terminated at 3.00 m
Target depth
4
5
Method Water Graphic Log/Core Loss Weathering Strength
AS - Auger Screwing FR - Fresh (indirect tensile strength)
Level (Date) Core recovered (hatching
WB- Washbore indicates material) SW - Slightly Weathered EL - Extremely Low
HQ3- HQ3 Core Barrel Inflow DW - Distinctly Weathered VL - Very Low
NQ3- NQ3 Core Barrel Partial Loss Core loss XW - Extremely Weathered L - Low
Complete Loss RS - Residual Soil M - Medium
H - High
Support VH - Very High
T - Timbering EH - Extremely High
Page 23
Cored Borehole No.
BH2
Page 1 of 1
Engineering Log - Cored Borehole Project No.: 20370
Client: Camtegan Pty Ltd Commenced: 02/12/2020
Project Name: Proposed Unit Development Completed: 02/12/2020
Hole Location: 31 Bottlebrush Ave, Noosa Heads Logged By: BH
Hole Position: 509166.0 m E 7080373.0 m N MGA94 Zone Checked By: DJP
56
Drill Model and Mounting: Hand Auger Inclination: -90° RL Surface: No survey
Barrel Type and Length: Bearing: 360° Datum: AHD Operator: MS/BH
Drilling Information Rock Substance Rock Mass Defects
Strength
Graphic Log
Weathering
Material Description Is(50) Defect Defect Description
RQD (%)
SCR (%)
rock type: grain characteristics, colour, Spacing thickness, type, inclination, planarity,
TCR (%)
Support
Method
structure, minor components - Axial (mm) roughness, coating/infilling
Water
RL Depth - Diametral
1000
3000
(m) (m)
100
300
Particular General
VH
EH
EL
VL
30
M
H
L
Silty SAND (TOPSOIL), fine to medium grained,
dark brown, grey, trace of organic
Silty SAND, fine to medium grained, grey brown
(AEOLIAN)
SAND, fine to medium grained, pale grey
(AEOLIAN)
1
TECTONIC 2.00.2 LIB-GINT.GLB Log 1 TECTONIC CORED BOREHOLE 20370.GPJ <<DrawingFile>> 17/12/2020 14:47 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 2.00.2 2016-10-13 Prj: Tectonic 2.00 2016-02-16
2
Not Encountered
HA
becoming pale grey and brown, with trace
organics
3
SAND, fine to medium grained, pale grey
(AEOLIAN)
4
5
Hole Terminated at 5.00 m
Target depth
Method Water Graphic Log/Core Loss Weathering Strength
AS - Auger Screwing FR - Fresh (indirect tensile strength)
Level (Date) Core recovered (hatching
WB- Washbore indicates material) SW - Slightly Weathered EL - Extremely Low
HQ3- HQ3 Core Barrel Inflow DW - Distinctly Weathered VL - Very Low
NQ3- NQ3 Core Barrel Partial Loss Core loss XW - Extremely Weathered L - Low
Complete Loss RS - Residual Soil M - Medium
H - High
Support VH - Very High
T - Timbering EH - Extremely High
Page 24
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
HA Hand Auger 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
Rev0
October 2013
Page 25
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 26
METHOD OF ROCK DESCRIPTION USED ON LOGS
CLASSIFICATION AND INFERRED STRATIGRAPHY
Rock 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.
STRENGTH
Point Load
Symbol Term Index, Is(50) Field Guide
(MPa)
VL Very 0.03 to 0.1 Material crumbles under firm blows with sharp end of pick; can be peeled
Low with knife; too hard to cut a triaxial sample by hand. Pieces up to 30 mm
can be broken by finger pressure.
L Low 0.1 to 0.3 Easily scored with a knife; indentations 1 mm to 3 mm show in the specimen
with firm blows of pick point; has dull sound under hammer. A piece of core 150
mm long by 50 mm diameter may be broken by hand. Sharp edges of core may
be friable and break during handling.
M Medium 0.3 to 1 Readily scored with a knife; a piece of core 150 mm long by 50 mm diameter
can be broken by hand with difficulty.
H High 1 to 3 A piece of core 150 mm long by 50 mm diameter cannot be broken by hand but
can be broken with pick with a single firm blow; rock rings under hammer.
VH Very 3 to 10 Hand specimen breaks with pick after more than one blow; rock rings under
High hammer.
EH Extremely >10 Specimen requires many blows with geological pick to break through intact
High material; rock rings under hammer.
Relationship between Is(50) and UCS (unconfined compressive strength) will vary with rock type and strength, and
should be determined on a site-specific basis. UCS is typically 10 to 30 x Is(50), but can be as low as 5.
ROCK MATERIAL WEATHERING
Symbol Term Field Guide
Soil developed on extremely weathered rock; the mass structure and
Residual
RS substance fabric are no longer evident; there is a large change in volume
Soil but the soil has not been significantly transported.
Extremely Rock is weathered to such an extent that it has soil properties - i.e. it either
EW
Weathered disintegrates or can be remoulded, in water.
Whole of rock is discoloured, usually by iron staining or bleaching to the
extent that the colour of the original rock is not recognizable. Rock strength
Highly
HW is significantly changed by weathering. Porosity may be increased by
Weathered
leaching, or may be decreased due to deposition of weathering products in
Distinctly
DW pores.
Weathered
Whole of rock is discoloured, usually by iron staining or bleaching to the
Moderately extent that the colour of the original rock is not recognizable; but shows little
MW
Weathered or no change of strength from fresh rock.
Slightly Rock is slightly discoloured but shows little or no change of strength relative
SW
Weathered to fresh rock.
FR Fresh Rock shows no sign of decomposition or staining.
ABBREVIATIONS FOR DEFECT TYPES AND DESCRIPTIONS
Defect Type Coating or Infilling Roughness
BP Bedding parting Cn Clean POL Polished
X Foliation Sn Stain S Smooth
C Contact Vr Veneer SL Slickensided
L Cleavage Ct Coating or Infill S Smooth
JT Joint Clay Clay RF Rough
SS/SZ Sheared seam/zone (Fault) Fe Iron oxide VR Very rough
Qz Quartz Planarity
CS/CZ Crushed seam/zone (Fault)
DS/DZ Decomposed seam/zone PR Planar
IS/IZ Infilled seam/zone UN Undulating
S Schistocity ST Stepped
V Vein
DB Drilling break
Rev3
October 2017
Page 27
PROPOSED UNIT DEVELOPMENT
31 BOTTLEBRUSH AVENUE, NOOSA HEADS
APPENDIX B
AGS Guidelines - Qualitative Terminology for Use in
Assessing Risk to Property
Some Guidelines for Hillside Construction
17 December 2020
Report No. 20370-001-Rev0
Page 28
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 29
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 30
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 31
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
114 Australian Geomechanics Vol 42 No 1 March 2007
Form No. 68029 RL2 August 2010
Page 32
PROPOSED UNIT DEVELOPMENT
31 BOTTLEBRUSH AVENUE, NOOSA HEADS
APPENDIX C
Limitations
17 December 2020
Report No. 20370-001-Rev0
Page 33
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)