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14169-001-Rev0 17 Webb Rd -Revised Draft · 132002.220527.1
Attached to the e-mail 132002.220527.1 Change to Existing Approval Engineering & Geo tech reports (1of 6 emails).
GEOTECHNICAL INVESTIGATION Proposed Residence 17 Webb Road Sunshine Beach T AF R D Report For Mr Murray Charlton Report No. 14169-001-Rev0 26 February 2015 Tectonic Geotechnical Pty Ltd PO Box 899 Buderim Qld 4556 Mobile: 0437 755 750 / 0437 756 711 www.tectonicgeo.com.au A.B.N. 83 165 727 828
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17 WEBB ROAD, SUNSHINE BEACH
PROPOSED RESIDENCE
Document Review
Document No. Revision Prepared By Reviewed By Date Issued
001 0 Ashley Davey Darryn Quinn 26 February 2015
Report Distribution
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Revision Method of Delivery Issued To
Mr Murray Charlton
0 Electronic
([email protected])
Mr Peter Barlow
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0 Electronic Barlow Shelley Consulting Engineers
([email protected])
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Prepared By: Reviewed By:
Ashley Davey RPEQ 8159 Darryn Quinn RPEQ 7602
Principal Geotechnical Engineer Principal Geotechnical Engineer
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Executive Summary
This report details the results of a geotechnical investigation carried out for the proposed renovation to the
existing residence at 17 Webb Road, Sunshine Beach. The geotechnical investigation was undertaken by
Tectonic Geotechnical Pty Ltd (Tectonic) for Mr Murray Charlton. This report summarises the results of the
investigation and provides an assessment of slope stability, together with advice regarding earthworks,
foundations, retaining walls and drainage for construction.
The development will comprise renovations to the residence within the footprint of the existing house. Up to
about 1 m of cut / fill is anticipated. Construction will comprise a combination of masonry and light-weight
cladding walls.
The site investigation comprised drilling of three boreholes up to depths of 3.2 m below ground level (BGL) at
the front and rear of the existing residence. A soil sample obtained from the boreholes was forwarded to a
geotechnical testing laboratory for soil classification analysis.
Subsurface conditions encountered in the boreholes comprised loose to medium dense sands (fill and
natural soils) to about 0.5 m BGL, then medium dense natural sands grading to dense and very dense with
increasing depth. Groundwater was not encountered in the boreholes during the investigation.
The site classification for the (existing) natural soil profile is Class S (in accordance with AS2780). The
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building shall be supported on footings which penetrate at least 0.2 m into the natural medium dense sand
(about 0.5 m BGL), or may be supported by screw-in piles taken into the dense to very dense sands at about
2.5 m BGL.
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Considering the existing site conditions, and subject to the implementation of recommendations given within
this report, it is our opinion that there is a Low (L) Risk of global slope instability affecting the proposed
residence, with a factor of safety against slope instability of at least 1.5.
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Table of Contents
1.0 INTRODUCTION........................................................................................................................................................ 1
2.0 PROPOSED DEVELOPMENT................................................................................................................................... 1
3.0 AIMS & METHOD OF INVESTIGATION ................................................................................................................... 2
3.1 Fieldwork ...................................................................................................................................................... 2
3.2 Laboratory Testing........................................................................................................................................ 2
4.0 THE SITE ................................................................................................................................................................... 2
5.0 SUBSURFACE INVESTIGATION FINDINGS ........................................................................................................... 6
5.1 Regional Geology ......................................................................................................................................... 6
5.2 Subsurface Conditions.................................................................................................................................. 6
5.3 Laboratory Test Results................................................................................................................................ 7
6.0 T
SLOPE STABILITY ASSESSMENT.......................................................................................................................... 7
6.1 Existing Conditions ....................................................................................................................................... 7
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6.2 Stability Assessment..................................................................................................................................... 8
6.2.1 Qualitative Assessment........................................................................................................................... 8
6.2.2 Quantitative Assessment ........................................................................................................................ 9
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7.0 ENGINEERING ASSESSMENT .............................................................................................................................. 11
7.1 Earthworks.................................................................................................................................................. 11
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7.1.1 Site Preparation and Trafficability ......................................................................................................... 11
7.1.2 Excavations........................................................................................................................................... 11
7.1.3 Filling..................................................................................................................................................... 11
7.2 Building Foundations .................................................................................................................................. 12
7.2.1 Site Classification.................................................................................................................................. 12
7.2.2 Footing Design...................................................................................................................................... 12
7.3 Retaining Structures ................................................................................................................................... 13
7.4 Permanent Drainage................................................................................................................................... 13
8.0 LIMITATIONS .......................................................................................................................................................... 13
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TABLES
Table 1: Stability Risk Levels .............................................................................................................................................. 8
Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007) ......................................................................... 9
Table 3: Retaining Structure Design Parameters .............................................................................................................. 13
TEXT FIGURES
Text Figure 1: Proposed development layout...................................................................................................................... 1
Text Figure 2: Aerial image of site and surrounding area (courtesy Queensland Globe) .................................................... 2
Text Figure 3: Contours illustrating topography of local area (courtesy NSC web mapping) .............................................. 3
Text Figure 4: Font of residence viewed from driveway ...................................................................................................... 4
Text Figure 5: Undulating grassed area to rear of house, viewed looking north-east.......................................................... 4
Text Figure 6: Sand dune slope to rear of grassed area, viewed looking north................................................................... 5
Text Figure 7: View from beach looking west towards residence........................................................................................ 5
Text Figure 8: Pieces of indurated sand recovered from borehole BH3.............................................................................. 6
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Text Figure 9: Extract from NSC landslide hazard overlay map......................................................................................... 7
Text Figure 10: Results of Slope/W modelling ................................................................................................................. 10
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Text Figure 11: Footing depth to minimize risk of undermining ........................................................................................ 12
FIGURES
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Figure 1: Site Plan
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APPENDICES
APPENDIX A
Borehole & DCP Reports and Explanatory Notes
APPENDIX B
Laboratory Test Certificate
APPENDIX C
AGS Guidelines - Qualitative Terminology for Use in Assessing Risk to Property
Some Guidelines for Hillside Construction
APPENDIX D
Report Limitations
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1.0 INTRODUCTION
This report details the results of a geotechnical investigation undertaken for the proposed renovation to the
existing residence at 17 Webb Road, Sunshine Beach. We understand that the structural integrity of the
existing building has been compromised by inadequate stormwater drainage, and sections of the building are
to be renovated to improve the current conditions.
The geotechnical investigation was performed by Tectonic Geotechnical Pty Ltd (Tectonic) for Mr Murray
Charlton, in accordance with Proposal P14259-Rev0, dated 2 December 2014. Barlow Shelley Consulting
Engineers (Barlow Shelley) are the consulting civil and structural engineers for the project.
The investigation comprised a site walk-over by an experienced geotechnical engineer, drilling of boreholes,
and subsequent laboratory testing of a soil sample. This report summarises the results of the investigation
and includes a slope stability assessment. Recommendations are provided regarding the design of
earthworks, retaining structures, footings, and drainage.
2.0 PROPOSED DEVELOPMENT
Based upon architectural drawing provided by PCA Architects, it is understood that the development will
comprise renovations to the residence within the building envelope of the existing residence. Construction is
anticipated to comprise slab on ground and masonry walls for the ground floor, with light-weight materials
used to construct the first floor. The proposed building area is approximately level, therefore minimal
earthworks are likely to be required. A site plan illustrating the proposed site layout is presented in Text
Figure 1 below (taken from the PCA Architects drawing).
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Text Figure 1: Proposed development layout
The property has access to town water and sewerage.
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3.0 AIMS & METHOD OF INVESTIGATION
The main aims of the investigation are to address geotechnical (including slope stability) issues for the
proposed residence, with our report prepared to address the requirements of the relevant Noosa Shire
Council (NSC) codes and policies.
3.1 Fieldwork
An experienced geotechnical engineer from Tectonic undertook a site walk-over on 16 February 2015 to
make a visual assessment of surface features relevant to the geotechnical investigation. The walk-over
included assessment of soil and rock outcrops, surface drainage conditions, topography, evidence of
erosion, condition of existing/surrounding structures, and vegetation coverage/condition.
This was incorporated with a subsurface investigation comprising three boreholes (designated BH1 to BH3)
drilled using hand auger equipment to depths of up to 3.2 m below ground level (BGL). Dynamic cone
penetrometer (DCP) testing was conducted adjacent to, and within, the boreholes, and at one additional
location (DCP1), to enable estimation of the in situ soil strength.
Disturbed soil samples were taken from the boreholes for laboratory testing. The boreholes were backfilled
with drilling spoil to the surface upon completion.
The fieldwork was undertaken in the presence of an experienced geotechnical engineer from Tectonic.
Borehole and DCP reports, along with explanatory notes, are presented in Appendix A. Borehole and DCP
locations are shown in the Figure 1 (at end of text).
3.2 Laboratory Testing
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One disturbed soil sample recovered from borehole BH1 was dispatched to Geotech (SC) Pty Ltd, a NATA
accredited geotechnical laboratory located in Kawana, for geotechnical testing. Laboratory testing was
undertaken in accordance with Australian Standard AS1289 Method for Testing Soils for Engineering
Purposes and comprised Particle Size Distribution analysis to assess the soil classification. Laboratory test
results are summarised in Section 5.3. The laboratory test certificate is attached in Appendix B.
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4.0 THE SITE
The site is described as Lot 1 on RP151243 and covers an area of 2,015 m². A ‘handle’ provides access
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from Webb Road to the west, with surrounding properties occupied by one to two storey residences.
Foredunes leading down to Sunshine Beach are located to the west. Text Figure 2 illustrates the site
position and surrounding development. Text Figure 3 shows the topography of the broader area.
Text Figure 2: Aerial image of site and surrounding area (courtesy Queensland Globe)
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Watercourses
Site
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Text Figure 3: Contours illustrating topography of local area (courtesy NSC web mapping)
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As illustrated in Text Figure 3, the site is located on land around RL 10 m to 15 m AHD between the
foredunes which run parallel to Sunshine Beach and the higher sand hills to the west (which range up to
about RL 50 m AHD). Natural watercourses flow from the sand hills to the beach about 100 m to the north
and south of the site.
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Surface gradients around the existing house are less than 10° (<15%) in an easterly direction, with relatively
flat grassed areas separated from the house/pool terrace by a short slope with a gradient of 15° to 20° (26%
to 36%). The foredune located about 20 m to 30 m east of the existing structures slopes at about 30° (58%)
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down towards the beach.
At the time of investigation the site was occupied by an existing two storey residence of masonry (lower) and
light-weight (upper) construction, with a tiled roof. The house is surrounded by garden beds and areas of
lawn, with a paved driveway and parking area at the front (leading from Webb Road) and in-ground pool to
the rear. Scattered trees including mostly palms and pandanus are located around the house.
No indications of erosion or slope instability were observed. The foredune to the east of the house was
relatively well vegetated and did not show any signs of recent scarping.
Refer to Text Figures 4 to 7 on the following pages for photographs showing site conditions at the time of
investigation.
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Text Figure 4: Font of residence viewed from driveway
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Text Figure 5: Undulating grassed area to rear of house, viewed looking north-east
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Text Figure 6: Sand dune slope to rear of grassed area, viewed looking north
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Existing house
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Text Figure 7: View from beach looking west towards residence
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Our observations of surface features relevant to the slope stability assessment are summarised as follows:
Structures on the immediately surrounding properties are in good condition and show no signs of
instability (i.e. no significant cracks in rigid structures, with walls and posts in vertical alignment).
The site is located close to a beach foredune, which has a steep slope about 20 m to 30 m from the
existing structures. No signs of recent instability were observed in the foredune, with the dune face
relatively well vegetated and having a relatively linear and planar slope.
No indications of global slope instability were observed on the site; i.e. no landslide scarps, tension
cracks, distressed structures or groundwater seepage was evident.
5.0 SUBSURFACE INVESTIGATION FINDINGS
5.1 Regional Geology
The 1:100,000 scale Gympie Special Geological Map (Sheet 9444 and Part 9544) indicates that the site is
underlain by a Pleistocene age quartz sand dune, with a younger Holocene age dune forming a lower berm
closer to, and parallel with, the beach.
5.2 Subsurface Conditions
The subsurface conditions encountered in boreholes BH1 and BH3 were relatively consistent and
comprised:
Silty sand fill of loose to medium density to between 0.15 m and 0.4 m BGL; then
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Natural sand / silty sand grading from medium dense to dense or very dense with depth.
Pieces of indurated sand (Ref. Text Figure 8) were encountered from 2.8 m and 2.5 m BGL in boreholes
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BH1 and BH3, respectively, with these boreholes terminating at 3.1 m and 3.2 m BGL.
Borehole BH2 encountered loose grading to dense sand and gravel fill, with hand auger refusal at 0.9 m
BGL. These fill materials may represent a stormwater or effluent soakage pit / trench.
DCP1 put down on the level grassed area to the east of the house indicates a similar density profile as
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encountered in boreholes BH1 and BH3, with very dense materials inferred from about 2.5 m BGL.
Groundwater seepage was not encountered in the boreholes during the investigation. It should be noted that
groundwater seepage may develop following periods of heavy or prolonged rainfall.
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For detailed descriptions of the soil units encountered in the boreholes, refer to the boreholes and DCP
reports, together with explanatory notes, attached in Appendix A.
Text Figure 8: Pieces of indurated sand recovered from borehole BH3
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5.3 Laboratory Test Results
Particle size distribution (PSD) analysis was carried out on a disturbed sample recovered from 0.15 m to
0.6 m BGL in borehole BH1, indicating that the sand is fine to medium grained with a trace (3%) of silt. The
PSD indicates that the sand has a D10 value of about 0.16 mm, that being the grain size that 10% of the sand
particles are smaller than.
The PSD laboratory test certificate is attached in Appendix B.
6.0 SLOPE STABILITY ASSESSMENT
6.1 Existing Conditions
NSC natural hazard overlay mapping indicates that the site may be susceptible to landslide (pink shading, as
shown in Text Figure 9).
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SITE
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Text Figure 9: Extract from NSC landslide hazard overlay map
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It should be noted that the NSC map is a broad-scale indication of the potential landslide susceptibility only
and is superseded by site specific investigation and analysis works. As detailed in Section 4, the site does
not exhibit any indicators of slope instability. No landslide scarps or areas of erosion were observed. The
existing and surrounding structures showed no signs of previous landslide activity. Medium dense grading
to dense and very dense sands were encountered in the boreholes at relatively shallow depth, and no
groundwater seepage was discovered.
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6.2 Stability Assessment
6.2.1 Qualitative Assessment
The risk assessment for this project has been carried out following the AGS 2007 Practice Note Guidelines
for Landslide Risk Management. Relative levels of risk and their implications are given in Table 1 below
and the Qualitative Terminology for Use in Assessing Risk to Property is attached in Appendix C.
Table 1: 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
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Acceptable. Manage by normal slope maintenance procedures.
Note: (1) The implications for a particular situation are to be determined by all parties to the risk assessment and may
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depend on the nature of the property at risk; these are only given as a general guide.
Given the geology and topography of this site, particularly the relative position of the residence (to be
renovated) to the foredune slope (20 m to 30 m west of the slope), it is unlikely that landslide could affect the
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proposed development. Sand dune slopes are generally close to the ‘limit of equilibrium’ where the surface
gradient is about 30°. Our measurements indicate that the dune slope is typically 30°. 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
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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).
Steep sand dune slopes generally remain marginally stable (i.e. FOS just greater than 1.0) when they are:
well vegetated (mix of ground cover, shrubs and small trees);
not subjected to concentrated stormwater flows;
not surcharged with additional loads (e.g. fill); and
when the ‘toe’ of the dune is not disturbed.
Where dunes are well vegetated, the plant roots can provide a surface reinforcing layer which may enable
dunes to stand up relatively steeply. Direct discharge of stormwater onto dune slopes may cause channel
erosion, undermining and disturbance of vegetation, and development of generally localized instability. It is
critical that stormwater runoff be collected (or re-directed) and disposed of off-site prior to reaching the dune
slopes.
The primary trigger for large-scale instability of sand dunes is when the toe of the dune is disturbed. This may
be caused by excavations or natural erosion. At this site, erosion of the dune toe and undercutting of the
slope could occur during high seas when waves surge over the low-height barrier dune. The annual likelihood
of such events may vary, and possibly increase, subject to factors including sea level rise.
On similar sites in the Noosa region, sand dune instability due to undercutting of the toe generally occurs as a
translational-type slide where a ‘slab’ of sand on the dune face slides down slope. The depth of such sliding
may range up to a few metres during one event, but on-going erosion can cause retrogressive failure of dune
slopes leading to multiple sliding events, if left unchecked.
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Considering the existing site conditions, and subject to the implementation of recommendations given in
Section 7, it is our opinion that there is a Low (L) Risk of global slope instability affecting the proposed
residence. Regulators (NSC) normally require that a Very Low or Low Risk of landslide affecting property
must be demonstrated to enable development approval. Summarised in Table 2 below is our qualitative
assessment of landslide risk for the site. A summary of qualitative terminology for use in assessing risk to
property is attached in Appendix C (taken from AGS 2007).
Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)
Assessed
Hazard Likelihood Consequence
Risk
Comments
The likelihood of a failure through the medium
dense sands is assessed as Unlikely due to the low
1: Localised landslide through to moderate gradients, lack of groundwater and
medium dense to dense sands effective friction angle of the sand. Numerical
on 15° to 20° slope near house, Unlikely Medium Low modelling (Ref. Section 6.2.2) also indicates that an
with slide extending below the acceptable factor of safety against instability for this
foundation depth scenario will be attained. Although the
consequence of instability could be Medium, the
resultant risk is Low as per AGS 2007.
Based upon current climatic conditions, it would be
Barely Credible that the 20 m to 30 m distant
foredune slope could be eroded to such an extent
2: Significant retrogressive
failure of foredune due to erosion
of toe during a high sea event(s)
leading to undermining of house
Rare
T Major Low
that the house could be undermined. However,
depending on the extent of sea level rise and
possible climate change over the design life of the
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building (at least 50 years), the likelihood of such a
foundations
failure could increase to Rare. Combined with a
Major consequence of such instability, the resultant
risk is Low as per AGS 2007.
Note: Barely Credible = the event is inconceivable or fanciful over the design life
Rare = the event is conceivable but only under exceptional circumstances over the design life
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6.2.2 Quantitative Assessment
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In order to calculate the factor of safety (FOS) against slope instability for the proposed residence, numerical
analysis has been conducted using the Slope/W computer program for the assumed ‘worst case’ conditions.
We have assumed a ground surface profile of 10° through the building area, increasing to 20° for a 2 m high
slope, then flattening to 10°. The analysed subsurface profile comprises medium dense sand to 1 m depth,
then becoming dense sand. Note that we have not analysed the stability of the foredune slope as this is
located well east of the proposed house on public land.
As recommended in Section 7, footings and retaining walls will be founded in medium dense (or denser)
sands. A surcharge load of 20 kPa has been applied to replicate the proposed construction, which is
equivalent to a two storey house or 1m depth of fill.
No groundwater was encountered at the time of investigation. However, as a conservative measure to
account for possible ‘worst case’ transient (short-term) conditions, a piezometric groundwater level has been
included in the model at a depth of 1 m BGL.
Results of the numerical slope stability analysis are illustrated in Text Figure 10. The key points from our
analysis are summarised as follows:
Shear strength and unit weight parameters adopted were based upon drained (or effective) soil
shear strength parameters taken from the values recommended for similar materials in Appendix D
of Australian Standard AS4678-2002 ‘Earth Retaining Structures’.
Analysis was undertaken for a specified range of slip circle centroids and radii. Text Figure 10
shows the slip circle with the lowest FOS value. Coloured zones indicate FOS contours.
For long-term (drained) conditions, the minimum calculated FOS is 2.1.
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This FOS result satisfies the generally accepted minimum requirement for hillside development (i.e.
minimum FOS of 1.5).
Our analysis indicates that the proposed development will achieve the required minimum FOS against slope
instability. Subject to implementation of the recommendations made in Section 7 during building works,
there would be a Low Risk of slope instability affecting the proposed residence.
General recommendations to help maintain the stability of the site are given in the document “Some
Guidelines for Hillside Construction”, which is attached in Appendix C.
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Text Figure 10: Results of Slope/W modelling
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7.0 ENGINEERING ASSESSMENT
7.1 Earthworks
It is assumed that cut and fill up to about 1.5 m BGL may be required to form the ground level building pad.
7.1.1 Site Preparation and Trafficability
Following removal of sections of the existing building, and clearing of vegetation and any unrequired below
ground elements (e.g. services), tree stumps and large roots must be ‘grubbed out’ and any organic rich
topsoil stripped from the construction area. Topsoil materials must not be used in structural fill, however may
be placed across landscaping areas.
The subgrade materials exposed after site stripping and excavation to design levels (up to 1.5 m BGL) are
expected to medium dense sands and silty sands. The soils would be subject to strength loss from repetitive
vehicle loading (particularly from rubber tyred plant). Due to the potential for poor trafficability, placement of
a minimum 150 mm thick granular working platform may be required to create a ‘confining’ layer to prevent
loosening of the sand, particularly across access and laydown areas.
The site should be graded to shed surface water runoff away from construction areas. Swale drains should
be constructed along the toes of any cuts, and above cuts where possible, with the drains graded to
discharge collected waters to a control point before release off-site.
7.1.2 Excavations
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Excavations to depths of up to 1.5 m BGL in the mostly loose to medium dense sands should be achievable
using conventional earthmoving plant (e.g. small to medium excavators) with toothed bucket attachments.
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Temporary cuts in loose to medium dense sand and batters in controlled fill may be formed no steeper than
1V:1H. Any permanent batter slopes in such materials should be formed at 1V:2H, or flatter if possible
(1V:3H). Flatter batters may be required if groundwater seepage is encountered, or if earthworks are
undertaken during a period of heavy rainfall.
Any excavations required adjacent to existing structures, including those on adjoining properties, will need to
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be specifically designed to ensure that the structures are not adversely affected (e.g. 'undermined').
The above recommendations do not supersede any existing safety regulations or legislation applicable to
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excavations (e.g. limits on personnel entry into trenches).
7.1.3 Filling
Should any importation of fill be required, the use of low reactivity materials (plasticity index less than 15%) is
recommended for any fill under the building.
All structural fill should be compacted at moisture contents within the range of ±2% of optimum moisture
content for Standard Compaction. Fill should be placed in 250 mm thick (loose thickness) layers and be
compacted by repeated rolling to achieve a dry density ratio of at least 95% of the maximum Dry Density
Ratio (DDR), based upon the Standard Compaction method, or 70% Dry Density Index.
To compact sand fill it is normally necessary to place the loose fill layer, flood the area with water and
compact with a vibratory smooth drum roller. Care will need to be taken with the addition of water if the
sands are particularly silty.
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 must be ‘benched’ into the natural slope, over-filled by 0.5 m (horizontally) and then trimmed back to the
well compacted material.
Due to the close proximity of houses on adjoining properties, care will need to be taken within any activities
which may cause excessive ground vibrations (e.g. fill compaction). It would be prudent to conduct a
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dilapidation survey of nearby structures before commencement of construction, and to monitor ground
vibrations during construction works. Vibration may need to be “switched off” on rollers if excessive
vibrations is encountered.
7.2 Building Foundations
7.2.1 Site Classification
Based on the results of the investigation, the site (existing natural soil profile) is classified as Class S in
accordance with AS 2870-2011 Residential Slabs and Footings. The estimated characteristic surface
movement (‘ys’) at this site is less than 20 mm. It should be noted that the predicted order of movement is
based on the existing natural soil profile (i.e. no cutting or filling), and moisture content changes within soils
due to normal seasonal moisture variations only.
7.2.2 Footing Design
All footings supporting the proposed residence and associated retaining walls must be taken through any fill
and loose sand to found at least 0.2 m into the underlying medium dense (or denser) natural sand. Based
upon the results of the investigation the recommended foundation materials are likely to occur at depths of
about 0.5 m BGL, or deeper where fill is proposed.
High level footings such as a slab beams, pad or strip footings would be suitable to support the proposed
building. Should the client wish to address the assessed low risk associated with retrogressive failure of the
sand dune affecting the building in the future, it is recommended that the building could be supported on
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screw-in piles taken to found in the dense to very dense natural sand at about 2.5 m BGL. These materials
should remain relatively stable even if exposed to wave erosion. Such piles could be designed using an
allowable end bearing capacity of 1 MPa.
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It is recommended that foundation materials should be inspected by a suitably qualified and experienced
engineer to confirm founding depth and allowable bearing capacity.
All footings should found such that they are not adversely affected by any adjacent excavations, batter slopes,
trenches, or retaining walls that are not designed to support building loads. To minimise the potential for any
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adverse interaction effects, footings should found at least below a plane extending 1 m horizontally from the
base of trenches/batter slopes/excavations/retaining walls, then rising up at 1V:1H. This requirement is
illustrated in Text Figure 11 below.
D
Text Figure 11: Footing depth to minimize risk of undermining
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.
26 February 2015
Report No. 14169-001-Rev0 12
Page 18
17 WEBB ROAD, SUNSHINE BEACH
PROPOSED RESIDENCE
7.3 Retaining Structures
Design for temporary or permanent retaining structures could be carried out using a triangular pressure
distribution applicable to the wall type and based on the parameters listed in Table 3. The values in Table 3
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 3: Retaining Structure Design Parameters
Lateral earth pressure coefficients
Unit Friction
Retained material weight angle
Ka Ko
(t/m3) (Degrees) Kp
(Cantilever wall) (Non-yielding wall)
Loose to Medium
1.8 30 0.3 0.5 3.0
Dense Sand
Future Fill * * * * *
Note: * depends on fill material type and level of compaction.
7.4 Permanent Drainage
T
Adequate site drainage must be installed to ensure that natural runoff is directed away from building walls
and footings.
AF
Subsurface drainage must be installed behind retaining walls in order to prevent the development of
hydrostatic pressure. This normally comprises slotted ‘aggi’ pipe wrapped in filter ‘sock’ and placed in gravel
backfill.
All excess stormwater collected around the site (including overflow from rainwater tanks and the swimming
pool) must be directed by pipes / channels / swales to an infiltration system located at least 5 m down slope
R
of the proposed building, and not closer than 10 m from the steep dune slope.
Design of the stormwater infiltration system requires an estimate of soil permeability.
D
Using Hazen’s equation, where soil permeability (k) = 10-2 x D10² m/s
For D10 = 0.16 mm (Ref. Section 5.3)
k= 10-2 x 0.16²
k= 0.000256 m/s (2.56 x 10-4 m/s)
= 22 m/day
This order of permeability is in line with expectations for a fine grained sand (typically 10-3 to 10-4 m/s).
8.0 LIMITATIONS
Your attention is drawn to the document “Report Limitations”, which is included in Appendix D of this report.
The statements presented in this document are intended to advise you of what your realistic expectations of
this report should be, and to present you with recommendations on how to minimise the risks associated with
the services provided by Tectonic for this project.
26 February 2015
Report No. 14169-001-Rev0 13
Page 19
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
M: 0437 755 700 / 0437 756 711
PROJECT:
PROPOSED RESIDENCE
17 WEBB ROAD
DCP1 SUNSHINE BEACH
TITLE:
SITE PLAN
T
CLIENT:
BH2 MR MURRAY CHARLTON
AF
DRAWN: DATE:
ACD 25/02/2015
R
BH3
CHECKED: DATE:
BH1
D DJQ
SCALE:
NOT DEFINED
25/02/2015
LEGEND:
BOREHOLE LOCATION
PROJECT NO.: FIGURE: REV:
Base plan courtesy Barlow Shelley 14169-001 1 0
Page 20
17 WEBB ROAD, SUNSHINE BEACH
PROPOSED RESIDENCE
APPENDIX A
Borehole & DCP Reports and Explanatory Notes
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AF
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Page 21
Borehole No.
BH01
Page 1 of 1
Engineering Log - Borehole Project No.: 14169
Client: Barlow Shelley Consulting Engineering Commenced: 16/02/2015
Project Name: Proposed Residence Completed: 16/02/2015
Hole Location: 17 Webb Road, Sunshine Beach Logged By: BIW
Hole Position: 511149.0 m E 7079185.0 m N Checked By: ACD
Drill Model and Mounting: Inclination: RL Surface: No survey
Hole Diameter: 100 mm Bearing: Datum: Operator:
Drilling Information Soil Description Observations
Relative Density
Classification
Hand
Penetration
DCP Test (Depth:Blows/100mm)/
Graphic Log
Consistency
Samples Material Description
Penetrometer Structure and
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
Support
Symbol UCS Additional Observations
Method
Remarks secondary and minor components, colour
Water
RL Depth (kPa)
(m) (m)
100
200
300
400
500
SM Silty SAND (FILL), fine to medium grained, 0.00: 2
D to
grey, roots to 0.15m depth M 0.10: 2
DS SP SAND, fine to medium grained, yellow brown, L to
0.15-0.6m trace of silt MD 0.20: 2
0.30: 3
0.40: 3
0.5
0.50: 5
SM Silty SAND, fine to medium grained, grey 0.60: 5
0.70: 7
MD
1.0
T 0.80: 7
0.90: 8
AF
1.00: 8
1.10: 7
1.20: 9
TECTONIC 1.01.1 LIB.GLB Log IS AU BOREHOLE 1 14169.GPJ <<DrawingFile>> 25/02/2015 13:16 8.30.004 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 1.01.1 2015-01-19 Prj: Tectonic 1.01.1 2015-01-19
1.30: Augered to 1.4m
1.40: 10
1.5
R
1.50: 10
D
HA
M 1.60: 14
1.70: 15
D
1.80: 18
1.90: 20
2.0
SM becoming red brown 2.00: 25
2.10: 25
2.5
VD
2.70: Augered to 2.8m
SM 2.80: 13
becoming grey, some pieces of indurated
sand 2.90: 20
3.0
3.00: 20
Hole Terminated at 3.10 m
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
AS - Auger Screwing U - Undisturbed Sample D - Dry VS - Very Soft
No resistance Level (Date) M - Moist
RR - Rock Roller ranging to D - Disturbed Sample S - Soft
WB- Washbore Inflow SPT - Standard Penetration Test W - Wet F - Firm
refusal
Partial Loss VSt - Very Stiff
H - Hard
Complete Loss
Graphic Log/Core Loss Plastic Limit VL - Very Loose
Core recovered (hatching Classification Symbols L - Loose
Support < PL MD - Medium Dense
indicates material) and Soil Descriptions = PL D - Dense
T - Timbering Core loss Based on Unified Soil < PL VD - Very Dense
Classification System
Page 22
Borehole No.
BH02
Page 1 of 1
Engineering Log - Borehole Project No.: 14169
Client: Barlow Shelley Consulting Engineering Commenced: 16/02/2015
Project Name: Proposed Residence Completed: 16/02/2015
Hole Location: 17 Webb Road, Sunshine Beach Logged By: BIW
Hole Position: 511169.0 m E 7079185.0 m N Checked By: ACD
Drill Model and Mounting: Inclination: RL Surface: No survey
Hole Diameter: 100 mm Bearing: Datum: Operator:
Drilling Information Soil Description Observations
Relative Density
Classification
Hand
Penetration
DCP Test (Depth:Blows/100mm)/
Graphic Log
Consistency
Samples Material Description
Penetrometer Structure and
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
Support
Symbol UCS Additional Observations
Method
Remarks secondary and minor components, colour
Water
RL Depth (kPa)
(m) (m)
100
200
300
400
500
SM Silty SAND (FILL), fine grained, grey 0.00: 1
L
0.10: 2
DS SM Clayey Silty SAND (FILL), fine grained sand,
0.15-0.5m 0.20: 4
grey, medium plasticity fines, trace of fine
sized angular gravel MD 0.30: 3
0.40: 7
M
HA
0.5
0.50: 10
0.60: 10
D 0.70: 12
1.0
GP T
Sandy GRAVEL, fine to medium sized angular
gravel, yellow brown and grey, fine grained
sand
0.80: 15
0.90: HB
AF
Hole Terminated at 0.90 m
Practical Refusal
TECTONIC 1.01.1 LIB.GLB Log IS AU BOREHOLE 1 14169.GPJ <<DrawingFile>> 25/02/2015 13:16 8.30.004 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 1.01.1 2015-01-19 Prj: Tectonic 1.01.1 2015-01-19
1.5
R
D
2.0
2.5
3.0
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
AS - Auger Screwing U - Undisturbed Sample D - Dry VS - Very Soft
No resistance Level (Date) M - Moist
RR - Rock Roller ranging to D - Disturbed Sample S - Soft
WB- Washbore Inflow SPT - Standard Penetration Test W - Wet F - Firm
refusal
Partial Loss VSt - Very Stiff
H - Hard
Complete Loss
Graphic Log/Core Loss Plastic Limit VL - Very Loose
Core recovered (hatching Classification Symbols L - Loose
Support < PL MD - Medium Dense
indicates material) and Soil Descriptions = PL D - Dense
T - Timbering Core loss Based on Unified Soil < PL VD - Very Dense
Classification System
Page 23
Borehole No.
BH03
Page 1 of 1
Engineering Log - Borehole Project No.: 14169
Client: Barlow Shelley Consulting Engineering Commenced: 16/02/2015
Project Name: Proposed Residence Completed: 16/02/2015
Hole Location: 17 Webb Road, Sunshine Beach Logged By: BIW
Hole Position: 511175.0 m E 7079185.0 m N Checked By: ACD
Drill Model and Mounting: Inclination: RL Surface: No survey
Hole Diameter: 100 mm Bearing: Datum: Operator:
Drilling Information Soil Description Observations
Relative Density
Classification
Hand
Penetration
DCP Test (Depth:Blows/100mm)/
Graphic Log
Consistency
Samples Material Description
Penetrometer Structure and
Condition
Recovery
Tests soil type: plasticity or particle characteristics,
Moisture
Support
Symbol UCS Additional Observations
Method
Remarks secondary and minor components, colour
Water
RL Depth (kPa)
(m) (m)
100
200
300
400
500
SM Silty SAND (FILL), fine grained, grey 0.00: 1
L to 0.10: 2
SM Clayey Silty SAND (FILL), fine grained, dark MD
0.20: 3
grey, medium plasticity fines, trace of fine
sized angular gravel 0.30: 4
DS SM Silty SAND, fine grained, grey and pale grey 0.40: 6
0.4-0.9m 0.5
0.50: 7
MD 0.60: 7
0.70: 8
1.0
T 0.80: 7
0.90: 8
AF
1.00: 9
1.10: 10
1.20: 11
TECTONIC 1.01.1 LIB.GLB Log IS AU BOREHOLE 1 14169.GPJ <<DrawingFile>> 25/02/2015 13:16 8.30.004 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 1.01.1 2015-01-19 Prj: Tectonic 1.01.1 2015-01-19
1.5
R
M
HA
D
1.80: Augered to 1.9m
1.90: 7
2.0
SP SAND, fine to medium grained, yellow brown 2.00: 8
D
2.10: 7
2.20: 10
2.30: 11
2.40: 12
2.5
SM 2.50: 13
Silty SAND, fine to medium grained, dark
grey, some pieces of indurated sand
2.80: Augered to 2.9m
2.90: 10
3.0
3.00: 10
3.10: 20
3.20: 22
Hole Terminated at 3.20 m
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
AS - Auger Screwing U - Undisturbed Sample D - Dry VS - Very Soft
No resistance Level (Date) M - Moist
RR - Rock Roller ranging to D - Disturbed Sample S - Soft
WB- Washbore Inflow SPT - Standard Penetration Test W - Wet F - Firm
refusal
Partial Loss VSt - Very Stiff
H - Hard
Complete Loss
Graphic Log/Core Loss Plastic Limit VL - Very Loose
Core recovered (hatching Classification Symbols L - Loose
Support < PL MD - Medium Dense
indicates material) and Soil Descriptions = PL D - Dense
T - Timbering Core loss Based on Unified Soil < PL VD - Very Dense
Classification System
Page 24
9 KG DYNAMIC CONE PENETROMETER
CLIENT : Barlow Shelley Consulting Engineering SHEET : 1 OF 1
CONTRACTOR : Tectonic
PROJECT : Proposed Residence
LOCATION : 17 Webb Road, Sunshine Beach
PROJECT No. : 14169
TEST: DCP1
LOGGED: BIW 16/02/2015 CHECKED: ACD
EASTING: 511186.0 m NORTHING: 7079195.0 m
Depth (m)
Blows per 100 mm (AS 1289.6.3.2-1997)
0 5 10 15 20 25
0.5
1.0
T
AF
TECTONIC 1.01.1 LIB.GLB Log IS DCP 3 PER PAGE 14169.GPJ <<DrawingFile>> 24/02/2015 16:47 8.30.004 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 1.01.1 2015-01-19 Prj: Tectonic 1.01.1 2015-01-19
1.5
R
D
2.0
2.5
3.0
Form Number: DGIS15 RL0
Comments
Page 25
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
FV
PP
Bulk disturbed sample
T
Field vane shear test expressed as uncorrected shear strength (sv = peak value, sr = residual value)
Pocket penetrometer test expressed as instrument reading in kPa
AF
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
R
Rev0
October 2013
D
Page 26
METHOD OF SOIL DESCRIPTION
USED ON LOGS
CLASSIFICATION AND INFERRED STRATIGRAPHY
Soil and rock is classified and described in borehole and test pit logs using the preferred method given in AS1726 – 1993,
(Amdt1 – 1994 and Amdt2 – 1994), Appendix A.The material properties are assessed in the field by visual/tactile methods.
Particle Size Plasticity Properties
Major Division Sub Division Particle Size40
BOULDERS > 200 mm
COBBLES 63 to 200 mm
Coarse 20 to 63 mm
GRAVEL Medium 6.0 to 20 mm
Fine 2.0 to 6.0 mm
Coarse 0.6 to 2.0 mm
C
SAND Medium 0.2 to 0.6 mm
Fine 0.075 to 0.2 mm
SILT 0.002 to 0.075
CLAY < 0.002 mm mm
MOISTURE CONDITION AS1726 - 1993
Symbol Term Description
D
M
Dry
Moist
T
Sands and gravels are free flowing. Clays & Silts may be brittle or friable and powdery.
Soils are darker than in the dry condition & may feel cool. Sands and gravels tend to cohere.
AF
W Wet Soils exude free water. Sands and gravels tend to cohere.
CONSISTENCY AND DENSITY AS1726 - 1993
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
R
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
D
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 – 1993, and may be subject to corrections for overburden pressure and
equipment type.
Rev0
October 2013
Page 27
17 WEBB ROAD, SUNSHINE BEACH
PROPOSED RESIDENCE
APPENDIX B
Laboratory Test Certificate
T
AF
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26 February 2015
Report No. 14169-001-Rev0
Page 28
Particle Size Distribution Report
Client: Tectonic Geotechnical Pty Ltd Report Number: G15001 - 20/1
Client Address: PO Box 899 Buderim QLD 4556
Job Number: G15001 Report Date: 18/02/2015
Project: Laboratory Testing Sample Supplied Order Number:
Location B & S,House , Webb Street Page 1 of 1
Lab No: 101600 Sample Location
Date Sampled: 16/02/2015 HA 1
Date Tested: 18/02/2015 Depth 0.15 - 0.6m
Sampled By: Client Supplied 17/02/15
Sample Method: N/A
Material Source: Site
For Use As: - Lot Number: -
Remarks: - Spec Number: -
Test Method:
T
A.S. Sieve Sizes
AS1289.3.6.1
Specification
Minimum
Percent Passing Specification
Maximum
AF
75.0mm
63.0mm
53.0mm
37.5mm
26.5mm
R
19.0mm
16.0mm
D
13.2mm
9.5mm
6.7mm
4.75mm
2.36mm
1.18mm 100
0.600mm 99
0.425mm 97
0.300mm 81
0.150mm 4
0.075mm 3
Approved Signatory Form Number
Accredited for compliance with ISO/IEC 17025
REP APSD-1-4
Mel Burnett
NATA Accred No:1551
Page 29
17 WEBB ROAD, SUNSHINE BEACH
PROPOSED RESIDENCE
APPENDIX C
AGS Guidelines - Qualitative Terminology for Use in
Assessing Risk to Property
Some Guidelines for Hillside Construction
T
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26 February 2015
Report No. 14169-001-Rev0
Page 30
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 UNLIKELY D
T
design life.
-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.
5x10-6
AF
-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
R
Approximate Cost of Damage
Description Descriptor Level
Indicative Notional
Value
200%
Boundary
D
Structure(s) completely destroyed and/or large scale damage requiring major engineering works for
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 31
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
T
-5
E - RARE 10 M L L VL VL
-6
F - BARELY CREDIBLE 10 L VL VL VL VL
AF
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
R
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
D 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 32
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,
ROCK OUTCROPS
& BOULDERS
T
Remove or stabilise boulders which may have unacceptable risk.
Support rock faces where necessary.
boulders, building rubble etc in fill.
Disturb or undercut detached blocks or
boulders.
AF
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.
R
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.
D
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 33
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
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114 Australian Geomechanics Vol 42 No 1 March 2007
Form No. 68029 RL2 August 2010
Page 34
17 WEBB ROAD, SUNSHINE BEACH
PROPOSED RESIDENCE
APPENDIX D
Report Limitations
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26 February 2015
Report No. 14169-001-Rev0
Page 35
REPORT LIMITATIONS
This report has been prepared for the purpose outlined in Tectonic’s proposal and no responsibility is
accepted for the use of this report, 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 report. 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 study 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
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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.
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Any assessments made in this report 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 report (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 report.
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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
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accepted by Tectonic for incomplete or inaccurate data supplied by others.
This report is provided for the sole use by the Client and its professional advisers. No responsibility
whatsoever for the contents of this report will be accepted to any person other than the Client. Any use
which a third party makes of this report, 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 report.
Rev 0 (October 2013)
Used in these records
14169-001-Rev0 17 Webb Rd -Revised Draft.pdfRelated documentApplication case desk ↗
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