Council archive · source document
Appendix4-SlopeStabilityAssessment · MCU18/0135
Attached to the e-mail Detached House (Report, Slope Stability, Proposal Plans, Landscaping, Engineering, DA Form) - MCU18/0135.
6 August 2018 Project No. 18197-001-Rev0
Structures Engineering Design
1 Indiana Place
Kuluin QLD 4558
Email: [email protected]
SLOPE STABILITY ASSESSMENT – PROPOSED RESIDENCE
LOT 15 ON SP111721, MARCUS DUNES COURT, CASTAWAYS BEACH
Dear Scott,
1.0 INTRODUCTION
As requested, Tectonic has undertaken a slope stability assessment for a proposed residence at Lot 15 on
SP111721 Marcus Dunes Court, Castaways Beach. This report presents the results of our 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 residence in accordance with the Australian Geomechanics Society “Guidelines for
Landslide Risk Management”, dated March 2007 (AGS 2007).
1.1 Details of the Site and Development
The subject site is described as Lot 15 on SP111721 and covers an area of 954 m2 (refer to Text Figure 1).
The site was vacant at the time of our site assessment. Further details describing the site are provided in
Section 2.
Site location
Marcus
Dunes Court
Text Figure 1: Aerial image of the site (image source: Nearmap dated 9 July 2018)
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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Structures Engineering Design 18197-001-Rev0
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Architectural building design drawings of the proposed residence were provided to Tectonic. Text Figures 2
and 3 below show the proposed location and style of construction of the residence. The drawings indicate
that the proposed residence will comprise a two storey structure with walls mostly comprising cladded
framing, along with some rendered blockwork walls to form the garage and on part of the northern side of the
house. A pool is proposed to be constructed on the eastern side of the residence and will be set mostly
above ground. The drawings indicate generally minor cut and fill earthworks (generally less than 0.5 m
height) to achieve a level building pad.
Text Figure 2: Extract of Reitsma architectural drawing Proposed Site Plan ref. 4225 Sheet 2/15 Rev A
Text Figure 3: Extract of Reitsma architectural drawing Perspective Views no. 04 ref. 4225 Sheet 14/15 Rev A
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Structures Engineering Design 18197-001-Rev0
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1.2 Method and Scope of Investigation
As part of our slope stability assessment, a desk-top study was carried out comprising a review of
published geological maps, council landslide hazard mapping and a ‘soil test’ report prepared by Ground
Drill (Ref. Job No. 18/180, dated 7 June 2018).
A walk-over assessment was carried out in order to make an appraisal of the general condition of the site
in regard to topography, drainage, vegetation cover, geology, erosion and slope stability. The walk-over
survey was carried out by an experienced geotechnical engineer from Tectonic on 19 July 2018.
The results of the desk-top study and walk-over survey are included in Section 2 below.
1.3 Qualifications of Responsible Engineer
This report has been prepared by Mr Scott Davis, an RPEQ with 10 years’ experience in geotechnical
engineering, including a number of slope stability projects on the Sunshine Coast.
2.0 DESCRIPTION OF EXISTING CONDITIONS
2.1 Geology
Available geological information1 indicates that the site is underlain by the Quaternary age Dunes, mainly
parbolic: quartz sand (refer to Text Figure 4).
LEGEND
Approximate
Site location
Text Figure 4: Extract of Gympie Special 1:100,000 Geology Map
The observed site conditions and ‘soil test’ report results, as summarised below, are consistent with the
published geological information.
1
Queensland Government, Department of Mines and Energy, Gympie Special Geology Map 1:100,000, Sheet 9445 & Part 9545, 1999
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Structures Engineering Design 18197-001-Rev0
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The Ground Drill investigation comprised two boreholes drilled to depths of 4 m below ground level
(BGL), which encountered the following:
Very loose sand to 1.4 m to 1.8 m depth; becoming
Loose sand to depths of about 2.7 m depth
Medium dense sand to the depth of investigation (i.e. 4.0 m BGL).
The Ground Drill investigation included dynamic cone penetrometer (DCP) testing to 4.0 m BGL which
has been used in assessing the above soil density descriptions.
Ground Drill classified the site Class P citing ‘poor bearing capacity’ as the reason. They also noted that
the ‘site would have the characteristics of a Class S site with a Ys (characteristic ground movement due
to moisture variation) of less than 20 mm if not a Class P site.
No groundwater seepage was recorded on the Global Testing borehole logs with the soils described as
‘moist’.
2.2 Topography
As illustrated in Text Figure 5, the site is located just below a topographical ridgeline formed to the west of
the site. The site slopes to the east/north-east at angles of between 5˚ and 7˚ across the building envelope
increasing to 12˚ to the east beyond the extent of the development area. Slope angles across the site were
measured using a hand held clinometer and are consistent with slopes interpolated from contour survey
information. Beyond the downslope site boundary the ground contours indicate a generally consistent slope
angle and direction.
Text Figure 5: Ground surface contours (courtesy Noosa Council Enterprise Mapping System)
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Site conditions are shown in Text Figure 6 below.
Text Figure 6: View looking east across the site on 19 July 2018
2.3 Groundwater
No signs of groundwater seepage (‘springs’) were observed during our walk-over, nor was groundwater
recorded in Ground Drill boreholes.
2.4 Surface Drainage
The topography is such that surface runoff would be shed generally to the north-east. Runoff is anticipated
to enter the site from the property to the north which is at a higher elevation than the subject site. No surface
drainage was noted to the sides of Marcus Dunes Court pavement and runoff is anticipated to enter the site
from the road pavement. Although field inlet pits were noted within the road pavement located along the
road centerline with a very slight grade in the concrete surface to the drains, which should collect some
surface water from the road. No evidence of significant erosion was observed on the site.
2.5 Vegetation
The ground surface across the site was mostly covered with long grass. Some small tress/shrubs were also
present on the site (refer to Text Figure 6 above). Dense vegetation existed downslope to the east of the
site.
2.6 Buildings and Other Structures
There were no buildings or other structures on the site at the time of our site visit other than perimeter
fencing to the northern and eastern boundaries. Fences were noted to be generally straight with no unusual
bows/deformation.
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3.0 ASSESSMENT OF LAND STABILITY
3.1 Existing Conditions
The Noosa Planning Scheme 2017 includes a landslide hazard overlay map (Ref. extract in Text Figure 7).
This site falls within the landslide hazard zone, therefore requiring this site specific slope stability
assessment to be undertaken.
Site location
Text Figure 7: Extract from Noosa Council landslide hazard overlay map
It should be noted that the Noosa landslide hazard map is a broad-scale indication of the potential
landslide susceptibility and is superseded by site specific investigation and analysis. The site did not
exhibit any indicators of global, natural slope instability. No landslide back scarps or areas of naturally
‘hummocky’ ground were observed.
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3.2 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 1 below and the
Qualitative Terminology for Use in Assessing Risk to Property is also attached.
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 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.
Sand dune slopes are generally close to the ‘limit of equilibrium’ where the surface gradient is about 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 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). Site mapping results
indicate that the maximum natural slope is about 12°, therefore landslide activity would be unlikely to occur
subject to adoption of conventional hillside construction practices.
Conventional construction practices on sand dune slopes include:
Maintaining and/or reinstating vegetation coverage outside of building areas (e.g. mix of ground
cover, shrubs and small trees);
Avoiding concentrated stormwater flows;
Providing adequate temporary and permanent support to excavations and fill embankments;
Limiting additional loads (e.g. fill); and
Preventing disturbance to the ‘toe’ of the dune (if possible, i.e. within control of the subject site).
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. Cut
and fill earthworks have the potential to overload and/or undermine the stability of sand dune, therefore must
be carefully planned and implemented.
Considering the existing site conditions (Ref. Section 2), and subject to the implementation of
recommendations given below, it is our opinion that there would be a Low (L) Risk of global slope instability
affecting the proposed development. Regulators (Noosa Shire Council) normally require that a Very Low or
Low Risk of landslide affecting the property must be demonstrated to enable development approval.
Summarised in Table 2 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).
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Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)
Assessed
Hazard Likelihood Consequence
Risk
Comments
Given the gentle natural gradients (i.e. (5˚ to 7˚)
through the building area and moderate grades
downslope (~12˚) it is considered Unlikely that a
1: Failure through very landslip would develop in these materials, subject to
loose/loose natural soils above Unlikely Medium Low implementation of the recommendations in
the foundation depth Section 4 including footings founded below the very
loos/loose materials. Given a potential Medium
impact from such instability the resultant risk would
be Low as per AGS 2007.
The likelihood of a deep failure through the medium
dense natural sand is assessed as Rare due to the
2: Deep failure through the gentle to moderate overall ground slopes, relatively
natural soil below the foundation Rare Major Low light building loads, and no signs of any existing slope
depth instability and lack of groundwater. 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.
4.0 RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document “Some
Guidelines for Hillside Construction”, which is attached.
4.1 Site Layout
The proposed location of the residence shown on the provided architectural drawings is acceptable from a
geotechnical viewpoint.
4.2 Earthworks
We understand that only minor earthworks are proposed to construct a levelled building pad (i.e. generally <
0.5 m cut and fill). If deeper fill embankments are required they should be limited to a maximum of 1 m in total
height and should be retained by engineer designed retaining walls.
Tree roots and organic rich topsoil must be stripped and stockpiled away from the construction area. Such
topsoil must not be re-used in structural fill, however may be retained on site for later use across landscaping
areas, if required. Sandy soils won from excavations on site may be reused as structural fill (where free of
vegetation i.e. excluding topsoil), subject to appropriate moisture adjustment.
Any fill should be compacted at moisture contents within the range of ±2% of optimum moisture content for
Standard Compaction. Fill particles greater than 100 mm must be excluded. Fill should be placed in
maximum 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) for building fill or 75% of the Dry
Density Index for cohesionless fills (e.g. sands).
Fill embankment edges must be over-filled by 0.5 m (horizontally) and then trimmed back to well compacted
material.
Confirmatory compaction testing should be carried out at regular intervals. Details for inspection and testing
of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for Commercial and
Residential Developments.
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Temporary cuts in the very loose to loose sands could be formed at 1V:1.5H for batters up to 2 m in height.
Deeper cuts, if required, should be specifically assessed by Tectonic. Permanent cut batters may be formed
at 1V:3H or flatter. Fill embankments greater than 0.5 m in height should be retained.
4.3 Footings
Footings for the proposed residence, pool and any retaining structures must penetrate through all very loose
and loose sand to found at least 1 m into natural medium dense sand. Based on the Ground Drill boreholes,
founding depths of at least 3.7 m BGL are estimated. Footings founded as per the recommendations above
may be designed using an allowable bearing capacity of 200 kPa. Given the sandy soil profile, steel screw
piles are considered to be a suitable foundation type.
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 pools) 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 8.
Text Figure 8: Zone of influence diagram – footings to be founded below this line
If any soil conditions encountered during construction are found to differ from those noted above, Ground
Drill and Tectonic must be notified immediately and an inspection carried out to determine if changes to
footing design are required.
4.4 Retaining Walls
Design for retaining structures could be carried out using a triangular pressure distribution applicable to the
wall type and based on the soil parameters given below. The soil parameters given below do not include
allowance for hydrostatic pressures, construction loading, adjacent footing loadings, the effects of sloping
ground and backfill compaction stresses, which should all be considered by the design engineer where
relevant.
Soil Type: Very loose to loose sand
Unit Weight: 18 kN/m3
Friction Angle: 28˚
Active earth pressure coefficient (Ka): 0.36
At-rest earth pressure coefficient (Ko): 0.53
Passive earth pressure coefficient (Kp): 2.77
Retaining walls 1 m in height or greater, should be designed by a professional engineer in accordance with
AS4678-2002 Earth retaining structures.
Retaining structures should be founded as per the recommendations in Section 4.3.
Subsurface drainage must be installed behind any retaining walls in order to prevent the development of
hydrostatic pressure, e.g. slotted ‘aggi’ pipe wrapped in filter ‘sock’ placed in gravel backfill.
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4.5 Drainage
Adequate site drainage should be constructed to ensure that stormwater runoff is directed away from the
house walls and footings. All collected surface water, roof water, and any pool water overflow should be
directed by pipes or lined swales to the council stormwater system. Where adequate fall cannot be achieved
to drain water to the council stormwater system, collected water could be directed by pipes to the east,
outletting well down slope (min. 8 m from structures). Stacked rock flow dissipaters should be constructed at
the drainage outlets along with erosion matting and/or vegetation to the surrounds.
As a minimum surface drainage should include a surface swale drain along the southern side of the
residence to intercept surface runoff from the neighboring property. Surface drainage such as swale drains,
diversion bunds or grated channel drains along the western property boundary should also be constructed to
intercept any runoff from the road.
Subsurface disposal of stormwater must not be undertaken.
5.0 SUMMARY & CONCLUSIONS
Based on the findings of our assessment we consider, from a geotechnical viewpoint, that the site is suitable
for the proposed development and that there would be a Low Risk of slope instability subject to
implementation of the recommendations given in this report.
6.0 LIMITATIONS
Your attention is drawn to the document Limitations, which is attached to this letter report. Please contact
the undersigned should you wish to discuss any of the above matters.
Yours faithfully
TECTONIC GEOTECHNICAL PTY LTD
Scott Davis BEng CPEng RPEQ 16439 Ashley Davey BEng (Geological) MIEAust RPEQ 8159
Senior Geotechnical Engineer Director/Principal Geotechnical Engineer
Attachments: Ground Drill Soil Test Report (ref. 18/180 dated 7 June 2018)
Qualitative Terminology for Use in Assessing Risk to Property
Some Guidelines for Hillside Construction
Limitations
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Ground Drill Pty Ltd
PH – 0407035220
Web- www.grounddrill.com.au
Email [email protected]
QBCC Lic – 15034580
Cooroy QLD 4563
Site Classification Report
Job No: 18/180
Date: 07/06/18
Client: Structures
Site Address: Lot 1515 Marcus Dunes Court, Castaways Beach
Proposed Structure: Proposed Residence
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Introduction
The purpose of this report is to classify the site in accordance with AS2870-2011. This
report is based on the field investigation/lab testing and information if any provided by the
client. Further investigation may be required. Further investigation is recommended when
deeper depths of fill or marine clays are thought to be present.
Site Classification
Class “P” (Due to poor bearing capacity)
Based on the soil profiles the site would have the
characteristics of an 'S' site with a approximate Ys of less than
20mm if not a “P”.
This report does not address slope stability, if a slope stability report is required the services
of a suitably qualified Geotechnical Engineer should be sought.
This site may experience settlement in the fill and/or underlying natural material and may
have deep settling marine clays present, the designing engineer should allow for this.
Allowable Bearing Capacity
An approximate bearing capacity of 100kpa was encountered at a depth of 2700mm
below existing ground surface level in the SAND at location BH1 and location BH2.
Bearing capacity can be highly variable over the allotment these depths are specific
to the test locations. Actual founding depth should be nominated by the designing
engineer whilst taking construction and footing type, fill, underground services,
retaining walls, settlement, proposed cut/fill and any trees into account. Soft and/or
settling soils may present within the investigated depths or at deeper depths, further
investigation may be required to establish this.
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Lab Results/Predicted Surface Movement Bore Hole N/A Shrink-Swell N/A Ys N/A Existing Retaining Walls Nil Site Description Future Site Works: Unknown Existing Earthworks: Nil Vegetation: Heavily grassed, scattered small to medium sized trees Slope: 12-20% Allotment Type: Residential Surrounding Allotments: Road to the right,vacant to the left and a bushland reserve to the rear. Surface Water: Surface water from adjoining allotments will traverse this site. Watercourses: Nil Road Status: Sealed Important Notes *Earthworks could affect the site classification and or founding depth. *If any fill is placed on the allotment post investigation the founding depth will change, furthermore placement of reactive fill may change the sites classification. *All top soil and vegetation is to be removed. *Surface water is to be diverted away from structure. *Do not plant trees near the structure which could interfere with the footings performance. *It is the owner’s responsibility to read and understand the CSIRO BTF 18 Foundation Maintenance and Footing Performance: A Home-owner’s Guide. *Strength of founding material can be highly variable dependent upon moisture content. *This investigation undertaken consisted of 2 boreholes only, given the size of the site it is possible that a problem could have been missed. eg. Filled dam/gully, soft soils, fill, springs, boulders, rock etc. We cannot give a definitive assurance that none of these problems exist on the site unless we did a greater number of boreholes which would be uneconomical and impractical. *This report may not provide all necessary information to design an adequate footing system, further investigation may be required using larger drill rigs and/or different testing methods. Trees Unless otherwise stated this report assumes that all trees near the site that could influence the performance of the footings will be removed and/or will be allowed for in the designing engineers design. Therefore, this report excludes the potential effect any trees nearby may have on the structure. Distance from proposed structure that trees can effect footings: 0.75 x 'h' 'M' sites 1.0 x 'h' 'H' sites 1.5 x 'h' 'E' Sites 'h' is the mature height of the tree. Where there are rows of trees the distance should be increased. It is the designing engineer’s responsibility to calculate the yt and add it to the ys.
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Limitations of Report
This report is based on information gathered from the field investigation. Ground Drill should
be notified immediately if ground conditions are found to differ from this report during initial
earthworks.
Unless otherwise stated this report does not address the following issues;
• Mining Subsidence.
• Slope Stability (If the site is in a known slip area or is steep, it is recommended that
a Geotechnical Engineer be engaged to conduct a Slope Stability assessment).
• Deep soft or settling soils
• Soils within investigated depths or deeper may be subject to settlement with
additional load of structure.
• Deep settling marine clays may be present.
• Soil Contamination, hazardous materials and or acid sulphate.
• Any slopes, dimensions or plans in this report are not to scale and only show
approximate testing locations.
• Flood levels (It is the clients responsibility to inform us of any flood levels on the
allotment).
• If water is found in the boreholes this depth may vary greatly over time. This report
does not address the influence any natural springs may have on the structure.
• It is the clients responsibility to inform us of any nearby underground services that
have been or will be installed near the proposed structure.
By using this report you are agreeing to the statements and limitations mentioned in this
report.
Authorised Signatory
Matthew Bennett
on behalf of Ground Drill Pty Ltd
QBCC Lic # 15034580
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Borelogs
BH 1 Soil Description DCP BH 2 Soil Description DCP
0 SAND (SP) – Fine to medium, pale grey, 0 SAND (SP) – Fine to medium, pale grey,
moist, loose. moist, loose.
100 0 100 0
200 0 200 0
300 0 300 0
400 0 400 0
500 0 500 0
600 0 600 0
700 0 700 0
800 0 800 0
900 0 900 0
1000 0 1000 0
1100 1 1100 0
1200 1 1200 0
1300 1 1300 0
1400 2 1400 0
1500 1 1500 0
1600 1 1600 0
1700 2 1700 0
1800 1 1800 1
1900 1 1900 1
2000 1 2000 2
2100 1 2100 1
2200 2 2200 1
2300 1 2300 1
2400 1 2400 1
2500 2 2500 2
2600 1 2600 2
2700 SAND (SP) – Fine to medium, pale grey, 3 2700 SAND (SP) – Fine to medium, pale grey, 5
moist, medium-dense. moist, medium-dense.
2800 4 2800 5
2900 4 2900 5
3000 4 3000 4
3100 4 3100 4
3200 5 3200 5
3300 5 3300 5
3400 5 3400 5
3500 5 3500 5
[OCR of page images]
Borelogs
BH 1 Soil Description DCP |BH 2 Soil Description DCP
0 SAND (SP) - Fine to medium, pale grey, || 0 SAND (SP) — Fine to medium, pale grey, i
moist, loose. moist, loose.
100 0 100 0
200 0 200 0
300 0 300 0
400 0 400 0
500 0 500 0
600 0 600 0
700 0 700 0
800 0 800 0
900 0 900 0
1000 0 1000 0
1100 1 1100 0
1200 1 1200 0
1300 1 1300 0
1400 2 1400 0
1500 1 1500 0
1600 1 1600 0
1700 2 1700 0
1800 1 1800 1
1900 1 1900 1
2000 1 2000 2
2100 1 2100 1
2200 2 2200 1
2300 1 2300 1
2400 1 2400 1
2500 2 2500 2
2600 1 2600 2
2700 |SAND (SP) — Fine to medium, pale grey, |3 2700 |SAND (SP) — Fine to medium, pale grey, 5
moist, medium-dense. moist, medium-dense.
2800 4 2800 5
2900 4 2900 5
3000 4 3000 4
3100 4 3100 4
3200 5 3200 5
3300 5 3300 5
3400 5 3400 5
3500 5 3500 5
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3600 5 3600 6 3700 5 3700 5 3800 4 3800 6 3900 5 3900 5 4000 Hole Terminated. 5 4000 Hole Terminated. 5 [OCR of page images] 3600 5 3600 6 3700 5 3700 5 3800 4 3800 6 3900 5 3900 5 4000 | Hole Terminated. 5 4000 | Hole Terminated. 5
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Site Photos [OCR of page images] Site Photos
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Foundation Maintenance _(() and Footing Performance: *~,. A Homeowner's Guide = Buildings can and often do move, This movement con be up, down, loteral or rotational. The fundamental couse of movement in buildings can usually be related to one of more problems in the foundation soil, It is important for She hesoerenener ip Wasa D0 Sel ype bn-soder So enemies Bex soeioerss Oot Healt be aol te giee inorder ensure that problems in the foundation soil con be prevented, thus protecting ogainst building movement. This Building Technology File is designed to couses of soilveloted building movement, and to suggest pore wpe Dene et pear regs Fr s Soil Types Lronon _— AB wails ae prome 0 eromon, but sandy onl is purticularly meceptible ‘The rypes of soils umaully presens under the copsed! im land zoned for saiikagsetbed aimee Wiser ag abv tak socoaanet GEG UN can be split inne two - or more can naffer from enonion. iene, eee ee Sicitca consent ae exually caused by erosion. Clay sou are te ‘This ix a problem in clay soils. Saturation creates a beg: sttetanion and vwelishrunk problems Lake suspenmon Lebar thoargetahy he baar ren lortab Clasifications for 4 given ates can generally be cbtaioed by Sct eianien ee ee sppbcation to the lexal ys bat there ate seenctimes unertabbe . 7 sand fill for oat FE eT Ea beeen ie eta ey Sees aa 4 Arar yal sa hn a np danificetion em scnding te sauialiy be the poortnce of the baiides aenount Weinkage they expenence with varuseed Seasonal welling water consent. The table below is Table 2.1 from AS 2870, the a ee a ee aad. baking Residential Stab and Footing Coube. the sol incteawe so (ese te. The ep: of tee ‘ wanes bereven different clays, x does the degree of [Castes of Murenent deren ding te abequet deying ou cued by bt weather sme dat in cata plan abe arog ane peo types of sectlement that occur as a reali of tainy 01 dry periods, uneilly of weeks o« months, ee cae fre hang ete spor frome tar * Immediate sertement ccoun when « budding i few placed oo int : foumdatioe sod, as » eeuult of compaction of the seal under the ‘The pwelling of soil coeaes an upward force om the foocings of the weight of che wrucreee, The cobeseve qualicy of clay soll teahding atl shrinkage conates mubenbence chat cokes the wee So te ponte quanto ea oe, c siuet aly Ga keabyimeeagliabens * Consolidation sectiement is « fearure of clay soil and may take Drecause of the expulior of moieure from the wil of becase — Shear failure Paani kot teens hank comentneraan mene This phenomeace occurs when the foundation soil doce aot bere Highly reactive clay ears, whach cam experience high ground movement from mourure changer Eaneemedy reactive wes, which can experience extreme ground movement from mounere changes Aw? Filed sons | Sepa iahrtrsra ee eee SIRS 0 ely es ples age St int test lie sulBicaret strength to support the wright of the footing. There see commmuction, but has knows co take many yeary in two majer pow-conmruction causes exceptional cases. * Significant load increse. ‘These problems ase the peovince of the beilder and should be ales * Reduction of Laseral support of the sell wecder the footing dae into comaiderstion at part of the of the sive fot Comune tress of excavation. thom. Building File 1 19) heals with tbsewe © be clay soil, sheae failure com be caused by saturachon of the soil peublern. adjacent to of wander the footing, GENERAL DEFINITIONS OF SITE CLASSES Os Foundation A Mou and and tock wens with ede ot po proce movement from mouture changes s Slightly reacure clay ware with colby algght ground minement (som mowcure chamyre M Morderacety reactive clay or silt ene, whach can experience modersce ground movement fecwn trmmture Chionges u &
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Tove root growth Trees and whrube that are allowed wu ln the vicinity of fooeings can cause foundstios vod seovernent 1h Two Wap © Room thet crow weber footings may increase in crene-sectsonual tite, exertang upreard premusce on foctang. © Roor im che vicinity of foceings will aboorb euch of the moenare iin the foundation soil, coating shrinkage of wubwidence. Unevenness of Movement The of ground movement des nhed shove oeet to connraction tends to be aneven © Diffceing compaction of foundstios il ptice to coneructine. © Diffcring moinee content of founducon wil prior in coomtinaction. Movemeas dar to pon-comittuction causes is usually more uneven will. Erosion can undermine a thar trawenses the flow or can create the conditions foe wbeat failure by erodeng woul adjacent so a footing that fare ies the same direceiow as the Aerwe. Seruration of day foundation wxl may occur where usbtloor wall creete a dam chat males water pood. |e can sho occ wherever there is a source of water near footings in clay x08 This leads wo a severe seduction in the mrength of the soll which may crease local shear Seasnaal nerilong sod. of clay soil aflec the perimeter of re Sehoastuae Tanenling So encber ade the od en nan Swelling gradually the intenoe wl at abaorpion cominucs Shnmkage wmually beguns where the sun heat m greases. | Effects of Uneven Soil Movement on Structures Erosion and seturation Erosion removes the from under footings tond.ag to covane the structure ander which § © Seep cracking ie the mortar beds im the of thee wealll of above! below openings each a door or ° : jg, in the bricks (usually but noe necessarily im lame with the beds oF perpendi). heotaned affecord by croson of eaturstion of foundation: will cron nc ott mh he buen fall over, floor that hawe lost this support will broome bouncy, sedeecenes rattling o¢nament eu. Effects om fall mascery strectures teickwork will resiat cracking where @ can. bt will sempe to span sites ae ele Wap betas oct eats or oe pain. Tee tumaal to see cracking at weak pow, rach Camphadalenetden. a Ie the event of comcruction wetlement, cracking will ussally eemsin unchanged afner the poocews of settlement has ceased. tantil the ha neutralised che affected portion of and the ee athe eeeneee
Page 22
Hi i ii i z li j i f Hi it i i | Let HE f 5 SLUG 5 seias jeri slgick ance emeane idiag bin and mench water flows alo encowtage cree amd shrub Beatin da ceon chose rompontog ad eoeecaing tee * Incorrect Gilly in roof guttering may erualt ie overflows, as nay qparvers blocked with heaves etc. © Corroded gutecring or dowapipes can spill water to ground. , paral peony feapsramen lcd 2 reer a OT Fee ach cmon, ean sd patio ae de i Ground drainage Jn all soils there is che capacity Sor water to travel on the purface and below ic. Surface waner flows can be cmablihed by inapection during aod aber of prodonged cain, If mrcrssary, a graund drain sytem connected po the wnormrwater collecmon wpterm 4 usually an cary Us a, however, semmetinece necesary when ig oS porwent ovale seigeaioe har Secling br caachal ans ts eau secant ighs and wabsodl wane flows. This mubpect ix ecferend to in BTF 19 may properly be erguaded as an area for an expert commdzant. Raietee eee Jt by exmcerial to remember thar the soil thar affece: foocings cenends well beyond the acrusd line. ‘Watering of garden planes shrabe and trees causes some of the most serious water CLASSIFICATION OF DAMAGE WITH REFERENCE TO WALLS of and rach width Desctiptioo of typical damage and required repair a TL) Dareage Haietine corsets «0.1 om o Fine cracks which do not mood eepair <tom ! (Coacks noticeable but canily filled. Doors and windows sick slightly <S oum 2 Cres an be scat powibly « amall aincrant of wall will nord 5-15 mmm for a samber of cracks 5 to be replaced. and windows stick. Service pipes can fracture. 3 mum of moce in one group) Weahertightnas often impaired Farensive repain work ¥ 7 and replacing sections of 15-25 amen but sho 4 seetie oeeaion tod naan on Generac we lean scm Or bulge mocaceably, wene lous of beating im beams. Service pipes disrupted
Page 23
should crend outwards 2 tranimum of 900 ene (more in highty pesctive seal) and should have a minimum fall way from the of 160. The finished paving should be ao lew than 100 = brick went basen hei wchocane drawage trown this va cenaeid complaaalons tapes heme this bs not (Cikttng eed te ira ol eo te Seti should be same toil type at the surrounding sod and compacted wo the same draaity, Excepe in areas where feeening of waner is an iver, it is wine to remorwe tapn in the buihdong aces and relocate them weil away (rom the building ~ prefeeshdy not uphill from it (ee BTF 19). Warning: this “Technology File deals with ia should be ssid that sahfloor meinture Soe © Water that a transmuted into mamonry metal or tamber beskding dlements causes damage exl‘or decay so those clements. © High subfloor humidicy and moistsee content cerate ao ideal emritonment for various pert, onchading termuses aod speders © Where high moleure fevels are cranametted wn the floorsng and walla, an increase in the dus mite count cas ensue within the | Frac par heer eet in genesal, can bea hatard to inhsbetani, pares those whe ace abmormally wameptitte to reapecatory The Ba The Seapets bie Hiss teen lane 92 elents See ee we endbaekatian meiataeaealente Where a tree is camsing a problem of soil is quanes an doa of aera of edldgp, calbed the of repose lor ons ee Socata Removal of wil wuhin the angie of pepose will amwe mabadomce: rte Ally i fl i H ep i I it if Fi it i! rt Hy ‘ # il li F i i f ‘This TF was prepared by John Lewer FAIS, MIAMA, Partner, regres | The rtercnaten 4) Dee ant Othe WeUeE in the Benen wen erent Pern VATU BOUCHE aret mae Celarwend to be Conme:t amen pulsed information iu eenory, Rt grenied bn ginid Math and et calmed Wo be On estouvve inmate cf te rebewane autyect. Fania protevmonel scvice eaeds to be ohtared beter Wing ary TEN beeed on Ow wtornation srmiid Oars by CSIRO PUBLISHING FO Box 1139, Collingwood 3066, Aurralic frescall 1800 645.051 tel (00) 9062 7666 fox (00) 9662 7555 wow publish cikocw (mat pthating vater®ore ay (© SRD 2003 Unezronees copying of tre Dunding feomrotegy Me 4 pronemned
Page 24
3-5m
Trees
BH2
12-13% 20%
Slope
10m
Slope
BH1
8m 15m
Marcus
Dunes
17%
4m
Court
Slope
3-4m Trees
Client- Structures Ground Drill Pty Ltd
Site - Lot 1515 Marcus Dunes Court, Castaways Beach Sunshine Coast, QLD.
Date - 07/06/18 QBCC # 150 345 80
Job# - 18/180 E: [email protected]
NTS W: www.grounddrill.com.au
P: 0407 035 220
Page 25
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 26
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 27
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 28
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
114 Australian Geomechanics Vol 42 No 1 March 2007
Form No. 68029 RL2 August 2010
Page 29
LIMITATIONS This document has been prepared for the purpose outlined in Tectonic’s proposal and no responsibility is accepted for the use of this document, in whole or in part, for any other purpose. The scope of Tectonic’s Services are as described in Tectonic’s proposal, and are subject to restrictions and limitations. Tectonic did not perform a complete assessment of all possible conditions or circumstances that may exist at the site referenced in the report. If a service is not expressly indicated, do not assume it has been provided. If a matter is not addressed, do not assume that any determination has been made by Tectonic in regards to it. Conditions may exist which were undetectable given that economic and time constraints limit the practical extent of geotechnical investigation. Variations in conditions may occur between investigation locations, and there may be special conditions pertaining to the site which have not been revealed by the investigation and which have not therefore been taken into account in the document. Where variations exist on site, additional studies and actions may be required. Tectonic’s opinions are based upon information that existed at the time that the work was performed. The passage of time, man-made or natural events, may alter the site conditions. It is understood that the Services undertaken allowed Tectonic to form an opinion of the actual conditions of the site at the time the site was visited and cannot be used to assess the effect of any subsequent changes in the quality of the site, or its surroundings, or any laws or regulations. Any assessments made in the preparation of this document are based on the conditions indicated from published sources and the findings of the investigation described. Actual subsurface conditions may differ from those indicated in the document (e.g. between boreholes or test pits). No warranty is included, either express or implied, that the actual conditions will conform exactly to the assessments contained in this document. Where data supplied by the client or other external sources, including previous site investigation data, have been used, it has been assumed that the information is correct unless otherwise stated. No responsibility is accepted by Tectonic for incomplete or inaccurate data supplied by others. This document is provided for the sole use by the Client and its professional advisers. No responsibility whatsoever for the contents of this document will be accepted to any person other than the Client. Any use which a third party makes of this document, or any reliance on or decisions to be made based on it, is the responsibility of such third parties. Tectonic accepts no responsibility for damages, if any, suffered by any third party as a result of decisions made or actions based on this document. Rev 1 (March 2016)
Used in these records
Appendix4-SlopeStabilityAssessment.pdfRelated documentApplication case desk ↗
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