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Slope Stability Report (rec. 16.04.25) · MCU25/0042
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Page 2
[email protected]
arcosgroup.com.au
ABN 51 640 311 841
Attention: Mark and Elle Bennet 27 Mar 2025
By Email ARCOS PROJECT:AG2500070.00
Report 01 Revision Rev A
Report on Geotechnical Investigation
Proposed Residential Development
19 Attunga Heights, Noosa Heads
Arcos Unit Group Pty Ltd (Arcos Group) has undertaken a geotechnical investigation for the above project and client.
SUMMARY OF INVESTIGATION
Results of Australian Geomechanic Society Landslide Risk Assessment
Low
Note: The above is a summary of the detailed investigation results discussed within this report. The entire report must be read,
understood and kept in entirety.
Senior Geotechnical Engineer
Andre Dos Santos B.Eng (Civ), MIEAust, RPEQ,
CPEng, NER
[email protected]
For and On Behalf of Arcos Group
Sunshine Coast | Brisbane | Gold Coast
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Sunshine Coast | Brisbane | Gold Coast
1 INTRODUCTION
Arcos Unit Group Pty Ltd (Arcos Group) was commissioned to undertake a geotechnical investigation for the project
at the location described on the title page of this report.
This report outlines the results of the investigation, laboratory testing, analysis, and interpretive reporting on the
following items:
Review of the existing slope stability hazards, their attributed risks and impacts of the proposed development in
alignment with the practices set out within the Australian Geomechanics Society guidelines; and,
Provide recommendations from a geotechnical context that will avoid or reduce any potential instability.
This report must be kept in entirety. The use of this document is exclusively undertaken in accordance with our terms
and conditions.
2 REGIONAL GEOLOGY
The site is in an area underlain by Pleistocene aged parabolic sand dunes, which typically comprises “quartz sand”.
3 EXISTING STABILITY RISK
Local authorities prepare mapping tools to aid in assessing potential slope stability requirements. The mapping tools
are a “high level” approach where the site specific investigations are specific to a particular site/allotment. It is
important to note that where a site specific investigation and slope stability assessment are undertaken, they take
precedence.
Reference to the available overlays for the area show the site has been initially mapped as “Moderate” in terms of
landslide hazard.
4 GEOTECHNICAL INVESTIGATION
A soil test has recently been undertaken by Australian Soil Investigations (ASI). The soil test comprised the drilling
of two bores to between 2 m and 3 m depth using hand-held auger equipment. In summary, the subsurface conditions
encountered in the bores generally comprised loose to medium dense silty sand (which is consistent with the
published geology). No groundwater seepage was encountered in the bores; however, it should be noted that
groundwater is transient and can fluctuate with seasonal changes and human influences (such as broken
infrastructure). A copy of the ASI report is attached.
5 WALKOVER ASSESSMENT
Geotechnical comments are based on the factual findings of the investigation, best practice, local experience,
published correlations; however, are fundamentally founded in opinion and this should be considered.
A site walkover assessment was undertaken by a Geotechnical Engineer on 26 March 2025. The site is located on
the western flank of a hill within the Yunaman Bushland Reserve. The site is occupied by an existing brick veneer
dwelling and an empty in-ground pool at the rear. These structures appeared to be stable, and no visible signs of
distress (associated with downhill slope movements) were observed. Topographically, the site is initially relatively flat
and level from the road but then gently slopes down towards the western boundary. Slopes angles are moderate and
range between 5° and 10°. No obvious signs of disturbed ground, tension cracks or hummocks were noted at the
site and surrounding area during the walkover assessment. A variety of vegetation ranging from small shrubs to
mature trees were observed. The mature trees at the site were all observed to be typically vertical with no misshapen
or curved trunks. Misshapen or curved trunks are usually good indicators for previous slope instability.
Sunshine Coast | Brisbane | Gold Coast
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Figure 1: Front of site Figure 2: Rear of site
6 AGS ASSESSMENT
Landslides are caused where a soil or rock mass has a decrease in strength, usually attributed to groundwater,
resulting in the material not being able to maintain its own self-weight resulting in a slope failure.
The Australian Geomechanics Society (AGS) developed a set of tools and procedures for assessing the stability of
a slope. The tools and procedures presented with the AGS documentation form the basis of the assessment
undertaken herein and their documentation is attached for reference.
The guidelines also identify that the regulator typically sets the standard for levels of tolerable risk. AGS defines
tolerable risk as “risks within a range that society can live with so as to secure certain benefits. It is a range of risk
regarded as non-negligible and needing to be kept under review and reduced further if practicable”.
The guides suggest that areas of moderate or greater risk should not be developed unless a rigorous remediation
plan be implemented to reduce the area to a level of Acceptable Risk. AGS defines acceptable risk as “risk which
everyone affected is prepared to accept. Action to further reduce such risk is usually not required unless reasonably
practicable measures are available at low cost in terms of money, time and effort.”.
AGS suggest that regulators generally accept risk levels of “low” or lower as a level of acceptable risk.
AGS prepared a semi-quantitative assessment tool for determining the level of risk for a site. The tool separates the
potential hazards for a site, from a stability context, and rates them with a level of risk frequency. The multiplication
of these individual risk frequency summates as the risk frequency rating which is then measured against the levels
of risk nominated by AGS.
The results of this analysis are shown in Table 1.
Sunshine Coast | Brisbane | Gold Coast
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TABLE 1: AGS ASSESSMENT
Hazard Likelihood Consequence Risk Level
Global failure Rare Medium Low
Creep in shallow sand Possible Insignificant Very Low
Rotational or translational slide down Unlikely Minor Low
the slope
Failure of engineered retaining walls Rare Medium Low
Based on the results of the AGS assessment, the perceived risk to property based on the conditions encountered
and information available at the time of the assessment is “Low”.
7 HILLSIDE CONSTRUCTION
The following works should be implemented in addition to other items highlighted within this document. These points
are considered to be typical good hillside construction practice as explained in attached documentation:
Footings should be founded into medium dense (or better) silty sand.
Fill should be limited to no more than 1.5 m and should be step keyed into the existing slope. The fill should be
formed at no steeper than 3H:1V, unless retained by an engineered retention system. All fill should be placed in
accordance with AS3798.
The design and integrity of retaining structures will need to be confirmed to adhere to good hillside construction
methodologies including being globally stable (ie. designed to achieve a minimum safety factor of 1.5 against
global instability).
All stormwater and surface water is to be discharged by an approved stormwater drainage system.
Avoid leakage from underground services and drains. Any leaking services or blocked drains should be remedied
promptly.
Erosion protection of cut and fill batters will be required. Batters should incorporate crest and toe drainage. Batters
should be vegetated appropriately to minimise erosion.
Overland flow paths will need to be carefully directed to approved outlets to minimise erosion possibility.
8 GEOTECHNICAL RECOMMENDATIONS
The following sections details specific geotechnical constraints or recommendations in addition to general hillside
construction notes.
8.1 FOOTINGS
In accordance with industry standards, a geotechnical engineer from Arcos should undertake the testing within the
footings to confirm that the encountered material is in alignment with the adopted parameters and assumptions
provided within this report. Where this does not occur, Arcos cannot be held liable for any of the information presented
within this report.
All footings will need to be designed to accommodate potential ground surface movement, settlement values and
any additional settlement values associated with the placement of new fill.
Settlement for suitably sized and designed high level footings should be in the order of 1-2% of the width of the
footing.
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If footings are located adjacent to an underground service or other obstruction that is not homogenous with the
founding strata, the footing should be extended a minimum 0.3 m below an imaginary line projected at a 45 degree
angle from the lowest point of the service/obstruction. This is depicted graphically for reference:
Where footings found into medium dense silty sand, they may be dimensioned for a maximum allowable bearing
pressure of 100 kPa. Based on the borelogs, the above material is encountered at approximately 1.1 m to 1.3 m
depth below existing surface levels at the time of the investigation.
The ultimate geotechnical end bearing and shaft adhesion parameters are presented in Table 2 for deep level
footings where high level footings are not suitable. The values given will need to reduced by applying a suitable
geotechnical strength reduction factor (Φg) for limit state or divided by a suitable factor of safety for working stress
methods. The Φg should be selected by the designer.
TABLE 2: DEEP LEVEL FOOTING – ULTIMATE GEOTECHNICAL PARAMETERS (LONG PILE)
Material Bored Bored Screw Screw
Fb (kPa) Fs (kPa) Fb (kPa) Fs (kPa)
Medium dense silty sand 450 5 450 NR
Notes: Fb = Base Bearing (Ultimate); Fs = Shaft Adhesion (Ultimate)
The upper 1 m of soil profile should be ignored in shaft calculations for bored piles to allow for shrinkage cracks. Due
to installation disturbance, shaft adhesion should be ignored for steel screw piles. The values presented in Table 2
assume that the material equal to four pile diameters below the base of any footings is as strong or stronger.
Settlement values are subjected to a variety of factors; however, a properly designed and constructed pile should
have a serviceability settlement between 1% and 2% of its’ diameter.
Lateral capacity of steel screw piles could be increased by constructing concrete pile caps or by using proprietary
head attachments which are dragged into the soil providing additional lateral resistance at the pile head. It should
be noted that the lateral support is generally limited and is generally suited to structures that can accommodate some
lateral movement.
Sunshine Coast | Brisbane | Gold Coast
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Sunshine Coast | Brisbane | Gold Coast
ATTACHMENTS
About Your Geotechnical Report
Interpretation of the Subsurface Sheets
Practice Note Guidelines
Client Supplied Information
Sunshine Coast | Brisbane | Gold Coast
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ABOUT YOUR GEOTECH REPORT
Reporting
These notes have been provided to clarify and The report has been prepared and reviewed by
enhance the reader’s understanding of the suitably qualified and experienced persons. The
terminology used throughout the report, and also to persons draw on previous experience, local
identify where limitations exist. All investigations are knowledge, published literature, and otherwise
undertaken based on budgetary constraints which standard engineering approaches and principals. The
impart a level of uncertainty as a result of limiting the context of which the report has been prepared for must
amount of investigation undertaken. be considered and if the context changes, due
consideration should be given to the possibility that the
report is no longer considered relevant and review by
Copyright Arcos Unit Group Pty Ltd must be undertaken.
This report remains the property of Arcos Unit Group Arcos Unit Group Pty Ltd undertakes quality
Pty Ltd at all times unless ownership is transferred in assurance checks in accordance with its’ quality
writing. It cannot be included in any documentation system requirements; however, restrictions on the
without the express written permission of Arcos Unit project outside of Arcos Unit Group Pty Ltd’s control
Group Pty Ltd can result in unanticipated variations, changes in
policy or interpretation of said policies by the relevant
authority, or the actions of contractors subject to
Subsurface Report Sheets (Bores etc) commercial pressure.
The provided subsurface sheets are inherently an
interpretation undertaken by a suitably qualified and
experienced person; however, the reliability of the
Site Variations
provided information will rely on the method of If site variations become evident at the time of
investigation. It is prudent to state that these sheets construction or after the release of a report, Arcos Unit
only represent a very small percentage of the Group Pty Ltd requests immediately notification. This
subsurface conditions across a particular project. notification is proposed in order to assist in
remediation prior to any permanent structures or
It reasons that given the relatively small representation
design procedures are undertaken.
of the subsurface conditions for a project, spacial
variability between testing locations must be taken into
consideration including the orientation of strata Collaboration
intersections.
Arcos Unit Group Pty Ltd strongly recommends open
The presence or lack of groundwater is usually stated and collaborative communication about the use and
on the subsurface sheets; however, it must be noted inherent interpretation of Arcos Unit Group Pty Ltd’s
that the measurements undertaken onsite are typically report. Please contact the author of the report to
very inaccurate and if the presence or lack of arrange for an obligation free discussion regarding the
groundwater will have any degree of affect on the potential benefits of having geotechnical consultants.
project, additional groundwater monitoring techniques
should be employed such as groundwater monitoring
wells.
Sunshine Coast | Brisbane | Gold Coast
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Interpretation of the Subsurface Sheets
The terminology included on Arcos Unit Group Pty the most important component. Typically, the strength
Ltd’s has been evolved from AS1726:2016. Typically of rock is based on laboratory testing, tactile
a soil’s strength, colour, plasticity, grain size, other assessment and other observations as relevant. The
inclusions, and moisture will be described. A rock’s industry standard method for assessing the strength of
strength, weathering, colour, grain, and other rock in the field is to use the point load strength index
inclusions are typically described. (AS4133.4.1). It is important to note that the point load
strength index does not take into consideration the
degree of fracturing of a rock mass which can both
Soil lower and increase the overall rock strength. The
Soil is typically described by the components that strength of rock is broken down as follows:
make it up by percentage or whichever has a Very Low Strength (VLS) < 2 MPa (UCS)
governing behaviour. The types and sizes reproduced Low Strength (LS) 2 to 6 MPa (UCS)
from AS1726 are: Medium Strength (MS) 6 to 20 MPa (UCS)
Boulder >200 mm High Strength (HS) 20 to 60 MPa (UCS)
Cobble 63 to 200 mm Very High Strength (VHS) 60 to 200 MPa (UCS)
Gravel 2.36 to 63 mm Extremely High Strength (EHS) > 200 MPa (UCS)
Sand 0.075 to 2.36 mm Very Low Strength (VLS) < 0.1 Is(50)
Silty 0.002 to 0.075 mm Low Strength (LS) 0.1 to 0.3 Is(50)
Clay < 0.002 mm Medium Strength (MS) 0.30 to 1.0 Is(50)
The strength of soil is usually assessed by suitably High Strength (HS) 1.0 to 3.0 Is(50)
experienced persons through the use of laboratory Very High Strength (VHS) 3.0 to 10.0 Is(50)
test results, published literature, field assessments or Extremely High Strength (EHS) > 10.0 Is(50)
a combination of the above. The strength of soil is The Is(50) values are based on a correlation between
characterised into either cohesive (clays and silts) or the unconfined compressive strength (UCS) of 20.
cohesionless (sands and gravels) as shown below: This value varies significantly and site specific testing
Cohessive Soil Strength Term must take precedence.
Very Soft < 12.5 kPa Rock weathering is broken down as follows:
Soft 12.5 to 25 kPa Extremely weathered (EW) Behaves as soil but rock structure
Firm 25 to 50 kPa evident
Stiff 50 to 100 kPa Highly weathered (HW) Colour and strength of original fresh rock
is not recognisable. Decomposition of rock evident
Very Stiff 100 to 200 kPa
Moderately weathered (MW) Defects are heavily stained with
Hard > 200 kPa
rock mass showing signs of discolouration
Cohesionless Soils Strength Term (uncorrected Qc) Slightly weathered (SW) Some staining but minimal to no
Very Loose <2 MPa change in strength
Loose 2 to 5 MPa Fresh stained (FS) Minor staining evident
Medium Dense 5 to 15 MPa Fresh rock (FR) No change
Dense 15 to 25 MPa Rock fracturing is broken down as follows and can only
Very Dense > 25 MPa be accurately described where undamaged
continuous sampling has been undertaken:
Fragmented (Fg) Defect spacings < 20 mm
Rock
Highly Fractured (HF) Defect spacings 20 to 50 mm
Rock is typically described by the components that Fractured (Fr) Defect spacings 50 to 200 mm
make it up by percentage or whichever has a Slightly Fractured (SF) Defect spacings 200 to 1000 mm
governing behaviour. The strength of rock is typically Unbroken (Ub) Defect spacings > 1000 mm
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SOIL TEST REPORT
Address : Lot 10 on RP89506
19 Attunga Heights
Noosa Heads
Client : M. Bennett
Date : 26 March 2025
Report No : 250131(S)
Phone: 0428 310 453
Email: [email protected]
Address: 174 Railway Road, Cooran Qld 4569
Australian Soil Investigations Pty Ltd
ABN: 11147854439
Page 15
1.0 INTRODUCTION:
Australian Soil Investigations has performed a limited site investigation and established a site classification in
accordance with AS 2870-2011 at the above address. This site classification report does not include an assessment
of Slope Stability or Landslide Risk. Fieldwork has been performed by an experienced geotechnician hand auguring
equipment.
This report must be read and considered as a whole. All of our recommendations and appendices
attached must be read, considered and followed by all people involved in this project including
the client to ensure adequate long term performance of a footing system constructed on this site.
If you are unsure of any of the requirements herein, you must seek clarification from this office.
2.0 SITE CLASSIFICATION:
After considering the results of our field investigation performed on 25/03/2025 we have classified this site as:
Class P
The classification has been calculated from test work performed on the soil profile encountered on the day of our
fieldwork and consideration of AS2870-2011. Any disturbance of the soil profile may result in a change to the
classification.
The ‘P’ classification relates to the poor bearing capacity and abnormal moisture conditions encountered during our
testing on site. Please refer to our definitions list appended to this report for further descriptions of these
characteristics.
The abnormal moisture conditions are due to the removal of the existing building, the presence and proximity of trees
to the allotment and existing trees located on the proposed construction area that will be removed.
With respect to potential surface movements through seasonal moisture variations, the site could be considered
equivalent to a class S site.
Site Classification: The site classification is calculated in accordance with the “AS2870-2011 Residential Slabs and
Footings-Construction” and relates to the estimation of Ys, “The characteristic surface movement” within reactive soil
profiles. The limits used for this classification are as follows:
Predicted Surface Movement Classification
Ys = <=20mm S Slight
Ys = >20 – 40mm M Moderate
Ys = >40 – 60mm H1 High-1
Ys = 60 – 75mm H2 High-2
Ys = > 75mm E Extreme
Problem sites P Problem
3.0 SITE DESCRIPTION:
The construction area has a gradient in the order of 8-9%.
Vegetation on the construction area (and nearby surrounds) consists of grasses and scattered trees.
The trees are located in the neighbouring allotment on and adjacent the proposed construction site.
The trees are of a height and proximity that could affect the moisture conditions within the proposed construction site.
Refer to the appendices to the rear of this report for guidance on Trees and Construction.
The existing surface drainage is good and sub-surface drainage is good.
Australian Soil Investigations 1 ASI Ref: 250131(S)
Page 16
4.0 FINDINGS:
The soil profiles encountered are shown on the attached borelog sections.
No water table was encountered during our testing program.
The sandy soils encountered are susceptible to collapse when unconfined. This may effect excavations and result
in additional earthworks and increased concrete volumes. Temporary shoring or Forma-Tube may be required to
retain the sands prior to concreting.
The samples classified on-site were assessed as having negligible plasticity, therefore laboratory testing was
considered unnecessary.
We have assessed the expected differential movement of the soil profiles encountered to be the equivalent of a site
with a Ys of less than 20mm.
Fill, which we have described as uncontrolled was encountered to the following depths
Test Site 1 - 500 mm Test Site 2 - 400mm
At the time of writing this report we were unable to describe the fill as controlled. This can be revised if documentation
is available indicating that this fill has been compacted and certified in accordance with AS 3798-2007.
The following foundation material will provide a safe bearing capacity (100 kPa) for buildings within the scope of AS
2870-2011.
FOUNDATION MATERIAL - NATURAL MEDIUM DENSE SILTY SAND
We strongly recommend that any footing design for this allotment be carried out by a suitably qualified
person in accordance with AS2870-2011.
Where site drainage and landscaping does not conform to the specifications of AS 2870-2011 and CSIRO
Information Service Sheet BTF-18 (2003) damage to the building can be expected. A single copy of this
document is issued with the original issue of this report. Please consult your builder or contact this office
to obtain a copy.
NOTE: The information contained herein has been compiled following our field and laboratory testing,
accepted engineering theory and discussions with and information supplied by our client, whom is
noted on the header page of this report. We offer no warranty for the use of this report by other
parties without prior written consent from this office.
The report must be read in conjunction with the attached appendices. If you do not have a copy of
these please contact our office and a copy can be issued to you.
WADE HOLMES – QBCC 1120066
for and on behalf of:
AUSTRALIAN SOIL INVESTIGATIONS – QBCC 15072110
Australian Soil Investigations 2 ASI Ref: 250131(S)
Page 17
APPENDICES
A. SITE PLAN
B. BORELOGS
C. DEFINITIONS
D. LIMITATIONS
E. RECOMMENDATIONS
C.1 - Builders
C.2 - Owners
C.3 - Builder/Owner - Trees
F. DETAIL SHEETS
D.1 - Plumbing Requirements Class M, H1, H2 & E Sites
D.2 - Site Drainage recommendations
G. CSIRO- Home Owners Guide
Page 18
Revision Description Date
.
.
.
BH 2
8-9%
BH 2
SITE PLAN
Lot 10
Site Drainage
RP89506
Vegetation
506sq.m AUSTRALIAN
BH 2
SOIL INVESTIGATIONS
Borehole location.
Slope
Title SITE PLAN
measured as a percentage gradient from
high ground to low ground. Project
DO NOT DIMENSION OFF THIS DIAGRAM. Date: Drg No.
Rev.
Page 19
Australian Soil Investigations LOG SECTIONS Ref No. 250131
Client: M. Bennett
Location: (Lot 10 on RP89506) 19 Attunga Heights, Noosa Heads
Date: 25/03/2025
(House Site)
Depth TEST SITE No 1 P Depth TEST SITE No 2 P
100 Fill Silty Sand (SM) 1 100 Fill Silty Sand (SM) 1
200 Fine to coarse grained dark 1 200 Fine to coarse grained dark 1
300 grey, roots, moist, loose 1 300 grey, roots, moist, loose 1
400 1 400 Silty Sand (SM) 1
500 Silty Sand (SM) 1 500 Fine to coarse grained, grey, 1
600 Fine to coarse grained, grey, 1 600 roots, moist, loose 1
700 roots, moist, loose 1 700 1
800 1 800 1
900 2 900 2
1000 2 1000 2
1100 2 1100 Silty Sand (SM) 3
1200 2 1200 Fine to coarse grained, pale 3
1300 Silty Sand (SM) 2 1300 grey, moist, becoming medium 2
1400 Fine to coarse grained, pale 2 1400 dense 3
1500 grey, moist, becoming medium 3 1500 3
1600 dense 3 1600 4
1700 4 1700 4
1800 4 1800 5
1900 4 1900 5
2000 4 2000 End 5
2100 4 2100 6
2200 5 2200 5
2300 5 2300 6
2400 5 2400 6
2500 6 2500 6
2600 6 2600 7
2700 7 2700 6
2800 7 2800 7
2900 6 2900 7
3000 End 7 3000 7
3100 7 3100
3200 7 3200
Depth = mm below ground level.
P = blows per 100mm penetration with an approved 9kg penetrometer.
Notation such as (SP) refers to the soil description to Table A1 AS1726 ‘Guide to the description
identification and classification of soils’.
Solid lines represent sharp interface between different soil types. Dotted lines represent
gradation form one soil type to another.
Abbreviations used
UTP - unable to penetrate, Bec. – becoming, N.S.L. – Natural Surface Level
Med. – medium, MW - Moderately weathered
EW - extremely weathered, Plast. - Plasticity
No recovery means unable to extract samples from the base of the bore hole because the soil
will not bind in the auger head.
The colour of the soil is often abbreviated, for example Gy = grey Or = orange.
Page 20
C. DEFINITIONS
Safe Bearing capacity: The soil nominated in this report as a suitable foundation material has an allowable bearing capacity of 100KPa and
is considered safe for the construction of a dwelling that is in accordance with AS2870-2011.
Cohesive Soils: Clays and silt soils that have inherent cohesive (binding) strength.
Granular Soils: Gravels and sand soils that have no cohesive strength. Individual particles can flow under certain conditions.
Controlled Fill: Manually placed soil which has been placed and compacted to achieve sufficient bearing capacity to support a structure
according to AS 2870-2011. Fill certified at Level 1 according to AS 3798 and 95% Relative Field Density is considered controlled fill.
Partially Controlled: Manually placed soil which appears to have been compacted under controlled conditions but, at the time of preparing
this report, no compaction certificate suitable for compliance to Level 1 of AS 3798-2007 had been presented.
Uncontrolled Fill: Manually placed soil (overlying the natural soils) which is not adequate to support a normally loaded footing or floor slab
or structural load.
Unexcavatable Rock: Strong material that does not soften in water or collapse under the combination of loading and wetting. Material that
cannot readily be excavated by a backhoe.
Excavatable Rock: A rock-like material including shaly material and strongly cemented sand or gravel which does not shrink or swell with
changes in soil moisture, but is readily excavatable with a conventional backhoe.
Load Bearing Wall: In our design work a load bearing wall is defined as any wall imposing on the footing a service load greater than 10kN/m.
A load bearing wall will normally be supported by a slab thickening or footing in our slab designs.
Natural (Strata): Refers to soil that is neither fill or imported material but one that is in its original undisturbed state and position.
Gravel: Coarse particles, larger than sand size, but less than 60mm in diameter.
Cobbles: Rocks greater than 60mm in diameter but less than 600mm in diameter.
Boulders: Rocks larger than 600mm in diameter.
SOIL STRENGTH INDICATIONS
NON-COHESIVE (GRANULAR) SOILS COHESIVE SOILS
Loose A 12mm rod/bar can be easily pushed in by hand Soft Can be moulded by light finger pressure.
Medium A 12 mm rod/bar can be pushed in 300mm with Firm Can be moulded by strong finger pressure.
Dense difficulty
Dense A 12mm rode cannot be pushed in by hand. Stiff Cannot be moulded by fingers. Can be indented by
thumb with pressure.
Very Stiff Can be indented only by thumb nail.
N.B. These indications should be used for guidance only. These indications can vary greatly under Abnormal Moisture Conditions.
Please contact Australian Soil Investigations for on-site clarification of soil strengths.
D. LIMITATIONS
AS2870-2011: This report has been completed in accordance with AS2870-2011 the Australian Standard for “Residential Slabs and
Footings” design and construction. The standard provides performance based criteria for its design recommendations. This criteria is not
based upon crack or movement free performance. The code states “It is acknowledged that minor foundation movements occur on nearly all
sites and that it is impracticable to design a footing system that will protect the building from movement under all circumstances”. The code
provides guidance on the assessment of crack sizes in walls and floors and suggests acceptable limits. Should the potential owner not be
satisfied with this criteria we should be notified such that any recommendations can be amended to suit their requirements. However, it should
be noted this could dramatically increase the construction costs.
Field Testing: Our investigation and the results and recommendations contained herein have been compiled following careful consideration
of our clients supplied information and instructions. Any variation to this information may render this report incorrect. Furthermore this report
must not be used by any person other than our client noted at the head of the report.
Client Supplied Information: In writing this report we have considered all the information supplied to us by the client. Should the client or
his agent have omitted to supply us with relevant information our report may be irrelevant and / or inappropriate. We do not accept
responsibility for the consequences in such cases.
Borelogs: The soil profiles reported in our Borelogs Section represent the soil conditions at our test sites and have been located were we
believe best represents the soils within the proposed building envelope. However soil conditions can change dramatically over short distances,
therefore such point type exploration programs may not locate all variations. If site preparations/excavations reveal soil conditions that are
different from those shown in our Borelogs we must be notified immediately. Changes to the site classification and/or footing design may be
necessary.
Site Information: The site information shown on the attached plans such as surface grades and levels are estimations taken during our field
testing and are provided for a rough guide. They must not be used for any design purposes. Site plan dimensions are as measured from the
noted visible site feature during our field testing.
Previous/Future Excavations: The recommendations contained in this report have not considered the effects of any previous, current or
future excavations, mines or slope instability problems that are not highlighted in the clients supplied information or, that was not clearly visible
during our field testing. If such features exist we must be advised so that our design can be adjusted to accommodate them.
Australian Soil Investigations Appendix Page 2 of 6 Appendices.1
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Trees: Trees can have a considerable influence over the over the performance of a structures foundation, in particular those founded on
reactive soils (Class S, M, H & E). The trees demand for moisture will change the moisture characteristics of the surrounding soils leading to
localised shrinking and swelling which can exceed the expected soil movement. This can include trees that have been removed prior to
construction. During our Field-testing we have considered trees that existed on or adjacent the site and allowed for them in our
recommendations. We are unable to assess for the potential effects of trees planted after our testing, reference should be made to
“Recommendations for Builders/Owners-Trees” in Appendix D that follows.
Moisture Conditions: The moisture conditions noted within this report are as recorded at the time of our field testing and have been included
in our assessment of the site. Changes to site drainage, the planting of trees or a rising water table can lead to increased levels of moisture
within the soils leading to either an increased classification or design requirements. We must be notified of any increase in moisture conditions.
Also refer to “Recommendations for Builders/Owners – Site Drainage in Appendix D that follows.
Aggressive/Contaminated Soils: This report does not consider the presence of contaminants or sulphates within the tested soils as this is
beyond the scope of this report and our expertise. Engagement of a specialist consultant is advised if this form of assessment is required.
Landslip: This report does not address slope stability issues. A specialist report must be obtained to assess such hazards.
Shrinkage Cracking: Shrinkage cracking of concrete occurs as the initial moisture in the concrete evaporates from mix causing
shrinkage to occur. The cracking as a result of this shrinkage is not a sign of structural failure and is to be expected in most concrete elements
poured on-site. AS2870-2011 states “Shrinkage cracking can be expected in concrete floors”.
E RECOMMENDATIONS
E.1 Recommendations for Builders and Foundation Designers
Codes of Practice: All construction work associated with this report must be undertaken in accordance with the BCA “part 3.1 – Site
Preparation” and “part 3.2 – Footings & Slabs” and AS2870-2011 “Residential Slabs and Footings”.
Underground Services/Plumbing: Where structures are built over filled, soft or loose soils, services will need to be supported so that
potential movement within the soils does not cause them damage or cause incorrect alignment which could cause leakage. Such measures
can include but are not limited to the provision of expansion joints, sleeved or foam lagged pipe penetrations throughout the structure or
treatment of the soils prior to construction. The attached illustrations detail minimum requirements.
Arrange plumbing fixtures so that the slab and beam penetrations are kept to a minimum and where necessary sleeved to allow for movement
with 40mm thick closed cell polythene or similar material. Where the penetration is within 150mm of the base of a beam or footing, the depth
of this footing element should be deepened by approximately twice the diameter of the penetration. All plumbing and drainage must comply
with the requirements of the National Plumbing and Drainage Code AS3500.
For Class H & E sites, AS2870 - 2011 requires that plumbing pipes servicing dwellings in class H & E sites be fitted with sleeved expansion
joints, rotational swivel joints and foam lagged penetrations.
Refer to the attached detail sheet “Plumbing Requirements Class M, H and E sites.
Site Drainage - Class A Sites: The ground surrounding the dwelling and the building site must be graded and drained so that stormwater is
shed away from the house area in all directions during and after construction. Particular attention should be given to all drainage so stormwater
is not introduced to the foundation soils leading to potential scour. Roof water must be diverted away from the building prior to and after the
roof is installed. Correct drainage is an essential part of our recommendations. If the site is not prepared correctly, excessive foundation
movements may occur leading to damage within the supported structure.
Site Drainage - Class S, M, H & E Sites: The ground surrounding the dwelling and the building site must be graded and drained so that
stormwater is shed away from the house area in all directions, during and after construction. A minimum grade of 1 : 20 (vertical : horizontal)
for 1.5m must be provided. Hard landscaping such as terrace slabs adjacent the dwelling can assist in this. Roof water must be diverted
away from the building site prior to and after the roof is installed. Where building delays occur, temporary downpipes may be necessary.
Constant maintenance of roof drainage is essential. If a rainwater tank (or similar) is to be sited within 6 meters of a structural footing, we
should be consulted for further advice. External water taps, air conditioner overflows, tank and hot water cylinder overflows should be over
grated pits connected to the drainage system. The ground surrounding the building must be graded and drained so water is shed away from
the house in all directions.
Particular care should be taken with drainage, plumbing and electrical trenches so that they do not introduce moisture into the soils supporting
the foundations or destabilise the footings by undermining them. The base of any trenches under the floor or within 1.5 meters of the building
should be sloped away from the house and should be backfilled with compacted clay plug.
Correct drainage is an essential part of our recommendations and is documented in the CSIRO handout BTF-18 attached to the clients copy
of this report. (Additional copies available upon request.) If the site is not prepared correctly, excessive soil moisture may occur in some
areas, which can lead to excessive foundation movements possibly damaging the supported structure.
Inspections: We require 24 hours notice if you require engineers site inspections. Inspections can be booked between 8.30am and 4.30pm
Monday to Friday by telephoning 07 5455 5604.
Silt Retention: The builder is responsible for ensuring appropriate silt retention measures are in placed and maintained throughout
construction.
Site Classification: The site classification is calculated in accordance with the “AS2870-2011 - Residential Slabs and Footings-Construction”
and relates to the estimation of Ys, “The characteristic surface movement” within reactive soil profiles. The limits used for this classification
are as follows:
Predicted Surface Movement Classification
Ys = <=20mm S Slight
Ys = >20 – 40mm M Moderate
Ys = >40 – 60mm H1 High-1
Ys = 60 – 75mm H2 High-2
Ys = > 75mm E Extreme
Problem sites P Problem
Australian Soil Investigations Appendix Page 3 of 6 Appendices.1
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E.2 Recommendations for Owners
Foundation Maintenance and Owners Responsibilities: The soils surrounding and under the foundations must be protected from scour
or washout from stormwater by ensuring adequate drainage as noted above.
Localised concentrations of moisture such as overflows from hot water cylinders or air conditioners can lead to excessive localised foundation
movements and must also be adequately drained away from the foundations as noted above.
In all types of soil conditions, if an automatic watering system irrigates within 2.5 meters of a foundations, instability problems and excessive
foundation movements are likely to occur. Also site drainage as discussed above must be maintained.
Ongoing foundation maintenance is documented in the CSIRO handout BTF-18, attached to the client’s copy of this report. (Additional copies
available upon request.)
Refer to the attached detail sheet “General Requirements for Site Drainage”
Additional Requirements - Class A & S Sites: Trees and dense shrubs must be kept well away from the building foundations. Refer to the
following section “Recommendations – Builders/Owners – Trees”. In all types of soil conditions, if an automatic watering system irrigates within
2.5 meters of a footing, instability problems may occur. Water should not be allowed to pond on the ground near the building. Finished
surface grades around the building should also ensure scour of soils cannot occur. Additional field gullies and drainage might be required.
In all instances the ground should be sloped away from the foundations at a grade of no less than 1 in 20 (vertical to horizontal) for at least
1.5m.
Additional Requirements - Class M, H & E Sites: Trees and dense shrubs must be kept well away from the building foundations. Refer to
the following section “Recommendations – Builders/Owners – Trees”.
The soil near the building should be protected against the increased moisture that occurs in gardens or permeable landscaping built adjacent
the foundations. Automatic irrigation systems must not be used adjacent structural foundations. If required, these forms of landscaping must
be constructed over impermeable membranes that drain the excessive moisture away from the foundations into correctly installed field gullies
and drains.
We strongly recommend the construction of hard landscaped paths or terrace slabs adjacent building foundations for at least a distance of
1.5m to protect the foundations from excessive moisture.
E.3 Recommendations – Builders/Owners - Trees
Trees and landscaped gardens can have a dramatic influence over the moisture content of the soils they are grown in. This can lead to
increased soil movement through shrinking and swelling. Where these trees or gardens are within close proximity of structural foundations
the soil movements can affect the structural integrity of the foundations.
For Class M, H and E sites the following recommendations for the minimum distance between trees and footings should be followed:-
Site Class Offset to Tree
Class M : 0.75 x h
Class H : 1.0 x h
Class E : 1.5 x h
Where ‘h’ is the mature height of the tree, further refinement of this recommendation can be pursued where tree species can be considered.
Where a row or group of trees exists the above recommendation should be doubled.
In some instances the installation of root barriers can lessen the effect of trees on foundation performance. Please contact Australian Soil
Investigations for options.
The following table provides some guidance on mature tree heights:-
APPROXIMATE TREE HEIGHTS
10 to 20m Height – Acacias, Ash, Athel Tree, Candlebark, Manna Gum, Pepper Tree, Willows, Yate, Yellow Gum
20 to 30m Height – But-But, Cedars, English Oak, Lemon Gum, Palms, Planes, Sheoaks, Silky Oak, Spotted Gum, Casuarina
30 to 60m Height – Blue Gum, Cypress, English Elm, Figs, Karri, Pines, River Gum, Sugar Gum
The removal of trees from the proposed construction can also greatly affect the moisture conditions of the soil. We recommend allowing the
soil time to reach moisture equilibrium prior to construction commencing. Please contact our office for further guidance on this matter.
Australian Soil Investigations Appendix Page 4 of 6 Appendices.1
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F DETAIL SHEETS F.1 Plumbing Requirements Class M, H1, H2 & E Sites Australian Soil Investigations Appendix Page 5 of 6 Appendices.1
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F.2 Site Drainage recommendations Australian Soil Investigations Appendix Page 6 of 6 Appendices.1
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BUILDING ‘Techotocy|nesounces FOUNDATION MAINTENANCE AND FOOTING PERFORMANCE Understanding and preventing soil-related building movement This Building Technology Resource is designed to identify causes of soil-related building movement, and to suggest methods of prevention of resultant cracking. Buildings can and often do move. This movement can be up, down, lateral or rotational. The fundamental cause of movement in buildings can usually be related to one or more problems in the foundation soil. It is important for the home owner to identify the soil type in order to ascertain the measures that should be put in place in order to ensure that problems in the foundation soil can be prevented, thus protecting against building movement. SOIL TYPES The types of soils usually present under the topsoil in land zoned for residential buildings can be split into two approximate groups — granular and clay. Quite often, foundation soil is a mixture of both types. The general problems associated with soils having granular content are usually caused by erosion. Clay soils are subject to saturation and swell/shrink problems. Classifications for a given area can generally be obtained by application to the local authority, but these are sometimes unreliable andif there is doubt, a geotechnical report should be commissioned. As most buildings suffering movement problems are founded on clay soils, there is an emphasis on classification of soils according to the amount of swell and shrinkage they experience with variations of water content. Table 1 below is a reproduction of Table 2.1 from Australian Standard AS 2870-2011, Residential slabs and footings. CAUSES OF MOVEMENT SETTLEMENT DUE TO CONSTRUCTION There are two types of settlement that occur as a result of construction: > Immediate settlement occurs when a building is first placed on its foundation soil, as a result of compaction of the soil under the weight of the structure. The cohesive quality of clay soil mitigates against this, but granular (particularly sandy) soil is susceptible. > Consolidation settlement is a feature of clay soil and may take place because of the expulsion of moisture from the soil or because of the soil’s lack of resistance to local compressive or shear stresses. This will usually take place during the first few months after construction but has been known to take many years in exceptional cases. These problems may be the province of the builder and should be taken into consideration as part of the preparation of the site for construction. EROSION Allsoils are prone to erosion, but sandy soil is particularly susceptible to being washed away. Even clay with a sand component of say 10% or more can suffer from erosion. SATURATION This is particularly a problem in clay soils. Saturation creates a bog- like suspension of the soil that causes it to lose virtually all of its bearing capacity. To a lesser degree, sand is affected by saturation because saturated sand may undergo a reduction in volume, particularly imported sand fill for bedding and blinding layers. However, this usually occurs as immediate settlement and should normally be the province of the builder. SEASONAL SWELLING AND SHRINKAGE OF SOIL All clays react to the presence of water by slowly absorbing it, making the soil increase in volume (see table below, from AS 2870). The degree of increase varies considerably between different clays, as does the degree of decrease during the subsequent drying out caused by fair weather periods. Because of the low absorption and expulsion rate, this phenomenon will not usually be noticeable unless there are prolonged rainy or dry periods, usually of weeks or months, depending on the land and soil characteristics. The swelling of soil creates an upward force on the footings of the building, and shrinkage creates subsidence that takes away the support needed by the footing to retain equilibrium. SHEAR FAILURE This phenomenon occurs when the foundation soil does not have sufficient strength to support the weight of the footing. There are two major post-construction causes: » Significant load increase. » Reduction of lateral support of the soil under the footing due to erosion or excavation. In clay soil, shear failure can be caused by saturation of the soil adjacent to or under the footing. TREE ROOT GROWTH Trees and shrubs that are allowed to grow in the vicinity of footings can cause foundation soil movement in two ways: » Roots that grow under footings may increase in cross-sectional size, exerting upward pressure on footings. TABLE 1. GENERAL DEFINITIONS OF SITE CLASSES. Class Foundation A Most sand and rock sites with little or no ground movement from moisture changes 5 Slightly reactive clay sites, which may experience only slight ground movement from moisture changes M Moderately reactive clay or silt sites, which may experience moderate ground movement from moisture changes 1 Highly reactive clay sites, which may experience high ground Movement from moisture changes 42 Highly reactive clay sites, which may experience very high ground Movement from moisture changes E Extremely reactive sites, which may experience extreme ground Movement from moisture changes Source: Reproduced with the permission of Standards Australia Limited © 2011. Copyright in AS 2870-2011 Residential slabs and footings vests in Standards Australia Limited. © CSIRO 2021
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Wall cracking due to uneven footing settlement FIGURE 1 Trees can cause shrinkage and damage. » Roots in the vicinity of footings will absorb much of the moisture in the foundation soil, causing shrinkage or subsidence. UNEVENNESS OF MOVEMENT The types of ground movement described above usually occur unevenly throughout the building’s foundation soil. Settlement due to construction tends to be uneven because of: > Differing compaction of foundation soil prior to construction. > Differing moisture content of foundation soil priorto construction. Movement due to non-construction causes is usually more uneven still. Erosion can undermine a footing that traverses the flow or can create the conditions for shear failure by eroding soil adjacent to a footing that runs in the same direction as the flow. Saturation of clay foundation soil may occur where subfloor walls create a dam that makes water pond. It can also occur wherever there is a source of water near footings in clay soil. This leads to a severe reduction in the strength of the soil which may create local shear failure. Seasonal swelling and shrinkage of clay soil affects the perimeter of the building first, then gradually spreads to the interior through absorption. The swelling process will usually begin at the uphill extreme of the building, or on the weather side where the land is flat. Shrinkage usually begins on the side of the building where the sun’s heat is greatest. EFFECTS OF UNEVEN SOIL MOVEMENT ON STRUCTURES EROSION AND SATURATION Erosion removes the support from under footings, tending to create subsidence of the part of the structure under which it occurs. Brickwork walls will resist the stress created by this removal of support by bridging the gap or cantilevering until the bricks or the mortar bedding fail. Older masonry has little resistance. Evidence of failure varies according to circumstances and symptoms may include: > Step cracking in the mortar beds in the body of the wall or above/below openings such as doors or windows. » Vertical cracking in the bricks (usually but not necessarily in line with the vertical beds or perpends). Isolated piers affected by erosion or saturation of foundations will eventually lose contact with the bearers they support and may tilt or fall over. The floors that have lost this support will become bouncy, sometimes rattling ornaments etc. SEASONAL SWELLING/SHRINKAGE IN CLAY Swelling foundation soil due to rainy periods first lifts the most exposed extremities of the footing system, then the remainder of the perimeter footings while gradually permeating inside the building footprint to lift internal footings. This swelling first tends to create a dish effect, because the external footings are pushed higher than the internal ones. The first noticeable symptom may be that the floor appears slightly dished. This is often accompanied by some doors binding on the floor or the door head, together with some cracking of cornice mitres. In buildings with timber flooring supported by bearers and joists, the floor can be bouncy. Externally there may be visible dishing of the hip or ridge lines. As the moisture absorption process completes its journey to the innermost areas of the building, the internal footings will rise. If the spread of moisture is roughly even, it may be that the symptoms will temporarily disappear, but it is more likely that swelling will be uneven, creating a difference rather than a disappearance in symptoms. In buildings with timber flooring supported by bearers and joists, the isolated piers will rise more easily than the strip footings or piers under walls, creating noticeable doming of flooring. As the weather pattern changes and the soil begins to dry out, the external footings will be first affected, beginning with the locations where the sun's effect is strongest. This has the effect of lowering the external footings. The doming is accentuated, and cracking reduces or disappears where it occurred because of dishing, but other cracks open up. The roof lines may become convex. Doming and dishing are also affected by weather in other ways. In areas where warm, wet summers and cooler dry winters prevail, water migration tends to be toward the interior and doming will be accentuated, whereas where summers are dry, and winters are cold and wet, migration tends to be toward the exterior and the underlying propensity is toward dishing. MOVEMENT CAUSED BY TREE ROOTS In general, growing roots will exert an upward pressure on footings, whereas soil subject to drying because of tree or shrub roots will tend to remove support from under footings by inducing shrinkage. COMPLICATIONS CAUSED BY THE STRUCTURE ITSELF Most forces that the soil causes to be exerted on structures are vertical — i.e. either up or down. However, because these forces are seldom spread evenly around the footings, and because the building resists uneven movement because of its rigidity, forces are exerted from one part of the building to another. The net result of all these forces is usually rotational. This resultant force often complicates the diagnosis because the visible symptoms do not simply reflect the original cause. A common symptom is binding of doors on the vertical member of the frame. EFFECTS ON FULL MASONRY STRUCTURES Brickwork will resist cracking where it can. It will attempt to span areas that lose support because of subsided foundations or raised points. It is therefore usual to see cracking at weak points, such as openings for windows or doors. In the event of construction settlement, cracking will usually remain unchanged after the process of settlement has ceased. With local shear or erosion, cracking will usually continue to develop until the original cause has been remedied, or until the subsidence has completely neutralised the affected portion of footing and the structure has stabilised on other footings that remain effective. In the case of swell/shrink effects, the brickwork will in some cases return to its original position after completion of a cycle, however it is more likely that the rotational effect will not be exactly reversed, and it is also usual that brickwork will settle in its new position and will resist the forces trying to return it to its original position. This means that in a case where swelling takes place after construction and cracking occurs, the cracking is likely to at least partly remain after the shrink segment of the cycle is complete. Thus, each time the cycle is repeated, the likelihood is that the cracking will become wider until the sections of brickwork become virtually independent. With repeated cycles, once the cracking is established, if there is no other complication, it is normal for the incidence of cracking to stabilise, as the building has the articulation it needs to cope with the problem. This is by no means always the case, however, and monitoring of cracks in walls and floors should always be treated seriously. Upheaval caused by growth of tree roots under footings is not a simple vertical shear stress. There is a tendency for the root to also © CSIRO 2021
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exert lateral forces that attempt to separate sections of brickwork after initial cracking has occurred. The normal structural arrangement is that the inner leaf of brickworkin the external walls and at least some of the internal walls (depending on the roof type) comprise the load-bearing structure on which any upper floors, ceilings and the roof are supported. In these cases, it is internally visible cracking that should be the main focus of attention, however there are a few examples of dwellings whose external leaf of masonry plays some supporting role, so this should be checked if there is any doubt. In any case, externally visible cracking is important as a guide to stresses on the structure generally, and it should also be remembered that the external walls must be capable of supporting themselves. EFFECTS ON FRAMED STRUCTURES Timber or steel framed buildings are less likely to exhibit cracking due to swell/shrink than masonry buildings because of their flexibility. Also, the doming/dishing effects tend to be lower because of the lighter weight of walls. The main risks to framed buildings are encountered because of the isolated pier footings used under walls. Where erosion or saturation causes a footing to fall away, this can double the span which a wall must bridge. This additional stress can create cracking in wall linings, particularly where there is a weak point in the structure caused by a door or window opening. It is, however, unlikely that framed structures will be so stressed as to suffer serious damage without first exhibiting some or all of the above symptoms for a considerable period. The same warning period should apply in the case of upheaval. It should be noted, however, that where framed buildings are supported by strip footings there is only one leaf of brickwork and therefore the externally visible walls are the supporting structure for the building. In this case, the subfloor masonry walls can be expected to behave as full brickwork walls. EFFECTS ON BRICK VENEER STRUCTURES Because the load-bearing structure of a brick veneer building is the frame that makes up the interior leaf of the external walls plus perhaps the internal walls, depending on the type of roof, the building can be expected to behave as a framed structure, except that the external masonry will behave in a similar way to the external leaf of a full masonry structure. WATER SERVICE AND DRAINAGE Where a water service pipe, a sewer or stormwater drainage pipe is in the vicinity of a building, a water leak can cause erosion, swelling or saturation of susceptible soil. Even a minuscule leak can be enough to saturate a clay foundation. A leaking tap near a building can have the same effect. In addition, trenches containing pipes can become watercourses even though backfilled, particularly where broken rubble is used as fill. Water that runs along these trenches can be responsible for serious erosion, interstrata seepage into subfloor areas and saturation. Pipe leakage and trench water flows also encourage tree and shrub roots to the source of water, complicating and exacerbating the problem. Poor roof plumbing can result in large volumes of rainwater being concentrated in a small area of soil: > Incorrect falls in roof guttering may result in overflows, as may gutters blocked with leaves etc. » Corroded guttering or downpipes can spill water to ground. » Downpipes not positively connected to a proper stormwater collection system will direct a concentration of water to soil that is directly adjacent to footings, sometimes causing large- scale problems such as erosion, saturation and migration of water under the building. SERIOUSNESS OF CRACKING In general, most cracking found in masonry walls is a cosmetic nuisance only and can be kept in repair or even ignored. Table 2 below is a reproduction of Table C1 of AS 2870-2011. AS 2870-2011 also publishes figures relating to cracking in concrete floors, however because wall cracking will usually reach the critical point significantly earlier than cracking in slabs, this table is not reproduced here. PREVENTION AND CURE PLUMBING Where building movement is caused by water service, roof plumbing, sewer or stormwater failure, the remedy is to repair the problem. It is prudent, however, to consider also rerouting pipes away from the building where possible and relocating taps to positions where any leakage will not direct water to the building vicinity. Even where gully traps are present, there is sometimes sufficient spill to create erosion or saturation, particularly in modern installations using smaller diameter PVC fixtures. Indeed, some gully traps are not situated directly under the taps that are installed to charge them, with the result that water from the tap may enter the backfilled trench that houses the sewer piping. If the trench has been poorly backfilled, the water will either pond or flow along the bottom of the trench. As these trenches usually run alongside the footings and can be at a similar depth, it is not hard to see how any water that is thus directed into a trench can easily affect the foundation's ability to support footings or even gain entry to the subfloor area. GROUND DRAINAGE In all soils there is the capacity for water to travel on the surface and below it. Surface water flows can be established by inspection during and after heavy or prolonged rain. If necessary, a grated drain system connected to the stormwater collection system is usually an easy solution. It is, however, sometimes necessary when attempting to prevent water migration that testing be carried out to establish watertable height and subsoil water flows. This subject may be regarded as an area for an expert consultant. PROTECTION OF THE BUILDING PERIMETER It is essential to remember that the soil that affects footings extends well beyond the actual building line. Watering of garden plants, shrubs and trees causes some of the most serious water problems. For this reason, particularly where problems exist or are likely to occur, it is recommended that an apron of paving be installed around as much of the building perimeter as necessary. This paving should extend outwards a minimum of 900 mm (more in highly reactive soil) and should have a minimum fall away from the building of 1:60. The finished paving should be no less than 100 mm below brick vent bases. It is prudent to relocate drainage pipes away from this paving, if possible, to avoid complications from future leakage. If this is not practical, earthenware pipes should be replaced by PVC and backfilling should be of the same soil type as the surrounding soil and compacted to the same density. Except in areas where freezing of water is an issue, it is wise to remove taps in the building area and relocate them well away from the building — preferably not uphill. It may be desirable to install a grated drain at the outside edge of the paving on the uphill side of the building. If subsoil drainage is needed this can be installed under the surface drain. CONDENSATION In buildings with a subfloor void, such as where bearers and joists support flooring, insufficient ventilation creates ideal conditions for condensation, particularly where there is little clearance between the floor and the ground. Condensation adds to the moisture already present in the subfloor and significantly slows the process of drying out. Installation of an adequate subfloor ventilation system, either natural or mechanical, is desirable. © CSIRO 2021
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TABLE 2. CLASSIFICATION OF DAMAGE WITH REFERENCE TO WALLS. Description of typical damage and required repair Hairline cracks Fine cracks which do not need repair Cracks noticeable but easily filled. Doors and windows stick slightly. Cracks can be repaired and possibly a small amount of wall will need to be replaced. Doors and windows stick. Service pipes can fracture. Weathertightness often impaired. Extensive repair work involving breaking-out and replacing sections of walls, especially over doors and windows. Window and door frames distort. Walls lean or bulge noticeably, some loss of bearing in beams. Service pipes disrupted. Approximate crack width limit Damage category <0.1mm 0—Negligible <imm 1—-Very Slight <5mm 2-Slight 5-15 mm (or a number of cracks 3 mm 3— Moderate or more in one group) 15-25 mm but also depends onnumber 4 - Severe of cracks Source: Reproduced with the permission of Standards Australia Limited © 2011. Copyright in AS 2870-2011 Residential slabs and footings vests in Standards Australia Limited. Warning: Although this Building Technology Resource deals with cracking in buildings, it should be said that subfloor moisture can result in the development of other problems, notably: >» Water that is transmitted into masonry, metal or timber building elements causes damage and/or decay to those elements. » High subfloor humidity and moisture content create an ideal environment for various pests, including termites and spiders, and mould. > Where high moisture levels are transmitted to the flooring and walls, an increase in the dust mite count can ensue within the living areas. Dust mites, as well as dampness in general, can be a health hazard to inhabitants, particularly those who are abnormally susceptible to respiratory ailments. THE GARDEN The ideal vegetation layout is to have lawn or plants that require only light watering immediately adjacent to the drainage or paving edge, then more demanding plants, shrubs and trees spread out in that order. Overwatering due to misuse of automatic watering systems is a common cause of saturation and water migration under footings. If it is necessary to use these systems, it is important to remove garden beds to a completely safe distance from buildings. EXISTING TREES Where a tree is causing a problem of soil drying or there is the existence or threat of upheaval of footings, if the offending roots are subsidiary and their removal will not significantly damage the tree, they should be severed and a concrete or metal barrier placed vertically in the soil to prevent future root growth in the direction of the building. If it is not possible to remove the relevant roots without damage to the tree, an application to remove the tree should be made to the local authority. A prudent plan is to transplant likely offenders before they become a problem. INFORMATION ON TREES, PLANTS AND SHRUBS State departments overseeing agriculture can give information regarding root patterns, volume of water needed and safe distance from buildings of most species. Botanic gardens are also sources of information. Garden bed covered with mulch Tree height selected for nce from house Drained pathway © Medium Q height oO Shrubs oo Carport Path Driveway FIGURE 2 Gardens for a reactive site. EXCAVATION Excavation around footings must be properly engineered. Soil supporting footings can only be safely excavated at an angle that allows the soil under the footing to remain stable. This angle is called the angle of repose (or friction) and varies significantly between soil types and conditions. Removal of soil within the angle of repose will cause subsidence. REMEDIATION Where erosion has occurred that has washed away soil adjacent to footings, soil of the same classification should be introduced and compacted to the same density. Where footings have been undermined, augmentation or other specialist work may be required. Remediation of footings and foundations is generally the realm of a specialist consultant. Where isolated footings rise and fall because of swell/shrink effect, the home owner may be tempted to alleviate floor bounce by filling the gap that has appeared between the bearer and the pier with blocking. The danger here is that when the next swell segment of the cycle occurs, the extra blocking will push the floor up into an accentuated dome and may also cause local shear failure in the soil. If it is necessary to use blocking, it should be by a pair of fine wedges and monitoring should be carried out fortnightly. @ CSIROPUBLISHING 1300 788 000 | +61 3 9545 8400 | [email protected] | www.publish.csiro.au For information about CSIRO testing services visit www.csiro.au/en/work-with-us/services ISBN 9781486312962 (print)/9781486312979 (digital) © CSIRO 2021 (replaces Building Technology File 18, 18-2011 and Information Sheet 10/91) Unauthorised copying of this material is prohibited. IMPORTANT DISCLAIMER: This information is prepared for Australia and general in nature. It may be incomplete or inapplicable in some cases. Laws and regulations may vary in different places. Seek specialist advice for your particular circumstances. To the extent permitted by law, CSIRO excludes all liability to any person for any loss, damage, cost or other consequence that may result from using this information. © CSIRO 2021
Page 29
ATTUNGA North Surveys Pty Ltd ACN 010 803 291 (trading as NorthGroup Consulting) hereby certify the contours shown on this plan represent Natural Ground Level as determined on site. D Director 24/3/LOL5 Date Scale 1:200 Lengths are in Metres. HEIGHTS ( cp cP BUP104992 BUPE8S7 0°03'00" 20.105 r2., : : © x g ; 5 s N § aubeeas 5 a 1” 8 & RPe9506 9 XN —_————_— © N . RP89506 Qe, Pe, <o 0'03'00" 20.105 a, we \ Ys, ee, Ss BENCH MARK RL 63.907 © 0 | 20/03/25] Original Issue No| Date | Revision Seat 1:200 V Datum: AHD | Contourint. 0.2m V Origin: CORS H Datum: Cadastral | H Origin: RP89506 Local Authority: Sunshine Coast RC Surveyed: BW Date: 19/03/25 Drawn: BW Date: 20/03/25 File Ref: 202068 003 | FB: GsI SHEET 1 OF 1 ‘This drawing was generated using AutoCAD Software other formats available on request. 10 0 5 10 15 Qi Pfiloraoaup Corrisulturig 4 Title/Project: Natural Ground Level Survey 19 Attunga Heights, Noosa Client: Beach Designs Creating exceptional value in delivering Surveying, Scanning & Town Planning Solutions >r'202068 003 NGL* 0
Page 30
190 5820 190 2200 190 6120 90 1110 190 4046 2000
3000 6200 2200 7700
590
2000
6000mm setback
4500mm setback
BALUSTRADE
190
3315
TV
living pool
EXISTING TREE
alfresco
3580
3600
BALUSTRADE
4200
9015
190600
1000 190
190
Attunga Heights
dining
1910
190
entry
PLANTER
2910
15805
910
1910
190 1000
190 1200 190 1000
190
190
190
F
lift study
1800
9720
2330
pdr
2930
2930
kitchen
190
ROBE
90
ROBE
90
90 900 90
4230
WINDOW SEAT
EXISTING TREES
3630
butlers
3200
bed 2
1500mm setback
2000mm setback
2500mm setback
3200
bed 3 bed 1
ROBE
bthrm
2210
ROBE
WINDOW SEAT
600190
190
190
WINDOW SEAT
190
190
2500mm setback
2000mm setback
2900
driveway
2300
1500mm setback
190 900 4920 1500 3640 190 1600 190 2510 100 total floor area = 180m²
90 90 90 90
190 1920 3200 600 2440 600 3000 3600 100 site cover = 206m²
90 90 90 90 90
3000 8620 7480 6046
Plan
Ground Level 1 : 100
No. Description Date
Project Client Drawing Drawn by A Draft Issue A 17/03/2025 Project number Scale at A3
19 Attunga Heights Bennett Residence GROUND LVL - DRH B Concept Issue B 20/03/2025
dennishillarchitect FLOORPLAN
065 1 : 100
mobile: 0438 20 55 66 | [email protected]
www.dennishillarchitect.com CONCEPT.06
Do not scale from drawings. Dimensions are to be checked on site prior to commencement of work. Discrepancies to be brought to the attention of the author. Any dimensions not nominated must be referred to the Architect for confirmation. The concepts and information contained in this document are the copyright of Architect. Use or copying of the document in whole or in part without the written permission of the Architect constitutes an infringement of copyright. 20/03/2025 8:00:23 PM
Page 31
6000mm setback
4500mm setback
master bed
ensuite
skylight
plunge
pool
lift
WIR
terrace
1500mm setback
2000mm setback
2500mm setback
retreat
FR BAR TV
2500mm setback
2000mm setback
1500mm setback
total floor area = 102m²
Plan
Upper Level 1 : 100
No. Description Date
Project Client Drawing Drawn by A Draft Issue A 17/03/2025 Project number Scale at A3
19 Attunga Heights Bennett Residence UPPER LVL - DRH B Concept Issue B 20/03/2025
dennishillarchitect FLOORPLAN
065 1 : 100
mobile: 0438 20 55 66 | [email protected]
www.dennishillarchitect.com CONCEPT.07
Do not scale from drawings. Dimensions are to be checked on site prior to commencement of work. Discrepancies to be brought to the attention of the author. Any dimensions not nominated must be referred to the Architect for confirmation. The concepts and information contained in this document are the copyright of Architect. Use or copying of the document in whole or in part without the written permission of the Architect constitutes an infringement of copyright. 20/03/2025 8:00:28 PM
Page 32
ROOF DRAINAGE
NOTES:
All work to conform with Part MP 4.2 of the 600 1500 7000
Queensland Development Code (QDC)
(Water Saving Targets).
6000mm setback
4500mm setback
Roof stormwater is to discharge to local
government requirements and approval.
Tank/s overflow and downpipes not
connected to rainwater tank/s to discharge
600
600
to interallotment drainage system/ to
nominated discharge points via bubbler
system/ to discharge to street channel system.
Based on assumed 5 minute rainfall intensity -
258mm/h 20 years recurrence interval.
line of upper level walls under
Gutters & downpipes shall be in accordance
5200
with AS/NZS3500.5 domestic & Part 3.5.2, Vol 2
of the NCC.
All downpipes to be 90mm/100mm U-PVC.
All gutters to be 150 Half Round Gutters
(7042mm² Cross section area).
Falls to be in accordance with clause 3.5.2.4,
Vol 2 of the NCC.
• Effective roof catchment area (dwelling
skylights
only) 145 m²
13700
• Roof catchment per downpipe 50m²
• Downpipes must not serve more than
12m of gutter length for each downpipe
• Total rainfall intensity 145m² X 258mm/50 =
748.2L/min
• Stormwater pipes - 100 dia. Laid at 1 in
100 minimum grade.
Downpipes are to be located where they will Roof Catchment Area
8500
not create a hazard to building users nor 145m²
impede window & door openings and the
like. kliplok roofing
3.0°
They are to be installed as close as
practicable to the supporting structure while
maintaining termite inspection clearances of
1500mm setback
2000mm setback
2500mm setback
25mm. Downpipes are to be protected from
potential mechanical damage, be installed
no less than 100mm from electrical cables &
gas pipes & no less than 50mm from other
services (AS3500.3.2 S4.11)
600
600
Downpipes are to service 12m maximum 2500mm setback
gutter length & be within 1.2m from each 2000mm setback
valley unless overflow is provided for (NCC
Vol2 7.4.5) 1500mm setback 600 8500
Plan
Upper Level Pitching 1 : 100
No. Description Date
Project Client Drawing Drawn by A Draft Issue A 17/03/2025 Project number Scale at A3
19 Attunga Heights Bennett Residence ROOF DRAINAGE DRH B Concept Issue B 20/03/2025
dennishillarchitect PLAN
065 1 : 100
mobile: 0438 20 55 66 | [email protected]
www.dennishillarchitect.com CONCEPT.09
Do not scale from drawings. Dimensions are to be checked on site prior to commencement of work. Discrepancies to be brought to the attention of the author. Any dimensions not nominated must be referred to the Architect for confirmation. The concepts and information contained in this document are the copyright of Architect. Use or copying of the document in whole or in part without the written permission of the Architect constitutes an infringement of copyright. 20/03/2025 8:00:29 PM
Page 33
Upper Level Pitching
RL 70.250 m
Upper Level
RL 67.550 m
Ground Level
RL 64.550 m
1 Elevation
East Elevation 1 : 100
Upper Level Pitching
RL 70.250 m
Upper Level
RL 67.550 m
Ground Level
RL 64.550 m
Basement Level
RL 61.850 m
2 Elevation
West Elevation 1 : 100
No. Description Date
Project Client Drawing Drawn by A Draft Issue A 17/03/2025 Project number Scale at A3
19 Attunga Heights Bennett Residence ELEVATIONS DRH B Concept Issue B 20/03/2025
dennishillarchitect 065 1 : 100
mobile: 0438 20 55 66 | [email protected]
www.dennishillarchitect.com CONCEPT.11
Do not scale from drawings. Dimensions are to be checked on site prior to commencement of work. Discrepancies to be brought to the attention of the author. Any dimensions not nominated must be referred to the Architect for confirmation. The concepts and information contained in this document are the copyright of Architect. Use or copying of the document in whole or in part without the written permission of the Architect constitutes an infringement of copyright. 20/03/2025 8:00:32 PM
Page 34
8m max heigh
t
Upper Level Pitching
RL 70.250 m
Upper Level
RL 67.550 m
Ground Level
RL 64.550 m
NGL
1 Elevation
North Elevation 1 : 100
Basement Level
RL 61.850 m
height
8m max
Upper Level Pitching
RL 70.250 m
Upper Level
RL 67.550 m
3000
Ground Level
RL 64.550 m
2278
NG L
Basement Level
RL 61.850 m
2 Elevation
South Elevation 1 : 100
No. Description Date
Project Client Drawing Drawn by A Draft Issue A 17/03/2025 Project number Scale at A3
19 Attunga Heights Bennett Residence ELEVATIONS DRH B Concept Issue B 20/03/2025
dennishillarchitect 065 1 : 100
mobile: 0438 20 55 66 | [email protected]
www.dennishillarchitect.com CONCEPT.12
Do not scale from drawings. Dimensions are to be checked on site prior to commencement of work. Discrepancies to be brought to the attention of the author. Any dimensions not nominated must be referred to the Architect for confirmation. The concepts and information contained in this document are the copyright of Architect. Use or copying of the document in whole or in part without the written permission of the Architect constitutes an infringement of copyright. 20/03/2025 8:00:35 PM
Page 35
Upper Level Pitching
RL 70.250 m
Upper Level
RL 67.550 m
1000m(h) from pool side to provide fall-prevention
500
2470
2000
1000
1100
2000
Ground Level
2746
RL 64.550 m
400
400
2000
190 2740 4280 100 1790 2610 100 8295
2190
2051 11695
Basement Level
RL 61.850 m
1 Elevation 2 Elevation 4000 4000 3400
East Elevation - Boundary Wall 1 : 150 North Elevation - Boundary Wall 1 : 150
Upper Level Pitching
RL 70.250 m
Upper Level
RL 67.550 m
400
400
400
Ground Level
400
2000
RL 64.550 m
400
400
200
400
200
2000
g lot
ighbourin
NGL at ne
2000
3200 3000 2800
Basement Level
RL 61.850 m
4546 3000 3000 2400 3200
2400 5800 11905
4 Elevation 3 Elevation
West Elevation - Boundary Wall 1 : 150 South Elevation - Boundary 1 : 150
Wall
No. Description Date
Project Client Drawing Drawn by A Concept Issue B 20/03/2025 Project number Scale at A3
19 Attunga Heights Bennett Residence BOUNDARY DRH
dennishillarchitect WALLS
065 1 : 150
mobile: 0438 20 55 66 | [email protected]
www.dennishillarchitect.com CONCEPT.13
Do not scale from drawings. Dimensions are to be checked on site prior to commencement of work. Discrepancies to be brought to the attention of the author. Any dimensions not nominated must be referred to the Architect for confirmation. The concepts and information contained in this document are the copyright of Architect. Use or copying of the document in whole or in part without the written permission of the Architect constitutes an infringement of copyright. 20/03/2025 8:00:39 PM
Page 36
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Sunshine Coast | Brisbane | Gold Coast
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Sunshine Coast | Brisbane | Gold Coast
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