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Attachment C - Geotechnical investigation
51 640 311 842
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Teeland Architects 09 Feb 2021
By Email Letter 01 Revision 0
Arcos Project: 200849
[email protected]
Dear Justyn and Sahra Douglas,
Report on Geotechnical Investigation
Proposed Residential Dwelling
20 Park Crescent, Sunshine Beach
At the request of Teeland Architects, Arcos Unit Group Pty Ltd (AG) undertook a geotechnical
investigation for the above project. The summary of the investigation and subsequent analysis
is detailed in Table 1. The value presented in Table 1 is condition upon the recommendations
within this report being implemented and is described in accordance with the Australian
Geomechanics Society “Guidelines for Landslide Risk Management”.
Table 1: Summary of Investigation Results
Result of AGS Slope Instability Assessment
Low if recommendations implemented*
Notes: 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.
Geotechnical Engineer Principal Geotechnical Engineer
Cody Surawski B.Eng(Civ)(Hons)/B.Env.Sc. Billy Blake B.Eng(Civ)(Hons), CPEng, RPEQ, NER, MIEAust
09 Feb 2021 Proposed Residential Dwelling
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1.0 Introduction
Arcos Unit Group Pty Ltd (AG) was commissioned to undertake a geotechnical investigation
for the Proposed Residential Dwelling located at 20 Park Crescent, Sunshine Beach.
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 report is undertaken in accordance with
our Company’s terms and conditions.
2.0 Regional Geology
The site is an area underlain by the Pleistocene aged Sand, which typically comprises “Quartz
sand; parabolic sand dunes”. The encountered conditions agree with anticipated geological
units.
3.0 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 allotment has been initially mapped
as “High” in terms of landslide hazard.
4.0 Previous Geotechnical Investigation
A geotechnical investigation for the proposed development has been undertaken by Arcos
Unit Group Pty Ltd. This report is attached and the encountered conditions in this investigation
have informed the analysis undertaken by this office. Given this, where discrepancies exist
between the encountered conditions in the referenced report and the encountered conditions,
our analysis cannot be considered to be accurate and reassessment will be required.
The referenced report encountered sand present through the whole profile, which aligns with
the predicted geological unit at the site. No groundwater seepage was observed in the
investigation undertaken.
09 Feb 2021 Proposed Residential Dwelling
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5.0 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.
An experienced geotechnical engineer undertook the walkover assessment on 05 Feb 2021.
As part of the walkover assessment, 'spot' measures were taken of the slope angles and
observations pertaining the any obvious previous slope instability on the allotment and
immediately adjoining areas that were readily accessible at the time of the inspection was
undertaken. The surface levels on the site fall away to the south to south east at varying grades
up to 33°. Signs of disturbed ground, tension cracks or hummocks were noted during the
walkover assessment. A variety of vegetation ranging from small shrubs to mature trees were
observed. Some of the mature trees were observed to have misshapen and curved trunks.
Misshapen or curved trunks are usually good indicators for previous slope instability.. The
photographs attached to this report show the conditions of the site at the time of the
inspection and assessment undertaken.
6.0 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.
09 Feb 2021 Proposed Residential Dwelling
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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.
Table 1: Results of AGS Qualitative Risk Assessment
Hazard Likelihood Consequence Risk Level
Global Failure Barely Credible Catastrophic Low
Shallow slumping of surface soils Likely Minor Moderate
Based on the results of the AGS assessment, the perceived risk based on the conditions
encountered and information available at the time of the assessment is “Low if
recommendations implemented*”.
7.0 Hillside Construction
The following works should be implemented in additional to other items highlighted within
this document. These points are considered to be typical good hillside construction practice
as explained in attached documentation:
• Foundations for lightly loaded or non-liveable structures as well as heavy structures
should be founded at least 1.5 m into medium dense (or stronger) natural sands. A
minimum of five lines of piles will be required to provide at least 250 kN in shear capacity
across this depth.
• Where slopes are not supported by an engineer designed support system, natural slopes
within or near building envelope or movement sensitive areas should be no steeper than
2H:1V.
• Building platform fill should be limited to a maximum height of 1 m. The filling should be
step keyed into the natural slope and battered no steeper than 3H:1V unless an engineer
designed retention system is in place.
• Unsupported cuts steeper than 3.5H:1V will require engineer designed retention systems.
• All stormwater and surface water is to be discharged by an approved stormwater drainage
system. The use of subsurface drainage systems are not suitable unless greater than 50
m downslope from the envelope at this site.
• Ongoing maintenance of the effluent wastewater area is also considered mandatory. The
location of the application area should be located below the proposed building. Plumbing
and services must also not be allowed to leak and regular maintenance and inspections
should be undertaken.
09 Feb 2021 Proposed Residential Dwelling
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8.0 Geotechnical Recommendations
The following sections details specific geotechnical constraints or recommendations in
addition to general hillside construction notes.
8.1 Site Preparation and Earthworks
The following comments are provided in relation to site preparation for earthworks.
• No fill at this site is to be placed unless supported by an engineer designed and certified
retaining structure
• Areas where fill is proposed should be stripped of uncontrolled fill, soft, overly wet,
foreign, or otherwise deemed unsuitable material (material that is potentially
compressible) down to a relatively stiff dry base ensuring no organics material is present.
• Stripped areas must be inspected by the geotechnical testing authority (GTA) to ensure
no soft spots or loose zones are present. This should be done with the use of a loaded
body truck or 12 tonne roller as a minimum. Areas showing signs of movement under the
action of the testing equipment should be either over excavated and replaced with select
fill or conditioned onsite through tyning, blending or other suitable methods.
• Areas sloping in excess of approximately 1 vertical unit to 10 horizontal units (1V:10H),
the surface will need to be benched at a minimum vertical bench height of 0.3 m to enable
keying in of the new fill and existing soil. The benches will also need to be shaped
adequately to promote drainage.
• Edge batters should be formed by over filling an area and ‘trimming’ back to the desired
profile.
• Although no standard exists for the moisture content of soils, it is recommended that the
site soils be placed at or near optimum moisture content (OMC) for general earthworks
operations. This increases efficiency during earthworks operations. A range of +/- 2% of
OMC is recommend for general earthworks.
• Where site soils are proposed for use as fill in other areas, won material will need to have
a maximum particle size of 75 mm or be observed to break down under the energy of
compactive equipment.
• Fill materials should be placed in relatively horizontal layers with a maximum placement
thickness of 200 mm. The materials should be compacted to a minimum dry density ratio
of 98% relative to Standard compactive effort.
• Highly plastic natural clays are very sensitive to the presence or lack of moisture and
therefore care should be used to place the material within the range nominated and to a
maximum dry density of 102% relative to Standard compactive effort. Where this does
not happen, the material could readily swell, soften, or be subject to significant
trafficability issues.
• Earthworks quality testing will be required on this site. The GTA will need to provide
supervision in accordance with AS3798 and undertake field density tests to monitor the
actual dry density and moisture content of placed materials.
09 Feb 2021 Proposed Residential Dwelling
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• Completed platforms should be sealed with a minimum 250 mm layer of relatively
granular material (CBR15% or greater) to minimise the effects of relatively clayey
subgrades drying out leading to excessive cracking.
• Earthworks activities should be undertaken in relatively homogenous sequences where
achievable (ie. do not place “pockets” of gravel material next to impermeable clays as this
will lead to zones where water could become trapped).
• Fill material will be subject to potential settlement post placement. Well compacted fill
placed in accordance with AS3798 and otherwise, good earthworks procedure should
typically be subject to settlement in the order of 0.5% to 1.0% of the fill thickness over a
log cycle of time.
Arcos can assist in preparing earthworks documentation or guidelines for contractors to
adhere to in order to achieve an efficient and “fit for purpose” end product.
8.2 Retaining Structures
Retaining walls must be designed by a suitably qualified and experienced engineer and
preferably in accordance with AS 4678. The geotechnical parameters for use in design of either
flexible or rigid wall systems are presented in Table 2.
Passive forces should be ignored in areas where disturbance may occur (ie. future trenching
or earthworks processes).
Compaction for retaining wall backfill should be undertaken with due care. Layers should be
placed thinner than for normal earthworks processes (say a maximum layer thickness of
100 mm) and compacted using light weight equipment such as hand controlled compactive
equipment to minimise the stresses on the wall. If hand controlled equipment is not practical,
temporary wall propping will be required.
Walls will need to incorporate full height drainage in accordance with good design practice to
minimise hydrostatic pressure. The below parameters do not include surcharge loadings.
Table 2: Retaining Wall Parameters (Unfactored)
Unit Weight Friction Angle Drained Cohesion
Material
(kN/m3) (Ø) (c’)
Medium Dense+ Sands 19 33 0
Notes: NR – Not Recommended
*- Compacted under Level 1 conditions and behaves as clayey material
MD - Medium Dense
09 Feb 2021 Proposed Residential Dwelling
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8.3 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.
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 sands, they may be dimensioned for a maximum
allowable bearing pressure of 100 kPa. Based on the borelogs, the above material is
encountered at approximately 2.0 m depth below existing surface levels at the time of the
investigation. It should be noted, however, that in order to obtain a “Low” risk rating the
footings must be constructed at least 1.5 m into the medium dense sands. Therefore, the
footings should be founded to at least 3.5 m below the current ground surface level.
The ultimate geotechnical end bearing and shaft adhesion parameter are presented in Table
3. 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.
09 Feb 2021 Proposed Residential Dwelling
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Table 3: Deep Level Footings – Ultimate Geotechnical Parameters (Long Pile)
Bored
Material
Fb (kPa) Fs (kPa)
Medium Dense Sands 1800 6.6
Notes: * - Fb = Ultimate End Bearing Pressure (unfactored) for long piles, Fs = Ultimate Shaft Adhesion (unfactored).
The upper 1 m of soil profile should be ignored in shaft calculations to allow for shrinkage
cracks. The values presented in Table 3 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.
9.0 Limitations
Arcos Unit Group Pty Ltd (AG) has prepared this document for 20 Park Crescent, Sunshine Beach
for Teeland Architects. The document is specific to this particular project and for the purposes
as described within the document. The document cannot be used for any other project on the
same site or other sites or relied upon by a third party. Any party relying upon this document
beyond its exclusive use and purpose as stated above, and without the express written consent
of AG, does so entirely at its own risk and without recourse to AG for any loss or damage. AG
has necessarily relied upon information provided by the client and/or their agents.
It is important to understand that ground conditions can be spatially variable over short
distances as a result of geological processes or human interference. These changes can occur
after the time of which field work was undertaken. Given this, the assumed subsurface
conditions within this document are only indicative of the conditions at the testing locations
to the depths investigated at the time of the fieldwork.
The advice given in this document is based upon the assumed subsurface conditions. The
relevance and accuracy of advice given is directly affected by variations in ground conditions
across the site between testing locations that has not been captured and time elapsed since
investigation works.
This document must be kept in entirety, read in full and understood. Interpretations or
conclusions made by others unless supported by an expressed written statement,
interpretation, outcome or stated within this document cannot be the responsibility of AG.
This document or parts of it should not be used as part of a specification or design for a project
without prior review and agreement by AG.
09 Feb 2021 Proposed Residential Dwelling
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__________________________________________________________________________________
We trust this information is satisfactory for your current needs. Should you have any questions,
please feel free to contact the signed authors.
09 Feb 2021 Proposed Residential Dwelling
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Sunshine Coast | Brisbane | Gold Coast
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Sunshine Coast | Brisbane | Gold Coast
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Sunshine Coast | Brisbane | Gold Coast
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GEOTECH REPORT
These notes have been provided to clarify and Arcos Unit Group Pty Ltd undertakes quality assurance
enhance the reader’s understanding of the terminology checks in accordance with its’ quality system
used throughout the report, and also to identify where requirements; however, restrictions on the project
limitations exist. All investigations are undertaken outside of Arcos Unit Group Pty Ltd’s control can result
based on budgetary constraints which impart a level of in unanticipated variations, changes in policy or
uncertainty as a result of limiting the amount of interpretation of said policies by the relevant authority,
investigation undertaken. or the actions of contractors subject to commercial
pressure.
Copyright
Site Variations
This report remains the property of Arcos Unit Group
Pty Ltd at all times unless ownership is transferred in If site variations become evident at the time of
writing. It cannot be included in any documentation construction or after the release of a report, Arcos Unit
without the express written permission of Arcos Unit Group Pty Ltd requests immediately notification. This
Group Pty Ltd notification is proposed in order to assist in remediation
prior to any permanent structures or design procedures
Subsurface Report Sheets (Bores etc) are undertaken.
The provided subsurface sheets are inherently an Collaboration
interpretation undertaken by a suitably qualified and
experienced person; however, the reliability of the Arcos Unit Group Pty Ltd strongly recommends open
provided information will rely on the method of and collaborative communication about the use and
investigation. It is prudent to state that these sheets inherent interpretation of Arcos Unit Group Pty Ltd’s
only represent a very small percentage of the report. Please contact the author of the report to
subsurface conditions across a particular project. arrange for an obligation free discussion regarding the
potential benefits of having geotechnical consultants.
It reasons that given the relatively small representation
of the subsurface conditions for a project, spacial
variability between testing locations must be taken into
consideration including the orientation of strata
intersections.
The presence or lack of groundwater is usually stated
on the subsurface sheets; however, it must be noted
that the measurements undertaken onsite are typically
very inaccurate and if the presence or lack of
groundwater will have any degree of affect on the
project, additional groundwater monitoring techniques
should be employed such as groundwater monitoring
wells.
Reporting
The report has been prepared and reviewed by suitably
qualified and experienced persons. The persons draw
on previous experience, local knowledge, published
literature, and otherwise standard engineering
approaches and principals. The context of which the
report has been prepared for must 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 Arcos Unit Group
Pty Ltd must be undertaken.
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Interpretation of the
Subsurface Sheets
It is important to note that the point load strength index
The terminology included on Arcos Unit Group Pty Ltd’s
does not take into consideration the degree of fracturing of
has been evolved from AS1726:2016. Typically a soil’s
a rock mass which can both lower and increase the overall
strength, colour, plasticity, grain size, other inclusions, and
rock strength. The strength of rock is broken down as
moisture will be described. A rock’s strength, weathering,
follows:
colour, grain, and other inclusions are typically described.
Very Low Strength (VLS) < 2 MPa (UCS)
Soil Low Strength (LS) 2 to 6 MPa (UCS)
Medium Strength (MS) 6 to 20 MPa (UCS)
Soil is typically described by the components that make it High Strength (HS) 20 to 60 MPa (UCS)
up by percentage or whichever has a governing behaviour. Very High Strength (VHS) 60 to 200 MPa (UCS)
The types and sizes reproduced from AS1726 are: Extremely High Strength (EHS) > 200 MPa (UCS)
Boulder >200 mm
Cobble 63 to 200 mm
Gravel 2.36 to 63 mm Very Low Strength (VLS) < 0.1 Is(50)
Sand 0.075 to 2.36 mm Low Strength (LS) 0.1 to 0.3 Is(50)
Silty 0.002 to 0.075 mm Medium Strength (MS) 0.30 to 1.0 Is(50)
Clay < 0.002 mm High Strength (HS) 1.0 to 3.0 Is(50)
Very High Strength (VHS) 3.0 to 10.0 Is(50)
The strength of soil is usually assessed by suitably Extremely High Strength (EHS) > 10.0 Is(50)
experienced persons through the use of laboratory test
results, published literature, field assessments or a The Is(50) values are based on a correlation between the
combination of the above. The strength of soil is unconfined compressive strength (UCS) of 20. This value
characterised into either cohesive (clays and silts) or varies significantly and site specific testing must take
cohesionless (sands and gravels) as shown below: precedence.
Cohessive Soil Strength Term Rock weathering is broken down as follows:
Very Soft < 12.5 kPa
Soft 12.5 to 25 kPa Extremely weathered Behaves as soil but rock
Firm 25 to 50 kPa (EW) structure evident
Stiff 50 to 100 kPa Highly weathered Colour and strength of original
Very Stiff 100 to 200 kPa (HW) fresh rock is not recognisable.
Hard > 200 kPa Decomposition of rock evident
Moderately Defects are heavily stained with
Cohesionless Soils Strength Term (uncorrected Qc) weathered (MW) rock mass showing signs of
Very Loose <2 MPa discolouration
Loose 2 to 5 MPa Slightly weathered Some staining but minimal to no
Medium Dense 5 to 15 MPa (SW) change in strength
Dense 15 to 25 MPa Fresh stained Minor staining evident
Very Dense > 25 MPa (FS)
Fresh rock No change
Rock (FR)
Rock is typically described by the components that make Rock fracturing is broken down as follows and can only be
it up by percentage or whichever has a governing accurately described where undamaged continuous
behaviour. The strength of rock is typically the most sampling has been undertaken:
important component. Typically, the strength of rock is
based on laboratory testing, tactile assessment and other Fragmented (Fg) Defect spacings < 20 mm
observations as relevant. The industry standard method Highly Fractured (HF) Defect spacings 20 to 50 mm
for assessing the strength of rock in the field is to use the Fractured (Fr) Defect spacings 50 to 200 mm
point load strength index (AS4133.4.1). Slightly Fractured (SF) Defect spacings 200 to 1000 mm
Unbroken (Ub) Defect spacings > 1000 mm
Page 24
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
EXAMPLES OF GOOD HILLSIDE pele
Surface wate: interception drainage
Watertight, adequately sited and founded
rool water storage larvke (with due regard for
Impact ef potertia) waabage)
Plesible sructure
Roof water piped aff ste cr aicred
Grssite creention tanks, walernght at
edequately founded. Poteriii! leakage
managed by sub-sol drains
— MANTLE OF SOM AND ROTH
FRAGMENTS (COLLUVILW)
SS Pier footings tena rock
~~ Sunsail drainage may be
required in slope
‘“— Cutting and filtng minimised in davelapment
*—_ Sewage efftuent pumped cut 61 connected to sower.
Tanke adequately founded and waterignt. Potential
lecieage managed bry suh-scoll drains
\
“> Engingered retaining walls with both surface and
subsurface drainage (constructed before dialing) ahiiac bishag
EXAMPLES OF POOR HILLSIDE PRACTICE
Unetebtised rock toppies
ond tirwals doensiage
Vegetnten removed ——
Diteherges. ot motwater soak Biosp unsupported \ 4
, !
eay rather than coducted off Dut fates
tile or to necore storage for reise
‘Sructure unatte tc tolerate an
eattherrent and cracks it ee
Poort) compacted fil entices 4
Uneverly and cracks pool 8,
jnadequate walling unatle
fo support Mi a
i
Loose. saturated 4 cites
and possibly Nowe dowemtope i
|
i
Inacoquetely supportad cut tlle
4
Sea rabed
slope hi —
Vegetation
rermcvett
Med fow |
ors
. |_—Antenos of scbeot drarage mthin sv
—— Pordect water enters shine and actiates landstde ret abe ied
* Rossitte waved GONRICOS whch loacts olvar develagmint downtt Srey alien ALCS (20500) Appgaewnctix
114 Australian Geomechanics Vol 42 No 1 March 2007
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 Landstide a ‘ict te rh Indicative Notional Recurrence Interval ee scriptor vel Value Boundary 107 5x107 10 years The event is expected to occur over the design life. ALMOST CERTAIN A 2 20 years The event will probably occur under adverse conditions over the ~ 10 ‘ 100 years design hie 7 LIKELY B 3 * : 107 azig 1000 years soo yeas The event could occur under adverse conditions over the design life. | POSSIBLE Cc 5x10° ares The event might occur under very adverse circumstances over the 107 10,000 years design life may UNLIKELY D = . E 10° 5x10 PUG years The event is conceivable but only under exceptional circumstances ) 1 QO, 000 yeas over the design life RARE E 10° ae 1,000,000 years | 700-000 vears [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 Indicative Notional Description Descriptor Level Value Boundary 5 Structure(s) completely destroyed and/or large scale damage requiring major engineering works for 200° S iS iS iS 200% 00% stabilisation. Could cause at least one adjacent property major consequence damage. Gos ernls : 60% 100% Extensive damage to most of structure, and/or extending beyond site boundaries requiring significant MAJOR 5 40° stabilisation works. Could cause at least one adjacent property medium consequence damage. ~ 20% 2 Moderate damage to some of structure, and/or significant part of site requiring large stabilisation works. MEDIUM 3 ease 10% Could cause at least one adjacent property minor consequence damage. = = = 5% 1% Limited damage to part of structure. and/or part of site requiring some reinstatement stabilisation works. MINOR 4 F Little damage. (Note for high probability event (Almost Certain), this category may be subdivided at a 0, = 4 J irs notional boundary of 0.1%. See Risk Matrix ) ASEAN ‘ 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. G3) The Approximate Cost is to be an estimate of the direct cost of the damage. such as the cost of restatement 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 mclude 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 RL2 August 2010
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 CON: SEQUEN CES TO PROPERTY (With Indicative Approximate Cost of Eomp. Indicative Value of 1; CATASTROPHIC 2: MAJOR 3: MEDIUM 4: MINOR Approximate Annual 200% 60% 20% 5% INSIGNIFIC ANT Probability 0.5% — ALMOST CERTAIN 107 H MorL (5) - LIKELY 107 H M i - POSSIBLE 107 M M VL - UNLIKELY 10+ L L VL - RARE 10° M £ “2 VL VL - 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 Rusk. (©) When considenng a nsk assessment it must be clearly stated whether it is for existing conditions or with nsk control measures which may not be implemented at the cwrent time RISK LEVEL IMPLICATIONS Risk Level Example Implications (7) Unacceptable without treatment. Extensive detailed investigation and research. planning and umplementation of treatment options essential to reduce msk to Low; may be too expensive and not practical. Work likely to cost more than value of the property. Unacceptable without treatment. Detailed vestigation, planning and implementation of treatment options required to reduce = Z ‘i nisk to Low. Work would cost a substantial sum m relation to the value of the property May be tolerated m certain circumstances (subject to regulator's approval) but requires investigation, planning and M MODERATE RISK unplementation of teatment options to reduce the nsk to Low. Treatment options to reduce to Low nsk should be umplemented as soon as practicable Usually acceptable to regulators. Where treatment has been required to reduce the nsk to this level, ongoing maimtenance is L LOW RISK rompived VL VERY LOW RISK Acceptable. Manage by normal slope maintenance procedures Note: (7) The implications for a particular situation are to be determined by all partes to the msk assessment and may depend on the nature of the property at nsk: these are only gtven as 2 general euide. Australian Geomechanics Vol 42 No 1 March 2007 Form No. 68039 RL2 August 2010
Page 27
APPENDIX G - SOME GUIDELINES FOR HILLSIDE CONSTRUCTION ADVICE GOOD ENGINEERING PRACTICE POOR ENGINEERING PRACTICE GEOTECENICAL ASSESSMENT Obuin advice Som a quabfed oxpensnced geotechnical practttonar 2t sarly segs of plannmg and before wie works. Prepare Getiiled plan and iast ute wor: Defcre geotechnical advice. ——__i—— - DESIGN AND CONSTRUCTION Having obtained advice, plan the development with the mk arising fom the identiGed hazards and consequences in mind Plan development withort regard for the Risk. ‘Use flexible scucture: which incorporate properly designed brickwork timber or steal Samees, timber or panel cladding Flocr plans which require emamive cuthag and Pus Provide dramase mozs=re; and erosion contol. Manzaise beight. Strip vegetation and topsoil and key into astuzal slopes prior to Gillins ‘Use clean 60) matecials and compact to engineering standards. Batter to appropriate slope or support with engineered retaining wall Provide surface drainags and appropriate subvariace drainage. ERE DESIGN” | Consader wie uk split levels Movement intolerant vructures Use decks for recreation: areas where appropriate. SITE CLEARING Retus sataral vegetation wherever practicable. Tndiscriminately clear the site. ACCESS & Satisfy requirements below for cuts, fil, retaimng walls 2nd dramage. Excavate and G0 for wite access before DRIVEWAYS Council specificatoms dor grades may need to be modified geotechnical advice. Driveways and parking areas mosy need to be filly supported on piers. EARTHWORES Retain aateral contours wherever posible. Todtscuiminstory bulk sarthworks. Manzase dopa. Large scale cut: and benches Cure ‘Support with enamecred retaining walls or batter to appropriate slope. Unsapported cuts. | Imers dramazerequamests Loose or pocsly compacted G2 whick if it fails, may flow a comsidesable distance including omto property below. Block natural drainage line: Fill over oxisting vegstaton and topscil. Incinds stumps, toss, vegetation, topsoil boulders buildins mbble otc in fill. Rock Ourcrors Remove or stabilise boulders which may have unacceptable nak. Dismrb or undercut detached block: or DRAWINGS AND SITE VISITS DURING CONSTRUCTION & Boers Support rock Sces where necessary. boulders. Enminser dewsn to veuist applied toil and water forces. Construct a stractarally inadequate wall such a RETAINING Found on rock where le sandstones flagging, brick or umroinforced WALLS Provide subsurface drainage within wall backSill and surface deeimage om slope | blockwork. above. Lack of sabsurface drains and weepholes. Conseuct wall as scon as possible after cut/fill operation Found within rock where practicable. Found om topseél, looss SE detached boulders FOOTINGS ‘Use rows of pier: or stip footing: oriented up and down slops. or undercut cliffs. Desi for interal cosep pressures if necessary. Back footing excavations to exclads mares: of surdace water Engineer dewimed. Support on pues to rock whare practicable. SWIMMING POOLS | Provide with under-drainage and smvity drain outlet where le. Desian for igh soil presvarss which may develop im aphil unde saat shorn cozy be Little or no Isteral sqpport on downhill sids. DRAINAGE Provide st tops of cat and Gill slopes. Discharge at top of ills and cuts. Discharge to street drainage or natural water comrues. Allow water to pond om beach areas. SUBS ACE Provide gemerel falls to prevent blockage by siltation and mccrporate silt traps. ‘Line to minimise infilration and make dloxible where possible. stractares to diss! at chanaes of slope and/or d=ecton Provide Glter around sabvarface draa. Discharge rood ranoff into absorption trenches Sumanrace Provide dram behind retainms walk. . Use Hexible pipelines with access for mamtenance Prevent inflow of sarface water. Sernc & Unaally requis: pamp-out cr mains sewer systems; absorption teaches may | Dischares millsas directly onto and mito slopes. SULLAGE be possible im some areas if risk is acceptabis. ‘Use absorption wenches without comsiderstion ios | Storage tanks should be water-tight and adequately founded of landslide risk. EROSION Control erosion as this may lead to instability. Faire to observe oasthworks and dramaso CONTROL & Revegetats cleared area Tecommendations when landscaping. LANDSCAPING DRAWINGS Building Application drawings thould be viewed by aeotechmical consultant SITE VISITS Site Visas by consultant may be appropriate gums comstrucson. INSPECTION AND VIENANCE BY OWNER CWNER'S Clean dremage systems, separ broken joits in drm: and lesks m supply RESPONSISLLITY i pipes Whore structural distress is evident ses advice Ti seepage observed, determine camses or sesk advice on consequences.
Page 28
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CONTACT
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Arcosgroup.com.au
OFFICES
Sunshine Coast | Brisbane | Gold Coast
Teeland Architects 09 Feb 2021
By Email Letter 01 Revision 0
Project: AG200849
[email protected]
Dear Team,
Report on Geotechnical Investigation
Proposed Residential Dwelling
20 Park Crescent, Sunshine Beach
At the request of Teeland Architects, Arcos Unit Group Pty Ltd (AG) undertook a geotechnical
investigation for the above project. The summary of the investigation is detailed in Table 1.
Table 1: Summary of Investigation Results
Site Classification in Wind Classification in Maximum Allowable
Ys (mm)
Accordance with AS2870 Accordance with AS4055 Bearing Pressure (kPa)
High Level
<20 Class S NA 100
Notes: 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.
We trust this information is satisfactory for your current needs. Should you have any questions,
please feel free to contact the undersigned.
Geotechnical Engineer Principal Geotechnical Engineer
Cody Surawski B.Eng(Civ)(Hons)/B.Env.Sc. Billy Blake B.Eng(Civ)(Hons), CPEng, RPEQ, NER, MIEAust
09 Feb 2021 Proposed Residential Dwelling
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CONTACT
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Arcosgroup.com.au
OFFICES
Sunshine Coast | Brisbane | Gold Coast
1.0 Introduction
Arcos Unit Group Pty Ltd (AG) was commissioned to undertake a geotechnical investigation
for the Proposed Residential Dwelling located at 20 Park Crescent, Sunshine Beach.
This report outlines the results of the investigation, laboratory testing, analysis and interpretive
reporting on the following items:
• All factual information resulting from the investigation (investigation methodologies,
detailed desktop review, test location plans, bore logs);
• Summary of subsurface conditions and adopted subsurface conditions including
groundwater;
• Earthworks and site preparation comments;
• Foundation soil reactivity in accordance with AS2870 (Site Classification);
• Suitable high level foundation options including allowable bearing pressures;
• Suitable deep level foundation options (if required);
This report must be kept in entirety.
2.0 Site Description & Geology
The site is described as 20 Park Crescent, Sunshine Beach totalling approximately 588 m2. The
block is steeply sloped requiring additional slope stability assessment, has good drainage, and
is irregular in shape.
Referencing available geology for the area, the site is underlain by Pleistocene aged Sand
which typically comprises Quartz sand; parabolic sand dunes. The encountered natural
materials are in agreement with the expected geology.
3.0 Fieldwork & Results
The fieldwork was undertaken on 5 February 2021 and included 1 bores drilled to to a
maximum depth of 3.5 m using a shovel and pick. The subsurface conditions were logged
through tactile and visual assessment of returned spoil by an experienced Geotechnical
Engineer.
The encountered subsurface conditions are described in detail on the attached bore logs;
however, in summary comprise natural sand.
Groundwater measurements or the lack of groundwater are made within the bore logs
attached; however, it must be noted that groundwater is transient and will fluctuate with
seasons and time.
09 Feb 2021 Proposed Residential Dwelling
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OFFICES
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4.0 Lab Testing
Laboratory testing is summarised in Table 2.
Table 2: Laboratory Testing Summary
Test
Depth (m) Material Shrink-Swell Index (%)
Location
BH1 0.0 - 0.5 Sand 1*
5.0 Geotechnical Comments
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.
5.1 Earthworks and Site Preparation
The following comments are provided in relation to site preparation for earthworks.
• The area should be stripped of uncontrolled fill, soft, overly wet, foreign, or otherwise
deemed unsuitable material (material that is potentially compressible) down to a relatively
stiff dry base ensuring no organics material is present.
• Stripped areas must be inspected by the geotechnical testing authority (GTA) to ensure no
soft spots or loose zones are present. This should be done with the use of a loaded body
truck or 12 tonne roller as a minimum. Areas showing signs of movement under the action
of the testing equipment should be either over excavated and replaced with select fill or
conditioned onsite through tyning, blending or other suitable methods.
• Although no standard exists for the moisture content of soils, it is recommended that the
site soils be placed at or near optimum moisture content (OMC) for general earthworks
operations. This increases efficiency during earthworks operations. A range of +/- 2% of
OMC is recommend for general earthworks.
• Where site soils are proposed for use as fill in other areas, won material will need to have
a maximum particle size of 75 mm or be observed to break down under the energy of
compactive equipment.
• Fill materials should be placed in relatively horizontal layers with a maximum placement
thickness of 200 mm. The materials should be compacted to a minimum dry density ratio
of 95% relative to Standard compactive effort.
• Highly plastic clays at this site will be very sensitive to the presence or lack of moisture and
therefore care should be used to place the material within the range nominated and to a
maximum dry density of 102% relative to Standard compactive effort. Where this does not
happen, the material could readily swell, soften, or be subject to significant trafficability
issues.
09 Feb 2021 Proposed Residential Dwelling
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OFFICES
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• Fill material will be subject to potential settlement post placement. Well compacted fill
placed in accordance with AS3798 and otherwise, good earthworks procedure should
typically be subject to settlement in the order of 0.5% to 1.0% of the fill thickness over a
log cycle of time.
5.2 Site Classification
The results of the investigation, previous experience, and published correlations were used to
estimate the maximum characteristic ground surface movement (ys) value in accordance with
AS 2870. A suction change value of 1.2 was adopted along with a suction zone (Hs) of 1.5 m
were used in the calculations. In addition to this, the cracking depth was nominated to be
0.5Hs.
The results of the calculations indicate that at the time of the investigation, a ys value
approximately equal to <20 mm is considered suitable.
It is important to understand that numerous things can affect and consequently increase or
decrease the ys value for a site.
The following are items that may affect the site and as a result change the site classification to
a “Class P”.
• Excessive moisture as a result of poor drainage, maintenance to drainage structures,
excessive watering of gardens;
• Placement or removal of vegetation that draws moisture from the soil surrounding the
structure;
• Additional earthworks outside the limitations set out in AS2870;
Long term maintenance is typically required for sites for maintenance. Useful information is
attached which should be read and understood by both the builder and property owner.
5.3 Foundations
It is recommended that all high level footings have perimeter, column and load bearing
footings found a minimum 0.3 m below surface levels. Where footings found into medium
dense (or stronger) sand, they may be dimensioned for a maximum allowable bearing pressure
of 100 kPa. All foundation excavations should be inspected by a suitably experienced and
qualified geotechnical engineer prior to the placement of concrete to confirm ground
conditions.
09 Feb 2021 Proposed Residential Dwelling
Page 32
51 640 311 842
CONTACT
[email protected]
Arcosgroup.com.au
OFFICES
Sunshine Coast | Brisbane | Gold Coast
6.0 Limitations
Arcos Unit Group Pty Ltd (AG) has prepared this document for 20 Park Crescent, Sunshine
Beach for Teeland Architects. The document is specific to this particular project and for the
purposes as described within the document. The document cannot be used for any other
project on the same site or other sites or relied upon by a third party. Any party relying upon
this document beyond its exclusive use and purpose as stated above, and without the express
written consent of AG, does so entirely at its own risk and without recourse to AG for any loss
or damage. AG has necessarily relied upon information provided by the client and/or their
agents.
It is important to understand that ground conditions can be spatially variable over short
distances as a result of geological processes or human interference. These changes can occur
after the time of which field work was undertaken. Given this, the assumed subsurface
conditions within this document are only indicative of the conditions at the testing locations
to the depths investigated at the time of the fieldwork.
The advice given in this document is based upon the assumed subsurface conditions. The
relevance and accuracy of advice given is directly affected by variations in ground conditions
across the site between testing locations that has not been captured and time elapsed since
investigation works.
This document must be kept in entirety, read in full and understood. Interpretations or
conclusions made by others unless supported by an expressed written statement,
interpretation, outcome or stated within this document cannot be the responsibility of AG.
This document or parts of it should not be used as part of a specification or design for a project
without prior review and agreement by AG.
__________________________________________________________________________________
We trust this information is satisfactory for your current needs. Should you have any questions,
please feel free to contact the signed authors.
09 Feb 2021 Proposed Residential Dwelling
Page 33
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Moffat Beach, QLD, 4551
OFFICES
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GEOTECH REPORT
These notes have been provided to clarify and Arcos Unit Group Pty Ltd undertakes quality assurance
enhance the reader’s understanding of the terminology checks in accordance with its’ quality system
used throughout the report, and also to identify where requirements; however, restrictions on the project
limitations exist. All investigations are undertaken outside of Arcos Unit Group Pty Ltd’s control can result
based on budgetary constraints which impart a level of in unanticipated variations, changes in policy or
uncertainty as a result of limiting the amount of interpretation of said policies by the relevant authority,
investigation undertaken. or the actions of contractors subject to commercial
pressure.
Copyright
Site Variations
This report remains the property of Arcos Unit Group
Pty Ltd at all times unless ownership is transferred in If site variations become evident at the time of
writing. It cannot be included in any documentation construction or after the release of a report, Arcos Unit
without the express written permission of Arcos Unit Group Pty Ltd requests immediately notification. This
Group Pty Ltd notification is proposed in order to assist in remediation
prior to any permanent structures or design procedures
Subsurface Report Sheets (Bores etc) are undertaken.
The provided subsurface sheets are inherently an Collaboration
interpretation undertaken by a suitably qualified and
experienced person; however, the reliability of the Arcos Unit Group Pty Ltd strongly recommends open
provided information will rely on the method of and collaborative communication about the use and
investigation. It is prudent to state that these sheets inherent interpretation of Arcos Unit Group Pty Ltd’s
only represent a very small percentage of the report. Please contact the author of the report to
subsurface conditions across a particular project. arrange for an obligation free discussion regarding the
potential benefits of having geotechnical consultants.
It reasons that given the relatively small representation
of the subsurface conditions for a project, spacial
variability between testing locations must be taken into
consideration including the orientation of strata
intersections.
The presence or lack of groundwater is usually stated
on the subsurface sheets; however, it must be noted
that the measurements undertaken onsite are typically
very inaccurate and if the presence or lack of
groundwater will have any degree of affect on the
project, additional groundwater monitoring techniques
should be employed such as groundwater monitoring
wells.
Reporting
The report has been prepared and reviewed by suitably
qualified and experienced persons. The persons draw
on previous experience, local knowledge, published
literature, and otherwise standard engineering
approaches and principals. The context of which the
report has been prepared for must 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 Arcos Unit Group
Pty Ltd must be undertaken.
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Interpretation of the
Subsurface Sheets
Very Low Strength (VLS) < 2 MPa (UCS)
The terminology included on Arcos Unit Group Pty
Low Strength (LS) 2 to 6 MPa (UCS)
Ltd’s has been evolved from AS1726:2016. Typically
Medium Strength (MS) 6 to 20 MPa (UCS)
a soil’s strength, colour, plasticity, grain size, other
High Strength (HS) 20 to 60 MPa (UCS)
inclusions, and moisture will be described. A rock’s
Very High Strength (VHS) 60 to 200 MPa (UCS)
strength, weathering, colour, grain, and other
Extremely High Strength (EHS) > 200 MPa (UCS)
inclusions are typically described.
Soil Very Low Strength (VLS) < 0.1 Is(50)
Low Strength (LS) 0.1 to 0.3 Is(50)
Soil is typically described by the components that Medium Strength (MS) 0.30 to 1.0 Is(50)
make it up by percentage or whichever has a High Strength (HS) 1.0 to 3.0 Is(50)
governing behaviour. The types and sizes Very High Strength (VHS) 3.0 to 10.0 Is(50)
reproduced from AS1726 are: Extremely High Strength (EHS) > 10.0 Is(50)
Boulder >200 mm
Cobble 63 to 200 mm The Is(50) values are based on a correlation
Gravel 2.36 to 63 mm between the unconfined compressive strength
Sand 0.075 to 2.36 mm (UCS) of 20. This value varies significantly and site
Silty 0.002 to 0.075 mm specific testing must take precedence.
Clay < 0.002 mm
Rock weathering is broken down as follows:
The strength of soil is usually assessed by suitably
experienced persons through the use of laboratory Extremely weathered Behaves as soil but rock
test results, published literature, field assessments or (EW) structure evident
a combination of the above. The strength of soil is Highly weathered Colour and strength of original
characterised into either cohesive (clays and silts) or (HW) fresh rock is not recognisable.
cohesionless (sands and gravels) as shown below: Decomposition of rock evident
Moderately Defects are heavily stained with
Cohessive Soil Strength Term weathered (MW) rock mass showing signs of
Very Soft < 12.5 kPa discolouration
Soft 12.5 to 25 kPa Slightly weathered Some staining but minimal to no
Firm 25 to 50 kPa (SW) change in strength
Stiff 50 to 100 kPa Fresh stained Minor staining evident
Very Stiff 100 to 200 kPa (FS)
Hard > 200 kPa Fresh rock No change
(FR)
Cohesionless Soils Strength Term (uncorrected Qc)
Very Loose <2 MPa Rock fracturing is broken down as follows and can
Loose 2 to 5 MPa only be accurately described where undamaged
Medium Dense 5 to 15 MPa continuous sampling has been undertaken:
Dense 15 to 25 MPa
Very Dense > 25 MPa Fragmented (Fg) Defect spacings < 20 mm
Highly Fractured (HF) Defect spacings 20 to 50 mm
Rock Fractured (Fr) Defect spacings 50 to 200 mm
Slightly Fractured (SF) Defect spacings 200 to 1000 mm
Rock is typically described by the components that Unbroken (Ub) Defect spacings > 1000 mm
make it up by percentage or whichever has a
governing behaviour. The strength of rock is typically
the most important component. Typically, the
strength of rock is based on laboratory testing, tactile
assessment and other observations as relevant. The
industry standard method for assessing the strength
of rock in the field is to use the point load strength
index (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 lower and increase the overall rock
strength. The strength of rock is broken down as
follows:
Page 35
CLIENT: Teeland Architects PROJECT #: 200849 BORE
PROJECT: Proposed Residential Dwelling
ADDRESS: 20 Park Crescent, Sunshine Beach
LOGGED: CS
1
EASTING:
DRILL RIG: NORTHING: TEST DATE: 05/02/2021
Sampling & Testing
Graphic Log
DCP Results
Material Description Results &
Type (blows per 100 mm)
Comments
Water
RL Depth
(m) (m) 5 10 15 20
SAND SW: loose, white, fine to coarse grained, moist 0
0
0
0
0
0.5 SAND SW: loose, white, fine to coarse grained, moist - Inferred
0
1
1
0
1
1
0
1
1
2
1
1
2
1
2
2
2
medium dense 3
3
4
5
5
5
5
6
7
7
3
8
8
8
8
8
3.5 Bore Terminated at 3.5 m.
4
DRILLING METHOD: Hand Auger CASING: Nil
GROUNDWATER: No groundwater observed at the time of investigation.
REMARKS:
LEGEND:
D - Disturbed Sample from Auger SPT - Standard Penetration Test - Groundwater Seepage Level
B - Bulk Sample from Auger Is50 - Point Load Result (MPa) - Standing Groundwater Level
C - Rock Core PP - Pocket Penetrometer (kPa) - Partial Groundwater Loss
U50 - Undisturbed Sample (mm) - Perched Groundwater Level
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Foundation Maintenance and Footing Performance: A Homeowner’s Guide cairo BIF 18 replaces Information Sheet 10/91 Bulidings can and often do move. This movement can be up, down, lateral or rotational. The fundamental cause of movement in bullcings can usually be related to one or more problems in the foundation soil. & is important for the homeowner 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 agains buliding movement. This Building Technology File is Gesigned to Identify causes of soll-related buliding movement, and to suqgest methods of prevention of resultant cracking in bulldings- ‘The rypes of setts usually presepr under the topsoil in land zoned for residential bulidings can be split Into reo approximate groupa — granidar and clay, Quite often, foundation soit ts a mlsnure of borh types. The general protilems associated with solls having gransilar contenr are usually caused by erosion Clay sotls are qubject ta saturation and swedll/shrink probleme. Classifications for a given area can generally be obrained by application te the local authortry, bur these are sometimes unreliable and If there Is dowhr, a geotechnical report should be commissioned. As mar buildings suffering movement problems are founded on chy sols, there & 2n emphasis om classification of snills according te the arnount of swell and shrinkage they experience whh warlations of water content. The table below ts Table 2.1 from AS 2870, the Residerriat Sab and Footing Code. Sertlement due to coustruction There are two types of sertiemenr that occur as a nepulr of construction. * lenmediore settiement occur when a bulding & first placed on its foundation soll, 23 a result of compaction of the soll uncer the weight of the sructure, The cohesive qualiry of clay sou miriganes agatast this, bur granular (particulary sandy) sall ts suxscepribhe. * Consotidation semiement Isa fearure of clay soll and may rake Pilace becaime of the expulsion of motmare fron the soll or because of the soil's lack of resterance to bocal compressive or shear stresses. This will usually take place during the firs few months after construction, but har been known to take macy years in exceptional cases. These problems are the province of the bullder and should be taken Eraston All solls are prone to erosion, but sindy soll Gs particularly suscepethle tm belng washed away. Even clay with a sand component of say 109 of more can suffer from erosion, Samuration ‘This ts particularly a problem tn clay sotls. Seruration creates a bog- Dike suspension of the soll thar causes ir to inae virmually afl of ts heartng capacity. To a lesser degree, sand 1s affected by saruration because saturated sand may undergo a reduction in volume particularly Imported sand fill for bedding and blinding Layers. However, this usually occurs as immediate seriement and should formally be the prowince of the tutlder. ‘Seasonal swelling and shrinkage of soli All clays react to the presence of water by sowty absorbing ir, making the soll Increase In volurne (see rable below). ‘The degree of increase varies considerably hetwnen different cays, 25 dines the degree af decrease during the swhsequent drying out caused by fair weather periods. Because of the low absorpeion and expulsion rate. this Phenomenon will not asually he norkeable unless there are prolonged rainy or dry periods, usually of weeks or months, depending on the land and sol) charactertsrics. ‘The swelling of s08 creates an upward force on the footings of the building, and shrinkage creates subgidence that taker away the support needed by the footing ro retain equilibrium. Shear fathare Tht phenomenon occurs when the foundation soll dors not have sufficient strength to suppor the weight of the fooring. There are Two Major pest-corsvruction causes + Significart load increase. * Reduction of lateral support of rhe soll under the fpoting due to don. Buacheg Tacrctngy Fae d 181 dese oa ee . Senses bar vee Rebate inset a saturation of the soll problems adjacene to or under the footing. GENERAL DEFINITIONS OF SITE CLASSES Class Foundation A Most sand and rock sites with little or no ground movement tram matsture changes s Rightly reactive clay sites with only slight ground movement from moisture changes M Moderately reactive clay or stk sites, which can experience moderae ground movement from maisture changes H Highly reactive clay sites, which can experience high ground movement from mokture changes E Extremely reactive sites, which can experionce extreme ground movement from moisture changes AwP Pied sires » || ecbibaetion as mere o Gear ee eceerr cree we
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Tree root growth Trees and shrubs that are allowed te grow in the vicinity of footings can cause foundation soil movement in two ways: © Roots that prow under footings may increase in cross-sectional size, exerting upward pressure on footings. * Roots in the vicinity of footings will absorb mach of the moisture in the foundation soil, causing shrinkage or subsidence. Unevenness of Movement The types of ground movernent 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 comstruction_ © Differing moisture content of foundation soil prior to construction. Movement due to non-constraction causes is usually more uneven still Erosion can undermine a footing that traverses the flow or can create the conditions for shear Gilure by eroding soil adjacent to 2 footing that rans in the same direction as the flow. Saturation of clay foundation soil may occur where subfloor walls create adam thar makes water pond. ft can also ocour wherever there isa source af 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 af the building first, then gradually spreads eo the interior. The swelling process will usually begin at the uphill extreme of the building, or on the weather side where the land is flat. Swelling gradually reaches the interior soil as absorption continues. Shrinkage usually begins where the sun's heat is greatest_ Effects of Uneven Soll 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 pap or cantilevering until the bricks or the mortar bedding fail. Older masonry has little resistance. Evidence of failure varies according tw circumstances and symptoms may include © Step cracking im the mortar beds in the body of the wall ar 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). Lsolated piers affected by erosion or saturation of foundations will eventually lose contact with the bearers they support and may tilt or fall ower. The floors that have los this support will become bouncy, sometimes rattling omaments etc Seasonal swelling/shrinkage in day Swelling foundation soil due te 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 footprin w 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 symptoxns 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 Mooring. 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 af lowering the external footings. The doming is accentuated and cracking reduces or disappears where it ocaurred because of dishing, but other cracks open up. The roof lines may become convex. Daring and dishing az 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 i 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 sirub roots will rend 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 — ie. 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 sympeoms 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. Ir will atrempt mm 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 che original cause has been remedied, or until the subsidence has completely neutralised the affected portion of footing and the structure has stabilised on ceher 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 mvt 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 w 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 chat the cracking will become wider until the sections of brickwork became virtually independent. With repeated cydes, once the cracking is eszablished, if there is no other complication, it is normal for the incidence of cracking stabilise, as the building has the articulation it needs to cope with the problem. This is by no means always the case, however, and monigoring of cracks in walls and floors should always be treated seriously. Upheaval caused by growth of tree roots under foceings is not a simple vertical shear stress. There is a tendency for the mot to also exert lateral forces that attempt to separate sections of brickwork after initial cracking has occurred.
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The normal structural arrangement is that the inner leaf of
brickwork in 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 thar 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 amy case, externally visible cracking
is important as a puide 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 2 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 ar all of the above
symptoms for a considerable period. The same warning period should
apply in the case of upheaval. [t 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 w 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 2 minuscule leak can be enough to
saturate 2 clay foundation. A leaking tap near a building can have the
same effect. In acktition, 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
foots 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 moof guttering may result in overflows, as may
gutters blocked with leaves ete
* 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 thar 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 & a cosmetic
nuisance only and can be kept in repair ot even ignored. The table
below is 2 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 /Cure
Plumbing
Where building movement is caused by water service, roof
plumbing, sewer or stormwater failure, the remedy is te 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 che building
vicinity. Even where pully 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 resulr 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 crench can easily affect the
foundation's ability to support footings or even gain entry to the
subfloor area.
Ground
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 of prolonged rain. If necessary, a grated drain system
connected to the stormwater collection system is usually an easy
solution.
{t 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 is referred to in BTF 19 and
may properly be regarded as an area for an expert consultant.
Protection of the building perimeter
[eis essential so 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 mast 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 ould
CLASSIFICATION OF DAMAGE WITH REFERENCE TO WALLS
Approximate crack width Damage
Description of typical damage and required repair limit (see Note 3) category
Hairline cracks <0.1 mm o
Fine cracks which do not need repair <l mm 1
(Cracks noticeable but easily filled. Doors and windows stick slightly. Simm 2
(Cracks can be repaired and possibly a small ammount of wall will need to be 5-15 mm (or a number of cracks 3
replaced. Doors and windows stick. Service pipes can fracture. Weathertightness 3 mm or more in one group)
often impaired.
Extensive repair work involving breaking-out and replacing sections af walls, 15—25 mm bur also depends on 4
especially over doors and windows. Window and door frames distort. Walls bean number af cracks
or bulge noticeably, some loss of bearing in beams. Service pipes disrupted.
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exend ourwards a minimum of 900 mum (more in highly reactive soil) and should have a minimum fal! away from the building of 1:60. The finished poving should be no les than 100 mm below brick vent bases. Tcis prudent ro relocate drainage pipes away from this paving, If possible, to. avold complications from future leakage If this is nor practical, earthenware pipes should be rephiced by PVC and backfilling should be of the same soil rype as the surrounding soil and compacted to che same density. Except in areas where freezing of water is an lasie, it is wise to remove taps in the buikting area and relocate chem well away frou the building — preferably noc uphill from ic (see BTF 19). Tr may he desirable to install a grated drain at the curside edge of the paving on the uphill side of the building. Ifsubsoll drainage ix 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 subfloorand significantly slows the process of drying our. Installation of an adequare subfloor ventilarion spscem, either ratural or mechanical, is desirable. Warning: Alchough this Building Technology File deals with cracking in buildings, it should be mid thar subfloor moisture can resulc in the development of other problems, notably: * Wacer char is eansmiteed into masonry, metal or timber building elements causes damage and/or decay two those elements. * High subfloor humidiry and moisture content create an ideal environment for various pests, including termites and spiders. * Where high moisture levels are transmitted vo the flooring and walls, an increase in the dust mine count can ensue within the living areas. Dust mites, as well as dampness in general, can be a health hazard tw inhabitants, particularly those who are abnormally aasceprtible to respimarory ailmenn: The garden The ideal vegetation layour is co have lawn ot plants thar require only Hight watering immedianely adjacene to the drainage ot paving edge, then moce demanding planes, shrubs and tsees spread our in thar order. Overwatering due to misuse of auvomaric watering symems iso common canse of sarusarion and water migzarion under footings. IF ic is necessaty to use these systems, it is important wm remove garden beds to a completely safe distance from buildings. Existing trees Where a tee is canting a problem of soil drying or there is the existence or threat of upheaval of footings, if the offending mow are subsidiary and their removal will noe significantly damage the tree, they should be severed and a concrete or metal harrier placed vertically in the sail to prevent fucure root growth in the direction of the building, If it is not poesible to remove the relevant mots withour damage to the tree, an application to remove the tee should be made wo the local authority, A prudent plan is w cransplanc likely offenders before they become a problem. Information on trees, plants and shrubs regarding root pacterns, volume of water needed and safe distance from buildings of most species. Boranic gardens ace also sources of information. For information on plant wow and drains, see Building Technology Pile 17. Excavation Excavation around footings must be properly engineered. Soil supporting foorings can only be safely excavared aran angle thar allows the soil under the footing to remain stable This angle Is called the angle of repose (or Friction) and yaries between soil types and condiriens Removal of sail within the angle of repose will canse subsidence. Where erosion has occurred that has washed away soil adjacent to feoriugs, soll of the same classification should be imroduced and ene ‘Where foorings have been undermined, augmentation or other specialist work may be required. Remediarion of footings and foundations is generally the realm of a specialie consulrant. Where isolated foorings rise and fall becanse of swell/shrink effect, the homeowner may be tempered to alleviate Floor bounce by filling the gup thar has appeared between the bearer and the pier with blocking. The danger hese is thar when the next swell segment of che cycle occurs, the extra blocking will push the floor up ino an. accentuated dome and may also cause local shear failure in the soil. If ir is necessary to use blocking, It should be by a pair of Fine wedges and monitoring should be carried our fortnightly, This BTF was prepared by John Lewer FAIR, MIAMA, Partner, Construction Diagnosis. ‘Tho Infermetion in this and other Issues in the series was denved from various scuross and was Dateved to be correct when published. The Information ts advisory. His provided In good falth and not claired to be an exhaustive treatment of the relevant subject, Further professional advice needs to be obtained before tahing any action based on the information provided. ‘Dishibutod by CSIRO PUBLISHING PO Bex 1139, Collingwood 3066, Australia Tal (03) 9542 7666 Fax [03] 96627555 wer w.publish.csiro.au Email: [email protected] © CSIRO 2008. Unauthorived copying of this Bullding Technology File is prohibited