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Attachment B - Geotechnical Analysis
51 640 311 842
CONTACT
[email protected]
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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Page 2
51 640 311 842
CONTACT
[email protected]
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
Page 3
51 640 311 842
CONTACT
[email protected]
Arcosgroup.com.au
OFFICES
Sunshine Coast | Brisbane | Gold Coast
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
Page 4
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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 5
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 6
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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.
Page 7
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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 8
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
Page 9
Foundation Maintenance and Footing Performance: A Homeowner’s Guide casino err is replaces Information Sheet 10/91 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. & 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 building movement. This Building Technology File is designed to identify causes of soil-related building movement, and to suggest methods of prevention of resultant cracking in buildings. The types of solls asually present under the topsoil In land zoned for residential buildings can be split Into two approximate groups ~ granular and clay. Quite often, foundation soll Is 2 mixture of both types. The general problems associated with solls having granular content are usually caused by eroston Clay sols are subject to saturation and swell/shrink problems Classifications for 2 given area can generally be obtained by application to the local authority, bur these are sometimes unreflable and if there Is dowhrt, a geotechnical report should be commissioned. As most bulldings suffering movement problems are founded on clay solls, there & an emphasis on classification of soils according to the aenqunt of swell and shrinkage they experience with variations of water content. The table below ts Table 2.1 fram AS 2870, the Residential Stab and Footing Code. Settlement due to construction ‘There are two types of settlement that occur as a result of construction. © Immediate settiement occurs when a building & first placed on Its foundation soll, 23 a result of compaction of the soll under the weight of the structure, The cohesive quality of clay soll mitigates against this, but granular (particularly sandy) soll ts susceptible. * Consolidation setriement sa fearure of clay soll and may take Place because of the expulsion of motsture from the soll or because of the soll's lack of resistance to local compmressive or shear stresies. This will usually take place during the first few months after construction, but has been known to take mary years in exceptional cases. ‘These problems are the province of the butider and should be taken Eraston All sols are prone to erosion, bur sandy sotl ts particularly suscepethle to being washed away. Even clay with 2 sand component of say 10% of more can suffer from erosion, Saturation ‘This & particularly a problem In clay sols. Saturation creates a bog- Nike suspension of the soll that causes if to lose virmuaily af] of ts bearing capactty. To a lesser degree, sand ts 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 norenally be the prowince of the builder. Seasonal swelling and shrinkage of soll All days react to the presence af water by slowly absorbing tr, making the soll Increase In volume (see table below). 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 norkceable unless there are Prolonged rainy or dry periods, usually of weeks or months, depending on the land and soll characteristics. ‘The swelling of sol creates an upward force on the footings of the bullding. and shrinkage creares subsidence that takes away the support needed by the footing to retain equilibrium. Shear failure ‘Tht phenomenon occurs when the foundation soll does not have sufficient strength to support the weight of the footing. There are two major post-comstruction causes: * Significant load increase. * Reduction of lateral support of the soll under the footing due to ce CE cg a aor la a problems. adjacent to or under the footing. GENERAL DEFINITIONS OF SITE CLASSES Class Foundation A Mast sand and rock sites with little or no ground movement fram matsture changes 5 Slightly reactive clay sites with only slight ground movement from malisture changes M Moderately reactive clay or sii sites, which can experience moderate ground movement from matsture changes H Highly reactive clay sites, which can experience high ground movement from molsture changes E Extremely reactive sites, which can experience extreme ground movement from matsture changes AwP Filted sites > || ee eee ae ee nee
Page 10
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 prow under footings may increase in cross-sectional size, exerting upward pressure on footings. * 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 prior to 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 rans in the same direction as the flow. Saturation of clay foundation soil may occur where subfloor walls create adam that makes water pond. [t 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 af the building first, then gradually spreads to 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 tm 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 ormaments etc. Seasonal swelling/shrinkage in day 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 sapported 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 chanpes and the soil bepins 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 ocourred because of dishing, but other cracks open up. The roof lines may become convex. Dorning 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 noe 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 segrnent 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 mot to also exert lateral forces that attempt to separate sections of brickwork after initial cracking has occurred.
Page 11
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 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 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 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 ome 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 sail: © 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 of even ignored. The table 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 /Cure Plumbing Where building movernent 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 of 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 ran 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 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. Ie 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 BT F 19 and may properly be regarded as an area for an expert consultant. Protection of the building perimeter Ie 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 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 (Cracks noticeable but easily filled. Doors and windows stick slightly. <Smm 2 (Cracks can be repaired and possibly a small amount 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 of walls, 15-25 mm but also depends on 4 especially over doors and windows. Window and door frames distort. Walls lean number of cracks or bulge noticeably, some loss of bearing in beams. Service pipes disrupted.
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extend ourwards 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 furure leakage. If this is not practical, earthenware pipes should be rephced by PVC and Pilling chnald beef te soos eal pve cathe marooasdng 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 noe uphill from it (see BTF 19). Tt 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 Warning: Although this Building Technology File deals with cracking in buildings, it should be said thar subfloor moisture can result in the development of other problems, notably: © Water that is transmiteed 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. © 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 oc plants that require only light watering immediately adjacere to the drainage or paving edge, then moce demanding plants, shrubs and trees spread our in thar order. Overwatering due to misuse of automatic watering systems isa common cause of saturation and water migration under footings. If ir 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 mots are they should be severed and a concrete or metal barrier placed vertically in the soil to prevent furure 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 teee 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. For information on plant roots and drains, see Building Technology Pile 17. Excavation Excavation around footings must be properly engineered. Soil supporting fooeings 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 pose (or fiction) and varies between soil types and conditions. Removal of sail within the angle of repose will cause subsidence. 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 specialise consultant. Where isolated footings rise and fall because of swell/shrink effect, the homeowner may be tempeed to alleviate floor bounce by filling the gap thar 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 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 FAIB, MIAMA, Partner, Construction Diagnosis. ‘The Information In this and other Issues in the series was derived from various sources and was belleved to be correct when published. ‘The Information ts advisory. Its provided In good falth and not claimed to be an exhaustive treatment of the relevant subject. Further profossional advice needs to be obtained before taking any action based on the Informatkn promded. Disinbutod by CSIRO PUBLISHING PO Box 1139, Collingwood 3066, Australia Tal (03) 9662 7666 Fax [03] 96627555 wew.publish.csira.au Email: publishing [email protected] © CSIRO 2003. Unauthorised copying of this Bullding Technology File ts prohibited