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Attachment B - Soil test report
SOIL TEST REPORT
Address : Lot 9 P9313
32 Plover Street
Location
Client : Ros & Graham Broadhurst
Date : 14 December 2020
Report No : 200365(S)
Phone: 07 5447 1304
Email: [email protected]
Address: PO Box 1661, Noosa Heads, Qld. 4567
Australian Soil Investigations Pty Ltd
ABN: 11147854439
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Page 2
1.0 INTRODUCTION:
Australian Soil Investigations has performed a limited site investigation and established a site classification in
accordance with AS 2870-2011 at the above address. This site classification report does not include an assessment
of Slope Stability or Landslide Risk.
This report must be read and considered as a whole. All of our recommendations and appendices
attached must be read, considered and followed by all people involved in this project including
the client to ensure adequate long term performance of a footing system constructed on this site.
If you are unsure of any of the requirements herein, you must seek clarification from this office.
2.0 SITE CLASSIFICATION:
After considering the results of our field investigation performed on 11/12/2020 we have classified this site as:
Class P
The classification has been calculated from test work performed on the soil profile encountered on the day of our
fieldwork and consideration of AS2870-2011. Any disturbance of the soil profile may result in a change to the
classification.
The ‘P’ classification relates to the loose sands, poor bearing capacity and abnormal moisture conditions encountered
during our testing on site. Please refer to our definitions list appended to this report for further descriptions of these
characteristics.
The abnormal moisture conditions are due to the presence and proximity of trees to the allotment and existing trees
located on the proposed construction area that will be removed.
With respect to potential surface movements through seasonal moisture variations, the site could be considered
equivalent to a class M site.
Site Classification: The site classification is calculated in accordance with the “AS2870-2011 Residential Slabs and
Footings-Construction” and relates to the estimation of Ys, “The characteristic surface movement” within reactive soil
profiles. The limits used for this classification are as follows:
Predicted Surface Movement Classification
Ys = <=20mm S Slight
Ys = >20 – 40mm M Moderate
Ys = >40 – 60mm H1 High-1
Ys = 60 – 75mm H2 High-2
Ys = > 75mm E Extreme
Problem sites P Problem
3.0 SITE DESCRIPTION:
The construction area has a gradient in the order of 5-6%.
Vegetation on the construction area (and nearby surrounds) consists of grasses and dense trees.
The trees are located on and adjacent the proposed construction site.
The trees are of a height and proximity that could affect the moisture conditions within the proposed construction site.
Refer to the appendices to the rear of this report for guidance on Trees and Construction.
The existing surface drainage is good and sub-surface drainage is good.
4.0 FINDINGS:
The soil profiles encountered are shown on the attached borelog sections.
Australian Soil Investigations 1 ASI Ref: 200365(S)
Page 3
The sandy soils encountered are susceptible to collapse when unconfined. This may effect excavations and result
in additional earthworks and increased concrete volumes. Temporary shoring or Forma-Tube may be required to
retain the sands prior to concreting.
The samples classified on-site were assessed as having negligible plasticity, therefore laboratory testing was
considered unnecessary.
We have calculated the following Ys value for the soil profile:
Ys = 20-30 mm
The following foundation material will provide a safe bearing capacity (100 kPa) for buildings within the scope of AS
2870-2011.
FOUNDATION MATERIAL - NATURAL MEDIUM DENSE SILTY SAND
We strongly recommend that any footing design for this allotment be carried out by a suitably qualified
person in accordance with AS2870-2011.
Where site drainage and landscaping does not conform to the specifications of AS 2870-2011 and CSIRO
Information Service Sheet BTF-18 (2003) damage to the building can be expected. A single copy of this
document is issued with the original issue of this report. Please consult your builder or contact this office
to obtain a copy.
NOTE: The information contained herein has been compiled following our field and laboratory testing,
accepted engineering theory and discussions with and information supplied by our client, whom is
noted on the header page of this report. We offer no warranty for the use of this report by other
parties without prior written consent from this office.
The report must be read in conjunction with the attached appendices. If you do not have a copy of
these please contact our office and a copy can be issued to you.
WADE HOLMES – QBCC 1120066
for and on behalf of:
AUSTRALIAN SOIL INVESTIGATIONS – QBCC 15072110
Australian Soil Investigations 2 ASI Ref: 200365(S)
Page 4
APPENDICES
A. DEFINITIONS
B. LIMITATIONS
C. RECOMMENDATIONS
C.1 - Builders
C.2 - Owners
C.3 - Builder/Owner - Trees
D. DETAIL SHEETS
D.1 - Plumbing Requirements Class M, H1, H2 & E Sites
D.2 - Site Drainage recommendations
E. SITE PLAN
F. BORELOGS
Page 5
A. DEFINITIONS
Safe Bearing capacity: The soil nominated in this report as a suitable foundation material has an allowable bearing capacity of 100KPa
and is considered safe for the construction of a dwelling that is in accordance with AS2870-2011.
Cohesive Soils: Clays and silt soils that have inherent cohesive (binding) strength.
Granular Soils: Gravels and sand soils that have no cohesive strength. Individual particles can flow under certain conditions.
Controlled Fill: Manually placed soil which has been placed and compacted to achieve sufficient bearing capacity to support a structure
according to AS 2870-2011. Fill certified at Level 1 according to AS 3798 and 95% Relative Field Density is considered controlled fill.
Partially Controlled: Manually placed soil which appears to have been compacted under controlled conditions but, at the time of preparing
this report, no compaction certificate suitable for compliance to Level 1 of AS 3798-2007 had been presented.
Uncontrolled Fill: Manually placed soil (overlying the natural soils) which is not adequate to support a normally loaded footing or floor slab
or structural load.
Unexcavatable Rock: Strong material that does not soften in water or collapse under the combination of loading and wetting. Material that
cannot readily be excavated by a backhoe.
Excavatable Rock: A rock-like material including shaly material and strongly cemented sand or gravel which does not shrink or swell with
changes in soil moisture, but is readily excavatable with a conventional backhoe.
Load Bearing Wall: In our design work a load bearing wall is defined as any wall imposing on the footing a service load greater than
10kN/m. A load bearing wall will normally be supported by a slab thickening or footing in our slab designs.
Natural (Strata): Refers to soil that is neither fill or imported material but one that is in its original undisturbed state and position.
Gravel: Coarse particles, larger than sand size, but less than 60mm in diameter.
Cobbles: Rocks greater than 60mm in diameter but less than 600mm in diameter.
Boulders: Rocks larger than 600mm in diameter.
SOIL STRENGTH INDICATIONS
NON-COHESIVE (GRANULAR) SOILS COHESIVE SOILS
Loose A 12mm rod/bar can be easily pushed in by hand Soft Can be moulded by light finger pressure.
Medium A 12 mm rod/bar can be pushed in 300mm with Firm Can be moulded by strong finger pressure.
Dense difficulty
Dense A 12mm rode cannot be pushed in by hand. Stiff Cannot be moulded by fingers. Can be indented by
thumb with pressure.
Very Stiff Can be indented only by thumb nail.
N.B. These indications should be used for guidance only. These indications can vary greatly under Abnormal Moisture Conditions.
Please contact Australian Soil Investigations for on-site clarification of soil strengths.
B. LIMITATIONS
AS2870-2011: This report has been completed in accordance with AS2870-2011 the Australian Standard for “Residential Slabs and
Footings” design and construction. The standard provides performance based criteria for its design recommendations. This criteria is not
based upon crack or movement free performance. The code states “It is acknowledged that minor foundation movements occur on nearly
all sites and that it is impracticable to design a footing system that will protect the building from movement under all circumstances”. The
code provides guidance on the assessment of crack sizes in walls and floors and suggests acceptable limits. Should the potential owner
not be satisfied with this criteria we should be notified such that any recommendations can be amended to suit their requirements.
However, it should be noted this could dramatically increase the construction costs.
Field Testing: Our investigation and the results and recommendations contained herein have been compiled following careful
consideration of our clients supplied information and instructions. Any variation to this information may render this report incorrect.
Furthermore this report must not be used by any person other than our client noted at the head of the report.
Client Supplied Information: In writing this report we have considered all the information supplied to us by the client. Should the client or
his agent have omitted to supply us with relevant information our report may be irrelevant and / or inappropriate. We do not accept
responsibility for the consequences in such cases.
Borelogs: The soil profiles reported in our Borelogs Section represent the soil conditions at our test sites and have been located were we
believe best represents the soils within the proposed building envelope. However soil conditions can change dramatically over short
distances, therefore such point type exploration programs may not locate all variations. If site preparations/excavations reveal soil
conditions that are different from those shown in our Borelogs we must be notified immediately. Changes to the site classification and/or
footing design may be necessary.
Site Information: The site information shown on the attached plans such as surface grades and levels are estimations taken during our
field testing and are provided for a rough guide. They must not be used for any design purposes. Site plan dimensions are as measured
from the noted visible site feature during our field testing.
Previous/Future Excavations: The recommendations contained in this report have not considered the effects of any previous, current or
future excavations, mines or slope instability problems that are not highlighted in the clients supplied information or, that was not clearly
visible during our field testing. If such features exist we must be advised so that our design can be adjusted to accommodate them.
Australian Soil Investigations Appendix Page 2 of 6 Appendices.1
Page 6
Trees: Trees can have a considerable influence over the over the performance of a structures foundation, in particular those founded on
reactive soils (Class S, M, H & E). The trees demand for moisture will change the moisture characteristics of the surrounding soils leading
to localised shrinking and swelling which can exceed the expected soil movement. This can include trees that have been removed prior to
construction. During our Field-testing we have considered trees that existed on or adjacent the site and allowed for them in our
recommendations. We are unable to assess for the potential effects of trees planted after our testing, reference should be made to
“Recommendations for Builders/Owners-Trees” in Appendix D that follows.
Moisture Conditions: The moisture conditions noted within this report are as recorded at the time of our field testing and have been
included in our assessment of the site. Changes to site drainage, the planting of trees or a rising water table can lead to increased levels of
moisture within the soils leading to either an increased classification or design requirements. We must be notified of any increase in
moisture conditions. Also refer to “Recommendations for Builders/Owners – Site Drainage in Appendix D that follows.
Aggressive/Contaminated Soils: This report does not consider the presence of contaminants or sulphates within the tested soils as this is
beyond the scope of this report and our expertise. Engagement of a specialist consultant is advised if this form of assessment is required.
Landslip: This report does not address slope stability issues. A specialist report must be obtained to assess such hazards.
Shrinkage Cracking: Shrinkage cracking of concrete occurs as the initial moisture in the concrete evaporates from mix causing
shrinkage to occur. The cracking as a result of this shrinkage is not a sign of structural failure and is to be expected in most concrete
elements poured on-site. AS2870-2011 states “Shrinkage cracking can be expected in concrete floors”.
C RECOMMENDATIONS
C.1 Recommendations for Builders and Foundation Designers
Codes of Practice: All construction work associated with this report must be undertaken in accordance with the BCA “part 3.1 – Site
Preparation” and “part 3.2 – Footings & Slabs” and AS2870-2011 “Residential Slabs and Footings”.
Underground Services/Plumbing: Where structures are built over filled, soft or loose soils, services will need to be supported so that
potential movement within the soils does not cause them damage or cause incorrect alignment which could cause leakage. Such measures
can include but are not limited to the provision of expansion joints, sleeved or foam lagged pipe penetrations throughout the structure or
treatment of the soils prior to construction. The attached illustrations detail minimum requirements.
Arrange plumbing fixtures so that the slab and beam penetrations are kept to a minimum and where necessary sleeved to allow for
movement with 40mm thick closed cell polythene or similar material. Where the penetration is within 150mm of the base of a beam or
footing, the depth of this footing element should be deepened by approximately twice the diameter of the penetration. All plumbing and
drainage must comply with the requirements of the National Plumbing and Drainage Code AS3500.
For Class H & E sites, AS2870 - 2011 requires that plumbing pipes servicing dwellings in class H & E sites be fitted with sleeved expansion
joints, rotational swivel joints and foam lagged penetrations.
Refer to the attached detail sheet “Plumbing Requirements Class M, H and E sites.
Site Drainage - Class A Sites: The ground surrounding the dwelling and the building site must be graded and drained so that stormwater
is shed away from the house area in all directions during and after construction. Particular attention should be given to all drainage so
stormwater is not introduced to the foundation soils leading to potential scour. Roof water must be diverted away from the building prior to
and after the roof is installed. Correct drainage is an essential part of our recommendations. If the site is not prepared correctly, excessive
foundation movements may occur leading to damage within the supported structure.
Site Drainage - Class S, M, H & E Sites: The ground surrounding the dwelling and the building site must be graded and drained so that
stormwater is shed away from the house area in all directions, during and after construction. A minimum grade of 1 : 20 (vertical :
horizontal) for 1.5m must be provided. Hard landscaping such as terrace slabs adjacent the dwelling can assist in this. Roof water must be
diverted away from the building site prior to and after the roof is installed. Where building delays occur, temporary downpipes may be
necessary. Constant maintenance of roof drainage is essential. If a rainwater tank (or similar) is to be sited within 6 meters of a structural
footing, we should be consulted for further advice. External water taps, air conditioner overflows, tank and hot water cylinder overflows
should be over grated pits connected to the drainage system. The ground surrounding the building must be graded and drained so water is
shed away from the house in all directions.
Particular care should be taken with drainage, plumbing and electrical trenches so that they do not introduce moisture into the soils
supporting the foundations or destabilise the footings by undermining them. The base of any trenches under the floor or within 1.5 meters of
the building should be sloped away from the house and should be backfilled with compacted clay plug.
Correct drainage is an essential part of our recommendations and is documented in the CSIRO handout BTF-18 attached to the clients copy
of this report. (Additional copies available upon request.) If the site is not prepared correctly, excessive soil moisture may occur in some
areas, which can lead to excessive foundation movements possibly damaging the supported structure.
Silt Retention: The builder is responsible for ensuring appropriate silt retention measures are in placed and maintained throughout
construction.
Site Classification: The site classification is calculated in accordance with the “AS2870-2011 - Residential Slabs and Footings-
Construction” and relates to the estimation of Ys, “The characteristic surface movement” within reactive soil profiles. The limits used for this
classification are as follows:
Predicted Surface Movement Classification
Ys = <=20mm S Slight
Ys = >20 – 40mm M Moderate
Ys = >40 – 60mm H1 High-1
Ys = 60 – 75mm H2 High-2
Ys = > 75mm E Extreme
Problem sites P Problem
Australian Soil Investigations Appendix Page 3 of 6 Appendices.1
Page 7
C.2 Recommendations for Owners
Foundation Maintenance and Owners Responsibilities: The soils surrounding and under the foundations must be protected from scour
or washout from stormwater by ensuring adequate drainage as noted above.
Localised concentrations of moisture such as overflows from hot water cylinders or air conditioners can lead to excessive localised
foundation movements and must also be adequately drained away from the foundations as noted above.
In all types of soil conditions, if an automatic watering system irrigates within 2.5 meters of a foundations, instability problems and excessive
foundation movements are likely to occur. Also site drainage as discussed above must be maintained.
Ongoing foundation maintenance is documented in the CSIRO handout BTF-18, attached to the client’s copy of this report. (Additional
copies available upon request.)
Refer to the attached detail sheet “General Requirements for Site Drainage”
Additional Requirements - Class A & S Sites: Trees and dense shrubs must be kept well away from the building foundations. Refer to
the following section “Recommendations – Builders/Owners – Trees”. In all types of soil conditions, if an automatic watering system irrigates
within 2.5 meters of a footing, instability problems may occur. Water should not be allowed to pond on the ground near the building.
Finished surface grades around the building should also ensure scour of soils cannot occur. Additional field gullies and drainage might be
required. In all instances the ground should be sloped away from the foundations at a grade of no less than 1 in 20 (vertical to horizontal)
for at least 1.5m.
Additional Requirements - Class M, H & E Sites: Trees and dense shrubs must be kept well away from the building foundations. Refer
to the following section “Recommendations – Builders/Owners – Trees”.
The soil near the building should be protected against the increased moisture that occurs in gardens or permeable landscaping built
adjacent the foundations. Automatic irrigation systems must not be used adjacent structural foundations. If required, these forms of
landscaping must be constructed over impermeable membranes that drain the excessive moisture away from the foundations into correctly
installed field gullies and drains.
We strongly recommend the construction of hard landscaped paths or terrace slabs adjacent building foundations for at least a distance of
1.5m to protect the foundations from excessive moisture.
C.3 Recommendations – Builders/Owners - Trees
Trees and landscaped gardens can have a dramatic influence over the moisture content of the soils they are grown in. This can lead to
increased soil movement through shrinking and swelling. Where these trees or gardens are within close proximity of structural foundations
the soil movements can affect the structural integrity of the foundations.
For Class M, H and E sites the following recommendations for the minimum distance between trees and footings should be followed:-
Site Class Offset to Tree
Class M : 0.75 x h
Class H : 1.0 x h
Class E : 1.5 x h
Where ‘h’ is the mature height of the tree, further refinement of this recommendation can be pursued where tree species can be considered.
Where a row or group of trees exists the above recommendation should be doubled.
In some instances the installation of root barriers can lessen the effect of trees on foundation performance. Please contact Australian Soil
Investigations for options.
The following table provides some guidance on mature tree heights:-
APPROXIMATE TREE HEIGHTS
10 to 20m Height – Acacias, Ash, Athel Tree, Candlebark, Manna Gum, Pepper Tree, Willows, Yate, Yellow Gum
20 to 30m Height – But-But, Cedars, English Oak, Lemon Gum, Palms, Planes, Sheoaks, Silky Oak, Spotted Gum, Casuarina
30 to 60m Height – Blue Gum, Cypress, English Elm, Figs, Karri, Pines, River Gum, Sugar Gum
The removal of trees from the proposed construction can also greatly affect the moisture conditions of the soil. We recommend allowing the
soil time to reach moisture equilibrium prior to construction commencing. Please contact our office for further guidance on this matter.
D DETAIL SHEETS
D.1 Plumbing Requirements Class P, H1, H2 & E Sites
Australian Soil Investigations Appendix Page 4 of 6 Appendices.1
Page 8
D.2 Site Drainage recommendations Australian Soil Investigations Appendix Page 5 of 6 Appendices.1
Page 9
Australian Soil Investigations Appendix Page 6 of 6 Appendices.1
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Guidelines for Site Drainage
1. The site must be prepared prior to construction works that enables the site to drain
throughout construction and not allow flooding of foundation works, temporary pumping
systems could be required existing drainage paths are trapped. Temporary down pipes must
be installed following roof construction and drained away from the construction area.
Drainage trenches should be clay capped to stop moisture entering foundations.
2. Upon completion the ground surrounding the dwelling should be graded away from the
dwelling as indicated. Paving and terrace slabs adjacent the dwelling improve this drainage.
Perimeter drainage should be provided around the dwelling as indicated and must be
drained to agproved drainage facilities downslope from the dwelling,
3, Rear of wall drainage beyond constructed retaining walls must be drained to approved
Orainage facilities downslope from the dwelling. These drains should be provided with flush
out facilities at the upstream end of the drainage line and regularly maintained
RETAINING WALL
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SITE DRAINAGE RECOMENDATIONS ALL SITES
‘CUT-OFF DRAIN ALONG
HIGH SIDE OF RETAINING
Australian Soil Investigations Appendix Page 6 of 6
Appendices.1
Page 10
Foundation Maintenance
and Footing Performance:
A Homeowner's Guide
2
BIF 18
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. It 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 against 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.
' Soil Types
The types of soils usually present under the topsoil in land zoned for
residential buildings can be split into two approximate groups ~
granular and clay. Quite often, foundation soil is a mixture of both
types. The general problems associated with soils having granular
content are usually caused by erosion. Clay soils are subject to
saturation and swell/shrink problems.
Classifications for a given area can generally be obtained by
application to the local authority, but these are sometimes unreliable
and if there is doubt, a geotechnical report should be commissioned.
As most buildings suffering movement problems are founded on clay
soils, there is an emphasis on classification of soils according to the
amount of swell and shrinkage they experience with variations of
water content. The table below is Table 2.1 from AS 2870, the
Residential Slab and Footing Code.
auses of Movement
Settlement due to construction
There are two types of settlement that occur as a result of
construction:
¢ Immediate settlement occurs when a building is first placed on its
foundation soil, as a result of compaction of the soil under the
weight of the structure. The cohesive quality of clay soil mitigates
against this, but granular (particularly sandy) soil is susceptible.
* Consolidation settlement is a feature of clay soil and may take
place because of the expulsion of moisture from the soil or because
of the soil’s lack of resistance to local compressive or shear stresses.
This will usually take place during the first few months after
construction, but has been known to take many years in
exceptional cases.
These problems are the province of the builder and should be taken
into consideration as part of the preparation of the site for construc-
tion. Building Technology File 19 (BTF 19) deals with these
problems.
Erosion
All soils are prone to erosion, but sandy soil is particularly susceptible
to being washed away. Even clay with a sand component of say 10%
or more can suffer from erosion.
Saturation
This is particularly a problem in clay soils. Saturation creates a bog-
like suspension of the soil that causes it to lose virtually all of its
_ bearing capacity. To a lesser degree, sand is affected by saturation
because saturated sand may undergo a reduction in volume —
particularly imported sand fill for bedding and blinding layers.
However, this usually occurs as immediate settlement and should
normally be the province of the builder.
Seasonal swelling and shrinkage of soil
All clays react to the presence of water by slowly absorbing it, making
the soil increase in volume {see table below). The degree of increase
varies considerably between different clays, as does the degree of
decrease during the subsequent drying out caused by fair weather
periods. Because of the low absorption and expulsion rate, this
phenomenon will not usually be noticeable unless there are
prolonged rainy or dry periods, usually of weeks or months,
depending on the land and soil characteristics.
The swelling of soil creates an upward force on the footings of the
building, and shrinkage creates subsidence that takes away the
support needed by the footing to retain equilibrium.
Shear failure
This phenomenon occurs when the foundation soil does not have
sufficient strength to support the weight of the footing. There are
two major post-construction causes:
° Significant load increase.
¢ Reduction of lateral support of the soil under the footing due to
erosion or excavation.
¢ In clay soil, shear failure can be caused by saturation of the soil
adjacent to or under the footing.
GENERAL DEFINITIONS OF SITE CLASSES
Slightly reactive clay sites with only slight ground movement from moistut ¢
hanes
~ Moderately reactive clay or silt sites, which can experience moderate ground movernent from moisture changes
Highly reactive clay sites, which can experience high ground movement from moisture changes
"Filled sites Be ie
E | ' |) Extremely reactive sites, which can experience extreme ground movement from moisture changes...
Pee Sites which include soft soils, such as soft clay ‘or silt or loose sands: landslip; mine subsidence, collapsing soils} soils subject
fo erosion’ reactive sites subject to abnormal moisture conditions or sites which cannot: be classified otherwise \o 8
Page 11
Tree root growth Trees and shrubs that are allowed to grow in the vicinity of footings can cause foundation soil movement in two ways: ¢ Roots that grow under footings may increase in cross-sectional size, exerting upward pressure on footings. ¢ 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 runs in the same direction as the flow. Saturation of clay foundation soil may occur where subfloor walls create a dam that makes water pond. It can also occur wherever there is a source of water near footings in clay soil. This leads to a severe reduction in the strength of the soil which may create local shear failure. Seasonal swelling and shrinkage of clay soil affects the perimeter of the building first, then gradually spreads to the interior. 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. Erosion and saturation Erosion removes the support from under footings, tending to create subsidence of the part of the structure under which it occurs. Brickwork walls will resist the stress created by this removal of support by bridging the gap or cantilevering until the bricks or the mortar bedding fail. Older masonry has little resistance. Evidence of failure varies according to circumstances and symptoms may include: * Step cracking in the mortar beds in the body of the wall or above/below openings such as doors or windows. * Vertical cracking in the bricks (usually but not necessarily in line with the vertical beds or perpends). Isolated piers affected by erosion or saturation of foundations will eventually lose contact with the bearers they support and may tilt or fall over. The floors that have lost this support will become bouncy, sometimes rattling ornaments etc. Seasonal swelling/shrinkage in clay Swelling foundation soil due to rainy periods first lifts the most exposed extremities of the footing system, then the remainder of the perimeter footings while gradually permeating inside the building footprint to lift internal footings. This swelling first tends to create a dish effect, because the external footings are pushed higher than the internal ones. The first noticeable symptom may be that the floor appears slightly dished. This is often accompanied by some doors binding on the floor or the door head, together with some cracking of cornice mitres. In buildings with timber flooring supported by bearers and joists, the floor can be bouncy. Externally there may be visible dishing of the hip or ridge lines. As the moisture absorption process completes its journey to the innermost areas of the building, the internal footings will rise. If the spread of moisture is roughly even, it may be that the symptoms will temporarily disappear, but it is more likely that swelling will be uneven, creating a difference rather than a disappearance in symptoms. In buildings with timber flooring supported by bearers and joists, the isolated piers will rise more easily than the strip footings or piers under walls, creating noticeable doming of flooring. Wail cracking po due to MNeVven. iio i i As the weather pattern changes and the soil begins to dry out, the external footings will be first affected, beginning with the locations where the sun's effect is strongest. This has the effect of lowering the external footings. The doming is accentuated and cracking reduces or disappears where it occurred because of dishing, but other cracks open up. The roof lines may become convex. Doming and dishing are also affected by weather in other ways. In areas where warm, wet summers and cooler dry winters prevail, water migration tends to be toward the interior and doming will be accentuated, whereas where summers are dry and winters are cold and wet, migration tends to be toward the exterior and the underlying propensity is toward dishing. Movement caused by tree roots In general, growing roots will exert an upward pressure on footings, whereas soil subject to drying because of tree or shrub roots will tend to remove support from under footings by inducing shrinkage. Complications caused by the structure itself Most forces that the soil causes to be exerted on structures are vertical — i.e. either up or down. However, because these forces are seldom spread evenly around the footings, and because the building resists uneven movement because of its rigidity, forces are exerted from one part of the building to another. The net result of all these forces is usually rotational. This resultant force often complicates the diagnosis because the visible symptoms do not simply reflect the original cause. A common symptom is binding of doors on the vertical member of the frame. Effects on full masonry structures Brickwork will resist cracking where it can. It will attempt to span areas that lose support because of subsided foundations or raised points. It is therefore usual to see cracking at weak points, such as openings for windows or doors. In the event of construction settlement, cracking will usually remain unchanged after the process of settlernent has ceased. With local shear or erosion, cracking will usually continue to develop until the original cause has been remedied, or until the subsidence has completely neutralised the affected portion of footing and the structure has stabilised on other footings that remain effective. In the case of swell/shrink effects, the brickwork will in some cases return to its original position after completion of a cycle, however it is more likely that the rotational effect will not be exactly reversed, and it is also usual that brickwork will settle in its new position and will resist the forces trying to return it to its original position. This means that in a case where swelling takes place after construction and cracking occurs, the cracking is likely to at least partly remain after the shrink segment of the cycle is complete. Thus, each time the cycle is repeated, the likelihood is that the cracking will become wider until the sections of brickwork become virtually independent. With repeated cycles, once the cracking is established. if there is no other complication, it is normal for the incidence of cracking to stabilise, as the building has the articulation it needs to cope with the problem. This is by no means always the case, however, and monitoring of cracks in walls and floors should always be treated seriously. Upheaval caused by growth of tree roots under footings is not a simple vertical shear stress. There is a tendency for the root to also 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 brick- work 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 ate supported. In these cases, it is Internally visible cracking that should be the main focus of attention, however there are a few examples of dwellings whose external leaf of masonry plays some supporting role, so this should be checked if there is any doubt. In any case, externally visible cracking is important as a guide to stresses on the structure generally, and it should also be remembered that the external walls must be capable of supporting themselves. Effects on framed structures Timber or steel framed buildings are less likely to exhibit cracking due to swell/shrink than masonry buildings because of their flexibility. Also, the doming/dishing effects tend to be lower because of the lighter weight of walls. The main risks to framed buildings are encountered because of the isolated pier footings used under walls. Where erosion or saturation cause a footing to fall away, this can double the span which a wall must bridge. This additional stress can create cracking in wall linings, particularly where there is a weak point in the structure caused by a door or window opening. It is, however, unlikely that framed structures will be so stressed as to suffer serious damage without first exhibiting some or all of the above symptoms for a considerable period. The same warning period should apply In the case of upheaval.-It should be noted, however, that where framed buildings are supported by strip footings there is only one leaf of brickwork and therefore the externally visible walls are the supporting structure for the building. In this case, the subfloor masonry walls can be expected to behave as full brickwork walls. Effects on brick veneer structures . Because the load-bearing structure of a brick veneer building is the frame that makes up the interior leaf of the external walls plus perhaps the internal walls, depending on the type of roof, the building can be expected to behave as a framed structure, except that the external masonry will behave in a similar way to the external leaf of a full masonry structure. Water Service and Drainage Where a water service pipe, a sewer or stormwater drainage pipe is in the vicinity of a building, a water leak can cause erosion, swelling or saturation of susceptible soil. Even a minuscule leak can be enough to saturate a clay foundation. A leaking tap near a building can have the same effect. In addition, trenches containing pipes can become watercourses even though backfilled, particularly where broken rubble is used as fill. Water that runs along these trenches can be responsible for serious erosion, interstrata seepage into subfloor areas and saturation. Pipe leakage and trench water flows also encourage tree and shrub roots to the source of water, complicating and exacerbating the problem. Poor roof plumbing can result in large volumes of rainwater being concentrated in a small area of soil: * Incorrect falls in roof guttering may result in overflows, as may gutters blocked with leaves etc. * Corroded guttering or downpipes can spill water to ground. © Downpipes not positively connected to a proper stormwater collection system will direct a concentration of water to soil that is directly adjacent to footings, sometimes causing large-scale problems such as erosion, saturation and migration of water under the building. ‘seriousness of Cracki 9 . In general, most cracking found in masonry walls is a cosmetic . nuisance only and can be kept in repair or even ignored. The table below is a reproduction of Table C1 of AS 2870. . AS 2870 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 to repair the problem. It Is prudent, however, to consider also rerouting pipes away from the building where possible, and relocating taps to positions where any leakage will not direct water to the building vicinity. Even where gully traps are present, there is sometimes sufficient spill to create _ erosion or saturation, particularly in modern installations using sinaller diameter PVC fixtures. Indeed, some gully traps are not situated directly under the taps that are installed to charge them, with the result that water from the tap may enter the backfilled trench that houses the sewer piping. If the trench has been poorly backfilled, the water will either pond or flow along the bottom of the trench. As these trenches usually run alongside the footings and can be at a similar depth, it is not hard to see how any water that is thus directed into a trench can easily affect the foundation's ability to support footings or even gain entry to the subfloor area. Ground drainage Jn 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 js usually an easy solution. Tt 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 i It is essential to remember that the soil that affects footings extends well beyond the actual building line. Watering of garden plants, shrubs and trees causes some of the most serious water problems. For this reason, particularly where problems exist or are likely to occur, it is recommended that an apron of paving be installed around as much of the building perimeter as necessary. This paving
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height selected ¢ for distance from house 2. Drained Carport pathway. Path--— Garden bed 5 “covered wilh Driveway! mulch iG ' should extend outwards a minimum of 900 mm (more in highly reactive soil) and should have a minimum fall away from the building of 1:60. The finished paving should be no less than 100 mm below brick vent bases. It is prudent to relocate drainage pipes away from this paving, if possible, to avoid complications from future leakage. Tf this is not practical, earthenware pipes should be replaced by PVC and backfilling should be of the same soil type as the surrounding soil and compacted to the same density. Except in areas where freezing of water is an issue, it is wise to remove taps in the building area and relocate them well away from the building — preferably not uphill from it (see BTF 19). It may be desirable to install a grated drain at the outside edge of the paving on the uphill side of the building. Tf subsoil drainage is needed this can be installed under the surface drain. Condensation In buildings with a subfloor void such as where bearers and joists support flooring, insufficient ventilation creates ideal conditions for condensation, particularly where there is little clearance between the floor and the ground. Condensation adds to the moisture already present in the subfloor and significantly slows the process of drying out. Installation of an adequate subfloor ventilation system, either natural or mechanical, is desirable. Warning: Aithough this Building Technology File deals with cracking in buildings, it should be said that subfloor moisture can result in the development of other problems, notably: ¢ Water that is transmitted into masonry, metal or timber building elements causes damage and/or decay to those elements. * High subfloor humidity and moisture content create an ideal environment for various pests, including termites and spiders. ¢ Where high moisture levels are transmitted to the flooring and walls, an increase in the dust mite count can ensue within the living areas. Dust mites, as well as dampness in general, can be a health hazard to inhabitants, particularly those who are abnormally susceptible to respiratory ailments. The garden The ideal vegetation layout is to have lawn or plants that require only light watering immediately adjacent to the drainage or paving edge, then more demanding plants, shrubs and trees spread out in that order. Overwatering due to misuse of automatic watering systems is a common cause of saturation and water migration under footings. If it is necessary to use these systems, it is important to rermove garden beds to a completely safe distance from buildings. Existing trees Where a tree is causing a problem of soil drying or there is the existence or threat of upheaval of footings, if the offending roots are subsidiary and their removal will not significantly damage the tree, they should be severed and a concrete or metal barrier placed vertically in the soil to prevent future root growth in the direction of the building. If it is not possible to remove the relevant roots without damage to the tree, an application to remove the tree should be made to the local authority. A prudent plan is to transplant likely offenders before they become a problem. Information on trees, plants and shrubs State departments overseeing agriculture can give information regarding root patterns, volume of water needed and safe distance from buildings of most species. Botanic gardens are also sources of information. For information on plant roots and drains, see Building Technology File 17. Excavation Excavation around footings must be properly engineered. Soil supporting footings can only be safely excavated at an angle that allows the soil under the footing to remain stable. This angle is called the angle of repose (or friction) and varies significantly between soil types and conditions. Removal of soil within the angle of repose will cause subsidence. ' Remediation Where erosion has occurred that has washed away soil adjacent to footings, soil of the same classification should be introduced and compacted to the same density. Where footings have been undermined, augmentation or other specialist work may be required. Remediation of footings and foundations is generally the realm of a specialist consultant. Where isolated footings rise and fall because of swell/shrink effect, the homeowner may be tempted to alleviate floor bounce by filling the gap that has appeared between the bearer and the pier with blocking. The danger here is that when the next swell segment of the cycle occurs, the extra blocking will push the floor up into an accentuated dome and may also cause local shear failure in the soil. If it is necessary to use blocking, it should be by a pair of fine wedges and monitoring should be carried out fortnightly. 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 believed to be correct when published. Further professional advice needs to be obtained before taking any action based on the information provided. The information is advisory. It is provided in good faith and not claimed to be an exhaustive treatment of the relevant Subject. Distributed by CSIRO PUBLISHING PO Box.1139, Collingwood 3066, Australia Freecall 1800 645 051. Tel (03) 9662 7666 Fax (03) 9662 7555. www.publish.csiro.au Email: [email protected] © CSIRO 2003. Unauthorised copying of this Building Technology file is prohibited
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Description Date Revision Plover Stree} ! Proposed House Site SITE PLAN Site Drainage Good. Vegetation Grasses BH 2 + oe Borehole location. d-7% Slope measured as a percentage gradient from high ground to low ground. DO NOT DIMENSION OFF THIS DIAGRAM. Drawn By : W.R.Holmes QBCC License. No.112066 Australian Soil Investigations} QBCC License No.15072110 (Property Boundaries are diagramatic only) AUSTRALIAN SOIL INVESTIGATIONS Unit 1/11 Project Ave, Noosaville ABN11 147 854 439 Title: SITE PLAN Project 32 Plover Street Rev, Peregian Beach Drg No.200365-—S| Date: Dec 2020 Rev. - 30.01.05
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Australian Soil Investigations LOG SECTIONS Ref No. 200365
Client: R & G Broadhurst
Location: (Lot 9 on P9313) 32 Plover Street, Peregian Beach.
Date: 11/12/2020
(House Site)
Depth TEST SITE No 1 P Depth TEST SITE No 2 P
100 Silty Sand SM 1 100 Silty Sand SM 1
200 Fine to med grained sand 1 200 Fine to med grained sand 1
300 Grey brown, moist, roots, loose. 1 300 Grey brown, moist, roots, loose. 1
400 1 400 1
500 1 500 1
600 1 600 1
700 1 700 1
800 1 800 1
900 1 900 1
1000 1 1000 1
1100 1 1100 Silty Sand SM 1
1200 Silty Sand SM 1 1200 Fine to coarse grained, pale 1
1300 Fine to coarse grained, pale 1 1300 Grey, moist, loose. 1
1400 Grey, moist, loose. 1 1400 1
1500 2 1500 1
1600 2 1600 1
1700 2 1700 2
1800 Becoming med dense 3 1800 Becoming med dense 3
1900 3 1900 3
2000 3 2000 3
2100 3 2100 3
2200 4 2200 3
2300 4 2300 4
2400 5 2400 4
2500 5 2500 5
2600 5 2600 5
2700 5 2700 5
2800 6 2800 5
2900 7 2900 6
3000 End 8 3000 End 6
3100 8 3100 6
Depth = mm below ground level.
P = blows per 100mm penetration with an approved 9kg penetrometer.
Notation such as (SP) refers to the soil description to Table A1 AS1726 ‘Guide to the description
identification and classification of soils’.
Solid lines represent sharp interface between different soil types. Dotted lines represent
gradation form one soil type to another.
Abbreviations used
UTP - unable to penetrate, Bec. – becoming, N.S.L. – Natural Surface Level
Med. – medium, MW - Moderately weathered
EW - extremely weathered, Plast. - Plasticity
No recovery means unable to extract samples from the base of the bore hole because the soil
will not bind in the auger head.
The colour of the soil is often abbreviated, for example Gy = grey Or = orange.