Attachment 3 Soil Test Report

Page 2

1.0 INTRODUCTION:

This company has performed 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 22/01/2014 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 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 poor drainage within the allotment, the presence and
proximity of trees to the allotment and existing trees located on the proposed construction area that will
be removed.

With respect to potential surface movements through seasonal moisture variations, the site could be
considered equivalent to a class S site.

Site Classification: The site classification is calculated in accordance with the “AS2870-2011
Residential Slabs and Footings-Construction” and relates to the estimation of Ys, “The characteristic
surface movement’ within reactive soil profiles. The limits used for this classification are as follows:

 

 

 

 

 

 

 

 

[ Predicted Surface Movement __| Classification |
Ys = <=20mm s Slight
Ys = >20 — 40mm M Moderate
Ys = >40 - 60mm Hi High-1
Ys = 60 — 75mm H2 High-2
Ys => 75mm E Extreme
Problem sites Pr Problem

 

 

 

 

3.0 SITE DESCRIPTION:
The construction area has a gradient in the order of 16%.
Vegetation on the construction area (and nearby surrounds) consists of grasses and dense trees.

The existing surface drainage is good and sub-surface drainage is good.

SCG CONSULTING ENGINEERS 1 SCG Ref: 24018(S)

Page 3

4.0 FINDINGS:

The soil profiles encountered are shown on the attached borelog sections.

No water table was encountered during our testing program.

The sandy soils encountered are susceptible to collapse when unconfined. This may effect
excavations and result in additional earthworks and increased concrete volumes. Temporary shoring

or Forma-Tube may be required to retain the sands prior to concreting.

The samples classified on-site were assessed as having negligible plasticity, therefore laboratory
testing was considered unnecessary.

We have assessed the expected differential movement of the soil profiles encountered to be the
equivalent of a site with a Ys of less than 20mm.

  

The foliowing foundation material ings within the

scope of AS 2870-2011.

ill provide a safe bearing capacity (100 kPa) for b

FOUNDATION MATERIAL - NATURAL MEDIUM DENSE 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.

 

for and on behalf of:
SCG CONSULTING ENGINEERS

SCG CONSULTING ENGINEERS 2 SCG Ref: 24018(S)

Page 4

SCG CONSULTING ENGINEERS LOG SECTIONS Ref No. 24018

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Depth 3s TESTESIIEMOM se erie P_| Depth TESTSITENO2 P
100 Silty Sand SM 1 100 | Silty Sand SM 1
200 Fine, Grey i 200 Fine, Grey 1
300 Roots, Moist, 4! 300 Roots, Moist, 1
400 Loose 4 400 Loose 1
500 1 500 fi
600 1 600 1
Peas . “ol a 1 ee ae i 1
800 “Silty Sand SM 1 800 ty Sand SM 1
900 Fine, Grey 1 900 Fine, Grey 1
1000 Pale Grey, (White) 1 1000 Pale Grey, (White) 1
4100 Moist, Loose 1 1100 | Moist, Loose 1
41200 1 1200 Ea
1300 1 1300 | | 1]
1400 Bec Med Dense 2 1400 Ligey
1500 2 1500 Bec Med Dense [2
1600 2 1600 2
1700 2 1700 2
1800 End 3 1800 End 2
1900 S 1900 3
2000 3 2000 3
2100 3 2100 3
2200 3 2200 3
2300 3 2300 3
2400 4 2400 4
2500 4 2500 5
2600 5 2600 5
2700 5 2700 Z
2800 7 2800 if
2900 7 2900 ae
3000 7 3000 7
3100 3100

 

 

 

 

 

 

 

 

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.

 

(

 

SCG CONSULTING ENGINEERS 3 SCG Ref: 24018(S)

Page 5

APPENDICES

 

A. DEFINITIONS
B. LIMITATIONS
Cc. 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 6

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.

 

Granuiar Soiis: _ Graveis 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 buf, 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 excavatabie with a conventional backhoe.

 

  

Load Bearing Wall: \n our design work a load bearing walt is defined as any wall imposing on the footing a service load greater than
40kN/m. A load bearing wall will normally be supported by a siab thickening or footing in our slab designs.

 

Natural (Strata): Refers to soil that is neither fill or imported material but one that is al 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 red/bar can be easily pushed in by hand Soft Can be moulded by light finger pressure.
Medium A 12mm 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 Cond
Please contact SCG Consulting Engineers 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 ail 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 associated design 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: \n 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.

SCG Consul

 

g Engineers Appendix Page 2 of 6 Appendices.1

Page 7

Trees: Trees can have a considerable effect over the over the performance of a structures foundation, in particular those founded on
reactive soils (Class S,M, H & E). Their pursuit for moisture will change the moisture characteristics of the susrounding 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/design. We are unable to allow for the potential effects 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
in the soils leading to either an increased classification or design requirements. We must be notified of any Increase in
ions. 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 conta

  
  

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”. Unless requested by our client we
do not design concrete floor slabs to be shrinkage crack free.

c RECOMMENDATIONS

C.1. Recommendations for Builders

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 ail drainage so
stormwater is not introduced to the foundation soils leading to potential scour. Roof water must be diverted away from the bu ing prior to
and after the roof is installed. Correct drainage is an essential part of our recommendations and design. 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 water to the foundation soil, do
not allow greater soil moisture evaporation and/or destabilise the footings by undermining them. The base of any trenches under the floor or
within 7.5 meters of the building should be sloped away fram the house and should be backfilled with compacted clay plug.

Correct drainage is an essential part of our recommendations and design 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 ts not prepared correctly, excessive soil moisture may
occur in some areas, which can lead to excessive foundation movements possibly damaging the supported structure.

 

Bracing for Wind Forces: Unless noted, we do not detail slab thickenings or pad footings to conform to wind bracing. Where a bracing
wall is to be bolted to a slab, 40mm bottom concrete cover attained for a radius of 150mm is required around the bolts unless noted by other
consultants.

Inspections: We require 24 hours notice if you require engineers site inspections. Inspections can be booked between 8.30am and 4.30pm
Monday to Friday by telephoning 07 5455 5604.

Silt Retention: The builder is responsible for ensuring appropriate si
construction.

  

n measures are in placed and maintained throughou

SCG Consulting Engineers Appendix Page 3 of 6 Appendices.1

Page 8

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 ight

Ys = >20-40mm M Moderate
Ys = >40- 60mm H1 High-1
Ys = 60— 75mm H2 High-2

Ys => 75mm EA Extreme
Problem sites iP Problem

 

 

 

 

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 sioped 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’.

ing 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 founda’ to 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 follo

 

1g recommendations for the minimum distance between trees and footings should be followed:-

 

Site Class Offset to Tree
Class M : 0.75 xh
Class H : 1.0 xh
Class E : 15 xh

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 SCG Consulting
Engineers for options.

The following table provides some guidance on mature tree heights:-
APPROXIMATE TREE HEIGHTS

 

10 to 20m Height — Acacias, Ash, Athe! 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
ime to reach moisture equilibrium prior to construction commencing. Please contact our office for further guidance on this matter.

 

SCG Consu!

 

IS} Engineers Appendix Page 4 of 6 Appendices.1

 

Page 9

D DETAIL SHEETS
D.1

Plumbing Requirements Class M, H1, H2 & E Sites

 

NTS.

 

WIS

SLEEVED OR EXPANDA tn
TH A WNIMUN OMERUP OF
(SOkmm BNR AS SHOWH

GROUND \

71:20 MN

‘STORM WATER
DRANACE PIPE
\

KES.

 

 

STORWPRATER OOWFPE

SURFACE FALL,

ALLOW PIPE BORK TO OYE /
‘VERTICALLY INDEPENDENT
OF BULONG FOOTNCS

TYPICAL STORM WATER DETAIL

SLAB POEIRATONS iN TO SATISFY
TERMITE PROTECTION REQUIREMENTS

   

 

FOR SLABS SUPPORTED ON PIERS
PROWE STAINLESS STEEL

‘SUSPENSION STRAPS FRM LAS
MESH TO UNOERSLAR ORANAGE,

 

 

 

 

 

 

FOOTING PENETRATION
ACCORGANCE WITH FOOTING
+ AND SLAB DETALS:

 

| Foonwe &
= 98

 

 

 

y

 

Ets
(EPu)}

 

 

| | (GAYS 10 wR APE
CONNECTOS GLASS H &

LEGEND.

SELECTED N-UNE “DPANOA’ ONT INSTALLED 70
MANUFACTURERS SPECIFICATIONS. STORMPLASNCS OR
EQUALLY APPROVED

(SW) SELECTED IN—UNE SHNEL WONT INSTALLED 10
WANUFACTURERS SPECACATIONS. STORMPLASICS OR
EQUALLY APPROVED

(CTP)  COMPACTED CLAY PLUMEANG TRENCH PLUG TO STOP
MOISTURE ENTERNG UNDER HE HOUSE SLAB

(SHL) SEWER MAN UNE

10. INSPECTION OPENING 10 SURFACE

UGGNG —-MINNUN LAGGNG THICKNESS, 20mm FOR CLASS

‘STES ANG 40mm KR CLASS H & € SITES

Guidelines for Drainage Installations

 

water Charged and where soll movement may effect the p:
plan and soecification should be providea by an aoproy

 

calculations showing oregosed method to protect the drainage from potential ground
movements may de required,

    

are to be
provided to accommodate movement in
comply AS71260.

3. Plumbing and drainage under the slab should be avoided where oract
AS/N253500 clause 4.
4, Grades in pipe work on M, Hand E sites should have a minimum grade of 1:50 within $5
matres of the building and 1:60 elsewhere. Grades in fe {ings to be set at the
minimum grade

5. All expansion and artic
recommencations. All
cirectica.
6, Stormplas

 

 

 

5 10 be installed in accordance with manufacturer's
ints to 5¢ set mid point so as to allow for maximum in either

s (SA) Pty Lcd ‘sui

       

movement. A minimum 15° bend to be installed before swivel
qrades From the face of the foot

7. Detail and supeort of
movements including isolation and a’

 

‘h the footing system on class Hand E

   
     

PVC pipe products is not permitted
in accordance AS3660 and is not showm cn these d

 

fixtures such as HWS and A.C. to approved drains as required by tl
authority.

relevant ‘acai

PLUMBING REQUIREMENTS — CLASS M Hi H2 & E SITES

 

 

SCG Consulting Engineers

Appendix Page 5 of 6

Appendices.1

Page 10

D.2 Site Drainage recommendations

 

 

 

 

 

 

 

 

 

 

          

     

‘CUT-OFF DRAIN AT HGH
SUE CF EMBANKMENT os

|
'

CUT-OFF ean ach
HGH SDE ra
RETAMING Se me
\
Ne ll

| GROUND SURFACE FAL

FOOTING & 41:20 WN FOR Sm NIB

AB HAD

 
   
  

REAR OF WALL DRAINAGE,

 

© PROWDE FLUSH OUT
: FACLITY
' CUT-OFF ORAN AT BASE
CUT-OFF GRAN AT TOE OF RETANING WALL
OF EMBANKMENT QUT
OWRECTED AROUND THE
ORECTED AROUND THE PERWETER OF THE
PERIMETER OF THE OWELUNG
DWELLING
~
TPICAL DRAINAGE ~ CUT FILL SITE

        

ite to drain
i flooding of foundation works, temporary sumoing
drainage paths are trapoed. Temporary down pipes must
'ed foliowing roof construction and drained away from the construction area.
Drainage trenches shou d be clay cagned to stop me
2, Upon comple ad surroundir

          

 

dramed ia agoroved drainage fa
3, Rear of waa

SITE DRAINAGE RECOMENDATIONS ALL SITES

 

 

 

SCG Consulting Engineers Appendix Page 6 of 6 Appendices.1

Page 11

Foundation Maintenance

and Footing Performance:
A Homeowner's Guide

csiro

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 bu

ings can usually be related to one or more problems in the foundation si

 

It

 

portant 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 soi! 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.

  

1 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.

  

Causes of Movement

Settlement due to construction

There are two types of settlement that occur as a result of

construction:

* Tmmediate 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 jt 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
normaily be the province of the builder.

Seasonal swelling and shrinkage of soll

All clays react to the presence of water by slowly absorbing it, making
the soif 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 fateral support of the soil under the footing due to
erosion or excavation.

 Inclay soil, shear failure can be caused by saturation of the soil
adjacent to or under the footing.

 

~ Filled sites

Foundation =
‘ Mast ‘sand and tock sites with litle or no ground movement from moisture changes 2
Slightly reactive clay sites with only slight ground movement from moisture changés

Moderately feactive clay or silt sites, which can experience ‘moderate ground movement from moisture changes
Extremely: reactive sites, ‘which can. experience extreme ground movement from moisture chabiges:

Sites which include soft soils, such as soft clay or silt of loose sands; |
to erosion: reactive sites subject to abnormal moisture conditions or sites which cannot be classified otherwise”

GENERAL DEFINITIONS OF SITE CASES. Z

 

 

Highly reactive clay sites, which can experience high ground thovement from moisture changes ey

 

Jandslip;. mine subsidence; collapsing soils; soils subject

 

 

 

 

Page 12

Tree root growth
Trees and shrubs that are allowed to grow in the vicinity of footings
can cause foundation soil movement in two way:

 

« Roots that grow under footings may increase in cross-sectionai
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
uneverily 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 soi! 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 stcength 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.

' Effects of Uneven Soil Movement on Structure

 

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,
sornetimes 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 visibie
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 bu gs 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 floorir

 

 

 

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
oc 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 constuction settlement, cracking will usually remain
unchanged after the process of settlement has ceased.

With local shear or erosion, cracking will usually continue to develop
until the original cause has been remedied, or until the subsidence
has completely neutralised the affected portion of footing and the
structure has stabilised on other footings that remain effective.

In the case of swell/shrink effects, the brickwork will in some cases
return to its original position after completion of a cycle, however it
is more likely that the rotational effect will not be exactly reversed.
and it is also usual that brickwork will settle in its new position and
will resist the forces trying to return it to its original position. This
means that in a case where swelling takes place after construction
and cracking occurs, the cracking is likely to at least partly remain
after the shrink segment of the cycle is complete. Thus, each time
the cycle is repeated, the likelihood is that the cracking 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.

Page 13

  

The norma! structural arrangement ts that the Inner leaf of brick-
work in the external wails and at least some of the internal walls
(depending on the roof type) comprise the load-bearing structure on
which any upper floors, ceilings and the roof are supported. In these
cases, it is Internally visible cracking that should be the main focus
of attention, however there are a few examples of dwellings whose
external leaf of masonry plays some supporting role, so this should
be checked if there is any doubt. In any case, externally visible
cracking is Important as a guide to stresses on the structure generally,
and it should also be rernembered that the external walls must be
capable of supporting themselves.

Effects on framed structures :

Timber or steel framed buttdings 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 car
double the span which a wall must bridge. This additional stress can
create cracking in wall Hinings, particularly where there Is a weak
point in the structure caused by a door or window opening. It is,
however, unlikely that framed structures wil! be so stressed as to suffer
serious damage without first exhibiting some or all of the abave
symptoms for a considerable perlod. 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. Tn this case, the subfloor
masonry walls can be expected to behave as full brickwork walls.

Effects on brick veneer structures s

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.

i Water Service and Drainage

‘Where a water service pipe, a sewer or stormwater drainage pipe isin
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 secious 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 volurnes 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 spilt water to ground.

+ Downpipes not positively connected to a proper stormwater
collection system will direct a concentration of water to soil ihai is
directly adjacent to footings, sometimes causing large-scale
problems such as erosion, saturation and migration of water under
the building.

usness of Cracking a

Serio

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 earller than cracking in slabs, this table is not
reproduced here.

iPrevention/Cure

Plumbing

Where building movement is caused by water service, roof plumbing,
sewer or stormwater failure, the remedy Is to repair the problem.

It ts 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

~ sthaller diameter PVC fixtures. Indeed, some guily 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 js
thus directed into a trench can easily affect the foundation's ability to
support footings or even gain entry to the subfioor 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.

It fs, however, sometimes necessary when attempting to prevent
water migcation that testing be carried out to establish watertable
height and subsoil water flows. This subject Is referred to in BIF 19
and may properly be regarded as an area for an expert consultant.

Protection of the building perimeter .
Te 4s 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 s recommended that an apron of paving be installed
around as much of the building perimeter as necessary. This paving

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Page 14

    

 

G sted
for distance

Drained
oathway

 

Garden bed
covered with
mulch

Medium
a8 height ree
ae oe Ly

ae

    

"

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
mun below brick vent bases.

It is prudent to relocate drainage pipes away from this paving, if
possible, to avoid complications from future leakage. If this is not
practical, earthenware pipes should be replaced by PVC and
backfilling should be of the same soil type as the surrounding soil
and compacted to the same density.

Except in areas where freezing of water is an issue, it is wise to
remove taps in the building area and relocate them well away from
the building — preferably not uphill 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. Tf subsoil drainage is
needed this can be installed under the surface drain.

Condensation

Tn buildings with a subfloor void such as where bearers and joists
support flooring. insufficient ventilation creates ideal conditions for
condensation, particuiaciy 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 desicable.

 

 

ng Technology File deals with
cracking in buildings, it should be said that subfloor moisture can
result in the development of other problerns, 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 2
health hazard to inhabitants. particularly those who are
abnormally susceptible to respiratory ailments.

The garden

The ideai vegetation layout is to have lawn or plants that require
only light watering immediately adjacent to the drainage or paving
edge, then more demanding plants, shrubs and trees spread out in
that order.

Overwatering due to misuse of automatic watering systems is a
common cause of saturation and water migration under footings. If
it is necessary to use these systems, it is important to remove garden
beds to a completely safe distance from buildings.

Existing trees

Where a tree is causing a problem of soil drying or there is the
existence or threat of upheaval of footings, if the offend ing roots are
subsidiary and their rernoval will not significantly darmage 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 te 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 swelt/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 wiil pust: the floor up into an
accentuated dome and may also cause focal 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.

‘The information is advisory. It is provided in good faith and not claimed to be an exhaustive vealmes Of the relevant subject,

Further prafessional advice needs to be obtained before taking ary action based on the information provided.

 

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