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J001783-001-R-Rev1
Geotechnical Investigation & Stability Assessment Proposed Residence 317 Lawnville Road, Black Mountain Prepared for: Ashley and Caroline Hermes C/- Darren Thompson K Architecture Email: ([email protected]) Report Number: J001783-001-R-Rev1
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Ashley and Caroline Hermes Table of Contents 1.0 INTRODUCTION ....................................................................................................................... 1 2.0 PROPOSED DEVELOPMENT .................................................................................................. 1 3.0 SITE DESCRIPTION ................................................................................................................. 1 4.0 METHOD OF INVESTIGATION ................................................................................................ 4 4.1 Fieldwork.................................................................................................................................... 4 5.0 RESULTS OF INVESTIGATION ............................................................................................... 4 5.1 Published Geological Information .............................................................................................. 4 5.2 Subsurface conditions ............................................................................................................... 5 5.3 Topography ................................................................................................................................ 5 5.4 Surface Drainage ....................................................................................................................... 5 5.5 Vegetation .................................................................................................................................. 5 5.6 Buildings, Other Structures, etc. ................................................................................................ 5 6.0 ASSESSMENT OF LAND STABILITY ...................................................................................... 6 6.1 Existing Conditions .................................................................................................................... 6 6.2 Stability Risk Assessment.......................................................................................................... 6 7.0 DEVELOPMENT IMPACTS & MITIGATION MEASURES ........................................................ 8 7.1 Earthworks ................................................................................................................................. 8 7.1.1 Site Preparation & Trafficability ............................................................................................. 8 7.1.2 Excavatibility .......................................................................................................................... 8 7.1.3 Re-use as Fill ......................................................................................................................... 8 7.1.4 Batter Slopes ......................................................................................................................... 9 7.1.5 Soil Dispersion & Erosion Protection ..................................................................................... 9 7.1.6 Filling and Compaction .......................................................................................................... 9 7.2 Retaining Structures .................................................................................................................. 9 7.3 Site Classification .................................................................................................................... 10 7.4 High Level Footings ................................................................................................................. 10 7.5 Drainage .................................................................................................................................. 12 7.6 General Foundation Maintenance ........................................................................................... 12 8.0 SUMMARY AND CONCLUSIONS .......................................................................................... 12 9.0 LIMITATIONS .......................................................................................................................... 12 Tables Table 1: Stability Risk Levels ............................................................................................................................. 7 Table 2: Qualitative Risk Assessment for Property (Based on AGS 2007)....................................................... 7 Table 3: Retaining structure design parameters. ............................................................................................ 10 Table 4: Pile design values. ............................................................................................................................. 11 J001783-001-R-Rev1 i
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Ashley and Caroline Hermes Figures Figure 1 – Geotechnical Test Location Plan Appendices Appendix A Reports of Test Pits, DCP’s and Explanatory Notes Appendix B Qualitative Risk Analysis Matrix (Australian Geomechanics Vol 42 No 1 March 2007) Appendix C General Guidelines for Hillside Construction Appendix D CSIRO Foundation Maintenance Guidelines Appendix E Limitations J001783-001-R-Rev1 iii
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Ashley and Caroline Hermes 1.0 INTRODUCTION This report presents the results of a geotechnical investigation and slope stability assessment for a proposed residence at 317 Lawnville Road, Black Mountain. The work was undertaken in accordance with proposal Q003778-001-L-Rev0. 2.0 PROPOSED DEVELOPMENT We understand the proposed development comprises construction of a two-level residence including a pool, garage and driveway. Drawings provided by K Architecture (SK.01 To SK.09, 18 November 2022) indicate a proposed cut of about 2.5 m vertical height into the slope at the south-western corner of the residence footprint, supported by a tiered retaining wall. Downslope filling works are also proposed (possibly up to about 2.5 m height) supported by a block retaining wall. Image 1: Layout of proposed development (K Archticture Project - Deakin - Black Mountain, Drawing No. SK.04, dated 18/11/2022). 3.0 SITE DESCRIPTION The property is described as Lot 2 on RP83801 and covers an area of 605,525 m2. The proposed residence footprint lies in the southern portion of the lot with access via a gravel driveway from Cooroy Belli Creek Road (refer Image 2). Site conditions observed at the time of our walkover are shown in Photographs 1 to 3 below. J001783-001-R-Rev1 1
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Legend:
Lot Boundary
Approximate Site Location
317 Lawnville Road, Black Mountain
Image 2: Aerial view of site (courtesy of Noosa Council Interactive Mapping website; annotations by Core).
Approximate residence footprint
TP4
TP5
Photograph 1: View from drone looking approximately south toward the proposed development footprint.
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Approximate residence footprint
Historic Landslide
Historic Landslide
Photograph 2: View from drone looking approximately southwest toward the proposed development footprint.
Photograph 3: Looking approximately west upslope of the development footprint.
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4.0 METHOD OF INVESTIGATION
4.1 Fieldwork
The investigation fieldwork was carried out on 22 December 2022, comprising two test pits (designated TP1
and TP2) and two dynamic cone penetrometer (DCP) tests (designated DCP1 and DCP2).
Test pits were excavated with a 5.5-tonne excavator, fitted with a 450 mm toothed bucket and ripper
attachment. DCP tests were also carried out adjacent to the test pits.
The fieldwork was carried out in the presence of a geotechnical engineer from Core, who logged the
subsurface conditions in accordance with Australian Standard AS1726-2017 Geotechnical site
investigations.
Test locations were recorded in the field using a handheld GPS unit and are shown on the attached Figure 1.
Test Pit and DCP reports are attached in Appendix A, together with photographs and explanatory notes.
Subsurface conditions are discussed in Section 5.3.
5.0 RESULTS OF INVESTIGATION
5.1 Published Geological Information
Published information 1 indicates that the site is underlain by middle Triassic age Kin Kin beds comprising
‘strongly cleaved and commonly kinked mudstone with thin siltstone laminae; minor volcanilithic sandstone’.
The site is adjacent to an area underlain by Tertiary age Basalt comprising ‘Mostly olivine basalt flows and
some plugs; some areas of nephelinite, basanite etc’. An extract of the geological map is shown in Image 3.
The subsurface conditions encountered in the test pits (described below) generally confirm the published
geology.
Approximate Site Location
Image 3 – Extract from Published Geology Map1
.
1
Queensland Geotechnical Database Website Geology Overlay Map
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5.2 Subsurface conditions
The general subsurface profile encountered in the test pits comprised:
Topsoil: comprising low to high plasticity silty clay to depths of between 0.1 m to 0.2 m below ground
level (BGL).
Colluvium: comprising medium plasticity, stiff to very stiff gravelly sandy clay to 0.6 m depth in TP1.
Residual Soils: comprising medium to high plasticity, firm to hard silty/sandy clay to depths of 1.0 m
and 2.0 m BGL; underlain by
Extremely Weathered Material: comprising low to medium plasticity, hard silty/silty clay to 1.2 m BGL;
in TP1; underlain by
MUDSTONE: very low to medium strength, highly weathered, thinly laminated mudstone, encountered
at depths of 1.2 m (TP1) and 2 m (TP2), and continuing to practical excavator refusal.
Practical excavator refusal was encountered in rock (mudstone) in both test pits.
DCP tests (DCP1 and DCP2) were completed in the proposed pool footprint and the southern extent of the
proposed residence footprint as shown on Figure 1.
Groundwater was not encountered in the test pits, however, seepage may occur at the soil/rock interface or
through fractures in the rock following periods of prolonged rainfall.
5.3 Topography
The proposed development site is on a small convex ridge generally sloping approximately 7° to 15° towards
the northeast. Slopes of approximately 20° were observed to the north of the development footprint (along
the northern side of the ridge) and 12° to the south. Slopes of up to 20° to 25° were observed directly
upslope of the proposed western retaining walls (adjacent to the proposed garage).
Ground surface contours and slope angles were measured on site with a handheld clinometer.
5.4 Surface Drainage
Surface drainage appears to be good, with runoff expected to be directed downslope toward the north and
south of the proposed footprint. To ensure that surface water from the building envelope and the remainder
of the site does not traverse the driveway, adequate drainage should be installed to divert water flow.
5.5 Vegetation
At the time of our investigation, the proposed residence footprint was cleared of all trees and predominantly
covered in grass.
Remnant natural vegetation (including large mature trees) is present to the west (upslope) of the proposed
footprint. No significant signs of tilting (a possible indicator of ground movement) were observed in the
existing vegetation.
5.6 Buildings, Other Structures, etc.
No existing buildings or structures were present in the proximity of the proposed footprint.
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6.0 ASSESSMENT OF LAND STABILITY
6.1 Existing Conditions
The Noosa Council (NC) Landslide Hazard Overlay Code indicates the site has areas of Moderate Landslide
Hazard (light yellow shading) (refer Image 4).
Approximate Site Location
Image 4: Extract from NC Landslide Hazard overlay map.
The Council Landslide Hazard Overlay Maps provide a broad-scale indication of potential landslide likelihood
based on ground slopes, geology and known landslip areas. The ratings can be superseded once site-
specific investigation and analysis are undertaken (i.e. this report).
Two small existing/historical landslides were identified on the site at the time of our fieldwork (refer attached
Figure 1 and Photograph 2). These are in steeper areas of the site, away from the proposed residence
footprint, and appear to be shallow slump/rotational failures in colluvium and/or residual soils. Colluvial
materials, due to their geological nature, are often associated with slope instability. In addition, our
experience indicates that residual soils and weathered rock of the Kin Kin Beds can be associated with slope
instability, particularly on steeper slopes and where surface/groundwater flows are prevalent. As a result,
recommendations have been provided in this report to manage the risk of slope instability.
6.2 Stability Risk Assessment
A qualitative slope stability risk assessment has been carried out following the Australian Geomechanics
Society (AGS) Guidelines for Landslide Risk Management (March 2007). The risk assessment relates to
property and potential development. Relative levels of risk and their implications are given in Table 1 below
and the qualitative terminology (i.e. likelihood and consequence definitions) used in assessing risk to
property are attached in Appendix B.
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Table 1: Stability Risk Levels
Risk Level Example Implications(1)
Unacceptable without treatment. Extensive detailed investigation and research, planning
VH VERY HIGH RISK and implementation of treatment options essential to reduce risk to Low; may be too
expensive and not practical. Work likely to cost more than value of property.
Unacceptable without treatment. Detailed investigation, planning and implementation of
H HIGH RISK treatment options required to reduce risk to Low. Work would cost a substantial sum in
relation to the value of the property.
May be tolerated in certain circumstances (subject to regulators’ approval) but requires
M MODERATE RISK investigation, planning and implementation of treatment options to reduce risk to Low.
Treatment options to reduce to Low risk should be implemented as soon as practicable.
L LOW RISK Usually acceptable to regulators. Where treatment has been required to reduce the risk
to this level, ongoing maintenance required.
VL VERY LOW RISK Acceptable. Manage by normal slope maintenance procedures.
Note: (1) The implications for a particular situation are to be determined by all parties to the risk assessment and may depend on the
nature of the property at risk; these are only given as a general guide.
The risk assessment essentially involves combining the elements of ‘Likelihood’ and ‘Consequence’ for the
potential hazards identified across the proposed development area in a qualitative manner. Relative levels of
risk and their implications are given in Table 2. It should be noted that the stability assessment above relates
to the global stability of the site. Our assessment does not include temporary/long-term stability of cut
excavations or permanent structural elements which are to be engineer-designed.
Table 2: Qualitative Risk Assessment for Property (Based on AGS 2007).
Assessed
Hazard Likelihood Consequence Comments
Risk
Shallow failure Shallow slope instability as noted in the existing
through landslides will have Insignificant impact on the residence
Likely Insignificant Low
colluvium/ provided that the recommendations in this report are
residual soils implemented
Failure
The likelihood of a deep failure through the residual soil
through
and weathered rock is assessed as Unlikely due to the
residual soil /
apparent absence of deep-seated failures in this area,
weathered
Unlikely Medium Low as well as the relatively low slope angles at the proposed
rock below the
residence and favourable discontinuity angles
residential
encountered in the test pits relative to the proposed
footings or
earthworks
retaining walls
Refer Appendix B, Qualitative Risk Analysis Matrix (Australian Geomechanics Vol 42 No 1 March 2007).
Based on our assessment, it is our opinion that there is a Low Risk of global instability of the proposed
development, provided that the recommendations in this report are implemented. This level of risk is
normally acceptable to regulators.
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7.0 DEVELOPMENT IMPACTS & MITIGATION MEASURES
It is our opinion that this site is suitable for the proposed development, from a geotechnical viewpoint, subject
to implementation of the recommendations provided in this report. The potential impacts on slope stability of
the proposed development have been considered, and the measures recommended below have been
designed to mitigate those impacts. Building development should follow normal slope maintenance
procedures and the document ‘General Guidelines for Hillside Construction’, which is attached in
Appendix C.
7.1 Earthworks
Earthworks should be carried out in accordance with Australian Standard AS 3798-2007 Guidelines on
earthworks for commercial and residential developments.
7.1.1 Site Preparation & Trafficability
Site preparation in building and pavement areas should include the following:
Strip the surface of vegetation, organic matter, organic rich soils (topsoils) and severely root affected
soils.
‘Proof roll’ the stripped surface by several passes of a minimum 8 tonne roller to identify loose or soft
areas.
Loose/soft areas identified by proof rolling and/or inspection will require treatment by either of the following
methods:
Over-excavation and replacement with suitable fill compacted in layers (refer Section 7.1.4); or
Re-compaction of the loose or soft material provided that it does not contain substantial organic
matter or deleterious substances.
At the time of the investigation the site was trafficable in a 4WD vehicle. However, following stripping of
topsoil materials, trafficability issues should be anticipated following rainfall. Due to the potential for poor
trafficability, it would be prudent to allow for the placement of a compacted granular fill layer particularly in
access road and laydown areas. A geotextile separation layer between the natural ground and granular fill
may also be required.
Site drainage should also be implemented during construction to prevent saturation of subgrade soils and
batters, with erosion protection provided.
7.1.2 Excavatibility
Excavations into the colluvium, residual soil, or extremely weathered material should be achievable using
conventional small to large earthmoving equipment (i.e. 6 to 20 tonne excavators). Ripper attachments
and/or hydraulic breakers may be required in medium strength (or stronger) mudstone or excavations
beyond the test pit termination depths.
7.1.3 Re-use as Fill
Fill won from excavations on the site may be suitable for reuse as structural fill, provided that oversize
material is removed (e.g. cobbles/boulders in colluvium). The residual/colluvial clays may also be difficult to
handle or compact when wet, and will require careful moisture conditioning. Due to the proposed volume of
fill and the aforementioned issues, it may necessary to replace some/all excavation spoil with suitable
imported fill.
Any organic rich topsoil must not be used as fill to support structural loads, however it may be used in
landscaping areas.
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Ashley and Caroline Hermes 7.1.4 Batter Slopes Any disturbance to natural slopes greater than about 25 degrees are not recommended, and existing slopes on the site should not be steepened due to the potential for slope instability. Cut batters must be inspected by a geotechnical RPEQ at the commencement of excavation, to assess slope stability. For short-term construction periods, excavated unsurcharged faces could be battered at 1V:1H in the natural stiff (or stiffer) clay soils and weathered rock. Shoring will be required to enable personnel entry into near vertical sided trenches deeper than 1 m. Flatter batters may be required if significant groundwater seepage is encountered or if exposed faces are not protected from erosion by rainfall. Permanent batters should not be steeper than 1V:2H to 1V:3H in the natural stiff (or stiffer) clays. Batters that are to be revegetated with lawn should be 1V:4H or less for maintenance (e.g. mowing). Batters in extremely weathered (or fresher) rock may be constructed at 1V:1H. Positive support by engineer-designed retaining structures will be required where space restrictions prevent trimming of batters to safe slopes and where slopes are surcharged or near movement sensitive structures. Batters must be protected from erosion (e.g. through revegetation or hard surfacing). 7.1.5 Soil Dispersion & Erosion Protection Any excavations or disturbance of soil should be carefully monitored and managed during the construction phase to minimise potential for scour/erosion and sediment run off. Exposed soil (i.e. on batters or drains etc.) must be protected from erosion by appropriate measures such as re-vegetation and hydro-seeding, protective matting, geotextiles or hard facings. Temporary sediment control should be adopted during construction where surface water will flow offsite. Concentrating surface runoff should be avoided unless adequate erosion protection and flow dissipation is constructed. Erosion can lead to or exacerbate slope instability, and must be carefully managed/avoided on this site. 7.1.6 Filling and Compaction Fill should be ‘benched’ into slopes following the above site preparation. Fill should be compacted at moisture contents within the range of -/+ 2% of optimum moisture content for Standard Compaction. Confirmatory testing must be carried out at regular intervals. A minimum of two tests per 300 mm vertical interval is recommended where structural fill heights are to exceed 300 mm. Further details for control and testing of fill are given in Australian Standard AS 3798-2007. Select fill should have a maximum particle size of 75 mm for an uncompacted layer thickness of 200 mm and shall be compacted by repeated rolling to achieve a dry density ratio of at least 95% of the Maximum Standard Dry Density for cohesive soils, or 70% Dry Density Index for cohesionless soils. In accordance with good construction practice, fill embankments should be ‘over built’ and then trimmed back to the well compacted material. Fill embankments that exceed 1 m in vertical height should be retained using engineer designed retaining structures (refer Section 7.2) if the batter slopes recommended in Section 7.1.4 cannot be achieved. 7.2 Retaining Structures It is recommended that the proposed upper tier retaining wall is moved further upslope to avoid interaction with the lower tier retaining wall, and to remove proposed steepening of the natural slope. Retaining walls must be founded as described in Section 7.4, and designed by a structural RPEQ (including global stability analyses). Design for retaining structures could be carried out using a triangular pressure distribution applicable to the wall type and based on the parameters listed in Table 3. The values in Table 3 assume that the walls are J001783-001-R-Rev1
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Ashley and Caroline Hermes
fully drained and no allowance is included below for construction loading, up-slope footing loadings, and
backfill compaction stresses.
If appropriate, an allowance of 10 kPa should be made for lateral stress induced by compaction plant
operating behind the walls. The effects of surcharge should be included by multiplying the vertical pressure
developed by the surcharge by the appropriate lateral earth pressure coefficient from Table 3. Allowance
should be made for additional surcharge on the wall caused by sloping backfill or natural soil slopes.
Positive permanent drainage (surface and subsoil) must be installed behind retaining walls to prevent the
development of hydrostatic pressures. Drainage material behind the wall should be installed for the full
height of the wall, for a width of at least 0.3 m. The material must be free draining and granular and have a
perforated or slotted drainage pipe at the heel of the wall to rapidly remove the water into the stormwater
system. Drainage outlets must extend beyond the ends of the walls. Installation and maintenance of
drainage will be important to reduce the risk of slope instability on this site.
Retaining wall backfill should be a loose, free draining granular material and should only be lightly
compacted as heavy compaction may raise the earth pressure to above the ‘at rest’ earth pressure. A
geotextile to prevent fine grained soil from migrating into the free draining backfill is also recommended.
Table 3: Retaining structure design parameters.
Lateral earth pressure coefficient
Non-
Yielding
yielding
Unit
Retained Cohesion,
weight Ka (cantilever)
material cu (kPa)
(t/m3)
Angle of retained slope (o) Kp Ko
0 10 20 30
Stiff clay 1.8 50 0.41 0.42 0.51 - 2.46 0.58
Very Stiff
to Hard 1.9 100 0.36 0.37 0.43 - 2.77 0.53
Clay
Very Low
Strength 2.0 200 0.18 0.18 0.19 0.21 5.6 0.3
Mudstone
7.3 Site Classification
The site classification derived in accordance with Australian Standard AS 2870-2011 Residential slabs and
footings can provide an indication of the likely magnitude of reactive (shrink and swell) movements
associated with normal seasonal soil moisture variations.
Based on the results of the investigation, the soil reactivity is within the range of Class M, with an estimated
‘ys’ value in the range of up to 20 mm to 40 mm.
The predicted order of movement is based on the existing soil profile (i.e. no cutting or additional filling), and
moisture content changes within soils due to normal seasonal moisture variations only (i.e. does not consider
soil settlement).
7.4 High Level Footings
The proposed residence and all retaining wall footings should be founded at least 0.5 m into the very low
strength (or stronger) mudstone.
For high-level footings, a design allowable bearing pressure of 500 kPa may be adopted.
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Where high-level footings are not viable, bored piles may be adopted.
Table 4 shows representative values of ultimate (unfactored) geotechnical parameters for pile design. A
sensitivity analysis should be undertaken to assess effects for the range of parameters. Settlement of the
piled footings is expected to be in the order of 1% of the pile width/diameter. Detailed design should be
carried out by the piling contractor.
Ultimate geotechnical capacities (Rdug) determined from the parameters provided must be multiplied by a
geotechnical strength reduction factor (øg) in accordance with Section 4 of AS 2159-2009 Piling – Design
and installation to determine the design geotechnical strength (Rdg). The geotechnical strength reduction
factor should be determined in accordance with AS 2159-2009 and is expected to be in the range of 0.45 to
0.55. An upper bound value may be adopted if supervision and certification of pile construction is carried out
by a geotechnical engineer.
The soils to a depth 1.5 times the pile diameter below the excavated surface should be ignored in the
assessment of lateral capacity. The lateral capacity of piles may be determined using various methods, and
which generally require an estimation of the Young’s modulus (Es) of the founding stratum.
Table 4: Pile design values.
Unit weight Elastic Ultimate Ultimate
Ƴ (kN/m3) Modulus skin base
Material type
(MPa) friction resistance
(kPa) (kPa)
Stiff clay 18 8 - 20 20 NR
Very stiff clay 19 15 - 40 40 NR
Hard clay 19 40 - 70 80 NR
Very low strength
20 50 - 250 100 3000
mudstone
Notes:
1) NR – Not recommended
2) Skin friction should be discounted for sections of pile shafts where liners are in place.
3) Indicative values taken from published paper, Site Characterisation, Terence Wiesner, Australian
Geomechanics – Dec 1999 and ‘Foundation Analysis & Design (Bowles, 4th Edition)
To achieve the recommended design values, founding materials must be dry and cleaned of any loose,
disturbed or saturated materials prior to pouring concrete. Footing excavations should be inspected by an
geotechnical RPEQ to confirm the foundation material.
If any soil conditions encountered during the footing excavations are found to differ from those noted in the
geotechnical investigation, an inspection of the footing excavations should be carried out by a geotechnical
RPEQ to assess if changes to footing design are required.
All proposed footings should found such that they are not adversely affected by any adjacent excavations,
batter slopes, trenches, or retaining walls that are not designed to support building or fill loads.
To minimise the potential for any adverse interaction effects, footings should found at least below a plane
extending 1 m horizontally from the base of trenches/batter slopes/excavations/ retaining walls, then rising
up at 1V:1H. This requirement is illustrated in the following diagram.
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Ashley and Caroline Hermes 7.5 Drainage Site drainage should be designed to readily remove surface water, minimise water infiltration into the slope, and to prevent ponding of water on subgrade areas during construction and also adjacent to foundations, perimeter slabs, and driveways once construction is completed. Roof water, including overflow from rainwater tanks, and water collected from hard surfaces (e.g. driveways) must be directed by pipes or lined channels to an engineer-designed point of discharge. Shallow subsurface cut-off drains should be installed upslope of building areas in order to intercept and divert potential subsurface seepage. Diversion drains (mounds) should be constructed above the crest of any cut or fill embankments. Implementation and maintenance of appropriate site drainage will be important to manage the risk of slope instability at this site. 7.6 General Foundation Maintenance The CSIRO document Foundation maintenance and footing performance: A Homeowner’s Guide (2003) is attached in Appendix D for your information. This advice should be considered in the construction and maintenance of the proposed development. 8.0 SUMMARY AND CONCLUSIONS From a geotechnical viewpoint, the site is suitable for the proposed development subject to the implementation of the recommendations in this report. 9.0 LIMITATIONS Your attention is drawn to the document, Limitations which is attached in Appendix E. J001783-001-R-Rev1
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Ashley and Caroline Hermes Core Consultants Pty Ltd Yours sincerely, Mitchell Dakin Walter Mastenbroek BEng(Civil)(Hons) UniSC MEngPr MSc BSc (Hons) MIEAust CPEng NER RPEQ 16149 Geotechnical Engineer Director/Principal Geotechnical Engineer MD/WM/DQ/md/wm A.B.N. 75 603 384 050 J001783-001-R-Rev1
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© CORE CONSULTANTS PTY. LTD. INFORMATION CONTAINED ON THIS DRAWING IS THE COPYRIGHT OF CORE CONSULTANTS PTY. LTD. UNAUTHORISED USE OR REPRODUCTION OF THIS PLAN EITHER WHOLLY OR IN PART WITHOUT WRITTEN PERMISSION INFRINGES COPYRIGHT.
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Esri Community Maps Contributors, Department of Resources, Dept.of Environment and Science, Geoscape, Esri, HERE, Garmin, Foursquare, METI/NASA, USGS 1:550
486060 486080 486100 486120 486140 486160 486180 486200 486220 486240
EASTING (m)
Legend
CLIENT PROJECT
{
}
v
x Approximate Test Pit Location 1 m Contour Lines (Department of Resources) K ARCHITECTURE PROPOSED RESIDENCE: 317 LAWNVILLE ROAD, BLACK MOUNTAIN
DRAWN BY DATE DRAWING TITLE
Approximate Slope Angle and Direction
MD 21/02/2023
GEOTECHNICAL TEST LOCATION PLAN
Enscarpment CHECKED BY DATE
WM 21/02/2023
SCALE SHEET SIZE PROJECT No DOC No DOC TYPE FIGURE No REVISION
Base plan drawn by K Architecture. Drawing Title - Ground Floor Plan. Drawing No. - SK.03. Dated 18 November 2022. Aerial
image sourced from Nearmap Pty Ltd, image dated 14 August 2022. Annotations by Core Consultants Pty Ltd.
www.coreconsultants.com.au 1:550 A3 J001783 001 R F001 1 SHEET 1 OF 1
Plot Date: 21 February 2023 Time: 11:31 AM By: CAD Path: J:\2022 - J1479\J001783 - KAchitecture-Residence-Lawnville Rd\PHASE 1000\Figures Drawings\J001783-GIS\J001783.aprx
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Ashley and Caroline Hermes Appendix A Reports of Test Pits, DCP’s and Explanatory Notes J001783-001-R-Rev1
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REPORT OF TEST PIT: TP1
East 486138.0 m Sheet 1 OF 1
Client K Architecture North 7075807.0 m MGA94 Zone 56 Logged: MD
Project Proposed Residence Contractor Aussie Enviro Excavations Logged Date: 21/12/22
Location 317 Lawnville Road, Black Mountain Machine 5.5 t excavator Checked:
Job No. J001783 Bucket Size 450 mm toothed Checked Date:
Excavation Sampling Field Material Description
GROUP SYMBOL
CONSISTENCY
RECOVERED
DCP TEST
EXCAVATION
RESISTANCE
CONDITION
MOISTURE
SAMPLE OR
GRAPHIC
METHOD
DENSITY
SOIL/ROCK MATERIAL DESCRIPTION Blows per 100 mm
(metres)
WATER
FIELD TEST
DEPTH
LOG
DEPTH 0 5 10 15 20 25
RL
0
CL- TOPSOIL Silty Sandy CLAY with gravel: low to medium F/
CI plasticity, dark grey brown; sand fine to coarse grained; gravel St
0.20
fine to coarse grained, sub-angular; organics and rootlets.
0.20-0.60 m CI
PP =350 kPa Gravelly Sandy CLAY (COLLUVIUM) with silt: medium St /
plasticity, brown and grey brown; sand fine to coarse grained; VSt
L-M gravel fine to coarse grained, sub-angular; frequent cobbles
0.60 and boulders up to 250 mm in diameter, occasional organics. w<
EX
0.60-0.90 m CI- Silty CLAY (RESIDUAL SOIL) with gravel with sand: medium PL
St
Not Encountered
PP =380 kPa CH to high plasticity, grey brown and grey; gravel fine to coarse
grained, sub-angular; sand fine to coarse grained.
0.90 VSt
1.00 0.90-1.20 m Tending to extremely weathered material.
1 PP =450 kPa
M CL- Silty CLAY (EXTREMELY WEATHERED MATERIAL) trace H
CI sand: low to medium plasticity, pale grey brown and brown;
1.20
sand fine to coarse grained; lenses of low strength mudstone.
MUDSTONE: pale grey brown and brown, low to medium
1.40
strength, highly weathered, possibly metamorphic in parts,
H thinly laminated, dipping at approximately 30-50 degrees D
R
northeast.
Tending to medium strength.
1.80
Hole Terminated at 1.80 m
Practical Bucket Refusal on inferred medium strength
2 Mudstone
Backfilled
CORE 2.01.1 LIB.GLB Log IS AU TEST PIT 3 J1783-K ARCHITECHTURE-TP1-2-DCP-1-2.GPJ <<DrawingFile>> 2/2/2023 08:30 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Core 2.01.1 2020-05-19 Prj: Core 2.00 2020-03-24
3
Sketch & Other Observations
This report must be read in conjunction with accompanying notes and abbreviations. It has been prepared for geotechnical
purposes only, without attempt to consider possible contamination. Any references to potential contamination are for information
only and do not necessarily indicate the presence or absence of soil or groundwater contamination.
Page 20
REPORT OF TEST PIT: TP2
East 486164.0 m Sheet 1 OF 1
Client K Architecture North 7075813.0 m MGA94 Zone 56 Logged: MD
Project Proposed Residence Contractor Aussie Enviro Excavations Logged Date: 21/12/22
Location 317 Lawnville Road, Black Mountain Machine 5.5 t excavator Checked:
Job No. J001783 Bucket Size 450 mm toothed Checked Date:
Excavation Sampling Field Material Description
GROUP SYMBOL
CONSISTENCY
RECOVERED
DCP TEST
EXCAVATION
RESISTANCE
CONDITION
MOISTURE
SAMPLE OR
GRAPHIC
METHOD
DENSITY
SOIL/ROCK MATERIAL DESCRIPTION Blows per 100 mm
(metres)
WATER
FIELD TEST
DEPTH
LOG
DEPTH 0 5 10 15 20 25
RL
0
CL- TOPSOIL Silty Sandy CLAY trace gravel: low to medium F
L CI plasticity, dark grey brown; sand fine to coarse grained; gravel
0.20
fine to coarse grained, sub-angular; organics and rootlets.
U50 0.20-0.70 m CI-
PP = 450 kPa CH Silty CLAY (RESIDUAL SOIL) with sand: medium to high
0.30-0.90 m plasticity, pale grey brown and yellow brown; sand fine to
PP =400-450 kPa medium grained. F/
St
Not Encountered
w<
EX
1 St
PL
M
VSt
1.60
CL- Silty CLAY trace sand: low to medium plasticity, pale brown,
CI pale grey and brown; sand fine to medium grained; zones of VSt /
very low strength, thinly laminated mudstone, tending to H
extremely weathered material in parts.
2.00
2
MUDSTONE: pale grey brown and brown, very low strength,
M-H D
R
highly weathered, thinly laminated, dipping at approximately
CORE 2.01.1 LIB.GLB Log IS AU TEST PIT 3 J1783-K ARCHITECHTURE-TP1-2-DCP-1-2.GPJ <<DrawingFile>> 2/2/2023 08:30 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Core 2.01.1 2020-05-19 Prj: Core 2.00 2020-03-24
2.20
30-50 degrees northeast.
Hole Terminated at 2.20 m
Practical Bucket Refusal on inferred very low to low strength
Mudstone
Backfilled
3
Sketch & Other Observations
This report must be read in conjunction with accompanying notes and abbreviations. It has been prepared for geotechnical
purposes only, without attempt to consider possible contamination. Any references to potential contamination are for information
only and do not necessarily indicate the presence or absence of soil or groundwater contamination.
Page 21
CLIENT : K Architecture SHEET : 1 OF 1
CONTRACTOR : Core Consultants Pty Ltd
PROJECT : Proposed Residence
LOCATION : 317 Lawnville Road, Black Mountain
PROJECT No. : J001783
TEST: DCP1 TEST: DCP2
LOGGED: MD 21/12/2022 LOGGED: MD 21/12/2022
EASTING: 486153.0 m NORTHING: 7075824.0 m EASTING: 486161.0 m NORTHING: 7075797.0 m
MGA94 Zone 56 MGA94 Zone 56
Depth (m)
Depth (m)
Blows per 100 mm Blows per 100 mm
0 5 10 15 20 25 0 5 10 15 20 25
0.5 0.5
1.0 1.0
CORE 2.01.1 LIB.GLB Log IS DCP 3 PER PAGE J1783-K ARCHITECHTURE-TP1-2-DCP-1-2.GPJ <<DrawingFile>> 2/2/2023 08:24 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Core 2.01.1 2020-05-19 Prj: Core 2.00 2020-03-24
1.5 1.5
2.0 2.0
2.5 2.5
3.0 3.0
Comments Comments
Page 22
Ashley and Caroline Hermes Appendix B Qualitative Risk Analysis Matrix (Australian Geomechanics Vol 42 No 1 March 2007) J001783-001-R-Rev1
Page 23
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX C: LANDSLIDE RISK ASSESSMENT
QUALITATIVE TERMINOLOGY FOR USE IN ASSESSING RISK TO PROPERTY
QUALITATIVE MEASURES OF LIKELIHOOD
Approximate Annual Probability
Implied Indicative Landslide
Description Descriptor Level
Indicative Notional Recurrence Interval
Value Boundary
10-1 5x10-2
10 years The event is expected to occur over the design life. ALMOST CERTAIN A
20 years The event will probably occur under adverse conditions over the
-2
10 100 years
design life.
LIKELY B
-3
-3 5x10 200 years
10 1000 years The event could occur under adverse conditions over the design life. POSSIBLE C
5x10-4 2000 years
The event might occur under very adverse circumstances over the
10-4 10,000 years
design life.
UNLIKELY D
-5 5x10-5 20,000 years
10 The event is conceivable but only under exceptional circumstances
100,000 years RARE E
over the design life.
-6 5x10-6 200,000 years
10 1,000,000 years The event is inconceivable or fanciful over the design life. BARELY CREDIBLE F
Note: (1) The table should be used from left to right; use Approximate Annual Probability or Description to assign Descriptor, not vice versa.
QUALITATIVE MEASURES OF CONSEQUENCES TO PROPERTY
Approximate Cost of Damage
Description Descriptor Level
Indicative Notional
Value Boundary
Structure(s) completely destroyed and/or large scale damage requiring major engineering works for
200% CATASTROPHIC 1
stabilisation. Could cause at least one adjacent property major consequence damage.
100%
Extensive damage to most of structure, and/or extending beyond site boundaries requiring significant
60% MAJOR 2
stabilisation works. Could cause at least one adjacent property medium consequence damage.
40%
Moderate damage to some of structure, and/or significant part of site requiring large stabilisation works.
20% MEDIUM 3
Could cause at least one adjacent property minor consequence damage.
10%
5% 1% Limited damage to part of structure, and/or part of site requiring some reinstatement stabilisation works. MINOR 4
Little damage. (Note for high probability event (Almost Certain), this category may be subdivided at a
0.5% INSIGNIFICANT 5
notional boundary of 0.1%. See Risk Matrix.)
Notes: (2) The Approximate Cost of Damage is expressed as a percentage of market value, being the cost of the improved value of the unaffected property which includes the land plus the
unaffected structures.
(3) The Approximate Cost is to be an estimate of the direct cost of the damage, such as the cost of reinstatement of the damaged portion of the property (land plus structures), stabilisation
works required to render the site to tolerable risk level for the landslide which has occurred and professional design fees, and consequential costs such as legal fees, temporary
accommodation. It does not include additional stabilisation works to address other landslides which may affect the property.
(4) The table should be used from left to right; use Approximate Cost of Damage or Description to assign Descriptor, not vice versa
91 Australian Geomechanics Vol 42 No 1 March 2007
Page 24
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX C: – QUALITATIVE TERMINOLOGY FOR USE IN ASSESSING RISK TO PROPERTY (CONTINUED)
QUALITATIVE RISK ANALYSIS MATRIX – LEVEL OF RISK TO PROPERTY
LIKELIHOOD CONSEQUENCES TO PROPERTY (With Indicative Approximate Cost of Damage)
Indicative Value of 1: CATASTROPHIC 2: MAJOR 3: MEDIUM 4: MINOR 5:
Approximate Annual 200% 60% 20% 5% INSIGNIFICANT
Probability 0.5%
A – ALMOST CERTAIN 10-1 VH VH VH H M or L (5)
-2
B - LIKELY 10 VH VH H M L
C - POSSIBLE 10-3 VH H M M VL
D - UNLIKELY 10-4 H M L L VL
-5
E - RARE 10 M L L VL VL
-6
F - BARELY CREDIBLE 10 L VL VL VL VL
Notes: (5) For Cell A5, may be subdivided such that a consequence of less than 0.1% is Low Risk.
(6) When considering a risk assessment it must be clearly stated whether it is for existing conditions or with risk control measures which may not be implemented at the current
time.
RISK LEVEL IMPLICATIONS
Risk Level Example Implications (7)
Unacceptable without treatment. Extensive detailed investigation and research, planning and implementation of treatment
VH VERY HIGH RISK options essential to reduce risk to Low; may be too expensive and not practical. Work likely to cost more than value of the
property.
Unacceptable without treatment. Detailed investigation, planning and implementation of treatment options required to reduce
H HIGH RISK
risk to Low. Work would cost a substantial sum in relation to the value of the property.
May be tolerated in certain circumstances (subject to regulator’s approval) but requires investigation, planning and
M MODERATE RISK implementation of treatment options to reduce the risk to Low. Treatment options to reduce to Low risk should be
implemented as soon as practicable.
Usually acceptable to regulators. Where treatment has been required to reduce the risk to this level, ongoing maintenance is
L LOW RISK
required.
Acceptable. Manage by normal slope maintenance procedures.
VL VERY LOW RISK
Note: (7) The implications for a particular situation are to be determined by all parties to the risk assessment and may depend on the nature of the property at risk; these are only
given as a general guide.
92 Australian Geomechanics Vol 42 No 1 March 2007
Page 25
Ashley and Caroline Hermes Appendix C General Guidelines for Hillside Construction J001783-001-R-Rev1
Page 26
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX G - SOME GUIDELINES FOR HILLSIDE CONSTRUCTION
GOOD ENGINEERING PRACTICE POOR ENGINEERING PRACTICE
ADVICE
GEOTECHNICAL Obtain advice from a qualified, experienced geotechnical practitioner at early Prepare detailed plan and start site works before
ASSESSMENT stage of planning and before site works. geotechnical advice.
PLANNING
SITE PLANNING Having obtained geotechnical advice, plan the development with the risk Plan development without regard for the Risk.
arising from the identified hazards and consequences in mind.
DESIGN AND CONSTRUCTION
Use flexible structures which incorporate properly designed brickwork, timber Floor plans which require extensive cutting and
or steel frames, timber or panel cladding. filling.
HOUSE DESIGN
Consider use of split levels. Movement intolerant structures.
Use decks for recreational areas where appropriate.
SITE CLEARING Retain natural vegetation wherever practicable. Indiscriminately clear the site.
ACCESS & Satisfy requirements below for cuts, fills, retaining walls and drainage. Excavate and fill for site access before
DRIVEWAYS Council specifications for grades may need to be modified. geotechnical advice.
Driveways and parking areas may need to be fully supported on piers.
EARTHWORKS Retain natural contours wherever possible. Indiscriminatory bulk earthworks.
Minimise depth. Large scale cuts and benching.
CUTS Support with engineered retaining walls or batter to appropriate slope. Unsupported cuts.
Provide drainage measures and erosion control. Ignore drainage requirements
Minimise height. Loose or poorly compacted fill, which if it fails,
Strip vegetation and topsoil and key into natural slopes prior to filling. may flow a considerable distance including
Use clean fill materials and compact to engineering standards. onto property below.
FILLS Batter to appropriate slope or support with engineered retaining wall. Block natural drainage lines.
Provide surface drainage and appropriate subsurface drainage. Fill over existing vegetation and topsoil.
Include stumps, trees, vegetation, topsoil,
boulders, building rubble etc in fill.
ROCK OUTCROPS Remove or stabilise boulders which may have unacceptable risk. Disturb or undercut detached blocks or
& BOULDERS Support rock faces where necessary. boulders.
Engineer design to resist applied soil and water forces. Construct a structurally inadequate wall such as
Found on rock where practicable. sandstone flagging, brick or unreinforced
RETAINING
Provide subsurface drainage within wall backfill and surface drainage on slope blockwork.
WALLS
above. Lack of subsurface drains and weepholes.
Construct wall as soon as possible after cut/fill operation.
Found within rock where practicable. Found on topsoil, loose fill, detached boulders
Use rows of piers or strip footings oriented up and down slope. or undercut cliffs.
FOOTINGS
Design for lateral creep pressures if necessary.
Backfill footing excavations to exclude ingress of surface water.
Engineer designed.
Support on piers to rock where practicable.
SWIMMING POOLS Provide with under-drainage and gravity drain outlet where practicable.
Design for high soil pressures which may develop on uphill side whilst there
may be little or no lateral support on downhill side.
DRAINAGE
Provide at tops of cut and fill slopes. Discharge at top of fills and cuts.
Discharge to street drainage or natural water courses. Allow water to pond on bench areas.
SURFACE Provide general falls to prevent blockage by siltation and incorporate silt traps.
Line to minimise infiltration and make flexible where possible.
Special structures to dissipate energy at changes of slope and/or direction.
Provide filter around subsurface drain. Discharge roof runoff into absorption trenches.
Provide drain behind retaining walls.
SUBSURFACE
Use flexible pipelines with access for maintenance.
Prevent inflow of surface water.
Usually requires pump-out or mains sewer systems; absorption trenches may Discharge sullage directly onto and into slopes.
SEPTIC &
be possible in some areas if risk is acceptable. Use absorption trenches without consideration
SULLAGE
Storage tanks should be water-tight and adequately founded. of landslide risk.
EROSION Control erosion as this may lead to instability. Failure to observe earthworks and drainage
CONTROL & Revegetate cleared area. recommendations when landscaping.
LANDSCAPING
DRAWINGS AND SITE VISITS DURING CONSTRUCTION
DRAWINGS Building Application drawings should be viewed by geotechnical consultant
SITE VISITS Site Visits by consultant may be appropriate during construction/
INSPECTION AND MAINTENANCE BY OWNER
OWNER’S Clean drainage systems; repair broken joints in drains and leaks in supply
RESPONSIBILITY pipes.
Where structural distress is evident see advice.
If seepage observed, determine causes or seek advice on consequences.
Australian Geomechanics Vol 42 No 1 March 2007 113
Page 27
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007 114 Australian Geomechanics Vol 42 No 1 March 2007
Page 28
Ashley and Caroline Hermes Appendix D CSIRO Foundation Maintenance Guidelines J001783-001-R-Rev1
Page 29
Foundation Maintenance
and Footing Performance: BTF 18-2011
A Homeowner’s Guide
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 Erosion
The types of soils usually present under the topsoil in land zoned for All soils are prone to erosion, but sandy soil is particularly susceptible
residential buildings can be split into two approximate groups – to being washed away. Even clay with a sand component of say 10%
granular and clay. Quite often, foundation soil is a mixture of both or more can suffer from erosion.
types. The general problems associated with soils having granular
content are usually caused by erosion. Clay soils are subject to Saturation
saturation and swell/shrink problems. 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
Classifications for a given area can generally be obtained by bearing capacity. To a lesser degree, sand is affected by saturation
application to the local authority, but these are sometimes unreliable because saturated sand may undergo a reduction in volume,
and if there is doubt, a geotechnical report should be commissioned. particularly imported sand fill for bedding and blinding layers.
As most buildings suffering movement problems are founded on clay However, this usually occurs as immediate settlement and should
soils, there is an emphasis on classification of soils according to the normally be the province of the builder.
amount of swell and shrinkage they experience with variations of
water content. The table below is Table 2.1 from AS 2870-2011, the Seasonal swelling and shrinkage of soil
Residential Slab and Footing Code. 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
Causes of Movement varies considerably between different clays, as does the degree of
Settlement due to construction decrease during the subsequent drying out caused by fair weather
There are two types of settlement that occur as a result of periods. Because of the low absorption and expulsion rate, this
construction: phenomenon will not usually be noticeable unless there are
• Immediate settlement occurs when a building is first placed prolonged rainy or dry periods, usually of weeks or months,
depending on the land and soil characteristics.
on its foundation soil, as a result of compaction of the soil under
the weight of the structure. The cohesive quality of clay soil The swelling of soil creates an upward force on the footings of the
mitigates against this, but granular (particularly sandy) soil is building, and shrinkage creates subsidence that takes away the
susceptible. support needed by the footing to retain equilibrium.
• Consolidation settlement is a feature of clay soil and may take
Shear failure
place because of the expulsion of moisture from the soil or because
This phenomenon occurs when the foundation soil does not have
of the soil’s lack of resistance to local compressive or shear stresses.
sufficient strength to support the weight of the footing. There are
This will usually take place during the first few months after two major post-construction causes:
construction, but has been known to take many years in
exceptional cases. • Significant load increase.
• Reduction of lateral support of the soil under the footing due to
These problems are the province of the builder and should be taken
erosion or excavation.
into consideration as part of the preparation of the site for
construction. Building Technology File 19 (BTF 19) deals with these In clay soil, shear failure can be caused by saturation of the soil
problems. adjacent to or under the footing.
GENERAL DEFINITIONS OF SITE CLASSES
Class Foundation
A Most sand and rock sites with little or no ground movement from moisture changes
S Slightly reactive clay sites, which may experience only slight ground movement from moisture changes
M Moderately reactive clay or silt sites, which may experience moderate ground movement from moisture changes
H1 Highly reactive clay sites, which may experience high ground movement from moisture changes
H2 Highly reactive clay sites, which may experience very high ground movement from moisture changes
E Extremely reactive sites, which may experience extreme ground movement from moisture changes
Notes
1. Where controlled fill has been used, the site may be classified A to E according to the type of fill used.
2. Filled sites. Class P is used for sites which include soft fills, such as clay or silt or loose sands; landslip; mine subsidence; collapsing soils; soil subject to erosion;
reactive sites subject to abnormal moisture conditions or sites which cannot be classified otherwise.
3. Where deep-seated moisture changes exist on sites at depths of 3 m or greater, further classification is needed for Classes M to E (M-D, H1-D, H2-D and E-D).
081203 BTF 18 3pp.indd 1 25/10/12 12:40:29
Page 30
Tree root growth
Trees can cause shrinkage and damage
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 Wall cracking
unevenly throughout the building’s foundation soil. Settlement due due to uneven
looting settlement
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 external footings. The doming is accentuated and cracking reduces
still. Erosion can undermine a footing that traverses the flow or can or disappears where it occurred because of dishing, but other cracks
create the conditions for shear failure by eroding soil adjacent to a open up. The roof lines may become convex.
footing that runs in the same direction as the flow.
Doming and dishing are also affected by weather in other ways. In
Saturation of clay foundation soil may occur where subfloor walls create areas where warm, wet summers and cooler dry winters prevail, water
a dam that makes water pond. It can also occur wherever there is a migration tends to be toward the interior and doming will be
source of water near footings in clay soil. This leads to a severe accentuated, whereas where summers are dry and winters are cold
reduction in the strength of the soil which may create local shear failure. and wet, migration tends to be toward the exterior and the
Seasonal swelling and shrinkage of clay soil affects the perimeter of underlying propensity is toward dishing.
the building first, then gradually spreads to the interior. The swelling
process will usually begin at the uphill extreme of the building, or on Movement caused by tree roots
the weather side where the land is flat. Swelling gradually reaches the In general, growing roots will exert an upward pressure on footings,
interior soil as absorption continues. Shrinkage usually begins where whereas soil subject to drying because of tree or shrub roots will tend
the sun’s heat is greatest. to remove support from under footings by inducing shrinkage.
Effects of Uneven Soil Movement on Structures Complications caused by the structure itself
Most forces that the soil causes to be exerted on structures are
Erosion and saturation vertical – i.e. either up or down. However, because these forces are
Erosion removes the support from under footings, tending to create seldom spread evenly around the footings, and because the building
subsidence of the part of the structure under which it occurs. resists uneven movement because of its rigidity, forces are exerted
Brickwork walls will resist the stress created by this removal of from one part of the building to another. The net result of all these
support by bridging the gap or cantilevering until the bricks or the forces is usually rotational. This resultant force often complicates the
mortar bedding fail. Older masonry has little resistance. Evidence of diagnosis because the visible symptoms do not simply reflect the
failure varies according to circumstances and symptoms may include: original cause. A common symptom is binding of doors on the
• Step cracking in the mortar beds in the body of the wall or above/ vertical member of the frame.
below openings such as doors or windows.
• Vertical cracking in the bricks (usually but not necessarily in line Effects on full masonry structures
with the vertical beds or perpends). Brickwork will resist cracking where it can. It will attempt to span
areas that lose support because of subsided foundations or raised
Isolated piers affected by erosion or saturation of foundations will points. It is therefore usual to see cracking at weak points, such as
eventually lose contact with the bearers they support and may tilt or openings for windows or doors.
fall over. The floors that have lost this support will become bouncy,
In the event of construction settlement, cracking will usually remain
sometimes rattling ornaments etc.
unchanged after the process of settlement has ceased.
Seasonal swelling/shrinkage in clay With local shear or erosion, cracking will usually continue to develop
Swelling foundation soil due to rainy periods first lifts the most exposed until the original cause has been remedied, or until the subsidence
extremities of the footing system, then the remainder of the perimeter has completely neutralised the affected portion of footing and the
footings while gradually permeating inside the building footprint to lift structure has stabilised on other footings that remain effective.
internal footings. This swelling first tends to create a dish effect, In the case of swell/shrink effects, the brickwork will in some cases
because the external footings are pushed higher than the internal ones. return to its original position after completion of a cycle, however it
The first noticeable symptom may be that the floor appears slightly is more likely that the rotational effect will not be exactly reversed,
dished. This is often accompanied by some doors binding on the and it is also usual that brickwork will settle in its new position and
floor or the door head, together with some cracking of cornice will resist the forces trying to return it to its original position. This
mitres. In buildings with timber flooring supported by bearers and means that in a case where swelling takes place after construction
joists, the floor can be bouncy. Externally there may be visible and cracking occurs, the cracking is likely to at least partly remain
dishing of the hip or ridge lines. after the shrink segment of the cycle is complete. Thus, each time the
As the moisture absorption process completes its journey to the cycle is repeated, the likelihood is that the cracking will become
innermost areas of the building, the internal footings will rise. If the wider until the sections of brickwork become virtually independent.
spread of moisture is roughly even, it may be that the symptoms will With repeated cycles, once the cracking is established, if there is no
temporarily disappear, but it is more likely that swelling will be other complication, it is normal for the incidence of cracking to
uneven, creating a difference rather than a disappearance in stabilise, as the building has the articulation it needs to cope with the
symptoms. In buildings with timber flooring supported by bearers problem. This is by no means always the case, however, and monitoring
and joists, the isolated piers will rise more easily than the strip of cracks in walls and floors should always be treated seriously.
footings or piers under walls, creating noticeable doming of flooring. Upheaval caused by growth of tree roots under footings is not a
As the weather pattern changes and the soil begins to dry out, the simple vertical shear stress. There is a tendency for the root to also
external footings will be first affected, beginning with the locations exert lateral forces that attempt to separate sections of brickwork
where the sun’s effect is strongest. This has the effect of lowering the after initial cracking has occurred.
081203 BTF 18 3pp.indd 2 25/10/12 12:40:49
Page 31
The normal structural arrangement is that the inner leaf of • Corroded guttering or downpipes can spill water to ground.
brickwork in the external walls and at least some of the internal walls • Downpipes not positively connected to a proper stormwater
(depending on the roof type) comprise the load-bearing structure on collection system will direct a concentration of water to soil that is
which any upper floors, ceilings and the roof are supported. In these directly adjacent to footings, sometimes causing large-scale
cases, it is internally visible cracking that should be the main focus of problems such as erosion, saturation and migration of water under
attention, however there are a few examples of dwellings whose the building.
external leaf of masonry plays some supporting role, so this should be
checked if there is any doubt. In any case, externally visible cracking Seriousness of 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 In general, most cracking found in masonry walls is a cosmetic
supporting themselves. nuisance only and can be kept in repair or even ignored. The table
below is a reproduction of Table C1 of AS 2870-2011.
Effects on framed structures AS 2870-2011 also publishes figures relating to cracking in concrete
Timber or steel framed buildings are less likely to exhibit cracking due floors, however because wall cracking will usually reach the critical
to swell/shrink than masonry buildings because of their flexibility. point significantly earlier than cracking in slabs, this table is not
Also, the doming/dishing effects tend to be lower because of the reproduced here.
lighter weight of walls. The main risks to framed buildings are
encountered because of the isolated pier footings used under walls. Prevention/Cure
Where erosion or saturation causes a footing to fall away, this can
double the span which a wall must bridge. This additional stress can Plumbing
create cracking in wall linings, particularly where there is a weak Where building movement is caused by water service, roof
point in the structure caused by a door or window opening. It is, plumbing, sewer or stormwater failure, the remedy is to repair the
however, unlikely that framed structures will be so stressed as to suffer problem. It is prudent, however, to consider also rerouting pipes
serious damage without first exhibiting some or all of the above away from the building where possible, and relocating taps to
symptoms for a considerable period. The same warning period should positions where any leakage will not direct water to the building
apply in the case of upheaval. It should be noted, however, that where vicinity. Even where gully traps are present, there is sometimes
framed buildings are supported by strip footings there is only one leaf sufficient spill to create erosion or saturation, particularly in modern
of brickwork and therefore the externally visible walls are the installations using smaller diameter PVC fixtures. Indeed, some
supporting structure for the building. In this case, the subfloor gully traps are not situated directly under the taps that are installed
masonry walls can be expected to behave as full brickwork walls. 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
Effects on brick veneer structures been poorly backfilled, the water will either pond or flow along the
Because the load-bearing structure of a brick veneer building is the bottom of the trench. As these trenches usually run alongside the
frame that makes up the interior leaf of the external walls plus footings and can be at a similar depth, it is not hard to see how any
perhaps the internal walls, depending on the type of roof, the water that is thus directed into a trench can easily affect the
building can be expected to behave as a framed structure, except that foundation’s ability to support footings or even gain entry to the
the external masonry will behave in a similar way to the external leaf subfloor area.
of a full masonry structure.
Ground drainage
Water Service and Drainage In all soils there is the capacity for water to travel on the surface and
below it. Surface water flows can be established by inspection during
Where a water service pipe, a sewer or stormwater drainage pipe is in and after heavy or prolonged rain. If necessary, a grated drain system
the vicinity of a building, a water leak can cause erosion, swelling or connected to the stormwater collection system is usually an easy
saturation of susceptible soil. Even a minuscule leak can be enough to solution.
saturate a clay foundation. A leaking tap near a building can have the
same effect. In addition, trenches containing pipes can become It is, however, sometimes necessary when attempting to prevent water
watercourses even though backfilled, particularly where broken migration that testing be carried out to establish watertable height
rubble is used as fill. Water that runs along these trenches can be and subsoil water flows. This subject is referred to in BTF 19 and
responsible for serious erosion, interstrata seepage into subfloor areas may properly be regarded as an area for an expert consultant.
and saturation.
Protection of the building perimeter
Pipe leakage and trench water flows also encourage tree and shrub It is essential to remember that the soil that affects footings extends
roots to the source of water, complicating and exacerbating the well beyond the actual building line. Watering of garden plants,
problem. Poor roof plumbing can result in large volumes of rainwater shrubs and trees causes some of the most serious water problems.
being concentrated in a small area of soil:
For this reason, particularly where problems exist or are likely to
• Incorrect falls in roof guttering may result in overflows, as may occur, it is recommended that an apron of paving be installed around
gutters blocked with leaves etc. as much of the building perimeter as necessary. This paving should
CLASSIFICATION OF DAMAGE WITH REFERENCE TO WALLS
Approximate crack width Damage
Description of typical damage and required repair limit (see Note 3) category
Hairline cracks <0.1 mm 0
Fine cracks which do not need repair <1 mm 1
Cracks noticeable but easily filled. Doors and windows stick slightly. <5 mm 2
Cracks can be repaired and possibly a small amount of wall will need to be 5–15 mm (or a number of cracks 3
replaced. Doors and windows stick. Service pipes can fracture. Weathertightness 3 mm or more in one group)
often impaired.
Extensive repair work involving breaking-out and replacing sections of walls, 15–25 mm but also depends on 4
especially over doors and windows. Window and door frames distort. Walls lean number of cracks
or bulge noticeably, some loss of bearing in beams. Service pipes disrupted.
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Gardens for a reactive site
• 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 remove garden
beds to a completely safe distance from buildings.
Existing trees
Where a tree is causing a problem of soil drying or there is the
existence or threat of upheaval of footings, if the offending roots are
subsidiary and their removal will not significantly damage the tree,
they should be severed and a concrete or metal barrier placed
vertically in the soil to prevent future root growth in the direction of
the building. If it is not possible to remove the relevant roots without
damage to the tree, an application to remove the tree should be made
to the local authority. A prudent plan is to transplant likely offenders
before they become a problem.
Information on trees, plants and shrubs
State departments overseeing agriculture can give information
regarding root patterns, volume of water needed and safe distance
from buildings of most species. Botanic gardens are also sources of
extend outwards a minimum of 900 mm (more in highly reactive information. For information on plant roots and drains, see Building
soil) and should have a minimum fall away from the building of Technology File 17.
1:60. The finished paving should be no less than 100 mm below
brick vent bases. Excavation
Excavation around footings must be properly engineered. Soil
It is prudent to relocate drainage pipes away from this paving, if supporting footings can only be safely excavated at an angle that
possible, to avoid complications from future leakage. If this is not allows the soil under the footing to remain stable. This angle is called
practical, earthenware pipes should be replaced by PVC and the angle of repose (or friction) and varies significantly between soil
backfilling should be of the same soil type as the surrounding soil types and conditions. Removal of soil within the angle of repose will
and compacted to the same density. cause subsidence.
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 Remediation
the building – preferably not uphill from it (see BTF 19). Where erosion has occurred that has washed away soil adjacent to
It may be desirable to install a grated drain at the outside edge of the footings, soil of the same classification should be introduced and
paving on the uphill side of the building. If subsoil drainage is compacted to the same density. Where footings have been
needed this can be installed under the surface drain. undermined, augmentation or other specialist work may be required.
Remediation of footings and foundations is generally the realm of a
Condensation specialist consultant.
In buildings with a subfloor void such as where bearers and joists Where isolated footings rise and fall because of swell/shrink effect,
support flooring, insufficient ventilation creates ideal conditions for the homeowner may be tempted to alleviate floor bounce by filling
condensation, particularly where there is little clearance between the the gap that has appeared between the bearer and the pier with
floor and the ground. Condensation adds to the moisture already blocking. The danger here is that when the next swell segment of the
present in the subfloor and significantly slows the process of drying cycle occurs, the extra blocking will push the floor up into an
out. Installation of an adequate subfloor ventilation system, either accentuated dome and may also cause local shear failure in the soil. If
natural or mechanical, is desirable. it is necessary to use blocking, it should be by a pair of fine wedges
Warning: Although this Building Technology File deals with and monitoring should be carried out fortnightly.
cracking in buildings, it should be said that subfloor moisture can This BTF was prepared by John Lewer FAIB, MIAMA, Partner,
result in the development of other problems, notably: 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 treatment of the relevant subject.
Further professional advice needs to be obtained before taking any action based on the information provided.
Distributed by
CSIRO PUBLISHING PO Box 1139, Collingwood 3066, Australia
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
081203 BTF 18 3pp.indd 4 25/10/12 12:41:26
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Ashley and Caroline Hermes Appendix E Limitations J001783-001-R-Rev1
Page 34
LIMITATIONS This Document has been provided by Core Consultants Pty Ltd (“Core”) subject to the following limitations: This Document has been prepared for the particular purpose outlined in Core’s proposal and no responsibility is accepted for the use of this Document, in whole or in part, in other contexts or for any other purpose. The scope and the period of Core’s Services are as described in C o r e ’s proposal, and are subject to restrictions and limitations. Core did not perform a complete assessment of all possible conditions or circumstances that may exist at the site referenced in the Document. If a service is not expressly indicated, do not assume it has been provided. If a matter is not addressed, do not assume that any determination has been made by Core in regards to it. Conditions may exist which were undetectable given the limited nature of the enquiry Core was retained to undertake with respect to the site. Variations in conditions may occur between investigatory locations, and there may be special conditions pertaining to the site which have not been revealed by the investigation and which have not therefore been taken into account in the Document. Accordingly, additional studies and actions may be required. In addition, it is recognised that the passage of time affects the information and assessment provided in this Document. Core’s opinions are based upon information that existed at the time of the production of the Document. It is understood that the Services provided allowed Core to form no more than an opinion of the actual conditions of the site at the time the site was visited and cannot be used to assess the effect of any subsequent changes in the quality of the site, or its surroundings, or any laws or regulations. Any assessments made in this Document are based on the conditions indicated from published sources and the investigation described. No warranty is included, either express or implied, that the actual conditions will conform exactly to the assessments contained in this Document. Where data supplied by the client or other external sources, including previous site investigation data, have been used, it has been assumed that the information is correct unless otherwise stated. No responsibility is accepted by Core for incomplete or inaccurate data supplied by others. Core may have retained subconsultants affiliated with Core to provide Services for the benefit of Core. To the maximum extent allowed by law, the Client acknowledges and agrees it will not have any direct legal recourse to, and waives any claim, demand, or cause of action against, Core’s affiliated companies, and their employees, officers and directors. This Document is provided for sole use by the Client and is confidential to it and its professional advisers. No responsibility whatsoever for the contents of this Document will be accepted to any person other than the Client. Any use which a third party makes of this Document, or any reliance on or decisions to be made based on it, is the responsibility of such third parties. Core accepts no responsibility for damages, if any, suffered by any third party as a result of decisions made or actions based on this Document. Limitations Page 1 of 1 Date: 12/07/2018 FRM-065 Uncontrolled When Printed Issue: 1.02
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