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Geotechnical Investigation Report
E Ce. Geotechnical Investigation Report PTG/01059 - 0001 - RevO Proposed Residential Development 23 Bottlebrush Avenue, Noosa QLD 4567 6 May 2025 www.ptgconsulting.com.au
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REPORT DETAILS Unique Document Identification Document Title Geotechnical Investigation Report - Proposed Residential Development Project Number PTG/01059 Document ID PTG/01059 - 0001 - RevO Client JTJH Developments Pty Ltd Client Contact Cheri Hill PTG Office Details [oo Location Sunshine Coast Address U2/9-13 Matheson Street, Baringa, QLD, 4551 Telephone 1300 911 304 Email [email protected] Web www.ptgconsulting.com.au Revision Details RevO Document Approval Written By: Matthew Earle Engineering Geologist p [0448 844 926 e | [email protected] 06/05/2025 Issued to client Reviewed By: Justin Taing Regional Director - Geotechnical RPEQ 30087 p | 0447 316 857 e | [email protected]
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1 REPORT SCOPE
2 SITE DESCRIPTION
3 REGIONAL GEOLOGY
4 FIELD INVESTIGATION
5 GEOTECHNICAL MODEL
6 GEOTECHNICAL COMMENTS
EARTHWORKS ADVICE
6.1.1 SUBGRADE PREPARATION
6.1.2 FILLING
6.1.3 EXCAVATION CONDITIONS
6.1.4 SUITABILITY OF SITE WON MATERIAL
SITE CLASSIFICATION AND SITE MOVEMENTS
FOUNDATIONS
6.3.1 HIGH LEVEL FOUNDATIONS
6.3.2 PILED FOUNDATIONS
SAFE TEMPORARY AND PERMANENT BATTER SLOPES
RETAINING WALL PARAMETERS
BASEMENT CONSTRUCTION CONSIDERATIONS
LANDSLIDE RISK ASSESSMENT
7 LIMITATIONS
Table 1: Summary of Materials Encountered in Boreholes
Table 2: Allowable Bearing Pressures for High Level Footings
Table 3: Ultimate Geotechnical Design Parameters for Bored Piles
Table 4: Design Parameters for Temporary and Permanent Retaining Walls
Table 5: Summary of the Qualitative Slope Risk Assessment
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1 REPORT SCOPE This report presents geotechnical reporting based on the results of a geotechnical investigation carried out by Core Consultants Pty Ltd, for the proposed residential development to be located at 23 Bottlebrush Avenue, Noosa QLD 4567 . PTG Consulting (PTG) was engaged to re-evaluate and report on the geotechnical investigation results considering new updated plans for the development. The investigation was commissioned by Cheri Hill on behalf of JTJH Developments Pty Ltd. Based on the plans provided by JTJH Developments (drawing package ref. MCU20-0116 dated 23 August 2021), it is understood that the final usage of the site will comprise a three-storey residential dwelling with basement level carparking and associated driveway, courtyard and swimming pool. Geotechnical investigation for the site was completed by Core Consultants in August 2021 (report ref. JOO1369-001- R-RevO Geotechnical Investigation Report). The investigation scope included two (2) hand auger boreholes with dynamic cone penetrometer (DCP) testing undertaken in general accordance with 'AS1726:2017-Geotechnical Site Investigations’. This report includes a brief description of the fieldwork procedures, the results of the fieldwork and reporting on the following: Subsurface conditions including groundwater (if encountered); Site classification and predicted ground surface movement (Ys) in accordance with AS 2870-2011; Earthworks recommendations; Allowable bearing pressures for high level footings and estimated settlements; Suitable pile types, ultimate base bearing, skin frictions and estimated settlement (if required); Landslide risk assessment per Council Legislation; Temporary and permanent batter slopes; Basement construction recommendations; and Any other geotechnical issues identified that would need management (if any). 2 SITE DESCRIPTION The site is located at 23 Bottlebrush Avenue, Noosa Heads and is identified as lot 140 on RP88934. The site has an area of 506 m? and is bordered by residential units to the northwest and southeast, a residential house to the northeast and Bottlebrush Ave to the southwest. Figure 1 shows an aerial view of the site and surrounds with the approximate site boundary shown in red. Review of contour plans provided indicates that the that the site currently slopes down from the rear of the property towards Bottlebrush Ave from approximately RL 37 m down to RL 31m ADH. At the time of the investigation, there was a house covering much of the lot surrounded by trees and other vegetation. Figures 2 and 3 are images that were taken at the time of the investigation and show the general site conditions.
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os Figure 1: Areial Imagery of the 3 REGIONAL GEOLOGY Reference to available geology mapping indicates that the site is underlain by Pleistocene aged Quartz sand (Qpd/2), which is comprised of parabolic sand dunes. Figure 2 shows an aerial view of the site (in red) with the regional geology overlay. site from QLD Globe (in red) The J IGA Noosa 7-Eleven Former bowling club Noosg Heads Motel oF ed Prince'sSUPA pz. PLEISTOCENE dunes. Qpd/2 | Quartz sand; parabolic sand Viewlang Dr Nairana Rest Eugarie St Figure 2: Regional geology as extracted from the Queensland Geotechnical Database. Aemel
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4 FIELD INVESTIGATION The fieldwork undertaken by Core Consultants included two (2) hand auger boreholes drilled to 4.0 m below existing ground levels. Dynamic cone penetrometer (DCP) testing was undertaken adjacent to the boreholes. Testing and subsurface logging of the boreholes was undertaken by a geotechnical engineer, in accordance with AS1762-2017 - Geotechnical Site Investigations. The geotechnical investigation report is attached in Appendix 1. 5 GEOTECHNICAL MODEL Table 1 summarises the soils encountered within the hand auger boreholes. In summary the soil profile encountered within the boreholes generally comprised a surficial 0.1m to 0.18 m thick layer of topsoil, potentially underlain by uncontrolled sand fill to depths up to 1.0 m, underlain again by natural dune sands to termination depths. Table 1: Summary of Materials Encountered in Hand Auger Boreholes ste Ra Topsoil\(m) Fill- SAND (m) Natural - SP SAND (m) oe 1 0.0 - 0.18 0.18 - 1.0 1.0 - 4.07 2 0.0 - 0.1 N/E 0.1- 4.0" Note: TD = termination depth, N/E = material not encountered in auger hole Dynamic cone penetrometer (DCP) testing undertaken indicated: Fill soils typically have a loose relative density; Natural sand soils from depths of 0.1 m to 1.6 m typically have a loose relative density; Natural sand soils from depths of 1.6 m typically have a medium dense relative density, grading to dense at depths of approximately 3.5 m. Groundwater was not encountered during the drilling of the hand auger boreholes. It should be noted that groundwater levels can be perched and fluctuate seasonally and during and after heavy rainfall events. Given this natural variability, it is prudent to assume that water levels can fluctuate. 6 GEOTECHNICAL COMMENTS The geotechnical comments in this report are based on the factual information collected during the fieldwork conducted by Core Consultants, best practice, local experience and published literature, however they are fundamentally opinion. In summary, the ground conditions that are likely to be encountered at the site can be characterised as comprising a 0.1 m - to 0.18 m surficial layer of topsoil, potentially underlain by loose uncontrolled sand fill to depths up to 1.0 m, underlain again by loose natural dune sands to depths up to 1.6 m. Below 1.6 m natural sands are expected to be medium dense, grading to dense with depth. Based on the ground conditions and the provided development plans, it is likely that the most suitable foundation system for the building would comprise high level pad and strip footings supported on natural medium dense sand. Piled foundations are recommended for heavily loaded or movement intolerant structures. 6.1 EARTHWORKS ADVICE 6.1.1 SUBGRADE PREPARATION To achieve a uniformly well compacted subgrade to support slabs and pavements, the subgrade should be uniformly compacted to a minimum 100% standard compaction. To prepare the subgrade, the upper 0.3 m depth (particularly in cut areas) may need to be scarified, moisture-conditioned and recompacted to a minimum 100% minimum dry density ratio (DDR) with a moisture variation not exceeding +2% of the optimum moisture content (OMC) followed by a test roll and sealing as soon as practical.
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6.1.2 FILLING All structural fill should be placed and compacted under Level 1 inspection and testing in accordance with site specific design drawings and specifications. Minimum earthwork requirements should be in accordance with ‘AS3798-2007 Guidelines on Earthworks for Commercial and Residential Developments’. In summary, AS3798 guidelines recommend the following: Strip vegetation and uncontrolled fill (if any); Test rolling using the following plant and load conditions. It is noted that sand/silty sand exposed at subgrade level can be prone to displacement during the test roll however when confined (i.e. beneath pavements) performs adequately: © astatic smooth steel wheeled roller with a mass not less than 12 tonne and a load intensity under a wheel load not less than 6 tonnes; © a pneumatic tyred plant with a mass not less than 20 tonnes and a ground pressure not less than 450 kPa per tyre; or o ahighway truck with rear axle loaded not less than 8 tonnes with tyres inflated to 550 kPa; Subject to site specific conditions, any soft areas identified might need to be removed and replaced with select material; and Structural fill should be in near horizontal layers, commonly termed ‘lifts’, and generally not to exceed 300 mm thick (uncompacted) and compacted to a 98% minimum dry density ratio (DDR) for general fill and 100% minimum DDR in the upper 0.5 m depth beneath slabs and pavements with a moisture variation not exceeding +2% of the optimum moisture content (OMC). The maximum particle size should be limited to two-thirds of the compacted layer thickness. Where structural fill abuts slopes generally steeper than 8H:1V (if any), benches equal to the height of the fill layer should be cut into the slope before filling. Other earthwork considerations include: The most suitable plant for compaction is a smooth drum roller for granular (i.e. clean sand soils); and PTG can provide Level 1 supervision and testing following site specific design drawings and specifications and AS 3798-2007 if required. 6.1.3 EXCAVATION CONDITIONS Excavation of the encountered fill and natural sand soils could be achieved using excavators of any size. Based on the development plans and site conditions, a 14t excavator is suggested as most suitable. 6.1.4 SUITABILITY OF SITE WON MATERIAL Topsoil encountered across the site is not considered suitable for reuse as engineered fill. Topsoil material (excluding rootlets) can be stockpiled and reused as topsoil post earthworks. Provided that there are no limitations on fill (ie shrink-swell, CBR, WPI), clean dune sands encountered onsite could be considered suitable for reuse as engineered fill. 6.2 SITE CLASSIFICATION AND SITE MOVEMENTS In accordance with AS2870, the site is classified as ‘P’ due to: The bearing strength is less than that specified in Clause 2.4.5 as per Section 2.1.3(a); The site contains uncontrolled or controlled fill as identified in Clause 2.5.3; o Removal of an existing building or structure likely to have significantly modified the soil moisture conditions under the footprint of the footing system of the building as per section 1.3.3 (a); o Removal of trees prior to construction as per section 1.3.3(b); o. Presence of trees on the building site or adjacent site as per section 1.3.3(c);
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The site can however be re-classified, and this re-classification is provided below, assigning an equivalent site class in response to normal soil moisture conditions. The estimated characteristic ground surface movement in normal soil moisture conditions for the site is expected to be between O mm and 20 mm, consistent with a ‘Class S’ site. This classification is relevant to sites subject to normal moisture conditions. Abnormal moisture conditions, such as from the removal or planting of trees (including on adjacent sites), poor site drainage, and development of gardens adjacent to the footings, may cause higher movements to occur, probably resulting in damage, which may or may not be within acceptable limits. It is noted that characteristic ground surface movement for the site is based on the existing soil profile, and the moisture content changes withing soils due to normal seasonal variations. It does not consider soil settlement under building foundation load. 6.3 FOUNDATIONS Based on an interpretation of the typical structural loads anticipated, basement levels for the building and subsurface conditions encountered during the investigation, both high level and piled foundations could be considered as suitable for the development. Discussion on the suitability of high level foundations can be found in section 6.3.1 below. Based on the information available at the time of writing this report, general design parameters and recommendations have been provided in the subsections below which can be used for design of the foundation system of the structure. The design of the structure must consider the structural loads against serviceability. All footing excavations should be inspected by PTG to confirm that bearing pressures have been achieved, and footings are clean and free from loose and/or water softened materials. 6.3.1 HIGH LEVEL FOUNDATIONS Preliminary design of high-level pad footings up to 3m wide or strip footings with a minimum 0.5m depth can be designed using the allowable bearing pressures in Table 2. Elastic settlements of properly designed and constructed high level footings are usually in the order of 10 mm for 0.5m wide strip footings to 25 mm for large square pad footings up to 3 m wide. It is anticipated that the ground conditions at basement foundation level across the majority of the buildings footprint will comprise medium dense or denser natural sands. Where medium dense natural sands are present at basement foundation levels, PTG’s below preliminary design of high level footings can be considered suitable. If any areas of uncontrolled fill or loose soils are found to be present at basement foundation levels, these would not be considered as suitable founding soils for the below high level footing design, and are suggested to be removed and replaced with engineered structural fill, in accordance with '‘AS3798-2007 Guidelines on Earthworks for Commercial and Residential Developments’. Table 2: Allowable Bearing Pressures for High Level Footings Material Type Allowable Bearing Pressure (kPa) ‘Uncontrolled’ fill Not Recommended ‘Controlled’ fill 100 Loose sand Not Recommended Medium dense sand 100 Dense sand 200 It is noted that in sand soils, bearing capacity increases with footing base depth. While suitable bearing capacity may be achieved in loose sands be designing the footings at greater depths, high level footings are not recommended on loose sands due to the potential for instantaneous settlement of foundations.
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6.3.2 PILED FOUNDATIONS Pile foundations can be used to support the proposed structures to transfer building loads to the more competent soils at depth. The piled foundation options which are suitable for the site include: Continuous flight auger (CFA) concrete. Driven steel tube, H pile or precast concrete. Screw piles. Bored piles can be designed using the ultimate skin friction and base bearing capacities in Table 3 below. Table 3: Ultimate Geotechnical Design Parameters for Bored Piles Material Type Ultimate Skin Friction (kPa) Ultimate Base Bearing (kPa) Loose sand/silty sand Not Recommended Not Recommended Medium dense sand/silty sand 2 500 Dense sand/silty sand 4 1000 The above parameters are only suitable where the excavation of piled foundations are supervised and at a minimum inspected by a suitably qualified geotechnical engineer to confirm the founding conditions and materials encountered in the side walls. The design of piled foundations should be undertaken in accordance with: AS 2159-2009: Piling - Design and installation; Any other relevant design standards (Australian or international); and Engineering Principles. The piled foundation design should also consider: Piles should be founded a minimum of two pile diameters into the nominated strata and have a minimum pile length of four times the pile diameter; The upper 1 m of pile length should be ignored due to pile load development and shrink swell effects; and Settlement of properly designed and constructed footings should be less than 1% to 2% of the pile diameter. To calculate the design geotechnical strength (Rd,g), the ultimate geotechnical strength should be multiplied by a suitable geotechnical strength reduction factor (@g) as per Section 4 of AS 2159-2009. The geotechnical strength reduction factor (@g) is based on: gb = The basic geotechnical strength reduction factor, calculated using a risk assessment procedure; otf = Intrinsic testing factor, based on the type of pile testing adopted; and K = The testing benefit factor, based on a percentage of the piles that are tested. Typically, where no pile testing is undertaken and the piles have a low redundancy, the assessed risk rating would be high and a $g value of 0.45 would apply. It should be noted this assessment has been undertaken by PTG to assist with the design of the foundations, however as assessment of each risk rating and factors must be undertaken by the designer of the piles for the final design. Specialist piling contractors should be consulted when selecting and installing piles. 6.4 SAFE TEMPORARY AND PERMANENT BATTER SLOPES Excavations up to 1.5 m depth could generally be designed with a safe 1.5H:1V temporary batter slope. This assumes that soils are not wet/saturated and groundwater is not present, and is subject to the below recommendations: All temporary batters should not have construction loads (i.e. plant, equipment or soil stockpiles) or people at the crest of the batters at a distance equal to the height of the slope; Permanent batters (at a minimum) should be protected from erosion. Topsoiling and planting, or erosion matting should be applied to the batter as soon as possible; Suitable drainage and stormwater provisions must be installed for the batters. Surface and stormwater runover must be directed away from batters and prevented from pooling at the base and crest. At a minimum, spoon drained should be installed at the crest and base of permanent batters; Temporary batters should not remain open for extended periods of time. Vertical excavations of up to 1.2 m are usually formed near vertical for short periods of time to allow for the installation of services and construction of
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footings. Any batters or excavations exceeding this should be inspected by a suitably qualified geotechnical engineer to assess to the temporary stability of the batter; and Batters exceeding the heights or slopes stated above, or batters that contain buildings or surcharge loads within a distance equal to one batter height from the crest, should undergo detailed stability analysis to determine risk levels. If temporary batters steeper than 1.5H:1V are proposed for the site these will require the design of a suitable retention system. 6.5 RETAINING WALL PARAMETERS It is understood that retaining walls may be required for the development. Retaining wall type and height are unknown at the time of writing this report. Any temporary or permanent retaining structures at the site should be designed in accordance with AS4678-2002 ‘Earth Retaining Structures’. Based on the results of the fieldwork, retaining wall design parameters for temporary or permanent walls are summarised in Table 4. Table 4: Design parameters for temporary and permanent retaining walls nee Coefficient of Melis oma) , Dry unit weight ite earth NS oTT aks) Material Type Angle (kKN/m3) ne IRS Ceee| mike g modulus . Co) (MPa) Loose sand 7 28 0.53 2 Medium dense sand 18 34 0.43 6 Dense sand 19 39 0.36 10 Retaining wall design should consider the below: The distance from the crest and magnitude of any surcharge loads (ie buildings, roads). Whether the selected wall type is suitable for the proposed loading conditions. Wall geometry and the presence of any slopes at the crest or toe of the wall. Type of backfill to be used behind the wall, and whether compaction will exert additional forces onto the wall. 6.6 BASEMENT CONSTRUCTION CONSIDERATIONS Based on the provided drawings, it is implied that a temporary soil retention system may be necessary for the excavation and construction of the building’s basement level. Temporary retention options and considerations are as follows: A secant pile wall can be used, however it should be noted that standard piling tolerances might lead to the formation of gaps within the wall, which could result in potential leakage issues. Sheet piles may also be contemplated, taking into account the vibrations caused by their installation and the challenges associated with reaching the required depths. The installation of sheet piles in loose sand can result in movement and damage to adjacent assets such as services, pavements and structures. The impact of potential ground movement, as well as noise and vibration, should be considered where f=driven or vibratory sheet piles are being considered for ground retention. It's important to recognise that some ground movement may occur behind retaining walls. The amount of movement will depend on factors such as the height of the wall, the type of wall chosen, and the construction methods used. These factors should be considered during the design and construction of the retaining walls to ensure that surrounding facilities are not negatively impacted.
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6.7 LANDSLIDE RISK ASSESSMENT
Noosa Shire Council mapping indicates that the proposed site is mapped as a ‘moderate hazards area’, as shown in
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Based on the results of the ground conditions encountered at the site, two potential failure mechanics can be
considered, these include:
Hazard 1- Small rotational failure through the natural loose sands - volume of failure less than 20m3 (failure will
required an unusual sever triggering event)
Hazard 2 - Large rotational failure through the natural loose sands - volume of failure less than 2000m3 (failure
will required an extreme triggering event)
A qualitative landslip risk assessment was completed for these potential failure mechanisms in general accordance
with Australian Geomechanics (2007) Guideline for Landslip Susceptibility, Hazard and Risk Zoning for Land Use
Planning). The slope risk assessment is summarised in Table 5.
The small and large rotational failures through the loose sands are of very low and low risk, respectively and are
unlikely to impact the property and people who live or spend time in the area, provided the following recommendation
are adhered too:
All temporary and permanent retaining walls and excavations shall be designed in accordance with AS4678, and
stability analysis be carried out by a geotechnical engineering ensuring minimum Factors of Safety (FOS) for
temporary and permanent conditions of 1.3 and 1.5, respectively are achieved.
All foundations of the house to be extended to the medium dense sand, as a minimum.
The development shall adhere to good hill side practice. Examples of good and poor hill side practice for the
construction of residential dwelling on slopes is presented in Appendix D, Practice Note Guidelines for landslide
risk management 2007, from Australian Geomechanics Journal Vo 42, No. 1 dated March 2007.
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Table 5: Summary of the qualitative slope risk assessment here Hazard 1 - small rotational failure though | Hazard 2 - Large rotational failure though the natural loose sands up to 20m? the natural loose sands up to 2,000 m? Property People, who either Property People, who either live, or may that live, or may that Risk Element spend some time in spend some time in Htilee-lecr dicate} LtuTeM-1 ect M-LAKreLn=xe| by the landslip by the landslip Likelihood Frequency POSSIBLE POSSIBLE BARLEY CREDIBLE = BARLEY CREDIBLE estimate, expressed Cc C F F as an annualised probability and taking into account the probability of spatial impact Measure of INSIGNIFICANT INSIGNIFICANT MAJOR CATASTROPHIC consequence 5 5 2 1 RISK LEVEL VERY LOW VERY LOW VERY LOW LOW VL VL VL L 7 LIMITATIONS PTG Consulting has prepared this report (or services) for this project in accordance with PTG's proposal and acceptance received from the Client. These limitations apply whether the report was created under PTG’s own terms and conditions or otherwise. This report is provided for the exclusive use of the JTJH Developments Pty Ltd for the Geotechnical scope of works at 23 Bottlebrush Avenue, Noosa QLD 4567 . The report should not be used by or relied upon for other projects or purposes on the same or other site or by a third party. Any party so relying upon this report beyond its exclusive use and purpose as stated above, and without the express written consent of PTG, does so entirely at its own risk and without recourse to PTG for any loss or damage. In preparing this report, PTG has necessarily relied upon information provided by the client and/or their agents. PTG's advice is based on information gained from limited subsurface excavations and sampling supplemented by knowledge of local geology and experience. The accuracy of the advice provided by PTG in this report may be affected by undetected variations in ground conditions across the site between and beyond the sampling and/or testing locations. For this reason our reports include an interpretation of conditions between the test points. There are unknowns or variations in ground conditions between test locations that cannot be inferred or predicted. Such variations may occur after PTG's field testing has been completed. The precision and reliability of interpretive assessment between discrete points is dependent on the uniformity of the subsurface strata, as well as the frequency, detail, and method of sampling or testing. Geotechnical information represents an opinion and is based extensively on judgment of both data and interpretive assessments or observation. This report and its associated documentation are provided explicitly based on PTG's opinion of the site at the time of inspection, and cannot be extended beyond this. Any recommendations or design suggestions will need to be verified on site during project implementation or construction. Inspection and verification onsite may be conducted by a suitably qualified geotechnical consultant or engineer, and where subsurface conditions or interpretations differ from those provided in this document or otherwise anticipated, PTG must be notified and be provided with an opportunity to review the recommendations The report has been prepared by qualified personnel, and is based on the information obtained from field and laboratory testing, and has been undertaken to current engineering standards of interpretation and analysis. The information and interpretation may not be relevant if the development proposal is changed. If this happens then PTG Engineering will be pleased to review the report and the sufficiency of the investigation work. Every care is taken with the report as it relates to interpretation of subsurface conditions, and the discussion and recommendations or suggestions relating to the geotechnical aspects of the scope of works. However, PTG Engineering cannot always anticipate or assume responsibility for: Unexpected variations in ground conditions.
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Changes in policy or interpretations of policy by statutory authorities. The actions of contractors responding to commercial pressures. The contents of this report do not constitute formal design components, as required by Health and Safety Legislation and Regulations, to be included in a Safety Report specifying the hazards likely to be encountered during construction and the controls required to mitigate risk. This design process requires risk assessment to be undertaken, with such assessment being dependent upon factors relating to the likelihood of occurrence and consequences of damage to property and to life. This, in turn, requires project data and analysis presently beyond the knowledge and project role respectively of PTG. This report must be read in conjunction with all of the attached documents and should be kept in its entirety without separation of individual pages or sections. PTG cannot be held responsible for interpretations or conclusions made by others unless they are supported by an expressed statement, interpretation, outcome, or conclusion stated in this report.
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Appendix 1 Geotechnical Investigation Report
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Geotechnical Investigation Report Proposed Development 23 Bottlebrush Avenue, Noosa Heads Prepared for: Russell Green RG Strategic PO Box 1818 Noosa Heads QLD 4567 Report Number: J001369-001-R-Rev0 August 2021
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J001369-001-R-Rev0 August 2021
Executive Summary
Core Consultants Pty Ltd (Core) has carried out a geotechnical investigation for a proposed development at
23 Bottlebrush Avenue, Noosa Heads.
The proposed development comprises a three-level apartment with a single-level basement and associated
driveway, visitor carparking, courtyard and pool. It is anticipated that earthworks for the project will generally
include cuts of between 2 m to 5 m depths, with minor filling to form finished surface levels.
The fieldwork comprised a walk-over survey and the drilling of two boreholes (designated HA1 and HA2) to
4 m below ground level (BGL).
The subsurface profile encountered in the boreholes generally comprised sand topsoil of between 0.1 m to
0.18 m thickness, overlying sand fill up to 1 m depth (HA1) over natural aeolian sand. The sand is generally
loose to medium dense, becoming dense from about 1.5 m depth. The fill encountered in HA1 is assumed to
be uncontrolled.
Groundwater was not encountered in the boreholes during the investigation. Due to the relatively permeable
nature of the sand, prolonged periods of high groundwater or saturated soils are not anticipated except
following periods of high rainfall.
The site is classified as ‘Class ‘P’ due to the presence of uncontrolled fill. However, the natural soils on site
may be classed as equivalent ‘Class ‘S’ in accordance with AS 2870-2011. The estimated characteristic
ground surface movement due to seasonal moisture variation (‘y s’ value) for this site is less than 20 mm.
Due to space constraints preventing trimming of batters to safe slopes, positive support by engineer-
designed retaining structures will be required for excavation of the basement. Possible retention systems
could include sheet pile walls.
High level footings may be designed for the basement using an allowable bearing capacity of 200 kPa in the
dense natural sand.
A qualitative slope stability risk assessment for this project has been carried out following the Australian
Geomechanics Society (AGS) Guidelines for Landslide Risk Management (March 2007). The assessed risk
is Low for the proposed development. This level of risk is normally acceptable to regulators.
Comments and recommendations regarding site preparation and trafficability, filling and compaction,
excavatability, retaining wall design parameters, drainage and general foundation maintenance are provided
in this report.
From a geotechnical viewpoint, our assessment is that the site is suitable for the proposed development
subject to the implementation of the recommendations in this report.
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J001369-001-R-Rev0 August 2021
Table of Contents
1.0 INTRODUCTION .................................................................................................................................... 4
2.0 PROPOSED DEVELOPMENT ............................................................................................................... 4
3.0 SITE DESCRIPTION .............................................................................................................................. 4
4.0 INVESTIGATION .................................................................................................................................... 6
4.1 Fieldwork................................................................................................................................................. 6
5.0 INVESTIGATION FINDINGS .................................................................................................................. 7
5.1 Desktop Study ........................................................................................................................................ 7
5.2 Subsurface Conditions ............................................................................................................................ 7
5.3 Groundwater ........................................................................................................................................... 7
5.4 Surface Drainage .................................................................................................................................... 7
5.5 Vegetation ............................................................................................................................................... 7
5.6 Existing Structures .................................................................................................................................. 8
6.0 ASSESSMENT OF LAND STABILITY ................................................................................................... 8
6.1 Existing Conditions ................................................................................................................................. 8
6.2 Stability Risk Assessment ....................................................................................................................... 8
7.0 DEVELOPMENT IMPACTS AND MITIGATION MEASURES ............................................................... 9
7.1 Site Preparation and Trafficability ........................................................................................................... 9
7.2 Filling and Compaction ........................................................................................................................... 9
7.3 Excavations...........................................................................................................................................10
7.4 Foundations ..........................................................................................................................................10
7.4.1 Site Classification .............................................................................................................................10
7.4.2 Footing Design ..................................................................................................................................10
7.5 Retaining Wall Design Parameters .......................................................................................................11
7.6 Drainage and Erosion ...........................................................................................................................11
7.7 General Foundation Maintenance ........................................................................................................12
8.0 SUMMARY AND CONCLUSIONS .......................................................................................................12
9.0 LIMITATIONS .......................................................................................................................................12
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J001369-001-R-Rev0 August 2021
Tables
Table 1: Stability Risk Levels. ............................................................................................................................ 8
Table 2: Qualitative Risk Assessment for Property (Based on AGS 2007) ....................................................... 9
Table 3: Retaining Wall Design Parameters.................................................................................................... 11
Figures
Figure 1 – Test Location Plan
Appendices
APPENDIX A Reports of Boreholes and Explanatory Notes
APPENDIX B AGS Practice Note Guidelines for Landslide Risk Management
APPENDIX C Guidelines for Hillside Construction
APPENDIX D CSIRO Foundation maintenance and footing performance: A Homeowner’s Guide
APPENDIX E Limitations
iii
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J001369-001-R-Rev0 August 2021
1.0 INTRODUCTION
As requested by RG Strategic, Core Consultants Pty Ltd (Core) has carried out a geotechnical investigation
for a proposed development at 23 Bottlebrush Avenue, Noosa Heads.
Presented in this report are the investigation results together with a qualitative slope stability assessment
and comments regarding:
▪ Site preparation and trafficability.
▪ Filling and compaction.
▪ Excavatability and temporary excavation support.
▪ Foundation design and parameters.
▪ Retaining wall design parameters.
▪ Drainage and general foundation maintenance.
2.0 PROPOSED DEVELOPMENT
Preliminary concept drawings were provided by the client (refer Drawing No. A202, dated 13 July 2021).
Based on these drawings we understand the proposed development will comprise a three-level apartment
development with a single-level basement and associated driveway, visitor carparking, courtyard and pool. It
is anticipated that earthworks will generally include cuts of between 2 m and 5 m depth and minor filling to
form finished surface levels.
3.0 SITE DESCRIPTION
The site is described as Lot 140 of RP88934 and covers an area of about 506 m2. The site is bounded by
Bottlebrush Avenue to the south-west and residential units and houses elsewhere. At the time of our
investigation there was an existing brick dwelling with an associated concrete driveway and footpath. The
dwelling was generally surrounded by scattered large trees and vegetation. Further details regarding site
conditions are given in Section 5.0.
The site generally slopes down to the south-west between about 10° and 12°, with the lower portion and
driveway steeper at about 18°. Available survey drawings (refer Drawing No. 12831-DTM-01, dated 25
March 2021) generally confirms the on-site slope measurements. Elevation levels across the site ranged
from between RL 37 m and RL 31 m. Image 1 below shows an extract of the abovementioned survey
drawing.
Photographs 1 to 3 show the general site conditions at the time of our investigation.
Image 1: Extract from survey drawings 12831-DTM-01 (dated 25 March 2021).
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J001369-001-R-Rev0 August 2021
Photograph 1: View looking approximately north-west across the rear of the site towards the northern boundary
(3 August 2021).
Photograph 2: View looking approximately north-east from Bottlebrush Avenue (3 August 2021).
5
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J001369-001-R-Rev0 August 2021
Brick retaining wall
Timber sleeper retaining wall
Photograph 3: View looking approximately north-west towards the existing retaining walls (3 August 2021).
4.0 INVESTIGATION
The investigation included the following:
▪ A review of geological and landslide hazard overlay plans
▪ Walk-over survey and subsurface investigation and sampling at two locations
4.1 Fieldwork
A walkover survey was carried out by a geotechnical engineer to map topographical and surface features,
such as slope angles, signs of slope instability and groundwater seepage.
Following the walkover, a subsurface investigation was undertaken, which comprised the drilling of two
boreholes (designated HA1 and HA2) to 4 m below ground level (BGL). Due to site access constraints, the
boreholes were drilled using hand augering techniques. Dynamic cone penetrometer (DCP) testing was
undertaken adjacent to the boreholes to assess soil density/consistency. Soil samples were also collected
from the boreholes.
Borehole positions were recorded in the field using a handheld GPS unit.
The test locations are shown on the attached Figure 1. Reports of Boreholes are attached in Appendix A,
together with explanatory notes. The subsurface conditions are discussed in Section 5.2.
The fieldwork was carried out on 3 August 2021 by a geotechnical engineer from Core who logged
subsurface conditions in accordance with AS1726-2017 Geotechnical site investigations and undertook the
field testing and sampling.
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J001369-001-R-Rev0 August 2021
5.0 INVESTIGATION FINDINGS
5.1 Desktop Study
The Gympie Special Geology Map1 indicates that the site is underlain by Pleistocene aged quartz sand dune
deposits (Qpd2). Image 2 below shows an extract from the geology map.
Approximate site location
Image 2: Extract from Gympie Special Geology Map1.
5.2 Subsurface Conditions
The subsurface conditions encountered in the boreholes generally comprised the following:
▪ TOPSOIL: comprising loose sand to depths of 0.1 m and 0.18 m BGL; overlying
▪ FILL: comprising loose sand to 0.5 m depth with possible fill further observed to 1 m depth BGL in
HA1; overlying
▪ AEOLIAN SOIL: comprising loose to medium dense sand becoming dense from about 1.5 m depth
to the termination depth of 4 m BGL.
Fill was only observed in borehole HA1 and was located on a garden bed on the southwest portion of the
site. The fill encountered is assumed to be uncontrolled. The fill material was generally consistent with the
aeolian soils, with the addition of occasional rootlets and organics.
5.3 Groundwater
Groundwater was not encountered in the boreholes during the investigation. Due to the relatively permeable
nature of the sand, prolonged periods of high groundwater or saturated soils are not anticipated except
following periods of high rainfall.
5.4 Surface Drainage
Surface drainage is anticipated to follow the natural contours of the land towards the south-west, with flows
directed into the roadside stormwater drainage system on Bottlebrush Avenue.
5.5 Vegetation
At the time of our investigation, site vegetation comprised short grass, shrubs and scattered large trees.
Densely vegetated areas (natural vegetation or garden beds) were concentrated in the south-west and north-
east portion of the site.
1
GYMPIE SPECIAL 1:100,000 Geological Series. Map Sheet 9445 and Part 9545, First Edition, Department of Mines and Energy, Brisbane, 1999.
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J001369-001-R-Rev0 August 2021
5.6 Existing Structures
The existing residence comprised a two-storey brick dwelling on a levelled building pad with an associated
concrete driveway and footpath. It is anticipated that cut and fill earthworks were required for construction of
the existing dwelling. The structures and ground conditions did not show any signs of instability. Tenants on
site further advised that no cracking or major issues have been observed within the existing dwelling.
A timber sleeper retaining wall of about 0.8 m height extends across part of the rear of the site. A brick
retaining wall of about 1.2 m to 1.5 m height extends along the along the northern boundary of the site. The
adjacent property is situated on the high side of the existing brick retaining wall.
6.0 ASSESSMENT OF LAND STABILITY
6.1 Existing Conditions
The Noosa Planning Scheme 2020 includes a landslide hazard overlay map. The overlay map indicates that
the site is within a moderate landslide hazard area. Image 3 below presents an extract of the overlay map.
Lot boundary
Image 3: Extract from Noosa Shire Council landslide hazard overlay mapping.
6.2 Stability Risk Assessment
A qualitative slope stability risk assessment for this project has been carried out following the Australian
Geomechanics Society (AGS) Guidelines for Landslide Risk Management (March 2007), refer Table 2. The
risk assessment relates to property. Relative levels of risk and their implications are given in Table 1 below
and the qualitative terminology (i.e. likelihood and consequence definitions) for use in assessing risk to
property are attached in Appendix B.
Table 1: Stability Risk Levels.
Risk Level Example Implications(1)
VERY HIGH Unacceptable without treatment. Extensive detailed investigation and research, planning
VH and implementation of treatment options essential to reduce risk to Low; may be too
RISK
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.
MODERATE May be tolerated in certain circumstances (subject to regulators’ approval) but requires
M investigation, planning and implementation of treatment options to reduce risk to Low.
RISK
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.
VERY LOW
VL Acceptable. Manage by normal slope maintenance procedures.
RISK
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.
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J001369-001-R-Rev0 August 2021
Table 2: Qualitative Risk Assessment for Property (Based on AGS 2007)
Assessed
Hazard Likelihood Consequence Comments
Risk
The likelihood of shallow failure is assessed
Shallow failure through
as Unlikely. The consequence is considered
loose fill and natural
Unlikely Medium Low Medium, if the proposed development is
aeolian soils above the
founded as per the recommendations in this
foundation depth
report. The resultant risk is Low.
The likelihood of a deep failure through the
Deep failure through the natural aeolian soil is assessed as Rare due
dense (or denser) to historically low prevalence of instability in
natural aeolian soils Rare Major Low this geological formation and no signs of
below the foundation slope instability. Although the consequence
depth of such a failure would be Major, the
resultant risk is Low.
Based on the available information and the results of our investigation, it is our opinion that there is a Low
Risk of slope instability for the proposed development, subject to implementation of the recommendations in
this report, assessed in accordance with the AGS guidelines (March 2007).
7.0 DEVELOPMENT IMPACTS AND MITIGATION MEASURES
The potential impacts of the proposed development on slope stability have been considered, and the
measures recommended below have been designed to mitigate potential impacts. Building development
should follow normal slope maintenance procedures and the document ‘Guidelines for Hillside Construction’,
which is attached in Appendix C.
7.1 Site Preparation and Trafficability
Site preparation across the development footprint should include the following:
▪ Remove vegetation and ‘grub out’ stumps, large roots and root balls
▪ Remove any topsoil and uncontrolled fil. Topsoil was encountered between 0.1 and 0.18 m BGL,
however deeper pockets may exist across the site. It is noted that dense vegetation was observed in
the south-west and north-east portion of the site, where deeper organic materials may be present.
The base of the excavation is anticipated to comprise dense sands, which may become disturbed/loose at
the surface from excavation/construction traffic. Compaction of such loose sands may be required, using a
smooth-drum roller (4 tonne). Vibration and the application of water may be required. However vibration
impacts on adjacent sites must be assessed.
Allowance should be made for the placement of a 150 mm thick layer of aggregate across the base to form
an even and stable working platform, or on access/laydown areas.
The site must be maintained to shed water and prevent ponding during the construction phase. Erosion and
sediment control measures must be put in place during construction.
It would be prudent to carry out a dilapidation survey of adjacent structures and sites prior to site works.
7.2 Filling and Compaction
It is anticipated that filling will be minimal and will only be required to form finished surface levels or on
removal and replacement of unsuitable material.
Where filling is undertaken, the following measures should be adopted:
▪ Fill should be compacted at moisture contents within the range of ±2% of optimum moisture content
for Standard Compaction.
▪ Confirmatory compaction testing must be carried out at regular intervals. Guidance on testing
frequency is provided in AS 3798-2007 Table 8.1.
▪ Fill should have a maximum particle size of 100 mm.
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J001369-001-R-Rev0 August 2021
▪ Fill should be compacted in layers, typically about 250 mm thick (loose thickness). However, layer
thickness will be dependent upon the type/size of compaction plant, use of vibration, material type
and condition.
▪ Fill 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.
▪ Imported fill (if required) should be cohesive in nature and have a plasticity index of < 15%, a
maximum particle size of 100 mm, and a soaked CBR of > 10%.
▪ Slopes and existing drainage channels should be benched to assist with fill placement and
compaction.
Further details for control and testing of fill are given in Australian Standard AS 3798-2007 Guidelines on
Earthworks for Commercial and Residential Developments.
If filling greater than 0.5 m thickness is proposed, Core must assess the impacts on slope stability before
construction. Fill greater than 1 m thickness (if required) must be retained (refer Section 7.6).
7.3 Excavations
Due to space constraints, basement excavation will require positive support by engineer-designed retaining
structures. Possible retention systems include sheet piles (cantilevered, anchored or propped). Design and
construction of temporary support must consider adjacent structures (e.g. loads or undermining). It is
recommended that information on adjacent footings is obtained through site investigation or certified ‘as built’
plans. Vibration impacts of sheet piling must be considered. Temporary support must be designed by a
suitably experienced engineer (RPEQ) and installed by a specialist piling/shoring contractor.
Temporary excavations of less than 1 m height into the loose to medium dense sand (e.g. trenches) could be
battered at 1V:2H. Any cuts greater than 1 m must be retained (refer Section 7.6).
Based on the materials encountered in the boreholes, excavation for the basement is expected to encounter
loose to dense sands. Excavations in the anticipated soil materials should be achievable using conventional
earthmoving equipment.
7.4 Foundations
7.4.1 Site Classification
Site classification derived in accordance with Australian Standard AS2870-2011 Residential slabs and
footings can provide an indication of the likely magnitude of reactive (shrink and swell) movements
associated with normal seasonal moisture variations.
Based on the results of the investigation the site is classified as ‘Class ‘P’ due to the presence of
uncontrolled fill.
However, the natural soils on site may be classed as equivalent ‘Class ‘S’ in accordance with AS 2870-2011.
The estimated characteristic ground surface movement due to seasonal moisture variation (‘ys’ value) for this
site is less than 20 mm.
It should be noted that the predicted order of movement is based on the existing soil profile (i.e. no cutting or
filling), and moisture content changes within soils due to normal seasonal moisture variations only (i.e. does
not consider soil settlement).
7.4.2 Footing Design
The proposed building could be supported on high-level footings founded in the dense natural sands. A
design allowable bearing pressure of 200 kPa may be adopted for the dense sand.
Footing excavations should be inspected by an engineer from Core to confirm the foundation material meets
the design pressure requirements.
To achieve the recommended allowable bearing pressures, founding materials must be dry and cleaned of
any loose, disturbed or saturated materials prior to pouring concrete. Allowance should be made for
compaction of disturbed sand in the base of footing excavations.
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J001369-001-R-Rev0 August 2021
If any soil conditions encountered during the footing excavations are found to differ from those noted in the
geotechnical investigation, Core should be notified immediately, and an inspection of the footing excavations
should be carried out to assess if changes to footing design are required.
Adequate site drainage should be carried out to ensure that natural runoff is directed away from the building
walls and footings.
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.
Diagram 1: Exclusion zone for base of footings.
7.5 Retaining Wall Design Parameters
Design for retaining structures could be carried out using a triangular pressure distribution applicable to the
wall type (i.e. active pressures for a cantilever wall or ‘at rest’ pressures for a propped wall) and based on the
parameters in Table 33. These values do not include an allowance for hydrostatic pressures, construction
loading, adjacent foundation loadings, the effect of sloping ground, or backfill compaction stresses.
Table 3: Retaining Wall Design Parameters.
Unit Friction Lateral Earth Pressure Coefficients
Retained Material Weight Angle Cantilever Wall Non-yielding Wall
Kp
(t/m3) (Degrees) (Ka) (Ko)
Loose Sand 1.7 28 0.36 0.53 2.77
Medium Dense Sand 1.9 34 0.27 0.43 3.61
Dense Sand 2.0 39 0.22 0.36 4.5
Compacted Fill * * * * *
*: Variable depending on the type of material used and the degree of compaction achieved.
7.6 Drainage and Erosion
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 a legal 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 should be constructed above the crest of any cut or fill
embankments.
Any exposed soil on sloping ground must be protected from erosion (e.g. through re-vegetation).
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7.7 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, our assessment is that the site is suitable for the proposed development, and
that there is a Low Risk of slope instability subject to implementation of the recommendations in this report.
9.0 LIMITATIONS
Your attention is drawn to the document, Limitations which is attached in Appendix E.
Yours sincerely,
CORE CONSULTANTS PTY LTD
Mark Conway Walter Mastenbroek
BSc (Earth Science) MEngPr MSc BSc (Hons) CPEng NER RPEQ 16149
Engineering Geologist Associate/Senior Geotechnical Engineer
MC/WM/mc
12
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C 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.
HA2
HA1
BO
TT
LE
BR
US
H
AV
EN
U E
0 4 8 12 m
1:200
CLIENT PROJECT
LEGEND RG STRATEGIC PROPOSED DEVELOPMENT - 23 BOTTLEBRUSH AVENUE, NOOSA HEADS
DRAWN BY DATE DRAWING TITLE
Denotes approximate hand auger borehole location
MD 05/08/2021
Denotes lot boundary
CHECKED BY DATE TEST LOCATION PLAN
MC 17/08/2021
SCALE SHEET SIZE PROJECT No DOC No DOC TYPE FIGURE No REVISION
Base plan drawn by Natani Design. Drawing Title - Landscale Areas. Drawing No.- A0002. Dated 13 July 2021. Aerial image sourced from Nearmap Pty Ltd, image dated 21 July 2021. Annotations by Core Consultants Pty Ltd.
www.coreconsultants.com.au
1:200 A3 J001369 001 R F001 0 SHEET 1 OF 1
Plot Date: 18 August 2021 Time:3:21:51 PM By: CAD Path: J:\2021 - J1228 -\J001369 - RGStrategic-Development-Bottlebrush Ave\PHASE 1000\Figures Drawings - File Name:J001369-001-R-Rev0-F001.dwg
Page 29
J001369-001-R-RevO August 2021 APPENDIX A Reports of Boreholes and Explanatory Notes
Page 30
REPORT OF HAND AUGER BOREHOLE: HA1
East 509106.0 m
North 7080405.0 m MGA94 Zone 56 Sheet 1 OF 1
Client RG Strategic Surface RL 31.50 m AHD Logged: MD
Project Proposed Development Contractor Core Consultants Logged Date: 03/08/21
Location 23 Bottlebrush Avenue, Noosa Heads Drill Rig Hand Auger Checked: MC
Job No. J001369 Inclination -90° Hole Dia. 100 mm Checked Date: 17/08/21
Drilling Sampling Field Material Description
GROUP SYMBOL
CONSISTENCY
PENETRATION
DCP TEST
RECOVERED
RESISTANCE
CONDITION
MOISTURE
SAMPLE OR
GRAPHIC
DENSITY
METHOD
SOIL/ROCK MATERIAL DESCRIPTION Blows per 100 mm
(metres)
FIELD TEST
WATER
DEPTH
LOG
DEPTH 0 5 10 15 20 25
RL
0.0
31.50 SP- TOPSOIL SAND with silt trace cobbles: fine to medium grained,
SM dark brown and pale grey; cobbles up to 200 mm in diameter;
0.18 rootlets up to 4 mm in diameter.
31.32 SP-
FILL SAND with silt: fine to medium grained, dark brown and pale D
SM
grey.
DS 0.37-0.50 m
0.50
0.5
31.00 DS 0.50-0.95 m SP- Possibly FILL SAND with silt: fine to medium grained, dark brown;
M SM occasional rootlets and organics up to 5 mm in diameter.
L
1.00
1.0
30.50 SP- SAND (AEOLIAN SOIL) with silt: fine to medium grained, grey
SM brown and pale grey.
1.20
30.30 Trace silt: pale grey with grey brown.
CORE 2.01.1 LIB.GLB Log IS AU BOREHOLE 3 J001369 RGSTRATEGIC-23 BOTTLEBRUSH AVE-BH1, BH2.GPJ <<DrawingFile>> 18/8/2021 17:55 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
L-
1.5 MD
M-H
Not Encountered
HA
2.0
DS 2.20-2.50 m D-M
2.5
D
2.90
28.60 Silt no longer observed.
3.0
H
3.5
4.00
4.0
Hole Terminated at 4.00 m
Target depth
Backfilled on completion
4.5
5.0
This report must be read in conjunction with accompanying notes and abbreviations. It has been prepared for geotechnical
purposes only, without attempt to assess 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 31
REPORT OF HAND AUGER BOREHOLE: HA2
East 509131.0 m
North 7080418.0 m MGA94 Zone 56 Sheet 1 OF 1
Client RG Strategic Surface RL 36.00 m AHD Logged: MD
Project Proposed Development Contractor Core Consultants Logged Date: 03/08/21
Location 23 Bottlebrush Avenue, Noosa Heads Drill Rig Hand Auger Checked: MC
Job No. J001369 Inclination -90° Hole Dia. 100 mm Checked Date: 17/08/21
Drilling Sampling Field Material Description
GROUP SYMBOL
CONSISTENCY
PENETRATION
DCP TEST
RECOVERED
RESISTANCE
CONDITION
MOISTURE
SAMPLE OR
GRAPHIC
DENSITY
METHOD
SOIL/ROCK MATERIAL DESCRIPTION Blows per 100 mm
(metres)
FIELD TEST
WATER
DEPTH
LOG
DEPTH 0 5 10 15 20 25
RL
0.0
36.00 SP TOPSOIL SAND: fine to medium grained, pale grey; rootlets up to
0.10
4 mm in diameter.
35.90 SP
SAND (AEOLIAN SOIL): fine to medium grained, pale grey;
occasional roots up to 10 mm in diameter.
0.30
D
35.70 With silt: grey brown.
0.5
0.60
M L
35.40 Trace silt: grey brown and pale grey.
1.0
1.20
34.80 Pale grey with grey brown; silt no longer observed.
CORE 2.01.1 LIB.GLB Log IS AU BOREHOLE 3 J001369 RGSTRATEGIC-23 BOTTLEBRUSH AVE-BH1, BH2.GPJ <<DrawingFile>> 18/8/2021 17:55 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
MD
1.5
Not Encountered
HA
2.0
D-M
2.5
M-H
D
3.0
3.5
4.00
4.0
Hole Terminated at 4.00 m
Target depth
Backfilled on completion
4.5
5.0
This report must be read in conjunction with accompanying notes and abbreviations. It has been prepared for geotechnical
purposes only, without attempt to assess 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 32
EXPLANATION OF NOTES, ABBREVIATIONS & TERMS
USED ON BOREHOLE AND TEST PIT REPORTS
DRILLING/EXCAVATION METHOD
AS Auger Screwing RD Rotary blade or drag bit NQ Diamond Core - 47 mm
AD Auger Drilling RT Rotary Tricone bit NMLC Diamond Core - 52 mm
*V V - Bit RAB Rotary Air Blast HQ Diamond Core - 63 mm
T TC - Bit, e.g. ADT RC Reverse Circulation HMLC Diamond Core – 63mm
HA Hand Auger PT Push Tube BH Tractor Mounted Backhoe
ADH Hollow Auger CT Cable Tool Rig EX Tracked Hydraulic Excavator
DTC Diatubre Coring JET Jetting EE Existing Excavation
WB Washbore or Bailer NDD Non-destructive digging HAND Excavated by Hand Methods
PENETRATION/EXCAVATION RESISTANCE
L Low resistance . Rapid penetration possible with little effort from the equipment used
M Medium resistance. Excavation possible at an acceptable rate with moderate effort from equipment used
H High resistance to penetration/excavation. Further penetration is possible at a slow rate
R Refusal or Practical Refusal. No further progress possible without the risk of damage or unacceptable wear to the digging implement
or machine.
These assessments are subjective and are dependent on many factors including the equipment power, weight, condition of excavation or drilling tools,
and the experience of the operator.
WATER
Water level shown at date Partial water loss
Water inflow Complete water loss
GROUNDWATER NOT The observation of groundwater whether present or not, was not possible due to drilling water, surface seepage or cave in
OBSERVED of the borehole/test pit.
GROUND WATER NOT The borehole/test pit was dry soon after excavation. However, groundwater could be present in less permeable strata.
ENCOUNTERED Inflow may have been observed had the borehole/test pit been left open for a longer period.
SAMPLING AND TESTING
SPT Standard Penetration Test to AS1289.6.3.1-2004
4,7,11 N=18 4,7,11 = Blows per 150mm N = Blows per 300mm penetration following 150mm seating
30/80mm Where practical refusal occurs, the blows and penetration for that interval are reported
RW Penetration occurred under the rod weight only
HW Penetration occurred under the hammer and rod weight only
HB Hammer double bouncing on anvil
DS Disturbed Sample
BDS Bulk disturbed sample
G Gas Sample
W Water sample
FP Field permeability test over section noted
FV Field vane shear test expressed as uncorrected shear strength (sv = peak value)
PID Photoionisation Detector reading in ppm
PM Pressuremeter test over section noted
PP Pocket penetrometer test expressed as instrument reading in kPa
U63 Thin walled tube sample - number indicates nominal sample diameter in millimetres
WPT Water pressure tests
DCP Dynamic cone penetration test
CPT Dynamic cone penetration test
CPTu Static cone penetration test with pore pressure (u) measurement
ROCK CORE RECOVERY
TCR = Total Core Recovery (%) SCR = Solid Core Recovery (%) RQD = Rock Quantity Designation (%)
Page 33
METHOD OF SOIL DESCRIPTION USED ON BOREHOLE AND TEST PIT
REPORTS
FILL CLAY (CL,CI, or CH)
GRAVEL (GP or SW) ORGANIC SOILS (OL or OH or Pt)
SAND (SP or SW) COBBLES or BOULDERS
SILT (ML or MH)
Combinations of these basic symbols may be used to indicate mixed materials such as sandy clay.
CLASSIFICATION AND INFERRED STRATIGRAPHY
Soil and Rock is classified and described in Reports of Boreholes and Test Pits using the preferred method given in AS 1726 - 2017. The material proper-
ties are assessed in the field by visual/tactile methods.
PARTICLE SIZE PLASTIC PROPERTIES
Major
Sub Division Particle Size
Division
Boulders >200 mm
Cobbles 63 - 200 mm
Gravel Coarse 20 - 63 mm
Gravel Medium 6.7 - 20 mm
Gravel Fine 2.36 - 6.7 mm
Sand Coarse 0.6 - 2.36 mm
Sand Medium 0.21 - 0.6 mm
Sand Fine 0.075 - 0.21 mm
Silt 0.002 - 0.075 mm
Clay <0.002 mm
MOISTURE CONDITION FOR COARSE GRAINED SOIL AS 1726 - 2017
Symbol Term Description
D Dry Non-cohesive and free running
M Moist Soil feels cool, darkened in colour, tends to stick together
W Wet Soil feels cool, darkened in colour, soil sticks together, free water forms when handling
MOISTURE CONDITION FOR FINE GRAINED SOIL AS1726 - 2017
Symbol Term Description
W<PL Moist dry of liquid limit Hard and friable or powdery
W = PL Moist near plastic limit Soils can be molded at a moisture condition approximately equal to the plastic limit
W >PL Moist, wet of plastic limit Soils usually weakened and free water forms on hands when handling
W = LL Wet near plastic limit
W > LL Wet, wet of liquid limit
CONSISTENCY TERMS FOR AS1726—2017 RELATIVE DENSITY OF COARSE GRAINED SOILS AS1726—2017
COHESIVE SOILS
Symbol Term Density Index % SPT ‘N’ #
Symbol Term Undrained Shear
VL Very Loose Less than 15 0 to 4
Strength
L Loose 15 to 35 4 to 10
VS Very Soft 0 to 12 kPa
S Soft 12 to 25 kPa MD Medium Dense 35 to 65 10 to 30
F Firm 25 to 50 kPa D Dense 65 to 85 30 to 50
St Stiff 50 to 100 kPa VD Very Dense Above 85 Above 50
VSt Very Stiff 100 to 200 kPa In the absence of test results, consistency and density may be assessed from correlations with
the observed behaviour of the material.
H Hard Above 200 kPa
Page 34
TERMS FOR ROCK MATERIAL STRENGTH & WEATHERING AND
ABBREVIATIONS FOR DEFECT DESCRIPTIONS
ROCK MATERIAL STRENGTH CLASSIFICATION AS1726—2017
Symbol Term Uniaxial Point Load Field Guide
Strength Is (50)
Compressive
(MPa)
Strength (MPa)
VL Very Low 0.6 to 2 0.03 to 0.1 Material crumbles under firm blows with sharp end of pick. Pieces up to 30 mm thick can
Strength be broken with finger pressure.
L Low Strength 2 to 6 0.1 to 0.3 Easily scored with knife. Indentations 1 mm to 3 mm show in the specimen with firm
blows of the pick point. A piece of core 150 mm by 50 mm may be broken by hand. Sharp
edges of core are friable and break during handling.
M Medium 6 to 20 0.3 to 1 Readily scored with a knife. A piece of core 150 mm by 50 mm can be broken by hand
Strength with difficulty.
H High Strength 20 to 60 1 to 3 A piece of core 150 mm by 50 mm cannot be broken by hand but can be broken by a pick
with a single firm blow. Rock rings under hammer.
VH Very High 60 to 200 3 to 10 Hand specimen breaks with pick after more than one blow. Rock rings under hammer.
Strength
EH Extremely High Above 200 Above 10 Specimen requires many blows with geological pick to break through intact material. Rock
Strength rings under hammer.
= Diametral Point Load Test = Axial Point Load Test
CLASSIFICATION OF MATERIAL AS1726—2017
WEATHERING
Symbol Term Field Guide
RS Residual Soil (Note 1) Material is weathered to such an extent that it has soil properties. Mass structure and material texture and
fabric of original rock are no longer visible but the soil has not been significantly transported.
XW Extremely Weathered Material is weathered to such an extent that is has soil properties. Mass structure and material texture and
(Note 1) fabric of original rock are still visible.
HW Highly Weathered (Note 2) The whole rock mass is discoloured, usually by iron staining or beaching to the extent that the colour of the
original rock is not recognizable. Rock strength is significantly changed by weathering. Some primary miner-
als have weathered to clay minerals. Porosity may be increased by leaching, or may be decreased due to
deposition of weathering products in pores.
MH Moderately Weathered The whole of the rock material is discoloured, usually by iron staining or bleaching to the extent that the
(Note 2) colour of the original rock is not recognizable, but shows little or no change in strength from fresh rock.
SW Slightly Weathered Pock is partially discoloured with staining or bleaching along joints but shows little or no change of strength
from fresh rock.
FR Fresh Rock shows no signs of decomposition of individual minerals or colour change.
Note 1 The term ‘Extremely Weathered rock’ is misleading as the material has soil properties. The word ‘rock’ should be replaced with the name
of the original rock of the word ‘material’, eg. Extremely Weathered granite or Extremely Weathered material.
Note 2 Where it is not possible to distinguish between ‘Highly Weathered’ and ‘Moderately Weathered’ rock the term ‘Distinctly Weathered’ may
be used.
DEFECT TYPE/DESCRIPTION DEFECT PROFILE DEFECT ROUGHNESS
Symbol Description DESCRIPTION
B Bedding Parting V Vein
PL Planar
Symbol Description
J Joint HB/DB Handling/Drilling St Stepped
Break Sl Slickenside
Un Undulating
EW Extremely Weathered C Contact Sm Smooth
DEFECT INFILL DESCRIPTION
Seam
Symbol Description Ro Rough
FZ Fracture Zone L Cleavage Vertical Boreholes - The dip
Cn Clean: No visible
coating (inclination from horizontal) for the
CZ/S Crushed Zone/Seam X Foliation defect is given.
Sn Stain: Coated 1 to
3 mm Inclined Boreholes - The inclination
IS Infilled Seam S Schistocity is measured as the acute angle to the
Vr Veneer: < 1 mm core axis.
SZ/S Sheared Zone/Seam Ct Coating: 1 to 3
mm
Page 35
J001369-001-R-Rev0 August 2021 APPENDIX B AGS Practice Note Guidelines for Landslide Risk Management
Page 36
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 37
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 38
J001369-001-R-RevO August 2021 APPENDIX C Guidelines for Hillside Construction
Page 39
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
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PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007 114 Australian Geomechanics Vol 42 No 1 March 2007
Page 41
J001369-001-R-Rev0 August 2021 APPENDIX D CSIRO Foundation maintenance and footing performance: A Homeowner’s Guide
Page 42
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).
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Page 43
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 44
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.
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Tel (03) 9662 7666 Fax (03) 9662 7555 www.publish.csiro.au
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© 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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J001369-001-R-RevO August 2021 APPENDIX E Limitations
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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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