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Appendix F - Geo-Environmental Investigation Report · RAL24/0003
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GEO-ENVIRONMENTAL INVESTIGATION
Proposed Subdivision
41 Tallowwood Place, Black Mountain
Report for: Romildo Raveane
23099-001-Rev0
22 May 2023
Tectonic Geotechnical Pty Ltd
PO Box 899, Buderim QLD 4556
Office: 07 5478 9016
Email: [email protected]
www.tectonicgeo.com.au
A.B.N. 83 165 727 828
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Page 2
PROPOSED SUBDIVISION
41 TALLOWWOOD PLACE, BLACK MOUNTAIN
Document Review
Document No. Revision Prepared By Reviewed By Date Issued
001 0 Michael Cocks Ashley Davey 22 May 2023
Report Distribution
Document Revision Method of Delivery Issued To
Romildo Raveane
001 0 Electronic
([email protected])
Prepared By: Reviewed By:
Michael Cocks BEng MIEAust NER RPEQ 27540 Ashley Davey RPEQ 8159
Senior Geotechnical Engineer Managing Director
22 May 2023
Report No. 23099-001-Rev0 i
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PROPOSED SUBDIVISION
41 TALLOWWOOD PLACE, BLACK MOUNTAIN
Executive Summary
This report details the results of a geo-environmental investigation undertaken for a proposed 1 into 2 lot
residential subdivision at 41 Tallowwood Place, Black Mountain. The investigation comprised a site walk-
over by an experienced geotechnical engineer, together with excavating test pits at four locations. This
report summarises the results of the investigation and includes a slope stability assessment along with
recommendations regarding earthworks, retaining structures, site classification, footings, and drainage.
Also included is a feasibility assessment for on-site wastewater treatment and disposal.
A concept layout plan indicates that the proposed subdivision will comprise the reconfiguration of the existing
allotment into two new allotments. The easternmost allotment will retain an existing residence and driveway,
with a new driveway and residence proposed on the allotment to the west.
Subsurface conditions encountered in the test pits across the proposed new building envelope (i.e. TP1, TP3
and TP4) are summarised as follows:
Topsoil/Fill – comprising friable silty clay of medium plasticity, with varying organic, gravel and
cobble content to depths between 0.3 m and 0.6 m below ground level (BGL); then
Residual Soils – very stiff to hard, silty clay of high plasticity and clayey silt of high liquid limit to
depths between 1 m and 1.2 m BGL; underlain by
Extremely Weathered (XW) Materials/Weathered Phyllite – hard, silty gravelly clay of medium
plasticity and very low strength phyllite, rapidly grading to low strength (or stronger), with toothed
bucket refusal or very slow digging achieved at depths between 1.7 m and 2.3 m BGL.
Test pit TP2 was excavated on the proposed driveway alignment, downslope of a rock fill embankment
(inferred to be work to remediate a landslide) and encountered a friable topsoil layer to 0.3 m BGL, then a
stiff to very stiff, silty gravelly clay of high plasticity, comprising colluvium 1/landslide debris, to 3 m BGL.
Based on our site observations this area appeared to have been impacted by previous landslide movement
and thus, the proposed driveway alignment will need to be repositioned. It is envisaged that the new
driveway alignment could trace an existing track to the south of the proposed new building area.
No signs of groundwater seepage at the surface (‘springs’) were observed during our walk-over around the
proposed development area. Increased soil moisture conditions were observed within the colluvium
materials in test pit TP2, excavated in the previous landslide.
Based upon the existing site conditions, together with our qualitative assessment and quantitative analysis,
and subject to the implementation of recommendations given in this report, it is our assessment that there
would be a Low Risk of global slope instability affecting the proposed new residential development.
Based on the results of the investigation, the likely new building area would be equivalent to Class H1 in
accordance with AS 2870-2011 Residential Slabs and Footings. Site classification will need to be
reassessed at building stage to consider the extent of any earthworks proposed.
All footings supporting the proposed new residence and ancillary structures (including all retaining walls) must
penetrate through any fill and natural soils to found at least 0.3 m into very low strength (or stronger) phyllite.
High-level footings (typically in deeper cut areas) and steel reinforced concrete bored piles (or similar)
founded at least 0.3 m into very low strength (or stronger) weathered phyllite may be designed using an
allowable bearing pressure 400 kPa (footings) and 600 kPa (piles), respectively.
It is recommended that on-site effluent treatment and land application for the new allotment should comprise
a household sewage treatment plant producing a minimum of Secondary standard effluent and connected to
a wastewater irrigation system. The soil profile across the likely effluent disposal area typically comprised
Light Clay (Soil Category 5). Including a slope reduction on the design irrigation rate, a minimum land
application area of 560 m2 will be required for the proposed new residence. There is sufficient room on the
proposed lot to accommodate this.
1
A mixture of soil and/or rock (of various sizes) deposited over geological time due to movement induced by gravitational force
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Table of Contents
1.0 INTRODUCTION ........................................................................................................................................................ 1
2.0 PROPOSED DEVELOPMENT ................................................................................................................................... 1
3.0 AIMS & METHOD OF INVESTIGATION ................................................................................................................... 2
3.1 Fieldwork ...................................................................................................................................................... 2
3.2 Laboratory Testing ........................................................................................................................................ 2
4.0 RESULTS OF INVESTIGATION ................................................................................................................................ 3
4.1 Site Description............................................................................................................................................. 3
4.2 Topography................................................................................................................................................... 4
4.3 Geology ........................................................................................................................................................ 7
4.4 Subsurface Conditions.................................................................................................................................. 7
4.5 Geotechnical Laboratory Test Results .......................................................................................................... 8
4.6 Groundwater ................................................................................................................................................. 8
4.7 Surface Drainage .......................................................................................................................................... 8
4.8 Vegetation .................................................................................................................................................... 8
4.9 Buildings and Other Structures ..................................................................................................................... 9
5.0 SLOPE STABILITY ASSESSMENT .......................................................................................................................... 9
5.1 Existing Conditions ....................................................................................................................................... 9
5.2 Slope Stability Assessment ........................................................................................................................ 10
5.2.1 Qualitative Assessment......................................................................................................................... 10
5.2.2 Numerical Modelling.............................................................................................................................. 11
6.0 GEOTECHNICAL RECOMMENDATIONS .............................................................................................................. 13
6.1 Site Layout and Geotechnical Constraints .................................................................................................. 13
6.2 Earthworks .................................................................................................................................................. 14
6.2.1 Site Preparation and Trafficability ......................................................................................................... 14
6.2.2 Excavations ........................................................................................................................................... 14
6.2.3 Batter Slopes ........................................................................................................................................ 15
6.2.4 Filling..................................................................................................................................................... 15
6.3 Building Foundations .................................................................................................................................. 16
6.3.1 Site Classification .................................................................................................................................. 16
6.3.2 Footing Design ...................................................................................................................................... 16
6.4 Retaining Structures ................................................................................................................................... 17
6.5 Drainage ..................................................................................................................................................... 18
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6.6 Geotechnical Certification of Operational Works ........................................................................................ 19
7.0 WASTEWATER TREATMENT AND DISPOSAL .................................................................................................... 19
7.1 Existing Wastewater Infrastructure ............................................................................................................. 19
7.2 Wastewater Flow Design Allowance ........................................................................................................... 20
7.3 Terrain-Soil Assessment............................................................................................................................. 20
7.4 Recommendations ...................................................................................................................................... 20
7.4.1 System Type ......................................................................................................................................... 20
7.4.2 System Positioning................................................................................................................................ 21
7.4.3 System Construction ............................................................................................................................. 22
7.4.4 Maintenance and Inspection ................................................................................................................. 22
8.0 LIMITATIONS .......................................................................................................................................................... 22
TABLES
Table 1: Stability Risk Levels ............................................................................................................................................ 10
Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007) ....................................................................... 11
Table 3: Retaining wall design parameters ....................................................................................................................... 18
Table 4: Setbacks for subsurface land application area for on-site sewage treatment plant ............................................. 21
Table 5: Setback distances for on-site sewerage facilities (Protection of surface and groundwater) ................................ 21
TEXT FIGURES
Text Figure 1: Proposed subdivision layout, courtesy of Callaghan & Toth ........................................................................ 1
Text Figure 2: 2022 aerial image of the site and immediate surrounds (courtesy Nearmap imagery)................................. 3
Text Figure 3: Westerly view of the proposed development area........................................................................................ 3
Text Figure 4: Oblique drone image of the site looking east ............................................................................................... 4
Text Figure 5: Site plan showing ground surface contours (courtesy Noosa Council ‘Intramaps’) ...................................... 4
Text Figure 6: Views of roadside fill embankments ............................................................................................................. 5
Text Figure 7: Oblique drone image of the proposed development area and rock embankment, looking south-east ......... 6
Text Figure 8: View of the rock fill embankment, looking west ............................................................................................ 6
Text Figure 9: Extract from Gympie Surface Geology Map ................................................................................................. 7
Text Figure 10: Subsurface conditions in test pits TP3 (LHS) and TP2 (RHS).................................................................... 8
Text Figure 11: Extract from NSC landslide hazard overlay mapping ................................................................................. 9
Text Figure 12: Slope/W Analysis Output for residential construction on proposed new lot .............................................. 12
Text Figure 13: Construction exclusion zones and recommended building area, base map courtesy of NC .................... 13
Text Figure 14: Footing depth required to prevent undermining or surcharge loading ...................................................... 17
Text Figure 15: Existing wastewater treatment system (LHS) and inferred application area (RHS).................................. 19
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FIGURES
Figures 1: Site Plan
APPENDICES
APPENDIX A
Test Pit Reports & Explanatory Notes
APPENDIX B
Geotechnical Laboratory Certificate
APPENDIX C
AGS Guidelines - Qualitative Terminology for Use in Assessing Risk to Property
Some Guidelines for Hillside Construction
APPENDIX D
Limitations
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1.0 INTRODUCTION
This report details the results of a geo-environmental investigation undertaken for the proposed subdivision
at 41 Tallowwood Place, Black Mountain. The investigation was carried out by Tectonic for Romildo
Raveane, generally in accordance with proposal P23173-Rev0, dated 15 March 2023.
The site investigation comprised a walk-over by an experienced geotechnical engineer from Tectonic,
excavation of four test pits, together with in situ soil strength and geotechnical laboratory testing. This report
summarises the results of the investigation and includes a slope stability assessment, together with
recommendations regarding geotechnical matters for the development pertaining to earthworks, retaining
structures, footings, and drainage. Quantitative and qualitative slope stability assessments are included, as
well as an assessment of feasibility for on-site wastewater treatment and disposal.
2.0 PROPOSED DEVELOPMENT
A concept layout plan provided to Tectonic (Ref. Callaghan & Toth, Drawing NO. 2251-01, Rev A, dated
3 March 2023) indicates that the proposed subdivision will comprise the reconfiguration of the existing
allotment into two new allotments. The easternmost lot will retain an existing residence and driveway
access, whilst the westernmost lot will be vacant for the construction of a future dwelling. The proposed
new building area has been nominated in a cleared section of land to the west of the existing dwelling, with
a new driveway alignment shown off Tallowwood Place to the east of this. Due to evidence of previous
slope instability, an alternative driveway alignment from Tallowwood Place will need to be designed.
No civil design or earthworks drawings were available at the time of reporting; however, based on the site
conditions at the time of this assessment, cut and fill earthworks in the order of about 1.5 m depth/height
would be anticipated. The site is unsewered and the new lot will be serviced by on-site roof water tank
supply together with an on-site wastewater management system.
Text Figure 1 below illustrates the proposed subdivision layout.
Proposed driveway alignment to be revised (Ref. Section 6.1)
Text Figure 1: Proposed subdivision layout, courtesy of Callaghan & Toth
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3.0 AIMS & METHOD OF INVESTIGATION
The aim of this investigation is to provide guidance regarding general geotechnical matters, such as
earthworks requirements for building works, and to address slope stability issues and on-site wastewater
management. It is understood that this report will be submitted to Noosa Council (NC) in support of a
Development Application for Reconfiguration of a Lot. The investigation and report have therefore been
designed to address the requirements of the relevant NC codes and policies. It should be noted that this
slope stability assessment only covers geotechnical matters to address relevant parts of the NC Landslide
Hazard Overlay Code and does not consider any other requirements of the Code (e.g. site aesthetics, scenic
amenity etc.).
3.1 Fieldwork
An experienced geotechnical engineer from Tectonic undertook a site walk-over on 12 April 2023 to visually
assess any indicators of past slope instability. The walk-over included assessment of soil and rock outcrops,
surface drainage conditions, topography, evidence of erosion, and vegetation coverage/condition.
This was incorporated with a subsurface investigation, which comprised the excavation of four test pits
(designated TP1 to TP4) to depths between 1.7 m and 3 m below ground level (BGL), across the new
development area. Test pits were excavated using a 5.5 tonne excavator owned and operated by Bebrok
Excavations.
Pocket penetrometer (PP) testing was carried out on clay samples recovered from the test pits and within
test pit sidewalls, where safe to enter. Disturbed samples were recovered from select test pits.
The test pits were backfilled progressively on completion, with excavation spoil left slightly mounded at the
surface. Co-ordinates and collar levels were obtained using a handheld GNSS survey device with a
recorded accuracy of ±0.5 m. Test pit reports, along with explanatory notes, are presented in Appendix A.
Test locations are shown in Figure 1, attached at the conclusion of the report text.
3.2 Laboratory Testing
A select soil sample was dispatched to Construction Sciences, a NATA accredited laboratory located in
Kunda Park, for geotechnical testing. Laboratory testing was undertaken in accordance with Australian
Standard AS1289 Methods of Testing Soils for Engineering Purposes and comprised:
1 (No.) Atterberg Limits and Particle Size Distribution (PSD) test for soil classification purposes.
Laboratory test results are discussed in Section 4.5. The laboratory test certificate is attached in Appendix
B.
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4.0 RESULTS OF INVESTIGATION
4.1 Site Description
The site is formally described as Lot 36 on RP897845, covers an area of about 2.5 ha, with frontage to
Tallowwood Place along the southern boundary. At the time of this assessment an existing residence was
positioned in the central part of the site, with a driveway connecting to Tallowwood Place to the south-east.
The proposed new building area is in a cleared area to the west of the residence. Areas in the central and
eastern parts of the site primarily featured grass and scattered mature trees. Dense vegetation occupied
most of the western part of the site and fringed the northern site boundary. Surrounding properties
comprised similar rural residential allotments, with houses. A 2023 aerial image of the site and surrounds is
provided in Text Figure 2 below.
Subject Site
Proposed Development Area
Residence
Tallowwood Place
Text Figure 2: 2022 aerial image of the site and immediate surrounds (courtesy Nearmap imagery)
Site conditions at the time of our assessment are shown in Text Figures 3 and 4 below and overleaf.
Proposed Development Area
Text Figure 3: Westerly view of the proposed development area
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Existing Residence
Proposed Development Area
Text Figure 4: Oblique drone image of the site looking east
4.2 Topography
During the site walk-over, topographic features were noted, and ground slopes were recorded using a hand-
held clinometer. As illustrated in Text Figure 5, the site is located on the northerly facing flank of a ridge
which crests on the southern side of Tallowwood Place. Northerly trending natural drainage lines commence
at four locations across the site, connecting with an easterly flowing creek beyond the northern boundary.
Proposed Development Area
Concave Ground Surface Subject Site
Existing Residence
Remediated Landslide
Text Figure 5: Site plan showing ground surface contours (courtesy Noosa Council ‘Intramaps’)
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The proposed new development area is located on a moderately sloping, relatively linear and planar shaped
part of the ridge flank, with gradients typically in the order of about 15° to 17°, steepening downslope up to
about 20°.
To the south of the proposed new building area, the ground surface had been altered by previous cut and fill
earthworks presumably during the construction of Tallowwood Place. The roadside fill embankments were
estimated to range up to about 1.5 m high, and were typically battered between 30° and 35°; however,
crestline slumping was observed in parts resulting in steeper sections. An apparent track was observed
cutting across the roadside fill embankment down to the proposed new building area. It appeared that cut/fill
earthworks less than 1 m depth/height had been undertaken to form the track; however, due to the long
grass visual appraisal was difficult.
Apparent Track
Rock Fill Embankment
Text Figure 6: Views of roadside fill embankments
A drainage line intersected the ridge flanks between the existing residence and proposed new building area.
The roadside embankment across the head of this drainage line comprised imported rock fill, being about
3 m high, and battered between about 25° and 30°. Rock spalls extended from the toe of the rock fill batter
to the southern property boundary, with a level track about 5 m wide traversing the head of the drainage line.
It was estimated that about 2 m of fill had been placed over the drainage line.
Based on the above observations, it appeared that a section of Tallowwood Place about 40 m to the south-
west of the existing residence had been impacted by a previous landslide. It appears that the area was
remediated using rock fill; however, no design details were available. A review of higher resolution aerial
imagery from Nearmap and Qimagery suggests that the rock fill embankment has been in place since 2006;
however, due to the low resolution of earlier images it cannot be confirmed prior to this.
A stormwater pit was observed at the crest of the rock fill embankment; however, there was no obvious
evidence of an outlet below the toe of the batter. Text Figures 7 and 8 overleaf illustrate this area at the time
of the investigation.
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Track
Drainage Line Rock Fill Embankment
Proposed Development Area
Text Figure 7: Oblique drone image of the proposed development area and rock embankment, looking south-east
Rock Fill Embankment Approx. Property Boundary
Track
Text Figure 8: View of the rock fill embankment, looking west
Previous cut and fill earthworks had also been undertaken during the construction of the existing residence
and driveway. Based on a visual appraisal it appeared that cut and fill earthworks in the order of about 2 m
deep and 2 m high had been undertaken, most of which were supported by timber sleeper and boulder
retaining walls. A fill batter about 2 m high was present downslope of the existing driveway which was
battered at about 30°. Inferred natural gradients around the residence typically ranged between 20° and 25°.
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4.3 Geology
The 1:100,000 scale Gympie Surface Geological Map 2 (Ref. Text Figure 9) indicates that the site is underlain
by materials derived of the early to middle Triassic age Kin Kin Beds (blue-green shading), which are
described as “commonly cleaved and commonly kinked mudstone…”. The Australian Stratigraphic Units
Database describes the Kin Kin Beds as “arenite, argillite and phyllite.”
Indicative Site Location
Text Figure 9: Extract from Gympie Surface Geology Map
4.4 Subsurface Conditions
Detailed descriptions of the subsurface conditions encountered in the test pits are provided in the reports
attached in Appendix A, along with definition sheets which describe terms and abbreviations used on the
reports. Subsurface conditions encountered across the proposed new development area (i.e. test pits TP1,
TP3 and TP4) were consistent summarised as follows:
Topsoil/Fill – comprising friable silty clay of medium plasticity, with varying organic, gravel and
cobble content to depths between 0.3 m and 0.6 m BGL; then
Residual Soils – very stiff to hard, silty clay of high plasticity and clayey silt of high liquid limit to
depths between 1 m and 1.2 m BGL; underlain by
Extremely Weathered (XW) Materials/Weathered Phyllite – hard, silty gravelly clay of medium
plasticity and very low strength phyllite, rapidly grading to low strength (or stronger), with toothed
bucket refusal or very slow digging achieved at depths between 1.7 m and 2.3 m BGL.
Test pit TP2 was excavated on the proposed driveway alignment, downslope of the rock fill embankment
(inferred remediated landslide) and encountered a friable topsoil layer to 0.3 m BGL, then a stiff to very stiff,
silty gravelly clay of high plasticity, being colluvium 3/landslide debris, with fissured and slickensided 4
surfaces to 3 m BGL (limit reach of the machine). Based on our site observations this area appeared to
have been impacted by previous landslide movements.
Text Figure 10 overleaf illustrates typical subsurface conditions encountered during the investigation.
2
State of Queensland, Dept. of Natural Resources, Mines and Energy, Gympie Surface Geology, Sheet 9445, 2018
3
A mixture of soil and/or rock (of various sizes) deposited over geological time due to movement induced by gravitational force
4
A smooth, often striated surface produced by movement along a plane of weakness within soil or rock
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Topsoil
Topsoil
Colluvium/Landslide Debris
Residual Soil
XW Material/Phyllite
Fissured/Slickensided Surfaces
Text Figure 10: Subsurface conditions in test pits TP3 (LHS) and TP2 (RHS)
4.5 Geotechnical Laboratory Test Results
Laboratory testing on a sample recovered from test pit TP3 between 0.4 m and 0.7 m BGL, indicates that the
sample was a clayey silt of high liquid limit, tending to a high plasticity silty clay. It should be noted that, due
to the high silt and clay content of the soils, the materials are expected to be susceptible to strength loss,
particularly if they become wet.
4.6 Groundwater
No signs of groundwater seepage at the surface (‘springs’) were observed during our walk-over around the
proposed development area. Groundwater was not encountered in the test pits at the time of investigation;
however, increased moisture conditions (moist to wet soils) were encountered in the deep colluvium profile in
test pit TP2. The soils within the test pits across the proposed new building area were dry to moist.
Groundwater conditions are expected to be reflective of prevailing weather conditions and seepage may
develop, particularly at depth following periods of prolonged or heavy rainfall.
4.7 Surface Drainage
Natural surface drainage follows the ground surface gradients from the proposed development area and
broader site to the north, ultimately into a creek beyond the site boundaries. Generally, surface water is
expected to drain well from the site considering the positive gradients and low permeability of the clayey
soils; however, poorer drainage conditions are anticipated on level areas.
No signs of significant erosion were observed around the proposed development area at the time of the
assessment; however, rill erosion was observed around the existing residence in areas where concentrated
stormwater flows appear to develop.
4.8 Vegetation
The proposed new building area was primarily covered by grass. Areas around the existing residence
comprised landscaped gardens and maintained grass with scattered trees. Relatively dense bushland
occupied most of the western part of the site and traced the northern boundary. Some of the trees on
steeper slopes and within the drainage lines were noted to be tilting/leaning with ‘J’ shaped curves which
can be a sign of previous instability. Generally, the trees around the proposed new building area were
relatively straight, exhibiting no obvious signs which would indicate global slope instability.
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4.9 Buildings and Other Structures
Although not covered by this slope stability assessment, the existing residence in the central part of the site
comprised a single storey structure elevated on posts, with a formalised undercroft area. Based on an
external assessment the residence appeared to be in good structural condition, considering age, with no
obvious signs of distress (e.g. tilting, cracking, misalignment etc.) which would indicate global slope
instability.
As mentioned previously, timber sleeper and boulder walls up to about 1.5 m high supported previous
earthworks undertaken around the residence. Some of the timber sleeper walls were noted to be
tilting/leaning, with large voids present within the boulder walls. Horizontal separations up to about 30 mm
were present between a concrete pathway and the north-wester corner of the residence, with parts of the
slab undermined. The distress observed in these structures appeared to be related to age, poor
construction, and adverse drainage conditions rather than global slope instability.
5.0 SLOPE STABILITY ASSESSMENT
5.1 Existing Conditions
The Noosa Planning Scheme 2020 includes a landslide hazard overlay map (Ref. extract in Text Figure 11)
which indicates that most of the site, including the proposed new development area has a Moderate to High
Landslide Hazard.
Proposed Development Area
Subject Site
Text Figure 11: Extract from NSC landslide hazard overlay mapping
It should be noted that the NC map is a broad-scale indication of the potential landslide susceptibility only
and is superseded by this site-specific assessment. The recommended building area as defined in
Section 6.1 did not exhibit any indicators of global, natural slope instability, with competent natural
materials and weathered rock encountered at shallow depths in the test pits excavated across the area.
Building exclusions and setbacks from areas of identified instability are recommended.
Surface cracks up to about 20 mm wide were observed across the proposed new building area which
appeared to be related to soil shrinkage due to drying, rather than slope instability.
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5.2 Slope Stability Assessment
5.2.1 Qualitative Assessment
The risk assessment for this project has been carried out following AGS 2007 Practice Note Guidelines for
Landslide Risk Management. Relative levels of risk and their implications are given in Table 1 and the
Qualitative Terminology for Use in Assessing Risk to Property is also attached in Appendix B.
Table 1: Stability Risk Levels
Risk Level Example Implications(1)
Unacceptable without treatment. Extensive detailed investigation and research, planning and implementation of
VH Very High Risk treatment options essential to reduce risk to Low; may be too expensive and not practical. Work likely to cost
more than value of property.
Unacceptable without treatment. Detailed investigation, planning and implementation of treatment options
H High Risk
required to reduce risk to Low. Work would cost a substantial sum in relation to the value of the property.
May be tolerated in certain circumstances (subject to regulators’ approval) but requires investigation, planning and
M Moderate Risk implementation of treatment options to reduce 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
L Low Risk
maintenance required.
VL Very Low Risk Acceptable. Manage by normal slope maintenance procedures.
Note: (1) The implications for a particular situation are to be determined by all parties to the risk assessment and may depend on the nature of the
property at risk; these are only given as a general guide.
Considering the existing site conditions, and subject to the implementation of recommendations given in
Section 6, it is assessed that there would be a Low (L) Risk of global slope instability affecting the proposed
subdivision. Regulators (NC) normally require that a Very Low or Low Risk of landslide affecting property
must be demonstrated to enable development approval. Summarised in Table 2 overleaf is our qualitative
assessment of landslide risk for the site. A summary of qualitative terminology for use in assessing risk to
property is attached in Appendix C (taken from AGS 2007).
This risk assessment excludes geotechnical risk associated with the existing structures and areas outside the
recommended building zone.
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Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)
Assessed
Hazard Likelihood Consequence
Risk
Comments
Given the presence of very stiff (or stiffer) residual
soils at shallow depth, together with no evidence of
1: Recommended building existing instability and apparent lack of groundwater
area and driveway alignment across the recommended building area, it is
(Ref. Section 6.1) - Failure Unlikely Minor Low considered Unlikely that a landslide would develop,
through fill and natural residual subject to implementation of the recommendations
soil above the foundation depth in Section 4. Given a potential Minor impact from
such shallow instability the resultant risk would be
Low as per AGS 2007.
The likelihood of a deep failure through the weathered
2: Recommended building phyllite is assessed as Rare due to the strength of
area and driveway alignment these materials, moderately sloping ground and no
(Ref. Section 6.1) - Deep seated Rare Major Low signs of previous deep-seated instability across the
failure within weathered phyllite recommended building area. Although the
below the foundation depth consequence of such a failure could be Major, the
resultant risk is Low as per AGS 2007.
The potential impacts on slope stability of the development components have been assessed, and the
measures recommended below in Section 6 have been designed to mitigate those impacts so that a Low Risk
of landslide can be achieved for the proposed new building area.
5.2.2 Numerical Modelling
In order to estimate the factor of safety (FOS) against slope instability for the proposed development,
numerical analysis has been conducted using Slope/W, including consideration of adverse short-term
groundwater conditions. The modelled conditions for future construction comprised a 40 kPa surcharge, to
represent the future dwelling, landscaping and up to 1.5 m of filling. A 10 kPa surcharge was also applied up
slope of the building envelope to represent a future driveway. As all footings for the future structures will be
founded on weathered phyllite, minimal building loads would surcharge the soil profile.
The subsurface profile for this scenario was modelled on the conditions encountered in the test pits,
comprising very stiff residual soil up to about 1 m deep overlying XW materials and weathered phyllite. The
model assumes any existing topsoil, colluvium, uncontrolled fill or firm/loose (or weaker) materials will be
stripped from the development areas prior to filling. Although groundwater was not encountered within the
test pits excavated around the proposed building area, groundwater conditions have been modelled to
assess the FOS during an adverse temporary case with a piezometric surface at about 1 m BGL.
Results of the numerical slope stability analysis for the proposed new house site are illustrated in
Text Figure 12 overleaf. The key points from our analysis are summarised as follows:
Unit weight and shear strength parameters adopted for the soil and weathered rock strata were
estimated based on our interpretation of the geotechnical investigation data and were typically within
the mid range of values recommended for similar materials in Appendix D of Australian Standard
AS4678-2002 Earth Retaining Structures.
Analysis was undertaken for specified slip circle centroids (over a grid) and radii to assess global
slope instability. The adopted ground surface profile was based on the steepest slope measured
during the field investigation across the proposed building area, that being about 17°. The analysis
returned an acceptable minimum FOS value of 1.5, with adverse groundwater conditions included.
This result indicates that the industry standard minimum FOS against slope instability for hillside
development (≥1.5) would be achievable for the proposed development.
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Text Figure 12: Slope/W Analysis Output for residential construction on proposed new lot
Our analysis indicates that an acceptable FOS against slope instability could be achieved for the proposed
new residential building area, and that there would be a Low Risk of slope instability affecting this area,
subject to implementation of the recommendations outlined in Section 6.
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6.0 GEOTECHNICAL RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached in Appendix C.
6.1 Site Layout and Geotechnical Constraints
A recommended building area is defined in Text Figure 13. No building, filling or effluent disposal areas shall
be undertaken outside of this area unless assessed and approved by a geotechnical RPEQ prior to
construction. The proposed driveway will need to be repositioned away from the exclusion zone. An
indicative new driveway alignment is also illustrated on Text Figure 13. The final lot boundaries should be
designed to ensure the exclusion zone is wholly within one allotment (i.e. not on a site boundary), to reduce
the consequence of potential future instability.
Recommended Low Risk Building Area Exclusion Zone
Not Assessed
Not Assessed
Indicative new driveway alignment
Text Figure 13: Construction exclusion zones and recommended building area, base map courtesy of NC
To achieve a Low Risk of instability, the following is recommended:
No structures, driveways, filling, or wastewater irrigation areas are to be constructed within the
exclusion zone shown in Text Figure 13, unless assessed and approved by a geotechnical RPEQ.
Proposed Operational and Building Works must be reviewed and approved by a geotechnical RPEQ
once detailed design drawings are available.
All retaining walls exceeding 1 m high and/or subject to surcharge loads must be engineer designed
and certified, which must include an assessment of global and internal stability.
Unretained fill heights shall be limited to no more than 1 m and shall be located on ground sloping at
less than 10°. All fill to be placed on ground sloping at 10° or steeper must be fully supported by an
engineer designed and certified retaining structure. Filling must not exceed 1.5 m high unless
assessed and approved by a geotechnical RPEQ.
Design and construction of footings shall be undertaken in accordance with Section 6.3.2.
Formal drainage should be constructed to ensure all stormwater is directed away from the proposed
structures and effluent disposal areas.
Although the remediated landslide is within the recommended exclusion zone, to prevent water ponding
around the area it is recommended that the existing track is removed, and the ground surface is graded such
that stormwater can freely drain into the drainage line downslope. Care must be taken to ensure that
grading works do not undermine the toe of the rock fill embankment and they should not extend beyond the
southern property boundary.
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6.2 Earthworks
6.2.1 Site Preparation and Trafficability
Following clearing of vegetation (where required), tree stumps and large roots must be ‘grubbed out’ and any
organic rich topsoil, firm/loose (or weaker) soils, colluvium/slopewash, overly wet materials and any
uncontrolled fill must be stripped and removed from the proposed development area. Topsoil materials must
not be used in structural fill; however, may be placed across landscaping or effluent disposal areas (if
required). It is recommended that, following removal of unsuitable materials, all building/pavement
subgrades should be proof rolled using a minimum 4 tonne roller in the presence of a civil/geotechnical
RPEQ to identify any ‘soft spots’. Materials in any such soft spots should be excavated and replaced with
select fill material, constructed as recommended in Section 6.2.4.
Based on the results of the investigation, it is likely that excavation depths up to about 0.3 m will be required
to remove the existing topsoil; however, deeper pockets may be present across the building envelope.
After stripping, the subgrade is expected to comprise mostly very stiff residual clays of high plasticity, tending
towards clayey silt, grading to weathered phyllite in areas of deeper excavations. The cohesive (clay/silt)
materials would be subject to strength loss from repetitive vehicle loading (particularly from rubber tyred
plant) or if they become overly wet. Due to the potential for poor trafficability during and after wet periods,
placement of a minimum 150 mm thick granular working platform may be required, particularly along access
ways and laydown areas.
Wherever possible, due to the potential loss of strength under elevated moisture content and sensitivity of
the natural subgrades, light construction equipment should be utilised and trafficking of subgrades should be
minimised. Subgrades should be graded and ‘sealed off’ at the end of each working day using a smooth
drum roller to prevent ponding of water and aid shedding of runoff, so that the risk of subgrade softening is
minimised. Earthworks would likely be particularly prone to disruption due to wet weather, which should be
considered accordingly during project planning.
The site should be graded to shed surface water runoff away from all construction areas. Swale drains
should be constructed along the toes of any cuts, and above cuts where possible, with the drains graded to
discharge collected waters to a control point away from any effluent disposal area before release off-site.
Appropriate erosion and sediment control measures must be installed prior to commencement of earthworks
at this site.
Specific design would need to be carried out to determine working platform requirements for any heavy plant
(e.g. mobile cranes and piling rigs), and a thicker rock fill platform may be required than suggested above.
6.2.2 Excavations
Excavations in the natural soils and very low to low strength phyllite to the test pit termination depths should
be achievable using conventional earthmoving plant, such as medium to large (8 to 20 tonne) excavators
with toothed buckets and/or ripper attachments (i.e. the material is rippable).
As indicated by toothed bucket refusal and very slow digging at depths of about 1.7 m and 2.3 m BGL, low
strength (or stronger) phyllite would be expected in deeper excavations. Excavations into any low strength
(or stronger) weathered phyllite may require the use of ripper and/or hydraulic rock breaking attachments
with large equipment (e.g. 20 to 40 tonne excavator(s)), particularly in any confined excavations (e.g. service
trenching). If high strength (or stronger) weathered phyllite requires excavation, other specialised excavation
methods (e.g. pre-splitting the rock using ‘Nonex’) may be required.
Excavations will need to be carefully monitored and managed so that excessive ground vibrations do not
cause damage to neighbouring structures.
Should groundwater seepage be encountered during construction, such seepage should be readily
removable using gravity drainage at a low point in the excavation.
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6.2.3 Batter Slopes
Unsurcharged cut batters to a maximum of 2 m deep may be temporarily formed at 1V:1H in the natural
residual soils and weathered phyllite, provided groundwater is not encountered. Steeper temporary batters
may be permissible in low strength (or stronger) weathered phyllite subject to an assessment during
construction by a geotechnical RPEQ. Where space limitations occur or the above temporary batter slopes
are not achievable, installation of temporary retention would be required.
Permanent batters in very stiff (or stiffer) residual clays and very low strength (or stronger) phyllite up to 2 m
deep may be formed at 1V:2H. Steeper and higher batters may be permissible in low strength (or stronger)
phyllite subject to an assessment during construction by a geotechnical RPEQ. Permanent batters up to 1 m
high in future controlled fill on slopes <10° may be formed no steeper than 1V:2.5H. All fill on slopes
exceeding 10° must be supported by engineer designed and certified retaining structures, unless assessed
and approved by a geotechnical RPEQ. Permanent batter slopes will require some form of erosion
protection such as revegetation by landscaping (e.g. topsoil, Jute matting and planting).
Placement of heavy ‘builders plastic’ or filter ‘cloth’, pinned to batters may be required if heavy of prolonged
rainfall occurs during construction. Exposure of temporary batters should be minimised in order to limit
shrinkage cracking in clayey soils and potential development of temporary instability.
6.2.4 Filling
The high plasticity cohesive (clay/silt) soils, where free of deleterious materials (e.g. organics, oversize etc.),
could be reused as structural fill, or as non-structural fill (e.g. in landscaping areas, batters, etc.). It should
be noted that reuse of high plasticity soils may have adverse implications for pavements (low CBR values)
and future house construction (high reactivity resulting in Class H2 or higher site classification). Site won
clay/silt materials should be placed in the lower fill layers at least 0.5 m below finished platform levels, where
possible.
It should also be noted that due to the high silt content the natural soils would develop poor engineering
qualities when wet of optimum moisture content and would be difficult to handle and place during
earthworks, which should be considered during earthworks planning.
The weathered phyllite could be used as structural fill provided the materials can be broken down to suitable
particle sizes (<100 mm). Depending on the method of excavation used, re-use of any medium strength (or
stronger) weathered phyllite as structural fill may not be possible without specialised processing (e.g. use of
a mobile crushing plant).
Should importation of fill be required, it is recommended that such fill should comply with the following:
Minimum CBR of 10%
Maximum plasticity index of 15%
Maximum particle size of 100 mm
All structural fill should be compacted at moisture contents within the range of ±2% of OMC for Standard
Compaction. Fill should be placed in 250 mm thick (loose thickness) layers and be compacted by repeated
rolling to achieve a dry density ratio of at least 95% of the maximum Dry Density Ratio (DDR), or 100% DDR
based upon the Standard Compaction method within 0.3 m of pavement subgrades.
Confirmatory compaction testing must be carried out at regular intervals. A minimum of two tests per vertical
lift is recommended where structural fill heights are to exceed 300 mm. Further details for control and testing
of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for Commercial and
Residential Developments. It is recommended that Level 1 geotechnical inspection and testing be
conducted for all Operational and Building Works filling where fill heights exceed 0.5 m.
Due to the sloping nature of the site, all fill must be ‘benched’ into the natural slope, over-filled by 0.5 m
(horizontally) and then trimmed back to the well compacted material.
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6.3 Building Foundations
6.3.1 Site Classification
Based on the results of the investigation, preliminary characteristic surface movements (‘ys’) for the natural
soil profile are estimated to range up to 40 mm, equivalent to Class H1 in accordance with AS 2870-2011
Residential Slabs and Footings. As mentioned previously, surface cracking was noted across the proposed
new building area which appeared to be related to soil shrinkage due to drying.
It should be noted that the predicted order of movement is based on the existing natural soil profiles (i.e. no
additional cutting or filling), and moisture content changes within soils due to normal seasonal moisture
variations only.
Reactive soil movements and site classification should be assessed by the footing design engineer at
building stage to consider the extent of earthworks across the proposed new building area, together with any
retained trees (trees located near footings can influence the potential ground movement, and result in more
severe site classifications). A site classification ‘soil test’ may be required prior to building works to confirm
the site classification and footing design parameters.
It should be noted that the placement of highly reactive clay fill may have an adverse impact on the site
classifications.
Due to the clayey nature of the site soils, it would be prudent to implement the following practices to prevent
changes in soil moisture:
Prevent drying of the clay soils during construction by minimizing exposure. This may be achieved
by measures such as covering subgrades with HDPE (‘black builders plastic’) or ‘Bidim’, and
placement of ‘blinding’ layers across the excavation subgrade and footing bases.
Install and maintain temporary drainage to prevent saturation of the site during construction.
Seal the ground surface around the building perimeter (e.g. concrete or paved pathway).
Plant shrubs/trees at least a distance from the building equal to the mature height of the shrub/tree.
Maintain stormwater drains to prevent overflow into soils and repair any damaged drains
immediately.
6.3.2 Footing Design
All footings supporting the proposed new residence and ancillary structures (including all retaining walls) must
penetrate any fill and natural soil to found at least 0.3 m into very low strength (or stronger) phyllite. Based on
the test pits, footing depths are anticipated to range between about 1.5 m and 2 m BGL (below existing
ground levels), however, depths are likely to be shallower in areas of future cut and deeper in areas of future
fill.
The subsurface conditions encountered indicate that steel reinforced concrete bored piles or ‘bucket piers’ will
generally be required unless excavations expose the required foundation materials at or near the subgrade.
High-level footings and steel reinforced concrete bored piles (or similar) founded at least 0.3 m into very low
strength (or stronger) weathered andesite may be designed using an allowable bearing pressure 400 kPa
(footings) and 600 kPa (piles), respectively.
It is recommended that the bases of all footings should be formed level/horizontal to ensure loads are well
keyed into the slope. Footing design should also account for potential soil reactivity. A suitably qualified and
experienced geotechnical RPEQ should inspect the footing excavations to confirm appropriate foundation
materials and cleanliness prior to pouring concrete.
All footings should found such that they are not adversely affected by any adjacent excavations, trenches, or
retaining walls that are not designed to support building loads. Where footings are located within a horizontal
distance of 1.5H (H being the batter height) of any cut or fill batter crest, these footings must be founded at a
depth level with the toe of the batter. Footings should found at least below a plane extending 1 m horizontally
from the base of trenches/excavations/retaining walls, then rising up at 1V:1H, as illustrated in Text Figure 14
overleaf.
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Text Figure 14: Footing depth required to prevent undermining or surcharge loading
Footing bases must be cleaned following mechanical excavation to expose undisturbed materials over the
full base area. It is essential that the piling contractor have a ‘mud bucket’ or similar device to enable clean
out of the pile bases.
If any soil conditions encountered during construction are found to differ from those noted in the geotechnical
investigation, Tectonic should be notified immediately, and an inspection carried out to determine if changes
to footing design are required.
6.4 Retaining Structures
Design for retaining structures could be carried out using a pressure distribution applicable to the wall type
and based on the parameters listed in Table 3 overleaf. The values in Table 3 assume that the walls are
fully drained, and no allowance is included for hydrostatic pressures, construction loading, up-slope footing
loadings, the effects of sloping ground and backfill compaction stresses.
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Table 3: Retaining wall design parameters
Lateral earth pressure coefficients
Unit Friction
Retained material weight angle Ko
Ka
(kN/m3) (Degrees) (Non-yielding Kp
(Cantilever wall)
wall)
Very Stiff (or Stiffer)
19 27 0.38 0.55 2.66
Residual Clays
Hard XW Materials 20 32 0.31 0.47 3.25
Very Low Strength (or
21 35 0.27 0.43 3.69
Stronger) Phyllite
Future Fill * * * * *
Note: * depends on fill material type and level of compaction.
As a minimum, retaining structures must be founded as per the recommendations in Section 6.3.2 above
with the footings also designed to account for lateral loads imposed by the retaining wall. Detailed design
must include an assessment of internal and global stability, together with required bearing capacity and
founding depth, by the retaining wall design engineer.
6.5 Drainage
We anticipate that construction activities should be minimally affected by groundwater, however some
seepage may occur. Control of seepage during construction activities may be achieved by grading the base
of the excavations towards a suitable discharge point.
During construction temporary open swales and diversion drainage should be installed to divert seepage
and/or runoff away from the building areas, to prevent saturation of the subgrade.
Specific drainage recommendations are as follows:
Construct diversion drainage along the upslope edge of the building area (e.g. turf, concrete or rock
lined drain or similar) to discharge any captured stormwater from the development area downslope
of any structure, embankment or effluent disposal area.
Grade any building platforms (minimum 1V:100H) to achieve positive drainage into edge drains.
If the proposed driveway runs sidelong across the natural slope, diversion drainage be constructed
above the proposed driveway cut(s).
To prevent the migration of stormwater into the proposed effluent disposal area, install diversion
drainage (e.g. landscaped swale) along the upslope side of the proposed disposal area.
Subsurface drainage must be installed behind any retaining walls (e.g. slotted ‘aggi’ pipe wrapped in filter
‘sock’ placed in gravel backfill). Depending on matters such as the extent of drainage installed and site-
specific groundwater conditions, the designer must make an assessment of hydrostatic pressure to be
accounted for in the design of the retaining structure. Any pools must include a hydrostatic pressure relief
valve (or similar), which must daylight at the ground surface.
All excess stormwater collected around the proposed development area, including the effluent disposal area,
must be directed by pipes or surface channels (e.g. rock lined ‘dry creek’ beds) to discharge at least 10 m
away from and downslope of any structure or embankment, and not towards the effluent disposal area. A
surface dissipation device such as rock weir or rock lined contour drain must be installed at the stormwater
outlet(s).
Subsurface disposal of stormwater must not be undertaken (including infiltration pits).
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6.6 Geotechnical Certification of Operational Works
NC may require the subdivision Operational Works to be certified by a geotechnical RPEQ prior to Plan
Sealing. Should Tectonic be required to certify the Operational Works, inspections must be completed by
Tectonic at various stages during construction (e.g. following site stripping, post completion etc.) to ensure
the recommendations provided within this report have been adhered too. Tectonic should be contacted prior
to commencement of Operational Works to confirm specific inspection requirements.
7.0 WASTEWATER TREATMENT AND DISPOSAL
An assessment of the type and configuration of wastewater system that may be suitable for a proposed
development requires:
Assumptions to be made regarding the typical building/visitor configuration and probable
wastewater flow; and
Evaluation of the terrain-soil capacity to accept treated wastewater; and
Consideration of NC wastewater treatment and disposal system construction and siting
requirements.
7.1 Existing Wastewater Infrastructure
The existing residence will be unaffected by the proposed subdivision and will continue to be serviced by an
existing wastewater treatment system, situated to the west of the existing house. The existing sewerage
treatment and disposal infrastructure servicing the residence was inspected during the walkover.
The residence appeared to be serviced by an operational aerated wastewater treatment system. It was
understood that the system produced at least Secondary standard effluent, with treated effluent from the
system piped to a surface application area downslope.
At the time of inspection no indications of inadequate operation or failure of the system were observed (e.g.
wet, soft ground, seepage or irregular grass growth).
The existing wastewater system is expected to be sufficient to continue to service the existing residence,
assuming the system was originally designed and installed to handle the respective residential outputs and is
able to meet current NC requirements. This system (including land application area) should be inspected
and serviced by a licensed plumber to confirm that it remains fit for purpose and conforms with NC
requirements.
Text Figure 15 below shows the existing wastewater treatment infrastructure observed.
Text Figure 15: Existing wastewater treatment system (LHS) and inferred application area (RHS)
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7.2 Wastewater Flow Design Allowance
For a typical four-bedroom house (or three bedrooms plus study), we have estimated a peak occupancy of
seven persons. This assumption is consistent with current NC development standards and has been used to
demonstrate feasibility of on-site effluent disposal. Should the proposed new residence exceed this size, it is
the owner’s responsibility to demonstrate feasibility of the design, meeting all relevant regulations.
For each occupant, a typical wastewater flow allowance of 120 L/person/day has been taken from
Appendix H of AS1547:2012. This represents the flow allowance for households with standard water
reduction fixtures (including duel flush toilets, shower flow restrictors, aerator faucets and water conserving
automatic washing machines) serviced by rainwater tank supply.
We therefore estimate a typical daily household wastewater flow rate of 840 L/day (7 x 120 L/person/day).
It should be noted that wastewater flow rates may be further reduced by the adoption of full water reduction
facilities (e.g. reduced flush 6/3 L toilets, shower flow restrictors, aerator faucets, front-load washing
machines and flow/pressure control valves on all water-use outlets, etc.). Conversely, the use of extra
wastewater producing fixtures (e.g. spa baths) has the potential to increase the household wastewater flow
rate.
Final wastewater flow rates must be calculated at the time of detailed design of the wastewater system, at
building stage once the house design is known.
7.3 Terrain-Soil Assessment
The terrain-soil combination(s) encountered at a site are assessed so that an Expected Available Area (EAA)
can be delineated for suitable methods of wastewater treatment and land application.
The terrain across the proposed new building area is categorised as Linear Planar in accordance with the
slope configurations described in Figure C2 of AS1547:2012.
Ground surface gradients typically range from 15° to 17° (up to ~30%) across the proposed effluent disposal
area. Sizing of the likely wastewater irrigation area on the proposed new lot will therefore need to incorporate
a slope reduction rate, as described in Table M2 of AS1547:2012, or shall be effectively terraced as
necessary to reduce slope to < 10% negating the effect of natural slopes. The addition of a slope reduction
rate will result in an increase to the land application area of approximately 50% to facilitate sloping ground
conditions.
It has been assessed from the results of the investigation that the soil profile across the likely effluent
disposal area on proposed Lot 2 comprises predominantly silty clay, with gravel throughout, which is
equivalent to Light Clay (Soil Category 5). This categorisation has been derived via the method described
in Table M1 of AS1547:2012.
Topsoil materials obtained from excavations or imported to site, should be used to supplement the soil profile
across the proposed irrigation area. Such materials could be used to form narrow mounds/swales along the
contours within the irrigation areas.
7.4 Recommendations
7.4.1 System Type
It is recommended that wastewater from the new lot be directed to a suitably sized Household Sewage
Treatment Plant (HSTP) connected to an irrigation system. The HSTP must be licensed to produce at least
Secondary standard effluent, with Chief Executive approval from the Department of Housing and Public
Works; however, to maximise available residential space and to reduce setback requirements, it may be
necessary/desired to use an Advanced Secondary treatment system.
Table M1 of AS1547:2012 recommends a Design Irrigation Rate (DIR) of 3 mm/day for Category 5 soil.
Therefore, a minimum irrigation area of about 280 m² (840 L/day / 3mm/day) would be required. However, an
additional 50% slope reduction rate for application areas with slopes between 20-30% has been applied in
accordance with Table M2 of AS1547:2012. The calculated land application area for is therefore 560 m².
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The nominal land application area as shown in Figure 1 would therefore be appropriate, and it is assessed that
that there is enough room to site the wastewater irrigation area with the necessary setbacks on the new lot.
The need for a reserve area is generally applied to septic tank systems, producing low quality (Primary
Standard) effluent, due to increased potential for fowling and failure of the trenched land application area to
occur. As the use of aerated wastewater treatment systems is proposed, which are capable of delivering high
quality (Secondary Standard or better) effluent, the risk of fouling and system failure is negligible. Proposed
wastewater irrigation can be easily repaired in-place as required, so the addition of a separate reserve area is
not warranted.
7.4.2 System Positioning
Positioning (‘setbacks’) of the land application systems must be in accordance with the horizontal and
vertical setback distances recommended in Tables T2, T3 and T5 of the Queensland Plumbing and
Wastewater Code 2019, as summarised in Tables 4 and 5 below.
Table 4: Setbacks for subsurface land application area for on-site sewage treatment plant
Horizontal separation distance
Site Feature
Upslope Downslope Level
Property boundaries, pedestrian paths, walkways, recreation areas, retaining wall, and
2m 4m 2m
footings for buildings and other structures.
Inground swimming pools. 6m
Inground potable water tank.
6m
(Secondary standard effluent or better)
Note: Distances measured from the edge of trench/bed excavation or subsurface irrigation distribution pipework to the nearest point of the feature.
Table 5: Setback distances for on-site sewerage facilities (Protection of surface and groundwater)
Separation Distance
Site Feature
Advanced Secondary Secondary Effluent
Effluent
Surface Waters:
Top of bank of permanent or intermittent water course, lake, bay or
estuary;
Top water level of a surface water source used for agriculture, 10 m 30 m
aquaculture or stock purposes;
Open stormwater drainage channel or drain;
Bore or a dam.
Unsaturated soil depth to a permanent water table (vertically) 0.3 m 0.6 m
Note: Distances measured from the edge of the irrigated wetted area to any point of the feature.
Unsaturated soil depths of 0.6 m (i.e. depth to rock or wet soil) and 0.3 m are recommended for Secondary
and Advanced Secondary effluent, respectively. Test pits indicate that such adequate unsaturated soil
depths are available across the proposed effluent disposal area.
The layout for effluent treatment and disposal on the new lot shall be decided at building stage, in
conjunction with a design provided by a NC registered evaluator.
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7.4.3 System Construction
Construction of wastewater land application areas must be carried out in accordance with Appendix M of
AS1547:2012 and NC requirements. In order to prevent any adverse impacts on the water quality from
effluent disposal, the elements given below shall be implemented:
Shallow subsurface drip systems must be installed at 100 mm to 150 mm depth into 150 mm to
250 mm of good quality sandy topsoil, in grassed of other suitably vegetated areas. Any sandy
topsoil material won from site works may be used to supplement the soil within the respective
disposal fields or alternatively shall be imported to the site.
Receiving native soils will be prepared by undertaking deep ripping / shallow cultivation combined
with the addition of organic matter (10 kg/m² raw mulch), together with gypsum (1 kg/m²) to ‘break
up’ any relatively hard clay subsoils, as required, and improve overall drainage characteristics.
Shallow subsurface irrigation lines will run parallel to slope contours. To evenly distribute
wastewater throughout the irrigation areas, pressure equalisation systems (i.e. pressure
compensating drip emitters) should be installed.
Surface diversion drainage shall be installed on the up-slope sides of the land application areas to
divert surface water and shallow subsurface seepage flows away. Such drainage should penetrate
to a minimum depth of 0.3 m BGL.
A low earthen bund shall be constructed, down slope of the effluent disposal areas up to 0.3 m high
to retain run-off and promote sheet flow.
Plant and maintain grasses, reeds and/or small shrubs within the land application areas. Preference
should be given to native plant species endemic to the local area, which are suitable for mostly wet
soils and are tolerant of nutrient loads (e.g. native riparian vegetation)
Erect signage at the boundaries of the area in at least two places in accordance with Council
requirements to warn people regarding the presence of wastewater pipes (e.g. “Sewage Effluent
Pipework Installed Below – DO NOT DIG” or “Recycled Water – Avoid Contact - DO NOT DRINK”).
Erect barriers where necessary to restrict access to public which may interfere or damage the
irrigation system.
Detailed design of the effluent disposal system must be carried out by an NC registered evaluator to
accompany the plumbing application at the building stage, once the building designs are finalised.
7.4.4 Maintenance and Inspection
Operation and maintenance of a HSTP is the responsibility of the property owner. A licensed service agent
must be appointed to undertake routine servicing works in line with regulatory authority approval conditions.
To comply with NC requirements, the following management and inspection shall be implemented once the
effluent disposal systems are established:
Continuous monitoring by the property owner for any signs of system failure such as septic odour,
seepage, soil and/or plant discoloration.
Should any signs of system failure be observed by the property owner, including the in-built HSTP
failure alarm, the manufacturer shall be contacted immediately to arrange for the necessary repairs.
Quarterly inspection, testing and repair (if necessary) to the HSTP and irrigation area by a Licensed
Inspector (normally a service provided by the HSTP manufacturer).
8.0 LIMITATIONS
Your attention is drawn to the document Limitations, which is included in Appendix D of this report. The
statements presented in this document are intended to advise you of what your realistic expectations of this
report should be, and to present you with recommendations on how to minimise the risks associated with the
services provided by Tectonic for this project.
22 May 2023
Report No. 23099-001-Rev0 22
Page 29
Tectonic Geotechnical Pty Ltd
PO Box 899
Buderim Qld 4556
Ph: 07 5478 9016
PROJECT:
Subject Site
PROPOSED SUBDIVISION
41 TALLOWWOOD PLACE,
BLACK MOUNTAIN
TITLE:
SITE PLAN
TP4 CLIENT:
ROMILDO RAVEANE
TP3
DATE:
TP1 TP2 DRAWN:
MCC 18/05/2023
CHECKED: DATE:
ACD 18/05/2023
Tallowwood Place
SCALE:
AS SHOWN (APPROX. ONLY)
LEGEND:
APPROX. TEST PIT
LOCATION
INDICATIVE LAND
APPLICATION AREA
(560 m2)
Notes:
PROJECT NO.: FIGURE: REV:
Base plan adopted from Nearmap imagery, dated 14 August 2022
0m 40m 80m 23099-001 1 0
Page 30
PROPOSED SUBDIVISION
41 TALLOWWOOD PLACE, BLACK MOUNTAIN
APPENDIX A
Test Pit Reports & Explanatory Notes
22 May 2023
Report No. 23099-001-Rev0
Page 31
Test Pit No.
TP1
Page 1 of 1
Engineering Log - Test Pit Project No.: 23099
Client: Romildo Raveane Commenced: 12/4/2023
Project Name: Proposed Subdivision Completed: 12/4/2023
Hole Location: 41 Tallowwood Place, Black Mountain Logged By: MCC
Hole Position: 7079268.0 m E 486709.0 m N MGA2020 Zone 56 Checked By: ACD
Equipment Type and Model: 5.5t Excavator RL Surface: 190.66 m
Excavation Dimensions: Datum: AHD Operator: Bebrok
Excavation Information Material Description and Observations
Relative Density
Classification
Pocket Shear
Penetration
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Recovery
Condition
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
Remarks secondary and minor components, colour Observations
Water
RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100 150200
CI Silty CLAY, (TOPSOIL), medium plasticity, grey, 0.00: TOPSOIL
with roots up to 30mm
Fr
CH Silty CLAY, high plasticity, pale brown, orange 0.30: RESIDUAL
400
brown, trace fine to coarse gravel, tending
DS to clayey silt
600
190.2
0.4-0.8m 0.5
400
600
D
Not Encountered
400
600
H
189.7
1.0
EX
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 23099.GPJ <<DrawingFile>> 18/5/2023 11:54 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 3.00.2 2021-03-30
600
CI Silty Gravelly CLAY, medium plasticity, pale 1.20: EXTREMELY
brown, yellow brown, fine to coarse gravel WEATHERED MATERIAL
PHYLITTE, distinctly weathered, pale grey, yellow 1.40: WEATHERED ROCK
189.2
1.5 brown, fine grained, very low to low strength, very
thinly foliated
becoming low strength
188.7
2.0
Hole Terminated at 2.00 m
Very slow digging
188.2
2.5
187.7
3.0
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
N - Natural Exposure VE - Very Easy Level (Date) U## - Undisturbed Sample (## mm) D - Dry VS - Very Soft
X - Existing Excavation E - Easy DS - Disturbed Sample M - Moist S - Soft
BH - Backhoe Bucket Inflow BDS - Bulk Disturbed Sample W - Wet F - Firm
R - Ripper F - Firm VSt - Very Stiff
EX - Excavator H - Hard H - Hard
RH - Rock Hammer VH - Very hard VL - Very Loose
Plastic Limit
L - Loose
Classification Symbols and < PL MD - Medium Dense
Soil Descriptions = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Classification System Fr - Friable
Page 32
Test Pit No.
TP2
Page 1 of 1
Engineering Log - Test Pit Project No.: 23099
Client: Romildo Raveane Commenced: 12/4/2023
Project Name: Proposed Subdivision Completed: 12/4/2023
Hole Location: 41 Tallowwood Place, Black Mountain Logged By: MCC
Hole Position: 7079272.0 m E 486734.0 m N MGA2020 Zone 56 Checked By: ACD
Equipment Type and Model: 5.5t Excavator RL Surface: 187.04 m
Excavation Dimensions: Datum: AHD Operator: Bebrok
Excavation Information Material Description and Observations
Relative Density
Classification
Pocket Shear
Penetration
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Recovery
Condition
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
Remarks secondary and minor components, colour Observations
Water
RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100 150200
CI Silty CLAY, (TOPSOIL), medium plasticity, 0.00: TOPSOIL
brown, with roots
D Fr
CH Silty Gravelly CLAY, high plasticity, pale brown, 0.30: COLLUVIUM/
red brown, pale grey, fine to coarse phylitte LANDSIDE DEBRIS
gravel
186.5
150
0.5
DS 250
0.5-0.8m
M to St to
W VSt
186.0
1.0
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 23099.GPJ <<DrawingFile>> 18/5/2023 11:55 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 3.00.2 2021-03-30
150
250
Not Encountered
185.5
1.5
EX
DS becoming pale grey, red brown, fine to
1.5-1.8m coarse gravel, with fissured & slickensided
surfaces
185.0
2.0 VSt
250
M to
W
184.5
2.5
100
150
St
184.0
3.0
Hole Terminated at 3.00 m
Limit reach
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
N - Natural Exposure VE - Very Easy Level (Date) U## - Undisturbed Sample (## mm) D - Dry VS - Very Soft
X - Existing Excavation E - Easy DS - Disturbed Sample M - Moist S - Soft
BH - Backhoe Bucket Inflow BDS - Bulk Disturbed Sample W - Wet F - Firm
R - Ripper F - Firm VSt - Very Stiff
EX - Excavator H - Hard H - Hard
RH - Rock Hammer VH - Very hard VL - Very Loose
Plastic Limit
L - Loose
Classification Symbols and < PL MD - Medium Dense
Soil Descriptions = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Classification System Fr - Friable
Page 33
Test Pit No.
TP3
Page 1 of 1
Engineering Log - Test Pit Project No.: 23099
Client: Romildo Raveane Commenced: 12/4/2023
Project Name: Proposed Subdivision Completed: 12/4/2023
Hole Location: 41 Tallowwood Place, Black Mountain Logged By: MCC
Hole Position: 7079283.0 m E 486726.0 m N MGA2020 Zone 56 Checked By: ACD
Equipment Type and Model: 5.5t Excavator RL Surface: 185.48 m
Excavation Dimensions: Datum: AHD Operator: Bebrok
Excavation Information Material Description and Observations
Relative Density
Classification
Pocket Shear
Penetration
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Recovery
Condition
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
Remarks secondary and minor components, colour Observations
Water
RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100 150200
CI Silty CLAY, (TOPSOIL), medium plasticity, brown 0.00: TOPSOIL
grey, with roots up to 25mm
D Fr
MH Clayey Silt, high liquid limit, orange brown, red 0.30: RESIDUAL
350
brown, trace fine to coarse gravel, tending to
DS silty clay
400
185.0
0.4-0.7m 0.5
VSt to
D
H
350
400
Not Encountered
184.5
1.0 1.00: EXTREMELY
CI Silty Gravelly CLAY, medium plasticity, pale grey, 500
red brown, fine to coarse gravel WEATHERED MATERIAL
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 23099.GPJ <<DrawingFile>> 18/5/2023 11:55 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 3.00.2 2021-03-30
H
EX
PHYLLITE, distinctly weathered, pale grey, red 1.30: WEATHERED ROCK
brown, fine grained, very low to low strength, very
timely foliated
184.0
1.5
becoming low strength
183.5
2.0
Hole Terminated at 2.30 m
Very slow digging
183.0
2.5
182.5
3.0
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
N - Natural Exposure VE - Very Easy Level (Date) U## - Undisturbed Sample (## mm) D - Dry VS - Very Soft
X - Existing Excavation E - Easy DS - Disturbed Sample M - Moist S - Soft
BH - Backhoe Bucket Inflow BDS - Bulk Disturbed Sample W - Wet F - Firm
R - Ripper F - Firm VSt - Very Stiff
EX - Excavator H - Hard H - Hard
RH - Rock Hammer VH - Very hard VL - Very Loose
Plastic Limit
L - Loose
Classification Symbols and < PL MD - Medium Dense
Soil Descriptions = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Classification System Fr - Friable
Page 34
Test Pit No.
TP4
Page 1 of 1
Engineering Log - Test Pit Project No.: 23099
Client: Romildo Raveane Commenced: 12/4/2023
Project Name: Proposed Subdivision Completed: 12/4/2023
Hole Location: 41 Tallowwood Place, Black Mountain Logged By: MCC
Hole Position: 7079304.0 m E 486707.0 m N MGA2020 Zone 56 Checked By: ACD
Equipment Type and Model: 5.5t Excavator RL Surface: 182.63 m
Excavation Dimensions: Datum: AHD Operator: Bebrok
Excavation Information Material Description and Observations
Relative Density
Classification
Pocket Shear
Penetration
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Recovery
Condition
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
Remarks secondary and minor components, colour Observations
Water
RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100 150200
Silty Gravelly CLAY, (FILL), medium plasticity, 0.00: FILL
brown, grey, fine to coarse gravel, with roots up
to 50mm, trace cobbles up to 300mm
D Fr
182.1
0.5
Not Encountered
CH Silty CLAY, high plasticity, red brown, trace fine 0.60: RESIDUAL
to coarse gravel, tending to clayey silt
600
EX
D to
H
181.6
1.0 M
CI Silty Gravelly CLAY, medium plasticity, pale grey, 1.00: EXTREMELY
red brown, fine to coarse gravel WEATHERED MATERIAL
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 23099.GPJ <<DrawingFile>> 18/5/2023 11:55 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 3.00.2 2021-03-30
600
PHYLLITE, distinctly weathered, pale grey, grey, 1.30: WEATHERED ROCK
fine grained, very low to low strength
181.1
1.5 1.50: BEDS DIPPING OUT
becoming medium strength, thinly foliated
OF SLOPE ~ 45-50 degree
Hole Terminated at 1.70 m
Toothed bucket refusal
180.6
2.0
180.1
2.5
179.6
3.0
Method Penetration Water Samples and Tests Moisture Condition Consistency/Relative Density
N - Natural Exposure VE - Very Easy Level (Date) U## - Undisturbed Sample (## mm) D - Dry VS - Very Soft
X - Existing Excavation E - Easy DS - Disturbed Sample M - Moist S - Soft
BH - Backhoe Bucket Inflow BDS - Bulk Disturbed Sample W - Wet F - Firm
R - Ripper F - Firm VSt - Very Stiff
EX - Excavator H - Hard H - Hard
RH - Rock Hammer VH - Very hard VL - Very Loose
Plastic Limit
L - Loose
Classification Symbols and < PL MD - Medium Dense
Soil Descriptions = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Classification System Fr - Friable
Page 35
TERMS USED ON LOGS
DRILLING/EXCAVATION METHOD
AD* Auger Drilling RA Rotary Air BH Tractor Mounted Backhoe
ADH Hollow Auger RD Rotary Blade or Drag bit EX Tracked Hydraulic Excavator
HA Hand Auger RT Rotary Tri-cone bit HMLC Core – 63mm
*T TC-Bit HQ Core – 63mm
*V V-Bit NMLC Core – 47mm
NQ Core – 52mm
R Ripper
RH Rock Hammer
WATER
GROUNDWATER NOT The observation of groundwater, whether present or not, was not possible due to drilling water,
OBSERVED surface seepage or cave in of the borehole/test pit.
GROUNDWATER NOT The borehole/test pit was dry soon after excavation. However, groundwater could be present in
ENCOUNTERED less permeable strata. 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
5,4,10 N=14 5,4,10 = Blows per 150mm. N = Blows per 300mm penetration following 150mm seating
30/65mm 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
SV Field shear vane test expressed as uncorrected shear strength (sv = peak value, sr = residual value)
PP Pocket penetrometer test expressed as instrument reading in kPa
U50 Thin walled tube sample - number indicates nominal sample diameter in millimetres
DCP Dynamic cone penetration test
CPT Electronic cone penetration test
CPTu Electronic cone penetration test with pore pressure (u) measurement
Rev1
February 2021
Page 36
METHOD OF SOIL DESCRIPTION
USED ON LOGS
CLASSIFICATION AND INFERRED STRATIGRAPHY
Soil is classified and described in borehole and test pit logs using the preferred method given in AS1726 – 2017.
The material properties are assessed in the field by visual/tactile methods.
Particle Size Plasticity Properties
Major Sub Division Particle Size
Division
BOULDERS > 200 mm
COBBLES 63 to 200 mm
Coarse 19 to 63 mm
GRAVEL Medium 6.7 to 19 mm
Fine 2.36 to 6.7 mm
Coarse 0.6 to 2.36 mm
SAND Medium 0.21 to 0.6 mm
Fine 0.075 to 0.21
SILT 0.002 to 0.075
CLAY < 0.002 mm
NOTE: The U line is an approximate upper bound for most materials.
Data which plot above the U line may represent unusual/problem soil
behavior, or unreliable data and should be considered carefully.
MOISTURE CONDITION AS1726 - 2017
Symbol Term Description
D Dry Sands and gravels are free flowing. Clays & Silts may be brittle or friable and powdery.
M Moist Soils are darker than in the dry condition & may feel cool. Sands and gravels tend to cohere.
W Wet Soils exude free water. Sands and gravels tend to cohere.
CONSISTENCY AND DENSITY AS1726 - 2017
Symbol Term Undrained Shear Symbol Term Density Index % SPT “N” #
Strength
VS Very Soft 0 to 12 kPa VL Very Loose Less than 15 0 to 4
S Soft 12 to 25 kPa L Loose 15 to 35 4 to 10
F Firm 25 to 50 kPa MD Medium Dense 35 to 65 10 to 30
St Stiff 50 to 100 kPa D Dense 65 to 85 30 to 50
VSt Very Stiff 100 to 200 kPa VD Very Dense Above 85 Above 50
H Hard Above 200 kPa
In the absence of test results, consistency and density may be assessed from correlations with the observed behaviour of
the material.
# SPT correlations are not stated in AS1726 – 2017, and may be subject to corrections for overburden pressure and
equipment type.
Rev1
October 2017
Page 37
METHOD OF ROCK DESCRIPTION USED ON LOGS
CLASSIFICATION AND INFERRED STRATIGRAPHY
Rock is classified and described in borehole and test pit logs using the preferred method given in AS1726 – 2017.
The material properties are assessed in the field by visual/tactile methods.
STRENGTH
Point Load
Symbol Term Index, Is(50) Field Guide
(MPa)
VL Very 0.03 to 0.1 Material crumbles under firm blows with sharp end of pick; can be peeled
Low with knife; too hard to cut a triaxial sample by hand. Pieces up to 30 mm
can be broken by finger pressure.
L Low 0.1 to 0.3 Easily scored with a knife; indentations 1 mm to 3 mm show in the specimen
with firm blows of pick point; has dull sound under hammer. A piece of core
150 mm long by 50 mm diameter may be broken by hand. Sharp edges of core
may be friable and break during handling.
M Medium 0.3 to 1 Readily scored with a knife; a piece of core 150 mm long by 50 mm diameter
can be broken by hand with difficulty.
H High 1 to 3 A piece of core 150 mm long by 50 mm diameter cannot be broken by hand but
can be broken with pick with a single firm blow; rock rings under hammer.
VH Very 3 to 10 Hand specimen breaks with pick after more than one blow; rock rings under
High hammer.
EH Extremely >10 Specimen requires many blows with geological pick to break through intact
High material; rock rings under hammer.
Relationship between Is(50) and UCS (unconfined compressive strength) will vary with rock type and strength, and
should be determined on a site-specific basis. UCS is typically 10 to 30 x Is(50), but can be as low as 5.
ROCK MATERIAL WEATHERING
Symbol Term Field Guide
Soil developed on extremely weathered rock; the mass structure and
Residual
RS substance fabric are no longer evident; there is a large change in volume
Soil but the soil has not been significantly transported.
Extremely Rock is weathered to such an extent that it has soil properties - i.e. it either
EW
Weathered disintegrates or can be remoulded, in water.
Whole of rock is discoloured, usually by iron staining or bleaching to the
extent that the colour of the original rock is not recognizable. Rock strength
Highly
HW is significantly changed by weathering. Porosity may be increased by
Weathered
leaching, or may be decreased due to deposition of weathering products in
Distinctly
DW pores.
Weathered
Whole of rock is discoloured, usually by iron staining or bleaching to the
Moderately extent that the colour of the original rock is not recognizable; but shows little
MW
Weathered or no change of strength from fresh rock.
Slightly Rock is slightly discoloured but shows little or no change of strength relative
SW
Weathered to fresh rock.
FR Fresh Rock shows no sign of decomposition or staining.
ABBREVIATIONS FOR DEFECT TYPES AND DESCRIPTIONS
Defect Type Coating or Infilling Roughness
CS/CZ Crushed seam/zone (Fault) Ca Calcite Po Polished
DB Drilling break Clay Clay Sm Smooth
EW Extremely weathered seam Cn Clean Sl Slickensided
HB Handling break Co Coating ( > 1mm) Ro Rough
IS/IZ Infilled seam/zone Fe Iron oxide VRo Very rough
Op Open
J Joint
Qz Quartz
Pt Parting St Stain Planarity
SS/SZ Sheared seam/zone (Fault) Vn Veneer (<1mm) Cu Curved
Vn Vein X Carbonaceous Dis Discontinuous
Ir Irregular
Pl Planar
St Stepped
Un Undulating
Rev4
February 2021
Page 38
PROPOSED SUBDIVISION
41 TALLOWWOOD PLACE, BLACK MOUNTAIN
APPENDIX B
Geotechnical Laboratory Certificate
22 May 2023
Report No. 23099-001-Rev0
Page 39
Construction Sciences Pty Ltd Laboratory: Sunshine Coast Laboratory
ABN: 74 128 806 735 Phone: 07 5452 0100
Fax: 07 5452 0133
Address: Email: [email protected]
32 Hi-Tech Drive,
Kunda Park QLD 4556
QUALITY OF MATERIALS REPORT
Client: Tectonic Geotechnical Pty Ltd Report Number: 3740/R/59450-1
Client Address: 924 David Low Way, Marcoola Project Number: 3740/P/2437
Project: Tallowwood Place, Black Mountain Lot Number:
Location: Various Internal Test Request: 3740/T/45237
Supplied To: Tectonic Geotechnical Pty Ltd Client Reference/s: O/N 23099
Area Description: Report Date / Page: 24/04/2023 Page 1 of 1
Test Procedures AS1289.3.6.1, AS1289.3.1.2, AS1289.3.2.1, AS1289.3.4.1, AS1289.2.1.1, AS 1289.3.3.1
Sample Number 3740/S/238924 Test Pit Number TP3
Sampling Method Tested As Received Test Pit Depth (m) 0.4-0.7
Date Sampled 14/04/2023 Chainage
Sampled By Client Sampled Cut/Fill Number
Date Tested 14/04/2023 Material Source Not Supplied
PSD Preparation Material Type Not Supplied (Not Supplied)
Atterberg Preparation Dry Sieved / Oven Dried Prep Material > 53.0mm (%)
Material Description MH Silt, high plasticity, trace of sand, trace of gravel
Specification Percent Specification PARTICLE SIZE DISTRIBUTION GRAPH
AS Sieve (mm)
Minimum (%) Passing (%) Maximum (%)
100
26.5 100
19.0 100
13.2 98 80
6.7 93
Percent Passing (%)
4.75 91
60
2.36 88
1.18 87
0.600 86 40
0.425 85
0.300 84
20
0.150 82
0.075 80
0
6.7
9.5
1.18
2.36
4.75
13.2
19.0
26.5
0.075
0.150
0.300
0.425
0.600
AS Sieve Size (mm)
Specification Specification Specification Specification
Test Result Result Test Result Result
Minimum (%) Maximum (%) Minimum (%) Maximum (%)
Liquid Limit (%) 61 0.075/0.425 Fines Ratio 0.94
Plastic Limit (%) 34 PI x 0.425 Ratio (%) 2292.3
Plastic Index (%) 27 LS x 0.425 Ratio (%) 891.4
Linear Shrinkage (%) 10.5 Linear Shrinkage Defects -
Remarks Results apply to the sample/s as received.,
Accredited for compliance with ISO/IEC 17025 – Testing
Accreditation Number: 1986
Corporate Site Number: 3740
Approved Signatory: Justin Harrex
Form ID: W85Rep Rev 3
Page 40
PROPOSED SUBDIVISION
41 TALLOWWOOD PLACE, BLACK MOUNTAIN
APPENDIX C
AGS Guidelines - Qualitative Terminology for Use in
Assessing Risk to Property
Some Guidelines for Hillside Construction
22 May 2023
Report No. 23099-001-Rev0
Page 41
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
Australian Geomechanics Vol 42 No 1 March 2007
Form No. 68039
68039 RL2Risk
Landslide August 2010
Management Issued 10/7/07
Page 42
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.
Australian Geomechanics Vol 42 No 1 March 2007
Form No. Landslide
68039 68039 RL2Risk
August 2010
Management Issued 10/7/07
Page 43
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
Form No. 68029 RL2 August 2010
Page 44
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
114 Australian Geomechanics Vol 42 No 1 March 2007
Form No. 68029 RL2 August 2010
Page 45
PROPOSED SUBDIVISION
41 TALLOWWOOD PLACE, BLACK MOUNTAIN
APPENDIX D
Limitations
22 May 2023
Report No. 23099-001-Rev0
Page 46
LIMITATIONS This document has been prepared for the purpose outlined in Tectonic’s proposal and no responsibility is accepted for the use of this document, in whole or in part, for any other purpose. The scope of Tectonic’s Services are as described in Tectonic’s proposal, and are subject to restrictions and limitations. Tectonic did not perform a complete assessment of all possible conditions or circumstances that may exist at the site referenced in the report. 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 Tectonic in regards to it. Conditions may exist which were undetectable given that economic and time constraints limit the practical extent of geotechnical investigation. Variations in conditions may occur between investigation 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. Where variations exist on site, additional studies and actions may be required. Tectonic’s opinions are based upon information that existed at the time that the work was performed. The passage of time, man-made or natural events, may alter the site conditions. It is understood that the Services undertaken allowed Tectonic to form 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 the preparation of this document are based on the conditions indicated from published sources and the findings of the investigation described. Actual subsurface conditions may differ from those indicated in the document (e.g. between boreholes or test pits). 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 Tectonic for incomplete or inaccurate data supplied by others. This document is provided for the sole use by the Client 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. Tectonic accepts no responsibility for damages, if any, suffered by any third party as a result of decisions made or actions based on this document. Rev 1 (March 2016)
Used in these records
Appendix F - Geo-Environmental Investigation Report.pdfRelated documentApplication case desk ↗
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