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Slope Stability Report-21190-001-Rev0 Pomona Kin Kin Rd
21 June 2021 Project No. 21190-001-Rev0 Phil Brierley C/- NDD Constructions Pty Ltd Attention: Tayla Jennings Email: [email protected] SLOPE STABILITY ASSESSMENT – PROPOSED SHED & WORKSHOP 906 POMONA KIN KIN ROAD, KIN KIN Dear Tayla, 1.0 INTRODUCTION Tectonic has undertaken a slope stability assessment for a proposed shed and workshop at 906 Pomona Kin Kin Road, Kin Kin. This report presents the results of our slope stability assessment, together with geotechnical advice for the development. In summary, subject to implementation of the recommendations made herein, there would be a Low Risk of slope instability affecting the proposed development in accordance with the Australian Geomechanics Society Guidelines for Landslide Risk Management, dated March 2007 (AGS 2007). 1.1 Details of Site and Development The subject site is described as Lot 4 on RP183110, covers an area of 3.2522 ha and has frontage to Pomona Kin Kin Road along the south-western boundary. At the time of the assessment a residence and shed were located in the northern part of the site, with the proposed shed to be located downslope to the south-west. It is understood that the proposed workshop will be situated adjacent to the existing residence. Access to the existing residence and proposed shed was via a partially unsealed and partially concrete driveway directly off Pomona Kin Kin Road. The proposed development areas had been altered by previous earthworks to create relatively level building platforms. Surrounding properties comprised similar rural residential allotments, with scattered residences and structures. A 2021 aerial image of the site and surrounds is provided in Text Figure 1 below. Further details describing the site are provided in Section 2. Existing Residence Proposed Workshop Subject Site Proposed Shed Location Text Figure 1: Aerial image of the site and surrounds (courtesy Nearmap imagery, dated 10 June 2021) 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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Phil Brierley 21190-001-Rev0
C/- NDD Constructions Pty Ltd 21 June 2021
Based on conversations with the client, it is understood that the proposed shed will be located south-west of
the existing residence on a relatively level platform as shown in Text Figure 1 above. The final location of
the proposed workshop had not been concluded; however, it is understood that it will be adjacent to the
existing residence in the northern part of the site.
Provided plans by NDD Constructions Pty Ltd (NDD) suggest that the shed and workshop will be of
conventional, lightweight construction comprising sheet metal roofing and walls, with portal steel framing
over concrete ground slabs. Overall, the shed will have three bays being about 12 m by 12 m (in plan), with
a height varying between about 4.5 m and 6.11 m. The workshop will have three bays being about 10 m by
4.5 m (in plan), with a height varying between about 2.3 m and 3.4 m.
At the time of the assessment the proposed shed and workshop areas had been altered by previous cut and
fill earthworks to create relatively level platforms. Based on a visual assessment it appeared that cut and fill
earthworks in the order of about 3 m depth/height had been undertaken at the proposed shed site, with the
proposed workshop to be situated on relatively level ground adjacent to the existing residence. It is
estimated that previous cut and fill earthworks in the order of about 2 m deep and 1.5 m high, respectively,
had been undertaken during previous residential construction.
Although no earthworks details were provided, based on the existing site conditions it is anticipated that
minimal (i.e. less than 0.5 m depth/height) additional earthworks will be required. Text Figure 2 below
provides some elevation views of the proposed shed and workshop.
Text Figure 2: Elevation views of the proposed shed (LHS) and workshop (RHS), courtesy of NDD
1.2 Method and Scope of Investigation
As part of our slope stability assessment, a desk-top study was carried out comprising a review of
published geological maps and slope stability studies.
A walk-over inspection was conducted in order to make an appraisal of the general condition of the site in
regard to topography, drainage, vegetation cover, geology, erosion, condition of existing structures and
slope stability. The walk-over survey was carried out by an experienced geotechnical engineer from
Tectonic on 28 May 2021.
The results of the desk-top study and walk-over survey are included in Section 2 below.
1.3 Qualifications of Responsible Engineer
This report has been reviewed by Mr. Ashley Davey, an RPEQ with more than 26 years’ experience in
geotechnical engineering, including a number of slope stability projects.
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2.0 DESCRIPTION OF EXISTING CONDITIONS
2.1 Geology
A published geological map for the region 1 indicates that the site is underlain by the early Triassic age Kin
Kin Beds comprising ‘arenite, argillite and phyllite’. An extract from the relevant geological map is provided
in Text Figure 3 below.
Indicative Site Location
Text Figure 3: Extract from Nambour Special Geology Map
At the time of the assessment, the shed cutting ranged up to about 3 m deep and typically exposed varying
very low to medium strength argillite. Cuttings along the existing driveway adjacent to the existing residence
also primarily exposed extremely weathered (XW) materials and very low to medium strength
argillite/phyllite.
Text Figure 4: Cutting on upslope side of shed platform (LHS) and along existing driveway (RHS)
To make an appraisal of the strength of the materials at the proposed shed site, Tectonic undertook four
standalone dynamic cone penetrometer (DCP) tests (designated DCP1 to DCP4). DCP1 to DCP3 were
undertaken along the crest of the existing fill platform working from south-east to north-west.
1
1:100,000 Gympie Special Geology Map, Sheet 9445 & Part 9545, DME, 1999
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DCP1 to DCP3 indicated the following subsurface conditions:
Firm to stiff/loose to medium dense materials from the ground surface to depths between 1.7 m and
2 m below ground level (BGL); then
Stiff/medium dense (or stronger) materials to the DCP termination depths at 2.3 m to 2.9 m BGL.
DCP4 was undertaken centrally in the cut side of the level platform and indicated the following subsurface
conditions:
Stiff/medium dense (or stronger) materials from the ground surface to 0.2 m BGL; then
Hard/dense (or stronger) materials to the DCP termination depth at 0.4 m BGL.
All DCP tests encountered practical refusal at the termination depths, which is inferred to be on XW
materials or very low strength (or stronger) argillite/phyllite as observed in the upslope cutting.
DCP reports are attached at the end of this report.
2.2 Topography
As illustrated in Text Figure 5, the subject site is located on the south-westerly facing flank of a ridge which
traces the north-eastern property boundary. The proposed development areas are generally governed by a
south-westerly dipping well rounded spur, interrupted by previous earthworks.
During the site walk-over, topographic features specific to the site were noted, and ground slopes were
recorded using a hand-held clinometer. As stated previously, the proposed development areas had been
altered by previous cut and fill earthworks to create relatively level building platforms. Based on our site
observations it appeared that cut and fill earthworks in the order of about 3 m depth/height had been
undertaken to create the platform at the proposed shed site, with previous cut and fill earthworks at the
existing residence (proposed workshop location) estimated to range up to about 2 m deep and 1.5 m high,
respectively.
Existing cuttings typically were battered between about 30° and 40°, with some isolated areas being near
vertical along the existing driveway. Downslope fill batters typically ranged up to about 26°; however, a fill
embankment associated with the driveway was noted to be about 1.5 m high battered at about 35°. Ground
slopes across the proposed development areas were relatively level, with inferred surrounding natural
ground slopes ranging between about 18° and 25°.
Existing Residence
Approx. Proposed Shed Location
Proposed Workshop
Subject Site
Driveway Alignment
Text Figure 5: Image showing ground surface contours (courtesy NC Interactive Mapping)
Text Figures 6 to 8 overleaf illustrate the site conditions at the time of the walk-over inspection.
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Proposed Shed Location
Text Figure 6: View of the proposed shed area looking south-east
Proposed Shed Location
Text Figure 7: View downslope of the proposed shed area, looking north-west
Text Figure 8: View of the likely workshop area, looking south-east from existing residence
2.3 Groundwater
No signs of groundwater seepage (‘springs’) were observed during our walk-over in the vicinity of the
proposed shed or workshop.
2.4 Surface Drainage
Natural surface drainage follows ground surface contours generally towards the south-west. Surface water
is expected to drain well from the natural slopes considering the positive natural gradients; however, poorer
drainage conditions are anticipated on level areas. No diversion drainage system was noted to be in place
above the cut or fill batters at the building sites. Culverts were present at the driveway crossovers along the
gravel driveway, with informal swale drains present along the cut side of the driveway. Rill erosion was
noted in the downslope fill batters and in isolated sections along the existing unsealed driveway alignment.
Recommendations to improve surface drainage are given in Section 4.5.
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2.5 Vegetation
At the time of the assessment, the surface of the proposed development areas comprised bare soil and
grass. Remaining areas in the south-western part of the site primarily featured long grass, with relatively
dense vegetation in the north-eastern corner of the site. Observable mature trees were noted to be
relatively straight and exhibited no obvious signs of tilting/leaning which could be attributed to slope
instability.
2.6 Buildings and Other Structures
At the time of the assessment an existing residence and shed were located in the northern part of the site. A
shipping container and additional small shed were also located on the level platform at the proposed new
shed site. Based on a visual assessment, observable areas were noted to be in relatively good structural
condition, displaying no signs of distress which could be attributed to slope instability. Cracking was evident
in the concrete driveway; however, this appeared to be related to age, ‘root jacking’ and poor construction
rather than global slope instability.
Text Figure 9: View of the existing residence and shed in northern part of the site
3.0 ASSESSMENT OF LAND STABILITY
3.1 Existing Conditions
The proposed development areas and much of the site are mapped by NC as being of Moderate (pale brown
shading) landslide susceptibility (Ref. Text Figure 10). Areas of Very Low/Low (no shading) susceptibility are
mapped around the existing residence and along the south-western and north-eastern boundaries.
Subject Site
Indicative Development Areas
Text Figure 10: Extract from NC Landslide Hazard Overlay mapping
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It should be noted that the NC map is a broad-scale indication of the potential landslide susceptibility and
is superseded by this site-specific assessment. In the vicinity of the proposed shed and workshop there
were no signs of global slope instability. Very low to medium strength argillite/phyllite were observed in
the cuttings on the upslope side of the development areas and along the existing driveway.
Based on review of available aerial imagery, it appears that the building platform at the proposed shed
site has been in place for over five years. Nevertheless, it should be noted that the fill platforms are
deemed to have been placed as uncontrolled fill, therefore, it is possible that zones within this fill may be
unsuitable, and that excessive settlement could occur over time, particularly following construction of non-
piled structures (e.g. landscaping structures, pavements etc.). Without verification that this fill was placed
under Level 1 inspection and testing per AS3798, the potential magnitude and extent of settlement within
this fill will be unknown.
3.2 Stability 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 below, and
the Qualitative Terminology for Use in Assessing Risk to Property is also attached.
Table 1: Stability Risk Levels
Risk Level Example Implications(1)
Unacceptable without treatment. Extensive detailed investigation and research, planning
Very High
VH and implementation of treatment options essential to reduce risk to Low; may be too
Risk
expensive and not practical. Work likely to cost more than value of property.
Unacceptable without treatment. Detailed investigation, planning and implementation of
H High Risk treatment options required to reduce risk to Low. Work would cost a substantial sum in
relation to the value of the property.
May be tolerated in certain circumstances (subject to regulators’ approval) but requires
Moderate
M investigation, planning and implementation of treatment options to reduce risk to Low.
Risk
Treatment options to reduce to Low risk should be implemented as soon as practicable.
Usually acceptable to regulators. Where treatment has been required to reduce the risk
L Low Risk to this level, ongoing maintenance required.
Very Low
VL Acceptable. Manage by normal slope maintenance procedures.
Risk
Note: (1) The implications for a particular situation are to be determined by all parties to the risk assessment and may
depend on the nature of the property at risk; these are only given as a general guide.
Considering the existing site conditions (Ref. Section 2), and subject to the implementation of
recommendations given below, it is assessed that there would be a Low (L) Risk of global slope instability
affecting the proposed development. Regulators (NC) normally require that a Very Low or Low Risk of
landslide affecting the 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 (taken from AGS 2007).
It should be noted that this risk assessment excludes geotechnical risk that may be associated with settlement
due to consolidation of any uncontrolled fill materials over time which could affect non-piled structures (e.g.
pavements, landscaping structures).
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Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)
Assessed
Hazard Likelihood Consequence Risk Comments
The likelihood of a failure through the fill or natural
residual soil materials is assessed as Unlikely due
to the low to moderate ground slopes immediate to
the proposed structures, apparent lack of
1: Shallow failure through fill or
groundwater and no signs of previous instability.
natural soils above the Unlikely Minor Low
The consequence of such a failure would be Minor
foundation depth
considering the anticipated confined extent of
instability, and the depth of foundations
recommended, with the resultant risk being Low as
per AGS 2007.
The likelihood of a deep failure through XW materials or
weathered rock below the foundation depth is assessed
2: Deep failure through XW
as Rare due to the strength of these materials, gentle to
materials or weathered rock Rare Major Low
moderate ground slopes and lack of groundwater.
below the foundation depth.
Although the 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 4 have been designed to mitigate those impacts.
4.0 RECOMMENDATIONS
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached.
4.1 Site Layout
Should the proposed shed and workshop locations be amended from that shown in Text Figure 1, Tectonic
must re-assess slope stability prior to construction. The proposed shed must be setback at least 3 m
horizontally from the crest of the fill platform.
4.2 Earthworks
Based on the proposed development and the existing site conditions it is anticipated minimal cut and fill
earthworks will be required (i.e. less than 0.5 m depth/height). Should proposed cut/fill exceed 0.5 m
depth/height, the impacts on slope stability must be reviewed by Tectonic before construction.
4.2.1 Site Preparation and Trafficability
Prior to construction, organic rich topsoil (e.g. placed post bulk earthworks for erosion control) or any water
softened materials (e.g. ponded water collected on the finished surface) must be stripped and removed from
the construction area. The platform subgrades should be proof rolled using a fully laden water cart (or
similar) to identify any ‘soft spots’. Any such soft spots should be excavated and replaced with select fill
material, constructed as recommended in Section 4.2.3.
The subgrade materials exposed after site stripping and excavations are expected to comprise mostly firm to
stiff clay materials and weathered argillite (in areas of existing cut). Such soils could be subject to strength
loss from repetitive vehicle loading (particularly from rubber tyred plant) or if they become 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 any laydown areas.
The site should be graded to shed surface water runoff away from construction areas. It should be noted
that during wet weather, the natural soils may cause turbid stormwater run-off. Appropriate erosion and
sediment control measures must be installed prior to commencement of earthworks at this site.
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4.2.2 Excavations
Excavations within the natural soils and very low to low strength weathered argillite/phyllite, should be
achievable using small to medium sized conventional earthmoving plant (e.g. 5 to 14 tonne excavators) with
toothed buckets. The use of larger earthmoving plant with ripper attachments may be required for efficient
excavations into stronger rock. Excavations into any medium strength (or stronger) weathered rock may
require the use of hydraulic rock breaking attachments or other specialised excavation techniques.
Temporary batter slopes may be formed at 1V:1H in the existing soils and weathered rock. Flatter batters
may be required if groundwater seepage is encountered, or if earthworks are undertaken during a period of
heavy rainfall.
Permanent batter slopes may be formed at 1V:2H in stiff (or stiffer) clays, medium dense sands, very low
strength rock and future controlled fill. Where such battering is not possible, fill batters and cuts will need to
be retained. All existing cut/fill batters should be trimmed back to the permissible grades outlined above,
otherwise must be retained by an engineer designed retaining wall (Ref. Section 4.4).
All batters should be protected from erosion by surface protection, the type of which will be dependent upon
a number of factors including batter slope, material type, aspect, aesthetic finish required, etc. As a
minimum, all soil batters should be topsoiled and seeded (or hydromulched) to establish a permanent grass
(or similar vegetation) cover.
Any excavations which may be required adjacent to existing structures will need to be specifically designed
to ensure that the structures are not adversely affected (e.g. 'undermined').
The above recommendations do not supersede any existing safety regulations or legislation applicable to
excavations (e.g. limits on personnel entry into trenches).
4.2.3 Filling
The existing natural soils where free of deleterious materials (e.g. vegetation, oversize etc.), are expected to
be suitable for re-use as structural fill, subject to appropriate moisture adjustment. It should be noted that
due to the highly reactive nature of the existing clay soils, the impacts on site classification must be
considered.
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%
Shrink-swell index ≤ 1%
Maximum particle size of 100 mm
Controlled fill materials should be compacted at moisture contents within the range of -2% to +2% of OMC for
Standard Compaction. Confirmatory testing must be carried out at regular intervals and further details for
control and testing of fill are given in Australian Standard AS 3798-2007 Guidelines on Earthworks for
Commercial and Residential Developments. Select fill should have a maximum particle size of 100 mm for
an uncompacted layer thickness of 200 mm and shall be compacted by repeated rolling with a small
compactor to achieve a dry density ratio of at least 95% of the Standard Maximum Dry Density for cohesive
soils, or 70% Dry Density Index for any imported cohesionless soils.
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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4.3 Footings
All footings supporting the proposed shed, workshop and ancillary structures (including retaining walls) must
penetrate through existing/future fill and unsuitable natural soils to found into competent underlying material
as follows:
In areas containing fill or deeper natural soil profiles, steel reinforced concrete bored piles must
socket at least 0.3 m in hard XW materials or very low strength (or stronger) weathered rock.
In areas where cut exposes hard XW materials or very low strength (or stronger) rock at or near the
subgrade level, footings must found at least 0.2 m into such materials.
Steel reinforced concrete bored piles so founded may be designed using an allowable end bearing pressure
(ABP) of 400 kPa in XW materials or very low strength (or stronger) weathered rock. High level footings in cut
areas may be designed using an ABP of 400 kPa in XW materials or very low strength (or stronger)
weathered rock.
Based on DCP testing undertaken from Tectonic high-level footings should be suitable in areas of cut, with
piles ranging up to about 3 m deep required towards the fill embankment crest. A suitably qualified and
experienced engineer should inspect the footing excavations to confirm appropriate foundation materials
and cleanliness prior to pouring concrete.
Footing design should also account for potential soil reactivity (to be determined by others). The site
classification should consider the potential variation of materials across the building platform.
All footings should found such that they are not adversely affected by (or affect) any adjacent excavations,
trenches, retaining walls (e.g. existing and future retaining walls), or in ground structures that are not
designed to support building loads. Footings should found at least below a plane extending 1 m horizontally
from the base of trenches/batter slopes/excavations/retaining walls/swimming pool, then rising up at 1V:1H,
as illustrated in Text Figure 11.
Text Figure 11: 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. Where piles are required, it is essential that the piling contractor have a ‘mud bucket’ or
similar to enable clean out of the pile bases.
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If any soil conditions encountered during construction are found to differ from those noted above, Tectonic
must be notified immediately and an inspection carried out to determine if changes to footing design are
required.
4.4 Retaining Walls
Retaining structures must be founded as described in Section 4.3 above. Engineer design and certification
of retaining walls is required where such walls:
Exceed 1 m height.
Are subjected to surcharge loads (e.g. from backslope, adjacent structures, etc.).
Are located within close proximity to existing structures.
Retaining structures should be engineer designed in accordance with AS4678-2002 Earth-retaining
structures. We suggest the following parameters may be adopted for retaining wall design:
Friction Angle: 25° (clay soils) 35° (weathered rock)
Active Earth Pressure Coefficient: 0.41 (clay soils) 0.27 (weathered rock)
Passive Earth Pressure Coefficient: 2.46 (clay soils) 3.7 (weathered rock)
Unit Weight: 18 kN/m³ (clay soils) 21 kN/m³ (weathered rock)
These parameters do not include allowance for surcharge above the wall, or additional loads imposed by
sloping ground.
4.5 Drainage
Adequate site drainage shall be installed to ensure that stormwater is directed away from the footings of the
proposed shed and workshop.
It should be ensured that guttering and downpipes around the proposed shed are sufficiently scaled to
minimise overflow on to the building pad and slope below. In addition, diversion drainage should be installed
above the crest of all cut/fill batters. Adequate site drainage must be installed to ensure that stormwater
runoff is directed away from building walls and footings (e.g. positive gradients and/or channel drains), and
also not allowed to flow over fill embankments. Uncontrolled flow of stormwater over cut or fill batters (e.g.
from gutter overflow during high intensity storms) has the potential to saturate and weaken the batter
materials, potentially leading to slumping failure. Future building and landscaping must be carried out to
maintain good drainage.
Specific drainage recommendations are as follows:
Install diversion drainage along the cut sides of the building platforms. The platforms should be
graded at a minimum 1V:100H to drain into the diversion drainage system.
Install/formalise diversion drainage (e.g. swale drain) along the upslope side of the existing driveway.
Install water bars at regular intervals along the gravel driveway to direct surface water into the swale
drain along the upslope side of the driveway.
All areas exposing erosion features (e.g. rill erosion, scours etc.) must be reinstated with select fill
material, constructed as recommended in Section 4.2.3 and erosion protected.
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.
All collected waters (including overflow from rainwater tanks, etc.) must be directed by pipes or rock-lined
channels to discharge at least 5 m downslope from any structure or embankment. A surface dissipation
device such as rock weir or rock lined contour drain should be installed at the stormwater outlet(s).
Subsurface disposal of stormwater must not be undertaken (including infiltration pits).
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5.0 SUMMARY & CONCLUSIONS
Based on the findings of our assessment we consider that there would be a Low Risk of slope instability
affecting the proposed shed and workshop subject to implementation of the recommendations given in this
report.
6.0 LIMITATIONS
Your attention is drawn to the document Limitations, which is attached to this letter report.
Please contact the undersigned should you wish to discuss any of the above matters.
Yours faithfully
TECTONIC GEOTECHNICAL PTY LTD
Michael Cocks BEng (Civil/Geotechnical) MIEAust Ashley Davey BEng (Geological) RPEQ 8159
Geotechnical Engineer Principal Geotechnical Engineer
Attachments: DCP Reports
Qualitative Terminology for Use in Assessing Risk to Property
Some Guidelines for Hillside Construction
Limitations
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CLIENT : Phil Brierley SHEET : 1 OF 2
CONTRACTOR : Tectonic
PROJECT : Proposed Shed
LOCATION : 906 Pomona Kin Kin Road, Kin Kin
PROJECT No. : 21190
TEST: DCP1 TEST: DCP2 TEST: DCP3
LOGGED: MCC 28/5/2021 CHECKED: ACD LOGGED: MCC 28/5/2021 CHECKED: ACD LOGGED: MCC 28/5/2021 CHECKED: ACD
Depth (m)
Depth (m)
Depth (m)
(AS 1289.6.3.2-1997) (AS 1289.6.3.2-1997) (AS 1289.6.3.2-1997)
0 5 10 15 20 25 0 5 10 15 20 25 0 5 10 15 20 25
0.5 0.5 0.5
1.0 1.0 1.0
TECTONIC 3.00.2 LIB.GLB Log IS DCP 3 PER PAGE 21190.GPJ <<DrawingFile>> 21/6/2021 15:23 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 2.00 2016-02-16
1.5 1.5 1.5
2.0 2.0 2.0
2.5 2.5 2.5
Comments Comments Comments
Page 14
CLIENT : Phil Brierley SHEET : 2 OF 2
CONTRACTOR : Tectonic
PROJECT : Proposed Shed
LOCATION : 906 Pomona Kin Kin Road, Kin Kin
PROJECT No. : 21190
TEST: DCP4
LOGGED: MCC 28/5/2021 CHECKED: ACD
Depth (m)
(AS 1289.6.3.2-1997)
0 5 10 15 20 25
>14
0.5
1.0
TECTONIC 3.00.2 LIB.GLB Log IS DCP 3 PER PAGE 21190.GPJ <<DrawingFile>> 21/6/2021 15:23 10.02.00.04 Datgel Lab and In Situ Tool - DGD | Lib: Tectonic 3.00.2 2021-03-30 Prj: Tectonic 2.00 2016-02-16
1.5
2.0
2.5
Comments
Page 15
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
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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 17
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.
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PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
114 Australian Geomechanics Vol 42 No 1 March 2007
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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)