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Reference Document - MCU24/0143 (As Published)
NOOSA COUNCIL
REFERENCE DOCUMENT
MCU24/0143 17 SEP 2025
Attachment 6
Updated Slope Stability + Geo Tech
Application for a Development Permit –
Material Change of Use to establish Short-
Term Accommodation – 2 cabins.
637 Black Mountain Rd, Black Mountain 4563 QLD
Lot 2 on RP167390
Joe and Heide Veraa (nee De Wald)
1st August 2025
Document Set ID: 24125427
24010296
Version: 1, Version Date: 17/09/2025
07/08/2025
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Page 2
4 June 2025 Ref.: 24378-001-Rev1
RG Strategic
Attention: Russell Green
[email protected]
RE: SLOPE STABILITY ASSESSMENT – EXISTING CABINS
637 BLACK MOUNTAIN ROAD, BLACK MOUNTAIN
Dear Russell,
1. INTRODUCTION
Tectonic has undertaken a geotechnical assessment for the existing short-term cabins at 637 Black
Mountain Road, Black Mountain. This report includes a slope stability assessment, together with
geotechnical advice for the buildings. In summary, following a recent reassessment of the site on
27 May 2025, subject to implementation of the recommendations made herein, there would be a Low
Risk of slope instability affecting the existing cabins in accordance with the Australian Geomechanics
Society Guidelines for Landslide Risk Management, dated March 2007 (AGS 2007).
1.1 Details of Site and Proposed Development
The site is described as Lot 2 on RP167390, covers an area of about 28.7 ha and has frontage to Black
Mountain Road along the northern boundary. At the time of the site visits a residence and shed were
situated centrally along the western boundary, with the existing cabins positioned about 150 m to the
north. Rural residential properties with scattered houses and outbuildings surrounded the site in all
directions. A 2024 aerial image of the site and surrounds is shown in Text Figure 1. A detailed
description of the site is given in Section 2.
Subject Site
Existing cabins
Residence & shed
Text Figure 1: 2024 aerial image of site and surrounds, with inset (courtesy of Nearmap)
Tectonic Geotechnical Pty Ltd
A.B.N. 83 165 727 828
PO Box 899, Buderim, QLD 4556 E [email protected]
P (07) 5478 9016
W tectonicgeo.com.au 1 of 12
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Although no design drawings were provided, based on a visual appraisal the existing cabins comprised
two trailer mounted ‘tiny homes’, both of which had timber decking extending off the eastern edges.
The decks appeared to be permanently fixed to the ground via piled footings, whereas the trailer
mounted cabins were sited on gravel hardstand areas. Ancillary structures included water tanks, raised
garden beds and effluent disposal units.
Access to the existing cabins was via an asphalt driveway which extended into the site in the north-
eastern corner. Both cabins were situated on relatively level cut and fill platforms, with previous cut to fill
earthworks estimated to range up to about 1 m deep and 1.5 m high, respectively.
Text Figure 2 below illustrates the existing cabins at the time of the site visits.
Text Figure 2: Typical views of the existing cabins
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. An initial walk-over survey was conducted by an
experienced geotechnical engineer from Tectonic on 21 November 2024 in order to make an appraisal of
the general condition of the site in regard to topography, drainage, vegetation cover, geology, erosion
and condition of existing structures.
As several signs of both historic and recent landslide activity were observed, a geotechnical investigation
was carried out to assess the ground conditions on 21 January 2025. The investigation comprised the
excavation of four test pits (designated TP1 to TP4) around the tiny homes to depths between 2.8 m and
5.5 m below ground level (BGL). Test pits were excavated using a 5.5 tonne excavator owned and
operated by Bebrok Excavations, generally with toothed buckets and ripper attachments. A pendulum
auger attachment and extensions also utilised in test pit TP2.
Test pit logs and explanatory notes are attached to this report. Logging was carried out in accordance
with Australian Standard AS1726 Geotechnical site investigations. The approximate test pit locations are
shown in the Figure 1, also attached to this report. One soil sample was dispatched to a NATA
accredited laboratory based in Birtinya, for geotechnical testing. Laboratory testing was undertaken in
accordance with Australian Standard AS1289 Methods for Testing Soils for Engineering Purposes and
comprised one Atterberg Limits and Particle Size Distribution test for soil classification purposes. The
laboratory report is also attached.
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A further site visit was made by a principal geotechnical engineer from Tectonic on 27 May 2025, in order
to assess the progression of the landslide activity following a period of prolonged and heavy rainfall.
The results of the desk-top study, walk-over surveys, test pits and laboratory testing are summarised in
Section 2 below.
1.3 Qualifications of Responsible Engineer
This report has been prepared by Ashley Davey, an RPEQ with more than 29 years of experience in
geotechnical engineering, including numerous slope stability projects.
2. DESCRIPTION OF EXISTING CONDITIONS
2.1 Geology
A published geological map for the region1 indicates that the site is underlain by low grade meta-
sedimentary strata forming the Triassic age Kin Kin Beds. Mapping also suggests that the ridge crest to
the north-east of the site comprises a Tertiary age basalt ‘cap’ of ‘mostly olivine basalt flows and some
plugs, some areas of nephelinite, basanite etc.’.
Approx. Site Location
Text Figure 3: Extract from Gympie surface geology map
Weathered phyllite of the Kin Kin beds was observed in driveway cuttings along the northern edge of the
property. Phyllitic colluvium (historic landslide debris), was also observed in some of the cuttings around
the existing cabins. Subsurface conditions encountered in the test pits are summarised as follows:
Topsoil – friable, silty clay of high plasticity, typically about 100 mm thick; then
Colluvium– stiff to very stiff, silty clay of high plasticity with varying gravel and cobble content to
depths between 1.5 m and 2.2 m BGL; overlying
Possible Residual Soil (test pit TP2 only) – very stiff, gravelly silty clay of high plasticity to 5 m BGL;
then
Extremely Weathered (XW) Materials/Weathered Phyllite – hard, gravelly clay and very low to
medium strength phyllite. The phyllite rock mass was noted to be heavily fractured often forming
1
1:100,000 Gympie Surface Geology Map, Sheet 9445, 11 July 2018
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blocks less than 300 mm across, with the relict bedding generally dipping with the direction of the
slope at about 20 to 30 degrees.
During the investigation it was noted that the sidewalls in test pit TP1 (excavated above an existing
landslide backscarp) were collapsing between about 0.3 m and 2 m BGL (in the colluvial materials), which
can be indicative of low shear strengths.
Laboratory testing indicated that the sample from test pit TP1 between 0.8 m and 1.2 m BGL was a
gravelly clay of high plasticity, tending towards a silt. The laboratory test certificate is attached.
2.2 Topography
During the site walk-overs, topographic features specific to the site were noted, and ground slopes were
recorded using a hand-held clinometer. As shown in Text Figure 5 overleaf, the site is dominated by
three southerly dipping ridgelines, all of which emanate off a ridge crest approximately traced by Black
Mountain Road to the north. Drainage lines between the ridges feed into a creek in the lower lying
ground in the southern part of the site. Concave shaped ground was present around the natural
drainage lines and near gully heads.
The existing cabins are situated below a saddle, on the easterly facing flank of a ridge which roughly
follows the western boundary. Although the ground surface around the cabins was somewhat convex in
shape, drainage lines and concave shaped ground was present to the north and south.
Both tiny homes were situated on relatively level earthworks platforms. Based on a visual appraisal it
appeared that cut and fill earthworks in the order of about 1 m deep and 1.5 m high had been
undertaken, with batters typically dipping between about 15° and 25°. Previous earthworks had also
been undertaken around the site to construct the existing driveway and walking tracks, estimated to
range up to about 2 m depth/height.
Gradients around the cabin area typically varied between about 10° and 15°, which increased to between
about 20° and 30° progressing eastwards. Steeper gradients were observed in drainage lines in the
north-western part of the site. The existing driveways and track cuttings around the cabin area were
battered between 40° and 60°, sometimes showing evidence of scouring and slumping.
Text Figure 4: Typical views of track and driveway cuttings
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Subject site boundary
Approx. location of cabins
Text Figure 5: Image showing ground surface contours (courtesy Noosa Council [NC] interactive map)
Text Figures 6 to 8 below and overleaf illustrate site conditions across the proposed development area at
the time of the assessment.
Text Figure 6: Oblique drone image of the cabins, looking north
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Text Figure 7: View looking north towards southermost cabin
Text Figure 8: Southerly view looking across the cabins from driveway
2.3 Groundwater
No signs of groundwater seepage (‘springs’) were observed around the cabin area during our walk-over,
nor was groundwater encountered in any of the test pits during the investigation. Minor seepage was
observed between rock fractures during the subsurface investigation, indicative of elevated moisture
conditions.
2.4 Surface Drainage
Natural surface drainage follows the ground surface contours from the existing cabin area primarily to
the east towards the central drainage line. Generally, surface water is expected to drain well from the site
considering the positive gradients; however, poorer drainage conditions are anticipated on level areas.
There were no obvious signs of significant erosion around the cabins at the time of the site visits. A
grassed swale drain was present above the southernmost tiny home, which discharged onto the ground
surface to the south. Although a formal drain was not apparent above the northernmost tiny home, it
appeared that the ground surface graded to an existing culvert between the cabins, ultimately
discharging downslope to the east.
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Swale drain
Culvert
Text Figure 9: Oblqiue drone image of the cabins looking west
2.5 Vegetation
During our walk-over assessment, the area immediately surrounding the existing cabins comprised
maintained grass, garden beds and scattered bushes. Dense vegetation occupied most of the northern
part of the site and around the drainage lines. Tilting, leaning and distortion of tree trunks was observed
in mature trees below the cabins, and within the surrounding drainage lines, which can be a sign of
previous slope instability.
2.6 Buildings and Other Structures
As mentioned previously, the cabins comprised trailer mounted tiny homes, with timber decking
extending off the eastern edges. Based on an external visual assessment, both cabins appeared to be in
good structural condition, with no obvious signs of distress (e.g. misalignment, etc.) which would indicate
global slope instability. Arc shaped cracking (<10 mm wide) and shallow surface depressions (<50 mm
deep) were observed within the asphalt seal at numerous places along the existing driveway. These
areas generally coincided with inferred fill zones which crossed natural drainage lines/paths away from
the existing cabins. The existing residence and shed were not assessed.
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3. ASSESSMENT OF LAND STABILITY
3.1 Existing Conditions
The NC Planning Scheme 2020 includes a landslide hazard overlay map (Ref. extract in Text Figure 10),
which indicates that most of the site, including the cabin area, has a Moderate to High landslide hazard.
Existing cabin area
Subject site boundary
Text Figure 10: Extract from NC 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. During our site visits, signs of slope instability
were observed around the existing cabins, summarised as follows:
Colluvium was observed in the test pits excavated around the tiny homes. Colluvium was also
exposed in the driveway cuttings above the tiny homes and within walking track cuttings downslope.
Concave shaped ground was present around the tiny homes.
A landslide was identified during the initial site visit below the northernmost structure, and was
again assessed during the more recent visit on 27 May 2025. This landslide was evidenced by a
backscarp about 0.5 m high and estimated to be about 15 m to 20 m wide. The crest of the
backscarp was measured to be about 15 m away from the northernmost tiny home structure, as
illustrated in Text Figure 11 overleaf.
Based upon our site visit on 27 May 2025:
» As shown in Text Figure 12 overleaf, the landslide backscarp was in the same position and of the
same height as observed previously on 21 January 2025 (i.e. the slide had not regressed). It is
noted that rainfall recorded at the nearest weather station at Eumundi was 552 mm in March
2025, being more than double the long-term mean of 241 mm. During this month, four days of
rainfall exceeding 84 mm were recorded, the greatest being 111 mm on 10 March. Rainfall
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during this period is known to have caused landslides at nearby locations in Cooroy and
Cootharaba so could therefore be considered as a ‘triggering’ event.
» The slide was observed to be confined along the northern and southern sides by slightly convex
ground, or spurs. Such spurs should prevent lateral ‘spread’ of the movement and, hence,
would minimise regression of the landslide upslope (towards the northern cabin).
Text Figure 11: Oblique drone image of the tiny homes, with insets of active landslide
Text Figure 12: Northerly and souterly views of landslide backscarp on 27 May 2025
It should also be noted that signs of slope instability were observed within steeper ground on other parts
of the site, particularly near drainage lines, however, assessment of those features was not part of
Tectonic’s commission.
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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, and the
Qualitative Terminology for Use in Assessing Risk to Property is attached.
Table 1: Stability Risk Levels
Risk Level Example Implications(1)
VH Very High Risk Unacceptable without treatment. Extensive detailed investigation and research, planning and implementation of
treatment options essential to reduce risk to Low; may be too expensive and not practical. Work likely to cost more
than value of property.
H High Risk Unacceptable without treatment. Detailed investigation, planning and implementation of treatment options required
to reduce risk to Low. Work would cost a substantial sum in relation to the value of the property.
M Moderate Risk May be tolerated in certain circumstances (subject to regulators’ approval) but requires investigation, planning and
implementation of treatment options to reduce risk to Low. Treatment options to reduce to Low risk should be
implemented as soon as practicable.
L Low Risk Usually acceptable to regulators. Where treatment has been required to reduce the risk to this level, ongoing
maintenance required.
VL Very Low Risk Acceptable. Manage by normal slope maintenance procedures.
Note: (1) The implications for a particular situation are to be determined by all parties to the risk assessment and may depend on the nature of
the property at risk; these are only given as a general guide.
To assist with our slope stability assessment, Tectonic was provided with the following information by the
client:
The value of the property would be in the range of $3M to $3.5M, based on sales nearby.
The tiny homes would add around $500,000 to $600,000 value to the property.
To relocate one of the tiny homes, the estimated cost would be around $50,000 to $100,000.
Based on the approximate value of the property, including the improved value based on the tiny homes,
we have estimated the approximate cost of damage should one of the homes require relocating due to
landslide movement would be between about 1% to 3% of the overall property value.
Considering the site conditions as observed over time, including during the recent site visit following a
period of heavy and prolonged rainfall (Ref. Section 2), and subject to the implementation of
recommendations given in Section 4, it is assessed that there would be a Low (L) Risk of global slope
instability affecting both cabins.
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 cabins. A summary of qualitative terminology for use in assessing
risk to property is attached (taken from AGS 2007). Given the slow-moving nature of the existing
landslide down slope from the northern cabin, and low likelihood of people occupying the tiny homes
during heavy rainfall events, it is assessed that there would be a Tolerable risk to people in both cabins
from landslide movements.
This assessment excludes geotechnical risk associated with other parts of the site away from the existing
tiny homes area.
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Table 2: Details of Qualitative Risk Assessment for Property (AGS 2007)
Assessed
Hazard Likelihood Consequence Comments
Risk
The landslide down slope from the
northern cabin is Unlikely to regress up
slope to a point where it would impact the
structure over the expected design life of
about 50 years. This is due to the lack of
regression of the slide observed following
recent heavy and prolonged rainfall,
Relatively shallow landslide
together with the favourable natural
through fill, natural soils
topography which would limit the spread
and/or upper, fractured Unlikely Minor Low
and up slope movement of the slide.
phyllite impacting the tiny
Based on the expected cost to relocate the
homes
tiny home in the unlikely event that the
landslide regresses close to the structure,
the consequence of such a failure would
be Minor. The resultant risk from this
hazard is therefore assessed as being Low
with respect to property as per the risk
matrix given in AGS 2007.
Considering the strength of these deeper
strata and relatively light loads imposed by
the structures, subject to implementation
Deep-seated landslide
of the recommendations in Section 4, it is
through deeper, less
Rare Minor Very Low considered Rare that a deep-seated
weathered phyllite impacting
landslide would develop and impact the
the tiny homes
buildings over the design life. Given a
potential Minor impact, the resultant risk
would be Very Low as per AGS 2007.
4. Recommendations
General recommendations to help maintain the stability of the site are given in the document Some
Guidelines for Hillside Construction, which is attached.
Based on the results of the geotechnical investigation and our site observations, it is assessed that a Low
Risk of global slope instability could be achieved for the tiny homes, subject to the following:
The existing drainage system should be assessed by a civil/hydraulic RPEQ and, if necessary, the
drainage system should be upgraded to ensure that stormwater is directed away from the existing
structures, embankments and effluent disposal areas. For the northern tiny home, we consider that
this should comprise excavation of a shallow swale (say around 300 mm deep) around the northern
and western sides of the pad, graded at 1V:100H (minimum) to discharge into the existing piped
culvert to the south. Soil won from the swale excavation could be used to form a low height bund
(say 300 mm high) along the crest of the fill batter on the eastern side of the tiny home to prevent
overtopping during storm events.
All excess stormwater collected around the cabin area must be directed by pipes or surface channels
(e.g. turfed or rock lined ‘dry creek’ beds) to discharge at least 10 m downslope of any structure,
effluent disposal area or embankment, and not towards the landslide. A surface dissipation device
such as rock weir or rock lined contour drain must be installed at the stormwater outlet(s).
No additional surcharge loads, including filling and landscaping, are permitted across the ground
surface around the tiny home area.
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Periodic visual inspections should be undertaken by the owner within a 50 m wide zone around the
tiny homes to assess whether any signs of erosion or instability develop (e.g. tension cracking,
slumping, surface depressions, etc.), particularly across the ground between the northern tiny home
of the landslide backscarp. Inspections should be undertaken immediately following 100 mm (or
more) of rainfall in a 24-hour period. A photographic record for each inspection should be
maintained. If any signs of erosion or instability are observed, Tectonic must be notified
immediately to assess the appropriate course of action.
The tiny homes should be maintained so that they are structurally separate from the existing deck
and ancillary structures, so that rapid relocation could be undertaken if required.
5. CONCLUSION
Based on the findings of our assessment we consider that there would be a Low Risk of slope instability
affecting the existing tiny homes, subject to implementation of the recommendations given in this
report.
6. LIMITATIONS
This assessment relates only to the existing tiny homes. Other parts of the site outside the development
area may be subject to risk of slope instability, but assessment of those matters was beyond the scope of
our commission.
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
Ashley Davey BEng (Geological) RPEQ 8159
Director/Principal Geotechnical Engineer
Attachments:
A. Figure 1 – Site Plan
B. Test Pit Logs & Explanatory Notes
C. Laboratory Test Report
D. Qualitative Terminology for Use in Assessing Risk to Property
E. Some Guidelines for Hillside Construction
F. Limitations
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[OCR of page images]
LEGEND
PROJECT oe APPROX. TEST PIT LOCATIONS
RG STRATEGIC SLOPE STABILITY ASSESSMENT - EXISTING CABINS
DRAWN BY 637 BLACK MOUNTAIN ROAD, BLACK MOUNTAIN
MCC a s DRAWING TITLE NOTES
[CHECKED BY SITE PLAN BASEMAP COURTESY OF NEARMAP, DATED 6 OCTOBER 2024
ACD
PROJECT NO. DOC NO, FIGURE NO. REVISION
Document Set ID: 24026298
Version: 1, Version Date: 07/08/2025
Page 15
Test Pit No.
TP1
Page 1 of 1
Engineering Log - Test Pit Project No.: 24378
Client: RG Strategic Commenced: 21/1/2025
Project Name: Retrospective Slope Stability Assessment Completed: 21/1/2025
Hole Location: 637 Black Mountain Road, Black Mountain Logged By: MCC
Hole Position: 483301.0 m E 7077321.0 m N MGA2020 Zone 56 Checked By: ACD
Equipment Type and Model: 5.5t RL Surface: No survey
Excavation Dimensions: Datum: AHD Operator: Bebrok
Excavation Information Material Description and Observations
Relative Density
Classification
Shear
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Condition
Recovery
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
secondary and minor components, colour Observations
Water
Remarks RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100150200
Silty CLAY (TOPSOIL), high plasticity, grey, F 0.01: TOPSOIL
with rootlets 0.15: COLLUVIUM
DS_0.2-0.6m CH
Silty CLAY, high plasticity, pale brown, red 0.30: SIDEWALLS CAVING
brown, trace fine to coarse sized gravel TO 2m BGL
200
250
220
DS_0.8-1.2m CH Gravelly Silty CLAY, high plasticity, red brown,
1 pale brown, fine to coarse sized gravel, with
Not Encountered
phyllite cobbles
w=
EX
PL VSt
2 2.00: ROCK
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24378.GPJ <<DrawingFile>> 4/2/2025 10:19 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
PHYLLITE, distinctly weathered, fine grained,
pale grey, grey, very low to medium strength,
heavily fractured to form blocks <300mm,
relict bedding dipping with ground slope
Hole Terminated at 2.80 m
3 Target depth
4
5
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 < PL MD - Medium Dense
and Soil Descriptions = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Classification System Fr - Friable
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Test Pit No.
TP2
Page 1 of 1
Engineering Log - Test Pit Project No.: 24378
Client: RG Strategic Commenced: 21/1/2025
Project Name: Retrospective Slope Stability Assessment Completed: 21/1/2025
Hole Location: 637 Black Mountain Road, Black Mountain Logged By: MCC
Hole Position: 483268.0 m E 7077312.0 m N MGA2020 Zone 56 Checked By: ACD
Equipment Type and Model: 5.5t RL Surface: No survey
Excavation Dimensions: Datum: AHD Operator: Bebrok
Excavation Information Material Description and Observations
Relative Density
Classification
Shear
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Condition
Recovery
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
secondary and minor components, colour Observations
Water
Remarks RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100150200
Silty CLAY (TOPSOIL), high plasticity, grey, Fr 0.01: TOPSOIL
CH with rootlets 0.10: COLLUVIUM
Silty CLAY, high plasticity, pale brown, trace
fine to coarse sized gravel
VSt
150
DS_0.8-1.3m CI Gravelly CLAY, medium plasticity, red brown, 200 0.80: FRIABLE
1 pale brown, fine to coarse sized gravel
St to
VSt
EX
2
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24378.GPJ <<DrawingFile>> 4/2/2025 10:19 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
300
CI Gravelly Silty CLAY, medium plasticity, red 2.20: Possible RESIDUAL
SOIL
Not Encountered
brown, pale grey, fine to coarse sized gravel
w<
PL
3
tending to extremely weathered material
VSt
4
AD/T
5
PHYLLITE, distinctly weathered, fine grained,
pale grey, grey, very low to low strength
Hole Terminated at 5.50 m
Target depth
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 < PL MD - Medium Dense
and Soil Descriptions = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Classification System Fr - Friable
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Test Pit No.
TP3
Page 1 of 1
Engineering Log - Test Pit Project No.: 24378
Client: RG Strategic Commenced: 21/1/2025
Project Name: Retrospective Slope Stability Assessment Completed: 21/1/2025
Hole Location: 637 Black Mountain Road, Black Mountain Logged By: MCC
Hole Position: 483305.0 m E 7077293.0 m N MGA2020 Zone 56 Checked By: ACD
Equipment Type and Model: 5.5t RL Surface: No survey
Excavation Dimensions: Datum: AHD Operator: Bebrok
Excavation Information Material Description and Observations
Relative Density
Classification
Shear
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Condition
Recovery
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
secondary and minor components, colour Observations
Water
Remarks RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100150200
Silty CLAY (TOPSOIL), high plasticity, pale St 20 0.01: TOPSOIL
CI brown, with rootlets 0.10: COLLUVIUM
Silty CLAY, medium plasticity, pale brown, red
brown, trace fine to coarse sized gravel
Not Encountered
w<
1
EX
with phyllite cobbles PL VSt
PHYLLITE, distinctly weathered, fine grained, 1.50: ROCK
pale grey, red brown, very low strength,
heavily fractured to form pieces <300mm,
thinly folated
2
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24378.GPJ <<DrawingFile>> 4/2/2025 10:19 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
Hole Terminated at 2.00 m
Target depth
3
4
5
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 < PL MD - Medium Dense
and Soil Descriptions = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Classification System Fr - Friable
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Test Pit No.
TP4
Page 1 of 1
Engineering Log - Test Pit Project No.: 24378
Client: RG Strategic Commenced: 21/1/2025
Project Name: Retrospective Slope Stability Assessment Completed: 21/1/2025
Hole Location: 637 Black Mountain Road, Black Mountain Logged By: MCC
Hole Position: 483298.0 m E 707727.0 m N MGA2020 Zone 56 Checked By: ACD
Equipment Type and Model: 5.5t RL Surface: No survey
Excavation Dimensions: Datum: AHD Operator: Bebrok
Excavation Information Material Description and Observations
Relative Density
Classification
Shear
Penetration
Pocket
Consistency
Graphic Log
Samples Material Description Structure and
Penetrometer Vane
Condition
Recovery
Tests soil type: plasticity or particle characteristics, Additional
Moisture
UCS Test
Symbol
Method
secondary and minor components, colour Observations
Water
Remarks RL Depth (kPa) (kPa)
(m) (m)
100
200
300
400
500
50 100150200
Silty CLAY (TOPSOIL), high plasticity, pale F 0.01: TOPSOIL
CH brown, with rootlets 150 0.10: COLLUVIUM
220
Silty CLAY, high plasticity, red brown, trace
fine to coarse sized gravel
w=
St to
PL
VSt
1
Not Encountered
450
CH Gravelly CLAY, high plasticity, red brown, pale 1.50: EXTREMELY
grey, fine to coarse sized gravel WEATHERED MATERIAL
EX
2
TECTONIC 3.00.2 LIB.GLB Log 1 TECTONIC BOREHOLE 24378.GPJ <<DrawingFile>> 4/2/2025 10:20 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
w<
H
PL 2.50: ROCK
PHYLLITE, distinctly weathered, fine grained,
pale grey, grey, very low to medium strength,
heavily fractured to form blocks <300mm,
relict bedding dipping with direction of slope
3
Hole Terminated at 3.40 m
Target depth
4
5
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 < PL MD - Medium Dense
and Soil Descriptions = PL D - Dense
Based on Unified Soil < PL VD - Very Dense
Classification System Fr - Friable
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TERMS USED ON LOGS
DRILLING/EXCAVATION METHOD
AD* Auger Drilling RD Rotary Blade or Drag bit NQ Diamond Core - 47 mm
*V V-Bit RT Rotary Tri-cone bit NMLC Diamond Core - 52 mm
*T TC-Bit RA Rotary Air HQ Diamond Core - 63 mm
HA Hand Auger HMLC Diamond Core – 63mm
ADH Hollow Auger BH Tractor Mounted Backhoe
EX Tracked Hydraulic Excavator
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
FV Field vane shear 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
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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
Coarse Grained Soils
Symbol Term Description
D Dry Sands and gravels are free flowing.
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
Fine Grained Soils
Symbol Description
w < PL Moist, dry of plastic limit, (hard and friable or powdery)
w = PL Moist, near plastic limit, (soils can be moulded at a moisture content approximately equal to the plastic limit)
w > PL Moist, wet of plastic limit, (soils usually weakened and free water forms on hands when handling)
w = LL Wet, near liquid limit
w > LL Wet, wet of liquid limit
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.
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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
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Sunshine Coast Laboratory
11/1 Metier Linkway
Birtinya QLD 4575
Report No: MAT:S25SC-00044/1
Material Test Report
Issue No: 1
Accredited for compliance with ISO/IEC 17025
Client: Tectonic Geotechnical Pty Ltd – Testing
Address: 924 David Low Way
Marcoola QLD 4564
Project: 637 Black Mountain Road
Project No.: 1097974
Accreditation Number: Approved Signatory: A. Collier
Order No.: CG Request No.: 12719 (Discipline Manager QLD)
TRN: 24378 Lot No.: Site Number: 25425 Date of Issue: 17/02/2025
THIS DOCUMENT SHALL NOT BE REPRODUCED EXCEPT IN FULL
Sample Details Particle Size Distribution
Location Black Mountain, QLD Method: AS 1289.3.6.1
Sample Location TP1, 0.80 - 1.20m Drying By: Oven
Field Sample ID 1 Date Tested: 11/02/2025
Date Sampled 21/01/2025
Source In-Situ Note: Sample Washed
Material MH Gravelly SILT with sand, red brown, high plasticity
Specification General Grading Requirement Sieve Size % Passing Limits
Sampling Method Submitted by client 26.5mm 100
Sample ID S25SC-00044 19.0mm 92
13.2mm 86
9.5mm 72
6.7mm 65
4.75mm 59
Other Test Results 2.36mm 52
Description Method Result Limits 1.18mm 47
Moisture Content (%) AS 1289.2.1.1 24.0 600µm 44
Date Tested 6/02/2025 425µm 42
Sample History AS 1289.1.1 Oven-Dried 300µm 41
Preparation AS 1289.1.1 Dry Sieved 150µm 39
Linear Shrinkage (%) AS 1289.3.4.1 8.0 75µm 37
Mould Length (mm) 250
Crumbling No
Curling No
Cracking No
Liquid Limit (%) AS 1289.3.1.2 53
Plastic Limit (%) AS 1289.3.2.1 30
Plasticity Index (%) AS 1289.3.3.1 23
Date Tested 11/02/2025
AS 1726 Laboratory Soil Classification AS 1726 (Laboratory tests only) MH
Date Tested 16/02/2025
Chart
Comments
These results apply to the sample as received.
Form No: 18909, Report No: MAT:S25SC-00044/1 © 2000-2025 QESTLab by SpectraQEST.com Page 1 of 1
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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
68039 Landslide Risk 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.
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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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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
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Limitations
August 2024 | Rev2
Document Set ID: 24125427
24010296
Version: 1, Version Date: 17/09/2025
07/08/2025
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Document Set ID: 24125427
24010296
Version: 1, Version Date: 17/09/2025
07/08/2025
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