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Geotechnical Report
REPORT TO FIONA HUGHES ON GEOTECHNICAL SLOPE STABILITY RISK ASSESSMENT FOR PROPOSED ALTERATIONS AND ADDITIONS AT 17 SPOONBILL STREET, PEREGIAN BEACH, QLD Date: 20 November 2023 Ref: 36409UR www.jkgeotechnics.com.au T: +61 7 3012 6339 JK Geotechnics Pty Ltd ABN 17 003 550 801
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Page 2
Report prepared by:
Paul Roberts RPEQ
Principal Associate | Engineering Geologist
For and on behalf of
JK GEOTECHNICS
PO Box 503,
Cooroy, QLD, 4563
Head Office:
PO BOX 976
NORTH RYDE BC NSW 1670
DOCUMENT REVISION RECORD
Report Reference Report Status Report Date
36409URrpt Final Report 20 November 2023
© Document copyright of JK Geotechnics
This report (which includes all attachments and annexures) has been prepared by JK Geotechnics (JKG) for its Client, and is
intended for the use only by that Client.
This Report has been prepared pursuant to a contract between JKG and its Client and is therefore subject to:
a) JKG’s proposal in respect of the work covered by the Report;
b) The limitations defined in the Client’s brief to JKG;
c) The terms of contract between JKG and the Client, including terms limiting the liability of JKG.
If the Client, or any person, provides a copy of this Report to any third party, such third party must not rely on this Report, except
with the express written consent of JKG which, if given, will be deemed to be upon the same terms, conditions, restrictions and
limitations as apply by virtue of (a), (b), and (c) above.
Any third party who seeks to rely on this Report without the express written consent of JKG does so entirely at their own risk and
to the fullest extent permitted by law, JKG accepts no liability whatsoever, in respect of any loss or damage suffered by any such
third party.
At the Company’s discretion, JKG may send a paper copy of this report for confirmation. In the event of any discrepancy between
paper and electronic versions, the paper version is to take precedence. The USER shall ascertain the accuracy and the suitability
of this information for the purpose intended; reasonable effort is made at the time of assembling this information to ensure its
integrity. The recipient is not authorised to modify the content of the information supplied without the prior written consent of
JKG.
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Table of Contents
1 INTRODUCTION 1
2 DETAILS OF THE SITE AND THE PROPOSED DEVELOPMENT 1
3 ASSESSMENT PROCEDURE 2
4 DESCRIPTION OF EXISTING CONDITIONS 2
4.1 Geology 2
4.2 Subsurface Conditions 3
4.3 Summary of Observations 4
4.3.1 Topography 4
4.3.2 Groundwater and Surface Drainage 5
4.3.3 Vegetation 6
4.3.4 Buildings and Other Structures 6
5 GEOTECHNICAL STABILITY ASSESSMENT 7
5.1 Existing Conditions 7
5.2 Risk Assessment 8
5.2.1 Potential Geotechnical Hazards 8
5.2.2 Risk Analysis 8
5.2.3 Additional Comments 9
5.3 Geotechnical Constraints to Development 9
6 COMMENTS AND RECOMMENDATIONS 9
6.1 Site Layout and Development Details 9
6.2 Site Classification 10
6.3 Excavation 10
6.3.1 Dilapidation Surveys 10
6.3.2 Excavation Methods 10
6.3.3 Seepage 11
6.4 Temporary Batter Slopes 11
6.5 Footing Design 11
6.6 Proposed Pool 12
6.7 Floors and Deck Areas 12
6.8 Sewer Pipeline Management 12
6.9 Overall Effect of the Development on Stability 13
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7 CONCLUSION 13 8 GENERAL COMMENTS 13 ATTACHMENTS Dynamic Cone Penetration Test Results Sheet Figure 1: Site Location Plan Figure 2: Geotechnical Site Plan Figure 3: Geotechnical Mapping Symbols Appendix A: Landslide Risk Management Terminology Appendix B: Some Guidelines For Hillside Construction Report Explanation Notes 36409UR iv
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1 INTRODUCTION
This report presents the results of a geotechnical assessment of the site and the proposed alterations and
additions at 17 Spoonbill Street, Peregian Beach, QLD. The assessment was commissioned by Fiona Hughes
by return of a signed ‘Acceptance of Proposal’ form dated 3 November 2023. The commission was on the
basis of our proposal (Ref. P59608UR) dated 1 November 2023.
The site was inspected by our geotechnical engineer (Cody Surawski) in order to assess the existing stability
of the site and the effect on stability as a result of the proposed development. This report presents a summary
of our site observations, our additional geotechnical investigation, a review of the subsurface conditions, the
results of our geotechnical assessment, and geotechnical comments and recommendations with regards to
the proposed development.
2 DETAILS OF THE SITE AND THE PROPOSED DEVELOPMENT
The site comprises Lot 353 on Plan Number P93145, as indicated on the Noosa Council’s ‘Noosa Plan 2020’.
The coordinates of the site are approximately Latitude -26.464666 and Longitude 153.093904. A site location
plan is presented as Figure 1.
We have been provided with the following documentation:
A ‘Soil Investigation & Foundation Design Report’ (Report Number S3786, dated 10 October 2012)
prepared by Geo Consulting (GeoCon2012).
Architectural drawings (Drawing Numbers A101-104, A201, A202, A301-303, Revision A06, dated 25
October 2023) prepared by Collins Building Designs.
Based on a review of the provided information, we understand that following partial demolition the proposed
alterations and additions will include:
The existing deck will be converted to an internal kitchen and living space together with some
reconfiguration of the adjacent sections of the existing house.
A new partially covered timber deck will be constructed which will extend north-eastwards from the
new kitchen and living space into the rear yard to the proposed pool. The proposed pool surrounds
will be 1.2m above the existing surface levels and excavations to a maximum depth of about 0.8m
will be required for the pool base.
A new fence comprising a rendered block wall with a breeze block parapet section (maximum total
height 2.8m) will form the south-eastern boundary adjacent to the pool timber deck surrounds.
Structural loads have not been provided and typical loadings for this type of development have been
assumed.
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3 ASSESSMENT PROCEDURE
This stability assessment is based upon:
A detailed inspection of the topographic, surface drainage and geological conditions of the site and
its immediate environs which was completed by our geotechnical engineer on 6 November 2023.
These features were compared to those of other similar lots in neighbouring locations to provide a
comparative basis for assessing the risk of instability affecting the proposed development. The
attached Appendix A defines the terminology adopted for the risk assessment together with a
flowchart illustrating the Risk Management Process based on the guidelines given in AGS 2007c
(Reference 1).
A review of the subsurface conditions presented in the Geo Consulting report.
A limited scope additional geotechnical investigation comprising two additional Dynamic Cone
Penetration (DCP) tests (DCP101 and DCP102) completed in the rear yard during our site inspection
and extended to 3.9m depth.
The attached Figure 2 presents a geotechnical site plan showing the principal geotechnical features present
at the site and is based on aerial imagery sourced from ‘Nearmap’ with the location of the proposed
alterations and additions superimposed. Additional features on Figure 2 have been measured by hand held
clinometer and tape measure techniques and hence are only approximate. Should any of the features be
critical to the proposed development, we recommend they be located more accurately using instrument
survey techniques. Figure 3 presents an explanation of the geotechnical mapping symbols used on Figure 2.
The test locations from the GeoCon2012 investigation and the current additional investigation completed by
JK Geotechnics (JKG) are indicated on the attached Figure 2. The JKG test locations were set out by taped
measurements from existing surface features.
The relative compaction of the fill and the relative density of the natural sands were assessed from the DCP
blow counts. Further details of the methods and procedures employed in the additional investigation are
presented in the attached Report Explanation Notes.
No geotechnical laboratory testing was carried out as it was not deemed necessary. Testing for possible
contamination of the site soils and groundwater was outside the agreed scope of the investigation.
4 DESCRIPTION OF EXISTING CONDITIONS
4.1 Geology
The Queensland Department of Resources online 1:100,000 geological map indicates the site is underlain by
Holocene aged blowout dunes, comprising “Quartz sand; Holocene blowout dunes”, shown in green in
Plate 1.
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Site Location
Plate 1: Extract of geology online mapping sourced from QLD Department of Resources
4.2 Subsurface Conditions
Based on our review of GeoCon2012, our DCP test results and site observations, the pertinent aspects of the
subsurface conditions are summarised below:
From the surface level in the rear yard, BH3 (GeoCon2012) encountered sandy fill which extended to
a depth of approximately 1.8m below the existing surface levels. Based on the results of DCP3
(GeoCon2012), the fill has been assessed to be poorly compacted. Assuming a similar subsurface
profile the results of the remaining GeoCon2012 DCP tests and DCP101 and DCP102 completed by
JKG have been interpreted to indicate that similar poorly compacted fill extends to depths between
about 1.4m and 1.8m. We also note that in the absence of formal records of placement and density
test results, the fill is regarded as “uncontrolled” as defined in AS2870-2011 “Residential slabs and
footings”.
Natural sands were encountered below the fill in BH3 (GeoCon2012) and based on the results of
DCP3 the natural sands have been assessed to be loose. The results of the remaining GeoCon2012
DCP tests and DCP101 and DCP102, assuming a similar subsurface profile, have been interpreted to
indicate loose to medium dense and medium dense natural sands below the fill. Based on DCP101
and DCP102 the natural sands were consistently medium dense below depths of about 1.5m
(DCP101) and 2.0m (DCP102). The medium dense sands extended to the termination depth of
DCP101 (3.9m) and DCP102 indicated that the sands improved to medium dense to dense below
about 2.5m to the termination depth of 3.9m.
No groundwater seepage was noted in BH3 (GeoCon2012) and the DCP rods were ‘dry’ when
extracted during the JKG investigation. However, there is a wetland area to the north-east of the site,
which is anticipated to have surficial or shallow groundwater levels particularly following heavy or
prolonged rainfall events.
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4.3 Summary of Observations
We recommend the summary of observations which follows in Sections 4.3.1 to 4.3.4 be read in conjunction
with the attached Figures 2 and 3.
4.3.1 Topography
The site is located towards the base of foreshore hillside that slopes down to the north-east at a
maximum of 20°. The site has a south-western frontage onto Spoonbill Street, which gently slopes down
to the north-west. The site surface levels within the site slope down to the north-east at between 5° and
8° to the north-eastern site boundary (see Plate 2).
Plate 2: Rear Yard, Proposed Location of the Pool and Deck, Looking South-East.
The north-eastern site boundary was lined by a steeper area (about 5m width) that sloped down to the
north-east at 15° to the relatively flat wetland area (see Plate 3).
Plate 3: Steeper Slope Lining the North-Eastern Site Boundary.
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The southern portion of the front yard included flat grass covered terraces supported by gabion basket
retaining walls; further description of the retaining walls is provided in Section 4.3.4 below.
The vegetated median strip (17m width) separating the two lanes of Spoonbill Street sloped down to the
north-east at approximately 20°.
The surface levels in the neighbouring property to the south-east were generally similar to the site
surface levels although the neighbouring front yard appeared to be supported by a low height timer
sleeper retaining wall; further description of the retaining walls is provided in Section 4.3.4 below.
The neighbouring house to the north-west appeared to have been constructed on a flat building platform
created by localised cut to fill earthworks; the fill appeared to have been placed over the rear yard area.
The front yard had been cut into the hillside and concrete block and timber sleeper retaining walls
(maximum 0.8m height) supported the cut faces. The timber sleeper retaining wall returned north-east
to form the central portion of the common boundary with the subject site. The north-eastern half of the
common boundary with the subject site and the north-eastern site boundary of the neighbouring
property were formed by a timber sleeper retaining wall (0.3m height) which supported the neighbouring
yard area.
4.3.2 Groundwater and Surface Drainage
As noted in Section 4.2, no groundwater seepage was noted in either the GeoCon2012 investigation or
the JKG investigation. A wetland area is present to the north-east of the site which is likely to have shallow
groundwater and we note that groundwater levels can rise, especially after heavy or prolonged rainfall
events.
Based on the topographic setting of the site, the majority of the surface run-off would be expected to
flow downhill to the north-east.
A concrete swale drain on the south-western side of Spoonbill Street is likely to capture run off from the
moderately steep vegetated median strip and direct it to the road stormwater system.
A stormwater outlet pipe is present in the northern corner of the neighbouring site to the north-west
and some erosion was evident at the pipe outlet (see Plate 4).
Plate 4: Stormwater Outlet Pipe on Neighbouring Property With Erosion
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4.3.3 Vegetation
The subject site included grass covered yard areas with some garden beds in the front yard and lining the
north-western and south-eastern site boundaries which contained small to medium shrubs and some
small trees.
Beyond the north-eastern site boundary several large trees lined the south-western edge of the wetland
area (see Plate 3) which comprised a thickly vegetated area containing shrubs and grasses.
Plate 5: Spoonbill Street Median Strip.
Some medium to large sized trees were present in the median strip to the south-west of the site (see
Plate 5).
All the trees described above had curved bases and/or were leaning over to the north-east, particularly
those close to the north-eastern site boundary. However, based on the steepness of the localised slopes
it is considered that the trees are growing towards the sunlight rather than indicating slope instability.
4.3.4 Buildings and Other Structures
The subject site was occupied by a single storey timber clad house with a suspended floor. A car port was
constructed on a flat building platform supported by concrete block retaining walls (maximum height
about 0.8m). The southern portion of the front yard included flat grass covered terraces supported by
gabion basket retaining walls (maximum 0.8m height).
To the south-east, the neighbouring site contained a single storey timber house situated over the central
section of the neighbouring site. The house was set-back approximately 2m from the common site
boundary. Whilst observations were restricted, it appeared that the neighbouring front yard was
supported by a low height timber sleeper retaining wall.
To the north-west, the site contained a one and two storey brick and timber house over the central and
south-eastern portion of the neighbouring site. The northern portion of the rear yard contained an
inground pool. The house and pool were set-back at least approximately 3m from the common site
boundary.
The asphaltic concrete (AC) paved Spoonbill Street contained some minor cracking orientated parallel
with the roadway which is interpreted to indicate localised weak pavement subgrade conditions and/or
poorly constructed pavement rather than slope instability.
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A sewer gravity main was located to the north-east of the site boundary and based on the information
from the Unitywater Infrastructure website, the invert level of the main is between RL8.81m and
RL8.56m. The architectural plans indicated the location of the sewer main (orientated sub-parallel to the
north-eastern site boundary) to be off-set 3.674m north-east of the eastern end of the proposed fence
to the south of the pool and 4.61m north-east of the northern corner of the proposed pool.
Based on a cursory inspection from within the site, and where observations were possible, there were
no obvious signs of damage to the buildings and structures within or neighbouring the site which indicate
past or on-going slope instability.
5 GEOTECHNICAL STABILITY ASSESSMENT
5.1 Existing Conditions
Reference to the Noosa Council’s online Landslide Hazard Overlay Map indicates that a portion of the site
contains terrain designated as a “Moderate Hazard Area” (see Plate 6).
Site Location
Plate 6: Extract of Noosa Council’s Online Landslide Hazard Overlay Map.
Based on our site observations, there were no obvious signs of major slope instability such as tension cracks,
bulging of retaining wall faces, debris slumping from cut faces, or structural damage on existing structures.
Based on the slope angles (maximum 20o), the curved and/or leaning trees located on steeper sloping
portions of the areas to the north-east and south-west of the site have been interpreted to be a result of tree
growth directed to the sunlight rather than slope instability. The retaining walls appeared to be performing
satisfactorily and we assume they were engineer designed.
As noted above in Section 4.2, the fill has been assessed to be poorly compacted and in the absence of formal
records of its placement and any density test results, the fill is regarded as “uncontrolled” as defined in
AS2870-2011 “Residential slabs and footings”.
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5.2 Risk Assessment
5.2.1 Potential Geotechnical Hazards
Based on our site observations, assessment of existing conditions provided above, and the form of the
proposed alterations and additions, we consider that the potential geotechnical hazards for the site are as
follows:
1. Deep seated slope instability.
2. Instability of existing retaining walls.
3. Instability of temporary excavation batters.
4. Instability of proposed pool walls.
It is important to be mindful that slope instability can occur at any time and it would be difficult or impossible
to predict when the identified potential hazards will occur. Also, we cannot predict when an extreme or
unusual event may occur (such as an earthquake, or 1 in 100 year rainfall event, etc.) and what impact it
would have on the stability of the identified potential hazards described above.
5.2.2 Risk Analysis
Our geotechnical assessment of the risk of instability is based on the methodology proposed by Australian
Geomechanics Society (2007c) ‘Practice Note Guidelines for Landslide Risk Management’ (Reference 1) and
the relevant site features described above.
Risk To Property
Table A below summarises our qualitative assessment of each potential landslide hazard and of the
consequences to property should the landslide hazard occur during and following construction of the
proposed alterations and additions. Based on the above, the qualitative risks to property have been
determined.
TABLE A: SUMMARY OF RISK ASSESSMENT TO PROPERTY DURING AND FOLLOWING CONSTRUCTION
Potential Landslide 1. 2. 3. 4.
hazard Deep seated slope Instability of existing Instability of Instability of
instability1 retaining walls2 temporary proposed pool
excavation batters3 walls2
Assessed Likelihood Barely Credible Rare Rare Rare
Assessed Major Medium Minor Medium
Consequences
Risk Very Low Low Very Low Low
Notes
1. Due to slope angles deep seated instability not expected to occur.
2. Existing retaining walls assumed to be engineer designed and new pool walls designed in accordance
with the advice presented in Section 6 of this report.
3. Assuming temporary batters are formed in accordance with the advice presented in Section 6 of this
report.
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Table A indicates the assessed risk to property is ‘Low’ and ‘Very Low’ during and following construction,
which would be considered ‘acceptable’ in accordance with the criteria given in Reference 1.
Risk To Life
We have not completed a comprehensive assessment of risk to life. However, based on the indicative
probabilities associated with the assessed likelihood of instability and assuming typical temporal,
vulnerability, evacuation and spatial factors for this type of site, we consider that the levels of risk to life
during and following construction to be “Acceptable” in relation to the criteria given in Reference 1, i.e. less
than 1x10-6. We note that this assumes the recommendations outlined in Section 6 below are adopted.
5.2.3 Additional Comments
It must be recognised that, due to the many complex factors that can affect a site, the subjective nature of a
risk analysis, and the imprecise nature of the science of geotechnical engineering, the risk of instability for a
site cannot be completely removed. It is, however, essential that risk be reduced to at least that which could
be reasonably anticipated by the community in everyday life and that landowners be made aware of
reasonable and practical measures available to reduce risk as far as possible. Hence, risk cannot be
completely removed, only reduced, as removing risk is not currently scientifically achievable.
In preparing our recommendations given below we have assumed that no activities on surrounding land
which may affect the risk on the subject site would be carried out. We have further assumed that all Council
owned buried services and other buried services within and neighbouring the site are, and will be regularly
maintained to remain, in good condition.
5.3 Geotechnical Constraints to Development
Based on the contents of Sections 5.1 and 5.2 we consider that there are no geotechnical constraints to the
proposed development. Provided the proposed development is designed and constructed in accordance
with the advice presented in Section 6, we consider that following construction, the levels of risk to life and
property will remain at “Acceptable” levels.
6 COMMENTS AND RECOMMENDATIONS
6.1 Site Layout and Development Details
As noted in Section 2 above, the proposed alterations and additions will comprise
Converting the existing deck to an internal kitchen and living space together with some
reconfiguration of the adjacent sections of the existing house.
A new partially covered timber deck which will extend north-eastwards from the new kitchen and
living space into the rear yard to the proposed pool. The proposed pool surrounds will be 1.2m above
the existing surface levels and excavations to a maximum depth of about 0.8m will be required for
the pool base.
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A new fence comprising a rendered block wall with a breeze block parapet section (maximum total
height 2.8m) will form the south-eastern boundary adjacent to the pool timber deck surrounds.
6.2 Site Classification
GeoCon2012 has identified the site as being Class P in accordance with AS2870-2011 due to “poor surface
bearing capacity within the founding soils”. We concur with the Class P site classification on this basis and
the presence of “uncontrolled fill”. Reactive soil movements are not expected for the sandy fill and natural
sandy soil profile. However, the proposed residence needs to be designed by engineering principles due to
the Class P site classification.
6.3 Excavation
6.3.1 Dilapidation Surveys
Prior to the commencement of demolition and excavation a detailed dilapidation report should be compiled
on the neighbouring property to the south-east. Consideration may be given to including the rear portion of
the neighbouring property to the north-west. In addition, Council may require that dilapidation surveys
report be completed on the Council assets lining the street frontage, i.e. the roadway and kerb and gutter.
Likewise, Unitywater may require that a dilapidation survey report be completed on the sewer main to the
north-east of the site. The property owners should be asked to confirm that the reports present a fair record
of existing conditions as the reports may assist the client in defending themselves from unfair damage claims.
6.3.2 Excavation Methods
The excavation recommendations provided below should be complemented by reference to the current Safe
Work Australia Code of Practice ‘Excavation Work’.
The outline of the proposed alterations and additions are indicated on the attached Figure 2. Bulk
excavations are expected to extend to a maximum depth of about 0.8m below existing levels for the proposed
pool. The pool excavations are not expected to extend beyond the site boundaries although they will extend
close to the fence forming the north-eastern site boundary. Monitoring of the fence should be undertaken
whilst excavating the north-eastern side of the pool and engineer designed temporary propping may be
required based on assessment by the structural engineer.
Based on the GeoCon2102 investigation results, the proposed excavations will encounter the sandy fill
profile. Any topsoil or root affected soils should be stripped and separately stockpiled for re-use in landscape
areas or disposed of off site.
Due to the small size of the site and restricted access, we expect the excavations will be completed using
small sized tracked excavators, and excavation of the sandy soils will be readily completed with buckets of
such equipment.
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The poorly compacted surficial fill encountered in the investigation may extend across the site boundaries. We therefore advise that sudden stop/start movements of any tracked equipment should be avoided in order to reduce transmission of ground vibrations to any adjacent buildings and structures within or neighbouring the site that are expected to be founded in the sands. 6.3.3 Seepage Groundwater seepage was not encountered in the GeoCon2012 investigation and the DCP testing completed by JKG did not indicate any traces of seepage within the 3.9m investigation depth. Elevated water levels are expected for the wetland area to the north-east although the wetland area is lower than the site. Some ephemeral seepage inflows may be encountered in the excavations, particularly after periods of heavy or prolonged rainfall. In general, we expect that inflows, if any, to be of very small volume and managed by infiltration into the sandy subgrade. Inspection and monitoring of groundwater seepage during excavations is recommended, so that any unexpected conditions, which may be revealed, can be incorporated into the drainage design. 6.4 Temporary Batter Slopes Temporary batter slopes through the sandy soil profile no steeper than 1 Vertical (V) in 1.5 Horizontal (H) are considered to be appropriate, though some surficial instability could still occur. These temporary batters will be achievable within the site geometry. Some instability of temporary sand batters may occur at, or below, the level of any groundwater seepage should it occur, especially after rain periods, and sand bagging may be required to stabilise the lower portion of these batters. Stockpiles of construction materials, excavated materials etc must be kept well clear of the crests to avoid surcharging the temporary batters, at a horizontal distance away from the cut batter slope crest equal to at least twice the height of the cut batter. 6.5 Footing Design The “uncontrolled” poorly compacted fill and very loose natural sands are not considered to be suitable foundation materials due to their low bearing capacity, potential for high elastic settlements and their susceptibility to additional settlements due to vibrations and infiltration of surface water run-off. Based on our assessment of the GeoCon2012 investigation results and our additional DCP test results, the natural sands of loose (or denser) relative density are considered to be a suitable foundation material. The loose (or denser) sands are expected to be encountered from depths of between about 1.4m and 1.8m below existing surface levels. 36409UR 11
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We recommend that all footings be founded into loose (or denser) natural sands. We expect that steel screw
piles or bored piles (with an allowance for sacrificial liners) formed using an auger attachment to an excavator
or hand auger techniques, depending on access constraints, would be required.
Lined hand drilled piles or steel screw piles (say 0.35m diameter) founded at a depth of least 2.0m or 4 pile
diameters (whichever is deeper) into loose (or denser) natural sands may be designed using an allowable end
bearing pressure of 250kPa.
6.6 Proposed Pool
The following earth pressure coefficients and subsoil parameters may be adopted for the design of the pool
walls:
For the sections of pool walls formed below existing surface levels, we recommend the use of a triangular
lateral earth pressure distribution with an ‘at rest’ earth pressure coefficient (ko) of 0.6 for the soil profile,
assuming a horizontal backfill surface.
A bulk unit weight of 21kN/m3 should be adopted for the retained profile.
Any surcharge affecting the walls (e.g. nearby footings, compaction stresses, sloping retained surfaces,
construction loads etc) should be allowed for in the design using the above earth pressure coefficient.
The pool base should be supported on piles founded in loose (or denser) natural sands in accordance with
the advice presented in Section 6.5 above.
The pool should be provided with a one-way or non-return valve at its lowest point so as to prevent buoyancy
in the event that external groundwater levels rise above the water level within the portions of the pool that
are below proposed surface levels, unless such groundwater could be fed into a gravity drain.
The pool backwash system should be piped and discharged to the main sewer system.
6.7 Floors and Deck Areas
We have assumed that the new timber floors and deck areas will be suspended between footings founded
in the loose (or denser) natural sands as outlined in Section 6.5 above.
If fill is proposed to be placed to raise site surface levels (not our preferences as effective compaction in such
a small and restricted site area would be difficult to achieve) then further geotechnical advice must be sought.
6.8 Sewer Pipeline Management
A Unitywater sewer pipeline orientated approximately north-west to south-east is present beyond the rear
boundary of the site. Unitywater’s online Infrastructure mapping indicates the invert levels of the main are
about RL8.81m to RL8.56m. Correlating this information with Noosa Council’s online Contour overlay maps,
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the buried services invert levels would be approximately between 1.2m and 1.5m below the existing surface levels beyond the north-eastern site boundary. It is recommended that the loads from any of the proposed structures do not intersect the zone of influence of the Unitywater asset. Whilst the currently available information does not indicate that the sewer line will be in close proximity to the proposed footings, we recommend that the invert level of the pipe be confirmed, and, if applicable, the design engineer should ensure that no loads from the new footings will impact the sewer main. Locally, in the unlikely event of any potential issues, this may require deeper pile footings founded below the sewer pipe invert levels. 6.9 Overall Effect of the Development on Stability We do not consider that the development will have any detrimental impact on the stability of the site. This is on condition that the design and construction of the proposed development is completed in accordance with the geotechnical advice presented in this report. 7 CONCLUSION We consider that the site is suitable for the proposed development. The geotechnical advice presented in the preceding sections of this report are intended to achieve “Acceptable” levels of risk of instability of the site and to control future risks. The above recommendations address geotechnical issues only and other conditions may be required to address other aspects. 8 GENERAL COMMENTS The recommendations presented in this report include specific issues to be addressed during the design and construction phase of the project. In the event that any of the advice presented in this report is not implemented, the general recommendations may become inapplicable and JK Geotechnics accept no responsibility whatsoever for the performance of the structure where recommendations are not implemented in full and properly tested, inspected and documented. The long term successful performance of floor slabs and pavements is dependent on the satisfactory completion of the earthworks. In order to achieve this, the quality assurance program should not be limited to routine compaction density testing only. Other critical factors associated with the earthworks may include subgrade preparation, selection of fill materials, control of moisture content and drainage, etc. The satisfactory control and assessment of these items may require judgment from an experienced engineer. Such judgment often cannot be made by a technician who may not have formal engineering qualifications and experience. In order to identify potential problems, we recommend that a pre-construction meeting be held so that all parties involved understand the earthworks requirements and potential difficulties. This meeting should clearly define the lines of communication and responsibility. 36409UR 13
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Occasionally, the subsurface conditions between and below the completed boreholes and DCP tests may be found to be different (or may be interpreted to be different) from those expected. Variation can also occur with groundwater conditions, especially after climatic changes. If such differences appear to exist, we recommend that you immediately contact this office. This report provides advice on geotechnical aspects for the proposed civil and structural design. As part of the documentation stage of this project, Contract Documents and Specifications may be prepared based on our report. However, there may be design features we are not aware of or have not commented on for a variety of reasons. The designers should satisfy themselves that all the necessary advice has been obtained. If required, we could be commissioned to review the geotechnical aspects of contract documents to confirm the intent of our recommendations has been correctly implemented. A waste classification is required for any soil and/or bedrock excavated from the site prior to offsite disposal. Subject to the appropriate testing, material can be classified as Virgin Excavated Natural Material (VENM), Excavated Natural Material (ENM), General Solid, Restricted Solid or Hazardous Waste. Analysis can take up to seven to ten working days to complete, therefore, an adequate allowance should be included in the construction program unless testing is completed prior to construction. If contamination is encountered, then substantial further testing (and associated delays) could be expected. We strongly recommend that this requirement is addressed prior to the commencement of excavation on site. This report has been prepared for the particular project described and no responsibility is accepted for the use of any part of this report in any other context or for any other purpose. If there is any change in the proposed development described in this report then all recommendations should be reviewed. Copyright in this report is the property of JK Geotechnics. We have used a degree of care, skill and diligence normally exercised by consulting engineers in similar circumstances and locality. No other warranty expressed or implied is made or intended. Subject to payment of all fees due for the investigation, the client alone shall have a licence to use this report. The report shall not be reproduced except in full. 36409UR 14
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JKGeotechnics We DYNAMIC CONE PENETRATION TEST RESULTS Client: FIONA HUGHES Project: PROPOSED ALTERATIONS AND ADDITIONS Location: 17 SPOONBILL STREET, PEREGIAN BEACH, QLD Job No. 36409UR Hammer Weight & Drop: 9kg/510mm Date: 6-11-23 Rod Diameter: 16mm Tested By: C.S. Point Diameter: 20mm Test Location 101 102 Test Location 101 102 Surface RL Surface RL Depth (mm) Blows per 100mm Penetration Depth (mm) Blows per 100mm Penetration 0 - 100 1 1 3000-3100 10 13 100 - 200 1 2 3100-3200 10 13 200 - 300 1 1 3200-3300 10 11 300 - 400 2 2 3300-3400 9 13 400 - 500 2 2 3400-3500 9 13 500 - 600 2 2 3500-3600 9 14 600 - 700 2 2 3600-3700 10 13 700 - 800 2 1 3700-3800 10 15 800 - 900 2 2 3800-3900 9 15 900 - 1000 2 1 3900-4000 END END 1000 - 1100 2 2 4000-4100 1100 - 1200 1 1 4100-4200 1200 - 1300 1 1 4200-4300 1300 - 1400 2 1 4300-4400 1400 - 1500 2 1 4400-4500 1500 - 1600 3 1 4500-4600 1600 - 1700 4 2 4600-4700 1700 - 1800 7 3 4700-4800 1800 - 1900 7 4 4800-4900 1900 - 2000 5 4 4900-5000 2000 - 2100 5 5 5000-5100 2100 - 2200 5 5 5100-5200 2200 - 2300 5 6 5200-5300 2300 - 2400 7 7 5300-5400 2400 - 2500 6 8 5400-5500 2500 - 2600 7 12 5500-5600 2600 - 2700 9 16 5600-5700 2700 - 2800 9 14 5700-5800 2800 - 2900 10 14 5800-5900 2900 - 3000 10 15 5900-6000 Remarks: 1. The procedure used for this test is described in AS1289.6.3.2-1997 (R2013) 2. Usually 8 blows per 20mm is taken as refusal Ref: JK Geotechnics DCP 0-6m Rev5 Feb19.
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SITE
SOURCE: http://www.whereis.com/
SP
OO
NB
ILL
ST
RE
ET
SP
OO
N
SITE
BIL
LS
TR
EE
T
DWG FILE: J:\6F GEOTECHNICAL JOBS\36000'S\36409UR PEREGIAN SPRINGS\CAD\36409UR.DWG
AERIAL IMAGE SOURCE: MAPS.AU.NEARMAP.COM Title:
SITE LOCATION PLAN
PLOT DATE: 10/11/2023 12:05:35 PM
Location:
17 SPOONBILL STREET, PEREGIAN BEACH, QLD
Report No: Figure No:
36409UR 1
This plan should be read in conjunction with the JK Geotechnics report.
© JK GEOTECHNICS
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L
0.1-0.3m
L
1°
L
15° APPROXIMATE OUTLINE
OF PROPOSED POOL
0.8m 0.2-0.8m
4
102
1 5-8°
L
0.4-1.2m 5 3
2 101
6
L
0.8m
DWG FILE: J:\6F GEOTECHNICAL JOBS\36000'S\36409UR PEREGIAN SPRINGS\CAD\36409UR.DWG
APPROXIMATE OUTLINE OF
L
0.4m PROPOSED ADDITIONS AND DECK
3°
20°
GABION BASKET WALLS
L
SP
3-5°
OO
NB
L
ILL
ST
RE
L ET
PLOT DATE: 10/11/2023 12:11:15 PM
AERIAL IMAGE SOURCE: MAPS.AU.NEARMAP.COM Title:
NOTES: GEOTECHNICAL SITE PLAN
LEGEND 1. TEST LOCATIONS 1 TO 6 ARE FROM A PREVIOUS
INVESTIGATION BY GEO CONSULTING, DATED OCTOBER 2012. Location:
0 3 6 9 12 15 17 SPOONBILL STREET, PEREGIAN BEACH, QLD
BOREHOLE
2. DCP TESTS 101 AND 102 ARE FROM OUR CURRENT
DCP TEST GEOTECHNICAL INVESTIGATION. SCALE 1:300 @A3 METRES Report No: Figure No:
3. REFER TO FIGURE 3 FOR GEOTECHNICAL MAPPING SYMBOLS. 36409UR 2
This plan should be read in conjunction with the JK Geotechnics report.
© JK GEOTECHNICS
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DWG FILE: J:\6F GEOTECHNICAL JOBS\36000'S\36409UR PEREGIAN SPRINGS\CAD\36409UR.DWG
Title:
GEOTECHNICAL MAPPING SYMBOLS
PLOT DATE: 10/11/2023 12:09:45 PM
Location:
17 SPOONBILL STREET, PEREGIAN BEACH, QLD
Report No: Figure No:
36409UR 3
This plan should be read in conjunction with the JK Geotechnics report.
© JK GEOTECHNICS
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APPENDIX A LANDSLIDE RISK MANAGEMENT TERMINOLOGY
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LANDSLIDE RISK MANAGEMENT
Definition of Terms and Landslide Risk
Risk Terminology Description
Acceptable Risk A risk for which, for the purposes of life or work, we are prepared to accept as it is with no regard to its
management. Society does not generally consider expenditure in further reducing such risks justifiable.
Annual Exceedance The estimated probability that an event of specified magnitude will be exceeded in any year.
Probability (AEP)
Consequence The outcomes or potential outcomes arising from the occurrence of a landslide expressed qualitatively
or quantitatively, in terms of loss, disadvantage or gain, damage, injury or loss of life.
Elements at Risk The population, buildings and engineering works, economic activities, public services utilities,
infrastructure and environmental features in the area potentially affected by landslides.
Frequency A measure of likelihood expressed as the number of occurrences of an event in a given time. See also
‘Likelihood’ and ‘Probability’.
Hazard A condition with the potential for causing an undesirable consequence (the landslide). The description
of landslide hazard should include the location, volume (or area), classification and velocity of the
potential landslides and any resultant detached material, and the likelihood of their occurrence within
a given period of time.
Individual Risk to Life The risk of fatality or injury to any identifiable (named) individual who lives within the zone impacted
by the landslide; or who follows a particular pattern of life that might subject him or her to the
consequences of the landslide.
Landslide Activity The stage of development of a landslide; pre failure when the slope is strained throughout but is
essentially intact; failure characterised by the formation of a continuous surface of rupture; post failure
which includes movement from just after failure to when it essentially stops; and reactivation when the
slope slides along one or several pre-existing surfaces of rupture. Reactivation may be occasional
(eg. seasonal) or continuous (in which case the slide is ‘active’).
Landslide Intensity A set of spatially distributed parameters related to the destructive power of a landslide. The parameters
may be described quantitatively or qualitatively and may include maximum movement velocity, total
displacement, differential displacement, depth of the moving mass, peak discharge per unit width, or
kinetic energy per unit area.
Landslide Risk The AGS Australian GeoGuide LR7 (AGS, 2007e) should be referred to for an explanation of Landslide
Risk.
Landslide The classification, and volume (or area) of landslides which exist or potentially may occur in an area or
Susceptibility may travel or retrogress onto it. Susceptibility may also include a description of the velocity and
intensity of the existing or potential landsliding.
Likelihood Used as a qualitative description of probability or frequency.
Probability A measure of the degree of certainty. This measure has a value between zero (impossibility) and 1.0
(certainty). It is an estimate of the likelihood of the magnitude of the uncertain quantity, or the
likelihood of the occurrence of the uncertain future event.
These are two main interpretations:
(i) Statistical – frequency or fraction – The outcome of a repetitive experiment of some kind like
flipping coins. It includes also the idea of population variability. Such a number is called an
‘objective’ or relative frequentist probability because it exists in the real world and is in principle
measurable by doing the experiment.
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Risk Terminology Description
Probability (ii) Subjective probability (degree of belief) – Quantified measure of belief, judgment, or confidence
(continued) in the likelihood of an outcome, obtained by considering all available information honestly, fairly,
and with a minimum of bias. Subjective probability is affected by the state of understanding of a
process, judgment regarding an evaluation,
or the quality and quantity of information. It may change over time as the state of knowledge
changes.
Qualitative Risk An analysis which uses word form, descriptive or numeric rating scales to describe the magnitude of
Analysis potential consequences and the likelihood that those consequences will occur.
Quantitative Risk An analysis based on numerical values of the probability, vulnerability and consequences and resulting
Analysis in a numerical value of the risk.
Risk A measure of the probability and severity of an adverse effect to health, property or the environment.
Risk is often estimated by the product of probability x consequences. However, a more general
interpretation of risk involves a comparison of the probability and consequences in a non-product form.
Risk Analysis The use of available information to estimate the risk to individual, population, property, or the
environment, from hazards. Risk analyses generally contain the following steps: scope definition,
hazard identification and risk estimation.
Risk Assessment The process of risk analysis and risk evaluation.
Risk Control or Risk The process of decision-making for managing risk and the implementation or enforcement of risk
Treatment mitigation measures and the re-evaluation of its effectiveness from time to time, using the results of
risk assessment as one input.
Risk Estimation The process used to produce a measure of the level of health, property or environmental risks being
analysed. Risk estimation contains the following steps: frequency analysis, consequence analysis and
their integration.
Risk Evaluation The stage at which values and judgments enter the decision process, explicitly or implicitly, by including
consideration of the importance of the estimated risks and the associated social, environmental and
economic consequences, in order to identify a range of alternatives for managing the risks.
Risk Management The complete process of risk assessment and risk control (or risk treatment).
Societal Risk The risk of multiple fatalities or injuries in society as a whole: one where society would have to carry
the burden of a landslide causing a number of deaths, injuries, financial, environmental and other
losses.
Susceptibility See ‘Landslide Susceptibility’.
Temporal Spatial The probability that the element at risk is in the area affected by the landsliding, at the time of the
Probability landslide.
Tolerable Risk A risk within a range that society can live with so as to secure certain net benefits. It is a range of risk
regarded as non-negligible and needing to be kept under review and reduced further if possible.
Vulnerability The degree of loss to a given element or set of elements within the area affected by the landslide
hazard. It is expressed on a scale of 0 (no loss) to 1 (total loss). For property, the loss will be the value
of the damage relative to the value of the property; for persons, it will be the probability that a
particular life (the element at risk) will be lost, given the person(s) is affected by the landslide.
NOTE: Reference should be made to Figure A1 which shows the inter-relationship of many of these terms and the
relevant portion of Landslide Risk Management.
Reference should also be made to the paper referenced below for Landslide Terminology and more detailed
discussion of the above terminology.
This appendix is an extract from PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT as presented in Australian
Geomechanics, Vol 42, No 1, March 2007, which discusses the matter more fully.
February 2019
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FIGURE A1: Flowchart for Landslide Risk Management. This figure is an extract from GUIDELINE FOR LANDSLIDE SUSCEPTIBILITY, HAZARD AND RISK ZONING FOR LAND USE PLANNING, as presented in Australian Geomechanics Vol 42, No 1, March 2007, which discusses the matter more fully. February 2019
Page 27
TABLE A1: LANDSLIDE RISK ASSESSMENT
QUALITATIVE TERMINOLOGY FOR USE IN ASSESSING RISK TO PROPERTY
QUALITATIVE MEASURES OF LIKELIHOOD
Approximate Annual Probability
Indicative Notional Implied Indicative Landslide Recurrence Interval Description Descriptor Level
Value Boundary
10-1 10 years The event is expected to occur over the design life. ALMOST CERTAIN A
510-2 20 years
The event will probably occur under adverse conditions over the
10 -2 100 years LIKELY B
design life.
510 -3 200 years
The event could occur under adverse conditions over the design
10-3 1000 years POSSIBLE C
510 -4 life.
2000 years
The event might occur under very adverse circumstances over the
10-4 10,000 years UNLIKELY D
-5 design life.
510 20,000 years
-5 The event is conceivable but only under exceptional circumstances
10 100,000 years RARE E
-2
over the design life.
510 200,000 years
10-6 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
Indicative Notional Description Descriptor Level
Value Boundary
Structure(s) completely destroyed and/or large scale damage requiring major engineering works for stabilisation. Could
200% CATASTROPHIC 1
100% cause at least one adjacent property major consequence damage.
Extensive damage to most of structure, and/or extending beyond site boundaries requiring significant stabilisation works.
60% MAJOR 2
40% Could cause at least one adjacent property medium consequence damage.
Moderate damage to some of structure, and/or significant part of site requiring large stabilisation works. Could cause at
20% MEDIUM 3
10% least one adjacent property minor consequence damage.
5% Limited damage to part of structure, and/or part of site requiring some reinstatement stabilisation works. MINOR 4
1% Little damage. (Note for high probability event (Almost Certain), this category may be subdivided at a notional boundary of
0.5% INSIGNIFICANT 5
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.
Extract from PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT as presented in Australian Geomechanics, Vol 42, No 1, March 2007, which discusses the matter more fully.
February 2019
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TABLE A1: LANDSLIDE RISK ASSESSMENT
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: INSIGNIFICANT
Approximate Annual 200% 60% 20% 5% 0.5%
Probability
A – ALMOST CERTAIN 10-1 VH VH VH H M or L (5)
B - LIKELY 10-2 VH VH H M L
C - POSSIBLE 10-3 VH H M M VL
D - UNLIKELY 10-4 H M L L VL
E - RARE 10-5 M L L VL VL
F - BARELY CREDIBLE 10-6 L VL VL VL VL
Notes: (5) 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.
VL VERY LOW RISK Acceptable. Manage by normal slope maintenance procedures.
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.
Extract from PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT as presented in Australian Geomechanics, Vol 42, No 1, March 2007, which discusses the matter more fully.
February 2019
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AUSTRALIAN GEOGUIDE LR2 (LANDSLIDES)
What is a Landslide?
Any movement of a mass of rock, debris, or earth, down a slope, constitutes a “landslide”. Landslides take many forms, some of
which are illustrated. More information can be obtained from Geoscience Australia, or by visiting its Australian landslide Database
at www.ga.gov.au/urban/factsheets/landslide.jsp. Aspects of the impact of landslides on buildings are dealt with in the book
“Guideline Document Landslide Hazards” published by the Australian Building Codes Board and referenced in the Building Code of
Australia. This document can be purchased over the internet at the Australian Building Codes Board’s website www.abcb.gov.au.
Landslides vary in size. They can be small and localised or very large, sometimes extending for kilometres and involving millions of
tonnes of soil or rock. It is important to realise that even a 1 cubic metre boulder of soil, or rock, weighs at least 2 tonnes. If it falls,
or slides, it is large enough to kill a person, crush a car, or cause serious structural damage to a house. The material in a landslide
may travel downhill well beyond the point where the failure first occurred, leaving destruction in its wake. It may also leave an
unstable slope in the ground behind it, which has the potential to fall again, causing the landslide to extend (regress) uphill, or expand
sideways. For all these reasons, both “potential” and “actual” landslides must be taken very seriously. The present a real threat to
life and property and require proper management.
Identification of landslide risk is a complex task and must be undertaken by a geotechnical practitioner (GeoGuide LR1) with specialist
experience in slope stability assessment and slope stabilisation.
What Causes a Landslide?
Landslides occur as a result of local geological and groundwater conditions, but can be exacerbated by inappropriate development
(GeoGuide LR8), exceptional weather, earthquakes and other factors. Some slopes and cliffs never seem to change, but are actually
on the verge of failing. Others, often moderate slopes (Table 1), move continuously, but so slowly that it is not apparent to a casual
observer. In both cases, small changes in conditions can trigger a landslide with series consequences. Wetting up of the ground (which
may involve a rise in groundwater table) is the single most important cause of landslides (GeoGuide LR5). This is why they often
occur during, or soon after, heavy rain. Inappropriate development often results in small scale landslides which are very expensive
in human terms because of the proximity of housing and people.
Does a Landslide Affect You?
Any slope, cliff, cutting, or fill embankment may be a hazard which has the potential to impact on people, property, roads and
services. Some tell-tale signs that might indicate that a landslide is occurring are listed below:
Open cracks, or steps, along contours trees leaning down slope, or with exposed roots
Groundwater seepage, or springs debris/fallen rocks at the foot of a cliff
Bulging in the lower part of the slope tilted power poles, or fences
Hummocky ground cracked or distorted structures
These indications of instability may be seen on almost any slope and are not necessarily confined to the steeper ones (Table 1).
Advice should be sought from a geotechnical practitioner if any of them are observed. Landslides do not respect property boundaries.
As mentioned above they can “run-out” from above, “regress” from below, or expand sideways, so a landslide hazard affecting your
property may actually exist on someone else’s land.
Local councils are usually aware of slope instability problems within their jurisdiction and often have specific development and
maintenance requirements. Your local council is the first place to make enquiries if you are responsible for any sort of development
or own or occupy property on or near sloping land or a cliff.
TABLE 1 – Slope Descriptions
Slope Maximum
Appearance Angle Gradient Slope Characteristics
Gentle 0 - 10 1 on 6 Easy walking.
Moderate 10 - 18 1 on 3 Walkable. Can drive and manoeuvre a car on driveway.
Steep 18 - 27 1 on 2 Walkable with effort. Possible to drive straight up or down roughened
concrete driveway, but cannot practically manoeuvre a car.
Very Steep 27 - 45 1 on 1 Can only climb slope by clutching at vegetation, rocks, etc.
Extreme 45 - 64 1 on 0.5 Need rope access to climb slope.
Cliff 64 - 84 1 on 0.1 Appears vertical. Can abseil down.
Vertical or Overhang 84 - 90 Infinite Appears to overhang. Abseiler likely to lose contact with the face.
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Some typical landslides which could affect residential housing are illustrated below:
Rotational or circular slip failures (Figure 1) - can occur on moderate
to very steep soil and weathered rock slopes (Table 1). The sliding
surface of the moving mass tends to be deep seated. Tension cracks
may open at the top of the slope and bulging may occur at the toe.
The ground may move in discrete "steps" separated by long periods
without movement. More rapid movement may occur after heavy
rain. Figure 1
Translational slip failures (Figure 2) - tend to occur on moderate to
very steep slopes (Table 1) where soil, or weak rock, overlies stronger
strata. The sliding mass is often relatively shallow. It can move, or
deform slowly (creep) over long periods of time. Extensive linear
cracks and hummocks sometimes form along the contours. The
sliding mass may accelerate after heavy rain.
Figure 2
Wedge failures (Figure 3) - normally only occur on extreme slopes, or
cliffs (Table 1), where discontinuities in the rock are inclined steeply
downwards out of the face.
Rock falls (Figure 3) - tend to occur from cliffs and overhangs (Table
1).
Cliffs may remain, apparently unchanged, for hundreds of years.
Collections of boulders at the foot of a cliff may indicate that rock falls
are ongoing. Wedge failures and rock falls do not "creep". Familiarity
with a particular local situation can instil a false sense of security since
failure, when it occurs, is usually sudden and catastrophic.
Figure 3
Debris flows and mud slides (Figure 4) - may occur in the foothills of
ranges, where erosion has formed valleys which slope down to the
plains below. The valley bottoms are often lined with loose eroded
material (debris) which can "flow" if it becomes saturated during and
after heavy rain. Debris flows are likely to occur with little warning;
they travel a long way and often involve large volumes of soil. The
consequences can be devastating.
Figure 4
More information relevant to your particular situation may be found in other Australian GeoGuides:
GeoGuide LR1 - Introduction GeoGuide LR7 - Landslide Risk
GeoGuide LR3 - Soil Slopes GeoGuide LR8 - Hillside Construction
GeoGuide LR4 - Rock Slopes GeoGuide LR9 - Effluent & Surface Water Disposal
GeoGuide LR5 - Water & Drainage GeoGuide LR10 - Coastal Landslides
GeoGuide LR6 - Retaining Walls GeoGuide LR11 - Record Keeping
The Australian GeoGuides (LR series) are a set of publications intended for property owners; local councils; planning authorities; developers;
insurers; lawyers and, in fact, anyone who lives with, or has an interest in, a natural or engineered slope, a cutting, or an excavation. They
are intended to help you understand why slopes and retaining structures can be a hazard and what can be done with appropriate professional
advice and local council approval (if required) to remove, reduce, or minimise the risk they represent. The GeoGuides have been prepared
by the Australian Geomechanics Society, a specialist technical society within Engineers Australia, the national peak body for all engineering
disciplines in Australia, whose members are professional geotechnical engineers and engineering geologists with a particular interest in
ground engineering. The GeoGuides have been funded under the Australian governments’ National Disaster Mitigation Program.
February 2019
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AUSTRALIAN GEOGUIDE LR7 (LANDSLIDE RISK)
Concept of Risk for a particular site you should expect to receive a report
prepared in accordance with current professional guidelines
Risk is a familiar term, but what does it really mean? It can be and in a form that is acceptable to your local council, or
defined as "a measure of the probability and severity of an planning authority.
adverse effect to health, property, or the environment." This
definition may seem a bit complicated. In relation to Risk to Property
landslides, geotechnical practitioners (see GeoGuide LR1) are
required to assess risk in terms of the likelihood that a Table 1 indicates the terms used to describe risk to property.
particular landslide will occur and the possible consequences. Each risk level depends on an assessment of how likely a
This is called landslide risk assessment. The consequences of landslide is to occur and its consequences in dollar terms.
a landslide are many and varied, but our concerns normally “Likelihood” is the chance of it happening in any one year, as
focus on loss of, or damage to, property and loss of life. indicated in Table 2. “Consequences” are related to the cost
of the repairs and temporary loss of use if the landslide occurs.
Landslide Risk Assessment These two factors are combined by the geotechnical
practitioner to determine the Qualitative Risk.
Some local councils in Australia are aware of the potential for
landslides within their jurisdiction and have responded by TABLE 2 – LIKELIHOOD
designating specific “landslide hazard zones". Development in Likelihood Annual Probability
these areas is normally covered by special regulations. If you Almost Certain 1:10
are contemplating building, or buying an existing house, Likely 1:100
particularly in a hilly area, or near cliffs, then go first for Possible 1:1,000
information to your local council. Unlikely 1:10,000
Rare 1:100,000
Landslide risk assessment must be undertaken by a Barely credible 1:1,000,000
geotechnical practitioner. It may involve visual inspection,
geological mapping, geotechnical investigation and The terms "unacceptable", "may be tolerable" etc. in Table 1
monitoring to identify: indicate how most people react to an assessed risk level.
However, some people will always be more prepared, or
potential landslides (there may be more than one that better able, to tolerate a higher risk level than others.
could impact on your site);
the likelihood that they will occur; Some local councils and planning authorities stipulate a
the damage that could result; maximum tolerable risk level of risk to property for
the cost of disruption and repairs; and developments within their jurisdictions. In these situations
the extent to which lives could be lost. the risk must be assessed by a geotechnical practitioner. If
stabilisation works are needed to meet the stipulated
Risk assessment is a predictive exercise, but since the ground requirements these will normally have to be carried out as
and the processes involved are complex, prediction tends to part of the development, or consent will be withheld.
lack precision. If you commission a landslide risk assessment
TABLE 1 – RISK TO PROPERTY
Qualitative Risk Significance - Geotechnical engineering requirements
Very high VH 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 the value of the property.
High H Unacceptable without treatment. Detailed investigation, planning and implementation of treatment
options required to reduce risk to acceptable level. Work would cost a substantial sum in relation to the
value of the property.
Moderate M May be tolerated in certain circumstances (subject to regulator's approval) but requires investigation,
planning and implementation of treatment options to reduce the risk to Low. Treatment options to
reduce to Low risk should be implemented as soon as possible.
Low L Usually acceptable to regulators. Where treatment has been needed to reduce the risk to this level,
ongoing maintenance is required.
Very Low VL Acceptable. Manage by normal slope maintenance procedures.
February 2019
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Risk to Life In NSW, the planning authorities consider that 1:1,000,000 is
the maximum tolerable risk for domestic housing built near
Most of us have some difficulty grappling with the concept of an obvious hazard, such as a chemical factory. Although not
risk and deciding whether, or not, we are prepared to accept specifically considered in the NSW guidelines there is little
it. However, without doing any sort of analysis, or difference between the hazard presented by a neighbouring
commissioning a report from an "expert", we all take risks factory and a landslide: both have the capacity to destroy life
every day. One of them is the risk of being killed in an and property and both are always present.
accident. This is worth thinking about, because it tells us a lot
about ourselves and can help to put an assessed risk into a TABLE 3 – RISK TO LIFE
meaningful context. By identifying activities that we either Risk (deaths per Activity/Event Leading to Death
are, or are not, prepared to engage in, we can get some participant per (NSW data unless noted)
indication of the maximum level of risk that we are prepared year)
to take. This knowledge can help us to decide whether we
really are able to accept a particular risk, or to tolerate a
1:1,000 Deep sea fishing (UK)
particular likelihood of loss, or damage, to our property
(Table 2). 1:1,000 to
Motor cycling, horse riding, ultra-
1:10,000
In Table 3, data from NSW for the years 1998 to 2002, and light flying (Canada)
other sources, is presented. A risk of 1 in 100,000 means that, Motor vehicle use
in any one year, 1 person is killed for every 100,000 people 1:23,000
undertaking that particular activity. The NSW data assumes
that the whole population undertakes the activity. That is, we 1:30,000 Fall
are all at risk of being killed in a fire, or of choking on our food,
but it is reasonable to assume that only people who go deep 1:70,000 Drowning
sea fishing run a risk of being killed while doing it.
1:180,000 Fire/burn
It can be seen that the risks of dying as a result of falling, using
a motor vehicle, or engaging in water-related activities 1:660,000 Choking on food
(including bathing) are all greater than 1:100,000 and yet few
people actively avoid situations where these risks are present. 1:1,000,000 Scheduled airlines (Canada)
Some people are averse to flying and yet it represents a lower
risk than choking to death on food. The data also indicate that, 1:2,300,000 Train travel
even when the risk of dying as a consequence of a particular
event is very small, it could still happen to any one of us today. 1:32,000,000 Lightning strike
If this were not so, there would be no risk at all and clearly
that is not the case.
More information relevant to your particular situation may be found in other Australian GeoGuides:
GeoGuide LR1 - Introduction GeoGuide LR7 - Landslide Risk
GeoGuide LR3 - Soil Slopes GeoGuide LR8 - Hillside Construction
GeoGuide LR4 - Rock Slopes GeoGuide LR9 - Effluent & Surface Water Disposal
GeoGuide LR5 - Water & Drainage GeoGuide LR10 - Coastal Landslides
GeoGuide LR6 - Retaining Walls GeoGuide LR11 - Record Keeping
The Australian GeoGuides (LR series) are a set of publications intended for property owners; local councils; planning authorities; developers;
insurers; lawyers and, in fact, anyone who lives with, or has an interest in, a natural or engineered slope, a cutting, or an excavation. They
are intended to help you understand why slopes and retaining structures can be a hazard and what can be done with appropriate professional
advice and local council approval (if required) to remove, reduce, or minimise the risk they represent. The GeoGuides have been prepared
by the Australian Geomechanics Society, a specialist technical society within Engineers Australia, the national peak body for all engineering
disciplines in Australia, whose members are professional geotechnical engineers and engineering geologists with a particular interest in
ground engineering. The GeoGuides have been funded under the Australian governments’ National Disaster Mitigation Program.
February 2019
Page 33
APPENDIX B SOME GUIDELINES FOR HILLSIDE CONSTRUCTION February 2019 JKGeotechnics
Page 34
SOME GUIDELINES FOR HILLSIDE CONSTRUCTION
GOOD ENGINEERING PRACTICE POOR ENGINEERING PRACTICE
ADVICE
GEOTECHNICAL Obtain advice from a qualified, experienced geotechnical consultant at Prepare detailed plan and start site works before
ASSESSMENT early 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
HOUSE DESIGN Use flexible structures which incorporate properly designed brickwork, Floor plans which require extensive cutting and
timber or steel frames, timber or panel cladding. Consider use of split filling. Movement intolerant structures.
levels. Use decks for recreational areas where appropriate.
SITE CLEARING Retain natural vegetation wherever practicable. Indiscriminately clear the site.
ACCESS & DRIVEWAYS Satisfy requirements below for cuts, fills, retaining walls and drainage. Excavate and fill for site access before
Council specifications for grades may need to be modified. Driveways and geotechnical advice.
parking areas may need to be fully supported on piers.
EARTHWORKS Retain natural contours wherever possible. Indiscriminant bulk earthworks.
CUTS Minimise depth. Large scale cuts and benching.
Support with engineered retaining walls or batter to appropriate slope. Unsupported cuts.
Provide drainage measures and erosion control. Ignore drainage requirements.
FILLS Minimise height. Loose or poorly compacted fill, which if it fails, may
Strip vegetation and topsoil and key into natural slopes prior to filling. flow a considerable distance (including onto
Use clean fill materials and compact to engineering standards. properties below).
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. Support Disturb or undercut detached blocks or boulders.
BOULDERS rock faces where necessary.
RETAINING WALLS Engineer design to resist applied soil and water forces. Construct a structurally inadequate wall such as
Found on bedrock where practicable. sandstone flagging, brick or unreinforced
Provide subsurface drainage within wall backfill and surface drainage on blockwork.
slope above. Lack of subsurface drains and weepholes.
Construct wall as soon as possible after cut/fill operation.
FOOTINGS Found within bedrock where practicable. Found on topsoil, loose fill, detached boulders or
Use rows of piers or strip footings oriented up and down slope. undercut cliffs.
Design for lateral creep pressures if necessary.
Backfill footing excavations to exclude ingress of surface water.
SWIMMING POOLS Engineer designed.
Support on piers to rock where practicable.
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
SURFACE 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 bench areas.
Provide generous 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.
SUBSURFACE Provide filter around subsurface drain. Discharge of roof run-off into absorption trenches.
Provide drain behind retaining walls.
Use flexible pipelines with access for maintenance.
Prevent inflow of surface water.
SEPTIC & SULLAGE Usually requires pump-out or mains sewer systems; absorption trenches Discharge sullage directly onto and into slopes.
may be possible in some areas if risk is acceptable. Use of absorption trenches without consideration
Storage tanks should be water-tight and adequately founded. of landslide risk.
EROSION CONTROL & Control erosion as this may lead to instability. Failure to observe earthworks and drainage
LANDSCAPING Revegetate cleared area. recommendations when landscaping.
DRAWINGS AND SITE VISITS DURING CONSTRUCTION
DRAWINGS Building Application drawings should be viewed by a 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 seek advice.
If seepage observed, determine cause or seek advice on consequences.
This table is extracted from PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT as presented in Australian Geomechanics, Vol 42, No 1, March
2007 which discusses the matter more fully.
February 2019
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AUSTRALIAN GEOGUIDE LR8 (CONSTRUCTION PRACTICE)
Sensible development practices are required when building on hillsides, particularly if the hillside has more than a low risk of
instability (GeoGuide LR7). Only building techniques intended to maintain, or reduce, the overall level of landslide risk should be
considered. Examples of good hillside construction practice are illustrated below.
EXAMPLES FOR GOOD HILLSIDE CONSTRUCTION PRACTICE
WHY ARE THESE PRACTICES GOOD?
Roadways and parking areas - are paved and incorporate kerbs which prevent water discharging straight into the hillside (GeoGuide LR5).
Cuttings - are supported by retaining walls (GeoGuide LR6).
Retaining walls - are engineer designed to withstand the lateral earth pressures and surcharges expected, and include drains to prevent
water pressures developing in the backfill. Where the ground slopes steeply down towards the high side of a retaining wall, the disturbing
force (see GeoGuide LR6) can be two or more times that due to level ground. Retaining walls must be designed taking these forces into
account.
Sewage - whether treated or not is either taken away in pipes or contained in properly founded tanks so it cannot soak into the ground.
Surface water - from roofs and other hard surfaces is piped away to a suitable discharge point rather than being allowed to infiltrate into the
ground. Preferably, the discharge point will be in a natural creek where ground water exits, rather than enters, the ground. Shallow, lined,
drains on the surface can fulfill the same purpose (GeoGuide LR5).
Surface loads - are minimised. No fill embankments have been built. The house is a lightweight structure. Foundation loads have been taken
down below the level at which a landslide is likely to occur and, preferably, to rock. This sort of construction is probably not applicable to soil
slopes (GeoGuide LR3). If you are uncertain whether your site has rock near the surface, or is essentially a soil slope, you should engage a
geotechnical practitioner to find out.
Flexible structures - have been used because they can tolerate a certain amount of movement with minimal signs of distress and maintain
their functionality.
Vegetation clearance - on soil slopes has been kept to a reasonable minimum. Trees, and to a lesser extent smaller vegetation, take large
quantities of water out of the ground every day. This lowers the ground water table, which in turn helps to maintain the stability of the
slope. Large scale clearing can result in a rise in water table with a consequent increase in the likelihood of a landslide (GeoGuide LR5). An
exception may have to be made to this rule on steep rock slopes where trees have little effect on the water table, but their roots pose a
landslide hazard by dislodging boulders.
Possible effects of ignoring good construction practices are illustrated on page 2. Unfortunately, these poor construction practices are not
as unusual as you might think and are often chosen because, on the face of it, they will save the developer, or owner, money. You should
not lose sight of the fact that the cost and anguish associated with any one of the disasters illustrated, is likely to more than wipe out any
apparent savings at the outset.
ADOPT GOOD PRACTICE ON HILLSIDE SITES
February 2019
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EXAMPLES FOR POOR HILLSIDE CONSTRUCTION PRACTICE
WHY ARE THESE PRACTICES POOR?
Roadways and parking areas - are unsurfaced and lack proper table drains (gutters) causing surface water to pond and soaks into the ground.
Cut and fill - has been used to balance earthworks quantities and level the site leaving unstable cut faces and added large surface loads to
the ground. Failure to compact the fill properly has led to settlement, which will probably continue for several years after completion. The
house and pool have been built on the fill and have settled with it and cracked. Leakage from the cracked pool and the applied surface loads
from the fill have combined to cause landslides.
Retaining walls - have been avoided, to minimise cost, and hand placed rock walls used instead. Without applying engineering design
principles, the walls have failed to provide the required support to the ground and have failed, creating a very dangerous situation.
A heavy, rigid, house - has been built on shallow, conventional, footings. Not only has the brickwork cracked because of the resulting ground
movements, but it has also become involved in a man-made landslide.
Soak-away drainage - has been used for sewage and surface water run-off from roofs and pavements. This water soaks into the ground and
raises the water table (GeoGuide LR5). Subsoil drains that run along the contours should be avoided for the same reason. If felt necessary,
subsoil drains should run steeply downhill in a chevron, or herringbone, pattern. This may conflict with the requirements for effluent and
surface water disposal (GeoGuide LR9) and if so, you will need to seek professional advice.
Rock debris - from landslides higher up on the slope seems likely to pass through the site. Such locations are often referred to by geotechnical
practitioners as "debris flow paths". Rock is normally even denser than ordinary fill, so even quite modest boulders are likely to weigh many
tonnes and do a lot of damage once they start to roll. Boulders have been known to travel hundreds of metres downhill leaving behind a
trail of destruction.
Vegetation - has been completely cleared, leading to a possible rise in the water table and increased landslide risk (GeoGuide LR5).
DON'T CUT CORNERS ON HILLSIDE SITES - OBTAIN ADVICE FROM A GEOTECHNICAL PRACTITIONER
More information relevant to your particular situation may be found in other Australian GeoGuides:
GeoGuide LR1 - Introduction GeoGuide LR7 - Landslide Risk
GeoGuide LR3 - Soil Slopes GeoGuide LR8 - Hillside Construction
GeoGuide LR4 - Rock Slopes GeoGuide LR9 - Effluent & Surface Water Disposal
GeoGuide LR5 - Water & Drainage GeoGuide LR10 - Coastal Landslides
GeoGuide LR6 - Retaining Walls GeoGuide LR11 - Record Keeping
The Australian GeoGuides (LR series) are a set of publications intended for property owners; local councils; planning authorities; developers;
insurers; lawyers and, in fact, anyone who lives with, or has an interest in, a natural or engineered slope, a cutting, or an excavation. They
are intended to help you understand why slopes and retaining structures can be a hazard and what can be done with appropriate professional
advice and local council approval (if required) to remove, reduce, or minimise the risk they represent. The GeoGuides have been prepared
by the Australian Geomechanics Society, a specialist technical society within Engineers Australia, the national peak body for all engineering
disciplines in Australia, whose members are professional geotechnical engineers and engineering geologists with a particular interest in
ground engineering. The GeoGuides have been funded under the Australian governments’ National Disaster Mitigation Program.
February 2019
Page 37
REPORT EXPLANATION NOTES
INTRODUCTION
These notes have been provided to amplify the geotechnical report Cohesive soils are classified on the basis of strength (consistency)
in regard to classification methods, field procedures and certain either by use of a hand penetrometer, vane shear, laboratory testing
matters relating to the Comments and Recommendations section. and/or tactile engineering examination. The strength terms are
Not all notes are necessarily relevant to all reports. defined as follows.
The ground is a product of continuing natural and man-made Unconfined Indicative Undrained
processes and therefore exhibits a variety of characteristics and Compressive Shear Strength (kPa)
properties which vary from place to place and can change with time. Classification Strength (kPa)
Geotechnical engineering involves gathering and assimilating limited
facts about these characteristics and properties in order to Very Soft (VS) 25 12
understand or predict the behaviour of the ground on a particular Soft (S) > 25 and 50 > 12 and 25
site under certain conditions. This report may contain such facts Firm (F) > 50 and 100 > 25 and 50
obtained by inspection, excavation, probing, sampling, testing or Stiff (St) > 100 and 200 > 50 and 100
other means of investigation. If so, they are directly relevant only to
the ground at the place where and time when the investigation was Very Stiff (VSt) > 200 and 400 > 100 and 200
carried out. Hard (Hd) > 400 > 200
Friable (Fr) Strength not attainable – soil crumbles
DESCRIPTION AND CLASSIFICATION METHODS Rock types are classified by their geological names, together with
The methods of description and classification of soils and rocks used descriptive terms regarding weathering, strength, defects, etc.
in this report are based on Australian Standard 1726:2017 Where relevant, further information regarding rock classification is
‘Geotechnical Site Investigations’. In general, descriptions cover the given in the text of the report. In the Sydney Basin, ‘shale’ is used to
following properties – soil or rock type, colour, structure, strength or describe fissile mudstone, with a weakness parallel to bedding. Rocks
density, and inclusions. Identification and classification of soil and with alternating inter-laminations of different grain size
rock involves judgement and the Company infers accuracy only to (eg. siltstone/claystone and siltstone/fine grained sandstone) is
the extent that is common in current geotechnical practice. referred to as ‘laminite’.
Soil types are described according to the predominating particle size
SAMPLING
and behaviour as set out in the attached soil classification table
qualified by the grading of other particles present (eg. sandy clay) as Sampling is carried out during drilling or from other excavations to
set out below: allow engineering examination (and laboratory testing where
required) of the soil or rock.
Soil Classification Particle Size
Disturbed samples taken during drilling provide information on
Clay < 0.002mm plasticity, grain size, colour, moisture content, minor constituents
Silt 0.002 to 0.075mm and, depending upon the degree of disturbance, some information
Sand 0.075 to 2.36mm on strength and structure. Bulk samples are similar but of greater
Gravel 2.36 to 63mm volume required for some test procedures.
Cobbles 63 to 200mm Undisturbed samples are taken by pushing a thin-walled sample tube,
Boulders > 200mm usually 50mm diameter (known as a U50), into the soil and
withdrawing it with a sample of the soil contained in a relatively
Non-cohesive soils are classified on the basis of relative density, undisturbed state. Such samples yield information on structure and
generally from the results of Standard Penetration Test (SPT) as strength, and are necessary for laboratory determination of shrink-
below: swell behaviour, strength and compressibility. Undisturbed sampling
is generally effective only in cohesive soils.
SPT ‘N’ Value Details of the type and method of sampling used are given on the
Relative Density (blows/300mm) attached logs.
Very loose (VL) <4
Loose (L) 4 to 10
Medium dense (MD) 10 to 30
Dense (D) 30 to 50
Very Dense (VD) > 50
February 2019 1
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INVESTIGATION METHODS Mud Stabilised Drilling: Either Wash Boring or Continuous Core
Drilling can use drilling mud as a circulating fluid to stabilise the
The following is a brief summary of investigation methods currently
borehole. The term ‘mud’ encompasses a range of products ranging
adopted by the Company and some comments on their use and
from bentonite to polymers. The mud tends to mask the cuttings and
application. All methods except test pits, hand auger drilling and
reliable identification is only possible from intermittent intact
portable Dynamic Cone Penetrometers require the use of a
sampling (eg. from SPT and U50 samples) or from rock coring, etc.
mechanical rig which is commonly mounted on a truck chassis or
track base.
Continuous Core Drilling: A continuous core sample is obtained
using a diamond tipped core barrel. Provided full core recovery is
Test Pits: These are normally excavated with a backhoe or a tracked
achieved (which is not always possible in very low strength rocks and
excavator, allowing close examination of the insitu soils and ‘weaker’
granular soils), this technique provides a very reliable (but relatively
bedrock if it is safe to descend into the pit. The depth of penetration
expensive) method of investigation. In rocks, NMLC or HQ triple tube
is limited to about 3m for a backhoe and up to 6m for a large
core barrels, which give a core of about 50mm and 61mm diameter,
excavator. Limitations of test pits are the problems associated with
respectively, is usually used with water flush. The length of core
disturbance and difficulty of reinstatement and the consequent
recovered is compared to the length drilled and any length not
effects on close-by structures. Care must be taken if construction is
recovered is shown as NO CORE. The location of NO CORE recovery
to be carried out near test pit locations to either properly recompact
is determined on site by the supervising engineer; where the location
the backfill during construction or to design and construct the
is uncertain, the loss is placed at the bottom of the drill run.
structure so as not to be adversely affected by poorly compacted
backfill at the test pit location.
Standard Penetration Tests: Standard Penetration Tests (SPT) are
used mainly in non-cohesive soils, but can also be used in cohesive
Hand Auger Drilling: A borehole of 50mm to 100mm diameter is
soils, as a means of indicating density or strength and also of
advanced by manually operated equipment. Refusal of the hand
obtaining a relatively undisturbed sample. The test procedure is
auger can occur on a variety of materials such as obstructions within
described in Australian Standard 1289.6.3.1–2004 (R2016) ‘Methods
any fill, tree roots, hard clay, gravel or ironstone, cobbles and
of Testing Soils for Engineering Purposes, Soil Strength and
boulders, and does not necessarily indicate rock level.
Consolidation Tests – Determination of the Penetration Resistance of
a Soil – Standard Penetration Test (SPT)’.
Continuous Spiral Flight Augers: The borehole is advanced using
75mm to 115mm diameter continuous spiral flight augers, which are The test is carried out in a borehole by driving a 50mm diameter split
withdrawn at intervals to allow sampling and insitu testing. This is a sample tube with a tapered shoe, under the impact of a 63.5kg
relatively economical means of drilling in clays and in sands above hammer with a free fall of 760mm. It is normal for the tube to be
the water table. Samples are returned to the surface by the flights or driven in three successive 150mm increments and the ‘N’ value is
may be collected after withdrawal of the auger flights, but they can taken as the number of blows for the last 300mm. In dense sands,
be very disturbed and layers may become mixed. Information from very hard clays or weak rock, the full 450mm penetration may not be
the auger sampling (as distinct from specific sampling by SPTs or practicable and the test is discontinued.
undisturbed samples) is of limited reliability due to mixing or
The test results are reported in the following form:
softening of samples by groundwater, or uncertainties as to the
original depth of the samples. Augering below the groundwater table In the case where full penetration is obtained with successive
is of even lesser reliability than augering above the water table. blow counts for each 150mm of, say, 4, 6 and 7 blows, as
Rock Augering: Use can be made of a Tungsten Carbide (TC) bit for N = 13
auger drilling into rock to indicate rock quality and continuity by 4, 6, 7
variation in drilling resistance and from examination of recovered In a case where the test is discontinued short of full penetration,
rock cuttings. This method of investigation is quick and relatively say after 15 blows for the first 150mm and 30 blows for the next
inexpensive but provides only an indication of the likely rock strength 40mm, as
and predicted values may be in error by a strength order. Where rock N > 30
strengths may have a significant impact on construction feasibility or 15, 30/40mm
costs, then further investigation by means of cored boreholes may
be warranted. The results of the test can be related empirically to the engineering
properties of the soil.
Wash Boring: The borehole is usually advanced by a rotary bit, with A modification to the SPT is where the same driving system is used
water being pumped down the drill rods and returned up the with a solid 60 tipped steel cone of the same diameter as the SPT
annulus, carrying the drill cuttings. Only major changes in hollow sampler. The solid cone can be continuously driven for some
stratification can be assessed from the cuttings, together with some distance in soft clays or loose sands, or may be used where damage
information from “feel” and rate of penetration. would otherwise occur to the SPT. The results of this Solid Cone
Penetration Test (SCPT) are shown as ‘Nc’ on the borehole logs,
together with the number of blows per 150mm penetration.
February 2019 2
Page 39
Cone Penetrometer Testing (CPT) and Interpretation: There are limitations when using the CPT in that it may not penetrate
The cone penetrometer is sometimes referred to as a Dutch Cone. obstructions within any fill, thick layers of hard clay and very dense
The test is described in Australian Standard 1289.6.5.1–1999 (R2013) sand, gravel and weathered bedrock. Normally a ‘dummy’ cone is
‘Methods of Testing Soils for Engineering Purposes, Soil Strength and pushed through fill to protect the equipment. No information is
Consolidation Tests – Determination of the Static Cone Penetration recorded by the ‘dummy’ probe.
Resistance of a Soil – Field Test using a Mechanical and Electrical
Cone or Friction-Cone Penetrometer’. Flat Dilatometer Test: The flat dilatometer (DMT), also known as the
Marchetti Dilometer comprises a stainless steel blade having a flat,
In the tests, a 35mm or 44mm diameter rod with a conical tip is
circular steel membrane mounted flush on one side.
pushed continuously into the soil, the reaction being provided by a
specially designed truck or rig which is fitted with a hydraulic ram The blade is connected to a control unit at ground surface by a
system. Measurements are made of the end bearing resistance on pneumatic-electrical tube running through the insertion rods. A gas
the cone and the frictional resistance on a separate 134mm or tank, connected to the control unit by a pneumatic cable, supplies
165mm long sleeve, immediately behind the cone. Transducers in the gas pressure required to expand the membrane. The control unit
the tip of the assembly are electrically connected by wires passing is equipped with a pressure regulator, pressure gauges, an audio-
through the centre of the push rods to an amplifier and recorder unit visual signal and vent valves.
mounted on the control truck. The CPT does not provide soil sample
The blade is advanced into the ground using our CPT rig or one of our
recovery.
drilling rigs, and can be driven into the ground using an SPT hammer.
As penetration occurs (at a rate of approximately 20mm per second), As soon as the blade is in place, the membrane is inflated, and the
the information is output as incremental digital records every 10mm. pressure required to lift the membrane (approximately 0.1mm) is
The results given in this report have been plotted from the digital recorded. The pressure then required to lift the centre of the
data. membrane by an additional 1mm is recorded. The membrane is then
deflated before pushing to the next depth increment, usually
The information provided on the charts comprise:
200mm down. The pressure readings are corrected for membrane
Cone resistance – the actual end bearing force divided by the stiffness.
cross sectional area of the cone – expressed in MPa. There are
two scales presented for the cone resistance. The lower scale The DMT is used to measure material index (ID), horizontal stress
has a range of 0 to 5MPa and the main scale has a range of 0 to index (KD), and dilatometer modulus (ED). Using established
50MPa. For cone resistance values less than 5MPa, the plot will correlations, the DMT results can also be used to assess the ‘at rest’
appear on both scales. earth pressure coefficient (Ko), over-consolidation ratio (OCR),
Sleeve friction – the frictional force on the sleeve divided by the undrained shear strength (Cu), friction angle (), coefficient of
surface area – expressed in kPa. consolidation (Ch), coefficient of permeability (Kh), unit weight (),
and vertical drained constrained modulus (M).
Friction ratio – the ratio of sleeve friction to cone resistance,
expressed as a percentage. The seismic dilatometer (SDMT) is the combination of the DMT with
an add-on seismic module for the measurement of shear wave
The ratios of the sleeve resistance to cone resistance will vary
velocity (Vs). Using established correlations, the SDMT results can
with the type of soil encountered, with higher relative friction in
also be used to assess the small strain modulus (Go).
clays than in sands. Friction ratios of 1% to 2% are commonly
encountered in sands and occasionally very soft clays, rising to
Portable Dynamic Cone Penetrometers: Portable Dynamic Cone
4% to 10% in stiff clays and peats. Soil descriptions based on
Penetrometer (DCP) tests are carried out by driving a 16mm
cone resistance and friction ratios are only inferred and must not
diameter rod with a 20mm diameter cone end with a 9kg hammer
be considered as exact.
dropping 510mm. The test is described in Australian Standard
Correlations between CPT and SPT values can be developed for both 1289.6.3.2–1997 (R2013) ‘Methods of Testing Soils for Engineering
sands and clays but may be site specific. Purposes, Soil Strength and Consolidation Tests – Determination of
Interpretation of CPT values can be made to empirically derive the Penetration Resistance of a Soil – 9kg Dynamic Cone
modulus or compressibility values to allow calculation of foundation Penetrometer Test’.
settlements. The results are used to assess the relative compaction of fill, the
Stratification can be inferred from the cone and friction traces and relative density of granular soils, and the strength of cohesive soils.
from experience and information from nearby boreholes etc. Where Using established correlations, the DCP test results can also be used
shown, this information is presented for general guidance, but must to assess California Bearing Ratio (CBR).
be regarded as interpretive. The test method provides a continuous Refusal of the DCP can occur on a variety of materials such as
profile of engineering properties but, where precise information on obstructions within any fill, tree roots, hard clay, gravel or ironstone,
soil classification is required, direct drilling and sampling may be cobbles and boulders, and does not necessarily indicate rock level.
preferable.
February 2019 3
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Vane Shear Test: The vane shear test is used to measure the GROUNDWATER
undrained shear strength (Cu) of typically very soft to firm fine
Where groundwater levels are measured in boreholes, there are
grained cohesive soils. The vane shear is normally performed in the
several potential problems:
bottom of a borehole, but can be completed from surface level, the
bottom and sides of test pits, and on recovered undisturbed tube Although groundwater may be present, in low permeability soils
samples (when using a hand vane). it may enter the hole slowly or perhaps not at all during the time
it is left open.
The vane comprises four rectangular blades arranged in the form of
A localised perched water table may lead to an erroneous
a cross on the end of a thin rod, which is coupled to the bottom of a
indication of the true water table.
drill rod string when used in a borehole. The size of the vane is
dependent on the strength of the fine grained cohesive soils; that is, Water table levels will vary from time to time with seasons or
larger vanes are normally used for very low strength soils. For recent weather changes and may not be the same at the time of
borehole testing, the size of the vane can be limited by the size of the construction.
casing that is used. The use of water or mud as a drilling fluid will mask any
For testing inside a borehole, a device is used at the top of the casing, groundwater inflow. Water has to be blown out of the hole and
which suspends the vane and rods so that they do not sink under self- drilling mud must be washed out of the hole or ‘reverted’
weight into the ‘soft’ soils beyond the depth at which the test is to chemically if reliable water observations are to be made.
be carried out. A calibrated torque head is used to rotate the rods More reliable measurements can be made by installing standpipes
and vane and to measure the resistance of the vane to rotation. which are read after the groundwater level has stabilised at intervals
With the vane in position, torque is applied to cause rotation of ranging from several days to perhaps weeks for low permeability
the vane at a constant rate. A rate of 6° per minute is the soils. Piezometers, sealed in a particular stratum, may be advisable
common rotation rate. Rotation is continued until the soil is in low permeability soils or where there may be interference from
sheared and the maximum torque has been recorded. This value perched water tables or surface water.
is then used to calculate the undrained shear strength. The vane
is then rotated rapidly a number of times and the operation FILL
repeated until a constant torque reading is obtained. This torque The presence of fill materials can often be determined only by the
value is used to calculate the remoulded shear strength. Where inclusion of foreign objects (eg. bricks, steel, etc) or by distinctly
appropriate, friction on the vane rods is measured and taken into unusual colour, texture or fabric. Identification of the extent of fill
account in the shear strength calculation. materials will also depend on investigation methods and frequency.
Where natural soils similar to those at the site are used for fill, it may
LOGS be difficult with limited testing and sampling to reliably assess the
The borehole or test pit logs presented herein are an engineering extent of the fill.
and/or geological interpretation of the subsurface conditions, and The presence of fill materials is usually regarded with caution as the
their reliability will depend to some extent on the frequency of possible variation in density, strength and material type is much
sampling and the method of drilling or excavation. Ideally, greater than with natural soil deposits. Consequently, there is an
continuous undisturbed sampling or core drilling will enable the increased risk of adverse engineering characteristics or behaviour. If
most reliable assessment, but is not always practicable or possible to the volume and quality of fill is of importance to a project, then
justify on economic grounds. In any case, the boreholes or test pits frequent test pit excavations are preferable to boreholes.
represent only a very small sample of the total subsurface conditions.
The terms and symbols used in preparation of the logs are defined in LABORATORY TESTING
the following pages. Laboratory testing is normally carried out in accordance with
Interpretation of the information shown on the logs, and its Australian Standard 1289 ‘Methods of Testing Soils for Engineering
application to design and construction, should therefore take into Purposes’ or appropriate NSW Government Roads & Maritime
account the spacing of boreholes or test pits, the method of drilling Services (RMS) test methods. Details of the test procedure used are
or excavation, the frequency of sampling and testing and the given on the individual report forms.
possibility of other than ‘straight line’ variations between the
boreholes or test pits. Subsurface conditions between boreholes or ENGINEERING REPORTS
test pits may vary significantly from conditions encountered at the Engineering reports are prepared by qualified personnel and are
borehole or test pit locations. based on the information obtained and on current engineering
standards of interpretation and analysis. Where the report has been
prepared for a specific design proposal (eg. a three storey building)
the information and interpretation may not be relevant if the design
proposal is changed (eg. to a twenty storey building). If this happens,
the Company will be pleased to review the report and the sufficiency
of the investigation work.
February 2019 4
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Reasonable care is taken with the report as it relates to be pleased to assist in this regard and/or to make additional report
interpretation of subsurface conditions, discussion of geotechnical copies available for contract purposes at a nominal charge.
aspects and recommendations or suggestions for design and
Copyright in all documents (such as drawings, borehole or test pit
construction. However, the Company cannot always anticipate or
logs, reports and specifications) provided by the Company shall
assume responsibility for:
remain the property of Jeffery and Katauskas Pty Ltd. Subject to the
Unexpected variations in ground conditions – the potential for payment of all fees due, the Client alone shall have a licence to use
this will be partially dependent on borehole spacing and the documents provided for the sole purpose of completing the
sampling frequency as well as investigation technique. project to which they relate. Licence to use the documents may be
Changes in policy or interpretation of policy by statutory revoked without notice if the Client is in breach of any obligation to
authorities. make a payment to us.
The actions of persons or contractors responding to commercial
pressures. REVIEW OF DESIGN
Details of the development that the Company could not Where major civil or structural developments are proposed or where
reasonably be expected to anticipate. only a limited investigation has been completed or where the
geotechnical conditions/constraints are quite complex, it is prudent
If these occur, the Company will be pleased to assist with to have a joint design review which involves an experienced
investigation or advice to resolve any problems occurring. geotechnical engineer/engineering geologist.
SITE ANOMALIES SITE INSPECTION
In the event that conditions encountered on site during construction The Company will always be pleased to provide engineering
appear to vary from those which were expected from the inspection services for geotechnical aspects of work to which this
information contained in the report, the Company requests that it report is related.
immediately be notified. Most problems are much more readily
resolved when conditions are exposed rather than at some later Requirements could range from:
stage, well after the event. i) a site visit to confirm that conditions exposed are no worse than
those interpreted, to
REPRODUCTION OF INFORMATION FOR CONTRACTUAL ii) a visit to assist the contractor or other site personnel in
PURPOSES identifying various soil/rock types and appropriate footing or
Where information obtained from this investigation is provided for pile founding depths, or
tendering purposes, it is recommended that all information, iii) full time engineering presence on site.
including the written report and discussion, be made available. In
circumstances where the discussion or comments section is not
relevant to the contractual situation, it may be appropriate to
prepare a specially edited document. The Company would
February 2019 5
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SYMBOL LEGENDS FILL rvs CLAY (CL, Cl, CH) SILT (ML, MH) SAND (SP, SW) o> N g | GRAVEL (GP, GW) SANDY CLAY (CL, Cl, CH) SILTY CLAY (CL, Cl, CH) CLAYEY SAND (SC) SILTY SAND (SM) GRAVELLY CLAY (CL, Cl, CH) es CLAYEY GRAVEL (GC) SANDY SILT (ML, MH) PEAT AND HIGHLY ORGANIC SOILS (Pt) OTHER MATERIALS ae *) CONCRETE 2 BRICKS OR PAVERS ROCK pO ° be | | ASPHALTIC CONCRETE CONGLOMERATE SANDSTONE SHALE/MUDSTONE SILTSTONE CLAYSTONE COAL LAMINITE LIMESTONE PHYLLITE, SCHIST TUFF GRANITE, GABBRO DOLERITE, DIORITE BASALT, ANDESITE QUARTZITE February 2019 JKGeotechnics
Page 43
CLASSIFICATION OF COARSE AND FINE GRAINED SOILS
Group
Major Divisions Symbol Typical Names Field Classification of Sand and Gravel Laboratory Classification Laboratory Classification Criteria
GRAVEL (more A well graded coarse grained soil is one for which the coefficient of uniformity
GW Gravel and gravel-sand mixtures, Wide range in grain size and substantial amounts of all intermediate sizes, not ≤ 5% fines Cu > 4
Cu > 4 and the coefficient of curvature 1 < Cc < 3. Otherwise, the soil is poorly
Coarse grainedsoil (more than 65%of soil excludingoversize fraction is
than half little or no fines enough fines to bind coarse grains, no dry strength 1 < Cc < 3
of coarse graded. These coefficients are given by:
fraction is larger GP Gravel and gravel-sand mixtures, Predominantly one size or range of sizes with some intermediate sizes missing, ≤ 5% fines Fails to comply
little or no fines, uniform gravels not enough fines to bind coarse grains, no dry strength with above ( )
than 2.36mm = and =
GM Gravel-silt mixtures and gravel- ‘Dirty’ materials with excess of non-plastic fines, zero to medium dry strength ≥ 12% fines, fines Fines behave as
sand-silt mixtures are silty silt Where D10, D30 and D60 are those grain sizes for which 10%, 30% and 60% of
greater than 0.075mm)
the soil grains, respectively, are smaller.
GC Gravel-clay mixtures and gravel- ‘Dirty’ materials with excess of plastic fines, medium to high dry strength ≥ 12% fines, fines Fines behave as
sand-clay mixtures are clayey clay
SAND (more SW Sand and gravel-sand mixtures, Wide range in grain size and substantial amounts of all intermediate sizes, not ≤ 5% fines Cu > 6 NOTES:
than half little or no fines enough fines to bind coarse grains, no dry strength 1 < Cc < 3 1 For a coarse grained soil with a fines content between 5% and 12%,
of coarse the soil is given a dual classification comprising the two group symbols
fraction SP Sand and gravel-sand mixtures, Predominantly one size or range of sizes with some intermediate sizes missing, ≤ 5% fines Fails to comply
separated by a dash; for example, for a poorly graded gravel with
is smaller than little or no fines not enough fines to bind coarse grains, no dry strength with above between 5% and 12% silt fines, the classification is GP-GM.
2.36mm) SM Sand-silt mixtures ‘Dirty’ materials with excess of non-plastic fines, zero to medium dry strength ≥ 12% fines, fines 2 Where the grading is determined from laboratory tests, it is defined by
are silty coefficients of curvature (Cc) and uniformity (Cu) derived from the
N/A particle size distribution curve.
SC Sand-clay mixtures ‘Dirty’ materials with excess of plastic fines, medium to high dry strength ≥ 12% fines, fines 3 Clay soils with liquid limits > 35% and ≤ 50% may be classified as being
are clayey of medium plasticity.
4 The U line on the Modified Casagrande Chart is an approximate upper
bound for most natural soils.
Field Classification of Laboratory
Silt and Clay Classification
Group
Major Divisions Symbol Typical Names Dry Strength Dilatancy Toughness % < 0.075mm Modified Casagrande Chart for Classifying Silts and Clays
according to their Behaviour
SILT and CLAY ML Inorganic silt and very fine sand, rock flour, silty or None to low Slow to rapid Low Below A line
ine grained soils (more than 35%of soil excluding
(low to medium clayey fine sand or silt with low plasticity
plasticity)
oversize fraction is less than 0.075mm)
CL, CI Inorganic clay of low to medium plasticity, gravelly Medium to high None to slow Medium Above A line
clay, sandy clay
OL Organic silt Low to medium Slow Low Below A line
SILT and CLAY MH Inorganic silt Low to medium None to slow Low to medium Below A line
(high plasticity)
CH Inorganic clay of high plasticity High to very high None High Above A line
OH Organic clay of medium to high plasticity, organic Medium to high None to very slow Low to medium Below A line
silt
Highly organic soil Pt Peat, highly organic soil – – – –
February 2019 7
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LOG SYMBOLS
Log Column Symbol Definition
Groundwater Record Standing water level. Time delay following completion of drilling/excavation may be shown.
Extent of borehole/test pit collapse shortly after drilling/excavation.
C
Groundwater seepage into borehole or test pit noted during drilling or excavation.
Samples ES Sample taken over depth indicated, for environmental analysis.
U50 Undisturbed 50mm diameter tube sample taken over depth indicated.
DB Bulk disturbed sample taken over depth indicated.
DS Small disturbed bag sample taken over depth indicated.
ASB Soil sample taken over depth indicated, for asbestos analysis.
ASS Soil sample taken over depth indicated, for acid sulfate soil analysis.
SAL Soil sample taken over depth indicated, for salinity analysis.
Field Tests N = 17 Standard Penetration Test (SPT) performed between depths indicated by lines. Individual
4, 7, 10 figures show blows per 150mm penetration. ‘Refusal’ refers to apparent hammer refusal within
the corresponding 150mm depth increment.
Nc = 5 Solid Cone Penetration Test (SCPT) performed between depths indicated by lines. Individual
7 figures show blows per 150mm penetration for 60 solid cone driven by SPT hammer. ‘R’ refers
to apparent hammer refusal within the corresponding 150mm depth increment.
3R
VNS = 25 Vane shear reading in kPa of undrained shear strength.
PID = 100 Photoionisation detector reading in ppm (soil sample headspace test).
Moisture Condition w > PL Moisture content estimated to be greater than plastic limit.
(Fine Grained Soils) w PL Moisture content estimated to be approximately equal to plastic limit.
w < PL Moisture content estimated to be less than plastic limit.
w LL Moisture content estimated to be near liquid limit.
w > LL Moisture content estimated to be wet of liquid limit.
(Coarse Grained Soils) D DRY – runs freely through fingers.
M MOIST – does not run freely but no free water visible on soil surface.
W WET – free water visible on soil surface.
Strength (Consistency) VS VERY SOFT – unconfined compressive strength 25kPa.
Cohesive Soils S SOFT – unconfined compressive strength > 25kPa and 50kPa.
F FIRM – unconfined compressive strength > 50kPa and 100kPa.
St STIFF – unconfined compressive strength > 100kPa and 200kPa.
VSt VERY STIFF – unconfined compressive strength > 200kPa and 400kPa.
Hd HARD – unconfined compressive strength > 400kPa.
Fr FRIABLE – strength not attainable, soil crumbles.
( ) Bracketed symbol indicates estimated consistency based on tactile examination or other
assessment.
Density Index/ Density Index (ID) SPT ‘N’ Value Range
Relative Density Range (%) (Blows/300mm)
(Cohesionless Soils) VL VERY LOOSE 15 0–4
L LOOSE > 15 and 35 4 – 10
MD MEDIUM DENSE > 35 and 65 10 – 30
D DENSE > 65 and 85 30 – 50
VD VERY DENSE > 85 > 50
( ) Bracketed symbol indicates estimated density based on ease of drilling or other assessment.
Hand Penetrometer 300 Measures reading in kPa of unconfined compressive strength. Numbers indicate individual
Readings 250 test results on representative undisturbed material unless noted otherwise.
February 2019 8
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Log Column Symbol Definition
Remarks ‘V’ bit Hardened steel ‘V’ shaped bit.
‘TC’ bit Twin pronged tungsten carbide bit.
Penetration of auger string in mm under static load of rig applied by drill head hydraulics
T60 without rotation of augers.
Soil Origin The geological origin of the soil can generally be described as:
RESIDUAL – soil formed directly from insitu weathering of the underlying rock.
No visible structure or fabric of the parent rock.
EXTREMELY – soil formed directly from insitu weathering of the underlying rock.
WEATHERED Material is of soil strength but retains the structure and/or fabric of the
parent rock.
ALLUVIAL – soil deposited by creeks and rivers.
ESTUARINE – soil deposited in coastal estuaries, including sediments caused by
inflowing creeks and rivers, and tidal currents.
MARINE – soil deposited in a marine environment.
AEOLIAN – soil carried and deposited by wind.
COLLUVIAL – soil and rock debris transported downslope by gravity, with or without
the assistance of flowing water. Colluvium is usually a thick deposit
formed from a landslide. The description ‘slopewash’ is used for thinner
surficial deposits.
LITTORAL – beach deposited soil.
February 2019 9
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Classification of Material Weathering
Term Abbreviation Definition
Material is weathered to such an extent that it has soil properties. Mass
Residual Soil RS structure and material texture and fabric of original rock are no longer visible,
but the soil has not been significantly transported.
Material is weathered to such an extent that it has soil properties. Mass
Extremely Weathered XW
structure and material texture and fabric of original rock are still visible.
The whole of the rock material is discoloured, usually by iron staining or
bleaching to the extent that the colour of the original rock is not recognisable.
Highly Weathered HW Rock strength is significantly changed by weathering. Some primary minerals
Distinctly have weathered to clay minerals. Porosity may be increased by leaching, or
Weathered DW may be decreased due to deposition of weathering products in pores.
(Note 1)
The whole of the rock material is discoloured, usually by iron staining or
Moderately Weathered MW bleaching to the extent that the colour of the original rock is not recognisable,
but shows little or no change of strength from fresh rock.
Rock is partially discoloured with staining or bleaching along joints but shows
Slightly Weathered SW
little or no change of strength from fresh rock.
Fresh FR Rock shows no sign of decomposition of individual minerals or colour changes.
NOTE 1: The term ‘Distinctly Weathered’ is used where it is not practicable to distinguish between ‘Highly Weathered’ and ‘Moderately Weathered’ rock.
‘Distinctly Weathered’ is defined as follows: ‘Rock strength usually changed by weathering. The rock may be highly discoloured, usually by iron staining.
Porosity may be increased by leaching, or may be decreased due to deposition of weathering products in pores’. There is some change in rock strength.
Rock Material Strength Classification
Guide to Strength
Uniaxial Point Load
Compressive Strength Index
Term Abbreviation Strength (MPa) Is(50) (MPa) Field Assessment
Very Low VL 0.6 to 2 0.03 to 0.1 Material crumbles under firm blows with sharp end of pick;
Strength can be peeled with knife; too hard to cut a triaxial sample by
hand. Pieces up to 30mm thick can be broken by finger
pressure.
Low Strength L 2 to 6 0.1 to 0.3 Easily scored with a knife; indentations 1mm to 3mm show
in the specimen with firm blows of the pick point; has dull
sound under hammer. A piece of core 150mm long by 50mm
diameter may be broken by hand. Sharp edges of core may
be friable and break during handling.
Medium M 6 to 20 0.3 to 1 Scored with a knife; a piece of core 150mm long by 50mm
Strength diameter can be broken by hand with difficulty.
High Strength H 20 to 60 1 to 3 A piece of core 150mm long by 50mm diameter cannot be
broken by hand but can be broken by a pick with a single
firm blow; rock rings under hammer.
Very High VH 60 to 200 3 to 10 Hand specimen breaks with pick after more than one blow;
Strength rock rings under hammer.
Extremely EH > 200 > 10 Specimen requires many blows with geological pick to break
High Strength through intact material; rock rings under hammer.
February 2019 10
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Abbreviations Used in Defect Description
Symbol
Cored Borehole Log Column Abbreviation Description
Point Load Strength Index 0.6 Axial point load strength index test result (MPa)
x 0.6 Diametral point load strength index test result (MPa)
Defect Details – Type Be Parting – bedding or cleavage
CS Clay seam
Cr Crushed/sheared seam or zone
J Joint
Jh Healed joint
Ji Incipient joint
XWS Extremely weathered seam
– Orientation Degrees Defect orientation is measured relative to normal to the core axis
(ie. relative to the horizontal for a vertical borehole)
– Shape P Planar
C Curved
Un Undulating
St Stepped
Ir Irregular
– Roughness Vr Very rough
R Rough
S Smooth
Po Polished
Sl Slickensided
– Infill Material Ca Calcite
Cb Carbonaceous
Clay Clay
Fe Iron
Qz Quartz
Py Pyrite
– Coatings Cn Clean
Sn Stained – no visible coating, surface is discoloured
Vn Veneer – visible, too thin to measure, may be patchy
Ct Coating 1mm thick
Filled Coating > 1mm thick
– Thickness mm.t Defect thickness measured in millimetres
February 2019 11