Council archive · source document
Attachment C - Soil Survey Report · MCU18/0013
Attached to the e-mail Response to info request part 1- MCU18/0013.
SLOPE STABILITY ASSESSMENT AND GEOTECHNICAL REPORT PROJECT NO. 1-20119 MARCH, 2018 SAM HOPPER PROPOSED RESIDENCE 24 ARAKON CRESCENT, SUNSHINE BEACH OFFICES IN BRISBANE AND GOLD COAST
See the original
The page text is free to read. Viewing or downloading an original file needs an account.
Log in to see the originalFull text of the other 70 pages
Page 2
Soil Surveys Engineering Pty Limited
A.B.N. 70 054 043 631
www.soilsurveys.com.au
Ph +617 3369 6000
Fax +617 3369 6660
PO Box 317, Paddington, QLD, 4064, Australia
[email protected]
Brisbane
Level 2, 19 Finchley Street, Milton, QLD, 4064, Australia
Gold Coast
Unit 8, 140 Millaroo Drive, Helensvale, QLD, Australia
Document Information
Project Number 1-20119
Document Title Slope Stability Assessment and Geotechnical Report - Proposed Residence
Site Address 24 Arakon Crescent, Sunshine Beach
Client Sam Hopper
File ref 1-20119, 2018-03-02, BR VER 2
Author Glen Burkitt
Review
Approved for Issue
Ver No. Document Type Reviewed By
Name Date
1 DRAFT Noel Perkins Noel Perkins 27/03/2018
2 FINAL Noel Perkins Noel Perkins 28/03/2018
Distribution List
Ver No. Organisation Contact Email Date Sent
1 Shaun Lockyer Architects Jen Negline [email protected] 27/03/2018
2 Shaun Lockyer Architects Jen Negline [email protected] 28/03/2018
Page 3
TABLE OF CONTENTS
1.0 INTRODUCTION .............................................................................................. 1
1.1 General .................................................................................................................. 1
1.2 Reason for this Report ......................................................................................... 1
1.3 Scope of Report .................................................................................................... 1
1.4 Controls and Procedures ..................................................................................... 1
1.5 Proposed Development ........................................................................................ 1
1.6 Provided Information ............................................................................................ 2
2.0 ASSESSMENT METHODOLOGY ................................................................... 3
2.1 Method ................................................................................................................... 3
2.2 Hazard & Risk Analysis ........................................................................................ 3
3.0 SITE ASSESSMENT AND DATA COLLECTION ............................................ 4
3.1 Field Investigation ................................................................................................ 4
3.2 Site Location ......................................................................................................... 4
3.3 Regional Geology ................................................................................................. 5
3.4 Published Stability Data ....................................................................................... 5
3.5 Site Factors ........................................................................................................... 5
3.6 Geotechnical Model .............................................................................................. 6
3.6.1 Subsurface Profile ........................................................................................................... 6
3.6.2 Groundwater and Seepage ............................................................................................. 7
3.6.3 Laboratory Testing .......................................................................................................... 7
3.7 Evidence of Possible Instability........................................................................... 7
4.0 HAZARD IDENTIFICATION ............................................................................. 9
4.1 General Discussion On Stability Assessment .................................................... 9
4.2 Typical Hazards .................................................................................................... 9
5.0 RISK ASSESSMENT ..................................................................................... 10
5.1 General ................................................................................................................ 10
5.2 Review of Stability Data...................................................................................... 10
5.3 Identification of Potential Hazards on Site ........................................................ 10
5.4 Likelihood Estimation ......................................................................................... 10
5.4.1 Methods of Assessment ................................................................................................ 10
5.4.2 Evaluation of Likelihood Rating for Existing Overall Site .............................................. 10
5.4.3 Hazard A - Natural Shallow Landslide .......................................................................... 11
5.4.4 Hazard B - Proposed Cuts ............................................................................................ 11
5.4.5 Hazard C - Scour of Exposed Surfaces ........................................................................ 12
5.5 Consequence Analysis ....................................................................................... 12
5.5.1 General .......................................................................................................................... 12
5.5.2 Site Factors ................................................................................................................... 12
5.5.3 Consequence to Property ............................................................................................. 13
5.5.4 Consequence to Persons .............................................................................................. 13
5.6 Risk Determination and Evaluation - Property.................................................. 13
5.7 Risk Determination and Evaluation - Persons .................................................. 14
5.8 Risk Summary ..................................................................................................... 15
6.0 ENGINEERING STABILITY RECOMMENDATIONS..................................... 16
6.1 General Recommendations with Respect to Construction .............................. 16
6.2 Stormwater Drainage .......................................................................................... 16
6.3 Site Specific Recommendations ........................................................................ 17
6.3.1 General .......................................................................................................................... 17
6.3.2 Scour ............................................................................................................................. 17
6.3.3 Retaining Structures ...................................................................................................... 17
6.3.4 Continued Maintenance ................................................................................................ 17
7.0 ENGINEERING ASSESSMENT ..................................................................... 18
7.1 Civil Works .......................................................................................................... 18
7.1.1 Trafficability and Site Preparation ................................................................................. 18
7.1.2 Earthworks .................................................................................................................... 18
7.1.3 Batters ........................................................................................................................... 19
7.2 Building Foundations ......................................................................................... 19
Page 4
TABLE OF CONTENTS
7.2.1 General .......................................................................................................................... 19
7.2.2 Site Classification as per AS 2870-2011 ....................................................................... 19
7.2.3 Further Comments Regarding Foundations .................................................................. 20
7.2.4 High Level Footings ...................................................................................................... 20
7.2.5 Deep Foundations ......................................................................................................... 21
7.2.6 Slab on Ground ............................................................................................................. 23
7.2.7 Design Considerations .................................................................................................. 23
7.2.8 Site Management .......................................................................................................... 24
7.3 Basement Excavation and Retention Methods ................................................. 25
7.3.1 Introduction .................................................................................................................... 25
7.3.2 Geotechnical Model ...................................................................................................... 25
7.3.3 Boundary Conditions ..................................................................................................... 25
7.3.4 Possible Retention Options ........................................................................................... 25
7.4 Retaining Walls ................................................................................................... 26
7.4.1 General .......................................................................................................................... 26
7.4.2 Pressure Distribution ..................................................................................................... 26
8.0 Soil Permeability Assessment .................................................................... 29
8.1 Introduction ......................................................................................................... 29
8.2 Field Testing........................................................................................................ 29
8.3 Textural Method .................................................................................................. 29
8.4 Conclusion .......................................................................................................... 29
9.0 CONSTRUCTION INSPECTIONS ................................................................. 30
10.0 REFERENCES............................................................................................ 30
11.0 LIMITATIONS ............................................................................................. 31
Appendices
Appendix A
NOTES RELATING TO THIS REPORT
Appendix B
ASSESSMENT GUIDELINES
Appendix C
SITE INVESTIGATION MAPS
Appendix D
FRAMEWORK FOR LANDSLIDE RISK MANUAL
Appendix E
PHOTOGRAPHS
Appendix F
HAND AUGER AND DCP LOGS
Appendix G
TYPES OF LANDSLIDES
Appendix H
LRM2007 – PRACTICE NOTE GUIDELINES – RISK MATRIX
Appendix I
DRAWINGS
Appendix J
HILLSIDE CONSTRUCTION GUIDELINES
Appendix K
SOIL PERMEABILITY TEST RESULTS
Page 5
Project No. 1-20119 Page | 1
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
1.0 INTRODUCTION
1.1 General
This report presents the results of the geotechnical investigation carried out by Soil Surveys
Engineering Pty Limited on the 26th February and 5th March, 2018, for the Proposed Residence
at 24 Arakon Crescent, Sunshine Beach.
The report was carried out following authorisation from Sam Hopper on 20th February, 2018.
The objectives of this investigation were to assess subsurface conditions at the site in
accordance with the Scope of Services detailed in Section 1.3.
1.2 Reason for this Report
It is understood that given the site location and Noosa Shire Council regulations, a slope
stability assessment is required for the proposed development.
1.3 Scope of Report
The objective of this study would be to undertake a geotechnical investigation and site mapping
to assess the existing geotechnical conditions to provide:-
A slope stability assessment of the overall site, in accordance with:-
o National Disaster Mitigation Program (NDMP), Landslide Risk Management
(LRM) Guidelines, Practice Notes and Geoguidelines as published in the
“Australian Geomechanics Journal” Volume 42 No. 1 March, 2007.
o State Planning Policy July, 2014-SPP.
o Noosa Shire Council Noosa Plan, 2017.
An investigation for the stormwater management plan, including permeability and
infiltration information.
Foundation design parameters.
Retaining wall design parameters.
1.4 Controls and Procedures
This report has been prepared in accordance with:-
National Disaster Mitigation Program (NDMP), Landslide Risk Management (LRM)
Guidelines, Practice Notes and Geoguidelines as published in the “Australian
Geomechanics Journal” Volume 42 No. 1 March 2007.
State Planning Policy July 2014-SPP.
The Noosa Plan, 2017, Part 7, Landslide Overlay.
1.5 Proposed Development
It is understood that the proposed development is to consist of the construction of a stepped
three level residence with the garage level and ground floor level partially cut into the rear of the
site.
Page 6
Project No. 1-20119 Page | 2
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
Building loads have not been provided, however based on the provided drawings, it is expected
that they would be generally consistent with domestic type structural loads.
Earthworks are expected to consist of cuts of up to approximately 3.5m with minor filling (refer
Figure 1).
We also understand that up to three sheet pile walls already exist at the front of the site, dating
back to approximately 2006 (installed as part of the construction of the neighbouring site No.
26).
FIGURE 1 - PROPOSED RESIDENCE – DECEMBER, 2018
1.6 Provided Information
As part of the slope stability assessment, the following information has been provided to Soil
Surveys Engineering:-
Preliminary Sheet Piling Layout by Macdonald Sheet Piling, refer BSQ06-03, Dwg.
BSQ06-01, Rev. A dated 10th January, 2006.
Detail Survey by Cadcon Surveying and Town Planning, refer 166808-01-01, dated 14th
June, 2016.
Identification Survey by Cadcon Surveying and Town Planning, refer 166808, dated 20th
June, 2016.
Schematic Design drawings by Shaun Lockyer Architects, refer drawing set 000.01 to
400.02, Rev. B, dated 5th December, 2017.
Preliminary Stormwater Management Plan drawing by Westera Partners, refer S18/003,
rev. P dated February, 2018.
Information from a previous geotechnical report for the lot to the north (dated November, 2004)
has also been utilised in our assessment.
Page 7
Project No. 1-20119 Page | 3
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
2.0 ASSESSMENT METHODOLOGY
2.1 Method
The assessment of the stability of slopes at the site has utilised a Hazard and Risk Assessment
approach. In this method, the potential stability hazards on the site are assessed using certain
features/properties of the site (i.e. slope angle, ground water conditions, etc.). This method
provides a ranking for each of the identified hazards.
Using this hazard ranking and based on assumed consequences, an assessment of risk can
then be made using a risk matrix.
2.2 Hazard & Risk Analysis
The general processes in assessment and management of risks associated with landslides are
given in detail in the National Disaster Mitigation Program (NDMP), “Landslide Risk
Management (LRM) Guidelines”, Practice Notes and Geoguidelines as published in the
Australian Geomechanics Journal Volume 42 No. 1, March 2007. Figure D1 (Appendix D) is an
extract from the paper showing the typical processes in flow chart form.
As shown in Figure D1, hazard identification is an initial step in this process, and is the basis for
this study. Due to unknowns associated with development applications and their influence on
the surrounding environment, this study has been restricted to a qualitative evaluation of hazard
rating, with respect to natural slope instability. Landslide management areas were then derived
from these hazard/likelihood ratings and assessed consequences to evaluate the assessed risk.
The effects of earthquake on slope stability have not been included in this study.
The terminology adopted in this report has been designed to be consistent, as far as
practicable, with national standards including the Australian New Zealand Standard AS/NZS
ISO 31000:2009 “Risk Management – Principles and Guidelines” and the above NDMP LRM
Guidelines.
The methodology undertaken by Soil Surveys Engineering Pty Limited in assessing the Hazard
Management Areas was based on the following steps:-
A review of published information and aerial photographs to identify areas that have
potential to be affected by slope instability;
A review of regional features including topography, geology and geomorphology;
Identification of potential hazard zones based on topography, geology and
geomorphology;
Site inspection and review of field investigation data;
Development of a Risk Assessment map that can be used to assess the proposed
development.
This study has identified hazard ratings using a classification system consistent with the
procedures detailed in the paper entitled “A Method of Zoning Landslide Hazards”, prepared by
McGregor and Taylor. This method has been adopted on a wide range of projects and has
proven to be robust.
Page 8
Project No. 1-20119 Page | 4
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
3.0 SITE ASSESSMENT AND DATA COLLECTION
3.1 Field Investigation
Due to poor site access the subsurface conditions at the site were investigated by the drilling
and sampling of two hand augers. In addition, dynamic cone penetrometer tests were carried
out adjacent to the hand auger holes and at two other locations. A permeability test (P05) was
also undertaken on the site.
A site inspection by an Experienced Engineering Geologist, experienced in the assessment of
slope instability, was carried out.
The description of the materials encountered in the field investigation is subjective, based on
the experience and judgement of the rig/site supervisor and some variations in the description,
from the actual material type may occur.
The soil classification descriptions, field and laboratory testing were carried out in general
accordance with the following Australian Standards:-
AS 1726 Geotechnical Site Investigations
AS 1289 Methods of Testing Soils for Engineering Purposes
Notes relating to this report, borehole records and a site plan showing the location of the
boreholes are included in the Appendices.
3.2 Site Location
The site is located at 24 Arakon Crescent, Sunshine Beach, also known as Lot 794 on
RP48111 (refer Figure 2). Access to the site is off Arakon Crescent (refer Figure 3).
FIGURE 2 - SITE LOCATION
Page 9
Project No. 1-20119 Page | 5
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
FIGURE 3 - SITE AERIAL VIEW (NEARMAP.COM, DEC, 2017)
3.3 Regional Geology
Based upon the 1:100,000 Gympie Special Geological Map (Department of Mines and Energy,
Queensland, 1999), the site is underlain by beach sand deposits of the Quaternary Age (1.8
Mya to present) described as Pleistocene dune sand (quartz sand) and Holocene beach ridge
and berm (quartz sand).
3.4 Published Stability Data
The searchable Geoscience Australia Landslide Database was reviewed. No recorded
landslides were located in the vicinity of the site (2km radius).
3.5 Site Factors
The principal site features were:-
The site is located on the eastern side of a low hill, with slopes falling relatively steeply
towards the east (to Sunshine Beach) (refer Plate E1, Appendix E).
Arakon Crescent has been cut into the natural slope with a crib retaining wall
constructed along the western side of the road, opposite the site. It is likely that as part
of the road construction, some filling was undertaken at the western side (upper part) of
the site (refer Plate E2, Appendix E).
The provided survey (refer Section 1.6) indicates a fall of approximately 9.5m across the
site with an RL of 27.5m at the western boundary and approx. RL 18.0m at the eastern
boundary (refer Plate E3, Appendix E).
A small gully head type feature exists near the centre of the eastern boundary of the
site, extending into the site by approx. 6.0m (refer Plate E4, Appendix E). This appears
to have been an area of scour at some time in the past.
A pedestrian access track also crosses the south eastern corner of the site, which has
caused scour and erosion of the sand over time.
An approx. 2.0m wide Council easement runs along the southern site boundary.
Page 10
Project No. 1-20119 Page | 6
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
The site is well grassed and essentially free from larger vegetation. Several small
shrubs are located along the southern easement and northern neighbouring property, as
well as medium sized trees on the beach frontage at the eastern side of the lot (refer
Plate E1, Appendix E).
We understand that three now buried sheet pile walls exist on the site, installed in
approx. 2006 (refer Section 1.6), installed as part of the construction of the neighbouring
residence to the north (refer approx. location on drawing 1-20119-01).
The site plan (1-20119-01) in Appendix I, shows an overlay of the provided survey (refer
Section 1.6), as well as the proposed residence location.
3.6 Geotechnical Model
3.6.1 Subsurface Profile
Given access was only available for hand equipment due to the steep slope off the street, Hand
Augers and DCP tests were undertaken to provide an assessment of the competency of the
subsurface profile and to assess the likely depth to dense to very dense sands (i.e. DCP
refusal). Information from the adjacent investigation in 2004 was also utilized to confirm the
material types encountered. Therefore, the subsurface profile adopted from the testing program
is summarized below:-
Fill – Encountered in hand augers to refusal depths (up to 0.7m in HA1) and described
as Silty SAND (SM), very loose to medium dense.
Sand - Assumed beneath the fill in all DCP tests to refusal depths and assessed as
being very loose to very dense, with DCP refusal at 4.68m (HA1), 6.19m (HA2), 3.28m
(DCP3) and 5.78m (DCP4).
Based upon our nearby investigation (No. 26) in 2004 (when access off the road for machinery
was possible), the deeper profile of the soils was assessed as:-
Natural very loose to medium dense sands to depths of the order of 3.5m to 3.8m.
Natural dense to very dense sands from ~3.5m to depths of the order of 12.0.
These materials are also known as indurated sands or “coffee rock”.
A summary of the profiles encountered in the hand auger and DCP’s is included in Table 1 with
HA logs and DCP results in Appendix F and the test locations shown on Drawing No. 1-20119-
01a in Appendix I.
Page 11
Project No. 1-20119 Page | 7
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
TABLE 1 SUBSURFACE PROFILE SUMMARY
Consistency based on DCP Tests and assuming
Fill - Very
(3) Full Sand Profile (m) DCP Refusal HA Total
Location RL (m) Loose (4)
Very Loose to Dense to Very (m) Depth (m)
Sand (m) Medium Dense
Loose Dense
0.70-1.80
0.00-0.70 2.10-3.40
HA01 27.0 0.00-TD 2.00-2.10 4.68 0.70
1.80-2.00 4.50-4.68
3.40-4.50
0.00-1.10
HA02 21.7 0.00-TD 1.10-3.70 5.30-6.19 6.19 0.60
3.70-5.30
DCP03 24.7 NO 0.00-0.50 0.50-2.10 2.10-3.28 3.28 -
0.00-1.20
1.20-2.20 3.00-3.90
DCP04 22.5 NO 2.20-3.00 5.78 -
3.90-5.40 5.40-5.78
3.90-5.40
P05 20.7 0.00-TD NT NT NT NA 0.50
Notes:-
1. NE - Not Encountered; NA - Not Applicable; NO - Not Observed; TD - Total Depth; NT - Not Tested.
th
2. All depths below existing ground level (5 March, 2018).
3. RL's based on provided survey data.
4. Blows >20 per 100mm.
3.6.2 Groundwater and Seepage
Groundwater seepage was not noted during the site investigation. However, seepage through
the upper granular material may be expected during and following periods of rainfall.
An onsite permeability test (P05) was undertaken on the site the results are included in
Appendix K and discussed in Section 8 of this report.
3.6.3 Laboratory Testing
Due to the subsurface profile of sands intersected, no laboratory testing was carried out.
Samples were retained should any future testing be required.
3.7 Evidence of Possible Instability
Existing Land Slips
No obvious visual evidence of landslide instability was noted on the site at the time of the site
walkover and investigation. However, vegetation obscures some areas of steeper slopes
towards the eastern side of the lot.
A review of air photos of the site does not indicate any likely areas of medium to large scale
instability on the natural slopes. Any existing small areas of instability would not be able to be
detected using this method due to photo scale.
Surface Scour
Minimal evidence of surface scour was noted on the site, however evidence was noted on the
pedestrian track exiting the south eastern corner of the lot. The majority of steeper areas were
generally well vegetated but overland flow paths could still produce continual scour paths during
major rain events.
Soil Creep
Slight leaning and/or bowed trunks of trees are generally considered to be indicative of soil
creep, with the affected trees being progressively tilted by the slow movement of soil down the
slope. The degree of tilting or bowing of these trees is considered to be a sign of relatively
Page 12
Project No. 1-20119 Page | 8 March, 2018 Ref: 1-20119, 2018-03-02, BR VER 2 Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach minor movements, and is typical for trees growing on such a steep slope. Rapid or gross movements of soil downslope would be likely to uproot or kill the trees. The small to medium sized trees on the existing natural slopes showed minor (if any) signs of curved or bowed trunks.
Page 13
Project No. 1-20119 Page | 9
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
4.0 HAZARD IDENTIFICATION
4.1 General Discussion On Stability Assessment
The stability of a site is usually controlled by a number of factors:-
The existing and proposed ground surface angles.
The properties and nature of the subsurface profile, existing and proposed.
Existing and future loadings of the site including the construction of structures and any
earthworks proposed.
The groundwater regime of the site.
Once the above factors have been evaluated and/or estimated, a geotechnical model is
developed to establish the possible site slope stability hazards. Based on the geotechnical
failure model, the potential of a failure eventuating either in the short or long term is assessed
and the site categorised accordingly.
Instability is usually associated with seepage. Near surface groundwater particularly at the toe
of slopes affects the slopes stability by:-
Reducing the in situ strength of the material.
Increasing pore pressures within the slope.
Lowering the effective “weight” of the toe material.
4.2 Typical Hazards
The rate of landslide movement varies from extremely slow (millimetres to centimetres per year)
to sudden and extremely rapid (metres per second) as with rock fall or debris flow. Sudden and
rapid events are the most dangerous because of the lack of warning and the high speed
resulting in an increased force of impact.
Typically landslides may be classified into the following main types (Refer Figure G1 Appendix
G):-
Translational Slides: where failure occurs on a planar surface or surfaces, usually
natural defects in the material such as fissures, joints or bedding. Material within the
slide can remain relatively undisturbed.
Creep Slides: where failure occurs as a gradual downslope progression of slope
material (often extremely slow rates). The slide area may appear relatively undisturbed
and identification of the slide is often reliant on surface features.
Rotational Slides: where failure occurs through the material substance commonly on a
concave surface. Material within the slide is considerably disturbed.
Topple: where failure occurs from the end over end motion of rocks down a slope. Often
resulting from closely spaced sub-vertical jointed rock outcrops.
Falls: where movement is by free-falling or rolling of fragments on steep slopes with
outcrops of closely jointed rock.
Flows: where, after failure along a planar or concave surface, the material is
transformed into a viscous fluid consisting of soil and rock particles suspended in water.
Complex: where there is a combination of one or more of the above mechanisms.
Page 14
Project No. 1-20119 Page | 10
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
5.0 RISK ASSESSMENT
5.1 General
For the purposes of this study, the assessment of Risk for the site has been based on risk to
property and risk to persons, where Risk is the product of Likelihood and Consequence.
This method is based on the method outlined in the “Practice Note Guidelines for Landslide
Risk Management 2007” (PNGLRM), produced by the Australian Geomechanics Society, 2007
and is based upon the Risk Matrix in Appendix H.
5.2 Review of Stability Data
The stability of the natural slopes at this site was assessed based on observations from the site
walkover, as well as a review of the published information and results of our drilling program.
Following a review of the above information, the subject area of the site was able to be divided
into two separate areas (refer drawing 1-20119-01, Appendix I). The areas include:-
Area I – Existing slopes
a – Area above the house to the west (Arakon Cres).
b – Area below the house to the east (includes proposed back yard, stormwater
management area) and extends to adjacent dunes.
Area II – Proposed building footprint at the front and centre of the lot where cuts will be
required to excavate the ground floor level, understood to be temporarily retained by
existing and additional sheet piles.
5.3 Identification of Potential Hazards on Site
Based on the site walkover, a review of the site information and experience on similar sites, the
following potential hazards have been identified for assessment at the location of the proposed
residence (subject site):-
A. Shallow landslides on the existing slopes – applies to Area I (both).
B. Proposed Cuts – applies to Area II.
C. Surface scour on the site during construction – applies to overall subject site.
5.4 Likelihood Estimation
5.4.1 Methods of Assessment
The site was assessed and zoned using the method as outlined in MacGregor and Taylor
(2001). The method has been adopted as a slope stability assessment tool and used in both the
Gold Coast and Redlands Shire regional stability assessments.
5.4.2 Evaluation of Likelihood Rating for Existing Overall Site
Once the relative frequency of slope instability for the site is calculated, MacGregor and Taylor
(2001) suggests a likelihood rating as outlined in Table 2 below.
This rating has then been compared to the Likelihood Descriptor from Appendix C of “Practice
Note Guidelines for Landslides Risk Management (PNGLRM) (2007c)”.
Page 15
Project No. 1-20119 Page | 11
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
TABLE 2 LIKELIHOOD RATING
MacGregor and Taylor (2001) Landslide Risk Management (2007c) Appendix C
Adopted Indicative
Relative Frequency Likelihood Rating Likelihood Descriptor Value of Annual
Probability
-6
< 0.2 Very Low Barely Credible 10
-5 -4
0.2 to 0.6 Low Rare to Unlikely 10 to 10
-4 -3
0.6 to 2.0 Moderate Unlikely to Possible 10 to 10
-3 -2
2.0 to 6.0 High Possible to Likely 10 to 10
-1
> 6.0 Very High Almost Certain 10
Note: 1. McGregor & Taylor (2001).
2. Likelihood adopted based on Landslide Risk Management (2007c), Appendix C.
5.4.3 Hazard A - Natural Shallow Landslide
The site was assessed using the parameters as described by MacGregor and Taylor (2001)
and the site features identified on the supplied information, observations made whilst on site
and where necessary worst case parameters.
Therefore, based on this assessment, natural shallow landslides on the site have been given
a likelihood hazard rating of Very Low for Area Ia and Low to Moderate for Area Ib (moderate
rating relates to eastern boundary slopes). These ratings translate to a Likelihood Descriptor of
Barely Credible for Area Ia and Unlikely for Area Ib.
5.4.4 Hazard B - Proposed Cuts
Cuts are understood to be proposed within the site for the ground and first level floors. Given
the adjacent structures, these cuts are expected to abut parts of the northern, southern and
western boundaries. We understand from original drawings of the site to the north (dating back
to 2006) that the existing residence has a basement at approx. RL 20.0m for the full length of
adjoining boundary.
The existing sheet piles understood to be installed on the site are proposed to be utilised to
partly support the internal cuts, with areas of new sheet piles also to be installed along the
southern boundary and to extend the western boundary.
Given the above, we understand that all cuts will be supported temporary during construction by
sheet pile walls then permanently by construction of other retaining structures. To assess these
cuts, the method outlined by MacGregor & Taylor (2001) for the assessment of cuts has been
adopted. No batters are understood to be adopted for excavations.
The assessment has taken into account the proposed wall geometry (based on provided
drawings and site measurements), expected subsurface profile (from site investigation) and
proposed development (based on provided drawings).
Information in relation to the design parameters or structural elements of the wall is not
available at this stage. Therefore, the assessment has also assumed that all retaining walls
(both temporary and permanent) will be adequately engineer (RPEQ) designed and certified.
Assuming all cuts are adequately supported by retaining structures and that no evidence of
instability is noted in the cuts once completed, then a likelihood hazard rating of Low to
Moderate would apply to the temporary cuts. This translates to a Likelihood Descriptor of
Unlikely.
Page 16
Project No. 1-20119 Page | 12
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
However, once suitable permanent retaining structures are in place, the hazard rating would
drop to Low (lower end) which translates to a Likelihood Descriptor of Rare.
Note: The above assumes that all retaining structures on the site are designed by a
suitably qualified RPEQ and constructed in accordance with their design.
5.4.5 Hazard C - Scour of Exposed Surfaces
As noted above, the methods as adopted for Hazards A and B do not have a corresponding
method for the analysis of scour (Hazard C). The following comments will allow the hazard to be
assessed:-
The proposed development is likely to require the clearing and exposure of soil over
essentially the entire site (slope angles generally of 5º to 30º).
The exposed surfaces would most likely be fill and sandy soils.
Experience with these types of materials would suggest that the exposed material would
scour easily if left exposed and water is allowed to run over the slopes.
Based on the above comments and observations on site, the likelihood rating for the scour of
exposed surfaces would be assessed as being Moderate to High which translates to a
Likelihood Descriptor of Unlikely to Likely.
However, if soils are protected from scour as would be expected to be required as part of the
development during and following construction, then the rating would reduce to Very Low or
Low which translates to a Likelihood Descriptor of Barely Credible to Rare.
5.5 Consequence Analysis
5.5.1 General
As part of the assessment of the risk of slope instability, the analysis of the consequence of any
failure must also be considered.
This analysis is based on the effect on the following for each type of hazard:-
i) Consequence to Property (proposed dwelling)
ii) Consequence to Persons within and around the proposed dwelling
5.5.2 Site Factors
The development consists of the construction of a new residence on the site. The following will
be used to assume consequence:-
A residence will be constructed with basement level formed by cuts into the existing
slope.
Based on the provided drawings, temporary cuts of up to approx. 4.0m to 5.0m will be
required, as tiered cuts for the basement and first floor near the middle of the site
(including near boundaries).
The cuts will be supported initially by temporary engineer designed and certified
retaining structures during construction and then with permanent retaining structures as
part of the residence.
Page 17
Project No. 1-20119 Page | 13
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
5.5.3 Consequence to Property
For the purposes of this study, a semi-qualitative measure of consequence to property will be
adopted, as outlined in Appendix C of PNGLRM 2007c.
If slope instability were to occur, the aspect of property most at risk would be the proposed
residential structure located on the subject part of the site.
Based on Appendix A of PNGLRM 2007c the residential structures at risk would be classified as
Importance Level 2.
Considering the above information the consequence to property for each of the hazards is as
follows:-
Hazard A – Area I – Existing slopes – Minor to Medium
a - Medium, given adjacent roadway and underground services.
b - Minor, may affect some of the adjacent dune area or eastern edge of the
structure.
Hazard B – Area II – Medium as could affect several areas of the site or adjacent sites
during construction of the retaining walls.
Hazard C – Initially Insignificant due to shallow soil profile but could be Medium if not
addressed in the long term.
5.5.4 Consequence to Persons
For the purposes of this study, the methodology as outlined in Section 7 of PNGLRM 2007, will
adopt the following assumptions with respect to persons on the lot. Different hazards have
been deemed to have varying probabilities based on their location on the site (Section 5.2):-
The affected study site will contain a proposed residential dwelling.
The probability of spatial impact (P(S:H)) - this has been based on the total width of the
site exposed to possible instability compared to the total width of the proposed structure
within that length. Assessed as 100%.
Occupancy in any one dwelling - 4 persons.
Proportion of time dwelling occupied - 50%.
Probability of not being able to escape - 20%.
Temporal Spatial Probability (P(T:S)) - Proportion of time dwelling occupied multiplied by
the Probability of not being able to escape - 10%.
Vulnerability (V(D:T)), (Appendix F - PNGLRM 2007):- 70%
Note: the consequences to Persons have not been assessed for hazard C prior to construction
as it is not considered applicable.
5.6 Risk Determination and Evaluation - Property
Appendix C of “PNGLRM (2007)” outlines a method of assessing Risk to Property. The
calculation of likelihood is based on the estimate outlined in Sections 5.4.3 to 5.4.5 of this
report.
Page 18
Project No. 1-20119 Page | 14
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
The consequence is based on the proposed development and the effects on the property of the
specific hazards in Section 5.5.
The risk is then assessed based on the Risk Matrix from LRMPNG, 2007. The assessment is
summarised in Table 3.
TABLE 3 SUMMARY OF RISK TO PROPERTY
Hazard Assessed Assessed Assessed Risk
Hazard Area of Site
Rating Likelihood Consequence to Property
Area Ia Very Low Barely Credible Medium Very Low
A
Area Ib Low to Moderate Unlikely Minor Low
2.
B Area II Low to Moderate Unlikely Medium Low
Overall Site – Moderate to
Unlikely to Likely Insignificant Very Low to Low
initially High
C
Overall Site – Barely Credible to
3. Very Low to Low Medium Very Low to Low
long term Rare
Note:- 1. Refer Appendix B of “Practice Note Guidelines for Landslides Risk Management (2007)”.
2. Assumes all cuts supported by engineer designed retaining walls.
3. Assumes it’s addressed by landscaping and control of drainage and overland flow.
A review of the table above indicates that provided the recommendations outlined in this
report are carried out, the risk of slope instability occurring on the site has been
assessed as no higher than Low.
5.7 Risk Determination and Evaluation - Persons
Evaluation of the risk to life must be carried out on a quantitative basis to be consistent and for
comparison with acceptance criteria. To do this, the indicative probabilities given in Appendix C
of PNGLRM (2007) may be adopted as there are no other frequency/probability data. The
assessment results are shown in Table 4.
The analysis is based on formula 1 in Section 7 of PNGLRM (2007), i.e.:-
R(LoL) = P(H) × P(S:H) × P(T:S) × V(D:T)
Where R(LoL) = The risk for Loss of Life
P(H) = Annual probability of the Landslide - based on Section 5.4
The other factors are outlined in Section 5.5.4
The acceptance criteria (Table 5) adopted for this assessment is outlined in Section 8 of
PNGLRM (2007) which suggests the following Risk to Life as outlined in Table 4.
Based on the assessment below, the risk to life for the three hazards has been assessed
to be Acceptable.
Page 19
Project No. 1-20119 Page | 15
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
TABLE 4 SUMMARY OF RISK TO LIFE CALCULATIONS
Assessed
Hazard Area of Site P(H) P(S:H) P(T:S) V(D:T) R(LoL) Assessment
Likelihood
-6 -8
Area Ia Barely Credible 10 1.0 0.1 0.7 7 x 10 Acceptable
A
-4 -6
Area Ib Unlikely 10 1.0 0.1 0.7 7 x 10 Acceptable
2. -4 -6
B Area II Unlikely 10 1.0 0.1 0.7 7 x 10 Acceptable
-6 -8
Overall Site – Barely Credible to 10 to 7 x 10 to
C 3 -5 1.0 0.1 0.7 -7 Acceptable
long term Rare 10 7 x 10
Note:- 1. Refer Appendix B of “Practice Note Guidelines for Landslides Risk Management (2007)”.
2. Assumes all cuts supported by engineer designed retaining walls.
3. Assumes it’s addressed by landscaping and control of drainage and overland flow.
TABLE 5 RISK CRITERIA
Situation Suggested Tolerable Loss of Life Risk Suggested Acceptable Loss of Life
limit for the person most at risk Risk limit for the person most at risk
Existing Slope 10-4 / annum 10-5 / annum
Existing Development 10-4 / annum 10-5 / annum
New Constructed Slope 10-5 /annum 10-6 /annum
New Development 10-5 /annum 10-6 /annum
Existing Landslide 10-5 /annum 10-6 /annum
Notes:
“Existing Slopes” in this context are slopes that are not part of a recognizable landslide and have demonstrated non-failure performance over at least several seasons or
events of extended adverse weather, usually being a period of at least 10 to 20 years.
“Existing Development” includes existing structures, and slopes that have been modified by cut and fill, that are not located on or part of a recognizable landslide and have
demonstrated non-failure performance over at least several seasons or events of extended adverse weather, usually being a period of at least 10 to 20 years.
“New Constructed Slope” includes any change to existing slopes by cut or fill or changes to existing slopes by new stabilisation works (including replacement of existing
retaining walls or replacement of existing stabilisation measures, such as rock bolts or catch fences).
“New Development” includes any new structure or change to an existing slope or structure. Where changes to an existing structure or slope result in any cut or fill of less
than 1.0m vertical height from the toe to the crest and this change does not increase the risk, then the Existing Slope / Existing Structure criterion may be adopted. Where
changes to an existing structure do not increase the building footprint or do not result in an overall change in footing loads, then the Existing Development criterion may be
adopted.
“Existing Landslides” have been considered likely to require remedial works and hence would become a New Constructed Slope and require the lower risk. Even where
remedial works are not required per se, it would be reasonable expectation of the public for a known landslide to be assessed to the lower risk category as a matter of
“public safety”
Acceptable risks are usually considered to be one order of magnitude lower than the Tolerable Risks.
It is important to distinguish between “acceptable risks” and “tolerable risks”.
Tolerable Risks are risks within a range that society can live with so as to secure certain benefits. It is a range of risk regarded as non-negligible and needing to be kept
under review and reduced further if practicable.
Acceptable Risks are risks which everyone affected is prepared to accept. Action to further reduce such risk is usually not required unless reasonably practicable measures
are available at low cost in terms of money, time and effort.
5.8 Risk Summary
A summary of the results of the risk assessment for the existing site condition as detailed in
Sections 5.6 and 5.7 are as follows:-
Risk to Property - This is outlined in Table 3 and provided the recommendations of this
report are followed, then the risk of any slope stability occurring on the site has been
assessed as Very Low or Low.
Risk to Persons – This is outlined in Table 4 and based on that assessment, the risk to
persons from the identified hazards was assessed as Acceptable.
We also recommend that once a retention design has been completed, it be reviewed by
Soil Surveys Engineering to ensure compliance with this report and that no additional
stability issues have been created.
Page 20
Project No. 1-20119 Page | 16
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
6.0 ENGINEERING STABILITY RECOMMENDATIONS
6.1 General Recommendations with Respect to Construction
Continued long term stability of the site is subject to development of the site taking place in
accordance with the guidelines of this report and relevant Australian Standards and good
building practices.
Based on the field observations, published hazard mapping and observed subsurface
conditions, it is concluded that provided the proposed development is undertaken using
our recommendations, it would not adversely affect the slope stability conditions at this
site. This conclusion is qualified by the following provisions:-
The earthworks should be designed and constructed in accordance with sound and
proper engineering principles.
Likewise, the future construction should be planned designed and constructed in
accordance with sound and proper engineering principles, and more specifically in
accordance with good hillside construction practices (refer Appendix J).
All construction works to be carried out in accordance with the recommendations of this
report.
The access and drainage infrastructure must be properly and effectively maintained, to
ensure that all stormwater is intercepted and controlled. This requirement extends to all
owners and occupiers being aware that ongoing maintenance of the site drainage is
essential for continued site stability.
The following recommendations should be adopted:-
All engineering works should follow the appropriate codes i.e.:-
o Earthworks - AS 3798 "Guidelines on Earthworks for Commercial and
Residential Developments".
o Footings for buildings - AS 2870 'Residential Slabs and Footings'.
o Retaining structures - AS 4678 ‘Earth Retaining Structures’.
Vegetation - where possible, the prompt re-establishment of ground cover should be
undertaken to reduce the risk of surface scour during and following rainfall. Where not
possible, other forms of surface protection should be adopted.
6.2 Stormwater Drainage
Appropriate drainage provisions are essential in any development. Adequate subsoil and
surface drainage should also be incorporated in any retaining wall construction.
Preferably, where possible, roof water should be taken via piped conduits to the road drainage
system or to water storage tanks. Any overflow from water storage tanks should be piped to the
road drainage system. Any outlet for pool backwash will also be required to be discharged into
an adequately designed system and piped to the road drainage.
Given the topography of the site however, we understand that provision of stormwater runoff
tank will be required to be installed near the rear of the residence. This will also cater for
capturing roof water.
Page 21
Project No. 1-20119 Page | 17
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
The proposed infiltration system is to utilise a buried Atlantis Flo-Tank system (refer Section
1.6) which we understand will allow for controlled infiltration of collected water into the
subsurface materials at a depth of approx. 1.6m below the existing surface. The location and
potential water infiltration of this device has been taken into account for the stability assessment
in Section 5.0.
Please refer to Section 8.0 for further details in relation to soil permeability recommendations.
Other usual treatment options associated with Good Hillside Practice, as outlined in Appendix J
should also be adopted. Some of these are implicit or assumed by the analysis. For example,
provision of surface water drainage measures (such as a lined drain across the slope uphill
from the dwelling) and properly engineered retaining walls. Such treatment options should be
clearly stated as part of the risk management requirements.
6.3 Site Specific Recommendations
6.3.1 General
The site risk assessment has assumed that several measures were in place including properly
designed and constructed retaining walls (where applicable), site drainage and scour protection.
6.3.2 Scour
It is essential that any permanent batters/slopes that result from the development (e.g. adjacent
to existing dunes etc.) are suitably protected from erosion and scour by appropriate drainage
and the establishment of ground cover and shrubs, etc. Runoff should not be allowed to
discharge directly across the batters without suitable scour protection.
Top soiling and seeding or hydromulching on any cut areas steeper than 1:5 (11 degrees) is
suggested so that protection could be provided until such time as the grass cover is
established. The type of protection may also need to be discussed with the local council given
the adjacent dune environment.
6.3.3 Retaining Structures
At this stage, we understand that retaining structures will be utilised for several parts of the
proposed development. It is assumed and expected that any walls (regardless of type) would be
designed and constructed to meet relevant retaining wall codes and good engineering practice
as well as the recommendations from this report for this site.
6.3.4 Continued Maintenance
As with all developments, continued maintenance of the proposed site works is essential to
maintain the assessed risks outlined in this report.
Maintenance should include but not be limited to the following:-
Maintaining clear drainage paths for surface water flows.
Maintaining and promoting revegetation of exposed batter areas.
Regular maintenance checks to ensure any damage is repaired in a timely manner.
Page 22
Project No. 1-20119 Page | 18
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
7.0 ENGINEERING ASSESSMENT
7.1 Civil Works
7.1.1 Trafficability and Site Preparation
The fieldwork for this investigation was carried out by hand equipment (due to the steep slope
which limited access onto the site for our machinery). It should be noted that some problems
may be anticipated during wet weather for even light weight 4WD vehicles.
The soils on site are sensitive to repetitive vehicle loading and water (i.e. they will lose strength
through repetitive vehicle loading or if they become overly moist or wet). Further, seepage may
also result in a subsequent loss of strength. This may limit trafficability and create difficulties for
earthworks operations. This situation would be more pronounced if rainfall followed initial
clearing, stripping and grubbing.
It is recommended that after stripping, clearing and grubbing, the exposed surface in the
construction area be proof rolled (where appropriate) to assist in identifying weak areas and to
improve trafficability.
Maintaining adequate drainage conditions is essential. It should be ensured that runoff is
diverted away from the construction area to prevent ponding of water.
Potential trafficability problems with this site should not be underestimated. The site will
very quickly become untrafficable if appropriate seepage and drainage control
measures, along with construction practices appropriate for site conditions, are not
maintained.
The contractor should fully inform himself of the ground conditions on site prior to
commencement of earthworks. This requirement should be explicit in any earthworks
specifications or contract.
Working Platforms For Tracked Plant and Heavy Construction Vehicles
The scope of Soil Surveys Engineering’s study DOES NOT include the design of a working
platform for heavy construction vehicles or heavy tracked plant on or around the site.
Detailed design of a working platform should be carried out considering the operation of actual
machinery proposed to be used. This is particularly important when considering the use of
heavy piling rigs and heavy cranes - the piling/crane contractor should be consulted regarding
their requirements.
7.1.2 Earthworks
It is envisaged that the basement platform will be created with maximum cuts of up to approx.
4m to 5m with minimal filling (if any).
Earthwork procedures should be carried out in a responsible manner in accordance with AS
3798-2007 'Guidelines on Earthworks for Commercial and Residential Developments'. It is
recommended that the earthworks contractor make themselves familiar with site conditions.
Note: The surface silty sands will cause problems with trafficability/workability should
this material be wet/become wet prior to or during construction.
Page 23
Project No. 1-20119 Page | 19
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
Given no structural filling is a currently proposed, no further specific earthworks
recommendation will be provided. The author can be contacted if further information is required.
7.1.3 Batters
It is understood that all cuts will be supported by temporary and later permanent retaining walls
with no requirements currently for batters on the site. Should batter angles be required, please
contact to author to discuss their use.
7.2 Building Foundations
7.2.1 General
Given the subsurface profile encountered, the expected loads and likely excavation depths, a
high level strip and pad footing system may be possible to be adopted for the proposed
development provided all footings are founded into at least medium dense sand and the
presence of loose sand is taken into account. Deep foundations could also be adopted as an
alternative foundation system and/or for retention systems.
7.2.2 Site Classification as per AS 2870-2011
General
A site classification, in accordance with AS 2870 'Residential Slabs and Footings' (it is
recommended that the reader satisfy themselves that the use of AS 2870 is applicable for the
proposed design) has been carried out with the following information:-
Subsurface profile:
Possible minor fill
Residual sand soils
Proposed earthworks:
Cuts of up to approx. 4.0m to 5.0m with minor filling (< 0.5m if any)
Soil Moisture Model:
A zone of moisture variation of 1.5m
A crack zone of 0.75m
pF = 1.2
Site Classification
According to AS 2870-2011, the site has been designated Class 'P' due to:-
The potential presence of uncontrolled fill in excess of 0.4m in depth as defined in AS
2870-2011 Clause 2.5.3;
The site being potentially subject to other factors resulting in foundation movement
beyond the reactive soil movements resulting from moisture changes due to the normal
site conditions described in AS 2870-2011 Clause 1.3.2 (i.e. Clause 1.3.3 abnormal
moisture conditions).
The site being potentially subject to landslip.
Page 24
Project No. 1-20119 Page | 20
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
7.2.3 Further Comments Regarding Foundations
Foundation Design
As noted above this site has been classified as ‘P’, however, if the site was classified based on
reactivity alone, under normal moisture conditions, a ground surface movement (ys) of <20mm
(maximum) could be adopted, which relates to a Class ‘S’ (slightly reactive) site (considering
the proposed development, existing subsurface profile as per boreholes records, and taking into
account other relevant geotechnical data held by Soil Surveys Engineering).
It should also be noted that the methodology adopted for determination of the site classification
assumes the structure has performance requirements similar to domestic type construction.
Development of Abnormal Soil Conditions
It is recommended that design works for the proposed development take into account the long
term effect of any design elements on the subsurface moisture conditions under and around the
structure.
These design works should consider aspects of the design that may contribute to the
development of abnormal moisture conditions i.e.:-
Site drainage
Gardens and landscaping
Future planting of trees and shrubs
Services and repair of leaks
The designer is directed to AS 2870-2011 Appendix B and Section 8.2.7 of this report which
outlines measures that should be considered.
7.2.4 High Level Footings
Where high level footings are adopted, our recommendation is that all perimeter footings,
footings under isolated columns and strip footings below internal load bearing walls be founded
at least 300mm below platform level and a minimum of 300mm into the natural sands.
Table 6 outlines minimum allowable bearing capacities for high level foundations on the site.
TABLE 6 ALLOWABLE BEARING CAPACITIES FOR HIGH LEVEL FOOTINGS
Allowable Bearing Capacity (kPa)
Material
Strip Footing Pad Footing
Fill Uncontrolled NR NR
Sand Loose NR NR
Compacted to 70% density index 100 125
Medium Dense 100 125
Dense 200 250
Very Dense 400 450
Note: NR - Not Recommended
The base of all pad and strip footings founding in sand should be individually re-compacted
using a vibrating plate compactor prior to placement of reinforcing steel and concrete as soils
may be loosened during the excavation process by machinery action.
Page 25
Project No. 1-20119 Page | 21
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
Should any loose areas be encountered in the footing excavations, the density of these areas
must be improved. Dynamic cone penetrometer (DCP) tests should be carried out to confirm
the adequacy of the founding soils. Note that it may be necessary to use formwork to prevent
trench side collapse in the sand profile.
It should be noted that any relevant stability recommendations contained in Section 5.0
will also apply to high level foundations. Also should excavations exceed 0.5m in depth
they may need to be assessed for stability on a case by case basis.
Where necessary, footings deeper than 300mm may be made up with mass concrete poured to
the underside of the footings, or alternatively, footings may be constructed over mass concrete
filled, backhoe excavated pedestals.
7.2.5 Deep Foundations
General
A deep pile system may also be utilised for the proposed structure and for retention systems on
the site. The choice of suitable pile types should be made from non-vibration piling methods.
Push piles, continuous flight auger (CFA), bored piles or screw piles could be considered as
suitable pile types, although the construction of the bored piers may be problematic in loose
sand, where collapse of the pile hole is likely. It is recommended specialist piling contractors be
consulted to make their own assessment of pile types considering subsurface conditions and
pile load requirements
Depending on the load requirements, and the piling contractors design, it is recommended that
the piles are founded in material which is at least medium dense, and at a minimum depth of
3m below existing ground surface.
Compressional Capacity
It is recommended that the deep foundation system on this project be designed in accordance
with AS 2159-2009 'Piling - Design and Installation'. This code uses the limit state design
method.
In the limit state design method the following must be taken into account:-
Considering limit state analysis (AS 2159-2009), the design geotechnical strength Rd,g is
calculated by multiplying the ultimate geotechnical strength Rd,ug by the geotechnical
strength reduction factor Øg, i.e.
Rdg = Rd,ug g
Ultimate strength - the design of a single pile or a pile group must be such that both the
design geotechnical strength (Rd,g) and the structural strength (Rd,s) are greater than or
equal to the Design action effect (Ed) i.e.
Rd,g ≥ Ed and Rd,s ≥ Ed
Serviceability - Single piles and pile groups shall be designed for serviceability by
controlling or limiting pile movements
Page 26
Project No. 1-20119 Page | 22
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
Durability - This is outlined in Section 6 of AS 2159-2009 and will not be discussed any
further here
Any other factors that need to be considered i.e. stability, scour, fatigue, cyclic loading or
seismic actions - As we are not aware that any of these factors will affect the pile design
they will not be considered any further.
The design geotechnical strength (Rd,g) can be calculated as the design ultimate geotechnical
strength (Rd,ug) multiplied by the geotechnical strength reduction factor (g). Uplift and lateral
capacities of piles are not considered, as these are both wholly dependent on the specific pile
type selected.
For design of piles in cohesionless soils, the following equations may be used. However, piling
contractors should be requested to provide their own calculations based on experience and
relevant pile load tests:-
Rug = Qb + Qs
Where: Qb = Ab Pd (Nq - 1)
And: Qs = Ks Pd' tan d As
Rg* = Rug x g
Where: Rug = ultimate geotechnical strength of pile
Qb = ultimate bearing capacity of pile base
Qs = ultimate capacity of pile skin friction
Rg* = allowable capacity of piles
g = geotechnical strength reduction factor, adopt 0.5
but refer also AS2159-2009
Nq = bearing capacity factor
Pd = effective overburden pressure
Pd' = effective overburden pressure at mid-layer height
Ab = area of pile base
As = circumferential area of pile
Ks = earth pressure coefficient
d = angle of wall friction
For this site and expected type of construction, the ultimate geotechnical strength pile
parameters for the material encountered on site are:-
Base Bearing
Dense Sand = 900kPa
Skin Friction
Loose Sand = Ignore
Medium Dense Sand = 10kPa
Dense Sand = 20kPa
Page 27
Project No. 1-20119 Page | 23
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
Lateral Capacity
Broms (1966) has related the values of Ks and d to effective angle of shearing resistance of
cohesionless soils and various pile materials, as shown in Table 7.
TABLE 7 VALUES OF KS
d Ks
Pile Material
Degrees Low Relative Density High Relative Density
Steel 20 0.5 1.0
Concrete ¾ 1.0 2.0
It should be noted that the calculated ultimate resistance of a given pile should also take into
account the installation effects of that particular type, i.e. whether displacement or non-
displacement pile performance can be expected.
7.2.6 Slab on Ground
General
Field and laboratory test results indicate that the existing natural soils are suitable for a
conventional slab on natural ground construction. In areas of any fill, localised pedestals would
be required to suspend the slab.
For constructability of the proposed slab, it is generally preferred to have the same type of slab
across the proposed development site.
Sub-Base
It is suggested that a layer of sub-base be provided under all concrete slabs. The sub-base
material should be compacted to a density not less than 95% of maximum dry density in
accordance with AS 1289 5.2.1 (Modified compaction). The sub-base is provided under a
concrete slab to:-
Provide a stable 'working platform' on which to operate construction equipment;
Facilitate the provision of a uniform bearing surface under the slab.
Sub-base material should be of good quality conforming to requirements (minimum) of Material
Type 2.4 as specified in the Queensland Department of Transport, Standard Specification MRS
11.05, Unbound Pavements (December, 1993).
7.2.7 Design Considerations
Inspections
It is recommended that inspections be undertaken by an experienced geotechnical engineer
from Soil Surveys Engineering following footing excavations to confirm the adequacy of the
founding soils. Inspections should be carried out prior to placement of reinforcing steel and
ordering of concrete.
Underground Services
Where footings are located adjacent to underground services, the footings should extend to
base a minimum of 200mm below the trench base level for a distance of 1.0m out from the
Page 28
Project No. 1-20119 Page | 24
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
trench. Beyond 1.0m the footings should be taken a minimum of 200mm below an imaginary
line drawn up at 450 from the trench base level. Figure 4 refers. These requirements do not
override minimum footing levels.
Service Trench 1
or 1
Retaining Wall 200mm
Found footings
1.0m Below these lines
200mm
FIGURE 4
7.2.8 Site Management
It is important that proper site management methods be observed for the existing soil conditions
by both the builder at the time of the construction and the owner throughout the life of the
proposed development.
Particular reference to this is set out in AS 2870-2011. It should be noted that where proper site
management, particularly with respect to change in moisture conditions, is not followed, the
foundation recommendations contained in this report could be considered void.
The following are some specific comments with respect to site management and the reader is
also directed to CSIRO pamphlet, 10-91, ‘to Home Owners on Foundation Maintenance and
Footing Performance’ for further information:-
It is important that the site be well drained. The ground around the building should
slope away at 1 in 20 for 2 metres and then fall to the stormwater system to prevent
ponding of water adjacent to the building.
Roof downpipes and garden taps should not be allowed to saturate founding soils.
Footings should be placed with minimal delay after excavation to avoid desiccation
or wetting of the founding soils. If footings cannot be poured on the same day as
excavation, a blinding layer of 50mm thickness is recommended. Piers should be
poured immediately following excavation.
Do not let the slab subgrade "dry out" prior to casting.
Page 29
Project No. 1-20119 Page | 25
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
7.3 Basement Excavation and Retention Methods
7.3.1 Introduction
The design and construction method adopted for basement retention depends upon a number
of factors. These include:-
Strength and type of subsurface.
Boundary conditions i.e. location and type (i.e. movement sensitivity) of nearby building,
need for underpinning, etc.
Final wall profile and need for waterproofing.
7.3.2 Geotechnical Model
Based on the supplied contour plan, the existing ground elevation varies from approximately RL
27.5m at the western side of the site down to approximately RL 18.0m at the eastern side of the
site. Assuming a basement (ground floor) excavation level of RL 20.5.0m, the overall cuts on
the site will vary from 0m up to approximately 7.0m, understood to be stepped as two smaller
cuts of up to approx. 5.0m.
DCP testing carried out, a site inspection as well as inspections of the adjacent site in 2007
indicate a consistent subsurface profile with very loose to loose sands to approx. 3.5m depth,
transitioning to dense to very dense sands extending to the base of the proposed cuts.
7.3.3 Boundary Conditions
Boundary conditions for each face consist of:-
Western Face – Arakon Crescent (single lane) with underground services (council
services, water) and crib retaining wall on western side of road.
Eastern Face – Internal portion of the site, adjoining nearby dune area.
Northern Face – Neighbouring three storey residential property with block retaining wall
approx. 1.0m to 2.0m high on boundary. Based upon our knowledge of the
development in 2006/2007, we understand that a basement exists on the boundary line
for the majority of its length at approx. RL 20m.
Southern Face – Council easement approx. 3.5m wide. South of the easement is a
neighbouring two to three storey residential property approx. 1.5m off the easement
boundary.
The effect of these boundary conditions must be taken into account in the design of a suitable
retention option for the south western, north western and south eastern boundary lines.
7.3.4 Possible Retention Options
The following options could be considered for temporary basement retention along the three
site boundaries noted above:-
1) Batter slope to stable batter angle - This method is only applicable where sufficient
space is available. Batters could be utilised where space allows within the site,
however given the adjoining properties on all sides, this would not be possible or
recommended.
Page 30
Project No. 1-20119 Page | 26
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
2) Structural Solution - This method includes the construction of retention systems
(temporary or permanent) along the boundaries to support the material on the
neighbouring properties and road. Given that the excavation is expected to be up to
7m deep overall, a braced retaining wall will be required. This retaining wall should be
installed prior to excavation to ensure stability of the sand profile.
Several types of retaining walls could be employed including steel sheet piles,
contiguous CFA piles or diaphragm wall. Each of these have relative advantages and
disadvantages (technical and economic) which are best evaluated at the detailed
design/tender stage.
Given the existing system on site (understood to be anchored sheet piles), it would be expected
that this system would again be utilised and improved upon (refer Section 7.4).
Once the preferred retention option for the site boundaries has been selected, SSE should be
contacted to provide further design detail (if required).
7.4 Retaining Walls
7.4.1 General
It is understood that retaining walls will be required for parts of the site. The lateral earth
pressure distribution that affects the retaining walls on the site will depend upon the following
parameters:-
In-situ and backfill material properties
Design water regime at the rear of the wall
Wall and cut geometry
Surcharges affecting the wall
Wall type
The structural bracing of the wall and the timing of backfilling behind the wall
7.4.2 Pressure Distribution
The following situations should be considered:-
For cantilever walls, which allow some movement at the top, (i.e. at least 0.005H in
clays) the active case (Ka) applies with a triangular distribution in both the short and
long term situations.
For cantilever walls which cannot tolerate this movement, the at rest case (Ko) applies
with a triangular distribution in both the short and long term situations.
For structurally braced walls the wall design should be checked for both a trapezoidal
(clay soils - short term conditions) and triangular distribution with Ko values (long term
conditions).
The pressure distributions as referred to above are shown in Figures 5 and 6. The parameters
selected for use in the figures are dependent on the preconstruction geometry of the face being
retained. It is expected that without battering, the earth parameters will control
The lateral pressure distributions shown in Figures 5 and 6 include hydrostatic pressure and
show typical pressure distributions due to surcharge loadings. It is recommended that where
Page 31
Project No. 1-20119 Page | 27
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
the retaining walls are expected to be surcharged (e.g. by footings, traffic loads, sloping ground
surface, etc.) Soil Surveys Engineering should be contacted to provide a recommended lateral
earth pressure distribution.
TRIANGULAR DISTRIBUTION
Lateral Earth Pressure Lateral Earth Pressure due to Surcharges
H K(H-hw)
hw
KH+hww(1-K)
K = appropriate earth pressure coefficient
H = Vertical height of the wall UDL Point Load or
Hw = Height of design water table Strip Footing
= Soil bulk density (kN/m3)
w= water bulk density (kN/m3)
FIGURE 5
As a general guide (using an elastic model) line loads located 2.5H away from the wall (where
H is the wall height) results in lateral forces of less than 10% of the line load. Parameters
(unfactored) for assessment of lateral earth pressures are outlined in Table 8.
Any backfill placed behind the wall should be loose granular material. The backfill should not
be heavily compacted since research has shown that compaction can raise the earth pressure
to above the 'at rest' pressure.
Adequate surface and subsoil drainage should be provided for all retaining walls on the site.
Cut-off / interceptor drains should also be provided around the high side of the wall to ensure
stormwater runoff from the area above the wall is suitably diverted.
The placement of a filter fabric between the retained soil and the drainage material (e.g.
granular backfill) for protection against silting of the drainage material is recommended. The
outlets to subsoil pipe drains must be located beyond the ends of the walls and connected to a
proper drainage system. It is suggested the pipes be wrapped in filter fabric to minimise silting.
Page 32
Project No. 1-20119 Page | 28
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
TABLE 8 RETAINING WALL DESIGN PARAMETERS (UNFACTORED)
Earth Pressure Coefficient Vertical
Density Long Term
Material 3 Wall o
(kN/m ) Drained Ø ( )
Ka Ko Kp
Back Fill 17 0.27 0.43 NR 35
2
Gravel 19 0.33 0.50 3.0 30
Loose Sand 17 0.33 0.50 3.0 30
Medium Dense Sand 18 0.29 0.46 3.4 33
Dense Sand 20 0.27 0.43 3.0 35
Very Dense Sand 22 0.21 0.36 4.7 40
Note: 1) NC – Not considered, NR Not recommended.
2) Infers granular free draining material placed behind the retaining wall as a drainage layer.
TRAPEZOIDAL DISTRIBUTION
Lateral Earth Pressure Lateral Earth Pressure due to Surcharges
0.65KaH
hw
hw
Earth Pressure Water UDL Point Load or
Strip Footing
FIGURE 6
In weather exposed locations, to reduce infiltration by surface runoff, the surface of the backfill
should be sealed. This can be achieved by either compacting a material of low permeability i.e.
on site clay or concrete, etc. with a slope towards an open drain.
Due to possible long term problems with blocking of gravel filters and drains and short term
storm conditions that could flood the fill behind retaining walls, it is recommended that all
retaining walls be designed for some water pressure distribution. For ultimate limit state the
suggested water pressure distribution for retaining walls on this site would be half height water
pressure.
During installation of any retaining walls, the in-situ soils should be battered back to minimise
fall-in and subsequent disruption of works. Temporary batter angles should be requested from
Soil Surveys should any battering on site be proposed. Suitable precautions to satisfy Health &
Safety requirements must also be adhered to.
Page 33
Project No. 1-20119 Page | 29
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
8.0 SOIL PERMEABILITY ASSESSMENT
8.1 Introduction
This Section presents the results of the onsite testing carried out for the purpose of determining
the hydraulic conductivity of the subsurface soils in relation to the proposed stormwater
detention system.
All testing and the assessment has been carried out in accordance with AS 1547-2012 ‘On Site
Domestic Wastewater Management’.
8.2 Field Testing
One field permeability test (HA P05) was carried out in approximately the requested location
(refer drawing 1-20119-01 in Appendix I).
The field test method employed in this investigation, i.e. Constant Head Test, was carried out in
accordance with AS 1547-2012, Appendix G.
At the test location, a 100mm diameter hand auger was drilled to a depth of 500mm. The test
hole was then filled to a depth of 350mm, the well permeameter was put in place and the test
commenced.
When the fall became constant, i.e. 10% or less change between successive readings, or flow
ceased, the test was completed. Readings were taken initially 30 second intervals to 10
minutes, then at one minute intervals to 15 minutes. Test results are included in Appendix K.
The subsurface conditions encountered at the test locations comprised silty sand fill to the total
depth of the hand auger, likely overlying natural very loose to loose silty sand. Refer attached
hand auger logs in Appendix F.
8.3 Textural Method
In addition to the Constant Head Tests, the permeability was also assessed from the textural
classification of the soils within the land application area. This method is in accordance with
AS1547-2012 (Table 5.1 ‘Determination of Soil Category’) and can be used where the field
testing may not provide representative permeability values, e.g. test may overestimate
permeability in sands and may not be a practical test for low permeability clays.
The soil types at this site expected to form the bulk of the disposal field are based on Table 5.1,
which provides representative permeabilities, based on the Soil Category:-
Soil Texture = Gravels & sands to sandy loams
Soil Category = 1 to 2
Permeability (ksat), (m/d) = 1.4 to >3.0
8.4 Conclusion
The soil type in the area of the proposed stormwater detention tank system consists of
gravels and sands and sandy loams - Soil Category 1 to 2.
In situ permeability test results recorded saturated hydraulic conductivity values (k sat) of
0.6m/day.
Page 34
Project No. 1-20119 Page | 30
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
9.0 CONSTRUCTION INSPECTIONS
It is recommended that all footing excavations be inspected by Soil Surveys Engineering Pty.
Limited. or a duly qualified Geotechnical Engineer.
Should subsurface conditions other than those described in this report be encountered, Soil
Surveys Engineering Pty. Limited. should be consulted immediately and appropriate
modifications developed and implemented if necessary.
10.0 REFERENCES
Australian Geomechanics Society (2000) Landslide Risk Management Concepts and
Guidelines, Australian Geomechanics, Vol 35 No.1 March 2000, pp49-92
Australian Geomechanics Society (2007) Landslide Risk Management Guidelines and
commentary, Australian Geomechanics, Vol 42 No. 1 March 2007, pp1-182
Geoscience Australia web site - www.ga.gov.au
McGregor P. and Taylor B. (2001) A Method of Zoning Landslide Hazard, Australian
Geomechanic Journal Volume 36, No. 3 September 2001.
Walker, BF (2002) An example of Semi Quantitation Landslide Basic Management for an
individual Lot in Northern Sydney, Australian Geomechanics, Vol 37 No.2 May 2002.
Page 35
Project No. 1-20119 Page | 31 March, 2018 Ref: 1-20119, 2018-03-02, BR VER 2 Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach 11.0 LIMITATIONS We have prepared this report for the use of Sam Hopper, for design purposes in accordance with generally accepted geotechnical engineering practices. No other warranty, expressed or implied, is made as to the professional advice included in this report. This report has not been prepared for use by parties other than Sam Hopper; it may not contain sufficient information for purposes of other parties or for other uses. Please note that any third party relying on the information contained in this report for any purpose whatsoever does so entirely at its own risk, and any duty of care to that third party is excluded. Any interpretation or recommendation given by Soil Surveys Engineering shall be understood to be based on judgement and experience and not on greater knowledge of the facts than the reported investigations would imply. The interpretation and recommendations are therefore opinions provided for our Client’s sole use in accordance with the specific brief. As such they do not necessarily address all aspects of ground behaviour on the subject site. Information provided by others has been taken in good faith, but no liability can be accepted for information provided by others. Your attention is drawn to ‘Appendix A’, ‘Notes Relating to this Report’. Interpretation of factual data given in this report is based on judgement, not a greater knowledge of facts other than those reported. Interpretation of the information shown on the logs, and its application to design and construction, should therefore take into account the spacing and depth of boreholes, the method of drilling, the frequency of sampling and testing and the possibility of other than “straight line” variations between the boreholes. Subsurface conditions between and below boreholes may vary significantly from conditions encountered at the borehole locations. Please note, if following detailed design, the founding depth of any footings or piers/piles is within 3B (B = footing width/pier diameter) above the termination depth of the boreholes/pits/CPTU or if any excavations extend below the borehole/pit/CPTU termination levels, then Soil Surveys Engineering should be contacted immediately. If the above were to occur then the geotechnical data in this report should be considered preliminary only; additional investigation is likely to be required. In the event that conditions encountered on site during construction appear to vary from those expected from the information contained in the report, the Company strongly recommends that it immediately be notified. Most problems are more readily resolved when conditions are exposed than at some later stage, after the event. Should Soil Surveys Engineering not be notified or if this notification is delayed, then Soil Surveys cannot be held responsible for the effect that any variation has on any aspect of the development. Soil Surveys Engineering consider that a documentation review service (during the design phase and prior to construction) to verify that the intent of geotechnical recommendations is properly reflected in the design, along with construction inspections, forms a very important component of the geotechnical engineering design service/process. The geotechnical review ensures geotechnical risks to our Client and their project are minimised at the design and tender stage of the project. Further, with Soil Surveys Engineering being commissioned to carry out geotechnical construction inspections, an opportunity at the time of construction to confirm any assumptions made in the preparation of the report and allow
Page 36
Project No. 1-20119 Page | 32 March, 2018 Ref: 1-20119, 2018-03-02, BR VER 2 Sam Hopper — Siope Stability A. and Ge ical Report - Prop Re e, 24 Arakon Cr St Beach the effect of any normally occurring variation in ground conditions to be assessed with respect to construction becomes available. The above statements are not intended to reduce the level of responsibility accepted by Soil Surveys Engineering in accordance with our commission, but rather to ensure that all parties who may rely on this report are aware of the responsibilities each assumes in doing so and the risks they accept should they decline to have Soil Surveys Engineering carry out a geotechnical documentation review and geotechnical construction inspections. It is highly recommended that the Client avail themselves of these review and inspection services; our standard rates will apply. = ae G.M. BURKITT N.T. PERKINS (RPEQ 7527) SENIOR ENGINEERING GEOLOGIST PRINCIPAL ENGINEERING GEOLOGIST For and on behalf of SOIL SURVEYS ENGINEERING PTY LIMITED ZSOIL SURVEYS —_— >
Page 37
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDICES
Page 38
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX A
NOTES RELATING TO THIS REPORT
Page 39
NOTES RELATING TO THIS REPORT
INTRODUCTION descriptive terms regarding weathering (AS1726-1993
These notes are provided by Soil Surveys Engineering Table A9), strength (refer Table 1 below), defects
Pty Limited (the Company) to complement the (AS1726-1993 Table A10), etc. Where strength testing
geotechnical report in regard to classification methods (ie Point Loads) is carried out, AS1726-1993 Table A8
and field procedures. Not all notes are necessarily is used. Where relevant, further information regarding
relevant to all reports. rock classification is attached.
The ground is a product of continuing natural and
Table 1 Estimated strength descriptions given to rock
man-made processes and therefore exhibits a variety
based on engineering examination
of characteristics and properties which vary from place
to place and can change with time. Geotechnical Strength Term Approximate Qu (MPa)
engineering involves gathering and assimilating limited Extremely Weak < 1.0
information about these characteristics and properties
Very Weak 1.0 - 5.0
in order to understand or predict the behaviour of the
Weak 5.0 - 25
ground on a particular site under certain conditions.
This report may contain such information obtained by Medium Strong 25 - 50
inspection, excavation, probing, sampling, testing or Strong 50 - 100
other means of investigation. If so, they are directly Very Strong 100 - 250
relevant only to the ground at the place where and at
Extremely Strong > 250
the time when the investigation was carried out.
Ref ISRM "Suggested Methods for the Quantitative
DESCRIPTION AND CLASSIFICATION METHODS
Description of Discontinuities in Rock Masses"
Soils - The methods of description and classification of
soils and rocks used in this report are based on
SAMPLING
Australian Standard 1726-1993 (Geotechnical Site
Sampling is carried out during drilling or from other
Investigations), where appropriate. In general,
excavations to allow engineering examination (and
descriptions cover the following properties - soil or rock
laboratory testing where required) of the soil or rock.
type, colour, structure, strength or density, and
inclusions. Identification and classification of soil and Disturbed samples taken during drilling provide
rock involves judgement and the Company infers information on plasticity, grain size, colour, moisture
accuracy only to the extent that is common in current content, minor constituents and, depending upon
geotechnical practice. sample disturbance, (information on strength and
structure).
Soil types are described according to the dominant
particle size and behaviour as set out in AS Undisturbed samples are taken by pushing a thin
1726-1993. walled sample tube, usually 50mm diameter (U50), into
the soil and withdrawing it with a sample of the soil
Cohesive soils are classified on the basis of strength
contained in a relatively undisturbed state. Such
(consistency) either by use of hand penetrometer,
samples yield information on structure and strength,
shear vane, laboratory testing or engineering
and are necessary for laboratory determination of
examination. The strength terms are defined in
shear strength, volume change potential and
AS1726-1993 Table A4.
compressibility. Undisturbed sampling is generally
Non-cohesive soils are classified on the basis of
effective only in cohesive soils.
relative density usually based on insitu testing or
Details of the type and method of sampling used are
engineering examination (see AS1726-1993 Table A5).
given on the attached logs.
Rocks - Rock types are classified by their geological
names (AS1726-1993 Table A6), together with
NOTES RELATING TO THIS REPORT - SEPT 2013 SOIL SURVEYS ENGINEERING
Page 40
-2- TEST LOCATIONS the drilling. The depth of refusal of the different bit Test locations (e.g. boreholes, CPT’s, test pits etc.) types can provide information as to the strength of the were based on available access at the time of testing material encountered. Generally two different bit types (access may need to be provided “by others”). Test are used. The 'V' bit is a V shaped steel bit and the locations may have been shifted if access was not 'TC' bit is a tungsten carbide tipped screw type bit. suitable. Wash Boring - The borehole is usually advanced by a Unless noted otherwise, accuracy of test locations are rotary bit with water or fluid pumped down the hollow to the accuracy of hand held GPS equipment. drill rods and returned up in the space between the INVESTIGATION METHODS rods and the soil or casing, carrying the drill cuttings. The following is a brief summary of investigation Only major changes in stratification can be determined methods currently adopted by the Company and some from the cuttings, together with some information from comments on their use and application. "feel" and rate of penetration. More accurate Test Pits - These are normally excavated with a information on soil strata is gained by regular testing backhoe or a tracked excavator, allowing close and sampling using the Standard Penetration Test examination of the insitu soils if it is safe to descend (SPT) and undisturbed thin walled tube samples (U50). into the pit. The depth of penetration is limited to about Mud Stabilized Drilling - Either Wash Boring or 3m for a backhoe and up to 6m for an excavator. Continuous Core Drilling can use drilling mud as a Limitations of test pits are the problems associated circulating fluid to stabilize the borehole. The term with disturbance and difficulty of reinstatement and the "mud" encompasses a range of products ranging from consequent effects on close-by structures. Care must bentonite to polymers such as Revert or Biogel. The be taken if construction is to be carried out near test pit mud tends to mask the cuttings and reliable locations to either properly recompact the backfill identification is only possible from regular intact during construction or to design and construct the sampling (eg. from SPT and U50 samples) or from structure so as not to be adversely affected by poorly rock coring, etc. compacted backfill at the test pit location. Continuous Core Drilling - A continuous core sample Hand Auger Drilling - A borehole of 50 to 100mm is obtained using a diamond or tungsten carbide diameter is advanced by manually operated tipped core barrel. Provided full core recovery is equipment. Refusal of the augers can occur on a achieved (which is not always possible in very weak variety of materials such as hard clay, gravel or rock rocks and granular soils), this technique provides a fragments and does not necessarily indicate rock level. very reliable method of investigation. In rocks, NMLC Continuous Spiral Flight Augers - The borehole is coring (nominal 52 mm diameter) is usually used with advanced using 75 to 300 mm diameter continuous water flush. The length of core recovered is compared spiral flight augers, which are withdrawn at intervals to to the length drilled and any length not recovered is allow sampling or insitu testing. This is a relatively shown as CORE LOSS. The location of losses is economical means of drilling in clays and in sands determined on site by the supervisor. If the location of above the water table. Samples are returned to the the loss is uncertain, it is placed at the top end of the surface by the flights or may be collected after run, when the core is placed in a storage tray and withdrawal of the augers. Information from the drilling recorded on the log. (as distinct from specific sampling) is of relatively lower Standard Penetration Tests - Standard Penetration reliability due to remoulding, inclusion of cuttings from Tests (SPT) are used mainly in non-cohesive soils, but above or softening of samples by groundwater, or can also be used in cohesive soils, as a means of uncertainties as to the original depth of the samples. indicating density or strength. The test procedure is Augering below the groundwater table has a lower described in Australian Standard 1289, "Methods of reliability than augering above the water table. Various Testing Soils for Engineering Purposes" - Test 6.3.1. drill bits are attached to the base of the augers during NOTES RELATING TO THIS REPORT - SEPT 2013 SOIL SURVEYS ENGINEERING
Page 41
-3-
The test is carried out in a borehole by driving a 50mm resistance, fs, in kPa). These forces are measured by
diameter split sample tube with a tapered shoe, under electrical transducers (strain gauges) within the cone
the impact of a 63 kg hammer with a free fall of 760 device. The ratio between friction resistance and cone
mm. It is normal for the tube to be driven in three resistance is also calculated as a percentage, ie.-
Friction Resis tan ce,f s kPa 100
successive 150 mm increments and the 'N' value is Friction Ratio FR cone resis tan ce, q c kPa
taken as the number of blows for the last 300 mm, the The friction ratio, FR, is generally low in sands (less
upper 150 mm being neglected due to possible than 1% or 2%) and generally higher in clays (say 3%
disturbance from the drilling method. In dense sands, or more). The interpretation of sandy clays, clayey
very hard clays or weak rock, the full 450 mm sands and material with a high silt content is more
penetration may not be practicable and the test is difficult, but intermediate values (between 1% and 3%)
discontinued at a reduced penetration. would be expected. Highly organic clays and peats
In the case where full penetration is obtained with generally have a friction ratio in excess of 5%.
successive blow counts for each 150 mm of, say 4, 6 Static cone data is recorded in the field on disc for later
and 7 blows, the record shows, presentation using computer aided drafting.
4, 6, 7 N = 13 The equipment can be operated from any conventional
In a case where the test is discontinued short of full drill rig. A total applied load in the range of 4 to 10
penetration, say after 15 blows for the first 150 mm tonnes is required for practical purposes, although
and 30 blows for the next 40 mm, the record shows: lighter loads may be used. The cone penetrometers
15, 30/40mm are available with various capacities of cone resistance
The results of the test can be related empirically to the ranging up to 100 MPa for general purpose
engineering properties of the soil. investigations, while a range of 0 to 10 MPa can be
Occasionally, the drop hammer is used to drive 50mm used where more sensitive investigations of soft clay
diameter thin walled sample tubes (U50) in clays. In are required.
such circumstances, it is noted on the borehole logs. The cone resistance value provides a continuous
A modification to the SPT test is where the same measure of soil strength or density, and together with
0
driving system is used with a solid 60 tipped steel the friction ratio, provide very useful indications of the
cone of the same diameter as the SPT hollow sampler. presence of narrow bands of geotechnically significant
The solid cone can be continuously driven for some layers such as thin, soft clay layers or lenses of sand
distance in soft clays or loose sands, or may be used which might otherwise be missed using conventional
where damage would otherwise occur to the SPT. The drilling methods.
results of this Solid SPT are shown as "Nc" on the The lithology of the encountered soils is interpreted
borehole logs, together with the number of blows per from static cone data and is generally presented on the
150 mm penetration. static cone log sheets.
Cone Penetration Tests - Test Method - Cone It is important to note that the lithology is interpreted
Penetration Tests (CPT) are carried out in accordance information and is based on research by Schmertmann
with AS 1289 Test 6.5.1-1977, using an electrical (1970), Sanglerat (1972), Robinson and Campinalli
friction-cone penetrometer. (1986), modified to suit local conditions as indicated by
The test essentially comprises the measurement of borehole information and laboratory testing.
resistance to penetration of a cone of 35.7 mm As soils generally change gradually it is sometimes
diameter pushed into the soil at a rate of 10-20 mm per difficult to accurately describe depths of strata
second by hydraulic force. The resistance to changes, although greater accuracy is obtained with
penetration is recorded in terms of pressure on the end the static cone compared with conventional drilling. In
area of the cone (cone resistance, qc, in MPa) and addition, friction ratios decrease in accuracy with low
friction on the side of the 135 mm long sleeve cone resistance values, and in desiccated soils. As a
immediately above the top of the cone (friction result, some overlap and minor discrepancies may
NOTES RELATING TO THIS REPORT - SEPT 2013 SOIL SURVEYS ENGINEERING
Page 42
-4-
exist between static cone and nearby borehole GROUNDWATER
information. Where groundwater levels are measured in boreholes,
Portable Dynamic Cone Penetrometers - Portable there are several potential problems.
Dynamic Cone Penetrometer (DCP) tests are carried wAlthough groundwater may be present in lower
out by driving a rod into the ground with a falling weight permeability soils, it may enter the hole slowly or
hammer and measuring the blows for successive perhaps not at all during the time the hole is open.
100mm increments of penetration. wA localized perched water table may lead to an
The DCP comprises a Cone of 20 mm diameter with erroneous indication of the true water table.
30 degree taper attached to steel rods of smaller wWater table levels will vary from time to time with
section. seasons or recent weather changes and may not be
The cone end is driven with a 9 kg hammer falling 510 the same at the time of construction.
mm (AS. 1289 Test 6.3.2). The test was developed wThe use of water or mud as a drilling fluid will mask
initially for pavement subgrade investigations, and any groundwater inflow. Water has to be bailed out of
empirical correlations of the test results with California the bore and mud must be washed out of the hole or
Bearing Ratio have been published by various Road "reverted" if water observations are to be made.
Authorities. The Company has developed their own
More reliable measurements can be made by use of
correlations with Standard Penetration tests and
standpipes which are read after stabilizing at periods
Density Index tests in sands.
ranging from several days to perhaps weeks for low
LOGS permeability soils. Piezometers, sealed in a particular
The borehole or test pit logs presented herein are an stratum, may be advisable in low permeability soils or
engineering and/or geological interpretation of the where there may be interference from perched water
subsurface conditions, and their reliability will depend tables or surface water.
to some extent on the frequency of sampling and the FILL
method of drilling or excavation. Ideally, continuous
The presence of fill materials can often be determined
undisturbed sampling or core drilling will enable the
only by the inclusion of foreign objects (eg. bricks,
most reliable assessment but is not always practicable
steel, etc.) or by distinctly unusual colour, texture or
or possible to justify on economic grounds. In any
fabric. Identification of the extent of fill materials will
case, the boreholes or test pits represent only a very
also depend on investigation methods and frequency.
small sample of the total subsurface conditions.
Where natural soils similar to those at the site are used
The attached explanatory notes define the terms and for fill, it may be difficult with limited testing and
symbols used in preparation of the logs. sampling to reliably determine the extent of the fill.
Interpretation of the information shown on the logs, The presence of fill materials is usually regarded with
and its application to design and construction, should caution as the possible variation in density, strength
therefore take into account the spacing of boreholes or and material type is much greater than with natural soil
test pits, the method of drilling or excavation, the deposits. Consequently, there is an increased risk of
frequency of sampling and testing and the possibility of adverse engineering characteristics or behaviour. If
other than "straight line" variations between the the volume and quality of fill is important to a project,
boreholes or test pits. Subsurface conditions between then frequent test pit excavations are preferable to
boreholes or test pits may vary significantly from boreholes.
conditions encountered at the borehole or test pit
locations.
NOTES RELATING TO THIS REPORT - SEPT 2013 SOIL SURVEYS ENGINEERING
Page 43
-5-
LABORATORY TESTING If differences occur, the Company will be pleased to
Laboratory testing is normally carried out in assist with investigation or advice to resolve any
accordance with Australian Standard 1289 "Methods of problems occurring.
Testing Soil for Engineering Purposes". Details of the SITE ANOMALIES
test procedure used are given on the individual report In the event that conditions encountered on site during
forms and the attached explanatory notes summarize construction appear to vary from those expected from
important aspects of the Laboratory Test Procedures the information contained in the report, the Company
adopted. requests that it immediately be notified. Most
ENGINEERING REPORTS problems are more readily resolved when conditions
Engineering reports are prepared by qualified are exposed than at some later stage, well after the
personnel and are based on the information obtained event.
and on current engineering standards of interpretation Extreme events including but not limited to the results
and analysis. The information provided in Soil Surveys of climate change, eg. flood levels above previously
Engineering reports is opinion and interpretation and identified levels, beach scour or erosion beyond
not factual. The client/contractor increases their risk normal expectations (as identified by local authorities)
by not retaining the person who authored the extreme rainfall events, war, espionage, sabotage may
geotechnical report, to carry out site inspection and result in different conditions between time of
review (overseeing role) during construction, to confirm investigation and time of construction.
opinion and interpretation expressed in the report is REPRODUCTION OF INFORMATION FOR
accurate. Where the report has been prepared for a CONTRACTUAL PURPOSES
specific design proposal the information and Attention is drawn to the document “Guidelines for the
interpretation may not be relevant if the design Provision of Geotechnical Information in Construction
proposal is changed. If this happens, the Company will Contracts (1987)”, published by the Institution of
be pleased to review the report and the sufficiency of Engineers, Australia. Where information obtained from
the investigation work. this investigation is provided for tendering purposes, it
Every care is taken with the report as it relates to is recommended that all information, including the
interpretation of subsurface conditions, discussion of written report and discussion, be made available. In
geotechnical aspects and recommendations or circumstances, where the discussion or comments
suggestions for design and construction. Since the section is not relevant to the contractual situation, it
test sites in any exploration represent a very small may be appropriate to prepare a specially edited
proportion of the total site and since the exploration document. The Company would be pleased to assist
only identifies actual ground conditions at the test sites, in this regard and/or to make additional report copies
even under the best circumstances actual conditions available for contract purposes at a nominal charge.
may vary from those inferred to exist. No responsibility REVIEW OF DESIGN
is taken for:- Where major civil or structural developments are
wUnexpected variations in ground and/or groundwater proposed or where only a limited investigation has
conditions. been completed or where the geotechnical conditions/
wChanges in policy or interpretation of policy by constraints are quite complex, it is prudent to have a
statutory authorities. joint design review which involves a senior
wThe actions of other persons. geotechnical engineer. We would be happy to assist in
wAny work where the company is not given the this regard as an extension of our investigation
opportunity to supervise the construction using the commission. Construction drawings should be
Companies designs/recommendations. reviewed by Soil Surveys Engineering, with sufficient
time to allow changes if required, prior to inspections.
NOTES RELATING TO THIS REPORT - SEPT 2013 SOIL SURVEYS ENGINEERING
Page 44
-6- Otherwise Soil Surveys Engineering reserves the right conservatism which is commensurate with the to refuse to carry out inspections. consequences of the risk of error. SITE INSPECTION Estimates of volumes based on our findings require The Company will always be pleased to provide interpolation and extrapolation between test locations engineering inspection services for geotechnical and as such may be significantly different from actual aspects of work to which this report is related. volumes. i) Site visits during construction to confirm reported ground conditions ii) Site visits to assist the contractor or other site personnel in identifying various soil/rock types such as appropriate footing or pier founding depths, the stability of a filled or excavated slope; or iii) Full-time engineering presence on site. In the vast majority of cases it is advantageous to the principal for the geotechnical engineer who wrote the investigation report to be involved in the construction stage of the project. The geotechnical engineer cannot take responsibility for variations in encountered conditions, where he is not given the opportunity to review plans for the proposed development with sufficient time to allow review and make changes to the proposed development if required, and where he is not given the opportunity to inspect the site and oversee construction methods with regard to site conditions with sufficient time to observe all relevant site conditions and operations. RESPONSIBLE USE OF GEOTECHNICAL INFORMATION Recommendations in our report are for design purposes only and provided on the basis that inspections are carried out to allow finalisation of opinions and recommendations contained in our report. The geotechnical investigation consisting of field and laboratory testing has been carried out to indicate typical conditions by indicating conditions and parameters at the specific locations of boreholes/test pits. Subsurface conditions are indicated at these locations only and the inference of conditions between or away from these locations (interpolation and extrapolation) involves a certain degree of risk. Persons inferring such conditions or carrying out such inferences should do so with a degree of caution and NOTES RELATING TO THIS REPORT - SEPT 2013 SOIL SURVEYS ENGINEERING
Page 45
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX B
ASSESSMENT GUIDELINES
Page 46
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
B.0 ASSESSMENT GUIDELINES
B.1 State Planning Policy (July, 2014)
B.1.1 General
In 2003 the Queensland State Government adopted under the Integrated Planning Act 1997
(IPA) the State Planning Policy 1/03 “Mitigating the Adverse Impacts of Flood, Bushfire and
Landslide” and an associated guideline.
In 2014, the Queensland State Government reissued all the State Planning Policies under a
single document (State Planning Policy July 2014 - SPP). Landslide has now been
addressed under two sections of the document these being:-
Part D – The State Interests and Plan Making policies - Planning for
Safety and Resilience to Hazards.
Making or amending a planning scheme and designating land for community
infrastructure
The planning scheme is to appropriately integrate the state interest by:
For all natural hazards:
3) Identifying natural hazard areas for flood, bushfire, landslide and coastal hazards
based on a fit for purpose natural hazard study, and
4) Including provisions that seek to achieve an acceptable or tolerable level of risk,
based on a fit for purpose risk assessment consistent with AS/NZS ISO 31000:2009
Risk Management, and
5) Including provisions that require development to:
a) Avoid natural hazard areas or mitigate the risks of the natural hazard to an
acceptable or tolerable level, and
b) Support, and not unduly burden, disaster management response or recovery
capacity and capabilities, and
c) Directly, indirectly and cumulatively avoid an increase in the severity of the
natural hazard and the potential for damage on the site or to other properties, and
d) Maintain or enhance natural processes and the protective function of landforms
and vegetation that can mitigate risks associated with the natural hazard, and
6) Facilitating the location and design of community infrastructure to maintain the
required level of functionality during and immediately after a natural hazard event.
Page 47
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
Part E - Interim Development Assessment Requirements
These requirements apply to development applications as follows:
A development application for a material change of use, reconfiguring a lot or operational
works on land within:
1) A flood hazard area, or
2) A bushfire hazard area, or
3) A landslide hazard area, or
4) A coastal hazard area.
The development application is to be assessed against the following
requirements:
For all natural hazards:
Development:
1) Avoids natural hazard areas or mitigates the risks of the natural hazard to an
acceptable or tolerable level, and
2) Supports, and does not unduly burden, disaster management response or recovery
capacity and capabilities, and
3) Directly, indirectly and cumulatively avoids an increase in the severity of the natural
hazard and the potential for damage on the site or to other properties, and
4) Avoids risks to public safety and the environment from the location of hazardous
materials and the release of these materials as a result of a natural hazard, and
5) Maintains or enhances natural processes and the protective function of landforms
and vegetation that can mitigate risks associated with the natural hazard.
The SPP defines the following:-
Landslide hazard area means an area that is:
a) Identified by a local government in its planning scheme as a landslide hazard
area, on the basis of a fit for purpose landslide study of the local government’s
area; or
b) If the local government has not identified landslide hazard areas in its planning
scheme in accordance with paragraph (a) above; an area of land with a slope
greater than, or equal to 15 percent.
Natural hazard means a naturally occurring situation or condition, such as a flood,
bushfire, landslide or coastal hazard, including erosion-prone areas and storm-tide
inundation areas, with the potential for loss or harm to the community, property or
environment.
Natural hazard area means a flood hazard area, a bushfire hazard area, a landslide
hazard area or a coastal hazard area.
Page 48
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
In accordance with the SPP, “risks to the community for proposed developments in identified
Natural Hazard Management Areas should be adequately considered during design and
assessment of a proposed development. Where risks are unacceptable they should be
suitably minimised and/or controlled”.
B.1.2 Application to Site
The applicability of State Planning Policy 2014 (SPP) to the development site was assessed
using the requirements as outlined in Section 3.1.1 above:-
Is the development proposal in a local government defined Landslide Hazard Area -
Yes - refer The Noosa Plan, November, 2017, Landslide Overlay Code.
On the basis of the above, the SPP is applicable to the development site.
B.2 The Noosa Plan, 2017
B.2.1 Landslide Hazards
The Noosa Shire Council’s Noosa Plan, 2017 addresses slope instability and landslide
hazards within its Eastern Beaches Locality Plan (Part 7) and Natural Hazards Map for the
Eastern Beaches.
B.2.2 Applicability to Development Site
Figure C1 (Appendix C) shows the relevant output from the Noosa Plan Online Overlay Map
indicating that the entire site is located within the Landslide Hazard Area (refer Figure C1).
Therefore the Noosa Plan Landslide Hazard Code (2017) will apply to the site.
Page 49
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX C
SITE INVESTIGATION MAPS
Page 50
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
FIGURE C1 - PORTION OF LANDSLIDE OVERLAY FROM NOOSA PLAN
Page 51
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX D
FRAMEWORK FOR LANDSLIDE RISK
MANUAL
Page 52
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
FIGURE D1 LRM FLOWCHART
Extract from “Landslide Risk Management Concepts and Guidelines”, Australian
Geomechanics Society Journal, Volume 42 No. 1, March, 2007.
Page 53
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX E
PHOTOGRAPHS
Page 54
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
PLATE E1 – SITE LOOKING WEST TOWARDS ARAKON CRES
PLATE E2 – WESTERN SIDE OF THE SITE LOOKING NORTH NORTH WEST
Page 55
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
PLATE E3 – SITE LOOKING EAST FROM WESTERN BOUNDARY
PLATE E4 – GULLY HEAD NEAR EASTERN BOUDNARY LOOKING NORTH EAST
Page 56
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX F
HAND AUGER AND DCP LOGS
Page 57
Soil Surveys Engineering Pty. Limited HAND AUGER RECORD SHEET
Specialist in Applied Geotechnics
PO Box 317, Paddington, 4064
Location Number: HA 01
+61 7 3369 6000
[email protected]
Project Number: 1-20119
www.soilsurveys.com.au Project Name: Proposed Residence
Location: 24 Arakon Crescent, Sunshine Beach
Easting: 511277 Northing: 7079958 RL: 27.0 m Client: Sam Hopper
Logger: RH Operator: RH Machine: Hand Auger Date: 05/03/2018 Page: 1 OF 1
Drilling Method DCP Test
Graphic (blows/100mm) Samples and
Depth Description
Casing
NMLC
Remarks
WB
RR
0 6 12 18 24 30
TC
0.12 FILL Silty SAND (SM) Very loose, fine to coarse grained,
dark brown, trace of fine to coarse sized gravel, with
organics, moist.
FILL Silty SAND (SM) Very loose, fine to coarse grained, D
dark brown, trace of fine to coarse sized gravel, moist.
0.70
HAND AUGER HA 01 TERMINATED AT 0.70 m
1.0
2.0
3.0
SOIL SURVEYS 2.00 LIB 2017-07-13.GLB Log SOIL_SURVEY_AUGER_LOG2 1-20119 GINT.GPJ <<DrawingFile>> 28/03/2018 08:57 10.0.000 Developed by Datgel
4.0
5.0
6.0
7.0
Weathering Grades Samples
Comments: RS - Residual Soil
XW - Extremely weathered U50
1. Groundwater not encountered.
HW - Highly weathered
DW - Distinctly weathered
2. DCP refusal at 4.68m. MW - Moderately weathered
SW - Slightly weathered SPT
3. Hand auger refusal at 0.70m. FR - Fresh
Rock Strength Disturbed
4. RLs estimated from provided survey. RS - Residual Soil
VL - Very low Sample
L - Low
M - Medium Bulk Approved: NTP
H - High
Sample
Water First Noted Water Steady Level VH - Very high
EH - Extremely high Date: 27/03/2018
Page 58
Soil Surveys Engineering Pty. Limited HAND AUGER RECORD SHEET
Specialist in Applied Geotechnics
PO Box 317, Paddington, 4064
Location Number: HA 02
+61 7 3369 6000
[email protected]
Project Number: 1-20119
www.soilsurveys.com.au Project Name: Proposed Residence
Location: 24 Arakon Crescent, Sunshine Beach
Easting: 511294 Northing: 7079959 RL: 21.7 m Client: Sam Hopper
Logger: RH Operator: RH Machine: Hand Auger Date: 05/03/2018 Page: 1 OF 1
Drilling Method DCP Test
Graphic (blows/100mm) Samples and
Depth Description
Casing
NMLC
Remarks
WB
RR
0 6 12 18 24 30
TC
0.13 FILL Silty SAND (SM) Very loose, fine to coarse grained,
dark brown, trace of fine to coarse sized gravel, with
0.30 organics, moist.
FILL Silty SAND (SM) Loose, fine to coarse grained, dark
0.60 brown, trace of fine to coarse sized gravel, moist.
FILL Silty SAND (SM) Medium dense, fine to coarse
grained, dark brown mottled light grey, with fine to coarse
sized gravel, moist.
1.0
HAND AUGER HA 02 TERMINATED AT 0.60 m
2.0
3.0
SOIL SURVEYS 2.00 LIB 2017-07-13.GLB Log SOIL_SURVEY_AUGER_LOG2 1-20119 GINT.GPJ <<DrawingFile>> 28/03/2018 08:57 10.0.000 Developed by Datgel
4.0
5.0
6.0
7.0
Weathering Grades Samples
Comments: RS - Residual Soil
XW - Extremely weathered U50
1. Groundwater not encountered.
HW - Highly weathered
DW - Distinctly weathered
2. DCP refusal at 6.19m. MW - Moderately weathered
SW - Slightly weathered SPT
3. Hand auger refusal at 0.60m. FR - Fresh
Rock Strength Disturbed
4. RLs estimated from provided survey. RS - Residual Soil
VL - Very low Sample
L - Low
M - Medium Bulk Approved: NTP
H - High
Sample
Water First Noted Water Steady Level VH - Very high
EH - Extremely high Date: 27/03/2018
Page 59
Soil Surveys Engineering Pty. Limited DYNAMIC CONE PENETROMETER TESTING
Specialist in Applied Geotechnics
Project Number: 1-20119
PO Box 317, Paddington, 4064
+61 7 3369 6000 Project Name: Proposed Residence
[email protected]
www.soilsurveys.com.au Location: 24 Arakon Crescent, Sunshine Beach
Client: Sam Hopper
DCP 03 DCP 04
Easting: 511283 Northing: 7079958 RL 24.7 Easting: 511288 Northing: 7079966 RL 22.5
DCP Test DCP Test
(blows/100mm) (blows/100mm)
0.0 0 6 12 18 24 30
0.0 0 6 12 18 24 30
1.0 1.0
2.0 2.0
3.0 3.0
Depth (m)
Depth (m)
4.0 4.0
5.0 5.0
6.0 6.0
7.0 7.0
Notes Notes
1. Operator : RH 1. Operator : RH
2. Date: 05/03/2018 2. Date: 05/03/2018
3. DCP refusal at 3.28m. 3. DCP refusal at 5.78m.
Page 60
Soil Surveys Engineering Pty. Limited BOREHOLE RECORD SHEET
Specialist in Applied Geotechnics
PO Box 317, Paddington, 4064
Location Number: PO5
+61 7 3369 6000
[email protected]
Project Number: 1-20119
www.soilsurveys.com.au Project Name: Proposed Residence
Location: 24 Arakon Crescent, Sunshine Beach
Easting: 511300 Northing: 7079964 RL: 20.7 m Client: Sam Hopper
Logger: RH Operator: RH Machine: Hand Auger Date: 05/03/2018 Page: 1 OF 1
Drilling Method
Graphic
Samples and
Depth Description
Casing
NMLC
Remarks
WB
RR
TC
FILL Silty SAND (SM) Very loose to loose, fine to coarse grained, dark brown
mottled light grey, trace of fine to coarse sized gravel, moist.
0.50
BOREHOLE PO5 TERMINATED AT 0.50 m
1.0
2.0
3.0
SOIL SURVEYS 2.00 LIB 2017-07-13.GLB Log SOIL_SURVEY_AUGER_LOG2 1-20119 GINT.GPJ <<DrawingFile>> 28/03/2018 08:57 10.0.000 Developed by Datgel
4.0
5.0
6.0
7.0
Weathering Grades Samples
Comments: RS - Residual Soil
XW - Extremely weathered U50
1. Constant hard soil permeability.
HW - Highly weathered
DW - Distinctly weathered
2. Hole diameter 100mm. MW - Moderately weathered
SW - Slightly weathered SPT
3. Water depth 350mm. FR - Fresh
Rock Strength Disturbed
4. RLs estimated from provided survey. RS - Residual Soil
VL - Very low Sample
L - Low
M - Medium Bulk Approved: NTP
H - High
Sample
Water First Noted Water Steady Level VH - Very high
EH - Extremely high Date: 27/03/2018
Page 61
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX G
TYPES OF LANDSLIDES
Page 62
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
FIGURE G1 TYPES OF LANDSLIDES
Ref: USGS Fact Sheet 2004-3072.
Page 63
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX H
LRM2007 – PRACTICE NOTE
GUIDELINES – RISK MATRIX
Page 64
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX C: – QUALITATIVE TERMINOLOGY FOR USE IN ASSESSING RISK TO PROPERTY (CONTINUED)
QUALITATIVE RISK ANALYSIS MATRIX – LEVEL OF RISK TO PROPERTY
LIKELIHOOD CONSEQUENCES TO PROPERTY (With Indicative Approximate Cost of Damage)
Indicative Value of 1: CATASTROPHIC 2: MAJOR 3: MEDIUM 4: MINOR 5:
Approximate Annual 200% 60% 20% 5% INSIGNIFICANT
Probability 0.5%
A – ALMOST CERTAIN 10-1 VH VH VH H M or L (5)
-2
B - LIKELY 10 VH VH H M L
C - POSSIBLE 10-3 VH H M M VL
-4
D - UNLIKELY 10 H M L L VL
-5
E - RARE 10 M L L VL VL
-6
F - BARELY CREDIBLE 10 L VL VL VL VL
Notes: (5) For Cell A5, may be subdivided such that a consequence of less than 0.1% is Low Risk.
(6) When considering a risk assessment it must be clearly stated whether it is for existing conditions or with risk control measures which may not be implemented at the current
time.
RISK LEVEL IMPLICATIONS
Risk Level Example Implications (7)
Unacceptable without treatment. Extensive detailed investigation and research, planning and implementation of treatment
VH VERY HIGH RISK options essential to reduce risk to Low; may be too expensive and not practical. Work likely to cost more than value of the
property.
Unacceptable without treatment. Detailed investigation, planning and implementation of treatment options required to reduce
H HIGH RISK
risk to Low. Work would cost a substantial sum in relation to the value of the property.
May be tolerated in certain circumstances (subject to regulator’s approval) but requires investigation, planning and
M MODERATE RISK implementation of treatment options to reduce the risk to Low. Treatment options to reduce to Low risk should be
implemented as soon as practicable.
Usually acceptable to regulators. Where treatment has been required to reduce the risk to this level, ongoing maintenance is
L LOW RISK
required.
Acceptable. Manage by normal slope maintenance procedures.
VL VERY LOW RISK
Note: (7) The implications for a particular situation are to be determined by all parties to the risk assessment and may depend on the nature of the property at risk; these are only
given as a general guide.
92 Australian Geomechanics Vol 42 No 1 March 2007
Page 65
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX I
DRAWINGS
Page 66
7079990
7079980
Sunshine Beach
Slope
7079970 Angle (o)
20
22
DCP04
24 P05
26
Area IIH 30
7079960 HA01 DCP03
HA02 Area Ib
15
Area Ia
5
Ara
7079950
kon
0
Cre
s
511265 511270 511275 511280 511285 511290 511295 511300 511305 511310 511315 511320 511325 511330 511335 511340 511345 511350 511355 511360
LEGEND
SSE Borehole Locations 2016 Approx. Lot Boundary based on
provided survey
Approx. location of Proposed
Residence II Designated Areas
Approx. location of Existing
Sheet Pile Wall Image from Nearmap.com (December 2017)
SCALE DRAWING TITLE CLIENT
1:400
Sam Hopper
REFERENCE
V:\Milton\Milton 20001 - 21000\1-20001 - 1-20200\1-20119 Sunshine Beach\Graphics
PROPOSED RESIDENCE
LOCATION
DRW. NO
A4 1-20119-01
DATE CHECKED TEST LOCATION PLAN 24 Arakon Cres, Sunshine Beach
23/03/18 NTP
Page 67
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX J
HILLSIDE CONSTRUCTION
GUIDELINES
Page 68
AUSTRALIAN GEOGUIDE LR8 (CONSTRUCTION PRACTICE)
HILLSIDE 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.
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 in 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 fulfil 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
174 Australian Geomechanics Vol 42 No 1 March 2007
Page 69
AUSTRALIAN GEOGUIDE LR8 (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
soak 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 herring bone,
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 LR6 - Retaining Walls
• GeoGuide LR2 - Landslides • GeoGuide LR7 - Landslide Risk
• GeoGuide LR3 - Landslides in Soil • GeoGuide LR9 - Effluent & Surface Water Disposal
• GeoGuide LR4 - Landslides in Rock GeoGuide LR10 - Coastal Landslides
• GeoGuide LR5 - Water & Drainage • 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.
Australian Geomechanics Vol 42 No 1 March 2007 175
Page 70
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
APPENDIX K
SOIL PERMEABILITY TEST RESULTS
Page 71
Project No. 1-20119
March, 2018
Ref: 1-20119, 2018-03-02, BR VER 2
Sam Hopper – Slope Stability Assessment and Geotechnical Report - Proposed Residence, 24 Arakon Crescent, Sunshine Beach
SOIL PERMEABILTY TEST RESULTS
Test Location: PO5
GPS Coordinates: E: 511300 N: 7079964
FILL Silty SAND (SM) Very loose to loose, fine to coarse
Soil Description at Test Location: grained, dark brown mottled light grey, trace of fine to coarse
sized gravel, moist.
Depth of Auger Hole (D): 50cm
Depth of Water in Auger Hole (H): 35cm
Average Radius of Auger Hole (r): 5cm
PERMEAMETER AND TIME READINGS
Time (minutes) Level in Tube (mm) Drop in Level (mm)
0 seconds 840 0
30 seconds 815 25
60 seconds 785 30
90 seconds 765 20
2 min 740 25
2min 30 seconds 715 25
3 min 690 25
3min 30 seconds 670 20
4 min 650 20
4min 30 seconds 625 25
5 min 605 20
5min 30 seconds 580 25
6 min 560 20
6min 30 seconds 540 20
7 min 520 20
7min 30 seconds 500 20
8 min 485 25
8min 30 seconds 460 25
9 min 440 20
9min 30 seconds 420 20
10 min 405 15
11 min 365 40
12 min 330 35
13 min 290 40
14 min 255 35
15 min 220 35
Q= 116.87 (cm3/min)
Ksat = 0.598 (m/day)
Used in these records
Attachment C - Soil Survey Report.pdfRelated documentApplication case desk ↗
About this file
- File size
- 4.1 MB (large file)
- File type
No other editions are linked here.
Original file
Log in to download the original file
The download may take up to a minute.