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Geotechnical Stability Assessment · MCU19/0008
GEOTECHNICAL STABILITY ASSESSMENT:
Proposed Residence
22 Arakoon Crescent
Sunshine Beach
Andrew and Michelle Douglas
April 2019
PG-2096
1
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Page 2
Ref: PG-2096, 2019-02-21, GR VER 2
Author: Peter Elkington
15 April, 2019
Andrew and Michelle Douglas
Email: [email protected]
Cc: [email protected]
ATTN: Andrew Douglas
Dear Sir,
GEOTECHNICAL STABILITY ASSESSMENT – PROPOSED RESIDENCE
22 ARAKOON CRESCENT, SUNSHINE BEACH
Enclosed is a copy of our report for the above project dated April 2019. An
electronic copy of the report has been issued.
This report has been revised to include commentary around the stability of the site as
requested by the Sunshine Coast Regional Council.
Should you have any queries regarding this report, please do not hesitate to contact
Peter Elkington at this office.
Yours faithfully,
P. ELKINGTON (RPEQ 7226)
For and on behalf of
PACIFIC GEOTECH PTY LTD
P: (07) 5636 4680 F: (07) 5636 0286 E: [email protected]
47 Brisbane Road, Biggera Waters, Qld, 4216 | PO Box 499, Paradise Point, Qld, 4216
www.pacgeo.com.au
ABN: 62 615 248 952
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TABLE OF CONTENTS
1.0 INTRODUCTION ..................................................................................................... 1
2.0 METHODOLOGY .................................................................................................... 2
3.0 SITE DESCRIPTION ................................................................................................. 2
4.0 GEOTECHNICAL MODEL ...................................................................................... 4
5.0 EARTHWORKS AND SITE PREPARATION CONSIDERATIONS ............................ 4
6.0 POTENTIAL GROUND SURFACE MOVEMENTS ................................................... 5
7.0 BUILDING FOUNDATIONS .................................................................................... 5
7.1 Deep Foundations ...................................................................................................... 6
8.0 RETAINING WALLS................................................................................................. 8
9.0 SITE MANAGEMENT .............................................................................................. 9
10.0 STABILITY EVALUATION ...................................................................................... 10
10.1 General .......................................................................................................................10
11.0 RESTRICTIONS/PRECAUTIONS ........................................................................... 10
11.1 General .......................................................................................................................10
11.2 Construction Recommendations ............................................................................10
11.3 Foundations ................................................................................................................11
11.4 Drainage .....................................................................................................................11
12.0 STABILITY ASSESSMENT ....................................................................................... 11
12.1 Landslip Frequency Analysis ...................................................................................11
13.0 CONCLUSION...................................................................................................... 11
14.0 LIMITATIONS ........................................................................................................ 12
Appendices
Appendix A
Notes Relating to this Report
Appendix B
Borehole Record Sheets
Appendix C
Site Plan
Appendix D
Guidelines for Hillside Construction
Appendix E
Landslide Susceptibility Analysis
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1.0 INTRODUCTION
This report contains the results of the geotechnical investigation and provides advice
and recommendations relating to the following:
Subsurface conditions in accordance with AS 1726
Stability considerations associated with the development
Foundation recommendations
Characteristic ground surface movements
Earthworks considerations
Retaining wall design parameters
Site stability considerations
Construction considerations
Proposed Development
It is understood that the proposed development is to comprise the construction of a
two storey residence at the above site. The earthworks are understood to involve
cuts of up to 4m to create the undercroft.
The proposed development is indicated below.
PROPOSED DEVELOPMENT
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2.0 METHODOLOGY
The geotechnical investigation comprised the drilling and sampling of 2 boreholes to
depths of 1.4m and 1.5m (drilling refusal), using hand held auger equipment.
Dynamic Cone Penetrometer (DCP) testing was conducted adjacent to the
boreholes and at two additional locations.
The soil classification descriptions and field tests were carried out in general
accordance with Australian Standards.
AS 1726 Geotechnical Site Investigations
AS 1289 Methods of Testing Soils for Engineering Purposes
Borehole records, Dynamic Cone Penetrometer test results and a site plan showing
the test locations are appended to the report.
3.0 SITE DESCRIPTION
The site of the proposed development is located at 22 Arakoon Crescent, Sunshine
Beach.
At the time of the investigation, the site was occupied by an existing split level
residence and swimming pool. Vegetation comprised short grass cover and
gardens, with medium to large shrubs and trees at the rear of the site.
The site sloped initially steeply from the road towards the east before flattening out
behind the existing residence. The drainage conditions were considered to be fair
to good.
Refer following aerial and site photographs for typical site conditions.
AERIAL IMAGE
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SITE PHOTOGRAPHS
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4.0 GEOTECHNICAL MODEL
The subsurface profile encountered in the boreholes consisted of initially very loose
to loose sands to depths of 1.9m in BH01 and 0.8m in BH02, overlying medium dense
to dense sands to the termination of testing. In Borehole 1, 600mm of very loose
gravelly sand was encountered.
The density of the sand has been interpreted on the basis of the DCP testing results.
Detailed borehole record sheets are appended to this report.
Groundwater or subsurface seepage was not encountered in the boreholes at the
time of drilling.
5.0 EARTHWORKS AND SITE PREPARATION CONSIDERATIONS
Earthworks are expected to comprise of a cut operation of up to 4m to create an
underground plant room and water tank. Minor filling removed from the excavation
and primarily adjacent Arakoon Crescent is expected.
Consideration should be given to maintaining the stability of the excavation
immediately adjacent Arakoon Crescent during earthworks.
It is recommended that the following site preparation and earthworks procedures be
carried out as part of the earthworks procedures during development.
All earthworks operations should be carried out in general accordance with
AS 3798-2007 "Guidelines on Earthworks for Commercial and Residential
Developments".
Trafficability across the site at the time of the investigation was assessed to be
poor due to the steepness of the site.
All topsoil (i.e. soil containing organic matter) and soils containing deleterious
matter should be stripped from the construction area at the commencement
of the earthworks operation.
The majority of the soils on site will be suitable for re-use as structural fill,
provided material is free of organic matter and deleterious material. It is likely
that the soils require conditioning to bring the soils to optimum If the soils were
overly moist, difficulty in achieving compaction of the materials will be
encountered and moisture conditioning will be required.
Imported fill should be of fair to good quality with a minimum Soaked CBR
value of 10%, a maximum Iss=1.0% and a maximum particle size of 75mm or a
‘clean’ sand.
All filling should be undertaken in layer thicknesses of approximately 250mm
(or as appropriate for the compaction equipment being used). Fill should be
compacted to a minimum dry density ratio of 95% Standard in accordance
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with AS1289 5.1.1 or a minimum density index of 65% in accordance with
AS1289 5.6.1.
Density testing should be carried out to check the standard of compaction
achieved and the placement moisture content. The frequency and extent of
testing should be as per guidelines in AS.3798-2007.
All earthworks operations should be performed under Pacific Geotech’s
supervision, in general accordance with the requirements of AS3798.
6.0 POTENTIAL GROUND SURFACE MOVEMENTS
It is recommended that the readers satisfy themselves that the use of AS 2870-2011 is
applicable for the proposed design and the above site classification re-confirmed
following the completion of the bulk earthworks operation.
Site investigation and laboratory test results indicate the development site would be
classified Class S in accordance with AS 2870-2011 'Residential Slabs and Footings',
from a reactivity perspective.
7.0 BUILDING FOUNDATIONS
Foundations
In order to provide a uniform and stable foundation and due to the site stability
issues, it is recommended a deepened foundation, incorporating either
appropriately founded pad footings or piers founded into medium dense or better
sands be adopted for the proposed constructions. Pad footings should socket a
minimum depth of 0.9m into the medium dense or better sands and piers should
found a minimum of 1.5m into the medium dense or better sands, if adopted.
Lateral Forces
In view of the global stability in the area, sloping natural terrain and the presence of
loose sands, it is recommended that all footing systems be designed to
accommodate forces due to potential soil creep within the surficial fill strata.
The potential lateral force due to creep in the soil strata may be determined from
the following:
Force = 1.5KpH2D
Where Kp = 2.5
= Soil Density=20kN/m3
H = Depth of sands, a depth of up to 2.8m was indicated in
the boreholes. Final depth subject to further
geotechnical assessment at time of pier excavations.
D = Footing/Pier Width (m) - perpendicular to slope
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7.1 Deep Foundations
A deep foundation incorporating a bored pier footing system is recommended for
the proposed developments and encountered subsurface conditions. It is
recommended piers be socketed not less 1.5m into the underlying medium dense to
better sand.
The deep foundation system should be designed in accordance with the
recommendations of AS 2159-2009 'Piling - Design and Installation'.
The ultimate geotechnical strength (Rd,ug) of piles can be calculated using the
unfactored, ultimate shaft adhesion and end bearing values given in Table 1. The
Rd,ug values given in Table 1 will need to be multiplied by a suitable geotechnical
strength reduction factor (øg) to obtain the design geotechnical strength (Rd,g) of
piles. In accordance with AS2159-2009, the øg value must be determined by the
designer, but based on the anticipated site, design and installation risk factors, a øg
value of 0.48 is recommended. Higher values may be applicable with suitable
supervision.
If working stress methods are used in the pile design, the Rd,ug values given in Table 1
will need to be divided by a factor of safety of 2.5 to caluculate the maximum single
pile working load.
TABLE 1 ULTIMATE (UNFACTORED) PILE DESIGN PARAMETERS
Ultimate Unfactored End
Bearing* Ultimate Unfactored Shaft
Material (kPa) Adhesion*
(kPa)
>4D
Very Loose to Loose NR NR
Sands
Medium Dense 900 30
Notes:
*Geotechnical strength reduction factor needs to be applied to these parameters.
1. NR – Not Recommended.
Lateral Capacity
The lateral capacity of a pile is a function of many factors including the soil profile,
pile fixity and eccentricity, embedment length and other factors such as failure
mode, strength of the pile and the shear strength of the surrounding founding
materials.
Horizontal pile capacities will be provided by passive resistance from the weathered
rock strata. However, the capacity from the soils should be neglected, given their
potential for creep.
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An assessment of a single pile's lateral capacity is provided by using Broms Charts as
shown in Figure 1. Refer to Table 2 for applicable parameters. Piles are usually
deemed to be classed as short when the L/B ratio is less than 10 to 12.
FIGURE 1 ULTIMATE LATERAL RESISTANCE OF PILES
TABLE 2 DESIGN VALUES FOR LATERAL PILE CAPACITY CALCULATION
Bulk Density
Material Design Kp
(kN/m3)
Loose 2.56 18
Sands Medium Dense 3.0 18.5
Dense 3.25 19
Should a 'working stress' approach be adopted, a factor of safety of between 2.5
and 3.0 should be adopted.
Lateral capacity may be achieved through the use of raked screw piles etc. if
required.
Construction Considerations
Given the non cohesive soil conditions encountered on site, it is likely that a bored
pier type foundation system will not be appropriate as side wall collapse of the piers
is likely to occur. Appropriate piling solutions could include CFA piles or possibly
screw piles, however screw piles are unlikely to provide significant lateral capacity
and a combination of vertical and raked piles may be required.
During construction, all piles must be inspected by a geotechnical engineer to
confirm the geotechnical strength parameters presented in Table 1 and Table 2 and
to check the capacity of the piles.
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8.0 RETAINING WALLS
Retaining walls up to 3m in height may be required as part of the development.
Walls should be specifically engineer designed in accordance with AS 4678-2002
(Ref 9).
It is recommended that all retaining walls be drained for full height in order to
minimise hydrostatic pressure build-up behind the wall. Additional guidelines on wall
drainage are provided in Appendix G of AS 4689-2002.
The design of flexible and rigid retaining walls could be undertaken using a triangular
pressure distribution and the earth pressure parameters given in Table 3. Flexible
walls are those which are free to rotate or tilt (such as cantilevered walls) and should
be designed using active (Ka) earth pressure coefficient. Rigid walls are those which
are restrained against rotation or tilt (i.e. single anchored/propped walls) and should
be designed using the at-rest earth pressure (Ko) and a trapezoidal pressure
distribution as per Figure 1.
FIGURE 1
0.25H
H
0.4 H
0.25H
KH
Trapezoidal Triangular
Passive resistance (Kp) at the toe of the wall should be ignored in the zone where
future disturbance (e.g. services trenches) could occur.
The effects of surcharge in the retained zone should be included by multiplying the
vertical pressure developed by the surcharge by the appropriate lateral earth
pressure coefficient. Allowance should also be made for the surcharge due to
sloping crests if applicable.
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TABLE 3 EARTH PRESSURE COEFFICIENTS (NON-SLOPING CREST BACKFILL)
Unit Friction
Active At Rest Passive
Material Weight Angle
Ka Ko Kp
(kN/m3) (degrees)
Loose 18 26 0.39 0.56 2.56
Sands Medium Dense 18.5 30 0.33 0.50 3.0
Dense 19 32 0.31 0.47 3.25
Preference should be given to adopting thin soil layers and using small hand-
controlled compaction equipment during backfilling against retaining walls. This is in
order to limit the stress applied to the walls during construction. Should heavy
compaction be required, then wall stresses will be well in excess of Ko and
temporary propping should be used.
It is recommended that all retaining walls be drained for full height in order to
minimise hydrostatic pressure build-up behind the wall. Additional guidelines on wall
drainage are provided in Appendix G of AS 4689-2002.
9.0 SITE MANAGEMENT
To maintain the long term performance of the structure, good management of the
soil conditions and the development is vital throughout the life of the development.
The following are some specific comments with respect to site management.
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.
Founding soils should not be allowed to become saturated.
Service trenches under the buildings should be kept to a minimum. Saturation
of the on-site material will result in an increase in potential ground surface
movements.
Footings should be poured immediately after excavation. If footings cannot
be poured on the same day as excavation, a blinding layer of 50mm
thickness is recommended.
Trees, garden beds and other vegetation should be planted at a distance at
least equivalent to three quarters of their mature height away from the
structures. This will assist in minimising shrinkage movements in the expansive
on-soils.
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10.0 STABILITY EVALUATION
10.1 General
The overall stability evaluation of the proposed building site has been carried out on
a broadscale basis by visual inspection and from the subsoil information from the
boreholes undertaken.
No signs of mass/global instability were noted across the proposed development
sites during the field assessments.
Building Type
The proposed structure is to comprise of a rigid/blockwork undercroft structure with
lightweight, flexible structure over the remainder of the site. Ground floor
construction should be designed as fully suspended.
Retaining Walls
Structural retaining walls will be required to support the excavations. The walls
should be structurally designed in accordance with the recommendations outlined
in Section 8.0 of this report. in the fill platform are not recommended for the site.
11.0 RESTRICTIONS/PRECAUTIONS
11.1 General
Good hillside engineering construction practice is considered mandatory during
development of the site for the proposed new residence. The notes and illustrations
attached to this report outline some typical hillside construction guidelines including,
earthworks, erosion control and drainage practices for hillside areas which should be
taken into account as applicable.
Furthermore, in order to ensure long-term stability of the site upon development, the
following restrictions/precautions should also be taken into account.
11.2 Construction Recommendations
The proposed residence would be suited to a structure either on posts or a slab on
ground with a fully suspended floor, where not supported by a structural retention
system. This type of construction would reduce the amount of earthworks necessary
to prepare a building platform and the extent of retaining systems required across
the site of the proposed house.
Retaining structures should be designed by an experienced Structural Engineer.
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11.3 Foundations
Foundations for any structure proposed to be constructed on the sloping terrain
must take into account potential lateral loading due to potential soil creep.
11.4 Drainage
Suitable drainage provisions are essential in the development of the overall site.
Adequate subsoil and surface drainage should be incorporated in retaining walls
and driveways and along the crest of the batters. Any stormwater discharge points
should be suitably protected against scour and erosion.
All roofwater and any other runoff from drains on the site should not be discharged
on the site, but should be taken to tanks and released via piped conduits downslope
and clear of the building envelope and existing fill batters.
Suitable spoon drains should be provided along the top and toe of all batters and
the access driveway. Subsoil drains should also be provided in areas where
seepage may be encountered.
12.0 STABILITY ASSESSMENT
12.1 Landslip Frequency Analysis
The following landslip frequency analysis of the proposed residence, shed platforms
and immediate surrounds have been made in accordance with Taylor &
MacGregor (2001) Relative Susceptibility recommended method based on the
findings of this stability assessment.
Landslip Frequency Analysis
Relative Frequency 0.32
Hazard Rating Low
13.0 CONCLUSION
Continued long term stability of the site is subject the development taking place in
accordance with the recommendations in this report and relevant Australian
Standards and good hillside engineering and building practices.
Refer to the attached ‘Guidelines for Hillside Construction’ for general practices for
hillside construction.
Pacific Geotech Pty Ltd provide a service to review
construction/building/development plans and it is recommended that any
designer/builder utilises this service to ensure that the proposed development is in
accordance with the intentions of this report.
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Project No. PG-2096 Page | 12 April 2019 Ref: PG-2096, 2019-02-21, GR VER 2 Andrew and Michelle Douglas – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach It is also recommended that all earthworks, drainage, erosion protection and foundation preparations be inspected by Pacific Geotech Pty Ltd to ensure that the works are in accordance with the intentions of this report. For review and inspection services, our standard rates will apply. 14.0 LIMITATIONS We have prepared this report for the Proposed Residence at 22 Arakoon Crescent, Sunshine Beach . The report is provided for the exclusive use of Andrew and Michelle Douglas, for this project only and for the purposes outlined in the report. It should not be used by, or relied upon, for other projects on the same or different sites or by a third party. In preparing this report, we have relied upon information provided by the client or their agents. The results are indicative of the subsurface conditions on site only at the specific testing locations. Subsurface conditions can change between test locations and the design and construction should take the spacing of the testing and testing methods adopted and the potential for variation between the test locations. It is recommended that Pacific Geotech be engaged to provide advice and ensure the development is undertaken in accordance with the assumptions made in writing this report. This is not to reduce the level of responsibility accepted by Pacific Geotech, but rather to ensure that the parties who may rely on the information contained in this report are aware of the responsibilities they assume in doing so. P. ELKINGTON (RPEQ 7226) For and on behalf of PACIFIC GEOTECH PTY LTD
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APPENDICES
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APPENDIX A
NOTES RELATING TO THIS REPORT
Page 18
Notes Relating to this Report
Reports other particles present (e.g. sandy clay) as set
out below:
The report has been prepared by qualified
personnel, is based on the information Soil
Particle Size
obtained from field and laboratory testing, and Classification
has been undertaken to current engineering Clay less than 0.002mm
standards of interpretation and analysis. Silty 0.002 to 0.06mm
Sand 0.06 to 2mm
Gravel 2 to 60mm
Every care has been taken with the report as it
relates to interpretation of subsurface
Non-cohesive soils are classified on the basis of
conditions, discussion of geotechnical
relative density which can be correlated from
conditions and contains recommendations or
the results of Standard Penetration Test (SPT) as
suggestions for design and construction.
below:
However, unexpected variations in ground
conditions will occur. The potential for this will
SPT ‘N’ Value
depend partly on testing, spacing and Relative Density
(blows/300mm)
sampling frequency. Very Loose less than 4
Loose 4 – 10
If variations are identified, Pacific Geotech Medium Dense 10 – 30
would be pleased to assist with additional Dense 30 – 50
investigations or advice to resolve the matter. Very Dense greater than 50
Copyright Cohesive soils are classified on the basis of
strength (consistency) and can be quantified
This report is the property of Pacific Geotech by the Pocket Penetrometer test, Vane Shear
Pty Ltd. The report may only be used for the test, laboratory testing or engineering
purpose for which it was commissioned and in examination. The strength terms are defined as
accordance with the Terms of Engagement of follows:
proposal. Unauthorised use of this report is
prohibited. Unconfined Compressive
Classification
Strength kPa
Borehole and Test Pit Logs Very Soft less than 25
Soft 25 - 50
The borehole and test pit logs presented in this Firm 50 – 100
report are an engineering and/or geological Stiff 100 – 200
interpretation of the subsurface conditions, and Very Stiff 200 - 400
Hard greater than 400
their reliability will depend to some extent on
Friable strength not attainable – soil
frequency of sampling and the method of crumbles
drilling or excavation.
Rock types are classified by their geological
Interpretation of the information and its
names, together with descriptive terms
application to design and construction should
regarding weathering, strength, defects, etc.
therefore take into account the spacing of
boreholes or pits, the frequency of sampling, Sampling
and the possibility of other than ‘straight line’
variations between the test locations. Sampling is undertaken during the fieldwork to
allow examination of the soil or rock and to
Description and Classification Methods allow laboratory testing to be undertaken.
The description and classification of soils and Disturbed samples taken during drilling provide
rocks used in this report are based on AS 1726. information on plasticity, grain size, colour,
moisture content and minor constituents. Bulk
Soil types are described according to the
samples are similar but of greater volume
predominating particle size and behaviour as
set out in the attached Unified Soil
Classification Table qualified by the percent of
October 2017 pg. 1
Page 19
required for some test procedures such as CBR A Tungsten Carbide (TC) bit for auger drilling
testing. into rock can be used to indicate rock strength
and continuity by variation in drilling resistance
Undisturbed samples are taken by pushing a and from examination of recovered rock
thin-walled sample tube, usually 50mm fragments but provides only an indication of
diameter (known as a U50), into the soil and the likely rock strength. Where rock strengths
collecting a sample of the soil contained in a may have a significant impact on construction
relatively undisturbed state. Such samples yield feasibility or costs, then further investigation by
information on structure and strength, and are means of cored boreholes may be warranted.
necessary for laboratory determination of shear
strength and compressibility. Undisturbed Wash Boring: The borehole is advanced by a
sampling is generally effective only in cohesive bit attached to the end of a hollow rod string,
soils. with water being pumped down the drill rods
and returned up the annulus of the borehole,
Details of the type and method of sampling carrying the drill cuttings. Changes in
used are given on the attached logs. stratification can be determined from the
return, together with information from “feel”
Investigation Methods
and rate of penetration.
Test Pits: These are typically undertaken with a
The borehole can be stabilised through the use
backhoe or a tracked excavator, allowing
of drilling mud as a circulating fluid. The term
examination of the insitu soils. Limitations of test
‘mud’ encompasses a range of products
pits are the problems associated with collapse
ranging from bentonite to polymers such as
of the pits, disturbance and difficulty of
Revert or Biogel.
reinstatement and the consequent effects on
close-by structures. Care must be taken if Continuous Core Drilling: A continuous core
construction is to be carried out near test pit sample is obtained using a diamond tipped
locations to either properly recompact the core barrel. This technique provides a reliable
backfill during construction or to design and (but relatively expensive) method of
construct the structure so as not to be investigation. In rocks, an NMLC triple tube
adversely affected by poorly compacted core barrel is used, which gives a core of about
backfill at the test pit location. 50mm diameter. The length of core recovered
is compared to the length drilled and any
Hand Auger Drilling: A borehole of typical
length not recovered is shown as CORE LOSS.
diameter of between 50mm to 75mm advance
manually operated equipment. Premature Standard Penetration Tests: Standard
refusal of the hand augers can occur on a Penetration Tests (SPT) are used mainly in non-
variety of materials such as fill, gravel, hard cohesive soils, but can also be used in cohesive
clays and collapse of the borehole (typically in soils as a means of indicating density or
non-cohesive soil). strength and also of obtaining a disturbed
sample. The test procedure is described in
Continuous Spiral flight Augers: The borehole is
Australian Standard 1289, “Methods of Testing
advanced using 65mm to 100mm diameter
Soils for Engineering Purposed”, Test 6.3.1.
continuous spiral flight augers, which are
withdrawn at intervals to allow sampling and The test is carried out in a borehole by driving a
insitu testing. Augers of up to 300mm in 50mm diameter split sample tube with a
diameter are used to recover larger volumes of tapered shoe, under the impact of a 63kg
sample. Samples are returned to the surface hammer, with a free fall of 760mm. The sample
by the flights or may be collected after is driven in three successive 150mm increments
withdrawal of the auger flights. Samples can and the ‘N’ value is taken as the number of
be disturbed and layers may become mixed. blows for the last 300mm. In dense soils, hard
Augering below the groundwater table can be clays or weak rock, the full 450mm penetration
less reliable than augering above the water may not be practicable and the test is
table. discontinued.
October 2017 pg. 2
Page 20
The test results are reported in the following resistance and friction ratios are only inferred
form: and must not be considered as exact.
In the case where full penetration is Stratification can be inferred from the cone
obtained with successive blow counts and friction traces and from experience and
for each 150mm of , say, 4, 6 and 7 information from nearby boreholes, etc. Where
blows, as shown, this information is presented for general
N = 13 guidance, but must be regarded as
4, 6, 7 interpretive.
In a case where the test is discontinued
short of full penetration, say after 15 Dynamic Cone Penetrometers:
blows for the first 150mm and 30 blows
Dynamic Cone Penetrometer (DCP) tests are
for the next 40mm, as
carried out by driving a 16mm diameter rod
N > 30
into the ground with a 9kg sliding hammer
15, 30/40mm
dropping 510mm and counting the blows for
Cone Penetrometer Testing (CPT): Cone
successive 100mm increments of penetration.
Penetrometer Testing with or without pore
pressure measurement (CPTu) is carried out
Logs
using a Cone Penetrometer in general
accordance with AS 1289 6.5.1, 1999. The borehole or test pit logs are an
interpretation of the subsurface conditions, and
In the tests, a 36mm diameter rod with a
their reliability will depend to some extent on
conical tip is pushed continuously into the soil,
the frequency of sampling and the method of
the reaction being provided by a hydraulic
drilling or excavation.
ram system. Measurements are made of the
end bearing resistance on the cone and the Interpretation of the information shown on the
fractional resistance on a separate 135mm logs, and its application to design and
long sleeve, immediately behind the cone. construction, should therefore take into
Pore Pressure is recovered through a pore ring account the spacing of the boreholes or test
located either within, or more usually pits, the method of drilling or excavation, the
immediately behind the cone/tip. frequency of sampling and testing and the
possibility of other than “straight line” variations
As penetration occurs (at a rate of
between the boreholes or test pits. Subsurface
approximately 20mm per second) and data is
conditions between boreholes or test pits may
recorded every 20mm of penetration, the
vary significantly from conditions encountered
results are presented graphically.
at the borehole or test pit locations.
The information provided on the plot
Groundwater
comprises:
Where groundwater levels are measured in
Cone resistance – expressed in mPa
boreholes, there are several potential
Sleeve friction – expressed in kPa
problems:
Friction ratio – the ratio of sleeve
friction to cone resistance expressed as Although groundwater may be
a percentage. present, in low permeability soils it may
Pore pressure in kPa enter the hole slowly or perhaps not at
Tilt of probe (in degrees). all during the time it is left open.
The ratios of the sleeve resistance to cone A localised perched water table may
resistance will vary with the type of soil lead to an erroneous indication of the
encountered, with higher relative friction in true water table.
clays than in sands. Friction ratios of 1% to 2% Water table levels will vary from time to
are commonly encountered in sands and rising time with seasons or recent weather
to 2% to as high as 8%, and higher in organic changes and may not be the same at
soils. Soil descriptions based on cone the time of construction.
October 2017 pg. 3
Page 21
The use of water or mud as a drilling Requirements could range from:
fluid will mask any groundwater inflow.
Water has to be flushed from the hole i. a site visit to confirm that conditions
and drilling mud must be washed out exposed are no worse than those
of the hole or ‘reverted’ chemically if interpreted, to
water observations are to be made. ii. a visit to assist the contractor or other
More reliable measurements can be made by site personnel in identifying various
installing standpipes from which ongoing soil/rock types such as appropriate
monitoring can be undertaken. footing or pier founding depths, or
iii. full time engineering present on site.
Fill
The present of fill materials can often be
determined only by the inclusion of foreign
objects (e.g. bricks, steel ,etc.) or by distinctly
unusual colour, texture or fabric. Identification
of the extent of fill materials will also depend on
investigation methods and frequency. Where
natural soils similar to those at the site are used
for fill, it may be difficult to reliably determine
the extent of the fill.
Laboratory Testing
Laboratory testing is carried out in general
accordance with Australian Standard 1289
‘Methods of Testing Soil for Engineering
Purposes’.
Site Anomalies
In the event that conditions encountered on
site during construction appear to vary from
those which were expected from the
information contained in the report, the
company requests that it immediately be
notified. Most problems are much more readily
resolved when conditions are exposed than at
some later stage.
Review of Design
Where major civil or structural developments
are proposed or where only a limited
investigation has been completed or where the
geotechnical conditions/constraints are quite
complex, it is prudent to have a design review.
Site Inspection
Pacific Geotech would be pleased to provide
engineering inspection services for
geotechnical aspects of work to which this
report is related:
October 2017 pg. 4
Page 22
Project No. PG-2096
April 2019
Ref: PG-2096, 2019-02-21, GR VER 2
Andrew and Michelle Douglas – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach
APPENDIX B
BOREHOLE RECORD SHEETS
Page 23
Borehole No.
BH 01
Page 1 of 1
Project No.: PG-2096
Client: Andrew and Michelle Douglas Commenced: 19/12/2019
Project Name: Proposed Residence Logged By: TTE
Hole Location: 22 Arakoon Crescent, Sunshine Beach Checked By:
Hole Position:
Drill Model and Mounting: Hand Auger RL Surface: No survey
Hole Diameter: Datum: AHD Operator: TTE
Drilling Information Soil Description DCP
DCP TEST
Classification
Graphic Log
Samples Material Description (AS 1289.6.3.2-1997)
Recovery
Tests Fraction, Colour, Structure, Bedding, Blows per 100 mm
Symbol
Method
Casing
Remarks Plasticity, Sensitivity, Additional
Water
RL Depth
(m) (m) 0 5 10 15 20 25
0.06 SP FILL Gravelly SAND (SP) Very loose, fine to medium grained, grey, fine
SP to medium grained gravel, organics throughout, moist.
FILL Gravelly SAND (SP) Very loose, fine to medium grained, grey, fine
to medium grained gravel, moist.
0.60
SP NATURAL SAND (SP) Very loose, fine to medium grained, red brown
HA
D 0.70-1.40 m and light grey, moist.
1
1.40
Hole Terminated at 1.40 m
PACGEO 1.01.1 LIB.GLB Log PACGEO BOREHOLE PG-2096.GPJ <<DrawingFile>> 21/02/2019 17:00 10.0.000 Datgel Lab and In Situ Tool - DGD | Lib: pacgeo 1.01.1 2018-05-15 Prj: Precise 1.01 2016-11-23
2
3
4
Method Water Samples and Tests Remarks
AS - Auger Level (Date) U - Undisturbed Sample
RR - Rock Roller D - Disturbed Sample 1. Groundwater not encountered.
WB- Washbore Inflow SPT - Standard Penetration Test 2. DCP refusal met at 4.16m.
B - Bulk Sample 3. Hand auger refusal met at 1.4m.
Classification Symbols and
Support Soil Descriptions
C - Casing
Based on Unified Soil
Classification System
Page 24
Borehole No.
BH 02
Page 1 of 1
Project No.: PG-2096
Client: Andrew and Michelle Douglas Commenced: 19/12/2019
Project Name: Proposed Residence Logged By: TTE
Hole Location: 22 Arakoon Crescent, Sunshine Beach Checked By:
Hole Position:
Drill Model and Mounting: Hand Auger RL Surface: No survey
Hole Diameter: Datum: AHD Operator: TTE
Drilling Information Soil Description DCP
DCP TEST
Classification
Graphic Log
Samples Material Description (AS 1289.6.3.2-1997)
Recovery
Tests Fraction, Colour, Structure, Bedding, Blows per 100 mm
Symbol
Method
Casing
Remarks Plasticity, Sensitivity, Additional
Water
RL Depth
(m) (m) 0 5 10 15 20 25
0.10 SP NATURAL SAND (SP) Very loose, fine to medium grained, light grey,
SP organics throughout, moist.
0.30 SAND (SP) Very loose, fine to medium grained, light grey, moist.
SP SAND (SP) Very loose, fine to medium grained, grey and red brown,
moist.
0.70
HA
0.80 SP SAND (SP) Loose, fine to medium grained, grey and red brown, moist.
SP SAND (SP) Medium dense, fine to medium grained, grey and red
brown, moist.
1
D 1.00-1.50 m
1.50
Hole Terminated at 1.50 m
PACGEO 1.01.1 LIB.GLB Log PACGEO BOREHOLE PG-2096.GPJ <<DrawingFile>> 21/02/2019 17:00 10.0.000 Datgel Lab and In Situ Tool - DGD | Lib: pacgeo 1.01.1 2018-05-15 Prj: Precise 1.01 2016-11-23
2
3
4
Method Water Samples and Tests Remarks
AS - Auger Level (Date) U - Undisturbed Sample
RR - Rock Roller D - Disturbed Sample 1. Groundwater not encountered.
WB- Washbore Inflow SPT - Standard Penetration Test 2. DCP refusal met at 2.16m.
B - Bulk Sample 3. Hand auger refusal met at 1.5m.
Classification Symbols and
Support Soil Descriptions
C - Casing
Based on Unified Soil
Classification System
Page 25
Borehole No.
DCP 03
Page 1 of 1
Project No.: PG-2096
Client: Andrew and Michelle Douglas Commenced: 19/12/2019
Project Name: Proposed Residence Logged By: TTE
Hole Location: 22 Arakoon Crescent, Sunshine Beach Checked By:
Hole Position:
Drill Model and Mounting: RL Surface: No survey
Hole Diameter: Datum: AHD Operator: TTE
Drilling Information Soil Description DCP
DCP TEST
Classification
Graphic Log
Samples Material Description (AS 1289.6.3.2-1997)
Recovery
Tests Fraction, Colour, Structure, Bedding, Blows per 100 mm
Symbol
Method
Casing
Remarks Plasticity, Sensitivity, Additional
Water
RL Depth
(m) (m) 0 5 10 15 20 25
1
PACGEO 1.01.1 LIB.GLB Log PACGEO BOREHOLE PG-2096.GPJ <<DrawingFile>> 21/02/2019 17:00 10.0.000 Datgel Lab and In Situ Tool - DGD | Lib: pacgeo 1.01.1 2018-05-15 Prj: Precise 1.01 2016-11-23
2
3
4
Method Water Samples and Tests Remarks
AS - Auger Level (Date) U - Undisturbed Sample
RR - Rock Roller D - Disturbed Sample 1. DCP refusal met at 3.97m.
WB- Washbore Inflow SPT - Standard Penetration Test
B - Bulk Sample
Classification Symbols and
Support Soil Descriptions
C - Casing
Based on Unified Soil
Classification System
Page 26
Borehole No.
DCP 04
Page 1 of 1
Project No.: PG-2096
Client: Andrew and Michelle Douglas Commenced: 19/12/2019
Project Name: Proposed Residence Logged By: TTE
Hole Location: 22 Arakoon Crescent, Sunshine Beach Checked By:
Hole Position:
Drill Model and Mounting: RL Surface: No survey
Hole Diameter: Datum: AHD Operator: TTE
Drilling Information Soil Description DCP
DCP TEST
Classification
Graphic Log
Samples Material Description (AS 1289.6.3.2-1997)
Recovery
Tests Fraction, Colour, Structure, Bedding, Blows per 100 mm
Symbol
Method
Casing
Remarks Plasticity, Sensitivity, Additional
Water
RL Depth
(m) (m) 0 5 10 15 20 25
1
PACGEO 1.01.1 LIB.GLB Log PACGEO BOREHOLE PG-2096.GPJ <<DrawingFile>> 21/02/2019 17:00 10.0.000 Datgel Lab and In Situ Tool - DGD | Lib: pacgeo 1.01.1 2018-05-15 Prj: Precise 1.01 2016-11-23
2
3
4
Method Water Samples and Tests Remarks
AS - Auger Level (Date) U - Undisturbed Sample
RR - Rock Roller D - Disturbed Sample 1. DCP refusal met at 3.28m.
WB- Washbore Inflow SPT - Standard Penetration Test
B - Bulk Sample
Classification Symbols and
Support Soil Descriptions
C - Casing
Based on Unified Soil
Classification System
Page 27
Project No. PG-2096
April 2019
Ref: PG-2096, 2019-02-21, GR VER 2
Andrew and Michelle Douglas – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach
APPENDIX C
SITE PLAN
Page 28
BH02
DCP04
BH01
DCP03
Drawn
Project: Proposed Residence
AB
Drawing No.
Date
Location: 22 Arakoon Crescent, Sunshine Beach A4
Jan 2019
PG-2096-01
Checked
Client: Andrew & Michelle Douglas
Page 29
Project No. PG-2096
April 2019
Ref: PG-2096, 2019-02-21, GR VER 2
Andrew and Michelle Douglas – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach
APPENDIX D
GUIDELINES FOR HILLSIDE CONSTRUCTION
Page 30
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007
APPENDIX G - SOME GUIDELINES FOR HILLSIDE CONSTRUCTION
GOOD ENGINEERING PRACTICE POOR ENGINEERING PRACTICE
ADVICE
GEOTECHNICAL Obtain advice from a qualified, experienced geotechnical practitioner at early Prepare detailed plan and start site works before
ASSESSMENT stage of planning and before site works. geotechnical advice.
PLANNING
SITE PLANNING Having obtained geotechnical advice, plan the development with the risk Plan development without regard for the Risk.
arising from the identified hazards and consequences in mind.
DESIGN AND CONSTRUCTION
Use flexible structures which incorporate properly designed brickwork, timber Floor plans which require extensive cutting and
or steel frames, timber or panel cladding. filling.
HOUSE DESIGN
Consider use of split levels. Movement intolerant structures.
Use decks for recreational areas where appropriate.
SITE CLEARING Retain natural vegetation wherever practicable. Indiscriminately clear the site.
ACCESS & Satisfy requirements below for cuts, fills, retaining walls and drainage. Excavate and fill for site access before
DRIVEWAYS Council specifications for grades may need to be modified. geotechnical advice.
Driveways and parking areas may need to be fully supported on piers.
EARTHWORKS Retain natural contours wherever possible. Indiscriminatory bulk earthworks.
Minimise depth. Large scale cuts and benching.
CUTS Support with engineered retaining walls or batter to appropriate slope. Unsupported cuts.
Provide drainage measures and erosion control. Ignore drainage requirements
Minimise height. Loose or poorly compacted fill, which if it fails,
Strip vegetation and topsoil and key into natural slopes prior to filling. may flow a considerable distance including
Use clean fill materials and compact to engineering standards. onto property below.
FILLS Batter to appropriate slope or support with engineered retaining wall. Block natural drainage lines.
Provide surface drainage and appropriate subsurface drainage. Fill over existing vegetation and topsoil.
Include stumps, trees, vegetation, topsoil,
boulders, building rubble etc in fill.
ROCK OUTCROPS Remove or stabilise boulders which may have unacceptable risk. Disturb or undercut detached blocks or
& BOULDERS Support rock faces where necessary. boulders.
Engineer design to resist applied soil and water forces. Construct a structurally inadequate wall such as
Found on rock where practicable. sandstone flagging, brick or unreinforced
RETAINING
Provide subsurface drainage within wall backfill and surface drainage on slope blockwork.
WALLS
above. Lack of subsurface drains and weepholes.
Construct wall as soon as possible after cut/fill operation.
Found within rock where practicable. Found on topsoil, loose fill, detached boulders
Use rows of piers or strip footings oriented up and down slope. or undercut cliffs.
FOOTINGS
Design for lateral creep pressures if necessary.
Backfill footing excavations to exclude ingress of surface water.
Engineer designed.
Support on piers to rock where practicable.
SWIMMING POOLS Provide with under-drainage and gravity drain outlet where practicable.
Design for high soil pressures which may develop on uphill side whilst there
may be little or no lateral support on downhill side.
DRAINAGE
Provide at tops of cut and fill slopes. Discharge at top of fills and cuts.
Discharge to street drainage or natural water courses. Allow water to pond on bench areas.
SURFACE Provide general falls to prevent blockage by siltation and incorporate silt traps.
Line to minimise infiltration and make flexible where possible.
Special structures to dissipate energy at changes of slope and/or direction.
Provide filter around subsurface drain. Discharge roof runoff into absorption trenches.
Provide drain behind retaining walls.
SUBSURFACE
Use flexible pipelines with access for maintenance.
Prevent inflow of surface water.
Usually requires pump-out or mains sewer systems; absorption trenches may Discharge sullage directly onto and into slopes.
SEPTIC &
be possible in some areas if risk is acceptable. Use absorption trenches without consideration
SULLAGE
Storage tanks should be water-tight and adequately founded. of landslide risk.
EROSION Control erosion as this may lead to instability. Failure to observe earthworks and drainage
CONTROL & Revegetate cleared area. recommendations when landscaping.
LANDSCAPING
DRAWINGS AND SITE VISITS DURING CONSTRUCTION
DRAWINGS Building Application drawings should be viewed by geotechnical consultant
SITE VISITS Site Visits by consultant may be appropriate during construction/
INSPECTION AND MAINTENANCE BY OWNER
OWNER’S Clean drainage systems; repair broken joints in drains and leaks in supply
RESPONSIBILITY pipes.
Where structural distress is evident see advice.
If seepage observed, determine causes or seek advice on consequences.
Australian Geomechanics Vol 42 No 1 March 2007 113
Page 31
PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007 114 Australian Geomechanics Vol 42 No 1 March 2007
Page 32
Project No. PG-2096
April 2019
Ref: PG-2096, 2019-02-21, GR VER 2
Andrew and Michelle Douglas – Geotechnical Stability Assessment - Proposed Residence, 22 Arakoon Crescent, Sunshine Beach
APPENDIX E
LANDSLIDE SUSCEPTIBILITY ANALYSIS
Page 33
Attachment F: City Plan policy – Geotechnical stability assessment
Appendix 1: Landslide susceptibility analysis form
LANDSLIDE SUSCEPTIBILITY ANALYSIS Analysis No. PG-2096-01
Location: Site No. Site Name:
1 Natural Surface Slope 9 Material in cutting
Site Level Factor Site Level Factor
Less than 5 degrees L 0.1 High strength rock L 0.5
0.5 Between 5 and 15 degrees M 0.5 Medium strength rock L 1
Between 15 and 30 degrees M 0.8 Low strength rock M 1.2
Between 30 and 45 degrees H 1.2 Very low strength rock and soil H 1.5
More than 45 degrees M 0.8 2 Soil VH 2
2 Slope Shape 10 Cut slope support
Site Level Factor Site Level Factor
Crest or ridge L 0.7 0.5 Concrete wall L 0.5
0.9 Planar / Convex M 0.9 Crib wall M 0.9
Rough / Irregular H 1.2 Gabion wall M 1
Concave H 1.5 Rock wall H 1.5
3 Site geology Unsupported H 2
Site Level Factor
Volcanic Extrusive rock H 1.1 11 Concentration of surface water
Sedimentary rock M 1 Site Level Factor
1 Low grade metamorphic rock M 1 Ridge L 0.7
High grade metamorphic rock L 0.9 Crest M 0.8
Volcanic Intrusive rock M 1 0.9 Upper slope M 0.9
4 Soils Mid slope H 1.2
Site Level Factor Lower slope H 1.5
Rock at surface VL 0.1 12 Wastewater Disposal
Residual soil < 1m deep L 0.5 Site Level Factor
Residual soil 1-3m deep M 0.9 1 Fully Sewered M 1
1.5 Residual soil > 3m deep H 1.5 Onsite disposal – Surface M 1.2
Colluvial soil < 1m deep H 1.5 Onsite disposal – Soak Pit/Trenches H 1.5
Colluvial soil 1-3m deep VH 2
Colluvial soil > 3m deep VH 4 13 Stormwater Disposal
5 Fill height Site Level Factor
Site Level Factor All stormwater piped into road drainage L 0.7
None L 1.0 1 Rain water tank with overflows M 1
1.1 Less than 1m M 1.1 Stormwater discharge on site H 1.5
Between 1 and 3m M 1.3
Between 3 and 6m H 1.7 14 Evidence of instability
More than 6m VH 2.5 Site Level Factor
6 Evidence of groundwater 0.8 No sign of instability L 0.8
Site Level Factor Soil Creep H 1.2
0.7 None apparent L 0.7 Minor irregularity VH 2
Minor moistness M 0.9 Major irregularity VH 5
Generally wet H 1.5 Active instability VH 10
Surface springs VH 3
Summary
7 Cut height Factor
Site Level Factor 1 Natural Surface Slope M 0.5
None (Go to section 11) L 1.0. 2 Slope Shape M 0.9
Less than 1m M 1.1 3 Site Geology M 1
Between 1 and 3m M 1.3 4 Soils H 1.5
1.7 Between 3 and 6m H 1.7 5 Fill Height M 1.1
More than 6m VH 2.5 6 Evidence of Groundwater L 0.7
7 Cut height H 1.7
8 Slope of cut face 8 Slope of Cut Face L 0.5
Site Level Factor 9 Material in Cutting VH 2
0.5 Less than 30 degrees L 0.5 10 Cut Slope Support L 0.5
Between 30 and 45 degrees M 1 11 Concentration of Surface Water M 0.9
Between 45 and 60 degrees H 1.5 12 Wastewater Disposal M 1
More than 60 degrees VH 3 13 Stormwater Disposal M 1
14 Evidence of Instability L 0.8
Relative Susceptibility (1x2x3x4x5x6x7x8x9x10x11x12x13x14) 0.32
Low
Major update to City Plan Policies (Schedule 6) – Draft for Adoption Page 8 of 11
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