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Appendix B - Geotechnical Assessment · OPW23/0179
GEOTECHNICAL REPORT: Proposed Residence
128 Gympie Terrace
Noosaville
Michael Cullen
June 2023
PG-10375
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Page 2
Ref: PG-10375, 2023-06-09, LTR VER 1
Author: James Daly
30th June, 2023
Michael Cullen
Email: [email protected]
ATTN: MICHAEL CULLEN
Dear Sir,
GEOTECHNICAL INVESTIGATION – PROPOSED RESIDENCE
128 GYMPIE TERRACE, NOOSAVILLE
Enclosed is a copy of our report for the above project dated June 2023. An electronic
copy of the report has been issued.
Should you have any queries regarding this report, please do not hesitate to contact
James Daly at this office.
Yours faithfully,
J. DALY (RPEQ 14293)
For and on behalf of
PACIFIC GEOTECH PTY LTD
[email protected]
www.pacgeo.com.au
Page 3
TABLE OF CONTENTS
1.0 INTRODUCTION ................................................................................................... 1
2.0 METHODOLOGY .................................................................................................. 2
3.0 SITE DESCRIPTION................................................................................................ 2
4.0 GEOTECHNICAL MODEL .................................................................................... 4
5.0 GROUNDWATER .................................................................................................. 5
6.0 SITE CLASSIFICATION.......................................................................................... 5
7.0 EARTHWORKS AND SITE PREPARATION CONSIDERATIONS ............................ 5
8.0 EARTHQUAKE CONSIDERATIONS ...................................................................... 6
9.0 BATTERS – SHORT TERM EXCAVATION PROFILE ............................................... 7
10.0 TEMPORARY BATTER SUPPORT ........................................................................... 7
11.0 PERMANENT RETAINING WALLS......................................................................... 8
12.0 BUILDING FOUNDATIONS ................................................................................... 8
12.1 Deep Foundations ................................................................................................... 10
13.0 DEWATERING CONSIDERATIONS .................................................................... 11
14.0 CONSTRUCTON MONITORING ........................................................................ 12
14.1 Monitoring ................................................................................................................ 12
14.2 Preconstruction Survey........................................................................................... 12
15.0 SITE MANAGEMENT .......................................................................................... 12
16.0 LIMITATIONS ...................................................................................................... 13
Appendices
Appendix A
Notes Relating to this Report
Appendix B
Borehole Record Sheets
Appendix C
Site Plan
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
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 1726-2017
• Groundwater conditions
• Indicative site classification for hydraulic design in accordance with AS 2870-
2011
• Earthworks recommendations including:
o Suitability of cut for use as fill
o Compaction standards
o Stripping depths
o Trafficability
o Excavatability
o Safe temporary batter slopes for cuts
o Fill batter slopes
• Retention considerations
• Retaining wall design parameters
• Earthquake/liquefactions considerations
• Foundation Recommendations including:
o High-level and deep support options
o Bearing capacity and skin friction design values
o Predicted settlements
o Preliminary raft design parameters
• Construction Considerations
Proposed Development
It is understood that the proposed development is to consist of the construction of a
double-storey residence, with a single level basement. Excavations are expected to
comprise cuts of up to 3m to create the proposed basement.
The proposed development is indicated below.
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
PROPOSED LAYOUT
PROPOSED SECTION
2.0 METHODOLOGY
The geotechnical investigation comprised the drilling and sampling of two (2)
boreholes (BH01 to BH02), extending to depths of 2.7m and 2.9m, using a Compac018
drilling rig utilising 100mm solid flight augers, across the proposed building footprint.
Dynamic Cone Penetrometer (DCP) testing was conducted adjacent to the
boreholes. Both boreholes were terminated at drill rig refusal.
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 128 Gympie Terrace, Noosaville
and is bound by Mill Street to the east, a park to the north, Gympie Terrace to the
south and another development to the west.
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
At the time of the investigation, the was clear of existing structures.
The site was relatively level and drainage was considered poor.
Refer following aerial and site photographs for typical site conditions.
AERIAL IMAGE
SITE PHOTOGRAPHS
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
4.0 GEOTECHNICAL MODEL
The subsurface profile encountered in the boreholes generally consisted of fill to
depths of 0.5m underlain by loose to medium dense sands underlain by indurated
sands. Borehole refusal occurred in the indurated sand layer in both boreholes.
Based on investigations we have done on adjacent sites it is considered likely that the
indurated sands will be underlain by stiff to very stiff clays, however this will need to be
confirmed during construction.
Table 1 presents a summary of the encountered subsurface profile. Detailed borehole
record sheets are appended to this report.
TABLE 1 SUBSURFACE PROFILE SUMMARY
NATURAL
SAND
BH No. FILL BH TD
Loose/ Very Dense
Medium Dense (Indurated Sand)
BH01 0.0 – 0.5 0.5 - 2.5 2.5 – TD 2.73
BH02 0.0 – 0.5 0.5 – 2.85 2.85 – TD 2.93
Notes:
1. All depths in metres below ground level at time of investigation.
2. TD - Termination Depth.
3. Drilling rig refusal
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
5.0 GROUNDWATER
Groundwater was noted in the boreholes at depths of 1.2m and 1.3m at the time of
drilling. Water levels can be expected to vary with seasonal and climatic conditions.
Typically, the groundwater levels in the area are encountered at levels of
approximately RL 0.5m to RL 1.0m. Fluctuations of +/- 0.5m are typically noted in the
area.
Increases in the groundwater levels often occur following significant rainfall events
(floods) with the groundwater levels to as much as RL 1.5m to RL 2.0m being noted in
the area.
6.0 SITE CLASSIFICATION
The investigation and laboratory test results indicate that from a reactivity perspective,
the development site could be considered equivalent to Class ‘M’, in accordance
with AS 2870-2011 'Residential Slabs and Footings', following appropriate ground
improvement works under the footings.
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.
7.0 EARTHWORKS AND SITE PREPARATION CONSIDERATIONS
Earthworks are expected to comprise cuts of up to 3m for the proposed basement
excavation. Some over-excavation may be required to allow for ground
improvement works.
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
fair to good with no difficulties encountered at the time of the investigation.
Following stripping and excavation for the basement, the exposed sands will
be difficult to traffic for conventional vehicles. Consideration could be given to
adopting a 150mm layer of pavement gravel as a working platform across 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. Dirty sands (i.e. >5% fine content) could be difficult
to manage and consideration could be given to the disposal of this material.
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
• The stripped surface should be proof rolled using a vibrating roller or a large
vibrating plate compactor (say 300kg), to identify areas of weak surficial soils
and to compact the upper level material.
• The “clean” sands on site will be suitable for re-use as structural fill, provided
material is free of organic matter and deleterious material. The silty sand and
clays may prove difficult to re-use and should be preferentially disposed of.
• 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 75% Density Index for non-
cohesive fill (i.e. sand).
• Field 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.
8.0 EARTHQUAKE CONSIDERATIONS
The design should consider the effects of an earthquake on the founding soils, as
outlined in AS.1170.4-2007, Part 4.
Liquefaction occurs as a result of pore pressures increasing and reducing the effective
stress to zero with consequent loss of strength.
The likelihood of liquefaction for an earthquake can be related to sand density. For
an acceleration of 0.08g, the following assessments as shown in Table 2 have been
made.
TABLE 2 EARTHQUAKE/LIQUEFACTION POTENTIAL
Liquefaction Potential Density Index (%)
<35
Very Likely
(very loose to loose)
35 – 54
Likely
(medium dense)
>64
Unlikely
(medium dense to very dense)
Testing results indicated that sands that are likely to undergo liquefaction extended
to depths in the order of 2.5m to 3.0m. These materials will require removal, or
recompaction, as part of the foundation improvement works and therefore all sands
likely to undergo liquefaction will be removed from site during construction.
Reference to Section 4.2 in AS1170.4-2007, it is recommended that a site classification
of “Class Ce – shallow soil site” be adopted, in accordance with the definitions
presented in “Section 4.2 – Class Definitions”.
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
9.0 BATTERS – SHORT TERM EXCAVATION PROFILE
It is understood that cut batters to 3.0m in height will be required as part of the
basement construction.
Considering the proposed maximum height of cut, the following recommendations
are made for the bulk excavation of the site.
Batters < 2.0m in height
• 1V:1.5H batter with crest of batter >2m from buildings or structures.
Batters > 2.0m in height
• 1V:1.5H batter with the crest of the batter at least 2.0m inside the site boundary.
• 2.0m minimum distance from any building or structure.
If batters are to be left exposed for an extended period of time, a battler angle of
1V:2H is recommended and berm widths are to be strictly maintained. The above
batter slopes assume no seepage is present in the batters and the batters are above
the water table.
10.0 TEMPORARY BATTER SUPPORT
Where the excavations cannot be battered to a stable angle, they will need to be
supported to prevent instability. Support systems could include:
• Sheet Piles – It is expected that cantilevered sheet piles will be an acceptable
retention system. Anchoring or cross-bracing of the excavation may be
required. Due consideration should be given to the potential for anchor
installation and vibration to adversely affect adjacent areas.
• Contiguous Piles – whilst no vibration is associated with their installation, it is likely
a more expensive solution.
Where sheet piles are to installed through medium dense or ‘denser’ sands, pre-drilling
may be required to ensure installation.
Where sands are retained, shoring pressures should be based on the lateral earth
pressure coefficients given in Table 3, in conjunction with a triangular pressure
distribution where the pressure can be calculated from P=0.5ka H2, provided the
excavation is not surcharged by adjacent buildings/services and some tolerance or
movement exists.
TABLE 3 LATERAL EARTH PRESSURE COEFFICIENTS
Lateral Earth Pressure Coefficients
Unit Weight
Material Strength (K)
(t/m3)
Flexible Propped
Very loose to loose 1.8 0.40 0.60
Sands Medium dense 2.0 0.30 0.50
Dense to very dense 2.1 0.25 0.45
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
Pressures for unsurcharged propped walls could be designed based on a uniform
pressure distribution with depth, where the pressure P = 0.65ka H (kPa) where H is the
depth of the excavation. The shoring wall should also be checked for a triangular
distribution calculated using the lateral earth pressure coefficients present in Table 3
for a propped wall.
The temporary support system should also take into consideration the possible needs
to over-excavate the basement for ground improvement works.
It should be noted that lateral deflection of the retention system will occur, irrespective
of the retention system adopted. In additional to lateral movements, vertical
movement of the soils behind the retention system will result. The effects of the vertical
and horizontal movements may be seen at a distance equal to 2 or 3 times the height
of the excavation.
Subject to detailed design, movements as much as 1% to 2% of the depth of the
excavation could occur behind a cantilevered pile wall.
11.0 PERMANENT RETAINING WALLS
Basement walls should be designed using a pressure coefficient for the at rest case of
K0 = 0.5.
Unit wall force P is given by:-
P = 0.5 K0 H12 (kN/m run of wall)
Passive resistance at the base of the wall can be calculated from:-
P = 0.5 Kp Hw2
where Kp = 3.00 (ignores wall friction effects) for loose sands
3.25 for medium dense sands
3.85 for very dense sands
Hw = front face of wall contributing to passive resistance (m)
For the sliding resistance calculation, the angle of friction for sand () compacted to
not less than 75% density index can be taken as 32° for walls with a key. For walls
2
without a key, the angle of friction for sliding resistance should be taken as 3 or 21°.
12.0 BUILDING FOUNDATIONS
Given the encountered subsurface profile, a high-level footing system would
generally be suitable for the support of the proposed structure, with appropriate
ground improvement works and due consideration of the potential hydrostatic uplift
forces and the potential for weaker layers above the indurated sand.
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
Assuming an excavation depth of 3m for the basement, it is expected indurated sands
will be exposed across the basement floor. Provided sands above the indurated sands
are removed, an allowable bearing pressure of 300kPa could be adopted in the
indurated sands. If any sands remain across the base of the excavation, provided they
are compacted to a minimum Density Index of 75%, an allowable bearing capacity
of 200kPa could be adopted for the foundation design.
Where sands are exposed at the foundation level, this compaction could be
achieved through the over-excavation of the founding soils, compaction of the
exposed material and the replacement of the excavation using “clean” sand.
It should be noted some difficulties have been experienced in compacting sands and
particularly silty sands immediately above the indurated stratum, due to the difficulties
in suitably dewatering.
It is strongly recommended that if a high-level footing raft type system is to be
adopted, sufficient “clean” sand from higher in the excavation profile be stockpiled
on-site, to allow for the replacement of the silty sands at the founding level, or the
sands removed to expose the indurated sand.
It should be further noted that immediately below the indurated sand layer, weaker
soil layers may be present that were not identified as part of the geotechnical
investigation. It is strongly recommended that following excavation to the basement
floor level that additional testing be carried out under the supervision of Pacific
Geotech to further assess the nature of the soils below the indurated sands.
To enable the required ground improvement works to be undertaken, the following
earthworks operation is recommended:
i. Install the temporary retention system and dewatering system.
ii. Dewater the site to at least 0.6m below the excavation level or to the top of
the indurated sand.
iii. Excavate the site to the design basement level and test the base of the
excavation to determine the extent of over-excavation required (if any).
iv. Following determination of the required extent of over-excavation, excavate
the site to the required level and compact the exposed sands using a large
(300kg plus) vibrating plate compactor or a small smooth drum roller. It should
be noted that the silty sands encountered at the test locations could be difficult
to compact and manage, if not appropriately dewatered. It may be
necessary to remove the silty sands and replace them with clean sands from
higher in the excavation profile or extend the foundation into the underlying
stiff clays.
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
v. Where required, replace the over-excavation with “clean” sand and compact
in layers to the design founding level. The founding soils should be compacted
to a minimum Density Index of 75% (in accordance with AS 1289 5.6.1).
Foundation Design Parameters
For footings founded 3m below the ground level, an allowable bearing capacity of
300kPa could be adopted in the indurated sand and 200kPa in the recompacted
sand above the indurated sand, following confirmation that a minimum Density Index
of 75% is present below the footings.
If the exposed sands are disturbed or loosened during the excavation operation, they
should be recompacted. Consideration should be given to placing a 50mm thick
(minimum) concrete binding layer across the footings, immediately following
excavation.
Settlement Potential
Settlements from a 30kPa raft type foundation system founding 3.0m below existing
ground level have been calculated to be in the order of 15mm with anticipated
differential settlements of between 25% and 50% of the calculated total settlement
for pad footings founded at a similar depth.
A modulus of subgrade reaction (k) of 6 to 8 kPa/mm could be adopted for
preliminary raft design. The value should be confirmed as raft loads are refined.
The settlement will occur as “immediate” settlement as the building loads are applied.
Hydrostatic Uplift Forces
For a fully tanked basement, hydrostatic uplift forces should be considered in the
design. It is recommended hydrostatic uplift forces in groundwater levels to at least
RL1.5 to 2.0 be taken into consideration on this site and checked for the Q100 flood
condition.
12.1Deep Foundations
Where the structure extends beyond the basement, consideration could be given to
adopting a deepened foundation system founding into a consistent founding stratum
of the main raft. Alternatively, a high level footing system could be adopted, with
appropriate ground improvement works, provided the structure can be suitably
detailed to tolerate the potential differential settlement between the structures.
Where the extent of over-excavation required or the foundation treatment is not
considered practical, a deep foundation system could be adopted.
Screw piles or possibly driven timber piles could be considered for the support of the
proposed structure.
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
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 4. The Rd,ug
values given in Table 4 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 4
will need to be divided by a factor of safety of 2.5 to caluculate the maximum single
pile working load.
TABLE 4 PRELIMINARY ULTIMATE (UNFACTORED) PILE DESIGN PARAMETERS
Ultimate Unfactored End
Bearing* Ultimate Unfactored Shaft
Material (kPa) Adhesion*
(kPa)
L < 4D L > 4D
Loose Sand NR NR 25
Medium Dense Sand 600 900 35
Indurated Sand 1800 2700 70
Stiff Clay NR NR 25
Very Stiff Clay 600 900 35
Hard Clay 1200 1800 50
Notes:
*Geotechnical strength reduction factor needs to be applied to these parameters.
1. NR – Not Recommended.
2. L – total pile length; D – pile diameter.
The above design parameters should be confirmed with additional assessment,
should a deep foundation system be adopted.
13.0 DEWATERING CONSIDERATIONS
Construction of the basement and foundation system will likely require dewatering.
The groundwater will need to be lowered to the top of the indurated sand which is
expected to be virtually impermeable. Groundwater was noted at approximately 1m
below ground level and excavation of up to 3m could be expected. Drawdown of
approximately 2m is therefore expected to be required.
Dewatering is typically achieved through the use of perimeter spears and internal
wells. Where the excavation extends through the indurated sand and exposes the
clays, dewatering would typically be achievable using base sump pumps to maintain
dry conditions.
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
Settlements inducted by 2m of drawdown (i.e. 20kPa effective stress increase) are
estimated to result in settlements of less than 5mm. Therefore, it is considered that the
effects of dewatering on the adjoining structures will be minimal.
14.0 CONSTRUCTON MONITORING
Construction vibrations could potentially cause settlement in the loose upper level
sands, thereby damaging nearby structures founded in these strata. Prior to
commencement of construction on site, it is recommended that a detailed
dilapidation survey be undertaken to establish the condition of all existing adjacent
structures.
14.1Monitoring
It is recommended that monitoring points should be established on the retention
system to check for deflections during excavation. A suggested spacing of the
monitoring points would be 10m along the walls. A regular monitoring program of
these stations should be implemented.
Monitoring must commence before any excavation to establish baseline readings.
14.2Preconstruction Survey
Prior to commencement of construction on site, it is recommended that a dilapidation
survey be undertaken on the adjacent structures.
This survey should include the following:
• The extent of exiting damage (if any)
• The general condition of the property, ie. Condition of all exposed columns
and beams, partition walls and cladding etc.
• Road, kerb and channel and footpath condition adjacent development site.
15.0 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.
• The ground surface around the perimeter of the buildings should slope away
from the structure and fall to the stormwater system. Water should not be
allowed to pond adjacent to the buildings.
• Founding soils should not be allowed to become saturated. Saturation of the
on-site material will result in an increase in settlement potential.
• Service trenches under the buildings should be kept to a minimum.
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• 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.
16.0 LIMITATIONS
We have prepared this report for the Proposed Residence at 128 Gympie Terrace,
Noosaville. The report is provided for the exclusive use of Michael Cullen, 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.
Yours faithfully,
J. DALY (RPEQ 14293)
For and on behalf of
PACIFIC GEOTECH PTY LTD
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Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
APPENDICES
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APPENDIX A
NOTES RELATING TO THIS REPORT
Page 19
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, Planarity
and the possibility of other than ‘straight line’ CU Curved
variations between the test locations. DIS Discontinuous
IR Irregular
Description and Classification Methods PR Planar
ST Stepped
The description and classification of soils and UN Undulose
rocks used in this report are based on AS 1726.
Soil types are described according to the
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 20
Roughness Investigation Methods
POL Polished
RJ Rough Test Pits: These are typically undertaken with a
S Smooth backhoe or a tracked excavator, allowing
SL Slickened examination of the insitu soils. Limitations of test
VR Very Rough
pits are the problems associated with collapse
of the pits, disturbance and difficulty of
Defects Type reinstatement and the consequent effects on
BP Bedding Parting close-by structures. Care must be taken if
CL Cleavage construction is to be carried out near test pit
CO Contact locations to either properly recompact the
CS Crushed Seam backfill during construction or to design and
CZ Crushed Zone
construct the structure so as not to be
DB Drilling Break
adversely affected by poorly compacted
DK Dyke
DL Drill Lift backfill at the test pit location.
DZ Decomposed Zone
FC Fracture Hand Auger Drilling: A borehole of typical
FL Foliation diameter of between 50mm to 75mm advance
FZ Fracture Zone manually operated equipment. Premature
HB Handling Break refusal of the hand augers can occur on a
IS Infilled Seam variety of materials such as fill, gravel, hard
JT Joint clays and collapse of the borehole (typically in
H Schistosity non-cohesive soil).
SI Sill
SM Seam Continuous Spiral flight Augers: The borehole is
SS Shear Seam advanced using 65mm to 100mm diameter
SZ Shear Zone
continuous spiral flight augers, which are
VN Vein
withdrawn at intervals to allow sampling and
VO Void
insitu testing. Augers of up to 300mm in
Sampling diameter are used to recover larger volumes of
sample. Samples are returned to the surface
Sampling is undertaken during the fieldwork to by the flights or may be collected after
allow examination of the soil or rock and to withdrawal of the auger flights. Samples can
allow laboratory testing to be undertaken. be disturbed and layers may become mixed.
Augering below the groundwater table can be
Disturbed samples taken during drilling provide less reliable than augering above the water
information on plasticity, grain size, colour, table.
moisture content and minor constituents. Bulk
samples are similar but of greater volume A Tungsten Carbide (TC) bit for auger drilling
required for some test procedures such as CBR into rock can be used to indicate rock strength
testing. and continuity by variation in drilling resistance
and from examination of recovered rock
Undisturbed samples are taken by pushing a fragments but provides only an indication of
thin-walled sample tube, usually 50mm the likely rock strength. Where rock strengths
diameter (known as a U50), into the soil and may have a significant impact on construction
collecting a sample of the soil contained in a feasibility or costs, then further investigation by
relatively undisturbed state. Such samples yield means of cored boreholes may be warranted.
information on structure and strength, and are
necessary for laboratory determination of shear Wash Boring: The borehole is advanced by a
strength and compressibility. Undisturbed bit attached to the end of a hollow rod string,
sampling is generally effective only in cohesive with water being pumped down the drill rods
soils. and returned up the annulus of the borehole,
carrying the drill cuttings. Changes in
Details of the type and method of sampling stratification can be determined from the
used are given on the attached logs. return, together with information from “feel”
and rate of penetration.
Page 21
The borehole can be stabilised through the use using a Cone Penetrometer in general
of drilling mud as a circulating fluid. The term accordance with AS 1289 6.5.1, 1999.
‘mud’ encompasses a range of products
ranging from bentonite to polymers such as In the tests, a 36mm diameter rod with a
Revert or Biogel. conical tip is pushed continuously into the soil,
the reaction being provided by a hydraulic
Continuous Core Drilling: A continuous core ram system. Measurements are made of the
sample is obtained using a diamond tipped end bearing resistance on the cone and the
core barrel. This technique provides a reliable fractional resistance on a separate 135mm
(but relatively expensive) method of long sleeve, immediately behind the cone.
investigation. In rocks, an NMLC triple tube Pore Pressure is recovered through a pore ring
core barrel is used, which gives a core of about located either within, or more usually
50mm diameter. The length of core recovered immediately behind the cone/tip.
is compared to the length drilled and any
length not recovered is shown as CORE LOSS. As penetration occurs (at a rate of
approximately 20mm per second) and data is
Standard Penetration Tests: Standard recorded every 20mm of penetration, the
Penetration Tests (SPT) are used mainly in non- results are presented graphically.
cohesive soils, but can also be used in cohesive
soils as a means of indicating density or The information provided on the plot
strength and also of obtaining a disturbed comprises:
sample. The test procedure is described in
Cone resistance – expressed in mPa
Australian Standard 1289, “Methods of Testing
Sleeve friction – expressed in kPa
Soils for Engineering Purposed”, Test 6.3.1.
Friction ratio – the ratio of sleeve
The test is carried out in a borehole by driving a friction to cone resistance expressed as
50mm diameter split sample tube with a a percentage.
tapered shoe, under the impact of a 63kg Pore pressure in kPa
hammer, with a free fall of 760mm. The sample Tilt of probe (in degrees).
is driven in three successive 150mm increments
and the ‘N’ value is taken as the number of
The ratios of the sleeve resistance to cone
blows for the last 300mm. In dense soils, hard
resistance will vary with the type of soil
clays or weak rock, the full 450mm penetration
encountered, with higher relative friction in
may not be practicable and the test is
clays than in sands. Friction ratios of 1% to 2%
discontinued.
are commonly encountered in sands and rising
The test results are reported in the following to 2% to as high as 8%, and higher in organic
form: soils. Soil descriptions based on cone
resistance and friction ratios are only inferred
In the case where full penetration is and must not be considered as exact.
obtained with successive blow counts
for each 150mm of , say, 4, 6 and 7 Stratification can be inferred from the cone
blows, as and friction traces and from experience and
N = 13 information from nearby boreholes, etc. Where
4, 6, 7 shown, this information is presented for general
In a case where the test is discontinued guidance, but must be regarded as
short of full penetration, say after 15 interpretive.
blows for the first 150mm and 30 blows
Dynamic Cone Penetrometers:
for the next 40mm, as
N > 30
Dynamic Cone Penetrometer (DCP) tests are
15, 30/40mm
carried out by driving a 16mm diameter rod
into the ground with a 9kg sliding hammer
Cone Penetrometer Testing (CPT): Cone
dropping 510mm and counting the blows for
Penetrometer Testing with or without pore
successive 100mm increments of penetration.
pressure measurement (CPTu) is carried out
Page 22
Logs for fill, it may be difficult to reliably determine
the extent of the fill.
The borehole or test pit logs are an
interpretation of the subsurface conditions, and Laboratory Testing
their reliability will depend to some extent on
the frequency of sampling and the method of Laboratory testing is carried out in general
drilling or excavation. accordance with Australian Standard 1289
‘Methods of Testing Soil for Engineering
Interpretation of the information shown on the Purposes’.
logs, and its application to design and
construction, should therefore take into Site Anomalies
account the spacing of the boreholes or test
In the event that conditions encountered on
pits, the method of drilling or excavation, the
site during construction appear to vary from
frequency of sampling and testing and the
those which were expected from the
possibility of other than “straight line” variations
information contained in the report, the
between the boreholes or test pits. Subsurface
company requests that it immediately be
conditions between boreholes or test pits may
notified. Most problems are much more readily
vary significantly from conditions encountered
resolved when conditions are exposed than at
at the borehole or test pit locations.
some later stage.
Groundwater
Review of Design
Where groundwater levels are measured in
Where major civil or structural developments
boreholes, there are several potential
are proposed or where only a limited
problems:
investigation has been completed or where the
Although groundwater may be geotechnical conditions/constraints are quite
present, in low permeability soils it may complex, it is prudent to have a design review.
enter the hole slowly or perhaps not at
Site Inspection
all during the time it is left open.
A localised perched water table may
Pacific Geotech would be pleased to provide
lead to an erroneous indication of the
engineering inspection services for
true water table.
geotechnical aspects of work to which this
Water table levels will vary from time to
report is related:
time with seasons or recent weather
changes and may not be the same at Requirements could range from:
the time of construction.
The use of water or mud as a drilling i. a site visit to confirm that conditions
fluid will mask any groundwater inflow. exposed are no worse than those
Water has to be flushed from the hole interpreted, to
and drilling mud must be washed out ii. a visit to assist the contractor or other
of the hole or ‘reverted’ chemically if site personnel in identifying various
water observations are to be made. soil/rock types such as appropriate
More reliable measurements can be made by footing or pier founding depths, or
installing standpipes from which ongoing iii. full time engineering present on site.
monitoring can be undertaken.
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
Page 23
Project No. PG-10375
June 2023
Ref: PG-10375, 2023-06-09, LTR VER 1
Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
APPENDIX B
BOREHOLE RECORD SHEETS
Page 24
Borehole No.
BH01
Page 1 of 1
Project No.: PG-10375
Client: Michael Cullen Commenced: 02/06/2023
Project Name: Proposed Residence Logged By: SR
Hole Location: 128 Gympie Terrace, Noosaville Checked By:
Hole Position:
Drill Model and Mounting: Compac 018 RL Surface: No survey
Hole Diameter: Datum: AHD Operator: SR
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
SM FILL Silty Gravelly SAND (SM) Medium dense to dense, fine to medium
grained, pale grey pale yellow brown pale brown, fine to medium sized
gravel, moist to dry.
D 0.20-0.50 m
0.30
SM FILL Silty SAND (SM) Medium dense, fine to medium grained, dark
grey, with low plasticity clay, moist.
0.50
0.5
ASS 0.50-1.00 m SP NATURAL SAND (SP) Medium dense, fine to medium grained, pale
grey, moist.
0.80
SP SAND (SP) Loose, fine to medium grained, pale grey, moist.
AG PACGEO 1.01.2 LIB.GLB Log PACGEO BOREHOLE PG-10375.GPJ <<DrawingFile>> 16/06/2023 12:58 10.03.00.09 Datgel Lab and In Situ Tool - DGD | Lib: pacgeo 1.01.2 2022-05-25 Prj: Precise 1.01 2016-11-23
1.0
ASS 1.00-1.50 m
1.20
SP SAND (SP) Medium dense, fine to medium grained, pale grey, with
medium to high plasticity clay, wet (with clay layering).
AD/T
1.5
ASS 1.50-2.00 m
1.90
SP SAND (SP) Loose to medium dense, fine to medium grained, pale grey,
2.0 with medium to high plasticity clay, wet (with clay layering).
ASS 2.00-2.50 m
2.30
SP SAND (SP) Medium dense, fine to medium grained, pale grey, with
medium to high plasticity clay, wet (with clay layering).
2.50
2.5
D 2.50-2.70 m SM Silty SAND (SM) Dense, fine to medium grained, dark brown, wet
(indurated sand).
2.70
Hole Terminated at 2.70 m
Method Water Samples and Tests Remarks
AS - Auger Level (Date) U - Undisturbed Sample
RR - Rock Roller D - Disturbed Sample 1. Groundwater encountered at 1.20m.
WB- Washbore Inflow SPT - Standard Penetration Test 2. DCP refusal at 2.53m.
B - Bulk Sample 3. Maximum TC refusal at 2.70m.
4. Standpipe installed to 2.40m.
Classification Symbols and
Support Soil Descriptions
C - Casing
Based on Unified Soil
Classification System
Page 25
Borehole No.
BH02
Page 1 of 1
Project No.: PG-10375
Client: Michael Cullen Commenced: 02/06/2023
Project Name: Proposed Residence Logged By: SR
Hole Location: 128 Gympie Terrace, Noosaville Checked By:
Hole Position:
Drill Model and Mounting: Compac 018 RL Surface: No survey
Hole Diameter: Datum: AHD Operator: SR
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
SM FILL Silty SAND (SM) Medium dense, fine to medium grained, dark
grey, with fine to medium sized gravel, moist to dry (with cobbles).
0.50
0.5
ASS 0.50-1.00 m SP NATURAL SAND (SP) Loose, fine to medium grained, pale grey, moist.
AG PACGEO 1.01.2 LIB.GLB Log PACGEO BOREHOLE PG-10375.GPJ <<DrawingFile>> 16/06/2023 12:58 10.03.00.09 Datgel Lab and In Situ Tool - DGD | Lib: pacgeo 1.01.2 2022-05-25 Prj: Precise 1.01 2016-11-23
1.0
ASS 1.00-1.50 m
D 1.10-1.50 m
1.30
SP SAND (SP) Loose to medium dense, fine to medium grained, pale grey,
wet.
AD/T
1.5
ASS 1.50-2.00 m
1.70
SP SAND (SP) Medium dense to dense, fine to medium grained, grey, wet
(with broken seashells throughout).
2.0
ASS 2.00-2.50 m
2.5
ASS 2.50-2.90 m
2.85
2.90 SM Silty SAND (SM) Very dense, fine to medium grained, dark brown, wet
(indurated sand).
Method Water Hole Terminated atSamples
2.90 m and Tests Remarks
AS - Auger Level (Date) U - Undisturbed Sample
RR - Rock Roller D - Disturbed Sample 1. Groundwater encountered at 1.30m.
WB- Washbore Inflow SPT - Standard Penetration Test 2. DCP refusal at 2.53m.
B - Bulk Sample 3. Maximum TC refusal at 2.70m.
Classification Symbols and
Support Soil Descriptions
C - Casing
Based on Unified Soil
Classification System
Page 26
Project No. PG-10375
June 2023
Ref: PG-10375, 2023-06-09, LTR VER 1
Michael Cullen – Geotechnical Investigation - Proposed Residence, 128 Gympie Terrace, Noosaville
APPENDIX C
SITE PLAN
Page 27
BH02
BH01
Drawn
Project: Proposed Residence
ER
Drawing No.
Date
Location: 128 Gympie Terrace, Noosaville A4
JUN23
PG-10375-01
Checked
Client: Michael Cullen
Used in these records
Appendix B - Geotechnical Assessment.pdfRelated documentApplication case desk ↗
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