Preliminary Geotechnical Site Investigation Report
Transcript of Preliminary Geotechnical Site Investigation Report
Preliminary Geotechnical Site Investigation Report
RE: Proposed five level mixed use development
318-320 Smith Street, Collingwood
File No: 191469
Date: 26 November 2019
Client: Orlcar Nominees Pty Ltd
737 Mount Alexander Road
MOONEE PONDS VIC 3039
Distribution: - Orlcar Nominees Pty Ltd
- Splinter Society Architecture Pty Ltd
- Structural Bureau
- Quadro Constructions
HARD ROCK GEOTECHNICAL PTY LTD Consulting Geotechnical Engineers
ABN: 24 066 600 002
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Introduction
A site investigation was undertaken on the 20th of November, 2019. The purpose of the investigation was to
provide foundation recommendations for the proposed five level mixed use development, constructed on
ground (no basement).
Scope of the Investigation
The preliminary investigation comprised the drilling of three hand augered boreholes. The subsurface profile
was logged and bulk sampled for visual identification. Borehole logs and locations are shown on pages 7 and
8 of this report.
Further detailed investigation is proposed following demolition and site clearing, and will include the drilling
of additional mechanically augered boreholes and exposure of adjacent boundary footings, as necessary.
Site Description
The site is occupied by a double storey solid brick shop fronted terrace building, with vehicle access via the
rear lane. Adjacent buildings are constructed to either side boundaries. The existing development extended to
all site boundaries. The investigation was limited to the rear ground level garage at 320 Smith Street. The site
is relatively flat and has poor surface drainage.
Subsurface Conditions
Regional geology
The site is identified on the ‘Geological Survey of Victoria’ Melbourne Sheet (1:63,360) as being within the
province of Silurian “Dargile Formation” and associated soils.
Subsurface profile
See borehole logs page 7. The boreholes encountered:
Concrete paving (80mm to 110mm nom. thickness) and FILLING of mixed composition to a
maximum depth of 0.60m, underlain by;
Natural stiff silty CLAY of medium plasticity/extremely weathered siltstone ROCK to depths of
between 0.55m and 0.90m, grading to;
Distinctly weathered (DW) siltstone ROCK.
All boreholes were extended to depths of between 0.55m and 0.90m, within the weathered siltstone ROCK.
The existing fill material can be considered the equivalent of rolled non sand fill in accordance with AS2870-
2011 clause 6.4.2.
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Soil moisture & groundwater
No groundwater was encountered in the boreholes; filling and natural soils were in a moist condition.
Site Classification
The site is classified as CLASS P in accordance with AS2870-2011.
The subsurface profile is moderately reactive (CLASS M).
The underlying siltstone ROCK is non-reactive (CLASS A).
Earthquake - Site Sub-Soil Class
A site sub-soil class of CLASS Be – Rock can be assumed with reference to AS1170.4-2007, Section 2.4.
Geotechnical Design Parameters
Geotechnical design parameters are provided in Appendix A of this report.
Foundation Recommendations
The siltstone ROCK is expected to exhibit a deep weathering profile; the upper rock is of relatively modest
strength. Higher bearing pressures may be available at depth and in consultation with this office and with
further detailed investigation.
Continuous strip & isolated pad footings
Conventional strip and pad footings should:
Penetrate through any FILLING and natural soils; and
Be founded within (DW) siltstone ROCK (bedrock).
Strip and pad footings can be proportioned for an allowable bearing pressure of 700kPa. This pressure can be
reviewed once the design pressures have been calculated.
Mass excavated pads/bored piers
Mass excavated pads/bored piers should penetrate and surface filling and natural soils, and be founded at
within (DW) siltstone ROCK (bedrock).
An allowable bearing pressure of 700kPa may be adopted beneath bored piers founding within (DW)
siltstone ROCK (bedrock). This pressure may be reviewed once design loads have been determined.
No skin friction is available for bored piers.
The base of the pier must to be clean and free of all loose material, and concrete poured without delay at the
completion of boring/excavation.
The contractor should be briefed and should supply means of insuring that the bored pier bases are clean and
free of disturbed and fallen material. An auger with a single cutting blade (i.e. no tines) may be an option to
cleaning the bases of the piers.
Rock socketed bored piles
Rock socketed bored piles should be founded a minimum of 2 pile diameters within competent siltstone
ROCK and can be proportioned for an allowable end bearing capacity of 1000kPa with an allowable skin
friction component of 100kPa within the competent SILTSTONE ROCK.
Excavation within the rock may be difficult and it is anticipated that specialist piling contactors may be
necessary.
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The piling contractor is to provide adequate means to ensure a clean base for the bored piles, free of any
debris.
Pavements
Sub-grade preparation
Preparation of pavements and floor slab subgrades should comprise the stripping of any organic material and
the surface fill to expose the natural silty CLAY (or weathered rock) subgrade.
The exposed surface should be proof rolled with the aim of achieving a dry density ratio of 98% as measured
by standard compaction (AS1289 5.1.1). Any soft, wet or loose material which does not respond to
compaction should be additionally excavated to expose a firm working base.
Depending on the moisture content of the subgrade at the time of construction, it may be necessary to add
water or allow the subgrade to dry back to achieve satisfactory compaction.
We recommend that the pavement construction be commenced without delay once the subgrade has been
exposed and proof rolled. A minimum compacted lift of 200mm imported filling should be placed
immediately once subgrade preparation is completed to protect the subgrade from moisture changes and
provide a working platform for vehicles.
Subgrade drainage
The subgrade should be provided with subsurface drainage to maintain any groundwater table to at least
300mm beneath the underside of the pavements, or a lower CBR value should be used in the design.
Pavements
Based on experience within the immediate area and the site investigation to date, it is recommended that
pavements be designed on the:
Natural silty CLAY soils using an estimated C.B.R value of 4.5% and a long term Young’s modulus Esl
of 18MPa and a correlation factor of 0.7 can be adopted as per the Cement and Concrete Association of
Australia ‘Industrial Floors and pavements’ section 3 Design for strength.
Natural weathered siltstone ROCK soils using an estimated C.B.R value of 15% and a long term
Young’s modulus Esl of 33MPa and a correlation factor of 0.9 can be adopted as per the Cement and
Concrete Association of Australia ‘Industrial Floors and pavements’ section 3 Design for strength.
Earthworks
The use of on-site filling and top soil material should be avoided and removed to spoil. The excavated
weathered siltstone ROCK should be suitable for structural filling.
Any imported filling used should comprise of clean, essentially of a granular nature, non-organic and have
a plasticity index of less than 12%. Suitable material may include crushed scoria, non-descript crushed rock,
mudstone or siltstone or equivalent. Fill material should have a nominal particle size of 75mm or less and as
a guide, appropriate material would meet the following criteria:
P.I x %pass 0.425 (AS sieve) 600
Any filling should be placed in lifts not exceeding 250mm loose thickness. Each layer should be compacted
to a dry density ratio of 98% measured by standard compaction (AS1289 5.1.1) using an appropriate medium
weight vibratory roller. The recommended moisture content is within 2% of optimum moisture content under
standard compaction.
HARD ROCK GEOTECHNICAL PTY LTD Consulting Geotechnical Engineers
ABN: 24 066 600 002
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Construction & Maintenance
Excavation within fill material and natural sand soils may experience short-term instability (particularly if
undertaken during the wetter months) and shoring and/or over excavation should be anticipated.
Disturbance of the filling and any natural soils may have resulted from previous site works and should be
anticipated.
Blinding concrete should be poured in the base of the footing trenches where founding depths exceed footing
dimensions.
Articulation of pavements and floor slabs where they abut walls should be provide to allow for the
differential movement between the foundations and the pavements.
Articulation of masonry walls should be provided as per details contained in reference (2) below, where
relevant.
Where footings are located in close proximity or adjacent to a backfilled service trench or easements, the
footing must be deepened and founded at a depth at or below the level of plane of inclination of 45 above
horizontal extending outwards from the base of the trench or filling (as illustrated by figure C6.4.1 AS 2870
2011). This includes service trenches which may be present on adjacent sites or on site prior to the current
development (such as abandoned stormwater and sewer trenches).
All contractors should be well briefed as to the requirements and specifications in this report. The subgrade
preparation, compaction testing, and inspection of foundation excavations should be conducted to insure that
they are in accordance with this report. It is recommended that fill material type is verified and that the
compaction be tested during placement. Testing should be conducted in accordance with AS3798-1990,
‘Guidelines of earthworks for commercial and residential developments’.
This report is based on the assumptions that conditions revealed through selective sampling are indicative of
the actual conditions throughout the site, i.e. correlation between boreholes. Variations between boreholes
may exist due to previous land use or natural geologic processes. Additional deepening of the foundations,
deeper than the minimum specified founding depths in this report, may be required. The actual subsurface
conditions can be discerned only during earthworks when the subsurface profile can be directly observed.
For further information regarding geotechnical site investigation reports, refer to reference (4) below.
Inspection of all foundation excavations, site works and compaction must be conducted by a suitably
qualified, experienced engineer, engineering geologist, building surveyor or similar to ensure that the
founding material and site works are in accordance with this report. Should there be any doubt, this office
should be immediately contacted.
Please do not hesitate to contact us, should there be any further queries.
Yours faithfully,
HardRock Geotechnical Pty Ltd
James Harrison B.E. (Geo.) M.E. (Env.)
(Geotechnical Engineer)
HARD ROCK GEOTECHNICAL PTY LTD Consulting Geotechnical Engineers
ABN: 24 066 600 002
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References
1. AS2870-2011. “Residential slabs and footings.”
2. The Cement and Concrete Association of Australia. Technical Note: TN61.
3. Institution of Engineers, Australia. 1987. “Guidelines for the Provision of Geotechnical Information in
Construction Contracts”.
4. AS1726-2017. “Geotechnical Site Investigations”.
5. AS2159- 2009. “Piling – Design and Installation”.
6. AS 3798-1996 “Guidelines on Earthworks for commercial and residential developments”.
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Hard Rock Geotechnical Pty Ltd Consulting Geotechnical Engineers
Borehole Logs
File:
191469
Date:
20/11/2019
Supervisor:
JH / CW
Client: Orclar Nominees Pty Ltd
Project: 318-320 Smith Street, Collingwood
Borehole No. 1 Drilling Method: HA Location: see Figure 1
Depth (m) Structure Description Cohesion/
density
Soil moisture/
groundwater Testing:
0.06
- 0.11
0.55
Pavement
SP
concrete pavement
silty CLAY(CL), medium plasticity, orange/light
brown/grey - extremely weathered (XW) siltstone
ROCK
Refusal at 0.55m on weathered siltstone rock
MD
M
Borehole No. 2 Drilling Method: HA Location: see Figure 1
0.09
0.60
0.70
Pavement
Fill
SP
concrete pavement
clayey SILT/gravel
silty CLAY(CL), medium plasticity, orange/light
brown/grey - extremely weathered (XW) siltstone
ROCK
Refusal at 0.70m on weathered siltstone rock
L/VL
MD
M
M
Borehole No. 3 Drilling Method: HA Location: see Figure 1
0.10
0.25
0.90
Pavement
Fill
SP
concrete pavement
non-descript crushed rock/gravel/clayey SILT/silty
CLAY
silty CLAY(CL), medium plasticity, orange/light
brown/grey - extremely weathered (XW) siltstone
ROCK
Refusal at 0.90m on weathered siltstone rock
L/MD
MD
M
M
Legend: Density Cohesion Moisture HA - Hand Auger A - Flight Auger Drill Rig
VL - Very Loose S - Soft W - Wet Unified Soil Classification Symbols: CL, SM, SW
L - Loose F- Firm M - Moist SP - Soil Profile
MD - Medium Density ST - Stiff D - Dry Some< 15%
D - Dense VST- Very Stiff Trace< 5%
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HARD ROCK GEOTECHNICAL PTY LTD Consulting Geotechnical Engineers
LOCATION PLAN
File: 191469
Date: 20/11/2019
Figure 1
Project: 318-320 Smith Street, Collingwood
Scale:
Not to Scale (sketch for borehole locations)
Legend:
Borehole
Footing inspection
BH1
BH3
BH2
HARD ROCK GEOTECHNICAL PTY LTD Consulting Geotechnical Engineers
ABN: 24 066 600 002
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Please note these parameters are difficult to measure and exhibit large natural variations. Sound engineering judgement is recommended in their use.
Appendix A - 318-320 Smith Street, Collingwood
Material
Design Parameters
Po
isso
n’s
Ra
tio
Dra
ined
Yo
un
g’s
Mo
du
lus
E´
(MP
a)
K0 Kp Ka
Drained Undrained Moist
bulk
weight
γ (kN/m3)
Saturated
bulk
weight
γsat
(kN/m3)
(1 -
sin
´)
(1 +
sin
´)
(1 -
sin
´)
(1 -
sin
´)
(1 +
sin
´)
c´ (kPa) ´ (°) Cu (kPa) (°)
FILL (loose) & top soils 0 28 0 28 17 20 0.1-0.2 1-5 0.53 2.76 0.36
silty CLAY (stiff)
including extremely weathered siltstone
ROCK
3 25 100 0 19 19 0.2- 0.4 8-15 0.58 2.46 0.41
Distinctly weathered siltstone ROCK
(high to moderately weathered)
3
(joint
strength)
25
(joint
strength)
0 37 24 24 0.2-0.3 150-500 0.58 4.02 0.41