Appendix D Geotechnical report · MCU18/0013

Page 2

Soil Surveys Engineering Pty Limited Directors

ew, Specialists in Applied Geotechnics PJ Dixon BE(Hons) RPEQ
A.B.N. 70 054 043 631 PR Cosh BE(Civil) CPEng MIE Aust RPEQ.
www.soilsurveys.com.au NT Perkins BAppSc(AppGeol) BEng(Hons1)
ay MV Geale BEng(Civil) MBA CPEng MIE Aust RPEQ
GEJ Gray
SOIL SURVEYS Associates

PElkington BE(Civil)

AM Rutten  BE(Honst) MEngSc LGE CPEng
MIE Aust RPEQ

SLGamble BE(Geol) CPEng MIE Aust RPEQ

Sunshine Coast Office
REF: 304-2014
Author: Brett Egen

30th November, 2004

Gabriel & Elizabeth Poole Design Company
PO Box 1158
NOOSAVILLE QLD 4566

ATTENTION: MR DAN SPARKS

 

Dear Sir,

RE: GEOTECHNICAL INVESTIGATION - PROPOSED RESIDENCE
26 ARAKOON CRESCENT, SUNSHINE BEACH

Enclosed is one copy of our report for the above project dated March, 2003. Three copies of
the report have been issued to Gabriel & Elizabeth Poole Design Company.

Authority to proceed with the investigation was received from Dan Sparks of Gabriel &
Elizabeth Poole Design Company dated 19" October, 2004.

Should you have any queries regarding this report, please do not hesitate to contact Stephen

Gamble at our Sunshine Coast Office.

Yours faithfully,

R. COSH (RPEQ 1821)

jhe

for and on behalf of
SOIL SURVEYS ENGINEERING PTY LIMITED

 

 

Brisbane Gold Coast Sunshine Coast

Level 2, 19 Finchley Street Unit 9, 39 Lawrence Drive 11 Production Avenue
Milton Qid Nerang Qid Kawana Waters Qid
PO Box 317 PO Box 2743. PO Box 2

Paddington Qld 4064 Nerang Qld 4211 Buddina Qid 4575
Australia Australia Australia

Ph 617 3369 6000 Ph 617 5596 1528 Ph 617 5493 1980
Fax 617 3369 6660 Fax 617 5578 3916 Fax 617 5493 2837

[email protected] [email protected] [email protected]

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TABLE OF CONTENTS

1.0 INTRODUCTION  ...........0 0.00 c cece cette eee
2.0 SCOPE OF GEOTECHNICAL SERVICES ...............-.
3.0 PROPOSED DEVELOPMENT ...............-..-++++55+++
4.0 GEOTECHNICAL INVESTIGATION ..............-+-++++++

4.1 Field Investigation ........... 0.0.60. cece cece eee
4.2 Site Description .......... 0.66.5 c eects
4.3 Laboratory Testing ........... 0.6.06 c eee eee e tenes
5.0 GEOTECHNICAL MODEL .................0.000 cece eee
5.1 Subsurface Profile ............ 0.6 ccc cece eens
5.2 Groundwater ........... 0500 e ccc eee nee ene
6.0 ENGINEERING ASSESSMENT .................-.-.50+55+
6.1 Traffickability and Site Preparation ................+++5+:
6.2 Earthworks .......... 0.00 ccc nets
6.2.1 General ...... 20.000.

6.2.2 Subgrade Preparation ............+-+.++ see ee eens

6.2.3 Fill Material ...........0. 0000 cece cence eee

6.2.4 Compaction Standards ..............+-+++0+ +5000

6.2.5 Earthworks Supervision .............-.00.0002000+

6.2.6 Excavation Characteristics ...............0..000es

6.2.7 Batters ©... 0... ent nnees

6.3 Building Foundations ...............-+ +2 see eee e eee ees
6.3.1 Site Classification .............0 0060 cece eee eee ee

6.3.2 High Level Footings ...........+-+:++s+e rece ences

6.3.3 Raft Foundation ............00. 00 c cence eee eee es

6.3.4 Deep Foundations .............0.0e cece eee eee

6.3.5 Construction Considerations ............-.++++++-

6.4 Slab On Ground ..........0. 0.60 c cece eens
6.4.1 General ........ 0.00 ccc nents

6.4.2 Sub-BaSe 0.0... tenets

6.5 Retaining Walls ............ 6.02 c cence ene
6.5.1 General .... 0.0... ccc eee eens

6.5.2 Pressure Distribution ..............00 0c cece eres

6.5.3 Water Regime ........... 6.620. e cence eee

6.5.4 Construction Considerations .............-..+++++

6.5.5 Construction Details ............ 6.660 c cece eee

7.0 CONSTRUCTION INSPECTION .............-..0000 000 eee
8.0 LIMITATIONS. ........... 000. c cece cnet es

Page 4

TABLE OF CONTENTS

APPENDICES

A __ Notes Relating to this Report

B Borehole Records

Cc Site Plan

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1.0

2.0

INTRODUCTION

This report presents the results of the geotechnical investigation carried out by Soil
Surveys Engineering Pty. Limited at the site of the proposed residence at 26 Arakoon

Crescent, Sunshine Beach.

The objective of this investigation were to assess subsurface conditions at the site in

accordance with the Scope of Services detailed in Section 2.0.

SCOPE OF GEOTECHNICAL SERVICES

The scope of geotechnical services provided by Soil Surveys Engineering Pty Limited

was directed towards evaluating the following items.

* Investigation of the subsurface profile at the proposed location area by drilling,
sampling and in-situ testing with four (4) boreholes.
* Engineering analysis of site investigation and laboratory test results to evaluate:-
- Foundation and slab recommendations
- Retaining wall design recommendations
- | Recommendations on site preparations
- Construction recommendations (where applicable)

PROPOSED DEVELOPMENT

 

We understand that a three-storey residence is proposed. Based on the architectural
plan included with the brief, the proposed building is to have suspended slab floors with

the ground floor supported on deep foundations.

Significant earthworks are expected for the proposed development, with a 6m retaining

wall proposed along the western site boundary adjacent to Arakoon Crescent.

 

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4.0 GEOTECHNICAL INVESTIGATION

 

4.1 Field Investigation

Subsurface conditions at the site were investigated by drilling and sampling a total of four

(4) boreholes to depths of between 3.3m and 12.0m.

Two (2) boreholes were drilled to depths of 12.0m, where access was permitted for our

Gemco HP7 top drive rotary drilling rig mounted on a 4x4 Mitsubishi Canter truck.

In addition, where vehicle access was not permitted, two (2) boreholes were drilled to
depths of 3.6m (HA3) and 3.3m (HA4) using hand auger equipment. Dynamic cone
penetrometer (DCP) tests were carried out adjacent to the hand auger boreholes to

depths of 5.0 meters.

The classification of soils in the field is subjective, based on the experience and
judgement of the supervising geotechnician and some variations in the soil description,

from the actual material type may occur.

The soil classification descriptions, field and laboratory testing were carried out in general

accordance with the following Australian Standards.

° AS.1726 - 1993 Geotechnical Site Investigations
. AS.1289 Methods of Testing Soils for Engineering Purposes

A description of the investigation method, borehole records and a site plan showing the

location of the boreholes are included in the Appendices.

4.2 Site Description

The site is located at 26 Arakoon Crescent, Sunshine Beach. The site is on the eastern
side of the street. At the time of the investigation, the land was seen to slope down from
the street frontage at an angle of approximately 20 degrees, and became relatively level
at the bottom of the site. The ground surface was partially grassed with medium sized
trees located adjacent to the access track which traversed down across the site from the

street frontage.

 

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Photograph 1 taken from the northern boundary indicates typical site conditions.

 

 

 

 

 

PHOTOGRAPH 1

4.3 Laboratory Testing

Due to the sandy nature of the subsurface profile, laboratory testing was not required for
this investigation. The nature of the soils was measured by field testing only.

5.0 GEOTECHNICAL MODEL

5.1 Subsurface Profile

The subsurface profile encountered in the two deep drilled boreholes consisted of fine to
medium grained sand inferred to be deposited as a beach ridge dune. The consistency of
the sand was seen to be medium dense sands for the upper 3.5 to 3.8 meters overlying
dense to very dense indurated sand. Dense to very dense sand was encountered at
depths of 5.7m and 6.3m beneath the indurated sands,.

The hand auger boreholes encountered similar fine to medium grained sand, but with
some gravelly sand fill material to a depth of 0.85m in borehole HA3. Dynamic cone
penetrometer soundings indicate medium dense sand conditions to depths of between
4.8m and 4.9m and becoming dense below this level.

A summary of the subsurface profile is presented in Table 1 with detailed borelogs
included in Appendix B.

 

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November, 2004 Page 4
TABLE 1 SUMMARY OF THE SUBSURFACE PROFILE
Material BH 1 BH2 HA3 HA 4
Fill (Gravelly Sand)|Medium Dense to Dense - - 0.00 - 0.85 -
(m)
Natural SAND (m) |Medium Dense 0.00 - 3.80] 0.00 - 3.50} 0.85- TD | 0.00 - TD
Dense to Very Dense 3.80-TD | 3.50- TD - -
Borehole Termination (m) 12.00 12.00 3.60 3.30
DCP Termination (m) - - 5.20 5.10

 

 

 

 

 

 

 

5.2 Groundwater

Groundwater was not encountered in the boreholes at the time of the investigation.
However, some seepage through the upper material may occur following periods of

extended heavy rainfall.

 

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6.0

ENGINEERING ASSESSMENT

 

6.1 Traffickability and Site Preparation

At the time of the field investigation, the site was only accessible (by vehicle) using the

existing access track which crosses the site diagonally from the street frontage.

Traffickability problems may be further exacerbated with the disturbance of the upper

level soil fabric with removal of vegetation.

It is recommended that after stripping, clearing and grubbing, the exposed surface in the
construction area be proof rolled and compacted to improve traffickability., although it is
noted that this would only apply to the lower parts of the site where excavation is minimal.

Maintaining adequate surface drainage conditions is essential to ensure that runoff is

diverted away from the construction area to prevent erosion.

The contractor should fully inform himself of the ground conditions, on site, prior to
commencement of earthworks. This requirement should be explicit in any earthworks

specifications or contract.

6.2. Earthworks

6.2.1 General

It is understood that the proposed earthworks will consist of cuts of up to 6.0 meters to

establish the proposed building platform.

Earthwork procedures should be carried out in a responsible manner in accordance with
AS.3798-1996 “Guidelines on Earthworks for Commercial and Residential

Developments".
6.2.2. Subgrade Preparation

Subgrade preparation procedures should include the following:-

* Clearing, stripping and grubbing should be carried out in areas subject to
earthworks. Also all soils containing organic matter should be stripped from the
construction area; this material is not considered suitable for use as structural fill.

* Depressions formed by the removal of vegetation, existing structures, underground
elements etc. should have all disturbed weakened soil cleaned out and be backfilled

with compacted select material.

 

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The subgrade should be proof rolled (where appropriate) under the supervision of
Soil Surveys Engineering using a vehicle with a tare of at least 5 tonnes and then
compacted to the required degree. In areas of cut, proof rolling may be deferred
until after the cut operation. Areas demonstrating excessive movement should be
treated (dried and recompacted) or removed and replaced with compacted fill.
Treatment should be to a standard sufficient so that the subgrade passes proof

rolling and that compaction can be achieved in the first layer of fill.

6.2.3 Fill Material

While it is noted that significant filling is not anticipated, backfilling around the proposed

in-ground water tank should be carried out in accordance with AS.3798-1996, and the

following should be noted:

The insitu soils, where free of organic and deleterious material, may be used for
structural fill provided the moisture content of the soils on placement approximates
the optimum moisture content required for compaction. This may require
conditioning to bring the soils to optimum.

Any imported fill, if needed to make up earthwork deficiencies, should have a soaked
CBR of not less than 10 percent and a maximum aggregate size of not greater than

75mm with not more than 20% greater than 20mm.

6.2.4 Compaction Standards

Guidelines for minimum relative compaction values for insitu soils and imported fill for the

building and pavements are presented in Table 2.

 

 

 

TABLE 2 COMPACTION RECOMMENDATIONS
Location Minimum Density Index
Building Area 70

 

 

 

 

* 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.3798-1996, Section 8.0.

Backfilling for service trenches etc. should use good quality material free of organic
and deleterious matter, either select fill won from site or imported fill. The backfill
should be placed in uniform layers over the full width of the excavations with the
layers not exceeding 200mm thickness, loosely placed. The backfill material should
be compacted to the specifications outlined above for insitu or imported cohesive

material.

 

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6.2.5 Earthworks Supervision

Given the building type and the nature of the earthworks operation associated with the
in-ground water tank, it is recommended that earthworks operations be carried out under

geotechnical engineering supervision as set out in Appendix B of AS.3798-1998.

It should be made clear in any earthworks specification as to what is actually required of
the Engineer/Supervisor/Geotechnical Testing Authority to provide in terms of

certification.

It is recommended that the following objectives (as a minimum) be incorporated into the

earthworks specification:-

* Certification that all general earthworks operations (ie. stripping, proof rolling of
subgrade, etc.) have been carried out in accordance with the earthworks

specification.
* Certification that uncontrolled fill has been replaced (if required) and compacted to

the required minimum density in accordance with the earthworks specification.
° Certification that the controlled fill material is suitable to support a conventional slab

on ground floor (slab loads of 10 to 15kPa).
* Certification that the quality of any imported fill complies with the earthworks

specification requirements.

Engineering certification should be provided by a Registered Professional Engineer of

Queensland.
6.2.6 Excavation Characteristics

It is anticipated that excavations will consist of the following:-

* Bulk Cuts - for site stripping and excavation to create basements, building platforms
and carpark/driveway areas.
*  Trenching - for high level footings and underground services.

* Drilling - for bored pier foundations.

Excavations on site should be within the capabilities of light plant, small dozer (Cat D4c
or similar) in bulk cuts and a medium sized backhoe (Case 580 or similar) or small
excavator (12t - 15t) in trenching, based on the investigation findings. Should substantial

excavations be required, larger plant could be budgeted to expedite workings.

 

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6.2.7 Batters

Maximum batter angles for different material types are outlined in Table 3 for the
unsurcharged temporary cut and fill batters less than 3m high on the site. Where
surcharges (eg. footings, live loads, etc.) are located within H (height of batter) of the top
of the batter, then some reduction in design angle will occur. Steeper batters are
possible with suitable surface protection such as stone pitching, etc. or by use of
retaining structures (temporary and permanent). Fill batter slopes are dependent on

suitable compaction being achieved.

TABLE 3 BATTER ANGLES (Slopes less than 3m high)

 

Material Batter Angle
Loose Sand 24 degrees (1V:2.25H)
Medium Dense Sand 26 degrees (1V:2H)
Dense to Very Dense Sand 28 degrees (1V:1.9H)

 

 

 

 

 

Notes:
1. These values assume no seepage. If seepage is present the recommended angles would need

to be significantly reduced or the use of dewatering considered.
2. Subject to inspection by an experienced geotechnical engineer/engineering geologist.

 

 

 

It is essential that any batters be suitably protected from erosion and scour by
appropriate drainage and placement of plastic or hession sheeting, etc. Pavement runoff
should not be allowed to discharge directly across the batters without suitable scour

protection.

6.3 Building Foundations
6.3.1 Site Classification

While a site classification in accordance with AS.2870 ‘Residential Slabs and Footings'
relates to conventional residential type construction and is not directly applicable for this

development, it is, however, a valuable method of classification.

Given the sandy nature of the site, the site may be designated Class 'A’ (non reactive) in
accordance with AS.2870.1-1996 'Residential Slabs and Footings’, where ground surface

movement is not expected to occur with changes in soil moisture content.

It is recommended that the designers satisfy themselves that the use of AS.2870 is

applicable for the proposed design.

 

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6.3.2 High Level Footings

Table 4 outlines allowable bearing capacities for high level footings on the site.

TABLE 4 ALLOWABLE BEARING CAPACITIES FOR HIGH LEVEL FOOTINGS

 

 

 

 

 

Material Allowable Bearing Capacity (kPa)
Strip Footing Pad Footing
Sand - Loose NR NR
- compacted to 70% Density Index 125 150
- Medium Dense 125 150
- Dense 200 250
- Very Dense 350 500

 

 

 

 

The base of all pad and strip footings should be individually recompacted using a
vibrating plate compactor prior to placement of reinforcing steel and concrete as soils

may be loosened during the excavation process by machinery action.

If the sand is dry, it should be saturated and left for a short period prior to vibration.
Should any loose areas be encountered in the footing excavations the density of these
areas must be improved. If any doubt exists as to whether ground improvement has
achieved the required density of 70% density index for support of the proposed building
loads, further testing in the way of dynamic cone penetrometer tests should be carried

out to confirm the adequacy of the founding soils.
6.3.3 Raft Foundation

Where sensitive and heavy masonry construction is proposed, consideration may be
given to the use of a raft foundation to reduce the effects of the differential settlements.

Compaction of the sand foundation as per high level footings is recommended.

Due to the raft size, bearing capacity failure is unlikely, however to limit local
overstressing a maximum design allowable bearing pressure of 125kPa should be
adopted based on 70% density index being achieved for a minimum distance of 1.0m

below foundation level.

Rafts have an advantage over individual strip and pad footings in that the effect of an

isolated loose area is much less under a raft than under an individual strip or pad footing.

 

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Footing bases should be individually recompacted, eg. by vibrating plate compactor, to
remedy disturbance of the sand foundation during excavation. Testing of footing bases is
recommended to confirm the compaction status of the foundation. If footing beams
cannot be cast on the same day as excavation, a concrete blinding layer of at least

50mm thickness is recommended across the footing base.
6.3.4 Deep Foundations

Deep foundations using piles are considered as an alternative solution for the proposed
residence. The choice of suitable pile types should be made from non-vibration piling

methods.

Push-in preformed piles, continuous flight auger (CFA) or bored piles are considered
suitable pile types, although the construction of the latter may be problematic in loose

sand, where collapse of the pile hole is likely.

Depending on the load requirements, and the piling contractors design, it is
recommended that the piles are founded in material which is at least medium dense, and

at a minimum depth of 3m below existing ground surface.
The design of piles in cohesionless soils may be carried out using the following method:
Ou =Q0+Qs ultimate pile resistance
where:

QO» =Ap-Pa- (Ng -1) ultimate base resistance

QO; =As+pa+ Ks + (tand) ultimate skin friction

As;= area of pile shaft

Ap= __ areaof pile base

Pa= effective overburden pressure at depth d
Pa= average effective overburden pressure
K,= lateral earth pressure coefficient

6 = __ pile-soil angle of friction

N,= bearing capacity factor

(Nq = 60 for medium dense sands, N, = 100 for dense sands)

 

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Broms (1966) relates the lateral earth coefficient (K) and pile-soil friction angle (6) to the

internal angle of friction of the soil (¢)and pile material as follows:

 

 

 

 

 

TABLE 5 LATERAL EARTH COEFFICIENTS
Pile Material 3 Ks
Loose Medium Dense Dense
Steel 20° 0.5 0.75
Concrete 0.75*¢ 1 1.5 2

 

 

 

 

 

 

 

It should be noted that the calculated ultimate resistance of a given pile should also take
into account the installation effects of that particular type, i.e. whether displacement or

non-displacement pile performance can be expected.

According to the limit state design approach in AS2159-1995 (Piling Code), the design
geotechnical strength R,* is calculated by multiplying the ultimate geotechnical strength
Rug (which is equivalent to Q. above) by the geotechnical strength reduction factor ($s).

For static design for piles on this project, we would consider $y = 0.45 to be appropriate.

Uplift and lateral capacities of piles are not considered, as these are both wholly

dependent on the specific pile type selected.

6.3.5 Construction Considerations
Inspections

It is recommended that inspections be undertaken by an experienced and qualified
geotechnical engineer following footing excavations to confirm the adequacy of the
founding soils. Inspections should be carried out prior to placement of reinforcing steel

and ordering of concrete.

Underground Services

Where footings are located adjacent to underground services, the footings should extend
to base a minimum of 200mm below the trench base level for a distance of 1.0m out from
the trench. Beyond 1.0m the footings should be taken a minimum of 200mm below an

imaginary line drawn up at 45° from the trench base level (Figure 1).

 

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These requirements do not override minimum footing levels.

(— >

 

 

1
. 1 &<
Service [4 ss

Trench £ 7

Found footings
below these lines

 

 

 

 

 

\ FIGURE 1 )

High Level Footings

 

 

It is recommended that the footings be poured as soon as possible following excavation.
Where the footings cannot be poured within a short period of time it is recommended that
a blinding layer of concrete, at least 50mm thick, be placed immediately following

excavation, cleaning and inspection of the footing bases.
Piles

As mentioned above, both cast insitu or preformed piles may be suitable on this site.
However, given the sandy soils, it is unlikely that unsupported bored pile excavation could
be successfully achieved. Casing or other forms of hole support would be necessary for
conventional bored piles. Continuous flight auger (CFA) piles may be a suitable
alternative cast insitu type pile. This type has the advantage of not requiring any casing

or other support, even when drilling loose sand.

Preformed driven or pushed piles may also be suitable, however the environmental
constraints that may be present at this site might preclude driven piles due to the noise
and vibration associated with this method. Pushed-in piles avoid these problems, but a
push-in rig of sufficient reaction capacity may not be able to successfully negotiate the

sloping site.

 

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6.4 Slab On Ground

6.4.1 General

The field test results indicate that the existing natural soils, along with any controlled fill,
are suitable for slab on ground construction provided that site preparation earthworks are

carried out in accordance with recommendations in Sections 6.1 and 6.2.

In addition, as noted in Section 6.3.1, the slab on ground floor should be designed to

accommodate the anticipated potential ground surface movement.

6.4.2 Sub-Base

It is suggested that a 150mm layer of sub-base be provided under all concrete slabs.
The sub-base material should be compacted to a density not less than 95% of maximum
dry density in accordance with AS.1289 5.2.1 (Modified compaction). The sub-base is

provided under a concrete slab to:-

* Provide a stable ‘working platform’ on which to operate construction equipment;

* Facilitate the provision of a uniform bearing surface under the slab.

Sub-base material should be of good quality conforming to requirements (minimum) of
Material Type 2.4 as specified in the Queensland Department of Transport, Standard
Specification MRS 11.05, Unbound Pavements (December, 1993).

6.5 Retaining Walls
6.5.1 General

It is understood that retaining walls would be required for the construction of the
proposed ground floor. We understand the expected maximum retained height will be up

to 6 metres.

The lateral earth pressure distribution that effects the retaining walls on the site will

depend upon the following parameters :-

¢  Insitu and backfill material properties

* Design water regime at the rear of the wall
¢ Wall and cut geometry

* Surcharges effecting the wall

¢ Wall type

* The structural bracing of the wall and the timing of backfilling behind the wall

 

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Given that the excavation is expected to be up to 6m deep, a braced retaining wall will be
required. This retaining wall should be installed prior to excavation to ensure stability of

the sandy profile.

Several types of retaining walls could be employed including steel sheet piles, contiguous
CFA piles or diaphragm wall. Each of these have relative advantages and disadvantages
(technical and economic) which are best evaluated at the detailed design/tender stage.

6.5.2 Pressure Distribution

In designing the retaining wall, consideration should be given to the following:-

* For cantilever walls, which allow some movement at the top, (ie. at least 0.001H in
sand) the active case (Ka) applies with a triangular distribution in both the short and
long term situations.

* For cantilever walls which cannot tolerate this movement, the at rest case (Ko)
applies with a triangular distribution in both the short and long term situations.

* For structurally braced walls the wall design should be checked for both a
trapezoidal (short term conditions) and triangular distribution with Ko values (long

term conditions).

The pressure distributions as referred to above are shown in Figures 2 and 3. The
parameters selected for use in the figures are dependent on the preconstruction
geometry of the face being retained. Where the material has been cut using the
recommendations (or a flatter) as outlined in section 6.2.7, the backfill parameters will

control. Where a steeper angle is used the earth parameters will control.

The lateral pressure distributions shown in Figures 2 and 3 include hydrostatic pressure
and show typical surcharge loadings pressure distribution. It is recommended that where
the retaining walls are expected to be surcharged (eg. by footings, traffic loads, sloping
ground surface, etc.) Soil Surveys Engineering should be contacted to provide a

recommended lateral earth pressure distribution.

As a general guide (using an elastic model) line loads located 2.5H away from the wall
(where H is the wall height) results in lateral forces of less than 10% of the line load.

Parameters for assessment of lateral earth pressures are outlined in Table 6.

 

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November, 2004 Page 15
(— TRIANGULAR DISTRIBUTION \
Lateral Earth Pressure Lateral Pressure Due to Surcharge

 

   

 

 

 

KyH + hwy w(1-K)

K = appropriate earth pressure coefficent UDL Point Load or

H = Vertical height of the wall ( ‘
hw = Height of design water table Strip Footing
Y = Soil bulk density (kKN/m3)

yw = Water bulk density (kKN/m3)

. —
r ‘

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TRAPEZOIDAL DISTRIBUTION
Lateral Pressure
Hydrostatic Due to Surcharge
Pressure
H + + +
0.65 KayH
hwy
Sand or Gravel UDL Point Load or
Strip Footing

 

 

LO FIGURE 3 —

 

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November, 2004 Page 16
TABLE 6 RETAINING WALL DESIGN PARAMETERS
Material Density Earth Pressure Coefficient Long Term
(kNim’) Flat Top Slope Top Slope 1V:4H__ | Drained
(degrees)
Ka Ko Ka Ko
Compacted Fill * 19 0.41 0.58 0.46 0.76 25
Fill? 17 0.27 0.43 0.31 0.56 35
Loose Sand 17 0.33 0.50 0.37 0.66 30
Medium Dense Sand 18 0.29 0.46 0.33 0.60 33
Dense Sand 20 0.27 0.43 0.31 0.56 35
Very Dense Sand 22 0.21 0.36 0.27 0.47 40
Notes:
1. If fill is compacted against a retaining wall the actual earth pressure could exceed the vertical
pressure (ie. Ka > 1.0).
2. Infers granular free draining material placed behind the retaining wall as a drainage layer.

 

 

6.5.3 Water Regime

Not withstanding the absence of groundwater in all the boreholes and due to possible
long term problems with blocking of gravel filters and drains and short term storm
conditions that could flood the fill behind retaining walls, it is recommended that all
retaining walls be designed for some water pressure distribution. A suggested water
pressure distribution for retaining walls on this site would be one third height water

pressure.
6.5.4 Construction Considerations

A suitable temporary support system must also be determined to ensure the stability of

the retaining wall during excavation for the proposed basement.

It is expected that temporary ground anchors would be required to provide lateral
restraint for the wall. In the long term, this lateral restraint would be provided by the

basement slab floors propping the wall.

It is expected that the temporary anchors would be installed in several rows, at staged
intervals during the excavation of the basement. The design of number of rows, spacing
of anchors and required anchor capacity, would be determined by the retaining wall

designer.

 

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6.5.5 Construction Details

With all retaining walls, it is essential that adequate drainage be provided behind the wall.
Any backfill placed behind the wall should be loose granular material. The backfill should
not be heavily compacted since research has shown that compaction can raise the earth
pressure to above the ‘at rest’ pressure. A permeable geofabric should be placed
between the natural soils and the loose granular backfill to prevent fine material piping

out of the natural soils and blocking the backfill.

During installation of any retaining walls, the insitu soils should be battered back to
minimise fall-in and subsequent disruption of works. Temporary batter angles are given
in Section 6.2.7. Suitable precautions to satisfy Health & Safety requirements must also

be adhered to; a maximum unsupported height of 1.5m is recommended.

CONSTRUCTION INSPECTION

 

It is recommended that placement of all structural fill, footing excavations, and cut batter
slopes in soil together with building subgrades should be inspected by Soil Surveys
Engineering Pty Limited. or a duly qualified Geotechnical Engineer. Should subsurface
conditions other than those described in this report be encountered, Soil Surveys
Engineering Pty Limited. should be consulted immediately and appropriate modifications

developed and implemented if necessary.

 

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Project No. 304-2014
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8.0 LIMITATIONS

We have prepared this report for the use of GABRIEL & ELIZABETH POOLE DESIGN
COMPANY, for design purposes in accordance with generally accepted geotechnical
engineering practices. No other warranty, expressed or implied, is made as to the
professional advice included in this report. This report has not been prepared for use by
parties other than GABRIEL & ELIZABETH POOLE DESIGN COMPANY or their
associated consultants. It may not contain sufficient information for purposes of other

parties or for other uses.

Soil Surveys Engineering offer a documentation review service to verify that the intent of
geotechnical recommendations is properly reflected in the design. It is recommended

that the client avail themself of this service; our standard rates will apply.

4
/
[re
/P. R. COSH (RPEQ 1821) S. L. GAMBLE (RPEQ 6644)
PRINCIPAL ENGINEER SUNSHINE COAST MANAGER

for and on behalf of
SOIL SURVEYS ENGINEERING PTY LIMITED

 

 

# SOIL SURVEYS ENGINEERING