michael adler and associates consulting geotechnical

MICHAEL ADLER AND ASSOCIATES

Consulting Geotechnical Engineer PO Box 91

Church Point, NSW 2105

AUSTRALIA

Tel: +61 (0)412 904 349

Fax: (02) 9999 5770

Mobile: 0412 904 349

EMAIL: [email protected]

Wednesday, June 23, 2021

Our Reference: 21/06795

G K N Developments Pty. Limited

308 Woolooware Road

Burraneer, NSW 2230

Attention: Geoffrey Mailey

Dear Sir

Geotechnical Assessment for

Proposed New Residential Development

Nos. 5 to 9 Prince Street, Cronulla

Background

This report presents a geotechnical assessment and site classification for Nos. 5 to 9 Prince Street,

Cronulla. The work was requested by Mr. Geoffrey Mailey of GKN Developments Pty. Limited.

The purpose of the assessment is to provide preliminary information on:

w The likely subsurface conditions below the site

w Allowable bearing pressures for foundation design

w Excavation and shoring conditions

w Retaining wall design parameters

w Depth to groundwater

w Site classification.

It should be noted that this is not a contamination investigation.

No detailed subsurface investigation has been undertaken. The following comments are based on

observations made both on-site and in the local vicinity as well as our experience with similar

geotechnical environments in the immediate area. This current assessment has been prepared on the

understanding that once the existing development is demolished boreholes and Cone Penetration

Testing (CPT) will be undertaken prior to construction. CPT is a specialised geotechnical insitu test

method that continuously with depth measures the strength of the underlying soils.

Proposed Construction

We understand that at this site it is proposed to construct a new five storey residential development.

The structure will comprise two attached towers. There will be two levels of basement car park below

the building This will require excavation to a maximum depth in the order of 6 m below the existing

ground surface. The bottom basement slab will be at RL 10.8. A ramp will provide access to the car

park from Mitchell Road.

The construction will be reinforced concrete walls and floor slabs.

During construction the proposal is to support the excavation using contiguous piling installed around

the perimeter of the new basement. A capping beam with bracing will be used as temporary support of

the top of this shoring. These piles will form the permanent retaining walls and will be ultimately be

supported by the basement and ground floor slabs.

Present Site Conditions

The site is located on the sand dunes immediately north east of North Cronulla Beach. It is some 50 m

west of the beach that fronts the Tasman Sea (Pacific Ocean).

Nos. 5 to 9 are located at the northern, uphill side of Prince Street. Mitchell Road forms the western

boundary. There is a relatively new three storey block of units to the south. This extend to within 6 m

of the common boundary. There is an open car park on the northern boundary.

The combined blocks are approximately rectangular in shape, some 34 m by 56 m in overall plan

dimensions. It is generally level with an overall fall across the site of some 0.5 m down to the south.

The land on the eastern side of Prince Street falls relatively steeply down to North Cronulla Beach

The existing development comprises three number two storey blocks of flats, one located on each lot.

All three are situated close to the centre of their respective lots. These structures are exhibiting no

significant signs of distress in their external walls. The remaining areas are either paved or vegetated

with gardens, lawns and a small number of shrubs.

Geology and Subsurface Conditions

Reference to the Wollongong geological series sheet, at a scale of 1:100,000, indicates that the area is

underlain by Quaternary Age fine to medium grained marine quartz sand deposits with minor shell

content. These are sand dunes typically associated with the adjacent beach development. This overlies

Triassic Age Hawkesbury Sandstone often at considerable depth. Both our experience and observations

of constructions works in the vicinity confirm these conditions.

We were involved with a geotechnical investigation at Nos. 2 to 4 Marlo Road which is some 20 m

west of Nos. 5 to 9 Prince Street. During that investigation six boreholes were drilled down to a

maximum depth of 12 m.

Copies of the logs for these boreholes, the results of adjacent penetrometer testing and a location plan

are attached together with notes that describe the terms used both in this report and on the logs.

5 to 9 Prince Street, Cronulla Wednesday, June 23, 2021

Michael A Adler

The boreholes at Marlo Road encountered similar conditions namely clean fine to medium grained

natural sand to the maximum depth investigated, 12.0 m. These extended down to RL 0, which is some

11 m below the proposed basement level for the Prince Street development.

The results of the Perth Penetrometer testing indicate that at the boreholes the sands generally varied in

relative density from loose to dense down to some 6 m depth. There were occasional very loose and

dense bands above this depth. The penetrometer refused in dense to possibly very dense sand below

say RL 6.0.

Groundwater was not observed in any of the boreholes. A piezometer was installed in one of the

boreholes at 8 m depth. This was dry 8 days after installation. Experience indicates that the ground

water table in this vicinity is usually controlled by the sea level in the adjacent ocean. There is the

possibility that the ground water table could raise locally due to seasonal affects.

Comments on Geotechnical Conditions

The following comments are based on the assumption that the conditions encountered in the boreholes

are representative of the subsurface conditions at this site. When making an assessment of the

subsurface conditions across a site from a limited number of test locations it should be recognised that

variations may occur between these locations. The data derived from the site investigation program are

extrapolated across the site to form a geotechnical model and then an engineering opinion is provided

about overall subsurface conditions and their likely behaviour with the proposed development. The

actual conditions may differ from those inferred herein. No subsurface exploration program, no mater

how comprehensive, can reveal all subsurface details and anomalies, especially in areas such as this

where there has been previous development. The investigation on the adjacent property did not

penetrate down to the underlying the rock surface. The conditions below 12 m depth are therefore only

inferred at this time, based on our experience in the area.

The subsurface conditions described above are typical of those found in this part of southern Sydney.

As noted before it is expected that the sands will be underlain by sandstone at depth. Occasionally

cemented bands, locally known as 'Coffee Rock', are found in these sand deposits.

It is important to note that the following comments should only be treated as preliminary. It will be

necessary to drill a limited number of boreholes on this site after the existing development is

demolished and there is clear access for an investigation rig. This will allow the subsurface conditions

assumed in this report to be confirmed. CPT testing is also planned after demolition. This testing will

provide important data required for the design of both the shoring piles as well as for the design of

other parts of the permanent foundations.

Site Classification

The site has been classified in accordance with the guidelines set out in the "Residential Slabs and

Footings", AS2870-1996.

Based on the subsurface conditions observed at Marlo Road the site is classified as a Stable (A) site

provided all footings bear below the very loose sands.


Michael A Adler

Excavation Conditions

Care will be required to ensure that the excavation, both in the long and short term, does not endanger

any adjacent development, including the roads and car parking areas to the east, west and north. The

existing adjacent structure to the south is 6 m from the common site boundary. The proposed

excavation will extend to within some 7 m of this building to the south. Many structures have been

damaged in this area of Sydney when adjacent buildings are being constructed, often when there is a

basement excavation.

We expect that the excavation will generally encounter loose and medium dense or dense sand for the

entire depth. The sands can usually be removed using small earth moving equipment such as a bob cat,

tractor mounted backhoe or excavator.

Retaining Wall Design

The sides of the excavation will be in sand and will not stand vertically unsupported even for short

periods. They will have to either be laid back or shored. Adequate support must be provided at all

times to all adjacent development. Particular care must be taken during the excavation process not to

endanger any existing adjacent development including the building to the south and the roadways/car

park.

A minimum excavation slope of 2:1 (Horizontal:Vertical) in sand is suggested for short periods of

time. It is unlikely that it will be practical to lay back the sides of the proposed excavation. Shoring and

permanent retaining wall support must be provided for all vertical excavations.

The shoring and retaining walls can be designed for active earth pressures if movement of the walls

and the land behind is acceptable. Alternatively "at rest" earth pressure conditions are considered

appropriate for stiff walls or when no movement is acceptable. When assessing the earth pressures the

weight of any soil above the top of the excavation must be taken into account. The loading from

adjacent structures must also be included as well as potential water loading that could develop in the

long term.

Cantilevered type piles are not recommended for the shoring as they need to move laterally in order to

develop their capacity. As already noted the proposal is to support top of the shoring piles using a

caping beam and bracing.

Given that such bracing is proposed the design using the at rest earth pressure coefficient is likely to be

appropriate.

Special care will be required to ensure that no sand runs between the individual piles as the excavation

is opened up. Some form of progressive grouting or shotcreting will be necessary as excavation

proceeds to immediately seal up space between all the piles.

The retaining wall could be designed assuming the following preliminary parameters:

At Rest earth pressure (ko) in sand 0.55

Active earth pressure (ka) in sand 0.35

Passive earth pressure (kp) in sand 2.8

Density of sand 19 kN/m3

The above parameters can also be used to design the permanent retaining walls.


Michael A Adler

Care is always required when both designing and installing any shoring/retaining walls. It may be

possible to use bored piers if ground water is not encountered though given the depth of pile required

for shoring a 6 m deep excavation open bored piers may not be practical. Alternatively grout injected

piles are often found to be cost effective for situations such as this. Given the loose nature of the upper

sands and the short distance to adjacent development it is recommended that temporary lining is used

for at least the upper sections if bored piers are used. These piles will also carry the long term building

load and so care will be required to ensure that the base is cleaned out before concreting. The concrete

should be placed as soon as practical after excavation, open pier holes must not be left open over night.

There is the possibility that there may be some long term seepage into the basement, if the groundwater

level was to rise in the future. Also stormwater runoff may flow down the access driveway. Some form

of sump and pump will likely need to be installed at a low point in the basement.

Foundation Design

All foundations should bear in material of similar stiffness, this will help reduce the potential for

differential settlement. Consideration must be given to the possible adverse affects of founding part of

the structures on the piles used for the excavation support at depth and part on high level footings

bearing in looser near surface sands. The present design will likely result in foundations bearing at the

base of the excavation or below, hence the potential for differential settlements will be reduced.

Strip or pad footings can be used provided that they found in the natural sand at the base of the

excavation. A minimum footing width of 0.6 m is considered appropriate, they should also be relatively

stiff to help reduce differential settlement. Footing bearing in medium dense to dense sand that will

likely be encountered at the proposed basement level can be proportioned assuming a maximum

allowable bearing pressure of 300 kPa. This assumes that the underside of the footing is at least 0.6 m

below the adjacent basement level. Consideration could also be given to a raft type foundation.

Shallow strip or pad footing bearing close to the existing ground surface level away from the basement,

excavation with a minimum width and depth of 0.6 m, can be designed assuming an allowable bearing

pressure of 100 kPa. Alternatively if piles are used they should found in the underlying medium dense

sand that will likely be found at a depth of at say 3.0 m below existing ground level. The following

details preliminary estimates of pile capacities:

Pile Diameter Allowable Working Pile Load

for bearing in medium dense sand at 3 m

depth below the existing ground surface.

300 mm 70 kN

450 mm 150 kN

600 mm 260 kN

It is possible that shallow open bored piers drilled down from the present ground surface will be

practical. General comment has already been provided above regarding pile construction for the

shoring.

In this geotechnical environment footing excavations usually loosens the sands. After excavation but

before the foundations are poured it is recommended that the exposed surface below all footings is

compacted using a small roller or wacker packer to ensure that the sand down to a depth of at least

0.5 m below the underside of the foundation has a density index of not less than 65%.


Michael A Adler

FINAL COMMENT

The above classification and suggested preliminary design parameters have been provided on the basis

that the conditions encountered in the boreholes and penetrometers on the near by Marlo Road site are

representative of the subsurface conditions at this site. Should the actual conditions vary from those

assumed a suitably experienced geotechnical engineer should review both the site and this report in the

light of the construction being undertaken. If groundwater is encountered then some the

recommendations made in this report may not be appropriate, in that case specialist alternative advice

must be sought.

As already stated it will be necessary to drill a limited number of boreholes to confirm the above

assumed subsurface conditions. CPT testing is also planned after demolition to provide important data

required for the design of both the shoring piles and other parts of the permanent foundations .

The attached Notes Relating To Geotechnical Report are an intrinsic part of this report.

We do note that we have assumed in our costing for this investigation that you, the client, will contact

us by phone on a number of occasions to discuss the proposed works, especially in regards to the

findings presented in this report. Please do not hesitate to ring our office.

Yours Sincerely

Michael A Adler BSc, BE, MSc, DIC, MIEAust, CPEng


Michael A Adler

Introduction

These notes outline some of the methodology and

limitations inherent in geotechnical reporting. The

issues discussed are not relevant to all reports and

further advice should be sought if there are any queries

regarding any advice or report.

When copies of reports are made, they should be

reproduced in full.

Geotechnical Reports

Geotechnical reports are prepared by qualified

personnel using information supplied or obtained.

They are based on current engineering standards of

interpretation and analysis.

Information may be gained from limited subsurface

testing, surface observations, previous work often

supplemented by knowledge of the local geology and

experience of the range of properties that may be

exhibited by the materials present. For this reason,

geotechnical reports should be regarded as

interpretative rather than factual documents, limited to

some extent by the scope of information on which they

rely.

Where the report has been prepared for a specific

purpose (e.g.. design of a three-storey building), the

information and interpretation may not be appropriate

if the design is changed (e.g.. a twenty storey building).

In such cases, the report and the sufficiency of the

existing work should be reviewed by Michael Adler &

Associates in the light of the new proposal.

Every care is taken with the report content, however, it

is not always possible to anticipate or assume

responsibility for all situations such as:

• Unexpected variations in ground conditions. The

potential for this depends on the amount of

investigative work undertaken.

• Changes in policy or interpretation by statutory

authorities.

• The actions of contractors responding to

commercial pressures.

• Interpretation by others of this report.

If these occur, Michael Adler & Associates would be

pleased to resolve the matter through further

investigation, analysis or advice.

Unforeseen Conditions

Should conditions encountered on site differ markedly

from those anticipated from the information contained

in the report, Michael Adler & Associates should be

notified immediately. Early identification of site

anomalies generally results in most problems being

more readily resolved, and allows reinterpretation and

assessment of the implications for future work.

Subsurface Information

Logs of a borehole, rock core, test pit, excavated face

or cone penetration test are an engineering and/or

geological interpretation of the subsurface conditions.

The reliability of the logged information depends on

the drilling/testing method, sampling and/or

observation spacing and the ground conditions. It is

not always possible or economic to obtain continuous

high quality data. It should also be recognised that the

volume or material observed or tested is only a fraction

of the total subsurface profile.

Interpretation of the available subsurface information

and application to design/ construction should take into

consideration the spacing of the test locations, the

frequency of observations and testing, and the

possibility that geological boundaries may vary

between observation points.

Groundwater observations and measurements not

based on specially designed and constructed

piezometers should be treated with care for the

following reasons:

• In low permeability soils groundwater may not

seep into an excavation or bore in the short time it

is left open.

• A localised perched water table may not represent

the true water table.

• Groundwater levels vary according to rainfall

events or season.

• Some drilling and testing procedures such as rock

coring or penetration testing mask or prevent

groundwater inflow.

The installation of piezometers and long term

monitoring of groundwater levels may be required to

adequately identify groundwater conditions.

Supply of Geotechnical Information For Tendering

Purposes

It is recommended that tenderers are provided with as

much geological and geotechnical information as there

is available. It is best practice to provide copies of all

geotechnical related reports, opinions and data.

[email protected]

NOTES RELATING TO GEOTECHNICAL REPORTS

Michael Adler & Associates

FIGURE 1

Michael Adler and AssociatesAPPROXIMATE LOCATION OF

BOREHOLES & PENETROMETERS2 - 4 Marlo Rd., Cronulla

Project: 16/08694May 2017NOT TO SCALE

BH103

BH102

BH101

N

MICHAEL ADLER & ASSOCIATES GEOTECHNICAL LOG - NON CORE BOREHOLE

Client: Mainsheet Constructions Pty. Ltd Project No.: 16/08694 BOREHOLE NO.: BH101 Project: Proposed New Residential Development Date : 12/5/2017

Location: Nos. 2 to 4 Marlo Road., Cronulla Logged: JK Sheet 1 of 1

CONSISTENCY M

W S (cohesive soils) O

A T A S or I

T A M Y RELATIVE S

E B P DESCRIPTION OF DRILLED PRODUCT M DENSITY T

R L L B (sands and U

E E DEPTH (Soil type, colour, grain size, plasticity, minor components, observations) O gravels) R

S (m) L E

FILL - Silty Sand, dark brown, fine to medium grained, occasional gravel Generally Loose Dry

SAND - Light brown, fine to medium grained SP Loose Moist/

Dry

1.0 Medium Dense

Loose/

2.0 Medium Dense

Medium Dense Moist

Loose

3.0

Medium Dense

4.0

Medium Dense/

Dense

Medium Dense

5.0

Dark Brown

Orange brown

BOREHOLE DISCONTINUED @ 6.0 m DEPTH

No Groundwater Observed Medium Dense/

Dense

NOTES: D - disturbed sample U - undisturbed tube sample B - bulk sample Contractor: STS

WT - level of water table or free water N - Standard Penetration Test (SPT) Equipment: MS

See explanation sheets for meaning of all descriptive terms and symbols Hole Diameter (mm): 100




CONSISTENCY M


A T A S or I

T A M Y RELATIVE S




S (m) L E

FILL - Silty Sand, dark brown, fine to medium grained, occasional gravel Generally Loose Moist/

Dry

FILL - Silty Clay, red brown - orange grey brown, medium to high plasticity,

trace gravel Some hard zones

Moist

Not well compacted

1.0

SAND - Light brown, fine to medium grained Medium Dense

Very Loose

2.0 Loose/

Medium Dense

Medium Dense

3.0

4.0

5.0

Orange brown


No Groundwater Observed







CONSISTENCY M


A T A S or I

T A M Y RELATIVE S




S (m) L E

FILL - Silty Sand, dark brown, fine to medium grained, occasional gravel Generally Loose Dry

Very Dense Zone

SAND - Light brown, fine to medium grained SP Medium Dense Moist

1.0

2.0

3.0

Dense

Medium Dense

Loose/

Medium Dense

4.0

Medium Dense

Loose/

Medium Dense

5.0

Medium Dense


No Groundwater Observed




14/05/2017 PERTH_MARLO.123

MICHAEL ADLER & ASSOCIATES PERTH PENETROMETER TESTING

Client: Mainsheet Constructions Pty. Ltd Project No.: 16/08694

Project: Proposed New Residential Development Date : 12/5/2017

Location: Nos. 2 to 4 Marlo Road., Cronulla Tested: JK

Test Method: AS 1289.63.3

Number: BH101 BH102 BH103

Depth Start of Test (m): 0 0 0

Location:

Depth (m) PENETRATION RESISTANCE (blows /150 mm)

0.00 - 0.15 1 2 6

0.15 - 0.30 1 4 22

0.30 - 0.45 2 10 Refusal

0.45 - 0.60 2 22 Drilled

0.60 - 0.75 1 Refusal Drilled

0.75 - 0.90 2 Drilled Drilled

0.90 - 1.05 2 Drilled Drilled

1.05 - 1.20 3 Drilled 2

1.20 - 1.35 2 Drilled 2

1.35 - 1.50 3 4 2

1.50 - 1.65 3 3 3

1.65 - 1.80 2 1 4

1.80 - 1.95 2 2 5

1.95 - 2.10 2 2 3

2.10 - 2.25 3 2 4

2.25 - 2.40 3 3 4

2.40 - 2.55 6 5 5

2.55 - 2.70 2 4 4

2.70 - 2.85 2 4 7

2.85 - 3.00 2 6 12

3.00 - 3.15 2 4 10

3.15 - 3.30 3 4 5

3.30 - 3.45 4 5 4

3.45 - 3.60 5 6 3

3.60 - 3.75 7 6 3

3.75 - 3.90 8 7 2

3.90 - 4.05 8 6 5

4.05 - 4.20 10 5 5

4.20 - 4.35 6 6 4

4.35 - 4.50 4 6 4

4.50 - 4.65 4 6 4

4.65 - 4.80 4 4 3

4.80 - 4.95 4 4 3

4.95 - 5.10 5 5 4

5.10 - 5.25 4 5 4

5.25 - 5.40 4 6 5

5.40 - 5.55 6 6 6

5.55 - 5.70 8 5 6

5.70 - 5.85 8 7 7

5.85 - 6.00 10 7 7

6.00 - 6.15 Discontinued Discontinued Discontinued

6.15 - 6.30

STS GeoEnvironmental Pty Ltd GEOTECHNICAL LOG - NON CORE BOREHOLE

Client: Michael Adler & Associates Project: 16353/7283C BOREHOLE NO.: BH 1 Project: 2-4 Marlo Road, Cronulla Date : 18/08/2016

Location: Refer to Drawing No. 16/2192 Logged: JK Sheet 1 of 2

CONSISTENCY M


A T A S or I

T A M Y RELATIVE S




S (m) L E

SAND: light brown, fine to medium grained SP D-M

1.0

M

Aeolian

2.0

3.0

4.0

5.0


WT - level of water table or free water N - Standard Penetration Test (SPT) Equipment: Edson RP70


Angle from Vertical (°) 0

Form I1 Date of Issue 05/03/99 Revision 4




CONSISTENCY M


A T A S or I

T A M Y RELATIVE S




S (m) L E

SAND: light brown, fine to medium grained SP M

7.0

8.0

M-VM

9.0

10.0

11.0

BOREHOLE DISCONTINUED AT 12.0 M









CONSISTENCY M


A T A S or I

T A M Y RELATIVE S




S (m) L E

SAND: light brown, fine to medium grained SP M-D

ASS 1 1.0

@ 1.0 m

M

2.0 SAND: dark brown and grey, fine to medium grained SP M


ASS 2 3.0

@ 3.0 m

4.0

5.0

ASS 3

@ 6.0 m









CONSISTENCY M


A T A S or I

T A M Y RELATIVE S




S (m) L E


7.0

8.0

9.0

10.0

11.0

Standpipe piezometer installed

BOREHOLE DISCONTINUED AT 12.0 M






SMEC Testing Services Pty Ltd14/1 Cowpasture Place, Wetherill Park NSW 2164

Phone: (02)9756 2166 Fax: (02)9756 1137 Email: [email protected]

Perth Sand Penetrometer Test ReportProject: 2-4 MARLO ROAD, CRONULLA Project No.: 16353/7283C

Client: MICHAEL ADLER & ASSOCIATES Report No.: 16/2192

Address: Po Box 91, Church Point, NSW Report Date: 23/08/2016

Test Method: AS 1289.6.3.3 Page: 1 of 1

Site No. P1 P2 P1 P2

Location

Refer to

Drawing No.

16/2192

Refer to

Drawing No.

16/2192

Starting LevelSurface

Level

Surface

Level

Depth (m) Depth (m)

0.00 - 0.15 1 1 3.00 - 3.15 6 3

0.15 - 0.30 2 1 3.15 - 3.30 7 4

0.30 - 0.45 1 2 3.30 - 3.45 8 4

0.45 - 0.60 1 2 3.45 - 3.60 8 4

0.60 - 0.75 1 2 3.60 - 3.75 9 5

0.75 - 0.90 1 2 3.75 - 3.90 10 6

0.90 - 1.05 1 3 3.90 - 4.05 11 7

1.05 - 1.20 1 2 4.05 - 4.20 12 7

1.20 - 1.35 2 2 4.20 - 4.35 14 8

1.35 - 1.50 2 2 4.35 - 4.50 16 10

1.50 - 1.65 3 2 4.50 - 4.65 18 11

1.65 - 1.80 3 2 4.65 - 4.80 22 11

1.80 - 1.95 3 3 4.80 - 4.95 Refusal 12

1.95 - 2.10 3 3 4.95 - 5.10 13

2.10 - 2.25 3 3 5.10 - 5.25 13

2.25 - 2.40 4 3 5.25 - 5.40 16

2.40 - 2.55 4 3 5.40 - 5.55 17

2.55 - 2.70 5 3 5.55 - 5.70 18

2.70 - 2.85 5 3 5.70 - 5.85 22

2.85 - 3.00 6 4 5.85 - 6.00 Refusal

Remarks: * = Pre-drilled hole prior to testing

Approved Signatory...................................................................

Technician: JK Laurie Ihnativ - Manager

Penetration Resistance (blows / 150mm) Penetration Resistance (blows / 150mm)

Form: RPS26Long Date of Issue: 01/06/15 Revision: 5

EXPLANATION SHEETS

Michael Adler & Associates A

1. CLASSIFICATION OF SOILS

1.1 Soil Classification and the Unified System

The descriptions presented on the attached geotechnical logsare essentially based on the visual observations made by thesupervisor in the field. They are dependent on hisinterpretation of the subsurface conditions as indicated by thevarious drilling, insitu testing and sampling methods used.

The system used in this report for the identification of soil isthe Unified Soil Classification system (USC) which wasdeveloped by the US Army Corps of Engineers duringWorld War II and has since gained international acceptanceand has been adopted in its metricated form by theStandards Association of Australia.

The Australian Site Investigation Code (AS1726-1981,Appendix D) recommends that the description of a soilincludes the USC group symbols which are an integralcomponent of the system.

The soil description normally contain the followinginformation:

Soil composition

• SOIL NAME and USC classification symbol• plasticity or particle characteristics• colour• secondary and minor constituents (name, estimated

proportion, plasticity or particle characteristics, colouretc)

Soil condition

• moisture condition• consistency or density index

Soil structure

• structure (zoning, defects, cementing)

Soil origin

interpretation based on observation e.g. FILL, TOPSOIL,RESIDUAL, ALLUVIUM.

1.2 Soil Composition

(a) Soil Name and ClassificationSymbol

The USC system is summarised in the Australian Code. Theprimary division separates soil types on the basis of particlesize into:

. Coarse grained soils - more than 50% of the material less than 60 mm is larger than

0.06 mm (60µm).

. Fine grained soils - more than 50% of the material less than 60 mm is smaller than 0.06 (60µm).

Initial classification is by particle size as shown in Table 1.Further classification of fine grained soils is based onplasticity.

TABLE 1 - CLASSIFICATION BY PARTICLE SIZE

NAME SUB-DIVISION SIZE

Clay < 2 µm

Silt 2 µm to 60 µm

Sand

Gravel

Cobbles

Boulders

FineMediumCoarse

Fine MediumCoarse

60 µm to 200 µm200µm to 600 µm600 µm to 2 mm

2 mm to 6 mm6 mm to 20 mm

20 mm to 60 mm

60 mm to 200 mm

> 200 mm

Where a soil contains an appropriate amount of secondarymaterial, the name includes each of the secondarycomponents (greater than 12%) in increasing order ofsignificance, e.g. sandy silty clay.

Minor components of a soil are included in the descriptionby means of the terms “some” and “trace” as defined inTable .2.

TABLE 2 - MINOR SOIL COMPONENTS

TERM DESCRIPTION APPROXIMATEPROPORTION

(%)

Trace

Some

presence just detectable,little or no influence onsoil properties

presence easilydetectable, little influenceon soil properties

0-5

5-12

The USC group symbols should be included with each soildescription as shown in Table 3

TABLE 3 - SOIL GROUP SYMBOLS

SOIL TYPE PREFIXGravelSandSiltClay

OrganicPeat

GSMCOPt

The group symbols are combined with qualifiers whichindicate grading, plasticity or secondary components asshown on Table 4

TABLE 4 - SOIL GROUP QUALIFIERS

SUBGROUP SUFFIX Well graded W Poorly Graded P Silty M Layered C Liquid Limit <50% - low to medium plasticity L Liquid Limit >50% - medium to high plasticity H

EXPLANATION SHEETS

Michael Adler & Associates B

(b) Grading

“Well graded” Good representation of all particle sizes from the largest

to the smallest.

“Poorly graded” One or more intermediate sizes poorly represented

“Gap graded” One or more intermediate sizes absent

“Uniformly graded” Essentially single size material.

(c) Particle shape and texture

The shape and surface texture of the coarse grained particlesare usually described.

Angularity may be expressed as “rounded”, “sub-rounded”,“sub-angular” or “angular”.

Particle form can be “equidimensional”, “flat” or elongate”.

Surface texture can be “glassy”, “smooth”, “rough”, pitted”or striated”.

(d) Colour

The colour of the soil is described in the moist conditionusing simple terms such as:

Black White Grey RedBrown Orange Yellow GreenBlue

These may be modified as necessary by “light” or “dark”.Borderline colours may be described as a combination oftwo colours, e.g. red-brown.

For soils that contain more than one colour terms such as:

• Speckled Very small (<10 mm dia.) patches• Mottled Irregular• Blotched Large irregular (>75 mm dia.)• Streaked Randomly oriented streaks

(e) Minor Components

Secondary and minor components are often individuallydescribed in a similar manner to the dominant component.

1.3 Soil Condition

(a) Moisture

Soil moisture condition is described as “dry”, “moist” or“wet”.

The moisture categories are defined as:

Dry (D) - Little or no moisture evident. Soils are running.Moist (M) - Darkened in colour with cool feel. Granular soilparticles tend to adhere. No free water evident uponremoulding of cohesive soils.

(b) Consistency

The consistency, or strength, of a soil is estimated frommanual examination, hand penetrometer tests, StandardPenetration Tests (SPT) results and other insitu tests, plus ifappropriate laboratory tests. These are used to estimate theundrained shear or unconfined compressive strengths. Theclassification is given in Table 5.

TABLE 5 - CONSISTENCY OF FINE GRAINED SOILS

TERM UNCONFINEDSTRENGTH, qu

(kPa)

FIELDIDENTIFICATION

VerySoft

<25 Easily penetrated by fist.Sample extrudes betweenfingers when squeezed infist

Soft 25 - 50 Easily moulded in fingers.Easily penetrated 50 mmby thumb

Firm 50 - 100 Can be moulded by strongpressure in fingers.Penetrated 50 mm withmoderate effort by thumb

Stiff 100 - 200 Cannot be remoulded infingers. Indented bythumb but penetrated onlywith great effort

VeryStiff

200 400 Very though. Difficult tocut with knife. Readilyindented by thumb nail

Hard >400 Brittle, can just bescratched with thumbnail. Tends to break intofragments

Unconfined compressive strength is approximately twice theundrained shear strength (qu = 2 cu)

(c) Density Index

The insitu density index of granular soils can be assessedfrom the results of SPT or cone penetrometer tests. Densityindex is not normally estimated visually. Table 6 applies.

TABLE 6 - DENSITY OF GRANULAR SOILS

TERM SPT NVALUE

STATICCONEVALUE qc

(MPa)

DENSITYINDEX

(%)

Very Loose 0 - 3 0 - 2 0 - 15Loose 3 - 8 2 - 5 15 - 35Med Dense 8 - 25 5 - 15 35 - 65Dense 25 - 42 15 - 20 65 - 85Very Dense >42 >20 >85

1.4 Soil Structure

(a) Zoning

A sample may consist of several zones differing in colour,grain size or other properties. Terms to classify these zonesare:

Layer - continuous across exposure or sampleLens - discontinuous with lenticular shapePocket or Nodule- irregular inclusion

Each zone can be described, with their distinguishingfeatures, and the nature of the interzone boundaries.

EXPLANATION SHEETS

Michael Adler & Associates C

(b) Defects

Defects which are present in a sample can include:

• fissures• roots (containing organic matter)• tubes (hollow)• casts (infilled)

Defects can be described giving details of dimensions andfrequency. Fissure orientation, planarity, surface conditionand infilling are often noted. If there is a tendency to breakinto blocks, block dimensions this is usually noted

1.5 Soil Origin

Information which may be interpretative but which maycontribute to the usefulness of the material description canbe included. The most common interpreted feature is theorigin of the soil. The assessment of the probable origin isbased on the soil material description, soil structure and itsrelationship to other soil and rock materials.

Common terms used are:

“Residual Soil” - Material which appears to have beenderived by weathering from the underlying rock. There is noevidence of transport.

“Colluvium” - Material which appears to have beentransported from its original location. The method ofmovement is usually the combination of gravity and erosion.

“Landslide Debris” - An extreme form of colluvium wherethe soil has been transported by mass movement. Thematerial is obviously distributed and contains distinctdefects related to the slope failure.

“Alluvium” - Material which has been transportedessentially by water. usually associated with former streamactivity.

“Fill” - Material which has been transported and placed byman. This can range from natural soils which have beenplaced in a controlled manner in engineering construction todumped waste material. The description normally includesthe constituents and a general preliminary assessment of thepossible method of placement and level of compaction. It isnot practical to accurately assess the level of compaction,this is usually provided by documentation and certificationfrom the testing authority who was present when the fill wasplaced and compacted.

1.6 Fine Grained Soils

The physical properties of fine grained soils are dominatedby silts and clays.

The definition of clay and silt soils is governed by theirAtterberg Limits. Clay soils are characterised by theproperties of cohesion and plasticity with cohesion definesas the ability to deform without rupture. Silts exhibitcohesion but have low plasticity or are non-plastic.

The field characteristics of clay soils include:

• dry lumps have appreciable dry strength and cannot bepowdered

• volume changes occur with moisture content variation• feels smooth when moist with a greasy appearance when

cut.

The field characteristics of silt soils include:

• dry lumps have negligible dry strength and can bepowdered easily

• dilatancy - an increase in volume due to shearing - isindicted by the presence of a shiny film of water after ahand sample is shaken. The water disappears uponremoulding. Very fine grained sands may also exhibitdilatancy.

• low plasticity index• feels gritty to the teeth

1.7 Organic Soils

Organic soils are distinguished from other soils by theirappreciable content of vegetable matter, usually derivedfrom plant remains.

The soil usually has a distinctive smell , low bulk densityand often has a high moisture content.

The USC system uses the symbol Pt for partly decomposedorganic material. The O symbol is combined with suffixes“O” or “H” depending on plasticity.

Where roots or root fibres are present their frequency and thedepth to which they are encountered is usually recorded.The presence of roots or root fibres does not necessarilymean the material is an “organic material” by classification.

Coal and lignite are normally described as such and notsimply as organic matter.

EXPLANATION SHEETS

Michael Adler & Associates D

2. CLASSIFICATION OF ROCKS

2.1 Uniform Rock Classification

The aim of a rock description for engineering purposes is toprovide an indication of the expected engineering propertiesof the material

In a similar manner to soil materials, the assessment of siteconditions where rock is encountered is usually based on theuse of a rational descriptive method which is uniform andrepeatable. The description typically:

• provides a clear identification of the rock substance andits engineering properties

• includes details of the features which affect theengineering properties of the rock mass

There is no internationally accepted system for rockdescription, Michael Adler and Associates have adopted amethod that incorporates terminology that is commonly usedin the engineering profession. Most feature definitions are asrecommended by the International Society of RockMechanics and the Standards Association of Australian.

For uniform presentation the different features are usuallydescribed in order:

Rock Substance:

• NAME (In blocks)• Mineralogy• Grain Size• Colour• Fabric• Strength• Weathering/Alteration

Rock Mass:

• Defect Type• Defect Orientation• Defect Features• Defect Spacing

2.2 Rock Substance

(a) Rock Name

Each rock type has a specific name which is based on:

• Mineralogy• Grain Size• Fabric• Origin

The only method of precisely determining the rock name isby thin mineralogy.

Field identification of rocks for engineering purposes isnormally based on the use of common, easily understood,simple geological names. In many cases knowledge of theprecise name is of little consequence in the assessment of thesite conditions. If required the “field name” can be qualifiedby reference to a petrographic report. Reference to localgeological reports or maps often provides information on therock type which may be expected

(b) Mineralogy

The rock description usually includes the identification ofthe prominent minerals. This identification is usuallyrestricted to the more common minerals in medium to coarsegrained rocks.

(c) Grain Size

Rock material descriptions often include general grouping ofthe size of the prominent mineral grains as defined in Table7. The maximum size, or size range, of the largest mineralgrain or rock fragments is often recorded.

TABLE 7 - GRAIN SIZE GROUPS

TERM GRAIN SIZE (mm)Very Coarse > 60Coarse 2 - 60Medium 0.06 - 2Fine .0.002 - 0.06Very Fine < 0.002Glassy

(d) Colour

The colour is normally described in the moist conditionusing simple terms such as:

Black White Grey RedBrown Orange Yellow GreenBlue

These are often modified by “light” or ‘dark”. Borderlinecolours are described by a combination of two or morecolours, e.g.: red brown

(e) Fabric

The fabric of a rock includes all the features of texture andstructure, though the term refers specifically to thearrangement of the constituent grains or crystals in a rock.The fabric can provide an indication of the mode offormation of the rock:

• in sedimentary rocks bedding indicates depositionconditions

• in igneous rocks the texture indicates the rate of cooling• in metamorphic rocks the foliation indicates the stress

conditions Descriptions of fabric typically include orientation, eitherwith reference to north or horizontal, or to a plane normal tothe core axis.

Tables 8, 9 and 10 list common textural features ofsedimentary, igneous and metamorphic rocks with thesubdivision of stratification spacing given in Table 11.

TABLE 8 - COMMON STRUCTURE IN SEDIMENTARY ROCK

STRATIFICATION(Planer)

STRATIFICATION(Irregular)

Bedding WashoutCross Bedding Slump StructureGraded bedding Shale BrecciaLaminationCross Lamination

EXPLANATION SHEETS

Michael Adler & Associates E

TABLE 9 - COMMON STRUCTURE IN IGNEOUS ROCK

FINEGRAINED

ROCK

COARSEGRAINED

ROCKUniform Grain Massive MassiveSize Flow Banded Granitic

Vesicular PegmaticDifferent GrainSize

Porphyritic Porphyritic

TABLE 10 - COMMON STRUCTURE IN METAMORPHIC ROCK

FINE GRAINEDROCKS

COARSE GRAINEDROCKS

Slatey Cleavage GramoblasticSpotted PorphyroblasticHornsfelsic LineatedFoliated GneissicMylonitic Mylonitic

TABLE 11 - STRATIFICATION SPACING

TERM SEPARATION (mm)Very Thickly Bedded > 2000Thickly Bedded 600 - 2000Medium Bedded 200 - 600Thinly Bedded 60 - 200Very Thinly Bedded 20 - 60Laminated 6 - 20Thinly Laminated < 6

(f) Strength

Substance strength is one of the more important engineeringfeatures of a rock, descriptions usually include an estimateof the rock strength class of the material. This estimate isoften calibrated by test results, such as Point Load StrengthIndex or by Unconfined Compressive Strength.

The rock strength class in AS 1726-1981 is defined by thePoint Load Strength Index Is (50). The relationship betweenPoint Load Index and the Unconfined Compressive Strength(Qu) is often assumed to be about 20, though it can rangefrom 4 (in some carbonate rocks) to 40 (in some igneousrocks). The classification is normally based on material atfield moisture content, as some rocks give a significantlyhigher strength when tested dry. In thinly beddedsedimentary rocks, such as shale the axial point loadstrength may provide a better estimate of the rock strengthclass, rather than the diametral value.

Table 12 defines the rock strength, with indicative field testslisted in Table 13. These can assist in classification whentesting apparatus is not available.

TABLE 12 - CLASSIFICATION OF ROCK STRENGTH

SYMBOL TERM POINTLOAD

STRENGTH(MPa)

APPROX

Qu(MPa)

EL Extremely Low < 0.03 < 1VL Very Low 0.03 - 0.1 1 - 3L Low 0.1 - 0.3 3 - 10M Medium 0.3 - 1 10 - 30H High 1 - 3 30 - 70

VH Very High 3 - 10 70 - 200

EH Extremely High > 10 > 200TABLE 13 - FIELD TESTS FOR ROCK STRENGTH

CLASSIFICATION

STRENGTHCLASS

FIELD TEST

Extremely Low Indented by thumb with difficultyVery Low Scratched by thumb nailLow Easily broken by hand or paired with a

knifeMedium Broken by hand or scratched with a knifeHigh Broken in hand by firm hammer blowsVery High Broken against solid object with several

hammer blowsExtremely High Difficult to break against solid object with

several hammer blows

(g) Weathering/Alteration

In addition to the description of the rock substance asexamined, an assessment of the extent to which the originalrock material has been affected by subsequent events isoften important. The usual processes include:

• Weathering - Decomposition due to the effects ofsurface or near surface activities

• Alteration - Chemical modification by the action of

materials originating from within the mantle below

The classification of weathering/alteration presented inTable 14 is based on the extent/degree to which the originalrock substance has been affected. This classification oftenhas little engineering significance, as the properties of therock as examined may bear no relationship to the propertiesof the fresh rock.

TABLE 14 - CLASSIFICATION OF ROCK WEATHERING/ALTERATION

TERMS DEFINITIONFresh (Fr) Rock substance unaffected

Fresh Stained (Fr.St) Rock substance unaffected, staining ondefect surfaces

Slightly (SW) Partial staining or discolouration of rocksubstance

Moderately (MW) Partial staining or discolourationextends throughout entire rocksubstance

Highly (HW) Rock substance partially decomposed

Completely (CW) Rock substance entirely decomposed

2.3 Rock Mass

The engineering properties of the rock mass reflect the effectwhich the presence of defects has on the properties of therock substance. Description of the rock mass propertiesconsists of supplementing the description covered bySection 2.2 with data on the defects which are observed.

It is important to note that the defects described in theGeotechnical Logs for Cored Boreholes include bothnatural defects and those in the recovered rock cores thatwere caused by the drilling process. Unless there isdefinitive evidence to the contrary, no attempt is made todifferentiate between natural defects and drilling breaks.

EXPLANATION SHEETS

Michael Adler & Associates F

The drilling breaks between the individual core runs are notdescribed in the logs as these are known drilling induceddefects.

(a) Defect Type

The different defect types are described in Table 15.

TABLE 15 - ROCK DEFECT TYPES

TYPE SYMBOL

DESCRIPTION

Parting Pt A defect parallel or subparallel to alayered arrangement of mineral grains ormicro-fractures which has caused planeranisotropy in the rock substance

Joint Jt A defect across which the rock substancehas little tensile strength and is notrelated to textural or structural featureswith the rock substance

ShearedZone

SZ A zone with roughly parallel planerboundaries or rock substance containingclosely spaced, often slickensided joints

CrushedZone

CZ A zone with roughly parallel planerboundaries of rock substance composedof disoriented, usually angular, fragmentsof rock

Bedding Bd Stratification from original layering inthe sediments that formed the rock.

Seam Sm A zone with roughly parallel boundariesin-filled with by soil or decomposed rock

(b) Defect Orientation

Descriptions of defects usually include orientation, either ofindividual fractures or of groups of fractures. Orientation isoften referenced to north, to the horizontal, or to a planenormal to the core axis (Hz = Horizontal)

(c) Defect Features

The character of a defect is usually described by itscontinuity, planarity, surface roughness, width and infilling.

Continuity: In an outcrop of rock it is the extent of a joint, bedding plane or similar defect both along and across the strike. In a core continuity measurement is restricted to defects nearly parallel to the core axis.

Planarity: Described as “Planer” (P), “Irregular” (I), “Curved” (C) or “Undulose” (U).

Roughness: Described as “Rough” (R), “Smooth” (S), “Polished” (P) or “Slickensided” (S).

Width; Measured in mm normal to the plane of the defect.

Infilling: Described as “Clean” (Cl), “Stained” (St), “Veneer” (<1 mm) (Vn) or “Infill” (>1 mm) (In). The coating or infill is sometimes identified.

(d) Defect Spacing

The spacing of defects, particularly where they occur inparallel groups or sets, provides an indication of the rockblock size which:

• have to be supported in the face or roof of an excavation• will be produced by excavation

Often discontinuity spacing is grouped as shown in Table16.

TABLE 16 - DISCONTINUITY SPACING

DESCRIPTION SPACING(mm)

Extremely widely spaced > 6000Very widely spaced 2000 - 6000Widely spaced 600 - 2000Medium Spaced 200 - 600Closely spaced 60 - 200Very closely spaced 20 - 60Extremely closely spaced < 20

(e) Results of Point Load Testing

Point Load test results for Is (50) are presented whenavailable in MPa:

Id = Diametral ValueIa = Axial Value

michael adler and associates consulting geotechnical

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