REPORT TO ON PRELIMINARY GEOTECHNICAL SITE …...4. Groundwater was encountered at very shallow depths (0.3m-1m) in one of the boreholes drilled in 1996 at 4 Churchill Avenue; it is

REPORT

TO

ESPERIA COURT PTY LTD

ON

PRELIMINARY GEOTECHNICAL SITE ASSESSMENT

FOR

PROPOSED MIXED USE DEVELOPMENT

AT

1 TO 9 THE BOULEVARDE, STRATHFIELD, NSW

18 August 2015

Ref: 28634Vrpt-Strathfield

JK Geotechnics GEOTECHNICAL & ENVIRONMENTAL ENGINEERS

PO Box 976, North Ryde BC NSW 1670 Tel: 02 9888 5000 Fax: 02 9888 5001 www.jkgeotechnics.com.au

Jeffery & Katauskas Pty Ltd, trading as JK Geotechnics ABN 17 003 550 801

28634Vrpt-Strathfield Page ii

Date: 18 August 2015 Report No: 28634Vrpt-Strathfield Revision No: 0

Report prepared by: Fernando Vega Senior Associate For and on behalf of

JK GEOTECHNICS

PO Box 976

NORTH RYDE BC NSW 1670

Document Copyright of JK Geotechnics.

This Report (which includes all attachments and annexures) has been prepared by JK Geotechnics (JK) for its Client, and is intended for the use only by that Client. This Report has been prepared pursuant to a contract between JK and its Client and is therefore subject to:

a) JK’s proposal in respect of the work covered by the Report;

b) the limitations defined in the Client’s brief to JK;

c) the terms of contract between JK and the Client, including terms limiting the liability of JK.

If the Client, or any person, provides a copy of this Report to any third party, such third party must not rely on this Report, except with the express written consent of JK which, if given, will be deemed to be upon the same terms, conditions, restrictions and limitations as apply by virtue of (a), (b), and (c) above. Any third party who seeks to rely on this Report without the express written consent of JK does so entirely at their own risk and to the fullest extent permitted by law, JK accepts no liability whatsoever, in respect of any loss or damage suffered by any such third party.

28634Vrpt-Strathfield Page iii

TABLE OF CONTENTS

1 INTRODUCTION 1

1.1 Proposed Development 1

2 PROCEDURE 2

3 RESULTS 2

3.2 Brief Site Description 2

3.3 General Geology and Inferred Subsurface Conditions 2

4 PRELIMINARY COMMENTS AND RECOMMENDATIONS 3

4.1 Summary of Findings and Main Geotechnical Issues 3

4.2 Detailed Geotechnical Investigations and Inspections 4

4.3 Preliminary Design Guidance and Geotechnical Parameters 5

4.4 Conclusions 7

5 GENERAL COMMENTS 7

VIBRATION EMISSION DESIGN GOALS

APPENDIX

SITE SURVEY PLAN

28634Vrpt-Strathfield Page 1

1 INTRODUCTION

JK Geotechnics have been commissioned by the architects Mr Andrew Elia and Ms Georgina Camp

of Integrated Design Group, on behalf of Esperia Court Pty Ltd (Mr Nick Soulos), to carry out a

preliminary geotechnical assessment, based on a desk study research, to assist with the

Development Application (DA) for a proposed mixed use development at 1 to 9 The Boulevarde

(corner Churchill Avenue), Strathfield, NSW. The work was completed in accordance to our fee

proposal, Ref: P40595V-Strathfield dated 1 June 2015.

A summary of the principal geotechnical issues, based on the findings of this desk study

research, is provided on Section 4.1.

This report presents the findings of the desk study research and goes on to make preliminary

recommendations on geotechnical aspects of the proposed development. We also provide

requirements for a detailed geotechnical subsurface investigation of the site. The recommendations

provided herein must be reviewed once further geotechnical work has been completed, after

demolition and at CC stage, and after the final development details such as footing system and

structural loads are decided upon and determined.

1.1 Proposed Development

The development was at DA stage. The proposed development involves demolition of the existing

structures and construction of a fifteen level building over three levels of basement car parking. The

basement level is proposed to cover most of the site area.

At this DA stage, preliminary architectural plans (by Integrated Design Group, Project No.

ESP13059) have been provided including development sections drawings (SK9200 Issue A 21 May

2015) and layout of basement (SK1001 Issue A 21 May 2015) with a proposed lowest (B3) floor

level at RL2.16m. Also provided was a site survey plan of the site which shows select adjoining

surface reduced levels (RL) (refer to the attached survey in the Appendix). Based on these levels,

it is estimated that excavations in the range of about 10m are likely to be required to achieve the

proposed lowest basement floor level. Structural loads had not been advised, but we have assumed

column loads in the moderate to high range will apply for the size of the building.


2 PROCEDURE

This preliminary desk study assessment included the research and review of relevant geotechnical

and geological information contained in our database for the site itself (test boreholes drilled at 4

Churchill Avenue in 1996 for other clients) and at nearby sites, and the Sydney geological map. No

current subsurface investigation on the site itself has been carried out as part of this preliminary

assessment.

3 RESULTS

3.2 Brief Site Description

The site is identified as Lot 1 in DP 173685, Lot 1 in DP 172769 and Lot 1 in DP173763 (or 1-9 The

Boulevard, corner Churchill Avenue). The attached Survey Plan (in the Appendix) shows the site

location and includes some select adjoining surface reduced levels and other site details including

some neighbouring information.

The site is located on the corner of The Boulevarde and Churchill Avenue extension, on the

southern side of Strathfield Square. The prevailing ground slope of the site falls slightly from around

RL12.2m-Rl12.5m in the south-east to around RL11.6m-RL11.9m in the north-west corner. The site

is almost entirely covered by commercial and retail buildings of two storey, brick construction. The

neighbouring properties to the south and west contain multi-level building with basements.

3.3 General Geology and Inferred Subsurface Conditions

Our site observations and research of available information, including a search of our in-house

database, has disclosed the following data on the geology and geotechnical conditions of the site:

1. The 1:100,000 geological map of Sydney indicates that the site is underlain by Ashfield

Shale of the Wianamatta Group, which typically consists of shale and laminite. This

geological profile does not take into account the residual soils derived from in-situ

weathering of the bedrock or earthworks (e.g. probable fill under tennis court area) that may

have previously been undertaken at the site.

2. Review of geotechnical information in the form of geotechnical boreholes discovered for

part of the site itself, which were drilled in 1996 at the rear of No. 4 Churchill Avenue,

confirmed the presence of shale bedrock at a depth of 5.4m below surface; the shale was

assessed in current terminology to be distinctly weathered and of medium strength. At

nearby sites to the west and south of the site, the shale was found a shallower depths of

2.8m-2.9m, but the rock was extremely weathered and extremely weak with residual clay


layers; medium or greater strength shale bedrock was encountered at greater depths of 4m

to 5m, which is similar to conditions encountered at 4 Churchill Avenue.

3. Above the bedrock there was limited depth of fill and residual silty clays of medium to high

plasticity and variable strengths (stiff to hard). The residual clays were estimated have a

moderate potential for shrink/swell reactive behaviour with changes in moisture content.

4. Groundwater was encountered at very shallow depths (0.3m-1m) in one of the boreholes

drilled in 1996 at 4 Churchill Avenue; it is considered very likely that these water levels might

be an anomaly or perched levels. However, groundwater should be expected below the site

since at nearby sites groundwater levels were measured in boreholes at depths in the range

of 3.7m to 4.4m.

4 PRELIMINARY COMMENTS AND RECOMMENDATIONS

4.1 Summary of Findings and Main Geotechnical Issues

Based on the results of our desktop study research, discussed in more specific detail in Section

3.2, we infer that the subsurface profile at the site most likely comprise some fill underlain by

residual clays grading into shale bedrock at general depths of around 3m-6m, based on nearby site

as well as geotechnical information on part of the site itself. The upper layers of shale might be of

an extremely low to very low strength nature, but improving with depth (probably around 5m-6m) to

at least medium strength. Groundwater levels are likely to be encountered within the depth of the

proposed three level basement excavation, since groundwater levels at nearby sites were at depths

of around 4m.

The above inferred subsurface profile must be confirmed by detailed geotechnical subsurface

investigations (refer to Section 4.2) involving cored boreholes, and standpipe wells for groundwater

monitoring, carried out prior to final structural design and issue of the Construction Certificate (CC)

and by geotechnical inspections of exposed rock during construction work.

Overall, it is considered that construction of the proposed development is viable and practicable,

provided detailed geotechnical borehole investigation is carried out prior to detailed final design

together with review of the preliminary recommendations provided in this report.

Based on the above inferred subsurface conditions and description of the proposed development

(refer to Section 1.1), the following are considered to be principal geotechnical issues for the

proposed development:


1. Prior to any demolition or excavation taking place at the site, we recommend that

dilapidation surveys of adjoining buildings, walls and pavements be carried out.

2. Maintaining stability of the adjoining land, buildings, stormwater services and any other

boundary structures during excavations. During the excavation, every care should be taken

to not undermine or render unstable the footings of any adjoining structure.

3. The basement excavation is likely to be carried through a variable profile of fill, residual clay,

and weathered shale. The excavation will, therefore, require support by shoring/retention

pile walls with rock anchors (e.g. soldier or contiguous or secant piles).

4. The shale excavation is likely to require assistance with rock excavation equipment, which

may transmit vibrations through the rock mass that could affect adjoining buildings. Vibration

effects (associated with general excavation but more critically rock excavation) on adjoining

structures must be considered.

5. Spread or pile footings may be embedded below the basement level and these are expected

to be founded in shale.

6. Groundwater seepage is likely to be an issue for the proposed three level deep basement

excavation.

7. Contamination or environmental investigations are likely to be required in order to classify

the material to be excavated for waste disposal purposes in accordance with the NSW DEC

(formerly EPA) guidelines as inert, solid, industrial or hazardous waste.

Further comments on these issues and preliminary design parameters are provided in the

subsequent sections of this report.

4.2 Detailed Geotechnical Investigations and Inspections

Detailed geotechnical subsurface investigation must be carried out after demolition is complete to

allow site access for truck mounted drilling rigs. The subsurface investigation must also be

completed and analysed prior to final structural design and issue of the Construction Certificate

(CC) to determine the site specific subsurface profile and geotechnical parameters for the design

of the retention systems and footings.

To complete final design on the basis of the geotechnical information provided from this desk study

research and preliminary report is not endorsed.

The geotechnical investigations should involve at least five boreholes drilled to depths below the

proposed excavations and the depth of influence of the proposed footings (estimated borehole

depths: 13m). The bedrock should be drilled with coring methods to allow strength testing of rock


core and examination of defects. Standpipe wells should be installed in select boreholes to allow

monitoring of groundwater levels. Pump out test should be completed to estimate seepage rates

and volumes.

Furthermore, it will be essential during earthworks and construction that regular geotechnical

inspections and testing be commissioned to check initial assumptions about excavation and

foundation conditions and likely variations that may occur between borehole locations and to

provide further relevant geotechnical advice. Irregular or ‘milestone’ inspections by a geotechnical

engineer are often not adequate for excavation and foundation works. It is recommended that the

Client be made aware of the need to commission a geotechnical engineer for inspections.

4.3 Preliminary Design Guidance and Geotechnical Parameters

The following are comments and recommendations on the geotechnical issues identified as

probable for the proposed development. These should be considered only for the preliminary

planning, design and construction assessment of the development. We have also included

approximate estimates of likely geotechnical parameters that may be used for preliminary design

purposes only. To complete final design on the basis of the geotechnical information provided from

this desk study research and preliminary report is not endorsed.

1. Dilapidation surveys should be carried out on the adjoining buildings that fall within the

influence zone of the excavation, which can be defined as a horizontal distance back from

the edge of the excavation of at least twice the excavation depth. During the excavation,

every care should be taken to not undermine or render unstable the footings of any

adjoining structure.

2. Excavations to achieve the basement levels are approximately estimated to have to be

carried down to depths of around 10m below existing site surface levels. Such excavations

are inferred to encounter fill and residual clays and the shale bedrock. Excavation of the

soils are expected to be achievable using conventional earthmoving equipment, such as

hydraulic excavators. The extremely weathered shale may also be removed using the latter

equipment. However, the presence of stronger or less weathered bedrock below inferred

depths of around 5m-6m is likely to require the use of rock excavation equipment for more

effective removal. The use of such equipment may result in transmission of vibrations

through the rock mass that could affect adjoining buildings. Vibration effects (associated

with general excavation but more critically rock excavation) on adjoining structures must

be considered. We recommend that the initial excavation in rock be commenced away from

likely critical areas, e.g. boundaries with adjoining buildings, with instrumental vibration


monitoring undertaken. Guideline levels of vibration velocity for evaluating the effects of

vibration in structures are given in the attached Vibration Emission Design Goals sheet. If

it is found that transmitted vibrations are unacceptable, then it may then be necessary to

change to a smaller excavator with a smaller rock hammer, or to a rotary rock grinder and/or

rock saws.

3. Hydrogeological (groundwater) Considerations: Groundwater inflow should be

expected into the basement excavation. However, we do not know what seepage rates are

to be expected. Hence, as part of the site specific subsurface testing work, we recommend

that pump out tests be completed in the standpipe wells recommended for installation in

Section 4.2. Notwithstanding, at this very preliminary stage, our suggestion is that the

basement be designed as an undrained, water-tight structure and designed against the

effects of groundwater pressures, in the short and long term, e.g. lowest basement floor

slab will be subjected to uplift pressures from the high groundwater level, which may require

additional slab mass or ground anchors. It is also important to note that in some cases that

local Council has advised in the past that continual pump-out and seepage into the street

gutter will not be accepted.

4. Retention systems should be installed prior to commencement of any vertical

excavations. The excavation sides should be supported by appropriate shoring/retention

systems, preferably, a closed, rigid system of secant or contiguous pile walls, with rock

anchors, which forms the perimeter cut-off to reduce the inferred groundwater inflow. We

do not prefer the use of a more open system of semi-contiguous or soldier pile walls with

shortcrete panels because we infer that there might be groundwater seepage issues.

Additional lateral support or restraint, if necessary, may be provided by rock anchors or by

internal props. Approval from neighbouring landowners will be required prior to installation

of anchors into their property. Some of the adjoining buildings have basements and hence,

their details should be determined to assess the feasibility and impacts of rock anchors

along some site boundaries.

5. Lateral Pressures: a high coefficient of lateral pressure, K, should be employed for

retention design within fill and residual soils and extremely weathered shale rock, to assist

in reduction of excavation induced movements. K values can be estimated once the results

of the geotechnical borehole tests has been completed and processed.

6. All applicable surcharge loadings (e.g. adjacent footings) should be taken into account in

the retaining system design. All retaining systems should incorporate permanent drainage

provisions and be designed to withstand some hydrostatic pressuresguidelines for design

of shoring/retention systems are provided herein. The presence of adjoining footings must

be taken into consideration in the assessment of lateral pressures.


7. Footings: the proposed building should be supported on footings (e.g. strip/pads or piles)

founded within the shale of at least very low strength; these footings may be designed on

a preliminary basis for an allowable bearing pressure of 700kPa. Higher bearing pressures

for shale of at least medium strength (e.g. 1500kPa-3500kPa) may be applicable below

say 5m-6m if this is proven by completing and testing the recommended boreholes on the

site itself.

8. Foundation Inspections: footing excavations and exposed foundation strata should be

inspected and correlated to nearest borehole test information by a geotechnical engineer

to ascertain that the recommended foundation material has been reached and to check

initial assumptions about foundation conditions and possible variations that may occur

between borehole test locations.

4.4 Conclusions

Overall, it is considered that construction of the proposed development is viable and practicable,

provided detailed geotechnical borehole investigation is carried out prior to detailed final design

together with review of the preliminary recommendations provided in this report. The proposed

development is similar to other developments in nearby sites with similar geotechnical and

geological conditions, which have been successfully constructed.

5 GENERAL COMMENTS

The comments and preliminary recommendations made in this report are based on geotechnical

information recovered from this desk study. The client should be aware that the subsurface

conditions can change over short distances and the recommendations made in this report may be

substantially altered as a result of site specific geotechnical investigations. The preliminary

recommendations may need to be changed substantially if the depth of soil cover is found to be

much deeper than assumed.

The text and recommendations of this report are not intended to directly form a Contract Document

or Specification. Such documents should be prepared only after the detailed geotechnical

investigations as recommended in this report. There may be design features we are not aware of

or have not commented on for a variety of reasons. The designers should satisfy themselves that

all the necessary advice has been obtained.

The recommendations presented in this report include specific issues to be addressed during a

later stage of the project. In the event that any of the construction phase recommendations


presented in this report are not implemented, the general recommendations may become

inapplicable and JK Geotechnics accept no responsibility whatsoever for the performance of the

structure where recommendations are not implemented in full and properly tested, inspected and

documented.

If there is any change in the proposed development described in this report then all

recommendations should be reviewed.

A waste classification will need to be assigned to any soil excavated from the site prior to offsite

disposal. Subject to the appropriate testing, material can be classified as Virgin Excavated Natural

Material (VENM), General Solid, Restricted Solid or Hazardous Waste. If the natural soil has been

stockpiled, classification of this soil as Excavated Natural Material (ENM) can also be undertaken,

if requested. However, the criteria for ENM are more stringent and the cost associated with

attempting to meet these criteria may be significant. Analysis takes seven to 10 working days to

complete, therefore, an adequate allowance should be included in the construction program unless

testing is completed prior to construction. If contamination is encountered, then substantial further

testing (and associated delays) should be expected. We strongly recommend that this issue is

addressed prior to the commencement of excavation on site. If there is any change in the proposed

development described in this report then all recommendations should be reviewed.

This report has been prepared for the particular project described and no responsibility is accepted

for the use of any part of this report in any other context or for any other purpose. Copyright in this

report is the property of JK Geotechnics. We have used a degree of care, skill and diligence

normally exercised by consulting engineers in similar circumstances and locality. No other warranty

expressed or implied is made or intended. Subject to payment of all fees due for the investigation,

the client alone shall have a licence to use this report. The report shall not be reproduced except

in full.

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APPENDIX

SITE SURVEY PLAN

Documents

REPORT TO ON PRELIMINARY GEOTECHNICAL SITE …...4. Groundwater was encountered at very shallow depths (0.3m-1m) in one of the boreholes drilled in 1996 at 4 Churchill Avenue; it is