Geotechnical Data Report Part 1 (1)

8/15/2019 Geotechnical Data Report Part 1 (1)

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METRO NORTH

ORAL HEARING

Geotechnical Data Report

Part


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Dublin Metro North


April 2008

B0307000-010/GEO.28/006/1


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JACOBS

Dublin Metro North

Geotechnfcal Data Report

Document control sheet Form IP180/B

Client:

Project:

Title:

RPA

Dublin Metro North


Job No: 80307000

Prepared by Reviewed by

Approved by

Original

NAM

NA NAE

Jonathan Gammon I

Stuart Cowan David Hobson

Roger Carter

DATE.

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April 2008

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~ .,. u-_ f) /l/J

WIl) ('

REVISION

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DATE SIGNTURE SIGNTURE

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REVISION

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DlTE

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This repor, and infooation or advce which it contains, is provided by Jacos solely for interl use and reliance by ils Oienl in perormance of Jaco duties an

liabmUes under Its cotrac with the Oient. Any advie, opnion, or recommendatis within lhs rep should be read and relied upo ony in Ihe coext of the repor

as a whle. The advice and opinios in this repo are based upo the information made available to Jacobs at the dale of this rep and on currnt UK stanards,

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Dublin Metro NorthGeotechnical Data Report

Contents

1

Introduction 1-1

1.1 Scheme Overview 1-1

1.2 Background 1-1

1.3 Scope of the Report 1-1

1.4 Report Format 1-2

1.5 Other Relevant Reports 1-3

1.6

Limitations and Exceptions 1-4

2 Site Conditions 2-1

2.1 Site Location and Topography 2-1

2.2 Site History 2-2

2.3 Geological Setting 2-2

2.4 Geotechnical Hazards 2-13

3

Ground Investigation Fieldwork 3-1

3.1 General 3-1

3.2 Light Cable Percussion Boreholes 3-3

3.3 Rotary Open Hole, Rotary Core and Geobor-S Drillholes 3-6

3.4 Trial Pits 3-10

3.5 Geophysical Surveys 3-10

3.6

Field installations 3-11

3.7 Field Testing 3-15

4 Ground Investigation Laboratory Testing 4-1

4.1 General 4-1

4.2 Previous Ground Investigation 4-1

4.3 Metro North Ground Investigation Programme 4-2

5

Previous Construct ion Experience 5-1


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5.1 Relevant Projects 5-1

5.2 Dublin Port Tunnel 5-1

5.3 Other Tunnel Projects 5-8

5.4 Basement Excavations 5-10

5.5 Foundation Construction 5-15

5.6 Other Projects / Relevant Papers 5-20

6 References 6-1

7 Appendices 7-1

Appendix Tit le

A Summary of GSI Ground Investigation ReportsB Summary of GSI Cable Percussion BoreholesC Summary of Previous Ground Investigation Trial Pit RecordsD Summary of Previous Ground Investigation Groundwater

Monitoring RecordsE Summary of Metro North Preliminary Ground Investigation

Groundwater Monitoring Records

Figures

Figure No. Title

Figure 1 Quaternary Geology MapFigure 2 Bedrock Geology MapFigure 3 GSI Dublin City Centre Rockhead Levels

Drawings

Drawing No. Title

B/MN/0000/GE/01 Rev. A01 Exploratory Hole Location Plan Sheet 1 of 13B/MN/0000/GE/02 Rev. A01 Exploratory Hole Location Plan Sheet 2 of 13

B/MN/0000/GE/03 Rev. A01 Exploratory Hole Location Plan Sheet 3 of 13B/MN/0000/GE/04 Rev. A01 Exploratory Hole Location Plan Sheet 4 of 13B/MN/0000/GE/05 Rev. A01 Exploratory Hole Location Plan Sheet 5 of 13B/MN/0000/GE/06 Rev. A01 Exploratory Hole Location Plan Sheet 6 of 13B/MN/0000/GE/07 Rev. A01 Exploratory Hole Location Plan Sheet 7 of 13B/MN/0000/GE/08 Rev. A01 Exploratory Hole Location Plan Sheet 8 of 13B/MN/0000/GE/09 Rev. A01 Exploratory Hole Location Plan Sheet 9 of 13B/MN/0000/GE/10 Rev. A01 Exploratory Hole Location Plan Sheet 10 of 13B/MN/0000/GE/11 Rev. A01 Exploratory Hole Location Plan Sheet 11 of 13B/MN/0000/GE/12 Rev. A01 Exploratory Hole Location Plan Sheet 12 of 13B/MN/0000/GE/13 Rev. A01 Exploratory Hole Location Plan Sheet 13 of 13


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1 Introduction

1.1 Scheme Overview

Metro North is the next phase of Dublin's integrated light rail network, which beganwith the opening of the Luas Green and Red lines. Metro North will provide parkand ride spaces and good quality bus, rail and air interchanges along an 18kmcorridor running from Belinstown in the North through Seatown, Swords,Fosterstown, Dublin Airport, Dardistown, Northwood, Ballymun, Dublin CityUniversity, Griffith Avenue, Drumcondra, Mater Hospital, Parnell Square andO'Connell Bridge to St. Stephen's Green in the city centre. Provision has beenmade for a further two stops (Lissenhall and Estuary) between Belinstown andSeatown; however, construction of these stops will not form part of the Metro Northworks.

Metro North will generally be segregated from road traffic which will be achieved byrunning in tunnel in the city centre and on road medians or elevated sections in theless congested outer suburbs. The proposed location and alignment of Metro Northis shown in Drawing Nos. B/MN/0000/GE/01 to 13. The alignment to which thisreport relates is the 15 November 2007 Revision E1 issue and this report does not,therefore, take account of any changes made to the alignment since that date.

1.2 Background

In July 2006, Jacobs was commissioned by the Railway Procurement Agency (RPA)to act as their Railway Engineering, Design and Safety Consultant for the Metro

North project. The scope of the framework agreement included:

• Preparation of Reference Design;

• New works assessment;

• New rolling stock assessment;

• Assistance with preparation of Railway Order;

• Assistance with the administration of tenders from pre-qualification throughto award; and

• Engineering support during the Railway Order Public Inquiry.

1.3 Scope of the Report

The Geotechnical Data Report (GDR) is solely a factual report and summarises thegeotechnical data obtained for the entire alignment from available publishedsources, previous ground investigations for adjacent projects and the Metro NorthGround Investigation Programme.

A Preliminary Ground Investigation (Reference 1) was carried out for Metro Northduring 2006 by IGSL Ltd. (RPA Contract M7081) under the direction of RPA’sTechnical Consultant, Parsons Brinckerhoff. Parsons Brinckerhoff was responsiblefor the preliminary engineering and conceptual design of the Dublin Metro AlignmentStudy. The purpose of the Preliminary Ground Investigation (PGI) was to providegeotechnical information on the ground conditions and groundwater regime for use

in preliminary design, optioneering and route selection, in particular the Emerging


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Preferred Route. The results of the PGI are presented in the GeotechnicalInterpretative Report prepared by Parsons Brinckerhoff (Reference 2). The scope ofthe Parsons Brinckerhoff interpretative report was reduced by the RPA in February2007, on the basis that Jacobs was carrying out interpretation of available data aspart of the Reference Design process and is responsible for the preparation of theReference Ground Conditions Report for Information (RGCRI) for Metro North. TheRGCRI includes interpretation of the ground conditions and groundwater regime asthey relate to the Reference Design and interpretation of engineering properties fortranslation into design parameters during the design process.

The Main Ground Investigation (MGI) for Metro North was carried out from May2007 to April 2008 as three separate contracts. IGSL Ltd. undertook two contracts(Group A works: Sections 1 to 3 and Group B works: Sections: 4 and 5), whileNorwest Holst Soil Engineering Ltd. undertook one contract (Group C works:Sections 6 and 7). All three contracts were under the direction and supervision ofJacobs. The purpose of the MGI was to provide sufficient geotechnical information

on the ground conditions and groundwater regime to inform the Reference Designand Railway Order Stages and particularly for use in the design and constructionplanning process.

The areas covered by the three separate MGI contracts were as follows:

• Group A works (Sections 1 to 3) from Belinstown to Dublin Airport southernboundary;

• Group B works (Sections 4 & 5) from Dublin Airport southern boundary tonorth of Dublin City University; and

• Group C works (Sections 6 & 7) from north of Dublin City University to St.Stephen’s Green.

The final factual reports for all three MGI contracts were received in April 2008. ThisGDR does not include the MGI data. It is recommended that this report is reviewedin light of the data contained in the MGI Final Factual Reports.

An interpretation of all geotechnical data collected for this report is given in theReference Ground Conditions Report for Information (Reference 3).

This report does not include contamination test data, which is outwith Jacobs’ scopeof work. We understand that RPA’s Environmental Consultant, ERM, has carriedout a review of available contamination test data along the proposed route of MetroNorth and that this information is reported separately (Reference 4).

1.4 Report Format

For ease of presentation, the route has been sub-divided into seven separate areas,from north to south, which correspond to the Railway Order Areas as defined on 29September 2007. These areas are as follows:

• Area 1 – Depot to south of Swords;

• Area 2 – South of Swords to Dublin Airport boundary (north);

• Area 3 – Dublin Airport boundary (north) to Dublin Airport boundary (south);

• Area 4 – Dublin Airport boundary (south) to south of Northwood;

• Area 5 – South of Northwood to Dublin City University (DCU);


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• Area 6 – DCU to south of Mater; and

• Area 7 – South of Mater to St Stephen’s Green.

A brief description of the content of the Geotechnical Data Report is given below:

Section 2 describes the site conditions including the history of site developmentinterpreted from historic maps and aerial photographs, the geological setting and thegeotechnical hazards that are likely to be encountered.

Section 3 presents a summary of the existing ground investigation fieldwork dataobtained from sources such as the Geological Survey of Ireland (GSI), previousground investigations for adjacent projects and the Metro North GroundInvestigation Programme. The numbers and locations of exploratory holes and fieldinstallations are presented, together with details of surface geophysical surveys andin situ tests.

Section 4 presents the existing laboratory test data.

Section 5 presents a discussion of various aspects of nearby previous constructionprojects involving underground excavations, which are considered to be relevant tothe proposed outline method of construction of Metro North. A list of relevanttechnical papers, which generally contain pertinent information in relation to groundprofiles, ground properties and construction methods for similar undergroundconstruction projects in the Dublin area, is also included. This list is by no meansexhaustive.

This report also contains ground investigation location plan drawings and geologicalmaps.

Existing exploratory hole records and results of field and laboratory testing fromprevious investigations are bound as separate volumes; copies of records areavailable via the RPA Data Room.

1.5 Other Relevant Reports

This report is to be read in conjunction with the following Reference Designsubmissions:

• Technical Note 023 - Desk Study Review;• Reference Ground Conditions Report for Information;• Alignment Strategy Report - Working Paper 40;• Outline Method of Construction Report;• Bored Running Tunnel Reference Design Report – Technical Note 010;• Stage 1 Preliminary Ground Movement Assessment Report; and• Stage 2A Preliminary Building Response Assessment Report.

Copies of the above documents, together with other relevant Reference Designdocuments are held in the Metro North Data Room.


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1.6 Limitations and Exceptions

This report has been prepared for the exclusive use of the Rail Procurement Agencyand unless otherwise agreed in writing by Jacobs, no other party may use, make

use of, or rely on the contents of the report. No liability is accepted by Jacobs forany use of this report, other than for the purposes for which it was originallyprepared and provided.

Opinions and information provided in the report are on the basis of Jacobs usingdue skill, care and diligence in the preparation of the same and no explicit warrantyis provided as to their accuracy.

Jacobs is not responsible for the validity or accuracy of the data obtained from thirdparties during this or previous studies or for data received from others. Jacobs hasnot been able to validate information supplied and have therefore taken suchinformation at face value.


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2 Site Conditions

2.1 Site Location and Topography

The proposed location and alignment of Metro North (November 2007, Revision E1issue) is shown in Drawing Nos. B/MN/0000/GE/01 to 13. The topography of eachof the Railway Order Areas (as defined on 29 September 2007), is summarisedbelow:

Area 1 – Depot to south of SwordsThe ground level at the Depot area generally varies between 6mOD and 10mOD.Between the Depot area and the Broad Meadow River the ground level along thealignment is relatively flat and lies between 6mOD and 9mOD. The ground level at

the (provisional) Lissenhall Stop is between 7mOD and 8mOD. The ground levelthen falls at the Broad Meadow River at Lissenhall Bridge to between approximately3mOD to 5mOD and then rises gradually to approximately 26mOD at the southernlimit of Area 1 at the Swords Stop.

The ground levels at the (provisional) Estuary and Seatown Stops lie between5mOD to 6mOD and 13mOD and 16mOD, respectively, while the level at theSwords Stop lies between 25mOD and 26mOD.

Area 2 – South of Swords to Dubl in Airpor t boundary (north)The ground level continues to rise from a level of approximately 26mODimmediately south of the Swords Stop to a level of between approximately 42mOD

and 44mOD at the Fosterstown Stop. The ground level then continues to rise, albeitless steeply, to a level of about 49mOD close to Fosterstown House. The groundlevel is then relatively flat before dipping to around 43mOD at the locations of twostream courses. The ground level then rises steeply to a level of approximately62mOD at the Dublin Airport northern boundary.

Area 3 – Dublin Airport boundary (north) to Dublin Airport boundary (south)North of the Airport Stop the ground level is relatively flat and generally variesbetween 64mOD and 68mOD. The ground level at the location of the Airport Stoplies between 66mOD and 68mOD. South of the Airport Stop the ground level fallsgently to approximately 60mOD at the Airport southern boundary.

Area 4 – Dublin Airport boundary (south) to south of NorthwoodThe ground level is relatively flat (58mOD to 60mOD) between the Airport southernboundary and the Dardistown Stop, which lies at between 60mOD and 61mOD.South of Dardistown Stop the ground level gradually rises to between 64mOD and66mOD before falling from 64mOD at the crest of the cutting of the M50 to 59mODat its base. To the south of the M50 the ground level falls to a level of approximately56mOD at the Santry River. The ground level at the Northwood Stop is between57mOD and 59mOD.

Area 5 – South of Northwood to Dublin City Universi tySouth of Norwood the ground level is relatively flat and lies between 60mOD and64mOD. At Ballymun Stop the ground level lies between 62mOD and 65mOD. The


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ground level then falls gradually to approximately 50mOD to 51mOD at the DCUStop.

Area 6 – DCU to south of MaterTo the south of the DCU Stop, the ground level falls gradually to between 33mODand 35mOD at the Griffith Avenue Stop and then falls more steeply to a level ofapproximately 7mOD at the Tolka River. The ground level then rises again south ofthe Tolka River to a level of approximately 12mOD at the Drumcondra Stop, beforefalling gently to around 10mOD at the Royal Canal and then rising again gently to alevel of between 14mOD and 15mOD at the Mater Stop.

Area 7 – South of Mater to St Stephen’s GreenThe ground level rises from approximately 14mOD at the Mater Stop to around17mOD to 18mOD at Dorset Street Lower and then falls relatively steeply tobetween 9mOD and 11mOD at the Parnell Stop and to around 4mOD to 5mODalong O’Connell Street. The ground level either side of the River Liffey at O’Connell

Bridge is approximately 3mOD to 4mOD. South of the River Liffey the ground levelrises gradually to approximately 12mOD at the St. Stephen’s Green Stop.

The results of topographical surveys carried out by Jacobs for the RPA have beenused to establish ground levels along and in the vicinity of the alignment. Referenceshould be made to the vertical alignment drawings for full details of ground levels.

2.2 Site History

Jacobs carried out a Desk Study Review (Reference 5) of selected historic mapsand aerial photographs in order to identify potential constraints along the proposedalignment, which could impact on the proposed works and also to inform the

planning and design of the Main Ground Investigation.

Historic maps were sourced from the Ordnance Survey of Ireland (OSI), TrinityCollege Library and RPA’s Archaeological Assessment Report (Reference 6).Limited aerial photography was obtained from OSI and reviewed.

The Desk Study Review specifically excluded assessment of the potentialenvironmental implications associated with the historic features identified, which isoutwith Jacobs’ scope of work. It is understood that RPA’s EnvironmentalConsultant, ERM, have carried out a stand alone review of available historicinformation in order to identify potential environmental hazards along the proposedroute of Metro North (Reference 4).

2.3 Geological Setting

2.3.1 Sources of Information

The main sources of geological information that have been consulted in theassessment of the geological conditions along the proposed route of Dublin MetroNorth are listed below:

• Geological Survey of Ireland, 1995: Geology of Kildare-Wicklow Sheet 161:100,000 scale (Reference 7);


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• Geological Survey of Ireland, 1994: Geology of Kildare-Wicklow: AGeological Description (Reference 8);

• Geological Survey of Ireland, 1999: Geology of Meath Sheet 13 1:100,000scale (Reference 9);

•

Geological Survey of Ireland, 2001: Geology of Meath: A GeologicalDescription (Reference 10);

• Geological Survey of Ireland, 2005: Quaternary Geology Map for CountyDublin 1:50,000 scale (Reference 11);

• IGSL Ltd. March 2007. Ground Investigation Factual Report. ContractM7081 (Reference 1);

• Geological Survey of Ireland. Existing ground investigation database(Reference 12);

• Wimtec Environmental Ltd. June 2000. Dublin Light Railway Tunnel Linkbetween St. Stephen’s green and Broadstone. Factual Report on GroundInvestigation Volumes 1 & 2 (Reference 13);

• Haswell Consulting Engineers, 2002. Geotechnical Desk Study City Centre

and Airport. Dublin Metro Alignments Study. Swords to City Centre (via Airport) and City Centre to Ranelagh and Tallaght. Working Paper(Reference 14); and

• Atkins McCarthy, January 2000. Dublin Light Rail. Sandyford to BallymunLine. Underground section between St. Stephen’s Green and Broadstone.Stage IV Report. Volumes 1, 3 and 4 of 4 (Reference 15).

Other sources of information consulted include relevant published literature andtechnical papers on the geology of the Dublin area (References 16 to 24) andseveral less extensive previous ground investigations, which are described inSection 3.1.1. The availability of geotechnical data from outwith the Dublin city

centre area is somewhat limited and has been addressed by the Main GroundInvestigation.

2.3.2 Superficial Geology

The superficial or quaternary, geological history of the Metro North alignment isdescribed in References 8, 10 and 17 and shown in Figure 1.

The generalised soil sequence along the Metro North alignment consists of glacialdeposits (described as glacial till, sands and gravels) overlying CarboniferousLimestone bedrock. In the centre of Dublin and in other urban areas, made groundoverlies the glacial deposits. Alluvial and estuarine deposits are found in the river

valleys.

The Pleistocene Epoch lasted from 1.6 million years ago to 10,000 years ago andduring this period alternating glacial and interglacial periods led to the growth anddecay of ice sheets which covered the area on a number of occasions. TheHolocene Epoch dates from 10,000 years ago to the present day. It is the widelyheld view that during the last glacial period the Dublin City area was glaciated by icefrom the Irish Midlands (the Midlandian Glaciation) moving in a northwest tosoutheast direction and ice from the Irish Sea Basin, which generally moved in anorth to south direction.

Most of the sediments were deposited during the Ice Age itself, either directly from

the extensive ice sheets that spread across the area or by meltwater flowing from


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the ice sheets as they finally melted. The ice sheets ground down the underlyingbedrock, breaking off protruding pieces and further grinding these down. The endresult of this process is the production of sediment, which may include particles of allsizes ranging from clay to boulder and which, when spread over the land surface byglacial ice, takes the form of till.

Alternatively, sediment may be carried and sorted by meltwater and deposited assand and gravel, with silt and clay deposited separately in lake systems or carriedaway to sea. The glacial deposits contain fragments of the type of bedrock overwhich the ice passed. Glacial and glaciofluvial (glacial meltwater) deposits aregenerally very thick in the area of Metro North with thicknesses of over 30m beingcommon. The glaciation of the Dublin area was not straightforward and thepresence of fluvioglacial and glaciomarine sediments almost certainly indicates localwithdrawal of the ice followed by re-advance or a complex depositional systembeneath and around the ice sheet itself (Reference 18).

The lateral movement of glaciers imparted a complex system of lateral stresseswithin the materials sandwiched between the glacial ice and the surface of thebedrock (termed ‘rockhead’). Where rockhead rose in elevation in the direction ofglacial movement this would have placed the sandwiched materials under increasedlateral and vertical stresses. These pressures produce a ‘locked-in’ horizontalstress regime akin to, but in excess of, over-consolidation due to the effects ofvertical overburden pressure alone.

The alluvial deposits of the River Liffey, River Tolka and Broadmeadow River weredeposited during the Holocene Epoch.

The Quaternary Geology Map for County Dublin indicates that the following soil

types are present along the Metro North route:

Till derived from Lower Carboniferous Limestone (Glacial Lodgement Till)

The till is derived from the Lower Carboniferous Limestone and is the predominantsoil type over the majority of the route. The till is typically sub-divided into a lowerblack, very stiff to hard, sometimes stiff, glacial till and a weathered upper brown,firm or stiff, sometimes soft, glacial till. The brown glacial till generally has a highervoid ratio and moisture content and lower strength than the black glacial till. Thethickness of the weathered brown glacial till is typically 2m to 3m, although it isnoted that Wall & Farrell (Reference 25) state that the thickness is very variable,from 1m to 6m and is usually thinner on the north side of the city. It is noted that

Skipper et al (Reference 23) identified four distinct units of the glacial till (upper andlower brown glacial till and upper and lower black glacial till) based on thestratigraphy encountered during ground investigations and excavations for theDublin Port Tunnel project.

The glacial till is typically heavily overconsolidated and is generally characterised byits low compressibility and low permeability. However, pockets, lenses and layers ofhigher permeability gravel and sand are present locally within the glacial till.Extensive deposits of gravel and sand, up to 20m thick and overlying the CalpLimestone bedrock, extend from the River Liffey to up to 1km north of the river.


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Cobbles and boulders with maximum dimensions up to 500mm are common, whileboulders with maximum dimensions greater than 500mm are encountered onlyinfrequently.

The glacial till is present close to the ground surface along the majority of the MetroNorth alignment, but is generally absent at the following locations:

• in the vicinity of the River Liffey; and

• at the location of the pre-glacial buried channel identified by Farrington(Reference 19), to the north of the River Liffey.

The geology of the pre-glacial channel area is complex with glacial tills occurringwithin glacial gravels and vice-versa and likely reflects the complexity of thevariations and different stages of ice sheet advance and withdrawal.

Made Ground

Locally extensive areas of made ground are shown at the following locations:

• immediately north of the Broadmeadow River, covering approximately 100mof the route;

• between the Broadmeadow River and Swords, covering approximately900m of the route;

• locally at the Royal Canal, covering approximately 50m of the route; and

• to the north and south of the River Liffey in Dublin City Centre, coveringapproximately 2km of the route

The ground levels of the formerly intertidal areas of the River Liffey have beenraised by the placement of made ground since medieval times in a generallyuncontrolled way. In some areas this may have been made possible by theplacement of wooden stockades and infilling behind them. The retaining walls forthe present-day course of the River Liffey were constructed in the 19 th century. Inthe vicinity of the River Liffey, the thickness of made ground deposits is typicallybetween 3m and 5m. In urban areas made ground deposits are likely to beencountered along the length of the alignment. In the city centre, the thickness isgenerally between 1m and 4m, but locally deeper, and in general reduces tobetween 1m and 2m to the north of Mater Stop.

The composition of the made ground varies widely and generally consists of a

mixture of waste materials including, for example, domestic refuse, clinker anddemolition rubble.

The locations of several former quarries and gravel pits are indicated by historicplans (Reference 5) in the vicinity of the Depot, close to the Estuary roundabout,adjacent to the Airport Stop and between the Griffith Avenue and DrumcondraStops. It is likely that these former quarries and pits were backfilled in anuncontrolled, or non-engineered, fashion.

There is anecdotal evidence to suggest that the present-day ground level in theParnell Square area has been raised above previous ground levels by the formationof a raised platform, which was created by infilling between houses constructed on

natural ground at a lower level.


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Till with Gravel

Locally extensive areas of ‘Till with Gravel’ are indicated at the following locations:

• from the Depot area to just north of the Broadmeadow River, covering

approximately 1.5km of the route;• to the north of the River Tolka covering approximately 600m of the route;

and

• between Trinity College and St. Stephen’s Green, covering approximately300m of the route.

Gravel derived from Lower Carboniferous Limestone

Two areas of ‘Gravel derived from Lower Carbonifeous Limestone’ are indicated asfollows:

• north of Nevinstown, covering approximately 300m of the route; and

• to the north of the northern boundary of Dublin Airport coveringapproximately 400m of the route.

The gravels are interpreted to be glaciofluvial terrace deposits and post-glacialterrace gravels.

Al luvial Gravel

Two isolated areas of ‘Alluvial Gravel’ are noted at:

• the Tolka River covering approximately 300m of the route: and

• between Parnell Street and Cathedral Street, covering approximately 100mof the route.

Al luvium

The presence of ‘Alluvium’ of limited extent is noted locally at:

• to the north of Dublin Airport within the zone of ‘Gravel derived from LowerCarboniferous Limestone’, occurring as two narrow zones of alluviumassociated with water courses; and

• the Broadmeadow River covering approximately 100m of the route.

Alluvium is also likely to be present beneath deposits of made ground, which havebeen laid in the vicinity of the River Liffey to raise ground levels and reclaim whatwas formerly intertidal land. It is noted that the course of the former River Stein runsclose to Grafton Street (Reference 17) and flows into the River Liffey at Burgh Quay.The course of this river has been incorporated into the public drainage system as afoul drain (Reference 26). The depth to the bed of this watercourse is noted to beapproximately 3m below ground level close to St. Stephen’s Green, which is similarto the depth of made ground and, therefore, it is unlikely that alluvial deposits arepresent beneath the made ground. Farrell and Wall (Reference 17) note thatisolated pockets of soft silts and clays can occur as infill to old ponds or hollows inthe glacial till as well as in old ditches and streams. Where present, the thickness ofthe alluvium is generally less than 3m to 4m.


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Additionally, the Quaternary Geology Map also records one location along thealignment of ‘Bedrock within 1m of the surface’. This is located at Dublin Airport,close to the existing terminal building and covers approximately 100m of the route.Farrington (Reference 19) has shown the existence of a pre-glacial channel whichdiverges from the present channel of the River Liffey from about Connolly Stationand returns near the mouth of the river. The channel contains glacial andfluvioglacial sands and gravels. Long and Menkiti (Reference 22) note that althoughthe mode of formation of the deposits within the channel has not been studied indetail it is likely that the deeper deposits were formed by drainage channels eitherbeneath or within the ice, while more recent deposits closer to the surface may beriver gravels or river terrace gravels.

A thorough description of the distribution and geotechnical properties of thesuperficial deposits likely to be encountered along the Metro North alignment isgiven in Reference 3.

2.3.3 Solid Geology

The expected solid geology of the Metro North alignment is described in References8 and 10 and shown in Figure 2. The published Lower Carboniferous bedrockstratigraphy of the Metro North alignment is summarised in Table 2.1 below:

Table 2.1: Summary of Lower Carboniferous stratigraphy

System Sub-System

Series Formation &Stratigraphic

Thickness

Main Litho logy Descriptions Presentin Areas

Lucan (Calp)(LU/CD)

300m to 800mthick

(Reference 10)

Dark grey to black, fine grained,graded limestone with interbedded

calcareous shale, local cherts &fossilerforous beds.

Areas 4to 7

Tober Colleen(TC)

Variable thicknessup to 250m thick(Reference 10)

Dark grey interbedded calcareousmudstone and very argillaceous

micrite, which is usually burrowed. Inits lower parts it comprises gradedbeds of reef derived debris and insome areas large slumped reef

blocks (Waulsortian).

Areas 1,3 & 4

L O W E R C A R B O N I F E R O U S

D I N A T I O N

V I S E A N

Waulsortian (WA)

Variable thicknessup to 400m thick(Reference 8)

Pale grey, commonly massive

biomicrite with stromatactis in moundforms or complexes, with depositional

dips of 30° to 40° or more.Commonly dolomitised.

Area 3


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System Sub-System

Series Formation &Stratigraphic

Thickness

Main Litho logy Descriptions Presentin Areas

T O U R N A I S I A N

( P A R S )

Malahide(ML)

300m to 1200mthick (Reference

10)

Calcareous shales, siltstones,sandstones and thin limestones

dominate the lower Malahide, whichare overlain by peloidal and

oncholitic, occasionally nodular,micrites and succeeded by

fossilferous limestone and shale, withoolites and sandstone, which are

overlain by argillaceous limestones,nodular wackestones and shales.

Areas 1to 3

It is evident from References 7 and 9 that a mismatch exists at the junction of themaps and there are differences in the descriptions of the respective formations andstratigraphic sequences. Notably the Lucan formation on GSI sheet 13 (Reference

9) is referred to as the ‘Calp’ on GSI sheet 16 (Reference 7). The MalahideFormation is not shown on GSI sheet 16; however, its stratigraphical equivalent isindicated to be the Boston Hill Formation (Reference 8). References 8 and 10include slightly different descriptions of the same rock formations and forcompleteness, the differences are discussed in the following sections.

The formations described above were deposited within a shallow marineenvironment of a subsiding structural basin, referred to as the Dublin Basin.Changes in depositional conditions as a result of the tectonic regime of the basin arereflected in marked changes in the properties and thickness of the deposits. Thisproduced a variety of sedimentary rocks and a variation in the sand and clay contentand the inclusion of shale or mudstone layers, some of which weathered to form

clay. Such variations affect the strength of the rock and its susceptibility toweathering and hence its engineering properties. Prior to the Ice Age, bedrock wasweathered and eroded and deeply incised channels were formed.

Lucan (Calp) Formation

The Lucan or Calp Formation comprises a dark grey to black, fine grained, gradedlimestone with interbedded calcareous shale, local cherts and fossiliferous beds andis expected to underlie the route of Metro North between St. Stephen’s Green andthe Northwood Stop.

From available investigation information the strength of the calp limestone is

indicated to vary from weak to very strong, while the bed thickness varies from60mm to over 3m, but is more typically between 100mm and 300mm, with thinnershale beds and occasionally thicker calcisiltite layers. The limestone containscalcite veining and bands and partings of calcareous shales or mudstones, whichgenerally correspond with the bedding planes.

As a result of the argillaceous nature of the calp limestone, the formation isgenerally not susceptible to karstification and no major voids or cavities have beenreported. However, some evidence of solution features near rockhead within thecity centre has been reported by Long & Murphy (Reference 27). The depth ofweathering of the bedrock is typically between 1m and 3m and the bedrock maycontain clay filled joints and fractures. The permeability of the weathered rock isgenerally higher than the less weathered rock.


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Tober Colleen Formation

The Tober Colleen Formation is the lowest facies of the Calp Limestone (Reference8) and consists of dark grey interbedded calcareous mudstone and very argillaceousmicrite, which is usually burrowed. The micrite is described as subordinate thinmicritic limestones (Reference 10). In its lower parts it comprises graded beds ofreef derived debris and in some areas large slumped reef blocks of Waulsortian.The Tober Colleen Formation is likely to be present in the vicinity of the Depot andfrom the Airport Stop to between the Dardistown and Northwood Stops.

Waulsor tian Formation

The Waulsortian Limestone is described as a pale grey, commonly massivebiomicrite with distinctive cavity-filling stromatactis in mound forms or complexes,

with shale interbeds with depositional dips of 30° to 40° or more. These moundscan be either discontinuous or coalesced (Reference 10). Horizontal beds, which

are laterally equivalent to the mounds or reefs can be variable in character, butgenerally include a higher proportion of shale beds (Reference 10). TheWaulsortian Limestone is locally dolomitised and is present within a relatively smallarea at Dublin Airport.

The Waulsortian Formation is more prone to karstification and is likely to be morepermeable and porous than the other limestone formations. Karstification can formcavities and hollows in the bedrock but such features are difficult to locate duringground investigations.

Malahide Formation

The Malahide Formation stratigraphically underlies the Waulsortian Formation and isfound between the Depot area and Dublin Airport. In its lower parts the MalahideFormation comprises calcareous shales, siltstones and sandstones with thinlimestones. These have then been succeeded by peloidal and oncholitic,occasionally nodular, micrites which in turn have been overlain by fossilferouslimestone and shale, with oolites and sandstone. The uppermost parts of theMalahide Formation comprise argillaceous limestones, nodular wackestones andshales.

Depth to Bedrock

Between Belinstown and just north of Fosterstown, depth to bedrock generallyappears to be between 5m and 15m below ground level, although data is sparse.To the south of Fosterstown, the limited available data suggests that bedrock falls todepths of greater than 40mbgl, before rising to within a few metres of ground level inthe vicinity of Dublin Airport. To the south of Dublin Airport, the bedrock level fallsrelatively steeply to depths of between 30mbgl and 40mbgl. Bedrock becomesshallower (between 10m and 20m below ground level) as the alignment approachesthe M50 motorway.

Bedrock is estimated to lie between 15mbgl and 25mbgl between the M50 andDCU, with locally greater depths of more than 30mbgl at the Griffith Avenue Stop,although it is noted that bedrock depth data are sparse. Between the Griffith

Avenue and Mater Stops, the depth to bedrock is typically between 10mbgl and


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25mbgl with depths increasing as Mater is approached. From Mater to the northernend of O’Connell Street, depth to bedrock increases to between approximately23mbgl and 32mbgl, as a result of a combination of a rise in ground levels and theexistence of the pre-glacial channel. Bedrock level then rises to approximately10mbgl at O’Connell Bridge and to the south of the River Liffey depth to bedrock istypically between 7mbgl and 12mbgl.

The Geological Survey of Ireland has prepared contour plans of estimated bedrocklevels in the Dublin city centre area (Figure 3). It is considered that the data fromthe recent MGI will allow the GSI bedrock levels in the vicinity of the alignment to berefined. The GSI consider that the data contained in Figure 3 are accurate to about+/- 3m; however, it is noted that Farrell and Wall, 1990 (Reference 17) report thatlocal rockhead level variations of 5m in elevation, over a 3m plan distance havebeen recorded. Depth to bedrock can vary significantly over short distances as aresult of the presence of incised drainage channels.

2.3.4 Structural Geology

The strata within the Metro North area were deposited within a subsided structuralbasin referred to as the ‘Dublin Basin’. The rate of subsidence was variable acrossthe basin resulting in variation in the thickness of accumulated sediment and wasparticularly variable during the Visean. At this time and towards the end of theWaulsortian mound growth, the basin began to subside further due to intermittentactivity of the basins boundary faults and continued during the deposition of theTober Colleen and Lucan (Calp) formations.

The formations within the basin were then subjected to a major tectonic phase at theend of the Carboniferous period of Variscan (Hercynian) Orogeny, with overall

compression along a NW-SE trend resulting in the folding, faulting and uplifting ofthe Carboniferous rocks commonly along earlier stretching faults. The foldingresulted in several synclinal and anticlinal structures with ENE-WSW trending axialtraces forming in the immediate area. The general route of Metro North crosses theaxial trace of a syncline at St. Stephen’s Green and an anticline just to the north ofO’Connell Bridge (Reference 15). Figure 2 shows that the proposed route crosses afurther anticline just south of the Fosterstown Stop and again at the (provisional)Estuary Stop.

The folding was post-dated by faulting along NNW-SSE to N-S trends, which appearto have involved strike-slip movement and are shown on Figure 2 to intersect theroute at DCU Stop and again between the Estuary and Seatown Stops. These

faults were offset by a later phase of faulting with traces trending ENE-WSW, whichare shown to intersect the route just to the north of the Airport Stop.

The bedrock has been tilted and folded in a variety of directions with typical dip

angles of between 5° and 30°. It should be noted that steeper dip angles can occur,notably close to fault zones and in areas where the depositional dips are alreadysteep such as within the Waulsortian and Tober Colleen Formations.

It is noted that Figure 2 shows very few faults in the Dublin city centre area and it isconsidered that this may be a result of the relatively large thickness of superficialdeposits present and also partly due to the fact that the limestone bedrock does not

contain distinctive marker beds. It has been suggested (Reference 17) that the


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existence of the pre-glacial channel to the north of the River Liffey may be as aresult of a structural weakness within the bedrock.

Dolomitisation is common near fault zones (Farrell & Wall, 1990) (Reference 17).

2.3.5 Hydrogeology

Reference 16 notes that data on the hydrogeology of the Dublin area is sparse andthat few hydrogeological investigations have been carried out as an adequate watersupply has been available from the Wicklow Mountains. The report includes a tableof abstraction records including locations, water levels, yields, depth to rock andtype of rock.

Well records for the County Dublin area have been obtained from the GeologicalSurvey of Ireland’s well database. The database identified 12 wells within 550m ofthe Metro North alignment. Reference 5 provides further details of the wells

identified in the GSI database and wells and pumps identified on historic maps. It isnoted that the approximate locations of two wells lie within 10m to 20m of theDardistown Stop and one well lies within 100m of the Parnell Square Stop.Reference 16 notes wells at Parnell Street and Swords and Reference 28 noteswells close to Dardistown.

Close to the River Liffey the groundwater level is generally at about 0m OD and,reportedly, is not significantly affected by tidal variations. Based on experience atthe Custom House Docks site (Reference 29), this was considered to be a result ofthe reasonably watertight river and dock walls and the presence of a lowpermeability silt or clay layer in the bed of the docks and river.

There are two main sources of groundwater along the Metro North alignment:shallow groundwater associated with fluvioglacial and alluvial sand and graveldeposits; and deeper groundwater associated with the Carboniferous Limestonebedrock. The extent of shallow groundwater within the superficial deposits isdependent on the extent of the sand and gravel deposits: sands and gravels close towatercourses are expected to be in hydraulic continuity with them. Fluvioglacialsands and gravels within the glacial till can be of limited extent, whereas, moreextensive deposits of sands and gravels may be in hydraulic continuity with adjacentwater courses. The glacial till generally has a low permeability and protects andrestricts recharge of, or confines, the underlying bedrock aquifers. The sand andgravel zones around Dublin permit a high level of recharge, give additional storagecapacity to the bedrock aquifers and, where deposits are extensive, are likely to be

classified as ‘locally important aquifers’.

The low permeability of the clay within the Glacial Tills often betrays the existence ofa high groundwater table, based on the apparent dryness of even deep excavations.Where made ground overlies soils of lower permeability, perching of thegroundwater can occur. Perched groundwater tables are vulnerable to significantvariation in level, both on a seasonal basis and over short periods of time, due to thefluctuation in the level of neighbouring bodies of water (e.g. tidal effects), or due torainstorm infiltration.

Groundwater flow in the bedrock is controlled by fissure permeability. Thelimestone, where this consists of fine grained and argillaceous limestones andshales, is characterised by its low permeability and is generally unproductive.


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Higher yields can be obtained in fault disturbed zones. The “Calp” limestone isconsidered a minor aquifer that can yield sufficient water for domestic supplies andis the main aquifer used for public water supply in County Meath. The Calp inMeath has been classified as a Locally Important Aquifer although it is noted that itis generally less productive in County Dublin. Reference 16 notes that thelimestones are generally recorded to be tight and dry, although individual fracturesystems can give flows in the range of 5 to 20 litres/second. The WaulsortianLimestones in the vicinity of Dublin Airport are likely to comprise ‘bedrock which ismoderately productive only in local zones’.

The Irish Groundwater Protection Scheme (Reference 30) provides guidelines forplanning and licensing authorities and a framework to assist in the control ofdevelopment, in order to protect groundwater resources. The two main integratedcomponents of the scheme are: land surface zoning; and groundwater protectionresponses for potentially polluting activities. The land surface zoning is presentedon a groundwater protection map, which is compiled by combining an aquifer map

and a groundwater vulnerability map. The aquifer and groundwater vulnerabilitymaps are derived from bedrock and drift maps, depth to bedrock andhydrogeological data.

The scheme also identifies source protection areas around significant groundwatersupply sources and it is noted that the Metro North alignment is not located in a GSIgroundwater source protection area. Source protection areas are combined with thevulnerability map to give source protection zones, although these zones areconsidered to be provisional only.

The GSI draft bedrock aquifer map classifies the majority of the bedrock along theMetro North alignment as ‘Ll’ i.e. locally important aquifer, where bedrock is

moderately productive only in local zones. The area of Waulsortian Limestone atDublin Airport is classified as ‘Ll’. Two areas are classified as ‘Pl’ i.e. poor aquifers,where bedrock is generally unproductive except for local zones. These areas occuralong the section of alignment between the M50 and Dublin Airport and also at theDepot area and are consistent with the extent of the Tober Colleen LimestoneFormation, shown in Figure 2.

The GSI has classified the area where Waulsortian Limestone is present at Dublin Airport as an area of extreme groundwater vulnerability as rock is at shallow depth.The remainder of the Metro North alignment is classified as ‘generally high to lowvulnerability’ as only an interim study has been carried out. There are fourvulnerability ratings: extreme, high, moderate and low. The rating category is a

function of the soil type, the type of recharge and the thickness of the unsaturatedzone. The majority of the alignment for Metro North is underlain by low permeabilityglacial till greater than 10m thick, which gives a low vulnerability rating. Where thethickness of low permeability glacial till is between 5m and 10m the vulnerabilityrating is moderate. Where extensive granular deposits are present the vulnerabilityrating would increase to high, or extreme.

Reference 14 describes records of two groundwater abstraction wells put down in1890 and 1891 and noted in a geological memoir. A well in St. Stephen’s GreenWest encountered dark shaly limestone at 7.6mbgl beneath gravelly boulder clay(glacial till). A ‘good’ supply of water was obtained from a 1.2m penetration intorock. A well in Upper Sackville Street (now O’Connell Street between Henry Street


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and Parnell Street) encountered limestone at 16.8mbgl; however, only brackishwater was recovered from a 76m penetration into rock at this location.

Reference 14 suggests that the annual fluctuation of the groundwater table is lessthan 5m, except where the limestone and gravel aquifers are more elevated.Groundwater in the vicinity of the River Liffey is likely to be saline and groundwaterlevels in the vicinity of the River Liffey are anticipated to exhibit tidal variations.Reference 17 suggests that tidal variations are likely to dissipate rapidly away fromthe river, although conditions will be somewhat dependent on the effectiveness ofthe cut-off provided by the retaining walls to the River Liffey.

2.4 Geotechnical Hazards

There are a number of potential ground related hazards that could impact upon theconstruction of the Metro North. A number of potential hazards are discussed in thefollowing sections; however, this section does not represent an exhaustive list of

hazards and it is recognized that other, as yet unidentified, hazards may be present. A more detailed assessment of the probability, consequence and mitigation of thesehazards is presented in the Outline Method of Construction Report and the BoredRunning Tunnel Reference Design Report (Technical Note 010), including risksassociated with TBM tunnelling operations.

2.4.1 Archaeological Remains

Dublin has a rich archaeological past and the planning of proposed constructionworks involving excavation below ground level (particularly Stop boxes andentrances) will need to consider the archaeological aspects. This issue is outwiththe scope of this report and reference should be made to the Metro North

Archaeological Assessment Report (Reference 6).

2.4.2 Relic Foundations and Obstructions

Given the long history of development in the city centre the presence of relicfoundations, basements, cellars and disused services and utilities within the madeground is to be expected. Specific ground investigation and/or appropriateconstruction contingency measures will be required for excavation within the madeground.

2.4.3 Boulders in Glacial Till

It is noted that many previous light cable percussion boreholes carried out in theDublin area report presumed bedrock at their termination levels. As a result of thepresence of boulders and cobbles within the glacial till, such presumed bedrocklevels are not considered to be reliable and, therefore, bedrock levels are morereliably estimated from rotary cored boreholes. Previous experience indicates thatboulders with maximum dimensions of greater than 0.5m are rarely encounteredduring construction works in Dublin.

2.4.4 Granular Materials within Glacial Till

Pockets, lenses and layers of granular material, of varying extent, exist within theglacial till, while extensive glacial gravel deposits are present to the north of theRiver Liffey. Therefore, there is potential for encountering groundwater in localised


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areas within the till; inflows may be sudden and variable, with the volume of inflowbeing dependent on the volume of granular material, interconnectivity with othergravel deposits and groundwater pressure. Saturated gravels with sub-artesianpressures are expected north of the Liffey; blowing sands and gravels have beenencountered in a number of exploratory holes during ground investigation works inthis area. Construction methods for tunnels and foundations in these materialsrequire careful consideration.

Where pumping is required to dispose of groundwater from excavations,consideration will need to be given to contamination levels. This issue is outside thescope of this report.

The presence of sandy or gravelly soils within cut slopes can potentially lead torapid dissipation of excavation induced negative pore water pressures and can leadto slope failures (References 23, 31 & 32). The presence of such materials can alsohave adverse effects on deep foundation and shaft construction (Reference 33).

Several authors (e.g. Reference 34) have noted that laboratory tests to determinethe particle size distribution of samples of granular materials obtained from groundinvestigations tend to underestimate the percentage of fine materials as a result ofwashout during sample collection. This, in turn, can give rise to an over-estimate ofpermeability.

2.4.5 Weathered and Rafted Rockhead

The occurrence of weathered rockhead (typically the first few metres) is variableacross the site. Where encountered, the engineering properties are likely to bepoorer and may cause problems for foundation construction and in achieving an

adequate cut-off for retaining walls. Skipper et al (Reference 23) encountered aglaciotectonised contact between the glacial till and the underlying rockhead duringexcavations for the Dublin Port Tunnel. A relatively undisturbed raft of limestone, upto 2m thick, was identified above a 2m to 5m thick zone of disturbed steeply dippinglimestone blocks in a clay matrix. Long and Murphy, 2003 (Reference 35) describeproblems associated with the installation of ground anchorages at a number of sitesin Dublin. The problems were thought to have arisen, in part, as a result of theweathered and variable nature of the rockhead surface.

Farrell and Wall, 1990 (Reference 17) report that rockhead levels can be variablewith local variations of 5m in level, over a 3m plan distance, having been recorded.

2.4.6 Alluvium

Soft silts and clays are likely to be present in the areas of the River Liffey, TolkaRiver and Broadmeadow River and other smaller streams and former river courses.There is the potential for ground stability issues and excessive settlementassociated with construction over and within these materials. There is also a risk ofunacceptable settlement, induced by groundwater drawdown, occurring in theseweak layers.

Bands of peat were encountered locally within the alluvium in the vicinity of the RiverLiffey: there is potential for ground gas associated with such organic deposits toimpact on the construction of the O’Connell Bridge Stop. Ground relatedcontamination issues are addressed in Reference 4.


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2.4.7 Karst

Karst features are most likely to be encountered within the Waulsortian Formation,which is present in the vicinity of Dublin Airport. Reference 14 reports the existenceof ‘water and clay filled voids proven as a local karst feature in the form of anelongated vertical pipe slightly widened in the east-west plane beneath the Block Ccar park in the Reef limestone’. The development of karst features results inunpredictable and variable size cavities which can impact on foundations andtunnels. Reference 35 reports that there are no available records of solutionfeatures within the Dublin limestone, although reference is made to a small cavewithin the quaternary deposits at Parkgate Street.

A search of the GSI karst database did not produce any records of karst featureswithin several hundred metres of the proposed alignment of Metro North. However,it is noted that this source of information is dependent on submission of data frominterested parties and, therefore, is by no means exhaustive.

2.4.8 Former Boreholes and Wells

The presence of a significant number of former wells and pumps in the vicinity of theproposed tunnel alignment could potentially present direct hazards to tunnelling viadamaging surface blow-outs or collapses, if a closed face pressurised TBM were tointercept them during tunnel driving.

Reference 36 recommends that a risk management approach is adopted to managesuch hazards. This would involve an assessment of the risk, possible investigationand treatment (if considered necessary) and identification and implementation ofconstruction contingency measures in order to manage the risk to the general public

and properties.

Reference 5 includes a schedule of the approximate locations of pumps and wellsidentified from historic maps. It would be prudent to assume that numerous other‘unknown’ wells and pumps are located in the vicinity of the alignment.

2.4.9 Tectonic Faulting and Folding

The locations of faults within the Dublin area are not well defined due to thethickness of the superficial deposits and the lack of marker beds in the CalpLimestone. Faults are known to be more prevalent in the limestones at the Airport.Reference 37 reports that a previously unidentified major fault, with a 4m to 5m

disturbed zone, was encountered during tunnelling for the DPT project. It isrecommended that sufficient flexibility is retained in the location of undergroundstructures i.e. crossovers to allow such structures to be re-located in the event thatdisturbed zones are encountered within the bedrock.

Faulting along earlier ENE-WSW fold trends and later NNW-SSE to N-S trends mayhave resulted in potential intense fracturing and cavities and the development ofclay gouge of variable consistency. The presence of such conditions would need tobe thoroughly investigated where underground excavation in rock is proposed.Folding may have resulted in the development of tight folds trending ENE-WSW andintense fracturing, particularly in the vicinity of axial traces.


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Reference 38 describes the existence of residual angles of shearing resistance of

13° within weak mudstone layers and also the occurrence of a rock slide during amajor trench excavation. This implies that a slide could occur even in shallowdipping ‘Calp’ limestone if the direction of the major discontinuities is unfavourable.

There is a potential for blocks of rock to fall onto TBM’s during tunnelling throughfissured rock, which could cause difficult driving and blockages.

2.4.10 Groundwater Drawdown

Reference 38 notes that dewatering in the city centre has generally not causedsignificant settlements, although there may have been some movements ofbuildings in one location due to extensive groundwater lowering. This lack of groundmovement due to dewatering is probably due to the limited extent and thickness(generally 3m to 4m) of the soft alluvial and estuarine deposits as well as the shortduration of the drawdown. However, soft alluvial deposits associated with the RiverLiffey are known to be present close to O’Connell Bridge and particular care will be

required to ensure dewatering settlements are maintained within acceptable limits.The retaining walls of stop boxes may require toe-grouting to ensure an effectiveseal and maintain drawdown within acceptable limits during dewatering.

2.4.11 Unexploded Bombs

Although Ireland declared itself neutral at the beginning of World War II, Dublin wasbombed by the German Luftwaffe on several occasions between January and May1941. The bombs from a raid on 31 May 1941 reportedly hit areas of NorthRichmond Street, Rutland Place, Phoenix Park, Dublin Zoo and the North Strand,claiming the lives of 34 people and damaging or destroying about 300 houses.None of the reported bombing areas are in the vicinity of the proposed Metro North

alignment and, therefore, the likelihood of encountering unexploded bombs appearsto be minimal.

2.4.12 Contamination

There is potential for soil, groundwater and ground gas contamination associatedwith former uses of the site area to exist within the ground, particularly within themade ground, encountered along the route of Metro North. Contamination issuesare outwith the scope of this report. Reference should be to Reference 4 forinformation on contamination issues.


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3 Ground Investigation Fieldwork

3.1 General

Ground investigation data from a number of previous ground investigation contractsin the vicinity of the Metro North alignment, together with data from the Metro NorthGround Investigation Programme, has been collated and reviewed.

The available exploratory hole, geophysical (surface) survey, field installation and insitu field test report records are listed in Sections 3.2 to 3.7, respectively, forreference. The available fieldwork records from both previous ground investigationsand the Metro North Ground Investigation Programme are presented separately inthe following sections of the report. The locations of previous ground investigationexploratory holes are presented in Drawing Nos. B/MN/0000/GE/01 to 13.

3.1.1 Previous Ground Investigations

Previous available ground investigation data in the vicinity of the Metro Northalignment has been collated from a number of sources, as shown in Table 3.1below.

Table 3.1: Previous Ground Investigation Reports

Report Title GroundInvestigationContractor

Client Year Remarks

Geological Survey of Ireland (GSI)Ground Investigation Database

(Reference 12)

Various Various Various -

Dublin Light Railway: Tunnel Linkbetween St. Stephen’s Green andBroadstone. Factual Report onGround Investigation Volume 1,Exploratory hole and in situ test

records, Volume 2, Laboratory Testsand separate report volume for

borehole video imaging survey byColas Camera (Reference 13).

WimtecEnvironmental Ltd.

Coras IompairEireann

2000 Volume 3 corephotographs missing;Geophysical survey

report (BELGeophysical, ReportJN:98532) missing.

Mater and Children's Hospital, Mater,Dublin (Reference 39)

Irish GeotechnicalServices Ltd.

O’Connor SuttonCronin

2002 -

Dublin Light Rail Track, O'ConnellStreet Substation, Dublin (Reference

40)

Irish GeotechnicalServices Ltd.

MVMBNI JV 2002 Report status: Draft

Dublin Airport Terminal 2: GroundInvestigation (Reference 41)

IGSL Ltd. Dublin Airport Authority

2007 Report status: Draft

Deskstudy, Walkover andGeophysical Survey of Hugo Byrne’s

Land at Ballymun, Co. Dublin(Reference 42)

B.J. Murphy & Associates

T.J. O’Connor & Associates

2000 Report status: Interim

M50 Upgrade (Contract 2)Supplementary Ground Investigation

IGSL Ltd. National Roads Authority

2006


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Report Title GroundInvestigationContractor

Client Year Remarks

Northern Cross Route, Phase 2, Site

Investigation Data. Volumes 1 to 3.

Site Investigations

Ltd.

Dublin County

Council RoadsDepartment

1991-92

A summary of the GSI ground investigation report numbers, locations and dates ispresented in Appendix A.

3.1.2 Metro North Ground Investigation Programme

3.1.2.1 Preliminary Ground Investigation

RPA appointed IGSL Ltd. in 2006, to carry out the Preliminary Ground Investigation(PGI) works for Metro North. The fieldwork was carried out between May and

November 2006 under the direction and supervision of Parsons Brinckerhoff. ThePreliminary Ground Investigation Factual Report was submitted in April 2007(Reference 1). The scope of the PGI was to provide geotechnical information on theground conditions and groundwater regime for use in preliminary design,optioneering and route selection, in particular the Emerging Preferred Route.Parsons Brinckerhoff submitted a Geotechnical Interpretative Report in April 2007(Reference 2).

The fieldworks comprised:

• Cable percussion boreholes in superficial deposits;

•

Rotary core drillholes in glacial till and rock using conventional triple tube andGeobor-S wireline drilling methods;

• Packer tests in rotary drillholes in rock;

• Variable head permeability tests in cable percussive boreholes;

• Downhole geophysical logging of boreholes in rock, including Caliper, CCTVand High Resolution Acoustic Televiewer;

• Surface refractive and reflective profiling of selected sections of thealignment; and

• Associated sampling and standard penetration testing.

The following soil laboratory testing was carried out: Atterberg limits; naturalmoisture content; particle size analysis; consolidated and quick undrained triaxial

compression; sulphate, pH and organic matter content. Rock laboratory testingincluded the following tests: uniaxial compressive strength (UCS) and deformabilityin uniaxial compression; point load strength index; porosity and density; slakedurability; Brazilian tensile strength; direct shear testing of rock joints; Chercharabrasivity; and cuttability.

3.1.2.2 Main Ground Investigation

The Main Ground Investigation (MGI) for Metro North was carried out from May2007 to April 2008 for RPA by IGSL Ltd. (Areas 1 to 5) and Norwest Holst SoilEngineering Ltd. (Areas 6 & 7) under the direction and supervision of Jacobs. Thepurpose of the MGI was to provide sufficient geotechnical information on the groundconditions and groundwater regime to inform the Reference Design and RailwayOrder Stages and more particularly for use in the design and construction process.


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The MGI was let by RPA as three separate contracts. IGSL Ltd. was awarded theGroup A works (Lissenhall to Dublin Airport northern boundary) and Group B works(Dublin Airport northern boundary to north of Dublin City University) contracts andNorwest Holst Soil Engineering Ltd. was awarded the Group C works (north ofDublin City University to St. Stephen’s Green) contract.

Final factual reports for the MGI were received in April 2008. The MGI data has notbeen included in this Geotechnical Data Report (GDR).

3.2 Light Cable Percussion Boreholes


The records of a total of 38 light cable percussion boreholes from previous groundinvestigations in the vicinity of the Metro North alignment have been obtained. Theborehole locations are shown in Drawing Nos. B/MN/0000/GE/01 to 13. All

boreholes are vertical boreholes. The depth of the boreholes ranged from 1.5m to36.5m below ground level.

A summary of the GSI cable percussion boreholes including the borehole reference,co-ordinates, ground level, depth and Railway Order Area, is presented in AppendixB. Summaries of boreholes from the remaining previous ground investigations arepresented in Table 3.2 below:

Table 3.2: Summary of Previous GI LCP Boreholes (excl. GSI)

BoreholeReference

Easting (m) Northing (m) Ground Level(mOD)

Depth (m bgl) RailwayOrder Area

G-BH1A 317320 243188 65 13.20 Area 3

G-BH2 317322 243130 65 8.75 Area 3

G-BH3 317269 243150 65 13.00 Area 3

G-BH4 317152 243216 65 15.20 Area 3

G-BH5 317053 243181 65 11.70 Area 3

G-BH6 317059 243141 65 12.50 Area 3

G-BH7 316974 243146 65 13.20 Area 3

G-BH8 316962 243213 65 9.15 Area 3

G-BH9 316886 243208 66 12.85 Area 3

G-BH102 316928.94 243222.07 66.30 6.30 Area 3

G-BH103 316958.24 243258.29 65.58 1.50 Area 3

G-BH104 317003.26 243268.40 65.40 9.00 Area 3

G-BH105 317010.72 243253.37 65.44 9.30 Area 3

G-BH106 317039.66 243279.44 65.18 9.10 Area 3

G-BH107 317085.22 243298.45 65.31 7.10 Area 3

G-BH108 317048.17 243236.80 65.27 10.00 Area 3

G-BH109 317116 243253 65.00 9.20 Area 3

G-BH110 317032.46 243206.22 66.07 8.80 Area 3

G-BH111 316983.07 243185.71 66.62 8.20 Area 3

G-BH112 317083.50 243229.21 65.51 10.00 Area 3

G-BH113 317032.03 243177.13 66.50 7.20 Area 3

G-BH114 317013.02 243128.75 66.14 10.00 Area 3

G-BH115 317066.72 243159.10 65.82 8.40 Area 3

G-BH116 317217.28 243184.29 62.56 10.00 Area 3G-BH117 317153.64 243179.61 64.15 8.50 Area 3


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BoreholeReference


Depth (m bgl) RailwayOrder Area

G-BH118 317090.09 243129.78 65.21 8.20 Area 3

G-BH119 317158.88 243132.00 64.35 10.10 Area 3

G-BH120 317136.88 243111.71 64.58 12.00 Area 3

G-BH121 317197.35 243107.47 63.87 11.30 Area 3

G-BH122 317174.25 243059.85 63.77 11.00 Area 3

M50-BH14/1 315414 241239 64.20 14.95 Area 4

M50-BH14/2 315442 241241 61.44 11.00 Area 4

M50-BH14/3 315413 241266 63.38 13.50 Area 4

M50-BH14/4 315443 241272 61.07 10.80 Area 4

M50-BH14/5 315408 241303 62.35 12.70 Area 4

M50-BH14/6 315434 241309 59.94 11.50 Area 4

M50-BH15/1 315326 241233 64.86 12.00 Area 4

M50-BH15/2 315292 241225 64.54 12.50 Area 4

M50-BH15/3 315323 241256 64.77 11.40 Area 4

M50-BH15/4 315292 241253 64.75 12.50 Area 4

M50-BH15/5 315320 241298 64.61 10.50 Area 4

M50-BH15/6 315290 241295 64.63 13.50 Area 4

M50-BH903 315404.26 241085.91 68.01 13.20 Area 4

M50-BH904 315409.23 241056.68 67.56 14.00 Area 4

M50-BH906 315355.25 241074.28 59.12 6.00 Area 4

M-BHB1 315507 235611 17.02 9.00 Area 6

M-BHC 315440 235698 17.60 8.00 Area 6

M-BHD 315517 235814 14.98 8.00 Area 6

M-BHE 315570 235644 17.28 7.90 Area 6

M-BHF 315587 235757 14.74 8.00 Area 6

M-BHG 315488 235774 15.82 2.10 Area 6M-BHH 315427 235637 18.33 8.00 Area 6

M-BHI 315517 235767 15.78 7.00 Area 6

WBH45 315037.00 234720.00 7.80 36.50 Area 7

WBH46 314969.00 234860.00 10.50 21.50 Area 7

WBH9 315636.00 234445.00 3.45 9.00 Area 7

LU-BH1 315954.47 234496.89 4.12 11.60 Area 7

LU-BH2 315958.80 234482.59 4.07 7.70 Area 7

Notes:

1. Co-ordinates and ground levels in bold font have been established by surveying and were provided with the

exploratory hole logs or by GSI.

2. Co-ordinates and ground levels in standard font have been estimated by GSI.

3. Co-ordinates and ground levels in italics have been estimated by Jacobs based on ground investigation location

plans and adjacent topographical survey information.



A total of 57 light cable percussion boreholes were completed during the PGI. Theborehole locations are shown in Drawing Nos. B/MN/0000/GE/01 to 13. Allboreholes are vertical boreholes. The depth of the boreholes ranged from 0.4m to27.0m below ground level. The majority of the boreholes were less than 10m deep.


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A summary of the completed PGI cable percussion boreholes, including theborehole reference, co-ordinates, ground level, depth and Railway Order Area, ispresented in Table 3.3 below:

Table 3.3: Summary of Metro North PGI LCP Boreholes

BoreholeReference


Depth(m bgl)

RailwayOrder Area

IGSLBH67 318662.04 246341.78 24.30 10.2 Area 1

IGSLBH68 318756.71 247067.30 11.64 3.3 Area 1

IGSLBH69 318616.41 247578.61 7.96 5.8 Area 1

IGSLBH70 318686.65 248102.45 3.95 6.1 Area 1

IGSLBH64 317790.60 244910.87 46.12 1.7 Area 2

IGSLBH64A 317790.60 244910.87 46.12 5.7 Area 2

IGSLBH65 317793.29 245323.40 46.75 10.0 Area 2

IGSLBH66 317965.87 245876.40 30.68 5.5 Area 2

IGSLBH33 316645.78 242764.11 62.25 5.2 Area 3

IGSLBH35 316972.91 243519.31 67.28 6.6 Area 3

IGSLBH36 317292.82 244321.90 62.99 1.5 Area 3

IGSLBH59 317071.44 242268.87 57.37 6.0 Area 3

IGSLBH60 317321.89 242695.15 59.12 7.5 Area 3

IGSLBH61 317395.20 243075.11 59.93 6.0 Area 3

IGSLBH62 317592.47 243394.38 59.01 6.6 Area 3

IGSLBH63 317767.99 244096.61 54.62 12.0 Area 3

IGSLBH28 315399.26 240627.54 60.60 8.0 Area 4

IGSLBH29 315487.06 241201.07 64.82 7.0 Area 4

IGSLBH30 315631.87 241379.23 63.55 6.3 Area 4

IGSLBH31 315768.76 241495.54 65.66 7.2 Area 4

IGSLBH32 316437.82 242254.31 61.46 6.2 Area 4

IGSLBH55 312695.82 240704.26 71.71 3.1 Area 4

IGSLBH56 312570.77 241022.11 76.73 1.4 Area 4

IGSLBH57 314040.93 241780.81 71.20 4.6 Area 4

IGSLBH58 315867.39 241901.91 60.98 6.1 Area 4

IGSLBH27 315496.59 239856.59 61.87 9.0 Area 5

IGSLBH17 315367.25 236150.70 20.89 10.6 Area 6

IGSLBH18 315184.65 236605.57 23.42 4.9 Area 6

IGSLBH22 315500.45 237701.59 29.05 5.1 Area 6

IGSLBH24 315499.55 238267.23 44.17 4.3 Area 6

IGSLBH25 315509.16 238511.13 48.16 7.3 Area 6

IGSLBH37 315889.75 235772.05 9.90 11.8 Area 6IGSLBH38 315850.20 235980.81 10.91 7.7 Area 6

IGSLBH39 316041.79 236287.53 13.75 8.5 Area 6

IGSLBH40 316155.23 236833.71 7.95 2.5 Area 6

IGSLBH41 316056.47 237285.11 16.91 11.6 Area 6

IGSLBH46 314321.08 236613.53 32.66 7.4 Area 6

IGSLBH49 314058.12 237530.59 71.49 1.0 Area 6

IGSLBH49A 314058.97 237546.72 74.09 1.0 Area 6

IGSLBH49B 314056.43 237553.07 71.01 4.4 Area 6

IGSLBH50 313736.91 238162.78 92.03 4.3 Area 6

IGSLBH51 313648.59 238295.46 93.66 4.0 Area 6

IGSLBH71 315942.56 236150.31 10.70 7.5 Area 6IGSLBH72 316145.02 236581.05 8.85 9.0 Area 6

IGSLBH73 316048.50 236948.19 9.54 8.0 Area 6


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BoreholeReference


Depth(m bgl)

RailwayOrder Area

IGSLBH74 316034.54 237554.14 25.55 11.0 Area 6

IGSLBH78 315924.84 236226.18 13.50 8.0 Area 6

IGSLBH01 315757.93 233130.92 14.23 9.0 Area 7

IGSLBH02 315803.83 233329.13 12.43 8.5 Area 7

IGSLBH03 315898.03 233536.35 11.30 8.4 Area 7

IGSLBH04 315877.51 233666.74 9.94 7.0 Area 7

IGSLBH05 316204.10 233862.21 - 10.0 Area 7

IGSLBH06 315933.36 234062.02 5.05 6.2 Area 7

IGSLBH07 315978.67 234186.00 4.50 9.0 Area 7

IGSLBH08 315944.10 234416.97 4.06 0.4 Area 7

IGSLBH09 315975.30 234756.50 4.18 11.2 Area 7

IGSLBH10 315855.01 234846.15 4.93 2.1 Area 7

IGSLBH10A 315823.28 234838.06 4.93 15.0 Area 7

IGSLBH11 315890.44 234934.29 4.88 11.8 Area 7

IGSLBH12 315743.39 235076.96 8.83 27.0 Area 7

IGSLBH14 315576.25 235409.49 17.13 7.8 Area 7

Notes:






3.2.2.2 Main Ground Investigation

Blank.

3.3 Rotary Open Hole, Rotary Core and Geobor-S Drillholes


The records of a total of 104 rotary drillholes from previous ground investigations inthe vicinity of the Metro North alignment have been obtained. The drillhole locationsare shown in Drawing Nos. B/MN/0000/GE/01 to 13. All drillholes are verticaldrillholes. The depth of the drillholes ranged from 5.0m to 39.0m below groundlevel. The drillholes were generally formed by light cable percussion boring or rotary

open drilling through superficial material and rotary core drilling in rock.

A summary of the previous ground investigation drillholes including the drillholereference, drilling method, co-ordinates, ground level, depth and Railway Order Area, is presented in Table 3.4 below:

Table 3.4: Summary of Previous GI Rotary Drillho les

DrillholeReference

DrillingMethod(s)

Easting(m)

Northing(m)

Ground Level(mOD)

Depth(m bgl)

Railway Order Area

2219-RC1 RC 318359 246925 18.31 6.00 Area 1

2219-RC2 RC 318359 246925 18.57 8.00 Area 1

3188-RC1 RSC+RC 318235 246605 - 6.00 Area 1

3188-RC2 RSC+RC 318240 246590 - 7.00 Area 1

3512-MW2 ROH 316806 243712 - 19.00 Area 3


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DrillholeReference

DrillingMethod(s)

Easting(m)

Northing(m)

Ground Level(mOD)

Depth(m bgl)

Railway Order Area

3512-MW3 ROH 317083 243696 - 20.00 Area 3

3512-MW4 ROH+RC 317306 243634 65.00 23.40 Area 3

3512-MW6 ROH+RC 316970 243616 66.30 20.30 Area 3

3512-S16 ROH 317101 243574 - 5.00 Area 3

3512-S18 ROH 317123 243662 - 5.00 Area 3

3512-S20 ROH 317150 243671 - 5.00 Area 3

3512-S22 ROH 317116 243692 - 5.00 Area 3

3512-S3 ROH 317101 243694 - 5.00 Area 3

3512-S7 ROH 317121 243626 - 5.00 Area 3

G-RBH1 ROH+RC 317082 243216 64.70 26.10 Area 3

G-RBH2 ROH+RC 317002 243131 65.00 30.00 Area 3

G-RBH3 ROH+RC 316984 243264 65.30 15.00 Area 3

G-RBH4 ROH+RC 316950 243207 66.50 30.00 Area 3

4265-RC1 ROH+RC 317082 243216 60.00 10.00 Area 4

4265-RC2 ROH+RC 315204 241114 60.00 11.50 Area 4

4265-RC3 ROH+RC 315273 240913 60.00 11.50 Area 4

M50-BH14/1 LCP+RC 315414 241239 64.20 14.95 Area 4

M50-BH14/2 LCP+ROH 315442 241241 61.44 11.00 Area 4

M50-BH14/3 LCP+ROH 315413 241266 63.38 13.50 Area 4

M50-BH14/4 LCP+RC 315443 241272 61.07 10.80 Area 4

M50-BH14/5 LCP+RC 315408 241303 62.35 12.70 Area 4

M50-BH14/6 LCP+ROH 315434 241309 59.94 11.50 Area 4

WBH15 ROH 315287 235516 21.40 34.75 Area 6

M-RCA RC 315453 235637 17.24 19.75 Area 6

M-RCB RC 315507 235611 16.64 15.00 Area 6

744-BH3 LCP+RC 316031 233737 10.61 19.00 Area 7744-BH4 LCP+RC 316031 233737 10.61 19.00 Area 7

744-BH6 ROH + RC 316031 233737 11.73 13.00 Area 7

820-BH1A LCP+ROH+RC 315860 234285 3.60 7.95 Area 7

820-BH2 LCP+ROH+RC 315854 234273 3.60 5.60 Area 7

2507-RC1 RSC+RC 315861 233528 11.88 14.00 Area 7

2507-RC2 RSC+RC 315852 233503 11.85 14.00 Area 7

2507-RC3 RSC+RC 315833 233521 11.75 17.08 Area 7

WBH1 ROH 316022 233827 7.80 30.00 Area 7

WBH3 ROH 316153 234221 3.95 30.00 Area 7

WBH4 LCP+ROH+RC 316016 234330 4.55 29.50 Area 7

WBH7 LCP+ROH 316251 234619 3.10 30.00 Area 7



WBH11 ROH 315864 234823 5.15 30.00 Area 7

WBH12 LCP+ROH 315798 234998 5.90 35.00 Area 7

WBH13 ROH 316312 234789 3.25 30.00 Area 7

WBH14 ROH 315738 234667 5.60 30.00 Area 7

WBH16 LCP+ROH 315588 234809 5.05 30.00 Area 7

WBH17 LCP+ROH 315705 234918 5.25 35.00 Area 7

WBH18 LCP+ROH 316145 235021 4.60 36.00 Area 7

WBH20 ROH 315579 235038 10.10 33.00 Area 7

WBH21 ROH 315344 235030 10.40 35.00 Area 7

WBH25 ROH 315254 235096 13.30 34.00 Area 7

WBH27 ROH 315704 235217 13.85 34.80 Area 7


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DrillholeReference

DrillingMethod(s)

Easting(m)

Northing(m)

Ground Level(mOD)

Depth(m bgl)

Railway Order Area

WBH28 ROH 315529 235367 17.85 39.00 Area 7

WBH30 ROH 315095 235121 14.10 30.00 Area 7

WBH32 LCP+ROH 315011 235156 20.70 33.40 Area 7


WBH34 LCP+ROH 314881 235310 21.60 21.50 Area 7

WBH34A RC 314881 235310 21.60 31.40 Area 7


WBH36 LCP+RC 315865 233467 11.75 23.30 Area 7

WBH37 ROH 316073 234682 3.65 30.00 Area 7

WBH38 LCP+ROH 316239 234347 3.20 30.00 Area 7

WBH39 LCP+ROH 316018 233936 6.05 30.00 Area 7

WBH40A ROH 315563 233746 9.80 30.00 Area 7

WBH41 ROH 315420 233973 11.35 30.00 Area 7

WBH42 LCP+ROH 315259 234140 2.90 30.00 Area 7

WBH43 ROH 315122 234197 3.95 30.00 Area 7

WBH44 LCP+RC 315080 234308 3.80 30.00 Area 7

LU-RC1 ROH+RC 315954 234497 4.12 18.60 Area 7

LU-RC2 ROH+RC 315959 234483 4.07 13.40 Area 7

Notes:






4. LCP = light cable percussion boring; RSC = rotary soil coring; ROH = rotary open hole drilling; and RC = rotary

coring.



A total of 58 rotary drillholes were completed during the PGI. The drillhole locationsare shown in Drawing Nos. B/MN/0000/GE/01 to 13. All drillholes are verticaldrillholes. The depth of the drillholes ranged from 12.0m to 54.6m below groundlevel. The drillholes were formed by a combination of rotary open hole drilling,

rotary core drilling and Geobor-S wireline drilling methods.

A summary of the completed PGI rotary drillholes, including the drillhole reference,drilling method, co-ordinates, ground level, depth and Railway Order Area, ispresented in Table 3.5 below:

Table 3.5: Summary of Metro North PGI Rotary Drillholes

DrillholeReference

Drilli ng Method(s) Easting(m)

Northing(m)

Ground Level(mOD)

Depth(m bgl)

RailwayOrder Area

IGSLRC67 LCP+ROH+RC 318662.04 246341.78 24.30 22.00 Area 1





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DrillholeReference

Drilli ng Method(s) Easting(m)

Northing(m)

Ground Level(mOD)

Depth(m bgl)

RailwayOrder Area

IGSLRC64A LCP+ROH 317790.60 244910.87 46.12 15.00 Area 2



IGSLRC33 LCP+ROH 316645.78 242764.11 62.25 30.00 Area 3

IGSLRC34 ROH+RSC+RC 316942.19 243366.73 66.42 31.20 Area 3



IGSLRC59 LCP+ROH 317071.44 242268.87 57.37 39.00 A

Documents

Geotechnical Data Report Part 1 (1)