Environmental Statement Appendix 4.A (6.3.4.1) Construction ...

Environmental Statement Appendix 4.A (6.3.4.1)

Construction Method Statement April 2016

Silvertown Tunnel

Construction Method Statement

Document Reference: 6.3.4.1

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Contents List of Abbreviations ................................................................................................ 7

Glossary of Terms .................................................................................................... 9

1. INTRODUCTION ......................................................................................... 19

1.1 Purpose ....................................................................................................... 19

1.2 Engineering Design ..................................................................................... 19

1.3 Envisaged construction ............................................................................... 19

1.4 Selection of a Project Company .................................................................. 20

1.5 Control of construction activities .................................................................. 20

2. ENVISAGED CONSTRUCTION PROGRAMME ......................................... 21

2.1 Introduction ................................................................................................. 21

2.2 Programme summary .................................................................................. 22

2.3 Summary of programme activities ............................................................... 24

2.4 Envisaged construction phasing .................................................................. 26

3. ENABLING & ADVANCED WORKS .......................................................... 37

3.1 Introduction ................................................................................................. 37

3.2 Utility connections ....................................................................................... 37

3.3 Utility diversions .......................................................................................... 38

3.4 Geotechnical, obstructions and UXO investigations .................................... 39

3.5 Greenwich car parking provision ................................................................. 39

3.6 Ecological surveys (and mitigation actions as necessary) .......................... 39

3.7 Archaeological surveys ............................................................................... 40

3.8 Design works for early TBM and segment procurement ............................. 40

3.9 Asset protection .......................................................................................... 41

3.10 River Thames walls, inspection, assessment and protection ...................... 44

3.11 Protection of other assets - general ............................................................ 45

3.12 Protection of other assets historical ......................................................... 45

4. SILVERTOWN WORKS AREAS AND CONSTRUCTION .......................... 47

4.1 Introduction ................................................................................................. 47

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4.2 Ground conditions ....................................................................................... 47

4.3 General construction activities .................................................................... 48

4.4 Silvertown worksite ..................................................................................... 48

5. BORED TUNNELLING ............................................................................... 75

5.1 Introduction ................................................................................................. 75

6. GREENWICH WORKS AREAS AND CONSTRUCITON ........................... 91

6.1 Introduction ................................................................................................. 91

7. CONSTRUCTION LOGISTICS ................................................................. 103

7.1 Philosophy of approach ............................................................................. 103

7.2 Logistics planning ...................................................................................... 104

7.3 Envisaged logistics proposals ................................................................... 104

8. CONSTRUCTION & ENVIRONMENTAL MANAGEMENT ....................... 129

8.1 The Reference Design .............................................................................. 129

8.2 Basis for assessed Scheme impacts ......................................................... 129

8.3 Appointment of the Project Company ........................................................ 129

8.4 Development of detailed design by construction Contactor ...................... 130

8.5 Mechanism for delivery of the Scheme within the assessed impacts ........ 130

Appendix A. PLANT LIST ................................................................................ 133

Appendix B. DRAWINGS ................................................................................. 138

Appendix C. ENVISAGED CONSTRUCTION PROGRAMME ......................... 140

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List of Tables

Table 2-1 Key milestones of the envisaged construction programme. ..................... 27

Table 4-1. Silvertown worksite access and egress arrangements ............................ 51

Table 7-1. Principal bulk materials for the envisaged Scheme ............................... 108

Table 7-2. Overall river transport movements for the envisaged Scheme .............. 112

Table 7-3. Overall road transport movements for the envisaged Scheme.............. 113

Table A-1. Plant List ............................................................................................... 133

List of Figures Figure 2-1. Summary envisaged construction programme for the Scheme. ............. 22

Figure 4-1. TBM in launch chamber in cradle, showing shove frame. (Courtesy of Crossrail TfL/ Ltd) ..................................................................................................... 59

Figure 4-2. Typical handling arrangements for barge delivered bulk materials (Courtesy of Crossrail TfL/ Ltd) ................................................................................ 63

Figure 4-3 Cut-and-Cover base slab construction (Courtesy of Crossrail) ............... 67

Figure 4-4. Typical arrangement of a reinforced cut-and-cover tunnel under construction (Courtesy of WSDOT). ......................................................................... 69

Figure 5-1. Silvertown Tunnel bored tunnel cross section, with envisaged space allocation. ................................................................................................................. 76

Figure 5-2. Diagram illustrating an Earth Pressure Balance TBM (Courtesy of Herrenknecht). ......................................................................................................... 77

Figure 5-3. Typical TBM temporary steelwork shove frame (Courtesy of MRT, Singapore). ............................................................................................................... 78

Figure 5-4. Typical tunnel segment handling gantry crane, and segment storage (Courtesy of Crossrail Ltd/ TfL) ................................................................................ 79

Figure 5-5. TBM during transit within reception chamber (Courtesy of Crossrail Ltd, TfL) ........................................................................................................................... 80

Figure 5-6 Transportation of spoil from an EPB TBM, conveyed via belted conveyor (Courtesy of AGP Metro, Poland) ............................................................................. 82

Figure 5-7. Typical installation arrangement of sheet waterproofing membrane (Courtesy of Crossrail/ TfL). ..................................................................................... 88

Figure 6-1 Piling rig (Courtesy of Bauer) .................................................................. 95

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Figure 6-2. Typical reinforced concrete wing wall (Courtesy of Kenny Plant and Civils). ...................................................................................................................... 97

Figure 7-1. Envisaged main lorry routes. ................................................................ 106

Figure 7-2. Barge for river transport spoil removal (Courtesy of Port of London Authority). ............................................................................................................... 110

Figure 7-3. Example of a temporary Jetty for 2000t ship berthing. ......................... 111

Figure 7-4. Silvertown materials removed from site. .............................................. 114

Figure 7-5. Silvertown materials delivered to site. .................................................. 115

Figure 7-6. Greenwich materials removed from site. .............................................. 115

Figure 7-7. Greenwich materials delivered to site. ................................................. 116

Figure 7-8. LGV movements during construction works at Silvertown site. ............ 116

Figure 7-9. LGV movements during construction works at Greenwich site. ........... 117

Figure 7-10. Silvertown worksite HGV and barge movements. .............................. 117

Figure 7-11. Greenwich worksite HGV and barge movements. ............................. 118

Figure 7-12. Construction worker numbers. ........................................................... 118

Figure 7-13. Example of a typical logistics organisation chart. ............................... 124

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List of Abbreviations ALARP As Low As Reasonably Practicable BPM Best Practicable Means BRE Building Research Establishment CD&E Construction, Demolition and Excavation CDM Construction Design and Management Regulations (2015) CoCP Code of Construction Practice CIRIA Construction Industry Research and Information Association CSH Cycle Superhighways DCO Development Consent Order DEFRA Department for Environmental, Food and Rural Affairs DLR Docklands Light Railway EA Environment Agency EAL Emirates Air Line EIA Environmental Impact Assessment EPB Earth Pressure Balance EU European Union HGV Heavy Goods Vehicle HSE Health and Safety Executive JCOP Joint Code of Practice KPI Key Performance Indicator LCN Local Cycle Networks LED Light-Emitting Diode LGV Light Goods Vehicle LoD Limits of Deviation M&E Mechanical & Electrical NAABSA Not always afloat but safely aground PLA Port of London Authority RWL River Works Licence SCADA System Controls And Data Acquisition SWMP Site Waste Management Plan TBM Tunnel Boring Machine TDSCG Tunnel Design and Safety Consultation Group TfL Transport for London UXO Unexploded Ordnance WID Water Injection Dredging WRAP Waste and Resources Action Programme

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WRRR Work Related Road Risk

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Glossary of Terms Adit A small tunnel, usually constructed without the means of a

TBM, often linking other underground structures such as tunnels or shafts.

Anti-recirculation Wall

Wall designed to prevent the recirculation of emissions between adjacent tunnels at portal area.

Aquiclude A strata of relatively low permeability which has the effect of limiting the transmission of groundwater across its deposition.

Assessed Case Scenario adopted for assessment of likely effects of the proposed scheme, in the context of central forecasts of transport conditions and with user charges set so as to achieve the Schemes traffic, environmental, socio-economic and financial objectives.

Bulk Material Construction materials required in large quantities, such as aggregate, crushed stone or fill materials.

Building Research Establishment (BRE)

Organisation whose research activities, guidance and specifications have in certain areas, become synonymous with good practice in the built environment.

CDM (2015) The Construction (Design and Management) Regulations 2015, which set out the roles and responsibilities of parties involved in construction projects in relation to health and safety during the project life cycle including design, construction operation and maintenance stages.

Closed Face TBM

A type of tunnel boring machine (TBM) which continuously supports the mined ground thereby providing full support to the excavated face.

Cofferdam

A form of ground excavation support, usually temporary works, used during construction of underground or near-surface engineering works.

Conditioning agents

Materials used in mechanised (TBM) tunnelling techniques to alter the mechanical properties of the ground being excavated (for example friction) by changing the grounds plasticity, texture or water permeability. Can include chemical polymers.

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Construction Phase

A defined period of works.

Contractor Anyone who directly employs or engages construction workers or manages construction work. Contractors include sub-contractors, any individual self-employed worker or business that carries out, manages or controls construction work.

Cross Passage A small tunnel usually linking two larger tunnels.

Cut-and-cover A form of construction usually involving in situ reinforced concrete, where a tunnel is built within an excavation which is undertaken from the ground surface.

Cutter Head The rotating front face of a tunnel boring machine (TBM) which physically mines the ground during TBM advancement.

Defect Survey A survey to record defects.

Detailed Design A finalised design, complete in all aspects and suitable for construction of the Scheme.

Development Consent Order (DCO)

This is a statutory order which provides consent for the project and means that a range of other consents, such as planning permission and listed building consent, will not be required. A DCO can also include provisions authorising the compulsory acquisition of land or of interests in or rights over land which is the subject of an application.

http://infrastructure.planninginspectorate.gov.uk/help/glossary-of-terms/

Docklands Light Railway (DLR)

An automated light metro system serving the Docklands and east London area. The DLR is operated under concession awarded by Transport for London to KeolisAmey Docklands, a joint venture between transport operator Keolis and infrastructure specialists Amey plc

Earth Pressure Balance (EPB) Tunnel Boring Machine

A type of tunnel boring machine used in soft ground. The machine uses the excavated material to balance the pressure at the tunnel face. Pressure is maintained in the cutter head by controlling the rate of extraction of spoil through the

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removal Archimedes screw and the advance rate of the machine.

Emirates Air Line (EAL)

A cable car service across the River Thames in east London, linking the Greenwich peninsula to the Royal Victoria Dock. The service is managed by TfL, and is part of the TfL transport network.

Excavated Material

Ground or other material removed during a construction process, usually by mechanical means.

Extrados The outer surface perimeter of a bored tunnel.

Falsework A temporary supporting structure usually of steel, timber or a combination of both, required to support the construction of elements of a permanent structure being built, and not required in the permanent condition.

Geohazards Hazards associated with encountering certain geological features of the ground.

Ground Freezing A form of ground treatment whereby unstable ground is made stable and groundwater flow arrested by freezing the ground.

Ground Treatment

A process whereby the natural state of the ground and groundwater is altered, usually associated with the use of grouts or other materials, in order to achieve preferable engineering properties of the ground and groundwater.

Hard Standing Ground improvement by the use of compacted stone or other materials which facilitates increased surface loading from vehicles or other plant.

HAV A type of materials transport ship which is capable of fully loaded open water navigation.

Heavy Goods Vehicle (HGV)

European Union term for any vehicle with a gross combination mass of over 3500kg.

in-situ A process of work completed in its final position.

Intrados The inner surface perimeter of a bored tunnel.

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Jet Grouted A ground treatment process involving the creation of interlocking columns of treated ground, formed using a very high pressure probe to install cementitious material into the ground.

Jetty A structure that projects from land out into water for the purposes of marine logistics.

Joint Code of Practice

Widely adopted best practice guide for planning, design and construction of tunnelling works, jointly authored by the British Tunnelling Society and the Association of British Insurers.

Launch Chamber A cofferdam or other underground space created to commence bored tunnel construction using a TBM.

Nadir sump A sump for collecting gravity drainage which occurs at the low point of a vertical alignment.

Niche A small recess in a wall or slab structure.

Permanent works Any elements of infrastructure of the Scheme, which form its permanent use and facility, used to distinguish from temporary works (see separate definition) which are only necessary for temporary construction purposes.

Reception Chamber

A cofferdam or other underground space created to receive a TBM which has been used to construct a bored tunnel.

Reference Design

The design proposals for the Scheme that the DCO application refers to, as modified and developed in response to the Statutory Consultation process. The Reference Design has been developed to a concept stage appropriate to prove engineering and construction feasibility and to inform the construction and operational land requirements, environmental impact assessments and Scheme cost estimate.

River Transport Transport of materials associated with the Scheme by river to or from locations within the Works Areas or within 4km of the Works Areas.

Secant Piles Interlocking circular concrete piles often used to form earth retaining or foundation structures.

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Service Building, Tunnel Service Building, Portal Building

The building housing all control, power supply, and other essential equipment for the operation of the tunnel. Also houses firefighting control and ventilation equipment. Serves as a maintenance base and has the facility to become a standby operations room.

Sheet Pile Profiled heavy duty steel elements which are installed in the ground from the surface and used to form temporary or permanent retaining structures.

Shove Frame A piece of Temporary Works comprising a rigid steel frame usually attached to a base slab or retaining wall, which is used to provide a reaction point against which a TBM is jacked forward at the commencement of a TBM tunnel drive.

Slit Trenches Investigatory narrow and shallow exploratory trenches carefully excavated from the surface to locate near-surface utility pipes, cables and other similar assets, whose position is are not known precisely.

Slurry A suspension of water, a clay mineral (called bentonite) and other additives which is used in a variety of ground-related construction purposes including ground support for bored pile and TBM tunnel construction.

Slurry Shield (SS) Tunnel Boring Machine

A form of soft ground closed face tunnel boring machine which is selected in certain types of ground containing sands and gravels, and where high groundwater pressures exists. The chamber containing the TBM cutter head is filled with pressurised slurry which applies pressure to the excavation face. The slurry acts as a ground support and transport medium for the excavated material, which is continuously circulated between the TBM and a slurry treatment plant, where the excavated material is separated out for disposal or reuse.

System Controls and Data Acquisition

Communications system forming part of the Schemes mechanical and electric equipment, and used to safely operate the future highway tunnel.

Temporary Works

Structures, means and measures selected and used by a Contactor undertaking construction works, which form no part of the permanent building or structure which is being constructed.

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Tail Skin The rear cylindrical steel section of the TBM, within which precast concrete segments are erected to form a continuously lined bored tunnel.

TBM Shield The assembly of the TBM providing ground support, advancement cutter head and main bearing.

Tension Piles Piled foundations resisting uplift or lateral loading which may be constructed vertically or inclined (raked).

The O2 A large entertainment district on the Greenwich peninsula, including an indoor arena, cinema, bars and restaurants. It is built largely within the former Millennium Dome

The Scheme The construction of a new bored tunnel under the River Thames between the Greenwich peninsula and Silvertown, as well as necessary alterations to the connecting road network and the introduction of user charging at both Silvertown and Blackwall tunnels.

The Tunnel, Silvertown Tunnel

Proposed new twin-bore road tunnels under the River Thames from the A1020 in Silvertown to the A102 on Greenwich Peninsula, East London.

Track Out Dirt, mud or other debris carried out of a construction worksite and onto the local road network, via wheeled construction equipment leaving the site.

Transport for London (TfL)

A London government body responsible for most aspects of the transport system in Greater London. Its role is to implement transport strategy and to manage transport services across London. These services include: buses, the Underground network, Docklands Light Railway, Overground and Trams. TfL also runs Santander Cycles, London River Services, Victoria Coach Station and the Emirates Air Line. As well as controlling a 580km network of main roads and the city's 6,000 traffic lights, TfL regulates London's private hire vehicles and the Congestion Charge scheme.

Tunnel Boring Machine (TBM)

A machine used to excavate tunnels with a circular cross section. There are two main types of closed face TBMs: Earth Pressure Balance (EPB) and Slurry Shield (SS). Please see

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those terms for further explanation.

Tunnel Design and Safety Consultation Group (TDSCG)

A formal group of stakeholders including emergency services, police, the tunnel promoter, the highway authorities, the tunnel and highway operator and maintainer and the tunnel designer, who meet regularly through the planning and detailed engineering design phases to consider and agree matters of safety provision in the proposed tunnels.

Tunnel Portal A structure which forms and defines the end of a section of tunnel.

Volume Loss An expression for the volume of a settlement trough arising per unit length from excavation-induced ground movement, expressed as a percentage of the excavated tunnel area.

Water Injection Dredging

A form of marine dredging of a river or sea bed entailing the use of pressurised water jets to disturb deposited material.

Worksite An area of land within the Scheme order limits which is temporarily occupied and used to undertake construction the Works.

Works area Land within the Scheme order limits temporarily occupied and used to undertake construction works, which may comprise a number of discrete worksites, or areas of construction activity that move during a construction programme.

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SUMMARY

S.1.1 This document has been prepared to describe the envisaged construction processes, programme, arrangements of temporary worksites and logistics considerations associated with construction of the proposed Silvertown Tunnel Scheme.

S.1.2 The information contained within this report has been used to inform the preparation of environmental and traffic impact assessments, for the Silvertown Tunnel Scheme.

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1. INTRODUCTION

1.1 Purpose

1.1.1 This document provides a description of the way the Silvertown Tunnel is envisaged to be constructed, and its contents including construction methodologies and associated processes have been used as inputs to the assessment of the environmental and traffic impacts of the Scheme, which are reported in the Environmental Statement and Transport Assessment, supporting Transport for Londons (TfLs) Development Consent Order (DCO) application.

1.2 Engineering Design

1.2.1 The engineering design for the Scheme has been developed to enable a Development Consent Order (DCO) application to be prepared. The design defines the Scheme in sufficient detail to allow stakeholders to understand the scope and extent of the Scheme, and to inform studies assessing the environmental, socio-economic, construction and transport-related impacts.

1.2.2 The Principal Designer for the Scheme under the requirements of the CDM regulations (2015), is Atkins Ltd. In this capacity a designers risk register of risks relating to the Scheme has been assembled, and this risk register, along with the appropriate duty holder obligations under the CDM Regulations will be transferred to the future Project Company, who will deliver Detailed Design and construction of the Scheme.

1.2.3 As required by the CDM Regulations, the Health and Safety Executive has been served an F10 notice (Notification of Construction Project) for the Scheme.

1.3 Envisaged construction

1.3.1 The method of construction described in this document is the method that TfL envisages could be adopted for construction of the Scheme. It represents a feasible and safe methodology which has been used to assess the likely significant effects of the Schemes construction. The precise methods adopted by the Contractor may vary from those described in this method statement.

1.3.2 The envisaged method of construction assumes that an experienced and competent contactor is used to undertake construction of the works, and that this organisation is efficient and effective in safely delivering construction in a

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way consistent with good practice. Some aspects of the Scheme, notably tunnelling, require particular means and methods that are highly specialised in nature, and require the particular skills and experience of a specialist tunnelling contractor (these are described in section 0), and it is assumed that these are an essential basis of the envisaged method of construction described in this Construction Method Statement.

1.4 Selection of a Project Company

1.4.1 TfL propose to deliver the Silvertown Tunnel through a private finance initiative, and have established that appointment of a Project Company with responsibilities for design, construction, financing, maintenance and certain operational aspects would best meet the Scheme objectives and constraints, and achieve an appropriate risk balance.

1.4.2 A suitable Project Company would be selected following a competitive tender process run in accordance with EU procurement procedures. The procurement process would assess, amongst other things, the bidders relevant construction experience and capability as well as bidders proposed approaches to the design and construction of the Scheme. TfLs specifications along with the requirements and commitments arising from the DCO examination would be incorporated in the contact documents for appointment (for further information refer to section 8.3).

1.4.3 The term Contractor used hereafter and throughout this document, is used to refer to the construction entity through which the Project Company would deliver the design and construction of the Scheme.

1.5 Control of construction activities

1.5.1 The Contractor appointed will be responsible for completing the Detailed Design and completing the Scheme construction. The Contractor will be obliged to ensure the Detailed Design and construction proposals do not have impacts environmentally worse than those assessed for the DCO (refer to section 8.3 for details of how the Contractor will be appointed to construct the Scheme).

1.5.2 The construction activities required of the Detailed Design will be subject to control and management procedures which will ensure that the impacts arising are not more adverse than those assessed for the DCO. These mechanisms are described in Section 8.5 of this document.

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2. ENVISAGED CONSTRUCTION PROGRAMME

2.1 Introduction

2.1.1 This section describes the envisaged construction programme and the planned sequence and phasing of construction operations.

2.1.2 The assessment of construction activities and the derived construction programme assumes contract award for the Scheme in September 2018, subject to a favourable outcome from the DCO application.

2.1.3 The commencement of this envisaged construction programme could be subject to change during both the detailed design and subsequent construction phases. These changes could be required for a variety of reasons, including as a result of changes to the timescales for statutory processes and construction award, or through the Contractor optimising the design and construction proposals.

2.1.4 Undertaking elements of advanced work ahead of the main construction activities will assist in providing programme surety.

2.1.5 It is considered that the envisaged construction programme provides a robust construction solution for the scheme, and demonstrates that the proposed time scales are achievable.

2.1.6 The envisaged construction programme is described in three levels of detail in the following sections:

in 2.2, an overall description of the Scheme construction period is provided, along with a brief description of the constraints and programming philosophy that have been adopted,

in 2.3, a summary of programme activities is provided, along with a schedule of key construction milestones and dates; and

in 2.4, a descriptive explanation of the Schemes construction phasing is provided for the Silvertown and Greenwich worksites.

2.1.7 A more comprehensive construction programme (in gantt chart format) is also provided in Appendix C (STWTN-ATK-GEN-XXXX-PR-W-0001).

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2.2 Programme summary

Overall construction period

2.2.1 With an assumed contract award in September 2018 it is envisaged that the new tunnel will be open in June 2023. The main construction activities will commence at both Silvertown and Greenwich in March 2019, and will continue for approximately four years. The tunnel boring machine (TBM) for the main tunnelling works will be launched in late 2020, and the main tunnel excavation works will be completed by late 2021.

2.2.2 A simplified construction programme is presented in Figure 2-1, below.

Figure 2-1. Summary envisaged construction programme for the Scheme.

Programme constraints

2.2.3 The programme is relatively complex and there are a number of constraints and requirements from the construction strategy which determine the overall programme duration. These include:

site clearance should be undertaken during ecological dormant seasons;

archaeological investigation works and subsequent responses;

detailed design, especially segment design and TBM specification;

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TBM procurement;

The provision of the jetty facility for excavated material disposal and bulk material provision (during ecologically dormant season);

site working hours;

shift patterns for tunnelling activities;

the requirement of utility diversions to allow the construction works to proceed; and

relocation of existing O2 car parking (and parking office) at Greenwich.

2.2.4 The envisaged construction programme has been developed to ensure these constraints are respected, and provides a robust assessment of the time needed for construction of the Scheme.

Location of bored tunnelling activities

2.2.5 It is considered that the Silvertown worksite is the more suitable for supporting the bored tunnelling activities (refer to Appendix B; drawing C.2, and worksite description in Section 4.4). This is due to a number of logistical factors which, taken together facilitate a lower environmental impact than would be possible at Greenwich. These include:-

suitable land availability; and

direct access to river frontage to permit use of marine logistics for disposal of demolition and excavated material and delivery of bulk construction materials.

2.2.6 The envisaged construction programme, worksite layout and other construction logistics arrangements have therefore been developed for tunnelling to be undertaken from the north side of the River Thames, at Silvertown.

Enabling and advanced works

2.2.7 Works undertaken ahead of the principal construction activities in the period immediately following the contract award will significantly aid in the efficient delivery of the Scheme and will be implemented at both the Silvertown and Greenwich worksites wherever feasible.

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2.2.8 These advanced works are described in Section 3 and comprise amongst other works:

utility connections;

utility diversions;

geotechnical, obstructions and UXO investigations;

Greenwich car parking and parking office provision;

ecological surveys (and mitigation actions as necessary);

archaeological surveys;

site clearance;

asset protection condition surveys and establishment of monitoring baselines as necessary; and

design works for early TBM and segment procurement.

2.3 Summary of programme activities

2.3.1 In addition to the description in Section 2.2 of approximate durations of the main activities of construction, in this section programme activities are described in more detail. A schedule of key activity milestones is also provided in Figure 2-1. Summary envisaged construction programme for the Scheme.

Silvertown

2.3.2 The initial construction activities will focus on establishing the site facilities at the Silvertown worksite, constructing the TBM launch chamber, and temporary jetty for materials handling, to support bored tunnelling construction. These activities will take about 12 months in total (complete March 2020).

2.3.3 Once the TBM launch chamber has been built, the TBM can be delivered to site, erected, commissioned and launched. This will allow the bored tunnelling (which does not lie on the critical path of the overall construction programme), to take place with an overall construction period of a further 12 months, including the removal of some temporary equipment inside the tunnel (complete November 2021).

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2.3.4 Tunnel secondary lining, cross-passage construction, carriageway and drainage installation within the tunnels, and tunnel mechanical and electrical equipment installation will then be undertaken, of approximately 16 months (complete February 2023).

2.3.5 Highway works (commencing November 2020) outside and separate from the bored tunnelling operations, will run concurrently with bored tunnel construction. These activities will encompass modifications to the existing highway network including Dock Road realignment and Tidal Basin roundabout reconfiguration, and will take place in a period of about 21 months (complete July 2022).

2.3.6 The tunnel services building and other surface construction will also run concurrently with the tunnel construction; (commencing in October 2020). These works will commence at a similar time to the road construction and continue for about 18 months (complete at the end of February 2022).

2.3.7 Testing and commissioning of the tunnel and highways services (commencing December 2022) and site reinstatement will conclude the construction activities. These will overlap with other construction activities (for both Silvertown & Greenwich works) and will finish approximately 3 months beyond all other works, allowing the tunnels to be opened (in June 2023).

Greenwich

2.3.8 The initial construction activity at Greenwich will involve the establishment of the worksite including all site support facilities, site clearance and the preparation of temporary highway diversions to permit subsequent heavy civil engineering construction works to begin.

2.3.9 After about six months from site construction mobilisation, the TBM reception chambers secant bored pile walls will be constructed (commencing August 2019), for use in receiving the future TBM, driven from the Silvertown worksite. Overall the worksite establishment and TBM reception chamber walls installation will take about 12 months (completion March 2020).

2.3.10 The cut-and-cover approach tunnel and all related deep in situ wall construction will continue, (commencing in July 2019 and overlapping the TBM reception chamber construction). In all this will continue for approximately 26 months (completion in August 2021).

2.3.11 Highway works (new infrastructure, and modifications to existing roads), taking about 48 months in total, will take place throughout the construction

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programme. The highway construction works are integrated with the operation of the existing highway network to minimise impacts to road users, and have been carefully phased (these more detailed arrangements are fully described in Section 2.4, and in drawings in Appendix B).

2.3.12 The tunnel services building, tunnel fire tanks and associated infrastructure including mechanical and electrical installations, will be constructed later in the programme, (commencing August 2021) and taking 17 months to complete.

2.3.13 As described in Section 2.3.7, as testing and commissioning spans all systems and facilities of the Scheme, this activity will commence (all sites) in December 2022 and will finish approximately 3 months beyond all other works, allowing the tunnels to be opened (in June 2023).

2.4 Envisaged construction phasing

2.4.1 The phasing of the construction works is determined by three prime issues:

timing of occupation of the worksites;

traffic management requirements for the maintenance of highway routes; and

sequencing of construction activities.

2.4.2 The sequencing (overall construction logic) and durations of the programme activities (including productivity rates) have been developed based on the current design, relevant experience and with reference to industry good practice from similar large infrastructure projects, including Crossrail, DLR Woolwich Extension and Tideway Lee Tunnel.

2.4.3 The overall sequencing of the construction is described below. Appendix B contains the construction phasing drawings. These show the envisaged sequence and progression of the construction works together with principal traffic management arrangements for each phase of the works. Also in Appendix B are the worksite layout drawings which illustrate an envisaged layout, occupation and use of the worksites.

2.4.4 The construction phasing drawings are colour coded to indicate for each phase of construction:

road closures and removals;

traffic routes;

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works under construction;

works completed; and

site boundaries and fence lines.

2.4.5 In some cases the colour coding on the drawings is simplified for ease of reference for example where construction is substantially completed in a preceding phase it may be shown as completed.

Key milestones from the envisaged programme

2.4.6 The envisaged construction programme and the narrative above show and describe the key programme events. The envisaged principal dates are shown in Table 2-1 below (based on the assumed award of contract timing) and the envisaged durations from award. Some activities are seasonally dependent and so will need to be reviewed during detailed design.

2.4.7 It is also worth reiterating that the appointed Contractor may elect to optimise the programme throughout detail design and construction, and this could alter the envisaged start dates, and hence elapsed time from award. The activities could also be longer or shorter than those of the envisaged construction programme.

Table 2-1 Key milestones of the envisaged construction programme.

Milestone Envisaged Date

Approximate (whole month) time elapsing from contract award

1 Contract award Sep 18 0 2 Commence advance works Sep 18 0 3 Commence detailed design Sep 18 0 4 Complete detailed design Sep 20 24 months 5 Commence Silvertown site

establishment Mar 19 6 months

6 Commence procurement of TBM Mar 19 6 months 7 TBM delivered to site Sep 20 24 months 8 Complete Silvertown TBM launch

chamber (roof installed later) Feb 20 17 months

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9 Commence TBM excavation Dec 20 27 months 10 Complete TBM tunnels

excavation Oct 21 37 months

11 Complete tunnels secondary lining

Apr 22 44 months

12 Complete tunnels services installation

Feb 23 53 months

13 Complete Silvertown cut-and-cover tunnels

Mar 21 30 months

14 Complete Silvertown tunnel services building, etc.

Feb 22 41 months

15 Complete Silvertown highways works

Jul 22 46 months

16 Complete Greenwich TBM reception chamber (roof installed later)

Jul 20 23 months

17 Complete Greenwich cut-and-cover tunnels

Aug 21 35 months

18 Complete Greenwich tunnel services building, etc.

Dec 22 51 months

19 Complete Greenwich highways works

Mar 23 54 months

20 Complete testing and commissioning

Jun 23 57 months

21 Complete reinstatement and open tunnels

Jun 23 57 months

Description of Scheme phasing

2.4.8 In this section a description is provided of the phases in which construction works of the Scheme will be undertaken. The phases have been identified to explain the sequence of construction events required to construct, fit-out and test and commission the Scheme.

2.4.9 Five discrete phases of work are described at the northern end of the project at Silvertown, including bored tunnelling activities, and eight discrete phases for the southern end at Greenwich. The phasing descriptions also detail how traffic routes will be modified and traffic services maintained throughout construction.

2.4.10 For ease of reference the relevant construction activities identification (IDs) from the envisaged detailed construction programme (provided in Appendix

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C) are provided along with the Schemes phasing description are provided below:

Silvertown

Phase 1 March 2019 to April 2020

(Programme activity: S1.1000)

2.4.11 Refer to construction phasing drawing B.9 and worksite layout drawing C.2 in Appendix B.

2.4.12 The works will start with the installation of temporary traffic management to create alternative routes and maintain access to surrounding properties. Accesses to and egresses from the site will be established. The site will be fenced and cleared where needed. The section of Dock Road within the site will be closed.

2.4.13 The initial on-site activities in this stage are associated with establishing the worksite in preparation for construction. Temporary site access roads, security controls, lighting, drainage and utility supplies will be established. Site offices and other support buildings such as workshops and stores will be erected. The temporary site plant and equipment will then be installed. These items include the temporary jetty and river transport facilities, hard standings, crane bases and conveyors.

2.4.14 Construction works will proceed as soon as sufficient site establishment is in place. The initial works will be piling for the TBM launch chamber and cut-and-cover tunnel (refer to Section 4.4.60). The TBM launch chamber excavation, walls and base slab will then be completed and the tunnel portals formed in readiness for tunnel construction. If needed, ground treatment adjacent to the TBM launch chamber to facilitate the safe launch of the TBM will be completed in this phase. The roof slab for a short section of cut-and-cover tunnel will be constructed initially to allow the diversion of Dock Road utilities over it. The remainder of the roof slab will be largely completed in this phase.

Phase 2 April 2020 to November 2021



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2.4.16 In this phase the cut-and-cover tunnel will be completed. The piling, excavation and structural works for the retained cut will be undertaken in this phase. The tunnel services building, including its general M&E fit-out, will be constructed.

2.4.17 The TBM will be delivered, erected and commissioned. It will then be launched and will excavate the northbound tunnel from the Silvertown worksite. When it reaches the TBM reception/launch chamber at Greenwich it will be turned and the Southbound Tunnel excavated. All tunnel support services (spoil removal, segment supply, power supply, personnel access, maintenance, etc.) will continue to be provided from the Silvertown site for this southbound tunnel drive. When the TBM has completed the excavation of the southbound tunnel it will be removed from the TBM launch chamber at Silvertown.

2.4.18 On completing the northbound tunnel drive the excavation and lining of the tunnel cross passages will commence in this phase. The waterproofing, invert fill and construction of the secondary lining of the northbound tunnel will be constructed.

2.4.19 With temporary highway management measures in place to permit safe construction near the live highway, and to maintain traffic routes, the permanent highway works will commence in this phase. This will entail the construction of a retaining wall for the realigned Dock Road and the elongation of the Tidal Basin roundabout along with the realignment of Lower Lea Crossing and the link to Dock Road.

2.4.20 An attenuation tank to capture surface water will be located in the centre island. Works access to the centre island will be controlled from the live carriageway.

Phase 3 November 2021 to March 2022



2.4.22 In this short phase the TBM launch chamber roof is constructed and backfilled, along with access to the utility reserve head house. The access road, landscaping and parking for the tunnel services building is constructed. In the main tunnels the drainage and fill for the southbound tunnel is completed and the waterproofing, invert fill and secondary lining of the southbound tunnel is commenced. Construction of cross passages

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continues. The temporary jetty, river transport facility and associated site installation are removed in this phase.

2.4.23 With the traffic now diverted onto the elongated Tidal Basin roundabout the associated link roads are constructed.

Phase 4 March 2022 to June 2023



2.4.25 In this last construction phase the remaining works in the tunnels waterproofing, secondary lining and fill in the southbound tunnel, the wall finishes to both tunnels, the in-tunnel carriageway construction the tunnel services M&E installations, and signals and gantry installation outside the tunnels are all completed. The systems are tested and commissioned.

2.4.26 The realigned Dock Road is constructed and the redundant carriageway broken out and all finishing works remaining including drainage, lighting, communications and landscaping works will be completed. The signals will become operational once these works are complete and the tunnel has been opened.

2.4.27 The user charging infrastructure (for example automated cameras) will be installed.

Phase 5 June 2023 onwards

(Programme activity: KD.1020)

2.4.28 Refer to construction phasing drawing B.13 in Appendix B.

2.4.29 In this phase no major construction work is undertaken and the tunnels are open for traffic. Minor landscaping and remedial works may be undertaken in this phase if necessary.

Greenwich

Phase 1 March 2019 to August 2019

(Programme activity: G1.1000)


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2.4.31 The works will start by installing temporary traffic management to provide alternative routes and maintain access to surrounding properties including the O2 car parking (O2 car parking reprovisioning to the Beckham Academy will also commence). Accesses to and egresses from the site will be established. The main worksites will be fenced and cleared where needed. Edmund Halley Way will be closed within the worksite.

2.4.32 The initial on-site activities in this phase are associated with establishing the worksite in preparation for construction. Security controls, lighting, drainage and utility supplies will be established. Site offices and other support buildings such as stores will be erected.

2.4.33 The construction to allow the temporary realignment of Millennium Way and the link to West Parkway will be undertaken in this phase, consisting principally of road works and roundabout. Existing utilities in Millennium Way will be diverted to the (realigned) Millennium Way location. Utilities in Edmund Halley Way and the link to West Parkway will be diverted locally.

2.4.34 Piling works for the cut-and-cover tunnel to the west of Millennium Way and to the east of the location for the diverted Millennium Way will commence in this phase.

2.4.35 Satellite worksites will be established at Boord Street and Blackwall Tunnel Approach (northbound) to facilitate construction of the new foot and cycle bridge to replace the existing footbridge. The existing footbridge deck at Boord Street will be demolished following the installation of the replacement bridge structure. This will be done during night shifts with road closures as the works are over the live carriageway.

2.4.36 Continuous ramped access across the A102 will be maintained at all times and from both sides, and disruption to users of the bridge minimised by delaying the demolition of the existing bridge until the new bridge has been opened.

Phase 2 August 2019 to July 2020


2.4.37 Refer to construction phase drawing B.2 and worksite layout drawing C.1 in Appendix B.

2.4.38 This phase commences once the temporary realignment of Millennium Way and the opening of the link road to West Parkside are completed.

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2.4.39 The remaining piling required for the cut-and-cover tunnel and the piling for the TBM reception/launch chamber will follow. The piling will be completed in this phase. Excavation and structural construction for these structures will follow. The TBM reception/launch chamber will be substantially completed in this phase. The cut-and-cover roof slab will be constructed in three sections. In this phase the first two sections will be completed. When the first section (under the original location of Millennium Way) is finished Millennium Way and its utilities will be reinstated. The second section (to the west of the original location of Millennium Way) will then be constructed.

2.4.40 The permanent highway works will commence in this phase with the start of piling for retaining wall RW2-1. The access ramps and stairs for the replacement pedestrian and cycle bridge at Boord Street will be completed by the end of this phase.

Phase 3 July 2020 to September 2021



2.4.42 In this phase the third section of cut-and-cover roof slab will be constructed (where the realigned Millennium Way was temporarily located). The cut-and-cover will then be completed with the remaining excavation, structural elements and tunnel finishes constructed.

2.4.43 The highway works for the realigned Blackwall Tunnel Approach southbound carriageway are commenced in this phase. This includes construction of the bridge over the northbound slip road for Silvertown Tunnel and the repositioned associated bus link. The initial activities concentrate on the remaining piling works for the retaining walls. Tension piles for the cuttings between the retaining walls are also installed. The bulk excavation and the commencement of construction of the concrete ground slab between the retaining walls for the tunnel access and exit roads follow. Finally the carriageway and finishing works to allow the permanent relocation of the Blackwall Tunnel Approach southbound carriageway are completed.

2.4.44 The construction of the tunnel fire tanks and tunnel services building will commence towards the end of this phase.

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Phase 4 September 2021 to November 2021


2.4.45 Refer to construction phase drawing B.4 and worksite layout drawing C.1 in Appendix B.

2.4.46 At the start of this phase the southbound traffic on the Blackwall Tunnel Approach will be diverted over the new bridge constructed in the previous phase. This facilitates the subsequent removal of the existing central reserve, consisting of crash barriers, kerbs and concrete infill, and construction of the full depth carriageway and temporary safety barrier. The carriageway works required across the existing central reserve of the Blackwall Tunnel Approach are completed in this phase. The ground slab between the retaining walls for the tunnel access and exits are largely completed in this phase.

2.4.47 The construction of the tunnel fire tanks and tunnel services building continues in this phase.

Phase 5 November 2021 to June 2022



2.4.49 Traffic on the northbound Blackwall Tunnel Approach will be diverted to the original southbound carriageway and will re-join its original alignment at the gatehouse structure. This allows construction in this phase of the new northbound alignment along with Tunnel Avenue Junction. Highway gantries will be erected over Tunnel Avenue in this phase.

2.4.50 The construction of the tunnel service buildings at the portal continues in this phase.

2.4.51 The roof slab of the TBM reception/launch chamber is constructed and backfilled in this phase. These works will include construction of internal shafts providing access to a surface head house facility. Edmund Halley Way is then reconstructed in its original position over the TBM reception/launch chamber and cut-and-cover tunnel.

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Phase 6 June 2022 to March 2023



2.4.53 Edmund Halley Way is re-opened at the start of this phase.

2.4.54 Northbound traffic is transferred to the new northbound carriageway alignment of the Blackwall Tunnel Approach. This allows the remaining piling, construction and carriageway works associated with the approaches to the Silvertown tunnels to be completed in this phase. The bus link is opened to traffic.

2.4.55 The Blackwall Tunnel Approach northbound and southbound traffic will be running in the permanent configuration. The remaining retaining walls will be completed (a piling rig will be remobilised to complete these works). Remaining bulk earthworks will be completed for all new alignments and a reinforced concrete slab will be cast at the base of the secant pile wall.

2.4.56 All highways and site finishing works remaining - including drainage, lighting, communications and landscaping works - will be completed.

2.4.57 The construction of the tunnel services building is completed in this phase.

2.4.58 Tunnel systems testing and commissioning commences in this phase. The user charging infrastructure (for example automated cameras) will be installed.

Phase 7 March 2023 to June 2023



2.4.60 In this phase the tunnel systems testing and commissioning is completed. The general (highways) systems are tested and commissioned. Finally the tunnel and general integrated systems are tested and commissioned in readiness for tunnel opening.

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Phase 8 June 2023 onwards

(Programme activity: KD.1020)

2.4.61 Refer to construction phase drawing B.8 in Appendix B.

2.4.62 In this phase no major construction work is undertaken and the tunnels are open for traffic. Minor landscaping and remedial works may be undertaken in this phase if necessary.

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3. ENABLING & ADVANCED WORKS

3.1 Introduction

3.1.1 Certain aspects of the design and construction of the Silvertown scheme may be undertaken in advance of the main construction works. Completion of the following activities are identified as bringing greater programme surety, and could be undertaken as enabling and advanced works:

utility connections;

utility diversions;

geotechnical, obstructions and UXO investigations;

Greenwich car parking provision;

ecological surveys (and mitigation actions as necessary);

archaeological surveys;

site clearance;

design works for early TBM and segment procurement; and

asset protection condition surveys and establishment of monitoring baselines as necessary,

3.2 Utility connections

Silvertown & Greenwich worksites

3.2.1 To enable construction of the Scheme, temporary utility services will be required at the principal worksite (Silvertown) and satellite worksite (Greenwich). The Silvertown site is currently occupied by a variety of businesses which are expected to have the primary services connections, and so on this worksite modifications may be more limited.

3.2.2 The services required on both the primary and the satellite site will include electricity supply, telephone/ broadband, sewers and water supply. Foul sewerage services will be provided by connection of the site facilities to the local foul drainage network, and potable water connection will be made (or adopted) from Thames Waters local distribution network.

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3.3 Utility diversions

3.3.1 A wide variety of temporary and permanent utility diversions are required at both Silvertown and Greenwich. Diversion corridors are proposed for services affected by the construction of the tunnel, tunnel portals and highways modifications. The principle underlying the provision of these diversion corridors is to have all services diverted along the same route in the same trench with the appropriate spacing as per the guidelines provided by the National Joint Utilities Group. It has been assumed that single service trenching for diversionary works is acceptable in principle to the asset owners, with the detail to be confirmed at later design stages. In some instances (principally water and sewer assets) certain utilities will require individual trench works, due to minimum bend radii constraints.

3.3.2 The diversionary work for the utilities, except the Royal Victoria Dock Drainage, could be considered under an advanced works proposals, in order to mitigate associated programme risks. However, as a large proportion of the utility diversions required for the Scheme are physically close to the highway relocation works, it is likely for them to be closely coupled with the surface work construction programme.

3.3.3 Investigatory works such as location slit trenches in advance of main construction would allow for efficient diversion sequencing as part of the main works programme.

3.3.4 As part of the wider commercial developments taking place on the Greenwich Peninsula there are plans by UKPN to install two 132kV underground power lines along Millennium Way. The current programme for these works indicates the cables will be installed before the start of the Scheme. As such the new cables will require diversion during the construction of the cut-and-cover tunnel under Millennium Way. Preliminary discussions with UKPN indicate that these diversion works would take a significant period of time in order to allow for cable jointing and pulling. Currently options to minimise this time period by making provision for this diversion in the current UKPN scheme are being explored.

3.3.5 Diversion corridors are proposed which seek to efficiently consolidate the space required for utility diversions, and help minimise the disruption caused by the diversion works.

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3.4 Geotechnical, obstructions and UXO investigations

Geotechnical investigation

3.4.1 Further intrusive ground investigation addressing the key areas of ground conditions risk will be undertaken in advance of the main construction works contract, to ensure that geotechnical risk is effectively managed as provided for in the Joint Code of Practice (JCOP) for Tunnelling works.

Obstructions investigation

3.4.2 Intensive historical land use is known to have resulted in the potential for underground obstructions along the route of the Scheme. The hazards that these potential obstructions present to construction and the way the associated ground-risk to the Scheme will be managed, is described in Sections 5.1.27 to 5.1.36. Undertaking exploratory obstructions investigation (as described in mitigation of risk to bored tunnelling activities), applies equally to all ground-related construction works, will be undertaken as enabling or advanced works to main construction.

UXO anomalies

3.4.3 Preliminary UXO surveys have been undertaken which identified a range of magnetic anomalies. These are not uncommon in preliminary surveys of this nature in areas east of central London. Further detailed surveys would be undertaken in advance of the construction works to further investigate these phenomena, along with controlled management of excavation to manage the UXO risk to the Scheme.

3.5 Greenwich car parking provision

3.5.1 TfL are required to provide a number of car parking spaces for the O2 to replace those on areas temporarily occupied by the Schemes construction activities. TfL would provide these replacement spaces on land within the Order Limits on a site immediately south of Emirates Greenwich Peninsula station. TfL are currently liaising with the Greenwich Masterplan developer to develop a joint car parking strategy aimed at maintaining car parking provision for the O2 throughout the construction of the Greenwich Masterplan and Silvertown Tunnel developments.

3.6 Ecological surveys (and mitigation actions as necessary)

3.6.1 Early activities in the construction programme will require pre-construction environmental surveys examples of this would include the construction of the temporary jetty, involving significant marine construction works including

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dredging and piling. Surveys to determine baseline ecology in the river in this vicinity will be required in support of applications for construction to the PLA/ EA, and advanced surveys will ensure that early start activities are not delayed.

3.6.2 Notwithstanding the above, some early sampling survey work has been undertaken as part of the environmental impact assessment in connection with the temporary jetty, and this is reported in the Environmental Statement. The need for future survey works for the establishment of a baseline will be conditioned by detailed examination of the results of this early ecology survey work.

3.6.3 The demolition of existing structures and site clearance activities will require confirmation that the habitats they form do not support ecological habitats.

3.7 Archaeological surveys

3.7.1 If required, archaeological surveys will be undertaken to demonstrate that subsequent deep excavations along the trace of the works do not impinge on archaeological remains. Any investigatory trial pitting that is required will be undertaken early in the worksite establishment process, in order to provide programme opportunities for full intervention; or otherwise to demonstrate that no further intervention is necessary.

3.7.2 In any event it is expected that an archaeologist will be retained by the Contractor, with a watching brief covering all excavation works where archaeological remains could be encountered.

3.8 Design works for early TBM and segment procurement

3.8.1 Early design work to support the TBM procurement will be undertaken as it is expected that the TBM will be manufactured specifically for the project. This will ensure that the lead-in time for this principal plant item is sufficient.

3.8.2 Initial works will focus on the establishment of a design freeze for the tunnel internal diameter. This along with other information, including ground conditions interpretation will enable the specification of the TBM. Determining the tunnel internal diameter will require consideration of information including the highways alignments, ground conditions, TBM launch methodology, installation tolerances, jacking loads, M&E systems space coordination, fire protection details, and waterproofing. Establishing a TBM design and methodology in accordance with these parameters will require the endorsement of the Tunnel Design and Safety Consultation Group (TDSCG).

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3.8.3 A two-step tunnel internal diameter confirmation protocol is anticipated. This will allow an early TBM design to proceed on the basis of a defined diameter range which is then followed by the specification of a precise tunnel internal diameter.

3.8.4 These design activities will also inform tunnel segment lining design and procurement.

3.9 Asset protection

Introduction

3.9.1 Asset protection is a process by which the impacts to all structures (that is buildings, utilities and highways or other structures) potentially at risk of damage from ground movements, or other effects arising from construction of the Scheme, are kept to acceptable levels.

3.9.2 The need for a carefully planned and robust asset protection process applies equally to assets owned by stakeholders or third parties to the scheme, and to TfL, who own and are responsible for operating services relying on the integrity of their own existing infrastructure assets.

The asset protection process

3.9.3 The asset protection process is a continuous one which spans the Reference Design, Detailed Design, construction and post-construction phases. The preparation of the Reference Design has included initial screening and damage risk assessment (phases I and II), and also the identification of land and certain DCO powers necessary to be able to protect existing assets.

3.9.4 Further activities would be required to continue the asset protection process, and some of these may be undertaken as enabling or advanced works. The further activities necessary include:-

further impact assessment screening and damage risk categorisation, based on the Detailed Design and construction proposals;

pre-construction surveys, and schedules of defects of certain assets both pre and post-construction;

development of settlement mitigation measures which may comprise:

o proposals for (and agreement with asset owners of) ground and structure movement instrumentation monitoring;

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o installation of movement monitoring equipment;

o establishment of monitoring baselines;

o monitoring actions plans, and (where necessary); and

o protective measures.

3.9.5 As part of the DCO process, TfL will provide a draft template settlement deed which asset owners can apply for. The template deed will set out a process addressing the above. It is also possible that TfL will enter into bespoke agreements with asset owners in the course of the DCO process.

Damage risk categorisation

3.9.6 Initial screening of damage impact, and damage risk categorisation has been undertaken (using as a basis, the envisaged works proposals) as part of the Reference Design, and the results are reported in the Environmental Statement. This has been undertaken to ensure that the impacts to all structures (buildings, utilities and highways or other structures) potentially at risk of damage from ground movements, are kept to acceptable levels.

3.9.7 The impact assessment and damage risk categorisation will be re-assessed at Detailed Design stage, when the Contractors detailed design and construction proposals have been developed. The results of this further assessment will be used to inform the need for settlement mitigation measures, which could include those described later in Section 3.9.9 to 3.9.17, therefore this further impact assessment work will be necessary prior to construction of the particular works giving rise to the particular ground movements being considered.

3.9.8 The Code of Construction Practice describes the industry-standard damage risk categorisation (after Burland), and damage risk assessment process that will apply to structures to be assessed. The damage impact assessments will identify requirements for settlement mitigation (where required) so as to ensure the residual damage risk categorisation on all assessed structures is category 2, Slight or less.

Pre-construction surveys

3.9.9 Pre-construction surveys, including condition surveys and defects surveys will be necessary for the Scheme, and the requirements for these and other survey types are described in the Environmental Statement and Code of Construction Practice.

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3.9.10 Certain pre-construction surveys, as maybe required by the asset protection process, will be undertaken on existing structures potentially affected by the scheme. The surveys will, in part, inform the requirements for development of subsequent settlement mitigation measures.

Instrumentation and monitoring

3.9.11 Development of instrumentation and monitoring proposals, where required by assessed damage risk, (or where specified by the asset owner as part of an agreement), may be required for particular assets.

3.9.12 The instrumentation and monitoring proposals will need to be developed with cognisance of the assets physical arrangement, access constraints, existing condition, operational regime and other requirements and constraints which may affect how monitoring can be undertaken, and the required frequency of monitoring.

3.9.13 In addition, the way in which data is collected, how it is used and integrated with the protocols for wider data collection and management during the design and construction proposals will be developed, and possibly trialled (see 3.9.17).

3.9.14 For these reasons, proposals for undertaking physical monitoring of ground and structure movements using instrumentation and monitoring equipment are likely to be developed well in advance of construction works, as enabling or advanced works.

Installation of movement monitoring equipment

3.9.15 Following the identification of instrumentation and monitoring requirements, and agreement to the principle of monitoring with the asset owners, the monitoring equipment must be installed, along with all the necessary signal controls, and data capture infrastructure, processes and systems.

3.9.16 For structures potentially at risk of damage impact, these tasks would be undertaken in advance of the relevant construction works, so as to be able capture necessary baselines (see 3.9.17, below), and ensure the sources of any damage arising are isolated, and understood.

Establishment of monitoring baselines

3.9.17 The Code of Construction Practice (Document Reference 6.10) will require that a series of monitoring baselines to third party, statutory authority, and other stakeholder assets (including structures assets, as relevant) be

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established. These will be used as a benchmark for demonstrating that the actual impacts of the Scheme are within the limits assumed in the Environmental Statement. Condition surveys will be used as a benchmark for establishing any actual settlement damage.

3.9.18 The establishment of baselines would commence in advance of the relevant construction works in order to capture prolonged stable, and predictable monitoring results.

Protective measures

3.9.19 In the event that assessed damage risk (with mitigation), exceeds acceptable levels as is described more fully in the Code of Construction Practice (CoCP) (Document Reference 6.10), (but typically with an assessed damage risk category of 3 or Moderate, or greater), then protective measures will be implemented, to ensure the structure is not damaged.

The nature and form of protective measures necessary for each structure will be dependent on the assessed damage risk, the asset type, function and a number of other factors, all of which must be developed with asset owner.

3.10 River Thames walls, inspection, assessment and protection

3.10.1 Construction activity below and adjacent to the existing River Thames river walls will be carefully controlled. The river walls form a part of Londons River Thames flood defences.

3.10.2 Given the criticality of this infrastructure, and the assessed impacts of construction, advanced works pre-construction defect surveys will be undertaken for both north and south river walls. The surveys undertaken with liaison with the Environment Agency, will form a pre-construction record of the condition of the infrastructure prior to any disturbance by the Scheme.

3.10.3 The surveys will also be used as part of the settlement damage mitigation process (part of the asset protection process described in 3.9, above), to protect the river walls from excavation-induced ground movements.

3.10.4 During construction a scheme of monitoring points on the river wall is anticipated, developed in liaison with the Environment Agency, which will comprise settlement monitoring points e.g. Building Research Establishment (BRE) studs, or precise levelling bar codes, which will be used to assess total settlement, longitudinal settlement (and associated tensile strain) and tilt, and will be used for design verification during the construction process. The monitoring will establish pre-construction movement baselines.

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3.10.5 The monitoring measures will form part of the Schemes settlement mitigation measures for the river walls, and will include associated contingency action protocols to assure in turn the Contractor and the asset owner, that the function and performance of the asset is not unduly compromised.

3.11 Protection of other assets - general

3.11.1 In addition to the River Thames river walls, other structures have been identified as being at moderate or greater damage risk from excavation induced ground movements, (these are fully reported in the Environmental Statement). These structures will be protected through settlement mitigation measures to ensure damage risk after mitigation, does not exceed Slight (damage risk category 2), in accordance with the requirements of the CoCP.

3.11.2 Where necessary, and after a detailed phase III settlement impact assessment has been undertaken, and mitigation measures are insufficient to ensure the assessed damage risk to structures is category is 0, 1 or 2, then protective measures will be developed to protect the asset.

3.11.3 The measures necessary and as described in Section 3.9, will be applied to these assets.

3.12 Protection of other assets historical

3.12.1 The 1897 Blackwall Tunnel masonry arch entrance structure on Tunnel Avenue is a Grade II listed structure, through which northbound traffic passes. Although the structure is approximately 30m distant from the excavation (and other earthworks) associated with the Silvertown Tunnel approach structures, to the east, a conservative preliminary assessment identified the possibility that the structure may fall within the 1mm settlement contour.

3.12.2 A Heritage Building survey along with more detailed damage risk assessment will be undertaken in advance of main construction.

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THIS PAGE HAS INTENTIONALLY BEEN LEFT BLANK.

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4. SILVERTOWN WORKS AREAS AND CONSTRUCTION

4.1 Introduction

4.1.1 In this section of the Construction Method Statement, a description of the envisaged construction processes at the Silvertown site is provided. This has been used as a basis for the Schemes environmental impact assessment.

4.1.2 A significant proportion of the works required of the Scheme are described as highly method dependent, that is; the way in which the works are constructed influences their form, arrangement, sequence of construction and associated temporary works. The envisaged construction methods described here, will be developed through a detailed design process which will permit sufficient flexibility to respond to improved future knowledge of ground conditions, existing site conditions including particularly obstructions, and allowing for any innovation which could potentially bring safety, programme or economic benefits.

4.1.3 Notwithstanding the above flexibility regarding construction method, the assessed impacts of the Scheme as implemented, will not be environmentally worse than the implementation of Scheme assessed in the Environmental Statement accompanying the DCO application.

4.2 Ground conditions

4.2.1 A significant amount of construction works associated with the Scheme entails earthworks, deep excavations, piling and tunnelling. In these circumstances it is essential that accurate characterisation of ground and groundwater conditions, and assessment of geohazards during construction is undertaken, to ensure the safe and cost-effective execution of the works.

4.2.2 The development of the Scheme, which is underpinned by this envisaged construction method statement, is supported by a commensurate level of knowledge of ground conditions. Desk Studies and intrusive investigations have been undertaken for the Scheme, which have permitted interpretation of geological strata and estimation of physical properties (strength, stiffness, permeability, and other geotechnical properties).

4.2.3 Good practice in the development of tunnelling projects requires a continuous geotechnical risk assessment and management process. This flows from planning stage through procurement, design and into

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construction. The use of Reference Ground Conditions documentation incorporated into the contractual arrangement is anticipated. This is a widely accepted method of ensuring an equitable risk allocation which addresses the intrinsic uncertainties associated with ground conditions risk.

4.3 General construction activities

4.3.1 The Silvertown Tunnel Scheme is a linear construction project approximately 2km in length (and 1.4km between north and south portals). Where access from the surface is required to build the works, construction activity will take place along the trace of the Scheme within the horizontal and vertical limits of deviation, as shown in the Works Plans (Document Reference 2.5). All tunnelling activities will be constructed and supported from the Silvertown worksite.

4.3.2 Two main worksites are proposed to construct the works: a principal worksite supporting all bored tunnelling activities, and construction of infrastructure on the north side of the River Thames, in Silvertown, and a satellite worksite serving construction of infrastructure in Greenwich.

4.3.3 The plant and equipment envisaged necessary for construction of the Scheme has been scheduled in Table A-1 in 0. This list in conjunction with the construction programme and this narrative has been used in the assessment of the environmental impacts and traffic impact of the Scheme.

4.4 Silvertown worksite

Purpose of the Worksite

4.4.1 The Silvertown worksite will be the principal Scheme worksite, and will serve as the organisational and logistical hub of construction for the Scheme as a whole. In addition to being used for construction of all permanent works on the north side of the river, the Silvertown worksite will service bored tunnelling operations.

4.4.2 All materials and construction logistics support necessary to construct the bored tunnels will be provided from the Silvertown worksite via the TBM launch chamber. This will include the precast concrete segmental linings, annular grout and temporary works elements such as conveyors, track, and ventilation. Similarly the excavated material (spoil) arising from construction will be received, assessed and disposed of from the Silvertown worksite.

4.4.3 All materials used to form the bored tunnels permanent works and the excavated material (spoil) arising from tunnel construction, will be received,

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Silvertown Tunnel



assessed, conditioned (if needed) and disposed of from the Silvertown worksite.

Worksite layout

4.4.4 An envisaged arrangement of the way in which the Silvertown worksite may be used, and the extent of land required is presented in drawing C.2 (Appendix B).

4.4.5 The size of the required worksite changes during the envisaged construction programme, as certain works are completed. The worksite drawings referred to in Section 4.4.4, illustrate how the worksite is envisaged to reduce in size, during the construction process.

4.4.6 The following section of this report the various act

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