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Engineering Options Report: Abbey Mills RouteDoc Ref: 9.10.01

Folder 82 September 2013110-RG-PNC-00000-000826

Engi

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Opt

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Rep

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Abbe

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ills R

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Thames Tideway Tunnel Thames Water Utilities Limited

Application for Development ConsentApplication Reference Number: WWO10001

Engineering options report Abbey Mills route

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Thames Tunnel


List of contents

Page number

1 Executive summary ......................................................................................... 1

2 Introduction ...................................................................................................... 3

2.1 Background ............................................................................................. 3

2.2 Purpose of this report .............................................................................. 4

2.3 Engineering design development ............................................................ 5

3 System design and engineering requirements .............................................. 7

3.1 System design and engineering assumptions ......................................... 7

3.2 Health and safety considerations ............................................................. 7

3.3 System requirements ............................................................................... 7

3.4 Engineering geology .............................................................................. 15

3.5 Tunnel engineering and construction requirements ............................... 20

3.6 CSO engineering and construction requirements .................................. 30

4 Main tunnel drive options .............................................................................. 35

4.1 Introduction ............................................................................................ 35

4.2 Main tunnel engineering: Options preparation ....................................... 35

4.3 Main tunnel engineering: Options assessment ...................................... 49

5 Connection tunnel drive options .................................................................. 57

5.1 CSO connection options ........................................................................ 57

5.2 Connection tunnel: Drive options ........................................................... 63

6 Conclusions and recommendations ............................................................ 69

7 Next steps ....................................................................................................... 71

The following can be found in the accompanying document Engineering options report - Appendices - Abbey Mills route (110-RG-PNC-000000-000827): Appendix A – Assumptions register Appendix B – Drawings Appendix C – Time chainage Appendix D – Geology


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List of figures

Page number

Figure 3.1 Main tunnel routes considered................................................................. 12

Figure 3.2 Typical CSO interception arrangement .................................................... 13

Figure 4.1 Main tunnel site types .............................................................................. 36

Figure 4.2 Main tunnel site zones for all three routes ............................................... 37

Figure 4.3 Main tunnel site zones for the Abbey Mills route ..................................... 37

Figure 5.1 Type A CSO connection .......................................................................... 58

Figure 5.2 Type B CSO connection .......................................................................... 59

Figure 5.3 Type C CSO connection .......................................................................... 60

Figure 5.4 Type D CSO connection .......................................................................... 61

Figure 5.5 Type E CSO connection .......................................................................... 62

List of tables

Page number Table 3.1 CSO control measures ............................................................................... 8

Table 3.2 Geology of the London Basin.................................................................... 16

Table 3.3 Chalk aquifer groundwater levels in 2008 and imposed pressure at tunnel invert (east of Shad) ................................................................................ 20

Table 4.1 Grouping of shortlisted main tunnel sites for the Abbey Mills route post-phase two consultation ............................................................................ 38

Table 4.2 Drive options: Consideration of practical drive lengths ............................. 43

Table 4.3 Initial provisional main tunnel drive options............................................... 44

Table 4.4 Interim main tunnel drive options .............................................................. 47

Table 4.5 Interim list of main tunnel drive options ..................................................... 48

Table 4.6 Programme assumptions for comparison of options ................................. 54

Table 4.7 Summary of construction durations for main tunnel drive options............. 55

Table 4.8 Final list of main tunnel drive options ........................................................ 56

Table 5.1 Frogmore connection tunnel: Drive options .............................................. 64

Table 5.2 Greenwich connection tunnel: Initial drive options .................................... 65

Table 5.3 Greenwich connection tunnel: Final drive options ..................................... 66

Table 5.4 North East Storm Relief Type A CSO connection tunnel drive options matrix ....................................................................................................... 67


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List of abbreviations

AOD above Ordnance Datum ATD above tunnel datum CSO combined sewer overflow Defra Department of Environment Food and Rural Affairs EA Environment Agency EU European Union EPB earth pressure balance (type of TBM) GWT groundwater table m/s metres per second m3/s cubic metres per second NESR North East Storm Relief OD Ordnance Datum (mean sea level at Newlyn in Cornwall) Ofwat Water Services Regulatory Authority PLA Port of London Authority PS pumping station SMP System master plan SR storm relief STW sewage treatment works TBM tunnel boring machine


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1 Executive summary

Engineering options report Abbey Mills route 1

1 Executive summary 1.1.1 The need for an engineering options report is outlined in the Site selection

methodology paper (Summer 2011) 1. 1.1.2 Following phase two consultation, this report was prepared as part of the

process to support the proposed sites and proposed route for the Thames Tunnel project (the ‘project’) that will be publicised in accordance with Section 48 of the Planning Act 2008. It is specific to the Thames Tunnel project, but also takes cognisance of the Lee Tunnel project, which is expected to be completed before the Thames Tunnel project.

1.1.3 This report should be read as a technical document; therefore the content has been kept brief in the understanding that the reader is familiar with the technical subject matter.

1.1.4 The report begins by defining the overall engineering requirements to be considered as part of the development of engineering options for the project. The requirements are broadly summarised without providing any in-depth justification since the main aim of the report is to identify tunnel drive options.

1.1.5 Three main tunnel routes between west London and Beckton Sewage Treatment Works (STW) were identified as part of design development, and the Abbey Mills route was chosen as the preferred option. The Report on phase one consultation concluded that, having considered the feedback received, following phase one consultation the Abbey Mills route remained the preferred route for phase two consultation. Following consideration of the second phase of consultation, only the Abbey Mills route was taken forward for further evaluation in this report as the proposed route.

1.1.6 The report also presents our methodology for determining possible options for constructing the main tunnel along the Abbey Mills route. The methodology is based on engineering requirements and the shortlist of main tunnel sites provided by the ‘site selection process’, which identifies potentially suitable sites for use as either main tunnel drive, intermediate or reception sites, in order to facilitate the construction of the main tunnel and its subsequent operation. Drive options associated with the shortlisted CSO sites for connection tunnels that link two or more CSOs are also considered in this report.

1.1.7 In order to build the project, it is necessary to ‘drive’ a series of tunnels to connect a number of tunnel sites. Possible permutations of tunnel drive scenarios (‘drive options’) for the presented sites are established systematically for evaluation.

1.1.8 There is an important relationship between tunnel drive optioneering and site selection. The relative desirability of the feasible drive options is also

1 Terminology: prior to the two phases of consultation the project identified ‘preferred sites’. These sites and the drive strategy were the subject to public consultation. Following phase two consultation, the project reviewed and identified the ‘proposed sites’ for Section 48 publicity.

1 Executive summary


examined in terms of engineering factors. These and factors identified by other disciplines, such as planning, environment, community and property, will be addressed in workshops and used in conjunction with the site suitability reports to determine the proposed sites and the proposed scheme, which will be presented in the Section 48: Report on site selection process.

1.1.9 This report describes the appropriate engineering options that are available to drive the tunnels. These options are presented as a schedule of feasible tunnel drive options to be taken forward to subsequent stages in the site selection process.

1.1.10 Finally, engineering factors that will be used to provide content to determine the proposed sites and associated drive options for the tunnels are presented. These factors will be used in the Section 48: Report on site selection process to examine the advantages and disadvantages of the drive options.

2 Introduction


2 Introduction

2.1 Background 2.1.1 The Site selection methodology paper and Site selection background

technical paper are the main documents that guide our site selection process.

2.1.2 In summary, the Site selection methodology paper comprises three main stages. Stage 1 includes a site identification and filtering process, which is carried out in three main parts: a. 1A: Creation of a long list of potential sites, with an explanation of how

information is to be verified and moved to part 1B b. 1B: Creation of a shortlist of potential sites, with an explanation of how

information is to be verified and moved to part 1C c. 1C: Creation of a preferred list of sites, with an explanation of how

information is to be verified and moved to Stage 2 (consultation). 2.1.3 Arriving at the preferred list of sites involves three steps: the first two steps

take place concurrently and the third step brings together the findings of the first two: a. The suitability of all sites on the final shortlist is assessed in more

detail in site suitability reports. b. An engineering options report sets out the tunnel drive options. c. Optioneering workshops bring together the disciplines to discuss

key factors from the site suitability reports and engineering options report in order to determine the preferred drive options and associated sites.

2.1.4 There is an important relationship between tunnel drive optioneering and site selection. The role of the engineering options report in the process is to define the engineering requirements and to set out the drive options to be taken forward for evaluation. It also explains how the possible options for delivering the three main tunnel routes are determined. Possible permutations of tunnel drive scenarios are considered in order to identify all the feasible drive options, based on the potential number of tunnel boring machines (TBMs) used and the shortlisted sites that they could be driven from and received at.

2.1.5 An engineering options report was produced at the following stages of the project to take account of information current at the time: a. prior to phase one consultation b. prior to phase two consultation c. post phase two consultation (prior to Section 48 publicity)

2.1.6 Prior to phase one consultation, the work for Stage 1 of the site selection process, from identification of the long list to the preferred list of sites for phase one consultation, was carried out in 2009 and 2010. As part of that

2 Introduction


process, the Engineering options report (Spring 2010) was prepared to consider the drive options associated with the shortlisted sites for three different tunnel routes: the River Thames route, the Rotherhithe route and the Abbey Mills route.

2.1.7 At phase one consultation (September 2010 to January 2011) we presented the preferred sites and preferred route along with the shortlisted sites and other routes that had been discounted. The phase one consultation feedback was collated into the Report on phase one consultation. Analysis of the consultation feedback received concluded that the Abbey Mills route remained the preferred route.

2.1.8 Prior to phase two consultation, consideration was given to phase one consultation feedback and a number of emerging factors that triggered a series of site selection ‘back-checks’. The back-checks led to a number of site changes and new drive options. As part of this process, the Engineering options report – Abbey Mills route (Summer 2011) was prepared to consider the drive options associated with the revised shortlisted sites for the Abbey Mills route. This process and the changes were presented in the Phase two scheme development report (Winter 2011).

2.1.9 At phase two consultation the revised preferred sites along the Abbey Mills route were presented together with the shortlisted sites that had been discounted. Some of the preferred sites presented at phase two consultation were different to those presented at phase one consultation, including changes to the associated drive strategy.

2.1.10 As a consequence of phase two consultation feedback and other emerging information, a review of sites and drive options was undertaken. As part of that process, this Engineering options report – Abbey Mills route (Spring 2012) has been prepared to consider the drive options associated with the shortlisted sites for the Abbey Mills route as part of the post phase two consultation review of sites.

2.2 Purpose of this report 2.2.1 This report has been prepared as part of the process to support the

proposed sites and proposed route for the project that will be publicised in accordance with Section 48 of the Planning Act 2008. It is specific to the project but also takes cognisance of the Lee Tunnel project, which is expected to be completed before the Thames Tunnel project.

2.2.2 The Site selection methodology paper states that the engineering options report should consider: a. how sites work in combination as well as options for the main tunnel

alignment and combined sewer overflow (CSO) connections b. how options for the tunnel alignment and CSO connection points can

be refined, having regard to the availability and spacing of suitable main tunnel sites, in addition to the potential for combined use of sites. Cost considerations associated with engineering options, transport and energy should be compared and discussed.

2 Introduction


2.2.3 This report identifies and refines possible main tunnel drive options for the Abbey Mills route and considers the overall location and grouping of the shortlisted sites. The information in this report will be used in subsequent workshops to identify the proposed sites and drive strategy.

2.2.4 The findings of this Engineering options report – Abbey Mills route (Spring 2012) will help to inform subsequent stages of the selection process for the proposed scheme that will be presented in the Section 48: Report on site selection process.

2.2.5 This Engineering options report – Abbey Mills route (Spring 2012) covers: a. Section 3: System design and engineering requirements. This section

sets out a high-level description of the system, geological, tunnelling and CSO engineering requirements to be considered in the development of engineering options, and the subsequent selection of a proposed drive strategy and the associated list of proposed main tunnel sites for the Abbey Mills route. This section states and broadly summarises the requirements without providing an in-depth justification for the system and engineering requirements.

b. Section 4: Main tunnel drive options and Section 5: Connection tunnel drive options: These sections summarise the tunnel options considered and the analysis and refinement of these options. The analysis also considers the relationship of the tunnel options to the available groups of shortlisted sites.

2.2.6 This report only considers the development of options from an engineering perspective. The suitability of each site is not discussed here and is presented in the site suitability reports.

2.2.7 In considering the tunnel drive options this report does not identify proposed tunnel routes or sites. The selection of the proposed tunnel alignment, CSO sites and main tunnel sites will be assessed at later stages in the process (selection of the proposed sites and proposed project). These stages will be carried out by a multidisciplinary team and reported in the Section 48: Report on site selection process. The considerations in this Engineering options report – Abbey Mills route (Spring 2012), along with site suitability reports, will feed into and inform these stages.

2.3 Engineering design development 2.3.1 The project comprises a main tunnel that would run from west to east

London and be integrated into the existing sewerage system via connection tunnels and drop shafts in order to control 34 ‘unsatisfactory’ CSOs. These tunnels would store and transfer the intercepted flows to Beckton STW via the Lee Tunnel.

2.3.2 The Lee Tunnel project, which comprises a tunnel to connect Abbey Mills Pumping Station to Beckton STW and works to control the Abbey Mills Pumping Station CSO, has been consented and construction started in 2010.

2 Introduction


2.3.3 The Thames Tunnel project’s site selection process recognises that the engineering design will need to proceed parallel to the site selection process and that there is an iterative relationship between the two.

2.3.4 Design development activities have included: a. engineering designs and studies of various components of the project

and identification of potentially feasible tunnel routes b. ‘system master planning’ to define the sewage system operation

changes and facilities that would be needed to control and limit overflows

c. logistics studies for construction, transportation and river navigation d. field investigations, including ground investigations and surveys.

2.3.5 This Engineering options report – Abbey Mills route (Spring 2012) draws on the relevant aspects of these studies and investigations, as well as the results of the site selection shortlisting process.

3 System design and engineering requirements



3.1 System design and engineering assumptions 3.1.1 The assumptions on which this report was based are identified and listed

in an assumptions register in Appendix A, which can be found in the accompanying document, Engineering options report – Abbey Mills route – Appendices (Spring 2012). These assumptions and other requirements are discussed in the sections below.

3.2 Health and safety considerations 3.2.1 Health and safety is of paramount importance to Thames Water and the

project team. 3.2.2 Through risk assessment and management, the project team is working in

accordance with industry codes and project standards, with the aim of achieving world-class health and safety objectives.

3.2.3 The project has a plan and policies in place to ensure compliance with the Construction (Design and Management) Regulations 2007. According to these statutory requirements, so far as is reasonably practicable, every designer shall avoid foreseeable risks to the health and safety of any person carrying out construction work; the designer shall eliminate hazards which may give rise to risks; and reduce risks from any remaining hazards.

3.2.4 In addition, the Health and Safety at Work etc Act 1974 places general duties on employers to conduct their operations in such a way as to ensure, so far as is reasonably practicable, that others (including the general public) are not exposed to risks to their health or safety.

3.2.5 In assessing health and safety risks there is a contrast in magnitude between above-ground work, where risk can generally be controlled through proven good management practices, and underground work, where the remaining risks are higher as they are dictated by confined space, restricted heavy-lifting facilities, a mechanically controlled atmosphere, risk of inundation, distance for escape or rescue, and variable ground conditions.

3.3 System requirements 3.3.1 The need and overarching requirements for the project are described in

the Needs Report. The Needs Report provides the legal and regulatory context and the need for a solution to meet the regulatory drivers.

3.3.2 The concept of the project is to: a. control discharges from 34 CSOs b. store CSO discharges c. transfer CSO discharges for treatment.



3.3.3 The engineering requirements to be taken forward in assessing the engineering tunnel route and alignment options are summarised and briefly discussed in the following sections. Design development is ongoing and therefore the implications of any future changes will need to be further assessed and reviewed.

3.3.4 This section of the report focuses on system requirements relevant to the selection of sites and tunnel alignments.

Developments in design requirements 3.3.5 Design developments have updated the requirements of the project such

that now only 18 of the 34 CSOs require direct interception. The remaining CSOs are to be controlled by other measures.

3.3.6 Table 3.1 lists the control measures proposed for the 34 CSOs. Table 3.1 CSO control measures

CSO ref CSO Method of overflow control

CS01X Acton Storm Relief Interception

CS02X Stamford Brook Storm Relief Control measures at other CSOs indirectly control this CSO

CS03X North West Storm Relief Interception and pumping station operation changes at Hammersmith Pumping Station indirectly control this CSO

CS04X Hammersmith Pumping Station

Interception and pumping station operation changes

CS05X West Putney Storm Relief Interception

CS06X Putney Bridge Interception

CS07A CS07B

Frogmore Storm Relief – Bell Lane Creek Frogmore Storm Relief – Buckhold Road

Interception

CS08A CS08B

Jews Row Wandle Valley Storm Relief Jews Row Falconbrook Storm Relief

Modifications already in place so CSO is indirectly controlled**

CS09X Falconbrook Pumping Station Interception

CS10X Lots Road Pumping Station Interception

CS11X Church Street Controlled indirectly by sewer relief works at other CSOs

CS12X Queen Street Controlled indirectly by sewer relief works at




other CSOs

CS13A CS13B

Smith Street – Main Line Smith Street – Storm Relief

Controlled indirectly by sewer relief works at other CSOs

CS14X Ranelagh Interception and additional sewer connection relief*

CS15X Western Pumping Station Controlled indirectly by sewer relief works at other CSOs

CS16X Heathwall Pumping Station Interception

CS17X South West Storm Relief Interception

CS18X Kings Scholars Pond Controlled indirectly by sewer relief works at other CSOs

CS19X Clapham Storm Relief Interception

CS20X Brixton Storm Relief Interception

CS21X Grosvenor Ditch Controlled indirectly by sewer relief works at other CSOs

CS22X Regent Street Interception via additional sewer connection relief*

CS23X Northumberland Street Controlled indirectly by sewer relief works at other CSOs

CS24X Savoy Street Controlled indirectly by sewer relief works at other CSOs

CS25X Norfolk Street Controlled indirectly by sewer relief works at other CSOs

CS26X Essex Street Controlled indirectly by sewer relief works at other CSOs

CS27X Fleet Main Interception and additional sewer connection relief*

CS28X Shad Thames Pumping Station

Pumping station modifications***

CS29X North East Storm Relief Interception

CS30X Holloway Storm Relief Local modifications***




CS31X Earl Pumping Station Interception

CS32X Deptford Storm Relief Interception

CS33X Greenwich Pumping Station Interception and pumping station operation changes

CS34X Charlton Storm Relief Pumping station operation changes at Greenwich Pumping Station and improvements at Crossness STW

* The additional sewer connection relief at Ranelagh, Regent Street and Fleet Main CSOs would be connections to the northern Low Level Sewer No.1. ** This CSO was planned to be controlled via interception at phase one consultation stage and does not require a worksite. *** These CSOs were planned to be controlled via interception at phase one consultation stage; they are now planned to be controlled by other methods and require a worksite.

3.3.7 Further elements that the project should provide as a minimum are listed below: a. The westerly start point of the project should connect to the Acton

Storm Relief CSO. b. The easterly end point of the tunnel should connect to the Lee Tunnel

at Abbey Mills Pumping Station (PS) (only for the Abbey Mills route). c. Relieving flows in the northern Low Level Sewer No.1 at the

Ranelagh, Regent Street and Fleet Main CSO sites should give sufficient control to reduce local CSO spills so that direct interception is no longer required for the Northumberland Street, Church Street, Smith Street, Kings Scholars Pond, Grosvenor Ditch, Savoy Street, Norfolk Street and Essex Street sewers.

d. The system should ensure the health and safety of operatives, the public and third parties. This means providing, during both the construction and operational phases, a hydraulically safe and robust system with no risk of flooding or adverse transient conditions; secure and resilient facilities; appropriate levels of ventilation and air treatment; and safe methods and facilities for access and egress into and out of the main and connection tunnels.

Main tunnel routes 3.3.8 Design development has identified three possible tunnel routes: the River

Thames route, the Rotherhithe route and the Abbey Mills route. 3.3.9 The River Thames route largely follows the route of the River Thames, the

Rotherhithe route alignment cuts across the Rotherhithe Peninsula, and the Abbey Mills route connects to the Lee Tunnel at Abbey Mills. The latter became feasible when the depth of the Lee Tunnel shaft at the Abbey Mills PS end was increased to avoid difficult geological conditions on the



Lee Tunnel route. This would enable a continuous gradient for the main tunnel and satisfy the design constraints for the overall vertical tunnel alignment and system hydraulic requirements.

3.3.10 The three routes were consulted on at phase one consultation and the Abbey Mills route was presented as the preferred route. Analysis of the consultation feedback received concluded that the Abbey Mills route remained the preferred route for phase two consultation. Following consideration of the consultation feedback, only the Abbey Mills route is evaluated further in this report as the ‘proposed route’.

3.3.11 The three routes are illustrated in Figure 3.1.



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Figure 3.1 Main tunnel routes considered



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Control and interception of CSO flows 3.3.12 The CSOs to be controlled by interception are listed in Table 3.1. 3.3.13 The interception and connection of CSO flows to the main tunnel typically

comprises four major elements: a CSO interception chamber, a connection culvert, a drop shaft, and a connection tunnel, as illustrated below in Figure 3.2. A description of the construction elements is provided in the Site selection background technical paper and discussed further in Section 3.6.

Figure 3.2 Typical CSO interception arrangement

Tunnel hydraulic requirements 3.3.14 The main purpose of the tunnel system is to store and transfer CSO flows

in order to reduce CSO discharges. The background for the size of the tunnels is provided in paragraph 3.5.3.

3.3.15 The tunnel system must be self-cleansing; therefore the velocity of flow must be high enough to move detritus without requiring further flushing. It has been determined that a gradient in excess of approximately one in 850 generates flow velocities that exceed 1m/s during event cycles and international experience has shown that this is sufficient to meet the project’s objective.

3.3.16 The gradient of the connection tunnels is generally between one in 400 and one in 500 in order to achieve flow capacities while not exceeding maximum peak velocities.



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3.3.17 Large tunnel systems can be prone to hydraulic pressure effects due to the generation of transient (temporary surge flow) conditions. Control features need to be incorporated into the tunnel design and mode of operation in order to manage these transient pressure effects.

System functional and operational requirements 3.3.18 In order to ensure safe operation, access to, and inspection and

maintenance of the tunnel, design development is based on the following criteria and features: a. The main tunnel and connection tunnels must be designed as

generally ‘maintenance free’ and have a design life of 120 years. Tunnel entry for inspection and maintenance is only planned to take place approximately every ten years.

b. The ten-year inspection would be a major undertaking in its own right, which would involve extensive planning and provision of temporary works to permit entry.

c. The designated access points to the tunnel system would be main tunnel shafts and CSO drop shafts that connect to the main tunnel directly. During construction, extensive temporary facilities are provided for safety purposes. Once after temporary facilities have been removed the long term maintenance requirements control the safe spacing of the main tunnel shafts. These shafts would allow the insertion and removal of specialist inspection and maintenance vehicles during the ten-yearly inspection of the tunnel. At this stage of design development, it is assumed that the spacing between the permanent access points should not exceed 9km. Long, large diameter connection tunnels would have similar access provisions.

d. The main tunnel shafts and on-line CSO drop shafts would be provided with large access openings to permit inspection plant to be lowered into/removed from the tunnel and provide emergency access/egress. CSO and main tunnel sites must be selected to ensure sufficient space for two mobile cranes to service the shafts.

e. Permanent air management facilities would be provided, including ventilation and monitoring of exhaust air quality, along with air treatment facilities (odour control).

f. Control gates would be provided to isolate the tunnel system and prevent flows from entering. These gates would be controlled from a central control room to provide an overview of the system from a single point. The gates would also be used to isolate the tunnel from in-flows during maintenance inspections, which are currently envisaged to take place every ten years.

g. The tunnel’s operating regime would be integrated with the operating regimes at pumping stations, particularly Abbey Mills PS, Greenwich PS, Beckton STW, and Crossness STW.

h. Fixed ladders and access ways would not be provided to the bottom of shafts or the main tunnel due to the potential for corrosion and the likelihood of damage during surge events, which has occurred on



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similar projects. Specific arrangements would be developed for safe access to carry out inspection and maintenance of the CSO drop shafts, connection tunnels and the main tunnel. Fixed ladder access would be provided to subsurface MEICA equipment, odour control equipment and other equipment that requires routine inspection and maintenance.

3.3.19 When considering the spacing of main tunnel shafts for the completed system, and based on the experience of other major CSO systems, it is assumed that maintenance and inspection teams would travel through the main tunnel by means of an inspection vehicle supported by a back-up standby vehicle. This would reduce the transit time and permit a wider range of equipment to be carried with relative ease. It would also facilitate access to the internal circumference of the tunnel for inspection purposes. Vehicular access is practicable in the tunnel system, given the diameter of the main tunnel and the fact that the system would be dry when inspections are carried out as all penstocks that control the flow into the system would be securely locked off.

3.3.20 Access to the connection tunnels would also be required during inspection. The length of the connection tunnels is highly variable depending on location, and varies from 16m to 4,600m. Provision for emergency egress would be made at the drop shafts by means of suitable access openings and space for cranes to operate a man-rider. The connection tunnel to Greenwich PS would be inspected using a similar inspection vehicle to that used for the main tunnel.

3.4 Engineering geology Route geology

3.4.1 The route geology has been established using the British Geological Survey (BGS) ‘Lithoframe50’ model, from which geological long sections have been prepared. This has been supplemented by project-specific site investigations, including a seismic refraction survey, ground and over-water boreholes, and field and laboratory testing, as well as the installation of piezometers to establish water levels.

3.4.2 The geological long section for the Abbey Mills main tunnel route, derived from the Lithoframe50 model, is provided in Appendix D of the Engineering options report – Abbey Mills route – Appendices (Spring 2012).

3.4.3 The basic geological descriptions within the London Basin geological sequence are provided in Table 3.2.



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Table 3.2 Geology of the London Basin

Era Group Formation Brief description of formation

Approximate range of

thickness (m)

Recent Alluvium Soft clays, silts, sands and gravels. May contain peat. 0 – 5

Floodplain Terrace

Medium to dense sand, flint and chert gravel, occasional cobbles and boulders. 0 – 10 Kempton

Park Terrace

Tertiary Thames London Clay

Very stiff, fissured, silty, locally fine to medium sandy clay.

>100

Harwich

Swanscombe member: Sandy clay to clayey sand (< 2m) with some fine to medium black rounded gravel. Blackheath member: Dense to very dense flint gravel (with occasional cobbles) in silty or clayey, glauconitic, fine to medium sand matrix. Oldhaven member: Very dense clayey sand with gravel and shells – often cemented as limestone.

0 – 10

Lambeth Group Woolwich

Stiff, dark grey to black clay with locally abundant shell debris and strong limestone beds (100 to 200mm thick).

10 – 20

Reading

Very stiff to hard, multi-coloured (light blue-grey mottled red, orange, brown and purple), locally sandy clay.

Upnor Gravel, glauconitic and organic sand, silt and clay. 5 – 7



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Era Group Formation Brief description of formation

Approximate range of

thickness (m)

Thanet Sand Formation (including Bullhead Bed at base <~0.5m)

Very dense silty to very silty sand. The lowest ~0.5m sometimes consists of fine, medium and coarse, angular flint gravel.

10 – 15

Cretaceous Chalk Seaford*

Homogeneous chalk with nodular flint horizons (>100mm thick).

circa 40

Lewes* Heterogeneous nodular chalk with nodular flint horizons and marl seams.

circa 50

NB: *Limited to those formations of the ‘White Chalk’ subgroup expected within the Thames Tunnel project. (Upper and Middle Chalk are now known collectively as ‘White Chalk’.)

3.4.4 The distribution of strata along the route is largely controlled by the London Basin Syncline, which plunges gently eastwards. Thus, beneath a cover of made ground and recent deposits, the succession of tertiary deposits is gradually exposed west to east along the river until Chalk occurs at an outcrop around Greenwich.

3.4.5 The anticipated geology at the proposed main tunnel invert is as follows: a. London Clay Formation: from the western end of the tunnel to just

west of Albert Bridge (Harwich at the base approximately between Cremorne Wharf and Albert Bridge).

b. Lambeth Group: starts to enter the tunnel invert just east of Albert Bridge, forming the lower third of the face by Chelsea Bridge, and the full-face by Tideway Walk. The tunnel continues in full-face Lambeth Group to just east of London Bridge.

c. Thanet Sand Formation: within the invert and the lower third of the face between Blackfriars Bridge and London Bridge, becoming full-face from just east of London Bridge to just west of Tower Bridge.

d. White Chalk subgroup: downstream from just east of Tower Bridge. 3.4.6 Faulting at London Bridge is expected to repeat the sequence, and mixed-

face conditions in the Lambeth Group and Thanet Sand Formation are expected from Chelsea Bridge through to Tower Bridge, with only a short section wholly in the Thanet Sand Formation close to Tower Bridge.

3.4.7 Various structural geological models provide different interpretations of the structural setting across the London Basin, but they all generally indicate regular faulted block groundmass in Chalk and northwest by southeast trending faults that cut the basic east–west main synclinal form.



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3.4.8 The dominant structural geological features are: a. the Hammersmith Reach Fault Zone, a series of north-northwest –

south-southeast trending faults beneath and adjacent to the east side of Hammersmith Bridge. A 5m displacement to the east is noted.

b. the Putney Bridge Fault, a series of southeast – northwest trending faults on the syncline with the axis to the west of Putney Bridge, with vertical displacement on top of Lambeth Group strata on the eastern hanging wall of approximately 2m.

c. the Chelsea Embankment (Albert Bridge) Fault Zone, a series of north – south and south-southwest – north-northeast trending faults between Battersea and Chelsea bridges, which would intersect the tunnel alignment at near to perpendicular. Up to 5m vertical displacement of strata has been noted over this zone, resulting in uplift of the top of Lambeth Group deposits on the east side of Albert Bridge.

d. the Lambeth Anticline, a north-northwest – south-southeast trending faulted anticline between Vauxhall and Lambeth Bridges that intersects the tunnel alignment at an oblique angle with a difference in strata level of approximately 5m.

e. the London Bridge Fault Graben, a southeast – northwest trending graben-type feature arranged between Cannon Street and Tower Bridge, with known vertical displacement in excess of 10m.

f. the Greenwich Fault Zone, a southwest – northeast trending feature, which was investigated in detail during the Lee Tunnel project ground investigation in 2008. Up to 20m downthrow is anticipated to the northwest in a series of stepped faults. The fault runs generally parallel to the main syncline, southwest – northeast from Greenwich to Beckton, crossing the River Thames downstream of the Thames Barrier, and is in close proximity to Greenwich PS.

3.4.9 Other structural features include the North Greenwich Syncline (now more generally known as the Plaistow Graben), Millwall Anticline and Beckton Anticline, all of which trend northeast – southwest, contrary to the main basin axis.

3.4.10 There is a risk of scour hollows located on previous drainage channels formed by the River Thames, which are often found at the confluence of the existing tributaries, eg, at the River Fleet, River Lee and River Wandle. The features usually contain a variety of granular deposits and/or disturbed natural materials and are localised and steep-sided.

3.4.11 The scour hollow in the vicinity of the Blackwall Tunnel is the only scour hollow known to penetrate into Chalk. Elsewhere, the hollows only affect the tertiary deposits and, more particularly, London Clay. Basal depths are normally 5m to 20m below ground level, with the exception of 33m at Battersea Power Station and Hungerford Bridge.

3.4.12 Of the known scour hollows, only the hollow at Hungerford Bridge is close to the main tunnel. This feature attains a base level of 72mATD in London Clay near the south bank, equivalent to only 10m above the tunnel crown.



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Such features may, however, have greater implications for the shallower connection tunnels in other locations.

3.4.13 The presence of flints within the Chalk may cause severe wear to the TBM, which would require frequent and hazardous interventions for inspection and maintenance of the TBM cutterhead. Therefore, an important part of the project’s ground investigations is to investigate the Chalk structure, permeability and characteristics of flint-related features.

3.4.14 A number of flint bands are present within the Chalk. Within the Seaford Chalk, two well-defined flint bands that are used as marker horizons (not necessarily the thickest seams) are the Bedwells Columnar and Seven Sisters. The Bedwells typically comprise a discontinuous layer of very large, irregular flints, up to approximately 500mm high by 300mm in diameter. Previous projects have found that they have a compressive strength of 600mPa. The Seven Sisters is a continuous band, with flints between 100mm and 150mm thick.

3.4.15 The selection of the appropriate TBM is important in this respect and a slurry TBM is preferred for the section of the route in Chalk. A slurry TBM was used successfully on the Channel Tunnel Rail Link Thames crossing next to the QE2 Bridge and, most recently, the same type was procured by the contractor for the Lee Tunnel project. The advantages of this type of TBM include the ability to deal with water-bearing fissures in Chalk and to convey flint pieces in a fluid slurry, as opposed to a potentially damaging abrasive paste from an earth pressure balance (EPB) TBM. The need for hazardous interventions would be reduced by selecting a slurry TBM for Chalk, however slurry TBMs are not appropriate for use in clay of the type expected on other sections of the tunnel alignment (see paragraph 3.5.20).

Hydrogeology 3.4.16 The major aquifer of the London Basin lies in the Chalk. It is wholly

unconfined to the east but confined to the west below the tertiary strata and the London Clay Formation in particular. The Chalk aquifer is generally in hydraulic continuity with the overlying Thanet Sand Formation and sometimes the base of the Lambeth Group, particularly the gravel part of the Lower Mottled Beds and the Upnor Formation. The Environment Agency (EA) refers to this combined aquifer as the Chalk-Basal Sands aquifer.

3.4.17 Local aquicludes can exist in the overlying Lambeth Group, in particular the Woolwich Formation Laminated Beds, leading to perched groundwater tables. Historical records of engineering schemes have stated that these ‘perched’ features retain hydrostatic pressures of up to 40m, which may result in high inflows at tunnel level and particularly into shafts during construction.

3.4.18 The Harwich Formation (Blackheath Member) is also known to contain high groundwater levels in places, which cause problems during tunnel construction.



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3.4.19 A minor regional aquifer lies within the floodplain and river terrace deposits; due to the connection to the River Thames, it is generally tidal, with an average level of 100mATD (0mAOD) +/- 2.5m.

3.4.20 Regional monitoring of the Chalk aquifer is reported by the EA and specific monitoring data is available over the years 2000 to 2008. Data indicates a depressed groundwater table in central London at 60mATD with groundwater levels close to Blackfriars Bridge at 62mATD (refer to the groundwater level contour plan of the London Basin in Appendix D). However, the latest ground investigations undertaken by the project indicate that groundwater levels in the Chalk from Rotherhithe to Charlton are 10m higher than the reported EA levels.

3.4.21 Groundwater pressure in the Chalk would have an important bearing on tunnelling, especially the construction of junctions between the main tunnel and the connection tunnels. Table 3.3 shows the 2008 levels in the Chalk aquifer eastwards from Tower Bridge, using the data obtained from the EA.

Table 3.3 Chalk aquifer groundwater levels in 2008 and imposed pressure at tunnel invert (east of Shad)

Tunnel section Tower Bridge NESR Abbey

Mills

Approx tunnel invert mATD 50 45 40

Approx GWT level 2008 mATD 72 78 92

Approx GWT pressure bar 2.5 3.5 4.0

NB: * Highest levels indicated in Lee Tunnel project and Thames Tunnel project monitoring holes.

3.4.22 Short-term effects of pumping can still have a demonstrable impact on regional equipotentials. For example, levels decreased significantly due to abstractions in supply wells at Battersea/Brixton that commenced in 2002. The groundwater level was drawn down approximately 18m local to the wells, 10m in central London near the River Fleet, and 6m in the vicinity of Tower Bridge and the Battersea Power Station area.

3.4.23 The EA reports that the groundwater that feeds the Chalk aquifer from the southeast interacts with the River Thames from Greenwich to Woolwich as it flows northwest to Stratford, then west to central London. In the Greenwich to Woolwich area, there is evidence of saline intrusion within the aquifer.

3.5 Tunnel engineering and construction requirements Risk management considerations

3.5.1 In addition to the health and safety requirements described in Section 3.2, there is a requirement that, in order to make the project insurable, project risk must be managed in accordance with the British Tunnelling Society and the Association of British Insurers’ Joint Code of Practice for Risk



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Management of Tunnel Works in the UK. The objective of the code is to promote and secure best practice to minimise and manage risks associated with tunnelling works and to set out best practices to be adopted. At the core of the code is an obligation for owners, designers and contractors to have processes in place to identify and manage risks throughout the life of the project.

3.5.2 The project has a risk management plan and procedures in place to manage and control risks and comply with the requirements of the Joint Code of Practice for Risk Management of Tunnel Works in the UK. Refer also to Health and safety engineering risk considerations in Section 4.3.

General tunnel considerations Tunnel diameters

3.5.3 Tunnels should be sized to suit the hydraulic performance of the system and the required storage capacity. The majority of the main tunnel needs to be 7.2m internal diameter, but the western most tunnel drive section may be smaller depending on the drive length as follows: a. between a site in the Acton area and a site in the Barn Elms area, the

internal diameter would be 6m b. between a site in the Acton area and the Wandsworth Bridge area, the

internal diameter would be 6.5m. 3.5.4 CSOs would be connected to the main tunnel via interception

chambers/drop shafts and connection tunnels. These tunnels should be sized to carry the design flows from the CSOs at a gradient that would limit maximum flow velocities to 5m/s in order to ensure hydraulic stability and limit scour potential. The size of the connection tunnels would vary from 2.2m to 5m internal diameter depending on the flow. The minimum tunnel size for safe man access is assumed to be 2.2m internal diameter. Vertical tunnel alignments

3.5.5 The overriding factors that control the tunnel slope and elevation (vertical tunnel alignment) are: a. hydraulic functional performance b. constraints imposed by existing and proposed third-party infrastructure c. tie-in connection level to the Lee Tunnel at Abbey Mills PS in order to

maintain gravity flow throughout (for the Abbey Mills Route). 3.5.6 The main third-party constraints for the main tunnel include:

a. the Thames Water Ring Main Barnes to Barrow b. the Thames Water Lee Valley Water Tunnel near Hammersmith

Bridge c. the proposed National Grid ‘Wimbledon to Kensal Green’ cable tunnel.

3.5.7 The vertical distance that separates the Lee Valley Raw Water Tunnel and the main tunnel crossing above is approximately 3m. Other existing deep-level service tunnels, including National Grid’s Richmond to Fulham high pressure pipeline tunnel and a number of BT Openreach tunnels, also



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present constraints on the alignment. In addition, the planned National Grid ‘Wimbledon to Kensal Green’ tunnel would require co-ordination to ensure that the projects remain compatible. The distance between the tunnel and other existing third-party underground tunnels not listed above is less critical to the vertical tunnel alignment.

3.5.8 The potential connection tunnel to connect the Earl PS, Deptford Storm Relief and Greenwich PS CSOs to the main tunnel would be restricted vertically by the Jubilee Underground line (which crosses the Rotherhithe Peninsula); the proposed UKPN cable tunnel from New Cross to Wellclose Square Scheme; and the proposed National Grid Hurst to New Cross cable tunnel.

3.5.9 The alignment would be designed to minimise the overall impact on third-party structures. A programme of work is underway to quantify the impacts on third-party infrastructure including bridges, tunnels, buildings and utilities. Horizontal tunnel alignments

3.5.10 Drive options between a number of geographic site zones are identified and compared in Section 4 of this report. Once the individual site options have been considered and assessed as part of the Final report on site selection process, the detailed tunnel alignment will be decided. The alignment must satisfy the hydraulic flow regime requirements as set out in paragraphs 3.3.14 to 3.3.17.

3.5.11 The minimum preferred horizontal radius for the main tunnel is 600m for practicable construction purposes; however this could be reduced to 500m when constrained. Smaller diameter, segmentally lined connection tunnels typically have a minimum radius of 300m, although techniques can be employed to achieve smaller radii.

3.5.12 In order to minimise the effect of tunnelling on third-party infrastructure, the tunnel should, as far as practicable: a. pass under the centre of the mid-deck span of bridges to maximise

clearance to the bridge foundations b. avoid interfaces with sensitive existing structures, such as the original

Thames Tunnel (Brunel’s ‘Thames Tunnel’, which now carries the Overground railway line) and the Rotherhithe road tunnel

c. avoid passing beneath tall buildings on deep piles d. maximise clearance to third-party infrastructure.

3.5.13 The alignment of the CSO connection tunnels would generally be based on the location of the main tunnel and main tunnel shafts, along with hydraulic considerations. In many cases the risks of setting up TBMs for the very short connection tunnels would offset the benefits in terms of ground control. Where connection tunnels are unlikely to be machine driven and ground conditions are expected to be poor, tunnel length should be minimised as far as practicable.



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Tunnel lining 3.5.14 The lining of the main tunnel is assumed to comprise a primary and

secondary lining system. The primary lining installed during the excavation cycle would consist of a ring of tapered, reinforced concrete segments, approximately 350mm thick. The secondary lining would be 300mm-thick, cast-in-situ reinforced concrete in order to provide the required internal diameter for the finished tunnel. For the purposes of this report, the connection tunnels are also assumed to have a secondary lining. Shaft sizes

3.5.15 The main tunnel drive shafts are anticipated to have an internal diameter between 25m and 30m, with depths ranging from approximately 30m in west London to 65m in east London. Shafts of 25m diameter are considered the minimum size required to launch a TBM and accommodate all the equipment required for the safe construction of the tunnel. Shafts of 30m diameter may be required to accommodate multiple hydraulic drop structures or for use as double drive shafts.

3.5.16 The intermediate shafts and reception shafts for the main tunnel are assumed to have an internal diameter of between 15m and 25m.

3.5.17 The internal diameter of CSO shafts ranges from 6m to 24m to suit the hydraulic requirements, although at some locations it may be advantageous to connect the CSO connection culvert directly to a main tunnel shaft.

Tunnelling and shaft construction methods Tunnelling construction methods

3.5.18 In order to construct the project within the required timeframe (paragraph 4.3.33), sections of the tunnel would need to be built concurrently. In addition, management of construction risk and the suitability of TBM types for the varying ground conditions along the route would also affect the determination of the number of TBMs to be used.

3.5.19 The geology and hydrogeology along each tunnel alignment influence the selection of the TBM type. Full-face TBMs would be required to support the ground during tunnelling in order to prevent excess excavation and groundwater inflow, and to minimise ground movement. Full-face TBMs are designed to incorporate a pressure bulkhead that separates the face – that is the unexcavated ground – from the completed segmentally-lined tunnel.

3.5.20 Full-face TBMs can be either earth pressure balance machines (EPB TBM) or slurry TBMs. Convertible TBMs, which have been used in other projects, can operate as either EPB or slurry TBMs; however, this is a necessary compromise that results in the need for additional plant and equipment. Convertible TBMs introduce additional risks and impact on the programme because there is a need to allow for changes to the operational method. They also perform sub-optimally in both modes. For the purposes of this report, it has been assumed that specific machines would be used according to the predicted ground conditions. It is assumed that EPB-type TBMs would be used for the tunnel drives through London



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Clay and the Lambeth Group west of Tower Bridge and a slurry-type TBM for the eastern drives through Chalk, as described in paragraph 3.4.15. Shaft construction methods

3.5.21 The geology, hydrogeology, depth and size of shafts would influence the method of construction. Various methods can be used, including: a. precast concrete segmental-lined caisson or underpinned construction b. sprayed concrete lining c. reinforced concrete sunk caisson d. secant piled wall e. diaphragm wall.

3.5.22 The construction of shafts in the London Clay is likely to be by conventional methods, with segmental lining either underpinned or sunk as a caisson. Sprayed concrete linings may also be used in conjunction with sheet piles for support of any groundwater-bearing superficial deposits.

3.5.23 Where the shafts are very deep and constructed through mixed ground conditions under high groundwater pressures, diaphragm wall construction is the most likely method of construction due to greater vertical accuracy. A secant piled wall method could also be used. In general, the diaphragm wall type of shaft construction requires a larger working area than other methods. A diaphragm wall shaft is a reinforced concrete lined shaft that comprises individually installed, abutting vertical concrete wall panels, which are constructed in the ground using specialist plant prior to the excavation of the ground within the centre of the shaft. Ground treatment and control of groundwater

3.5.24 For all methods of shaft construction, groundwater would need to be controlled to enable safe excavation and sinking of the shaft and to construct the base slab.

3.5.25 In some locations, ground treatment may be required to improve the natural state of the ground in advance of shaft construction or tunnelling. The term ‘ground treatment’ covers a variety of techniques to strengthen or stabilise the ground, including: a. injection of chemical or cementitious grouts (depending on the ground

encountered) to form blocks that can be excavated without collapsing b. ground freezing, where injection pipes circulate brine or liquid nitrogen

to freeze the groundwater and produce a stable block that can be excavated, but this is costly and takes a long time to implement.

c. compressed air, where the air pressure at the face of the tunnel is increased using air locks and compressors to resist the inflow of groundwater and maintain face stability. Over the years this technique has been replaced by closed-face tunnelling machines due to severe health and safety implications such as bone necrosis. The 8.8m-high face of the main tunnel and the potentially high compressed air pressures required to resist groundwater pressures (5.5bar) make it



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unlikely to be appropriate except for TBM face interventions. The 7.2m internal diameter main tunnel has an approximate external diameter of 8.8m, based on a 350mm primary lining thickness, a 300mm secondary lining thickness, and an assumed 150mm overcut.

d. de-watering to control the inflow of groundwater into shafts and tunnel excavations to ensure excavation stability. This can take the form of either regional (widespread) or localised de-watering methods, depending on the purpose and the extent of the pressure reduction required. These methods include deep borehole wells or localised drains, well points and injector wells.

Main tunnel site requirements Main tunnel sites

3.5.26 Three types of main tunnel site may be needed to construct the main tunnel: drive sites, reception sites and intermediate sites.

3.5.27 The main tunnel would be driven from main tunnel drive shafts, which would be equipped to enable the efficient excavation and construction of the tunnel.

3.5.28 Reception shafts would be used to remove the TBM from the tunnel at the end of a drive. Where a site is a sufficient size, a shaft could be used for both drive and reception purposes.

3.5.29 Intermediate shafts could be used to gain access to the main tunnel bore during construction, either to inspect and/or maintain the TBM or to provide access for secondary lining construction (should a secondary lining be required). Location of sites

3.5.30 The required number and spacing of sites for tunnel construction would be subject to the following considerations: a. the project construction period b. the TBM types, which must be appropriate to the predicted geological

conditions c. the risk of TBM breakdowns/servicing requirements and their severity

and frequency, which increase with the length of the drive d. the emergency egress for the construction workforce, which would

become more difficult the longer the length of the drive. 3.5.31 The number of TBMs, and hence the number of associated drive sites,

would depend on balancing the appropriate type of TBM for the ground conditions, the available main drive site locations , geology, programme, environment, amenity, health and safety, risk, cost, and procurement considerations.

3.5.32 Where possible, CSO connection tunnels would be constructed from main tunnel sites in order to reduce the space required at the CSO sites. Where CSO connection tunnels are driven from main tunnel sites, the CSO sites



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would comprise smaller reception sites. Excavated material from the CSO connection tunnels could also be handled at the main tunnel sites. Main tunnel site requirements

3.5.33 The Site selection background technical paper (Summer 2011) provides information on construction activities at main tunnel sites and their size requirements. The sizes are summarised as follows: a. main tunnel drive sites from which slurry TBMs would be driven

require approximately 20,000m2, whereas sites that drive EPB TBMs would require approximately 18,000m2. If site space is constrained, it may be possible for an EPB TBM to be driven from a 15,000m2 site; however, this may reduce the efficiency of tunnel operations and increase the risk of delays.

b. main tunnel reception or intermediate sites would range from 5,000m2 for sites with shafts constructed in the London Clay to 7,500m2, if deep diaphragm walling is proposed.

3.5.34 The construction activities that follow tunnel excavation would be less onerous with respect to site spatial requirements. Activities would include secondary tunnel lining (if required), shaft lining, buildings and surface works, and mechanical and electrical fit-out works.

Construction logistics 3.5.35 For the purposes of this Engineering options report – Abbey Mills route

(Spring 2012), the following logistical needs have been considered: a. the ability to provide efficient site layouts b. logistics hubs c. critical services (power) d. transport of materials and equipment e. main tunnel segment fabrication and supply. Site layouts for logistics

3.5.36 The layout of individual sites for logistics purposes would depend on the specific site use and local constraints. The Site selection background technical paper (Summer 2011) indicates illustrative layouts for different types of site. Logistics hubs

3.5.37 The supply and servicing of the smaller CSO sites could be carried out as satellites to the main tunnel sites. Main tunnel sites might therefore require an allowance for a logistics hub area for facilities to service the satellite sites. This has not been taken into account at this stage of the project and would likely be the contractor’s responsibility. Critical services: power

3.5.38 The temporary power supply requirements for construction sites typically varies from 1.25MVA to 3.5MVA for the smaller CSO sites, and up to



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12.5MVA to 17.5MVA for large main tunnel drive sites that serve a single TBM and 25MVA for a double drive site.

3.5.39 The number and potential spacing of sites for main tunnel drives is such that, for the majority of areas, it is unlikely that current capacity would be sufficient or available from existing UK Power Networks when construction commences. Therefore, power supply improvement works would be required at main tunnel drive sites and should be planned to accommodate new substation installations.

3.5.40 Discussions with UK Power Networks have established that it would be prudent to plan for the early procurement of power supplies for main tunnel drive sites to ensure that sufficient supply would be available for the TBMs in order to meet the project programme. Transport of materials and equipment

3.5.41 Construction of the shafts and tunnel works would require a wide variety of materials and equipment to be transported to and from the working sites.

3.5.42 Excavated material from the main tunnel would need to be taken away from the drive sites and a variety of materials delivered, in particular the concrete segments for the main tunnel lining. Other logistical activities would include workforce arrival/departure, equipment deliveries/return, consumables and, for drive sites, delivery of the large TBM components.

3.5.43 Due to the large volume of materials to be transported, the objective is to use the river to transport main tunnel excavated material by barge and to enable the contractor to move other materials by river where practicable and cost-effective.

3.5.44 The practicality of rail freight transportation depends on the proximity of main tunnel sites to suitable rail sidings and the local network’s capacity for freight movements.

3.5.45 It is anticipated that some deliveries would also need to be transported by road even where barge and/or rail transport facilities are available. Any necessary highway routes would be identified as part of project development. Major deliveries/removals would be subject to specific movement restrictions and conditions imposed by police and traffic authorities. Main tunnel segment fabrication and supply

3.5.46 The supply of tunnel lining segments to individual drive site locations would depend on the final site location and the location of the fabrication facility or facilities. This has not been taken into account at this stage of the project and it would be the contractor’s responsibility to fabricate and supply segments.

Handling and disposal of excavated material Material type and handling

3.5.47 The main types of excavated material would be London Clay, Lambeth Group, Thanet Sand Formation and Chalk.



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3.5.48 The type of material and choice of TBM would dictate the material handling and treatment requirements. The consistency of the excavated material would vary from relatively firm London Clay paste to Chalk slurry.

3.5.49 For site planning purposes, allowance has been made for onsite storage of excavated material for five days’ production. This would allow for resolution of issues relating to maintenance, plant breakdown and barge operations on the River Thames. Where there are site space constraints but good transport links, it may be possible to reduce the allowance to three days’ storage at the risk of delays should this prove insufficient. Quantities and programme requirements

3.5.50 The total quantity of excavated material for all tunnels and shafts is anticipated to be in the region of 1.7million m3 (in situ quantity). This would vary, depending on the tunnel alignment and connections.

3.5.51 The in situ volume of (unbulked) excavated material arising per drive at main tunnel drive sites would be approximately 300,000m3 to 500,000m3, assuming a tunnel length of between 5km to 8km.

3.5.52 Where two drives are carried out from the same site location, the required storage capacity would increase if the drives are to be carried out simultaneously.

3.5.53 Tunnelling advance rates would dictate the requirements for material removal. For preliminary planning purposes, a rate of approximately 1,000m3 to 2,000m3 is assumed per day from a site, depending on TBM type and ground conditions. Marine transport

3.5.54 The feasibility and use of marine transport for the removal of excavated material from potential main tunnel drive sites along the river is dependent on location.

3.5.55 Operations in the upper reaches of the River Thames beyond Hammersmith Bridge are considered impractical due to restrictions of bridge height, tidal range, and the width of the navigable channel. These factors would impose constraints on barge movements that would substantially reduce the quantity of material and rate of removal, making the viability of exclusive marine transport in these areas unacceptable.

3.5.56 Operations between Putney Bridge and Hammersmith Bridge are considered challenging, especially when servicing peak tunnelling rates. Sites along this length of the River Thames could be accessed and serviced, however it would require careful planning to mitigate the problems associated with navigational constraints.

3.5.57 Downstream of Putney Bridge there are fewer navigational constraints and therefore it would be possible to reduce the number of barge movements by using larger barges on the lower reaches of the River Thames to the east. Hence, only 350t barges could be used around Putney Bridge, 1,000t barges in the vicinity of Battersea Power Station, and 1,500t barges or larger downstream of Tower Bridge.



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3.5.58 The Abbey Mills Pumping Station site is located on the River Lee, adjacent to the Three Mills Lock. At this location, the river is tidal and only navigable for about four hours on each tide. Downstream of the site, the river is narrow and constrained by physical features, including low bridges. Although not impossible, using the river to transport the materials required to service a main tunnel drive would introduce cost and programme risks that would need to be carefully investigated before taking the final decision to use a site to drive the main tunnel. For the purposes of this options report, a drive from Abbey Mills is included as a feasible option to be evaluated against other options during subsequent stages of site selection. In-river facilities

3.5.59 Jetty/wharf structures and their location with respect to the navigational channel, together with associated dredging of the river for access purposes, would be site specific. Each main tunnel drive site with no substantial jetty or deep water wharf facilities would likely require a bespoke solution with specific consents from the Port of London Authority and the EA.

3.5.60 The above issues in respect of in-river facilities are more onerous on the upper reaches of the river. Consequently, upstream of Hammersmith Bridge – and to a lesser extent upstream of Putney Bridge – the scale of facilities required for barges would likely impinge on the river and river users, in such a way that would challenge feasibility and create risks to other river users.

3.5.61 Some risks to in-river facilities and barge movements relate to other river users and depend on the need to obtain a marine risk assessment for operations. It is noted that in the upper reaches of the river beyond Putney Bridge the presence of recreational users, such as rowers and small boats, presents a significant hazard and risk to be considered when evaluating sites. Disposal of material

3.5.62 The methods of treatment, transport and disposal of excavated material are dependent on the nature and consistency of the material and the requirements for final disposal.

3.5.63 The overall policy is to favour marine transport for main tunnel excavated material along the River Thames, where practicable and cost-effective.

3.5.64 Details of potential disposal sites are not discussed or considered in this report. This will be covered by the project’s ‘waste management strategy’, as part of the Environmental Impact Assessment.

CSO connections to the main tunnel 3.5.65 Where the CSO connection tunnels would connect directly to the 7.2m

internal diameter main tunnel, it is assumed that the internal diameter of the connection tunnel would be no greater than 4.5m. The junctions would be axis-to-axis and have a horizontal angle to the main tunnel of approximately 70 degrees, where practical. Where the internal diameter of the main tunnel is smaller than 7.2m, the connection tunnel diameter



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would need to be of an appropriate size. The limitation on connection tunnel diameter is due to constructability and the design requirement to achieve a stable structural opening.

3.5.66 The CSO connections to the main tunnel are grouped into five generic options/types, which are outlined in greater detail in Section 5.1.

Connection to the Lee Tunnel 3.5.67 The main tunnel would connect to the Lee Tunnel at Abbey Mills PS. The

proposed arrangement is for the main tunnel to connect to the Lee Tunnel ‘Shaft F’ (the proposed Lee Tunnel shaft located at Abbey Mills PS). The connection would need to provide a smooth hydraulic confluence to combine the flows from both the Abbey Mills CSO and the main tunnel. The design of the connection would need to minimise disruption to the operation of the Lee Tunnel.

Impact on third-party infrastructure 3.5.68 The nature of the operations involved in the construction of the main

tunnel and associated shafts has the potential to cause ground movements that could affect existing third-party infrastructure and buildings. The horizontal and vertical alignment of the main tunnel shaft locations and construction methodologies would be selected to avoid or minimise, as far as reasonably practical, the impact of ground movement on third-party infrastructure.

3.5.69 Searches of historical and other records have revealed groundwater abstraction wells located within the alignment corridor, some of which are operational. The tunnel alignment would avoid any adverse effect on these wells wherever reasonably possible.

3.5.70 In addition to road and underground rail transport tunnels, searches have revealed a number of existing deep-level service tunnels, including National Grid’s Richmond to Fulham high pressure pipeline tunnel and a number of BT Openreach tunnels. The planned National Grid ‘Wimbledon to Kensal Green’ tunnel is also noted, along with the proposed UK Power Networks New Cross to Wellclose Square cable tunnel. The alignment of the main tunnel and connection tunnels would avoid these assets with acceptable clearances.

3.5.71 Liaison with third parties has commenced with the objective of obtaining ‘Approval in Principle’ agreements to cross major assets where possible. This includes an assessment of all significant assets, development of preliminary instrumentation and monitoring plans, and identification of mitigation works where necessary. The scope includes tunnels, bridges, river walls, utilities and existing buildings.

3.6 CSO engineering and construction requirements General considerations

3.6.1 The design requirements for CSOs are outlined in Section 3.3 together with a list of the controls required for all 34 CSOs. Current findings indicate that 18 CSOs require interception, including three connections to the



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existing northern Low Level Sewer No.1. The remaining 16 CSOs could be controlled indirectly (see Table 3.1).

3.6.2 The CSO interceptions identified comprise a combination of direct gravity overflows and pumping stations. In each case, the location of the CSO interception works would be constrained by the layout of the existing sewer system.

3.6.3 In general, interception of gravity CSOs would be downstream of the last incoming connection to the overflow before the overflow sewer reaches the river in order to ensure that the CSO interception would not be bypassed during a storm event.

3.6.4 In terms of intercepting flows from pumping stations, there are advantages and disadvantages associated with both pre- and post-pumping interception. For example, intercepting flows pre-pumping allows for direct gravity interception without reliance on the pumps, which would create energy savings, whereas post-pumping interception allows the pumps to be used regularly and reduces the need for special maintenance facilities. If the pumps are not used regularly, maintenance procedures are required periodically to start pumps manually to ensure that they do not seize up. In practice, the criterion that governs whether pumping station flows are intercepted pre- or post-pumping is likely to be the availability of suitable CSO sites.

CSO interception: Design and construction 3.6.5 The CSO interceptions typically consist of the following elements:

a. interception chamber b. connection culvert c. drop shaft d. connection tunnel.

3.6.6 Details of each of these elements are outlined below and illustrated in Figure 3.2. CSO interception chambers

3.6.7 The CSO interception chamber would typically be a box-shaped structure positioned on the line of the existing sewer pipe. The purpose of this structure is to intercept the CSO flow and direct it into the connection culvert that leads to the drop structure.

3.6.8 The size of the interception chamber would be determined to suit the existing sewer and to accommodate the maximum flow requirements for interception. This would be achieved by means of a combination of calculations and physical modelling.

3.6.9 The depth of the interception chamber would be determined by the depth of the existing sewer.

3.6.10 It is envisaged that the interception chambers would be constructed as a reinforced concrete structure. However, the construction methodology for the chamber would depend on depth, ground conditions and other site-



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specific criteria. In general, sheet piling may be used to carry out the excavation in order to construct the chamber. Where the depth of the chamber precludes the use of sheet piling, an alternative method such as secant piling may be required.

3.6.11 The CSO overflow facility would be retained permanently for use as an overflow for the system. The overflow would also need to be maintained during the construction of the interception works in order to construct the interception chamber and maintain the functionality of the existing sewerage system during storm events for the duration of the construction period prior to commissioning the project.

3.6.12 The overflow to the river would be protected by double isolation in the form of two lines of flap gates. The flap gates would either utilise the existing flap gate arrangement (where acceptable) or, in some cases, a new structure and flap gate arrangement.

3.6.13 The interception chamber would also be protected against reverse surcharge flows from the drop shaft by means of two lines of flap gates located on the line of the proposed connection culvert. An actuated motorised penstock would also be positioned within the interception chamber at the junction with the connection culvert. This penstock would remain open during normal operative procedures, but would be closed to prevent diversion of flows through the connection culvert during tunnel maintenance activities.

3.6.14 A control kiosk would be required at each CSO interception site to operate the motorised penstock. This kiosk might also be used to accommodate other control and monitoring equipment.

3.6.15 An opening would be required in the roof of the interception chamber to facilitate maintenance access and allow for repair or replacement of the flap gates and penstock in the future. These openings would be fitted with suitable lockable covers. It is envisaged that the roof of the chamber would be at or below ground level. The covers to the openings would be positioned at ground level. CSO connection culverts

3.6.16 The CSO connection culvert would join the interception chamber to the drop shaft. The intention is to minimise the length of the CSO connection culvert by positioning the chamber and shaft as close together as possible, although this would depend on the individual constraints at each site.

3.6.17 The depth of the connection culvert would typically be determined by the depth of the existing sewer, which in turn would set the depth of the interception chamber. In some cases, it might be necessary to increase the depth of the connection culvert to minimise the impact on third-party assets, particularly where the culvert needs to pass under existing structures or utilities.

3.6.18 The connection culvert would be sized to accommodate the required controlled or maximum design flow rate.

3.6.19 The means of construction of each CSO connection culvert would be determined by the constraints at each site. Typical means of construction



33

might include open cut supported by sheet piling or an open cut trench support system, micro-tunnelling (utilising precast concrete pipe units), or sprayed concrete lining tunnelling connections. Therefore, the cross section of the connection culvert could be either circular or box-shaped and could comprise precast concrete pipes, precast concrete culvert units, or sprayed or in situ concrete.

3.6.20 A series of access manholes might also be required along the length of the culvert to facilitate the installation, removal, inspection and maintenance of the flap gates and penstocks.

3.6.21 For foreshore interception of CSOs, the interception chamber might be accommodated within the top of the drop shaft. No connection culvert would be required. CSO drop shafts

3.6.22 The purpose of the drop shaft is to drop the intercepted flows from the CSO to the level of the main tunnel or, in some cases, to the level of the connection tunnel, with an acceptable amount of air entrainment. Three forms of mechanism have been considered to drop the flows within the drop shaft, which are summarised as follows:

3.6.23 Straight drop: Due to energy dissipation, the use of a straight drop is only considered appropriate where the drop is less than 10m in height. The direct drop approach would maintain the flow within the pipe rather than allowing it to become a ‘waterfall’. For the majority of CSOs, the drop is greater than 10m and therefore a straight drop would not be used.

3.6.24 Cascade drop: Cascade platforms are used within shafts to dissipate energy for drops greater than 10m. The cascade would typically include alternating platforms at intervals of approximately 3m to 6m over the total depth of the shaft, which dissipates the energy in stages as the flows drop to the required level. Due to the regular inspection and maintenance regime required for cascade-type drops and the associated health and safety issues, cascade type drop shafts are not preferred.

3.6.25 Vortex drop: Vortex drop tubes can be used for drops greater than 10m. In order to generate the vortex at the top of the drop tube, vortex tubes are envisaged to be between 0.9m and 3m in diameter. A vortex drop is a system that accelerates and spins the flow so that it adheres to the wall of the tube, which is a proven and robust means of transferring flows from a shallow structure to a deep tunnel.

3.6.26 Drop shafts would be sized to accommodate maximum flows, having regard to the mechanism used to drop the flow to tunnel level. Connection tunnels

3.6.27 Connection tunnels would take flows either between two drop shafts or from one drop shaft to the main tunnel/main tunnel shaft.

3.6.28 Details of the types and methods of connecting CSOs to the main tunnel are outlined in Sections 4.3 and 5.1.



34

Air management 3.6.29 When the tunnel system fills with CSO discharges the air would be

displaced and, when the flow is removed from the system, the air would need to return. When the tunnel system is empty, the design includes a means of refreshing the air within the system. Therefore, the interaction between combined sewage inflow and management of air requirements needs to be considered and addressed.

3.6.30 The air management system would involve a combination of air extraction and intake structures as well as buildings to house air treatment equipment. The size and configuration of the structures would depend primarily on how air moves through the system and the amount of air to be moved.

Construction sites and logistics Site requirements

3.6.31 CSO site requirements would depend on the size of the connection tunnels; diameter, depth, and type of drop shaft; space requirements for construction activities; access constraints; and whether the drop shaft is to be used as a drive or reception shaft for a connection tunnel. Considerations for in-river sites

3.6.32 In-river (foreshore) sites are under consideration at a number of locations. In general, these locations are not the favoured engineering solution due to the added complications of working in the river and access to sites. Nevertheless, in certain areas, the complexity of the connection to the main tunnel and availability of suitable sites means that such sites are considered the only feasible sites. Transport of materials and equipment

3.6.33 Construction of the CSO works would require a wide variety of materials and equipment to be transported to and from the working sites. These smaller sites could also be managed as satellites to main tunnel drive site locations, which would minimise the need for offices, stores, and other site facilities.

3.6.34 For the purposes of this report, it is assumed that all transport to and from CSO sites would be by road. Power supply and site services

3.6.35 The temporary service requirements for CSO sites would be less demanding than those for main tunnel drive sites.

Third-party infrastructure impact 3.6.36 The works at CSO sites would have the potential to affect third-party

infrastructure and buildings, specifically near-surface services and the river walls that form the River Thames flood defences. Near-surface services would be present at all sites, but the complexity of the existing layouts and the possibility of diversionary routes would vary. Construction works would be designed to avoid or minimise potential impacts on third-party infrastructure and buildings as far as practicable.


i

Thames Tunnel


List of contents

Page number

1 Executive summary ......................................................................................... 1

2 Introduction ...................................................................................................... 3

2.1 Background ............................................................................................. 3

2.2 Purpose of this report .............................................................................. 4

2.3 Engineering design development ............................................................ 5

3 System design and engineering requirements .............................................. 7

3.1 System design and engineering assumptions ......................................... 7

3.2 Health and safety considerations ............................................................. 7

3.3 System requirements ............................................................................... 7

3.4 Engineering geology .............................................................................. 15

3.5 Tunnel engineering and construction requirements ............................... 20

3.6 CSO engineering and construction requirements .................................. 30

4 Main tunnel drive options .............................................................................. 35

4.1 Introduction ............................................................................................ 35

4.2 Main tunnel engineering: Options preparation ....................................... 35

4.3 Main tunnel engineering: Options assessment ...................................... 49

5 Connection tunnel drive options .................................................................. 57

5.1 CSO connection options ........................................................................ 57

5.2 Connection tunnel: Drive options ........................................................... 63

6 Conclusions and recommendations ............................................................ 69

7 Next steps ....................................................................................................... 71

The following can be found in the accompanying document Engineering options report - Appendices - Abbey Mills route (110-RG-PNC-000000-000827): Appendix A – Assumptions register Appendix B – Drawings Appendix C – Time chainage Appendix D – Geology

4 Main tunnel drive options


36

52 main tunnel sites and 71 CSO sites on the shortlist for phase one consultation. Main tunnel sites could be used either individually or combined with an adjoining site to provide the required site area.

Main tunnel site types 4.2.7 The number of locations from which the individual drives could be

launched and received would vary according to the direction in which the drives would be constructed. There are potential benefits from reducing the number of drive sites by selecting double drive sites where two TBMs are driven in opposite directions, which makes site servicing requirements and logistics more efficient. However, additional space would be required.

4.2.8 Figure 4.1 summarises the possible main tunnel site types that could be used to establish feasible drive options.

Figure 4.1 Main tunnel site types

Single main tunnel drive site- main tunnel driven in one direction- main tunnel received from another direction

Double main tunnel drive site- main tunnel driven in two directions sequentially

Double main tunnel drive site- main tunnel driven in two directions concurrently

Main tunnel reception site- main tunnel received from one direction

Main tunnel reception site- main tunnel received from two directions

Main tunnel intermediate site- main tunnel drive through

tunnel

Note: any of these main tunnel site scenarios could include the drive or reception of CSO connection tunnels

Intermediate/reception site setuptunnel drive direction

Single main tunnel drive site- main tunnel driven in one direction

r

d - r

d + d

r - r

i

d - d

dri intermediate

receptiondrive

drive site setup

shaft

d

It may be possible to use one shaft instead of two



37

Site zones 4.2.9 In order to manage the total number of combinations of main tunnel drive

site options, the shortlisted sites were grouped into a limited number of main tunnel site zones. This was based on the sites’ geographical proximity. Figure 4.2 illustrates the zones for all three tunnel routes.

Figure 4.2 Main tunnel site zones for all three routes

4.2.10 As Zones S8, S9 and S10 are only associated with the River Thames

route and Rotherhithe route, they are not considered further in this report. Figure 4.3 illustrates the zones associated with the Abbey Mills route. Figure 4.3 Main tunnel site zones for the Abbey Mills route

4.2.11 Table 4.1 identifies which zone each of the shortlisted main tunnel sites

belongs to for the Abbey Mills route (ie, zones S0 to S7 and S11). These are illustrated in drawings in Appendix B of the Engineering options report – Abbey Mills route – Appendices (Spring 2012).

S0 – Acton

S1 – Hammersmith

S2 – Barn Elms

S3 – Wandsworth Bridge

S4 – Lots Road

S5 – Battersea

S6 – Shad

S7 – Limehouse

S11 – Abbey Mills

S10 – Beckton

S9 – Charlton

S8 – Deptford

S0 – Acton

S1 – Hammersmith

S2 – Barn Elms

S3 – Wandsworth Bridge

S4 – Lots Road

S5 – Battersea

S6 – Shad

S7 – Limehouse

S11 – Abbey Mills



38

4.2.12 The assessments of the available worksites within each specific zone are not considered in this report. The site specific factors are examined in the site suitability reports, which address the use of sites as temporary worksites and in terms of the final permanent works requirements.

4.2.13 Table 4.1 provides the potential usage of the shortlisted main tunnel sites. Table 4.1 Grouping of shortlisted main tunnel sites for the Abbey Mills route

post-phase two consultation Site zone Site ID Site name Local

authority Site usage

S0

S01EG Acton Storm Tanks

Ealing reception

S02EG Commercial units, Stanley Gardens

Ealing reception

S03EG Acton Park Industrial Estate

Ealing reception

S04EG Industrial units, Allied Way

Ealing reception

S1 No shortlisted sites

S2 S17RD Barn Elms Richmond double drive

single drive reception/intermediate

S3

S18WH Feathers Wharf Wandsworth reception/intermediate

S72HF Fulham Depot, next to Wandsworth Bridge

Hammersmith and Fulham

reception/intermediate

S87HF Carnwath Road Riverside

Hammersmith and Fulham


S4 No shortlisted sites

S5

S61WH Battersea Park Wandsworth double drive single drive reception/intermediate

S68WH Battersea Power Station

Wandsworth double drive with S92WH single drive reception/intermediate

S72WH Kirtling Street with Cringle Street

Wandsworth spilt double drive with S93WH

spilt single drive with S93WH split reception/intermediate

with S93WH reception/intermediate



39

NB: ‘Split sites’ refers to sites that are too small on their own but could be used in combination with another site/sites to form a suitable site.

Definition of drive options

4.2.14 The overall development of options and selection of sites includes consideration of the following:

a. main tunnel drive options: there are a number of drive options for which the number of TBMs, number of sites and length of drives vary. Main tunnel sites from which tunnels could be driven in one or two directions are differentiated

S86WH Post Office Wandsworth spilt double drive with S80WH

spilt single drive with S80WH reception/intermediate

S92WH Part of Battersea Power Station

Wandsworth double drive single drive reception/intermediate

S93WH Kirtling Street Wandsworth double drive single drive reception/intermediate

S94WH Post Office Way Wandsworth single drive spilt single drive with S80WH reception/intermediate

S95WH Depots, Ponton Road

Wandsworth double drive single drive reception/intermediate

S6

S54SK King’s Stairs Gardens

Southwark single drive reception/intermediate

S76SK Chambers Wharf Southwark single drive reception/intermediate

S7

S020T Shadwell Basin Tower Hamlets


S021T King Edward Memorial Park

Tower Hamlets


S024T/ S025T

Heckford Street sites

Tower Hamlets

split reception/split intermediate

S036T Limehouse Basin Tower Hamlets

reception/intermediate

S11 S84NM Abbey Mills

Pumping Station Newham single drive

reception



40

b. main tunnel site options: there are a number of sites could be used for each drive option where the space, tunnel alignment, and other factors vary

c. CSO connection options: the type of CSO connection would depend on flow, geology, proximity of the main tunnel or a main tunnel site, and a number of other factors

d. CSO site options: a number of CSO sites might be available for each CSO drop shaft, and the type of connection would vary according to a number of factors, including the proximity of the main tunnel or a main tunnel site.

4.2.15 In order to establish the range of drive options, each drive is considered between two zones, with a drive site in one zone and a reception site in the other. Combining different zones together yields a number of drive options. The basic constraints below are applied in order to establish the initial number of drive options:

a. drive lengths (maximum and minimum)

b. site type (potential as a double drive, single drive or intermediate/reception site).

4.2.16 For the purposes of this report, main tunnel drive options were determined in terms of zones, which each include a number of sites (see paragraph 4.2.9). The individual site options will be considered and assessed as part of the site selection process and discussed in the Section 48: Report on site selection process.

4.2.17 Other more unconventional drive options considered include use of convertible TBMs, docking TBMs underground, and TBM abandonment as a means of extending drive lengths or avoiding the need for a main tunnel site. However, these options were not taken forward in the selection of the tunnel drive strategy for a range of reasons as described in the following paragraphs.

4.2.18 One such option is to convert a TBM from EPB to slurry (or vice versa) mid-drive, as could be necessary at the eastern end of the proposed route (just east of Tower Bridge) when traversing the Chalk to Thanet Sand/Lambeth Group interface. However, there is no comparable precedent for full conversion of a large diameter, high pressure TBM from earth pressure balance mode with conveyor muck handling to slurry pressure balance with slurry pipe muck handling. Such a change, if feasible, would require major structural rebuilding more suited to the conditions of a fabrication factory than hazardous confined space conditions under the river with limited access and lifting facilities. Compromises in TBM design, including increased use of bolted connections, would be required to effect the conversion; however this would make the TBM inherently more flexible, affect efficiency, and threaten the TBM’s ability to cut through flint-bearing Chalk, especially given the longer total drive length. The excavated material handling and



41

disposal systems would also need to be changed. Furthermore, since the sections of tunnel in these conditions would be excavated sequentially rather than simultaneously and would require a period of downtime for TBM conversion, the programme would increase beyond the six-year total construction period for the project as set out in paragraph 4.3.34.

4.2.19 Another option is to drive two TBMs to meet at an underground ‘docking point’ where the internal mechanical equipment would be removed from the TBM leaving the shell in the ground. This has been done in Tokyo on a much smaller scale, and also in the Storebælt Tunnel in Denmark. However, the Storebælt Tunnel is under the sea, which precluded other lower-risk options. Stabilising the ground in order to dismantle the cutterheads involves significant health and safety risks and greater risk due to heavy lifting and flame-cutting underground without support from above ground or in a shaft.

4.2.20 Bearing in mind the large internal diameter of the main tunnel, the drive alternatives discussed above have a number of disadvantages including: a. the health and safety risks involved in constructing a cavern through

the body of the TBM within which to dismantle the cutterhead b. the difficulties associated with stabilising the ground to facilitate

construction of a ‘docking cavern’ in poor saturated ground using ground treatments such as freezing. This would likely involve using jack up barges in the River Thames to drill holes to pump liquid nitrogen or super cooled brine into the ground for a prolonged period in order to create a stable section of ground within which to excavate the cavern

c. the need to convert a TBM’s excavated material handling and processing facilities from screw and conveyor, for handling EPB TBM paste, to slurry pipes and liquid separation plant for a slurry TBM. There is no comparable precedent for this

d. the need to dismantle the innards of two TBMs using flame-cutting in hazardous, confined conditions. The risks cannot be over emphasised as the components can weigh up to 100 tonnes

e. the need for unusual heavy lifting operations underground in confined conditions.

4.2.21 The clear outcome from studying these alternatives was that they represent unacceptably high health and safety risks to workers and an unacceptable project risk.

4.2.22 The project has adopted a goal of zero accidents, zero harm and zero compromise. These alternatives are not compatible with these aspirations and the project requirements described in Section 3.2 and paragraph 3.5.1.

Drive constraint assumptions 4.2.23 The initial list of drive options was established using the following

considerations:



42

a. The construction period shall not exceed six years (see paragraph 4.3.33).

b. Initial assessments indicate that to keep to the six-year construction period programme constraint and to reduce programme risk, the maximum drive length should not exceed approximately 12km. However, for tunnels driven from deep diaphragm wall shafts, the maximum drive length is approximately 8km in order to compensate for the greater time required to construct this type of shaft. The disadvantages of longer drive lengths include greater TBM wear and the greater risk of major component failure. Some of the longest drives of comparable diameter in London are on the Channel Tunnel Rail Link (HS1) where the 7.5m drive from Stratford International Station to London West Portal (King’s Cross) wore out the TBM head and screw conveyor.

c. The minimum drive length is 3km as the set-up costs for an operation of this scale would be disproportionate to the tunnelling costs for lengths less than 3km.

d. Drive options are constrained by the type of site available in each zone (potential as a double drive, single drive or intermediate/reception site).

Derivation of the drive options 4.2.24 The main tunnel would be split into a number of drives each constructed

using a separate TBM. 4.2.25 Table 4.2 provides a matrix from which the initial possible drive options

have been established, starting with consideration of drive length and site type.

4.2.26 The table illustrates a matrix of possible drive scenarios (that is, which zones could be connected together), using the zones available for tunnel drive and tunnel reception. The matrix is colour-coded, with coloured squares denoting possible options for driving the tunnel from a zone that has an available drive site to a zone that has an available reception site. The lines on the matrix indicate which drive lengths are too short, too long or potentially acceptable. The matrix also indicates the approximate overall chainage drive lengths in metres (drive lengths are measured from the average chainage of sites within each zone).

Drive options: Comprehensive list of initial possible options

4.2.27 The information from the matrix in Table 4.2 has been used to identify the initial provisional main tunnel drive options, which are presented in Table 4.3.

4.2.28 Table 4.3 shows that, based solely on consideration of drive length and site type constraints, there are six drive options for the western zones (S0 Acton to S5 Battersea), which need to be matched to one of the six drive options for the eastern zones (S6 Shad, S7 Limehouse and S11 Abbey Mills) to create 36 different drive options.



43

Table 4.2 Drive options: Consideration of practical drive lengths

Zone

nam

e

Act

on

Bar

n E

lms

Wan

dsw

orth

B

ridge

Bat

ters

ea

Sha

d

Lim

ehou

se

Abb

ey M

ills

Zone number S0 S2 S3 S5 S6 S7 S11Chainage (m) 0 3,954 6,682 11,543 18,981 20,454 24,064

S0 3954 6682 11543 18981 20454 24064

S2 2728 7589 15027 16500 20110

S3 4860 12298 13772 17381

S5 7438 8912 12521

S6 1474 5083

S7 3609

No sites available in the zone S1 (Hammersmith) or zone S4 (Lots Road) S11

Keydrive length too shortdrive length too longdrive length potentially acceptable

Drive length acceptableDrive length potentially too long from a deep diaphragm wall shaftDrive length too long or too short

Potential to be a double or single drive or intermediate/reception sitePotential to be a single drive or intermediate/reception sitePotential to be an intermediate/reception site



44

Table 4.3 Initial provisional main tunnel drive options

Drive options: Further development 4.2.29 Further to the derivation of initial provisional drive options, a further, more

detailed review was carried out to determine what other factors affect or preclude specific options. Double drive site in Zone S2 Barn Elms

4.2.30 Zone S2 Barn Elms contains only one site, S17RD (Barn Elms), which has been identified as a possible drive site (refer to Table 4.1). Table 4.3 identifies one drive option using a double drive site in this zone (option W2). The suitability of S17RD as a double drive site has been reviewed, considering in particular the ability to transport double the quantity of excavated material by barge.

Act

on

Bar

n E

lms

Wan

dsw

orth

B

ridge

Sha

d

Lim

ehou

se

Abb

ey M

ills

S0 S2 S3 S6 S7 S11W1 r d-r - dW2 r d-d - rW3 r - d-r dW4 r - - dW5 r - i dW6 r i - dE1 d - r-r dE2 d - r-d rE3 d r-r - dE4 d r-d - rE5 r d-r - dE6 r - d-r d

No site required

Single Reception

Double Reception Intermediate Single Drive Double

Drive- r r-r i d d-d

Zone

Drive option

Drive and Reception

r-d

Bat

ters

ea

S5

Eas

tern

The site type for the Zone S5 (Battersea) depends on which eastern drive option is matched with which western drive option. There are no sites available in Zone S1 (Hammersmith) and Zone S4 (Lots Road).

Legend: The following nomenclature/legend is used in the table to define the types of site required in the defined zones. Where 'd' denotes drive site, 'r' denotes reception site and 'i' denotes intermediate site. The tunnel is driven from a ‘d’ drive location to a ‘r’ reception location and through an 'i' intermediate location.

Wes

tern



45

4.2.31 The available river depth and width, coupled with the maximum barge size able to service this site, makes transporting the quantity of excavated material required for a double drive site highly unlikely. There is a limited tidal window in which to load and move barges, and this may be insufficient to meet the predicted demands. The conclusion is that this double drive option should remain on the list of options and the concerns noted here will be taken into account when the multidisciplinary team compares the drive options to select the proposed drive option for Section 48 publicity. Long tunnel drives through different geological strata

4.2.32 Table 4.3 shows a number of initial provisional drive options, including driving a tunnel from Zone S5 Battersea to either Zone S6 Shad or S7 Limehouse. All of these drives would start in London Clay and traverse the Lambeth Group and Thanet Sand Formation into Chalk. Because the tunnel drops on a continuous gradient towards the east, longer drives would also be deeper and therefore subject to higher groundwater pressure.

4.2.33 As noted in Section 3.5, different types of tunnelling machines are preferred for different ground conditions. Since these drives would traverse mainly London Clay, the Lambeth Group and Thanet Sand Formation, an EPB TBM would most likely be used. However, while this type of TBM is most suited to London Clay and the Lambeth Group, which make up approximately 7.5km of the drives, it is less suitable for use in Chalk. For this reason, a specific risk assessment is necessary to determine the viability of longer drives from Zone S5 Battersea to the east, terminating in Chalk.

4.2.34 This risk assessment identified a number of consequences associated with driving an EPB TBM into Chalk, including: a. reduced tunnel advance rates: the assumed long average advance

rate for an EPB TBM in the Lambeth Group and Thanet Sand Formation is taken to be 90m/week. However, it is considered that the advance rate for this TBM in Chalk should be reduced to 50m/week, due to inefficient working and additional maintenance

b. increased health and safety hazards for work required to maintain the TBM

c. increased risk of mechanical TBM failure (seals, bearings and screw conveyor)

d. increased risk of wear on the cutterhead e. increased risk of excavated material transfer problems due to

groundwater content f. increased risk mitigation costs resulting from the factors above.

4.2.35 In order to reduce the risks associated with tunnelling across the change from the Lambeth Group and Thanet Sand Formation to Chalk, it is preferable to keep the final length of tunnel bored in Chalk at the end of a long EPB drive to a minimum. However, it is considered that for both drive



46

options from Zone S5 Battersea to Zone S7 Limehouse (E1 and E2) and both drive options from Zone S5 Battersea to Zone S6 Shad (E3 and E4), the distance in Chalk is not long enough to remove them from the list of feasible drive options.

4.2.36 Similar risks and assumptions apply to drive options that include driving a tunnel from either Zone S6 Shad or S7 Limehouse to Zone S5 Battersea (E5 and E6). Deep diaphragm wall shafts

4.2.37 Sites in Zone S5 Battersea, S6 Shad, S7 Limehouse and S11 Abbey Mills require deep diaphragm wall shafts due to the depth of the tunnel. The drive length for drives from these shafts is restricted to approximately 8km due to the longer duration of construction of this type of shaft and the need to keep to the six-year overall construction period programme constraint.

4.2.38 The drive length is potentially too long for the following drive options, which are over 8km in length (see Table 4.2): a. Zone S5 Battersea to Zone S0 Acton (ie, drive options W4, W5 and

W6) b. Zone S5 Battersea to Zone S7 Limehouse (ie, drive options E1 and

E2) c. Zone S7 Limehouse to Zone S5 Battersea (ie, drive option E6).

4.2.39 The drive lengths are potentially too long; however, drive options W4, W5, W6, E1, E2 and E6 will not be removed from the list of feasible options for drive length reasons alone. The 8km constraint is approximate; therefore further programme assessment will be undertaken (see Table 4.7). Access points

4.2.40 Main tunnel drive shafts and CSO drop shafts that are on-line (the main tunnel passes directly through the shaft bottom) would be the designated access points to the tunnel system. The spacing between these permanent access points should not exceed 9km.

4.2.41 The drive length for drive option W4 (Zone S5 Battersea to Zone S0 Acton) is over 9km; therefore an intermediate site needs to be considered. Although the W4 main tunnel drive length is too long without an intermediate site for access purposes, it will not be removed from the list of feasible options for that reason, in case a CSO drop shaft can instead be incorporated on-line to provide the required access point. Tunnel vertical alignment and gradient

4.2.42 The western drive options involve drives between Zone S5 Battersea and Zone S0 Acton. However, there is a vertical tunnel alignment constraint imposed by the London Ring Main and other existing tunnels in this section of tunnel; therefore the tunnel vertical alignment needs to change along the route. The change in tunnel vertical alignment can be accommodated at a shaft in either Zone S2 Barn Elms or Zone S3 Wandsworth Bridge.



47

4.2.43 Drive options W1 to W3 have drive/reception shafts in either Zone S2 Barn Elms or Zone S3 Wandsworth Bridge to accommodate the vertical alignment change.

4.2.44 Drive options W5 and W6 have an intermediate shaft in Zone S2 Barn Elms or Zone S3 Wandsworth Bridge to accommodate the vertical alignment change.

4.2.45 However, drive option W4 has no shafts in Zone S2 Barn Elms or Zone S3 Wandsworth Bridge to accommodate the vertical alignment change and therefore was removed from the list of feasible drive options.

Drive options: Interim list of options 4.2.46 Having reviewed the drive options from Table 4.3, an interim list of drive

options is presented below in Table 4.4. Table 4.4 Interim main tunnel drive options

4.2.47 Table 4.4 shows that the interim list of potentially feasible drive options

includes five drive options for the western zones (S0 Acton to S5 Battersea), one of which needs to be matched to one of six drive options for the eastern zones (S5 Battersea to S11 Abbey Mills) to create 30 different drive options. The full list of interim drive options is provided below in Table 4.5.

Act

on

Bar

n E

lms

Wan

dsw

orth

B

ridge

Sha

d

Lim

ehou

se

Abb

ey M

ills

S0 S2 S3 S6 S7 S11W1 r d-r - dW2 r d-d - rW3 r - d-r dW5 r - i dW6 r i - dE1 d - r-r dE2 d - r-d rE3 d r-r - dE4 d r-d - rE5 r d-r - dE6 r - d-r d

Wes

tern

Zone

Drive option

Bat

ters

ea

S5

Eas

tern

The site type for the Zone S5 (Battersea) depends on which eastern drive option is matched with which western drive option. There are no sites available in Zone S1 (Hammersmith) and Zone S4 (Lots Road).



48

Table 4.5 Interim list of main tunnel drive options

4.2.48 Table 4.5 lists the 30 potentially feasible drive options and indicates that: a. 18 options use four TBMs and 12 options use three TBMs b. Four options use four drive sites and one reception site; 14 options

use three drive sites and two reception sites; four options use three drive sites, one intermediate site and one reception site; and eight options use two drive sites, one intermediate site and two reception sites.

c. All options require a main tunnel reception site in Zone S0 Acton, ie, at one end of the main tunnel.

d. All options require a main tunnel site (drive or reception) in Zone S11 Abbey Mills, ie, at the other end of the main tunnel.

Act

on

Bar

n E

lms

Wan

dsw

orth

Brid

ge

Sha

d

Lim

ehou

se

Abb

ey M

ills

Drive option S0 S2 S3 S6 S7 S11W1/E1 r d-r - d d - r-r d 3 0 2 4W1/E2 r d-r - d d - r-d r 3 0 2 4W1/E3 r d-r - d d r-r - d 3 0 2 4W1/E4 r d-r - d d r-d - r 3 0 2 4W1/E5 r d-r - d r d-r - d 4 0 1 4W1/E6 r d-r - d r - d-r d 4 0 1 4W2/E1 r d-d - r d - r-r d 3 0 2 4W2/E2 r d-d - r d - r-d r 3 0 2 4W2/E3 r d-d - r d r-r - d 3 0 2 4W2/E4 r d-d - r d r-d - r 3 0 2 4W2/E5 r d-d - r r d-r - d 3 0 2 4W2/E6 r d-d - r r - d-r d 3 0 2 4W3/E1 r - d-r d d - r-r d 3 0 2 4W3/E2 r - d-r d d - r-d r 3 0 2 4W3/E3 r - d-r d d r-r - d 3 0 2 4W3/E4 r - d-r d d r-d - r 3 0 2 4W3/E5 r - d-r d r d-r - d 4 0 1 4W3/E6 r - d-r d r - d-r d 4 0 1 4W5/E1 r - i d d - r-r d 2 1 2 3W5/E2 r - i d d - r-d r 2 1 2 3W5/E3 r - i d d r-r - d 2 1 2 3W5/E4 r - i d d r-d - r 2 1 2 3W5/E5 r - i d r d-r - d 3 1 1 3W5/E6 r - i d r - d-r d 3 1 1 3W6/E1 r i - d d - r-r d 2 1 2 3W6/E2 r i - d d - r-d r 2 1 2 3W6/E3 r i - d d r-r - d 2 1 2 3W6/E4 r i - d d r-d - r 2 1 2 3W6/E5 r i - d r d-r - d 3 1 1 3W6/E6 r i - d r - d-r d 3 1 1 3

Zone

Num

ber o

f driv

e si

tes

Num

ber o

f rec

eptio

n si

tes

site

s

Num

ber o

f TB

Ms

Num

ber o

f in

term

edia

te s

ites

Bat

ters

ea

S5



49

e. All options require a main tunnel site in Zone S5 Battersea, which is approximately halfway along the main tunnel.

f. Not all drive options require a main tunnel site in Zone S2 Barn Elms and not all drive options require a main tunnel site in S3 Wandsworth Bridge. However, a main tunnel site is required in one of these two zones.

g. Not all drive options require a main tunnel site in Zone S6 Shad and not all drive options require a main tunnel site in S7 Limehouse. However, a main tunnel site is required in one of these two zones.

4.3 Main tunnel engineering: Options assessment 4.3.1 This section describes the engineering-related factors that affect the

desirability of the tunnel drive options. 4.3.2 All the options presented in Table 4.5 are considered potentially feasible in

engineering terms. The areas for engineering assessment are risk (comprising engineering and health and safety risks), programme, cost, transport and energy.

4.3.3 Other factors that are specific to each drive option, including planning, community, environment, and property, will also be compared in the next site selection process to determine which drive option is selected for the proposed scheme and presented in the Section 48: Report on site selection process.

Health and safety and engineering risk considerations 4.3.4 The following risk criteria are considered relevant for the comparison of

drive options. Most of the risk criteria can be considered in terms of health and safety risk and/or engineering construction risk. Health and safety issues: General

4.3.5 Overall health and safety risks were considered in relation to the overall extent of work and the total quantity of man hours required. Specific health and safety risks are considered along with other hazards and risks detailed below.

4.3.6 In general terms, the effort required and the risks associated with building the tunnel would be proportional to the length of the tunnel. The relative benefits or adverse effects are similarly proportional. The scale of differences was relevant when considering all three tunnel routes, but is not discussed further in this report, which only considers one route (the Abbey Mills route) for which all drive options have essentially the same tunnel length. Health and safety issues: Access

4.3.7 Access and egress from the main tunnel would be via main tunnel shafts and CSO drop shafts directly on the line of the tunnel. Paragraph 4.2.40 identifies which drive options are of concern in terms of access points. The distance between shafts would be minimised as far as practicable; however, for comparison purposes, the relative benefits or adverse effects from a long-term inspection and maintenance perspective would be



50

proportional to the number of access shafts provided. There are different numbers of sites associated with the Abbey Mills route depending on the drive options; therefore this is an issue for consideration. Geology

4.3.8 Flints and flint bands cause wear to TBM cutters and TBM cutterhead face protection coatings, which increases the likelihood and frequency of interventions at the excavation face in front of the TBM to replace worn components. Face interventions involve sending workers in front of the TBM cutterhead, often in compressed air or oxygen enriched air, and are considered to be hazardous operations. Although face interventions are essential and normal procedure for tunnelling, the number should be minimised in order to reduce the associated safety risk of entering the TBM cutterhead in proximity to unsupported ground, and potential delay. The likelihood and frequency of face interventions for each option is related to the tunnel length. The principle consideration is the drive length in flint-bearing Chalk formations as well as the type and design of the TBM. Designing the cutterhead to incorporate wear indicators and endoscope inspection and to allow rear replacement of discs reduces the need to carry out face interventions. Extending the drive length increases the risk of the need for major refurbishment of the cutterhead to replace worn armour plating that protects the body of the machine.

4.3.9 High groundwater pressures at the face might increase the programme risk arising from failure of TBM bearings, which occurs when ground is forced past the seals into the main bearings under pressure. It is also more complex to undertake routine inspection and maintenance interventions and might result in longer periods between inspections, which increases the risk of unexpected component failure. There are also increased health and safety hazards associated with face interventions. The risks to tunnelling are therefore proportional to the maximum groundwater pressures likely to be encountered and the length over which they would occur.

4.3.10 Tunnel face interventions and appropriate face control become more difficult where there are mixed geological conditions at the face; such conditions can vary over short distances. The level of risk is higher in Chalk where there is little or no cover below the interface with the Thanet Sand Formation because Chalk is less stable under these conditions.

4.3.11 The risk of delay due to disturbed ground conditions and sudden groundwater ingress increases at geological faults. The major geological structures identified by the site investigations are described in paragraph 3.4.8. The impacts are likely to be minimal for closed-face tunnelling, ie both EPB TBM and slurry TBM tunnelling methods. The level of risk for each drive option is related to the number of likely fault zones along each route.

4.3.12 This was a relevant factor when comparing the three tunnel routes but is not discussed further in this report, which only considers one route (the Abbey Mills route) as the geology is essentially the same across all the drive options.



51

Third-party assets 4.3.13 The excavation required for the project, including the deep shafts and

main tunnel, would result in ground movements that have the potential to affect adjacent properties and infrastructure. The number of assets potentially impacted is related to the length of the tunnel. The magnitude of the influence is related to the extent and depth of the excavation, ground conditions, the geometric relationship to the infrastructure, and the method of construction.

4.3.14 The level of risk to major infrastructure for each option, including bridges and tunnels, would depend on how many structures are within the tunnels’ range of ground movement influence.

4.3.15 The presence of unknown obstructions or future planning proposals along the tunnel route presents a risk to the delivery of the project. The level of risk is reduced where the tunnel follows the line of the river.

4.3.16 This was a relevant factor when considering the three tunnel routes, but is not discussed further in this report, which only considers the Abbey Mills route, which encounters essentially the same third-party assets for all drive options. Site requirements

4.3.17 The risks associated with drive sites may include carrying out works in proximity to major utility services or railways and completing associated development works such as temporary jetties or cofferdams. The level of risk is related to the number of worksites required.

4.3.18 Servicing the tunnel drive sites presents risks in terms of establishing transport links to and from sites to deliver construction materials and remove excavated material. Levels of risk would increase where there are no established connections to main roads or existing wharf facilities. Larger sites would offer more flexible worksite arrangements and therefore present lower risk.

4.3.19 The drive options for the Abbey Mills route require different numbers of drive sites. Tunnel alignment

4.3.20 Construction risks associated with tunnelling using a TBM are proportional to the total length of the tunnel. General tunnelling risks are associated with working with heavy machinery and handling heavy structural elements at depth in a confined environment.

4.3.21 This was a relevant factor when considering all three tunnel routes, but is not discussed further in this report, which only considers the Abbey Mills route as all the drive options are essentially the same length. TBM

4.3.22 The potential for unplanned interventions due to mechanical breakdowns or cutterhead/tool wear presents a health and safety and construction risk. This risk reduces with shorter drive lengths and can be mitigated more effectively where there are opportunities to provide ground treatment from



52

surface locations such as roads, canals or river courses, where there are no buildings or other significant structures.

4.3.23 There is a further risk of additional interventions where a tunnel drive passes from the Thanet Sand Formation into Chalk compared to tunnelling through the geological units above the Thanet Sand Formation. Tunnelling through Chalk, especially Chalk that contains a high percentage of flint boulders up to 800MPa strength, is likely to increase the frequency and duration of interventions for inspection and maintenance.

4.3.24 Mixed-face conditions might cause the TBM to run less efficiently, with more delays and possible breakdowns, which increases the risk of over-excavation due to balancing the different support requirements for firm ground overlaid with softer material, which results in increased ground movement. This level of risk would be higher when the tunnel drive follows the interface boundary between two geological strata (either clay/sand or sand/chalk interfaces).

4.3.25 The various drive options associated with the Abbey Mills route require different numbers of TBMs. Constructability

4.3.26 The risks associated with long tunnel drives are discussed in Section 4.2. It is most preferable to reduce the risks associated with tunnelling across the change from the Lambeth Group and Thanet Sand Formation to Chalk in order to keep the final length of tunnel bored in Chalk at the end of a long EPB TBM drive to a minimum. It is therefore considered that, based on engineering risk, options with drives from Zone S5 Battersea to Zone S7 Limehouse are not favoured and, where possible, should be avoided.

4.3.27 Failure of construction contractual arrangements is a project risk. Dividing the main tunnel works into packages of already proven physical and financial scale reduces the overall risk to the project.

4.3.28 There might be an opportunity for savings where double drive sites are used. Larger contracting organisations might be able to construct two drives from a single shaft and omit a shaft by sharing some worksite facilities. CSO connections

4.3.29 The health and safety and construction risks associated with CSO sites and interception structures are proportional to the number of drop shafts required for each option and the depth of the shafts. Some drop shafts need to be as deep as the main tunnel and it is desirable to minimise the number of such drop shafts.

4.3.30 Similarly, the health and safety and construction risks associated with the construction of the connection tunnels are related to the connection tunnel length for each option and the predicted ground conditions.

4.3.31 Furthermore, the health and safety and construction risks associated with the construction of connections to the main tunnel are proportional to the number of connections. It is inherently less risky, and therefore preferable, to make connections to main tunnel shafts rather than directly to the main



53

tunnel. This is because maintenance and inspection access to a connection point located in a shaft is more straightforward than a connection point located inside a tunnel. It is also more difficult to construct a connection directly into the tunnel. Moreover, connection works at a shaft would not interfere with the progress of the main tunnel construction. Options that require construction of a junction with large diameter open face excavations in deep, water-bearing ground would carry higher risk.

4.3.32 While the relative benefits or adverse effects of each tunnel route are not examined as part of this report, it is noted that each of the main tunnel routes would provide different storage volumes and different system performances (ie, volume and frequency of spills into the river). This was a relevant factor when considering all three tunnel routes, but is not discussed further in this report, which only considers the Abbey Mills route for which the CSO connections are essentially the same for all drive options.

Programme considerations 4.3.33 The overall project programme is based on a construction period of six

years, which includes local site mechanical and electrical testing and commissioning but does not include system-wide testing and commissioning. These construction programme activities follow on from the overall project design, planning and procurement activities.

4.3.34 A maximum six-year construction period has been assumed in order to construct the project in an efficient manner and to enable it to be completed as early as possible given the legal drivers for the project, as set out in the Needs Report. A six-year period would allow the TBMs to be matched to the geology in order to maximise tunnelling production rates. It would also ensure that drive lengths are reasonable (ie, the risk of interventions to repair the face of TBMs is not excessive) and that the size of the construction contracts is viable (ie, they can be financed and there are contractors in the market that are large enough to take on the contracts). Drive options that would extend construction beyond six years, require longer drives through variable geology, require larger contracts, and increase the risk of fines from the European Union for breaching the Urban Waste Water Treatment Directive will be avoided.

4.3.35 The main factors that would affect the duration of the construction programme include the following: a. Location of drive shafts: the time it takes to construct a shaft from

which to launch a TBM is critical to the duration of the programme. Therefore, deep shafts in more difficult ground conditions that require dewatering activities and diaphragm wall methods would add time to the programme, compared to shallower shafts in more favourable ground.

b. Length of drive: the duration of a drive is generally proportional to the length, although average drive rates would reduce for very short drives where the proportion of time taken to establish the full TBM back-up is longer. The geological conditions also affect the rate of tunnelling.



54

c. CSO connection works to main tunnel shafts: some CSO connections to drive shafts could only be constructed on completion of the main tunnel drive, which could affect the time required to complete the project. At main tunnel reception shafts, there would likely be more time to complete any CSO connections before the arrival of the TBM.

4.3.36 The programme assumptions regarding the essential construction activities used for the comparison of drive options are provided in Table 4.6.

Table 4.6 Programme assumptions for comparison of options

Zones Zones

S0 to S4 S5 to S11

Key Activity Comment

Mobilise shaft site 20 wks 26 wks Includes dewatering for sites in the east

Build and excavate shaft 20 wks 50 wks

Based on segment, SCL or caisson for zones S0 to S4 and diaphragm wall for zones S5 to S11

Base slab to shaft 4 wks 6 wks Based on permanent base slab of reinforced concrete

Tunnel eye 10 wks 10 wksBased on opening in segment shafts and internal collar arrangement for d'wall shafts

Tunnel worksite setup 2 wks 2 wks

Transform the site from shaft construction setup to tunnel construction setup

TBM installation 12 wks 15 wks Main body only. Excludes backup which goes in during the slow start

200m drive for TBM burial and backup installation

22 m/wk 22 m/wk 200m slow start based on no backshunt being provided

Main tunnel drive 100 m/wk 80 m/wk

Long average excludes 200m long TBM installation length. 90m/week for EPB TBM when in Lambeth Group/Thanet Sand. 50m/week for EPB TBM when in Chalk.

Tunnel strip out 4 wks 4 wks For removal of conveyor and for extraction of CSO TBMs if necessary

Main tunnel secondary lining 140 m/wk 140 m/wk Based on reinforced in situ lining

Shaft lining 5 wks 10 wks In situ concrete lining

Shaft internal structures 25 wks 30 wks Internal slabs and cover structures

Local M&E testing and commissioning

8 wks 8 wks Excludes project-wide M&E testing and commissioning

Duration/rate



55

4.3.37 Table 4.7 summarises the potential construction durations for each drive option in weeks, based on the assumptions set out in Table 4.6.

Table 4.7 Summary of construction durations for main tunnel drive options

4.3.38 Table 4.7 identifies the duration of the drive options presented in Table 4.5

and highlights the drive options that would take longer than six years (312 weeks) to construct. The longest options would take 356 weeks, which is significantly longer than the programme requirements and, for this reason, all 12 W5 and W6 drive options were removed from the list of feasible options. The options that exceed the six-year period by up to ten weeks were considered close enough to keep on the list of feasible options. For the remaining options, the difference in duration was small enough to conclude that programme risk is not a significant differentiating factor.

4.3.39 Time-chainage diagrams have been produced for five representative drive options (W1/E1, W1/E3, W2/E6, W3/E4 and W3/E5). The diagrams were only provided for five drive options as all the other drive options essentially have the same overall construction duration as one of those five. These diagrams provide more detail on the overall duration given in Table 4.7 (refer to Appendix C of the Engineering options report – Abbey Mills route – Appendices (Spring 2012)).

Cost considerations 4.3.40 The Engineering options report (Spring 2010) included a comparison of

relative costs using key quantities of work. It considered cost differences across the three different tunnel routes and across drive options with different numbers of TBMs. The costs proved very similar where the number of TBMs was the same.

4.3.41 This report is only concerned with the Abbey Mills route and therefore the relative cost comparison has only been applied to drive options that use three or four TBMs. The drive options that use only three TBMs would cost less than those with four TBMs due to the saving on the manufacture of one TBM.

Drive Option

Weeks Drive Option

Weeks Drive Option

WeeksW1/E1 321 W3/E1 321 W6/E1 356W1/E2 321 W3/E2 321 W6/E2 356W1/E3 294 W3/E3 286 W6/E3 330W1/E4 294 W3/E4 286 W6/E4 330W1/E5 284 W3/E5 284 W6/E5 330W1/E6 319 W3/E6 319 W6/E6 330W2/E1 321 W5/E1 356W2/E2 321 W5/E2 356W2/E3 286 W5/E3 330W2/E4 286 W5/E4 330W2/E5 284 W5/E5 330W2/E6 319 W5/E6 330

Drive options with durations over 312 weeks (6 years)



56

Transport considerations 4.3.42 Transport considerations are not discussed in this report, but are

examined on a site-by-site basis in the site suitability reports.

Energy considerations 4.3.43 Energy was a relevant factor when considering all three tunnel routes, but

is not discussed further in this report, which only considers the Abbey Mills route, as all the drive options have similar energy needs.

Drive options: Final list 4.3.44 Table 4.8 shows the final list of 18 feasible main tunnel drive options to be

taken forward to the next stage of the site selection process for multidisciplinary consideration.

Table 4.8 Final list of main tunnel drive options

Act

on

Bar

n E

lms

Wan

dsw

orth

Brid

ge

Sha

d

Lim

ehou

se

Abb

ey M

illsDrive option S0 S2 S3 S6 S7 S11

W1/E1 r d-r - d d - r-r d 3 0 2 4W1/E2 r d-r - d d - r-d r 3 0 2 4W1/E3 r d-r - d d r-r - d 3 0 2 4W1/E4 r d-r - d d r-d - r 3 0 2 4W1/E5 r d-r - d r d-r - d 4 0 1 4W1/E6 r d-r - d r - d-r d 4 0 1 4W2/E1 r d-d - r d - r-r d 3 0 2 4W2/E2 r d-d - r d - r-d r 3 0 2 4W2/E3 r d-d - r d r-r - d 3 0 2 4W2/E4 r d-d - r d r-d - r 3 0 2 4W2/E5 r d-d - r r d-r - d 3 0 2 4W2/E6 r d-d - r r - d-r d 3 0 2 4W3/E1 r - d-r d d - r-r d 3 0 2 4W3/E2 r - d-r d d - r-d r 3 0 2 4W3/E3 r - d-r d d r-r - d 3 0 2 4W3/E4 r - d-r d d r-d - r 3 0 2 4W3/E5 r - d-r d r d-r - d 4 0 1 4W3/E6 r - d-r d r - d-r d 4 0 1 4

Num

ber o

f driv

e si

tes

Num

ber o

f in

term

edia

te s

ites

Num

ber o

f rec

eptio

n si

tes

site

s

Num

ber o

f TB

Ms

S5

Bat

ters

ea

Zone

5 Connection tunnel drive options


57


5.1 CSO connection options 5.1.1 For the purposes of this report, five different connection types have been

identified for connecting the existing CSO sewers to the main tunnel, as follows: a. Type A: connection tunnel to main tunnel shaft connection b. Type B: connection tunnel to main tunnel connection c. Type C: two or more CSOs connected by connection tunnels prior to

connection to main tunnel or main tunnel shaft d. Type D: drop shaft adjacent to main tunnel (no connection tunnel) e. Type E: connection culvert to main tunnel shaft (or to drop shaft on

line of the main tunnel) connection (no connection tunnel).



58

Type A CSO connection 5.1.2 The Type A connection is illustrated schematically in Figure 5.1. This type

of connection would be used where a connection tunnel is required between a CSO interception point and a main tunnel shaft. The interception point would be on a site some distance from the main tunnel site where the two could not be connected by a connection culvert. An interception chamber would be built around the existing CSO sewer and connected to a drop shaft by a connection culvert. The drop shaft would then be connected to a main tunnel shaft by a connection tunnel.

5.1.3 In some cases, the connection tunnel might need to be driven from the CSO site, which has implications for CSO site selection because the site would have to be large enough to support the necessary tunnelling plant set-up. Where possible, the connection tunnel would be driven from the main tunnel site.

Figure 5.1 Type A CSO connection

Interception chamber

Connection culvert

Drop shaft

Connection Tunnel

Main Tunnel

Main Tunnel Shaft

Vortex/ direct drop

PLAN VIEW

SECTION VIEW



59

Type B CSO connection 5.1.4 The Type B connection is illustrated schematically in Figure 5.2. This type

of connection would be used where a connection tunnel is required between the CSO interception point and the main tunnel, and where the main tunnel is located in competent ground, such as London Clay, so that a direct tunnel-to-tunnel connection could be made. In other less favourable ground conditions, depending on the nature of the ground and groundwater, this method might require ground treatment. In deep, water bearing ground such as Chalk, it is preferable to avoid this type of connection. All four other connection types are easier to construct in poor ground conditions than Type B.

5.1.5 An interception chamber would be built around the existing CSO sewer and connected to a drop shaft by a connection culvert. The drop shaft would then be connected directly to the main tunnel by a connection tunnel.

5.1.6 In most cases, the connection tunnel would have to be driven from the CSO site, which has implications for CSO site selection as the site would have to be large enough to support the necessary tunnelling plant set-up.

Figure 5.2 Type B CSO connection

Connection culvert

Drop shaft

Connection Tunnel

Main Tunnel

SECTION VIEW

PLAN VIEW

Main Tunnel

Vortex/ direct drop




60

Type C CSO connection 5.1.7 The Type C connection is illustrated schematically in Figure 5.3. This type

of connection would be used where two or more CSOs are intercepted and brought together before they are connected to the main tunnel, either directly or at a main tunnel shaft.

5.1.8 An interception chamber would be built around the existing CSO sewer and connected to a drop shaft by a connection culvert. The drop shaft would then be connected to a second drop shaft by a connection tunnel and the second drop shaft would be connected to the main tunnel or a main tunnel shaft by a connection tunnel.

5.1.9 In some cases, the connection tunnel would need to be driven from one of the CSO sites, which has implications for CSO site selection as the site would need to be large enough to support the tunnelling plant set-up.

Figure 5.3 Type C CSO connection

Second CSO Connection

Connection culvert

Drop shaft Connection Tunnel

Main Tunnel

Connection Tunnel

Drop shaft

Vortex/ direct drop

Vortex/direct

drop

PLAN VIEW

SECTION VIEW

Either directly to main or a

main tunnel shaft




61

Type D CSO connection 5.1.10 The Type D connection is illustrated schematically in Figure 5.4. This type

of connection would be used where the drop shaft is located directly adjacent to the main tunnel.

5.1.11 An interception chamber would be built around the existing CSO sewer and connected to a drop shaft by a connection culvert. The connection between the drop shaft and the main tunnel could be via a single or multiple cell junction detail, depending on hydraulic flow requirements and ground conditions. This connection type is easier to construct in poor ground conditions than a Type B.

Figure 5.4 Type D CSO connection

Connection culvert

Drop shaft

Multiple/single connection junction

Main Tunnel

Vortex drop

PLAN VIEW

SECTION VIEW




62

Type E CSO connection 5.1.12 The Type E connection is illustrated schematically in Figure 5.5. This type

of connection would be used where the CSO interception point can be connected directly to a shaft located on the line of the main tunnel. An interception chamber would be built around the existing CSO sewer and connected to a shaft by a connection culvert. The shaft could be either a CSO drop shaft or a main tunnel shaft. If it is a drop shaft, it would be built before the main tunnel, which would be driven through the drop shaft. It would therefore need to be large enough to allow the main tunnel to pass through the bottom.

5.1.13 This type of connection is considered easier to build in poor ground conditions at depth. This arrangement provides an opportunity to inspect and possibly maintain the main tunnel TBM and, once the project is operational, a possible additional means of main tunnel access, ventilation and overflow (depending on the location).

Figure 5.5 Type E CSO connection

Connection culvert

Main Tunnel

Main Tunnel Shaft or CSO

Drop Shaft

Vortex Drop

PLAN VIEW

SECTION VIEW

Main Tunnel




63

5.2 Connection tunnel: Drive options 5.2.1 The main tunnel shortlisted sites have been grouped into zones. The CSO

connection type selected for individual CSOs is dependent on the proximity of the main tunnel and main tunnel sites to the CSO sites. For this reason, the selection of the appropriate connection type for most CSO sites is not considered in this report, but is discussed in the Section 48: Report on site selection process. However, the Type C CSO connection, where two or more CSOs are intercepted and brought together prior to connecting to the main tunnel, is discussed in this report because there may be more than one connection tunnel drive option and it may impact on the main tunnel drive options.

5.2.2 Engineering factors to be considered when selecting the CSO connection types for each CSO site include: a. main tunnel drive strategy and site selection b. hydraulic system preferences c. location of the CSO interception site and whether it could be

connected to a main tunnel shaft by a connection culvert d. distance between the CSO interception site and the main tunnel or

main tunnel shaft e. whether two or more CSOs could be connected before connecting to

the main tunnel f. local ground conditions – in poorer ground conditions, junctions would

be more difficult and tunnel-to-shaft connections (Types A, C, D and E) may be preferred over tunnel-to-tunnel connections (Type B)

g. potential for impacts on existing or planned infrastructure h. maximum flow rates – for larger flows, the connection tunnel may be

too big to connect directly to the main tunnel i. overall number and size of shafts required j. cost and programme.

Type C CSO connection options 5.2.3 There are two examples of Type C CSO connections associated with the

Abbey Mills route: a. the Frogmore connection tunnel: a connection tunnel that brings

together flows from the Frogmore Storm Relief – Bell Lane Creek CSO (CS07A) and Frogmore Storm Relief – Buckhold Road CSO (CS07B) before connecting to the main tunnel

b. the Greenwich connection tunnel: a connection tunnel that brings together flows from the Greenwich Pumping Station CSO (CS33X), Deptford Storm Relief CSO (CS32X) and Earl Pumping Station CSO (CS31X) before connecting to the main tunnel.



64

Frogmore connection tunnel 5.2.4 Table 5.1 below presents the list of Frogmore connection tunnel drive

options to be taken forward to the next stage of the site selection process for multidisciplinary consideration.

Table 5.1 Frogmore connection tunnel: Drive options

Frogmore SR - Buckhold Road

Frogmore SR - Bell Lane Creek Main tunnel

Connection tunnel drive optionFA d r-d rFB r d then d rFC d r-r dFD r d-r d

Frogmore SR - Buckhold Road

Frogmore SR - Bell Lane Creek

Zone S3 main tunnel site

Connection tunnel drive optionFE d r-d rFF d through rFG d r-r dFH r d then d rFI r d-r dFJ r through d

Single reception Single drive Sequential double drive

r d d then d

Double reception Drive and reception Tunnel drive through CSO drop shaft

r-r r-d or d-r through

Connected directly to the main tunnel

Connected to the Zone S3 main tunnel shaft

Legend: The following nomenclature/legend is used to define the types of site required. Where 'd' denotes drive site, 'r' denotes reception site and 'through' denotes the tunnel drives through a CSO drop shaft

CSO

CSO



65

Greenwich connection tunnel 5.2.5 The potentially feasible drive options for the Greenwich connection tunnel

are presented below in Table 5.2. All the Greenwich connection tunnel drive options connect to the main tunnel via a main tunnel shaft in either Zone S6 Shad or Zone S7 Limehouse. As this would be a long connection tunnel, the drive options need to be considered in conjunction with the main tunnel drive options concerning Zone S6 Shad and Zone S7 Limehouse. The location of Zones G1, G2 and G3 are illustrated in Figure B5 in Appendix B (refer to the Engineering options report– Abbey Mills route – Appendices (Spring 2012)). Table 5.2 Greenwich connection tunnel: Initial drive options

5.2.6 If the Greenwich connection tunnel connected to the main tunnel in Zone

S7 Limehouse, the flows would join the main tunnel along with flows from the intercepted North East Storm Relief CSO. The engineering would be complex and challenging as there are both hydraulic and pneumatic (air movement) concerns surrounding introducing too much flow at a single location. Therefore, all the drive options associated with Zone S7 Limehouse were removed from the list of feasible options.

5.2.7 To drive the connection tunnel from the main tunnel site in Zone 6 Shad to Greenwich PS after the main tunnel has been driven from Zone 6 Shad to the main tunnel site in Zone 11 Abbey Mills, and receive the TBM from Zone S5 Battersea at Zone S6 Shad is estimated to require a total construction period of at least 350 weeks. This is 38 weeks longer than the maximum six-year construction period and, for this reason, Option GE1 (seq – tunnel driven sequentially in two directions) associated with Zone S6 Shad was removed from the list of feasible options.

5.2.8 The programme for the other options will need to be checked in conjunction with the preferred main tunnel option at the next stage of evaluation.

Zone

G3

Gre

enw

ich

PS

Dep

tford

SR

Zone

G2

Zone

G1

Ear

l PS

Zone

S11

A

bbey

Mill

s

Connection tunnel drive optionGA r through n/a n/a through d r-r dGB d through n/a n/a through r r-r dGC r through n/a d then d through r r-r dGD r through d then d n/a through r r-r d

GE (seq) r through n/a n/a through d after MT r-d rGF (con) r through n/a n/a through d with MT r-d r

GH d through n/a n/a through r d rGI r through n/a d then d through r d rGJ r through d then d n/a through r d r

Zone

S6

Sha

d or

Zon

e S

7 Li

meh

ouse

Greenwich connection tunnelCSO or Zone

Main tunnel

Main tunnel



66

5.2.9 Table 5.3 presents the final list of Greenwich connection tunnel drive options to be taken forward to the next stage of the site selection process for multidisciplinary consideration. Table 5.3 Greenwich connection tunnel: Final drive options

North East Storm Relief CSO connection options 5.2.10 The post phase one consultation site selection back-check associated with

North East Storm Relief CSO sites identified two feasible CSO connection types, as follows: a. The King Edward Memorial Park Foreshore (C29XA) and King Edward

Memorial Park (C29XB) shortlisted sites could be connected to the main tunnel via a CSO drop shaft constructed on the line of the main tunnel. This would be a Type E CSO connection and no connection tunnel would be required.

b. The King Edward Memorial Park Foreshore (C29XA) and King Edward Memorial Park (C29XB) shortlisted sites could be connected to the main tunnel via a connection tunnel, and an intermediate shaft located on one of the shortlisted Zone S7 Limehouse main tunnel sites. This would be a Type A CSO connection.

Zone

G3

Gre

enw

ich

PS

Dep

tford

SR

Zone

G2

Zone

G1

Ear

l PS

Zone

S11

A

bbey

Mill

s

Connection tunnel drive optionGA r through n/a n/a through d r-r dGB d through n/a n/a through r r-r dGC r through n/a d then d through r r-r dGD r through d then d n/a through r r-r d

GF (con) r through n/a n/a through d with MT r-d rGH d through n/a n/a through r d rGI r through n/a d then d through r d rGJ r through d then d n/a through r d r

CSO or Zone

Main tunnel

Greenwich connection tunnel Main tunnel

Zone

S6

Sha

d



67

5.2.11 Table 5.4 presents the two NESR connection tunnel drive options associated with the Type A CSO connection to be taken forward to the next stage of the site selection process for multidisciplinary consideration.

Table 5.4 North East Storm Relief Type A CSO connection tunnel drive options matrix

CSO site:KEMP (C29XB)/

KEMP Foreshore (C29XA)

Main tunnel site zone:S7 Limehouse

Connection tunnel drive optionNA d rNB r d

CSO site/Zone



68

6 Conclusions and recommendations


69

6 Conclusions and recommendations 6.1.1 This report outlines the drive options that are available for the main tunnel

(refer to Table 4.8); for the connection tunnels where two or more CSOs would be intercepted and brought together prior to connecting to the main tunnel (refer to Table 5.1 and Table 5.3); and for the connection tunnel options where the connection tunnels connect to the main tunnel via an intermediate shaft on the main tunnel (refer to Table 5.4). It supports the site selection process by providing options for evaluation and selection.

6.1.2 The other four CSO connection types identified for connecting the existing CSO sewers/outfalls to the main tunnel are dependent on the selection of the proposed main tunnel drive strategy and proposed main tunnel sites. Therefore, further work will be carried out on CSO connections once the main tunnel proposals have been identified. System hydraulic preferences for CSO connections will also be considered at this time.

6.1.3 The review of the engineering criteria that affect the various main tunnel drive options is discussed in Sections 4.2 and 4.3. The results show that there are advantages and disadvantages associated with each drive option. These will be used as a basis for the engineering assessments in the Section 48: Report on site selection process.

6.1.4 The report has demonstrated that there are appropriate engineering options available to drive the main tunnel that meet the required criteria. It also provides the basis on which to evaluate and determine the proposed sites and proposed drive option for the main tunnel and connection tunnels for Section 48 publicity.

6 Conclusions and recommendations


70

7 Next steps


71

7 Next steps 7.1.1 The information in this report, along with the assessments in the site

suitability reports, will be brought together and discussed at a series of optioneering workshops attended by the five disciplines (engineering, planning, environment, community and property). The process for these workshops for main tunnel sites and CSO sites is outlined below. The drive options will be considered and the direction of the individual TBM drives determined based on the site assessments carried out as part of the site suitability reports in order to determine the use of each site.

7.1.2 For the main tunnel sites, this will involve workshops for the five disciplines: a. firstly, to consider the site suitability reports in order to determine the

most suitable site in each zone b. secondly, to consider this Engineering options report – Abbey Mills

route (Spring 2012) in order to select the preferred drive option associated with the most suitable sites in each zone.

7.1.3 The purpose of the workshop is to identify the proposed main tunnel sites and proposed drive strategy (ie, sites, types of site, and drive direction).

7.1.4 For the CSO sites, this will involve workshops for the five disciplines: a. firstly, to consider the site suitability reports in order to determine the

proposed site to intercept each CSO b. secondly, to consider this Engineering options report – Abbey Mills

route (Spring 2012) in order to select the proposed drive strategy associated with proposed CSO sites that have more than one drive option.

These considerations and assessments will be presented in the Section 48: Report on site selection process.

Copyright notice Copyright © Thames Water Utilities Limited September 2013. All rights reserved. Any plans, drawings, designs and materials (materials) submitted by Thames Water Utilities Limited (Thames Water) as part of this application for Development Consent to the Planning Inspectorate are protected by copyright. You may only use this material (including making copies of it) in order to (a) inspect those plans, drawings, designs and materials at a more convenient time or place; or (b) to facilitate the exercise of a right to participate in the pre-examination or examination stages of the application which is available under the Planning Act 2008 and related regulations. Use for any other purpose is prohibited and further copies must not be made without the prior written consent of Thames Water. Thames Water Utilities LimitedClearwater Court, Vastern Road, Reading RG1 8DB The Thames Water logo and Thames Tideway Tunnel logo are © Thames Water Utilities Limited. All rights reserved.

Copyright notice Copyright © Thames Water Utilities Limited September 2013. All rights reserved. Any plans, drawings, designs and materials (materials) submitted by Thames Water Utilities Limited (Thames Water) as part of this application for Development Consent to the Planning Inspectorate are protected by copyright. You may only use this material (including making copies of it) in order to (a) inspect those plans, drawings, designs and materials at a more convenient time or place; or (b) to facilitate the exercise of a right to participate in the pre-examination or examination stages of the application which is available under the Planning Act 2008 and related regulations. Use for any other purpose is prohibited and further copies must not be made without the prior written consent of Thames Water. Thames Water Utilities LimitedClearwater Court, Vastern Road, Reading RG1 8DB The Thames Water logo and Thames Tideway Tunnel logo are © Thames Water Utilities Limited. All rights reserved.

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