HS2 Tunnel Extension: Reducing the Environmental, Social and Economic Burden in Hillingdon

On behalf of London Borough of Hillingdon

Document Control Sheet

Project Name: HS2 in Colne Valley Project Ref: 30780/001 Report Title: Tunnel Feasibility Assessment Doc Ref: R01 Date: December 2014

Name Position Signature Date

B Blaine Technical Lead BB C Edmonds Geology CE Prepared by: Dec 14 D Page Tunnelling DP S Ring Railway SR

Reviewed by: S Witchalls Project Director SW Dec 14

Approved by:

For and on behalf of Peter Brett Associates LLP

Revision Date Description Prepared Reviewed Approved

Peter Brett Associates LLP disclaims any responsibility to the Client and others in respect of any matters outside the scope of this report. This report has been prepared with reasonable skill, care and diligence within the terms of the Contract with the Client and generally in accordance with the appropriate ACE Agreement and taking account of the manpower, resources, investigations and testing devoted to it by agreement with the Client. This report is confidential to the Client and Peter Brett Associates LLP accepts no responsibility of whatsoever nature to third parties to whom this report or any part thereof is made known. Any such party relies upon the report at their own risk.

© Peter Brett Associates LLP 2014

Office Address: Caversham Bridge House, Waterman Place, Reading, Berkshire RG1 8DN T: +44 (0)118 950 0761 F: +44 (0)118 959 7498 E: [email protected]

HS2 in the Colne Valley ii Tunnel Feasibility Assessment

Contents

1 Scope of Study ...... 1 1.1 Introduction ...... 1 1.2 The Brief ...... 3 2 Route Options ...... 5 2.1 General constraints ...... 5 2.2 Colne Valley Tunnel ...... 8 3 Technical Constraints - Ground Conditions ...... 15 3.1 Introduction ...... 15 3.2 The HS2 Reference Route ...... 15 3.3 Proposed tunnel route Options A and B...... 17 3.4 Groundwater impacts ...... 18 4 Technical constraints - Rail ...... 21 4.1 Introduction ...... 21 4.2 Heathrow Spur and potential maintenance sidings ...... 21 5 Technical Constraints – Tunnels ...... 24 5.1 Introduction ...... 24 5.2 Tunnel Spoil ...... 24 6 Impact and Cost Estimates ...... 25 6.1 Introduction ...... 25 6.2 Significant Impacts – Construction ...... 25 6.3 Significant Impacts – Operations ...... 27 6.4 Cost estimates ...... 28 7 Other options ...... 29 7.1 General ...... 29 7.2 Westward extension of Northolt Tunnel ...... 29 7.3 Alignment running between Harefield and South Harefield ...... 29 7.4 Extend the Chilterns Tunnel to West Ruislip ...... 29 7.5 Extend the Northolt Tunnel to West Hyde ...... 29 7.6 Required Mitigation for Reference Route ...... 30 8 Conclusions and Recommendations ...... 32 8.1 Tunnel options ...... 32 8.2 Other mitigation ...... 32

Figures Figure 1.1: Locations of Key Features on HS2 Reference Route ...... 2 Figure 2.1: Reference Alignment and associated features ...... 7 Figure 2.2: Locations of Sustainable Placement Areas ...... 9 Figure 2.3: HS2 Reference Route ...... 14 Figure 2.4: Proposed Colne Valley Tunnel ...... 14 Figure 3.1: Illustration of TBM types ...... 20 Figure 4.1: London facing turnouts ...... 22 Figure 4.2: Birmingham facing turnouts - Plan ...... 22

HS2 in the Colne Valley iii Tunnel Feasibility Assessment

Tables

Table 2.1: Summary of key aspects of comparative routes ...... 13 Table 6.1: Comparison of costs between HS2 and CVT Option B...... 28 Table E1 : Cost Estimates for HS2 Reference Route and Colne Valley Tunnel Alternative ...... 6 Table E.2: Indicative Overview Programme ...... 8

Appendices

Appendix A Drawings Appendix B Delivering the Colne Valley Tunnel Appendix C Alignment and Track Maintenance through the Tunnels Appendix D Correspondence Appendix E Cost Estimate

HS2 in the Colne Valley iv Tunnel Feasibility Assessment

HS2 in the Colne Valley v Tunnel Feasibility Assessment

1 Scope of Study

1.1 Introduction

1.1.1 The government proposes to construct a high speed railway between London (Euston) and Birmingham (Curzon Street), known as HS2. The route has been the subject of consultation at defined stages over the past 3 years and culminating in a Hybrid Bill before Parliament. The Bill has received its Second Reading and will now be scrutinised by a Select Committee.

1.1.2 As part of its formal responses to the consultation over this period the London Borough of Hillingdon has made representations to place HS2 in a tunnel through the whole of the borough to minimise the construction and operational impacts, particularly given that the borough and its residents believe they will receive very little benefit from the line.

1.1.3 From central London, the proposed railway will run in tunnel for most of the urban areas, but will emerge at the surface route at Ickenham High Road in West Ruislip and travel at the surface in cuttings, on embankments and on a viaduct over the Colne Valley before entering the Chiltern Tunnel at its South Portal near the M25. The locations of the key features are identified on the Figure 1.1 below.

1.1.4 The emergence of the route at Ickenham High Road is the first section above ground after the proposed Old Oak Common station. The area west of Ickenham High Road has therefore been selected for a large scale construction operation that will subject the area to 10 years of significant construction impacts and permanently change the character and use of the tract of land along its corridor.

1.1.5 In addition to the construction impacts, the Environmental Statement prepared by HS2 confirms there are permanent adverse impacts from the operation of the surface route. Noise, landscape, ecology, the reduction of available agriculture and the loss of important recreational facilities will have lasting adverse impacts on the environment from direct loss, changes in character and severance of corridors connecting habitats and residents with no mitigation for these effects identified.

1.1.6 The Borough believes that the myriad of impacts, both over the decade long construction period, and then into the permanency of the operational phases warrant finding an alternative to the preferred route option. Despite repeated requests by the Borough, evidence has not been presented of the options considered by HS2 Ltd in relation to the provision of HS2 in a tunnel extending to the west side of the Colne Valley, rather than the proposed surface route and viaduct.

1.1.7 This report is the outcome of a study by Peter Brett Associates LLP, working with OTB Engineering Ltd and Beazely Sharpe (Railwise) Ltd, into such a solution, commissioned by London Borough of Hillingdon. The primary aim of the study is to investigate the feasibility of a tunnel to ensure that all is practicably done to reduce the impacts on the borough and its residents. This report assesses the feasibility of relocating the railway within a tunnel and identifies the residual impacts that could be generated as a result of doing so and indeed whether a tunnel would be less impactful than the original proposal.

1.1.8 Costs associated with a tunnel option are presented and compared against those associated with the HS2 proposal.

HS2 in the Colne Valley 1 Tunnel Feasibility Assessment

Chiltern Tunnel - South Portal

Colne Valley Viaduct

Northolt Tunnel - West Ruislip Portal

Greenpark Way Vent Shaft

EUSTON STATION

OLD OAK COMMON STATION

Figure 1.1: Locations of Key Features on HS2 Reference Route

HS2 in the Colne Valley 2 Tunnel Feasibility Assessment

1.2 The Brief

1.2.1 The brief for the study required consideration of the options for a tunnel solution across the Colne Valley assuming that the routes to the east and west were fixed and there was no means of significantly changing the horizontal alignment at these end points.

1.2.2 The study includes evaluation of the geology and the hydrogeology in proposing a tunnel solution and development of a construction strategy which would allow the tunnel option to be implemented should it prove feasible.

1.2.3 The study uses desktop mapping information as well as any records made available through the Borough and other sources with regard to the Colne Valley lakes and adjacent landfills. This assisted in determining the feasibility, taking account of design standards applied to HS2 with respect to vertical and horizontal alignments. It also considered the potential level changes which might be needed for the Chilterns Tunnel to achieve a suitable alignment.

1.2.4 The implications of a tunnel solution on safety requirements as well as vent shaft locations taking account of the whole tunnel length south/east to Old Oak Common and north into the Chilterns form a key part of the study.

1.2.5 The impacts from the adoption of a tunnel solution are outlined and considered, together with construction and operational effects to determine if it is a viable option. The costs and issues such as construction infrastructure are also evaluated using HS2 information and other industry standards. This seeks to present a comparative cost to the above ground solution presented by HS2.

1.2.6 In developing the potential tunnel solution other options aimed at achieving a better outcome than that proposed by HS2, should the tunnel not be acceptable or not be viable are considered. This includes partial extension of the existing tunnel or other options for surface routes with a shorter tunnel across the Colne Valley.

HS2’s proposals for construction through LB Hillingdon

1.2.7 HS2’s proposals include the construction of the following elements

° Northolt tunnel from the West Ruislip to Greenpark Way, 5.5km of which is within LB Hillingdon;

° A ventilation shaft at South Ruislip (2.8km from West Ruislip)

° A 600m long tunnel portal and related surface structures at West Ruislip (Ickenham High Road), incorporating a headhouse for ventilation and access/egress;6.4km long surface railway from West Ruislip to West Hyde comprising:

o 1.7km long, 20m deep cutting, including a 120m long retaining structure

o 3.6km viaduct over the River Colne

o Turnouts/junctions for future tie-in to Heathrow Spur

° Spoil disposal over wide tracts of land north and south of the route.

1.2.8 In delivering these works it will be necessary to tunnel from West Ruislip to Greenpark Way, a distance of 7.8km. To facilitate construction a linear construction site is required all the way from West Hyde to West Ruislip. The construction site is 6.4km long and up to 300m wide, reaching 3.8km wide where it incorporates spoil disposal on adjacent lands.

HS2 in the Colne Valley 3 Tunnel Feasibility Assessment

Key elements of the proposed railway

1.2.9 Key elements that we have assumed are to be retained should an alternative alignment and configuration be proposed.

° South Ruislip Shaft, which includes ventilation, access/egress and emergency facilities

° Electricity Grid station and Substations for traction power – the final locations of which will depend on availability of source power on the grid.

° Turnouts/junctions for future tie-in to possible Heathrow Spur

° Alignment corridor that follows existing Chilterns Line railway to avoid wider impacts on surrounding residential areas.

1.2.10 The alternative tunnel solutions considered take these elements into account and, in particular are influenced by the provision for the Heathrow Spur.

HS2 in the Colne Valley 4 Tunnel Feasibility Assessment

2 Route Options

2.1 General constraints

2.1.1 The potential options available for developing alternative routes to that proposed are limited by the scope to avoid significant change to the horizontal alignment of HS2 to the east and the west.

2.1.2 To the east of the study area, the line is in tunnel (Northolt Tunnel) beneath the rail corridor carrying the existing Chiltern Line and London Underground lines. This tunnel runs almost the whole way to Euston, save for the final 1 km (although this is the subject of substantial redesign to minimise impacts on London Borough of Camden and create a more commercially viable station at Euston).

2.1.3 It is proposed to create a station at Old Oak Common, currently a major rail maintenance depot. In this tunnelled section of HS2 it is also proposed to create four Vent Shafts, at South Ruislip, Mandeville Road, Green Park Way and Westgate (near the Hanger Lane Gyratory). The Green Park Way (GPW) vent shaft will also be designed to remove the tunnel boring machines driven from the east at Victoria Road Box (VRB) adjacent to Old Oak Common (OOC) and west at Ickenham High Road (West Ruislip). The total distance between Old Oak Common Station (OOC) and West Ruislip Portal is 13.6 km. The drive length from West Ruislip to GPW VS is 7.8 km.

2.1.4 On the western side of the Colne Valley, at the M25 the line enters the proposed Chiltern Tunnel at its South Portal near Chalfont Lane. The North Portal of this tunnel is proposed at Mantles Wood, near Great Missenden, a distance of 13.3km. A summary image of the tunnel elements is shown below (taken from the HS2 Information Paper D7 – Tunnel Construction and Methodology).

2.1.5 The distance between these two constraints on the proposed route, which is called the Reference Alignment in this report, is a total of 7.7km of which some 3.4km is on viaduct across the Colne Valley itself.

2.1.6 Figure 2.3 at the end of this section summarises the description, indicating the lengths between key elements.

HS2 in the Colne Valley 5 Tunnel Feasibility Assessment

Safety in Long Tunnels

2.1.7 In considering an alternative route alignment to avoid the significant impacts on the environment and the communities in the Colne Valley from the works on or above the surface, the solution requires extension of the Northolt Tunnel by approximately 7 km from the portal at Ickenham High Road to a location on the west side of the Colne Valley, ideally linking directly into the Chiltern Tunnel at its south portal adjacent to the M25 near West Hyde.

2.1.8 Tunnels on major railways such as HS2 need to comply with the Technical Specification for Interoperability (TSI) on Safety in Railway Tunnels (TSI 2008/163/EC). This document sets out specific requirements with regard to safe evacuation under emergency circumstances and the provision of emergency facilities. A long tunnel (over 20 km) requires a special safety case to be prepared. In the current version of the TSI the length of a long tunnel can be broken by an Intervention Gap to make it less than 20 km in length so as not to require a special safety case to be prepared (though national or local requirements may dictate this). This gap has to be open to the air for a distance of more than 500 m and have an access/egress facility for evacuation of passengers to a safe area within the open section.

2.1.9 Whilst HS2 will run in tunnel from close to Euston Station the equivalent of an Intervention Gap would be provided at the proposed Old Oak Common Station as there is clearly means of escape to a safe area within a typical station. The distance of 21.3 km from here to the Chiltern Tunnel South Portal means that an Intervention Gap is required should the Colne Valley be tunnelled rather than traversed by surface route and viaduct.

2.1.10 Furthermore, the Gap should be close to the M25 to avoid affecting the location of an additional Gap in the Chilterns, should the Chilterns Tunnel be extended to the full distance of the Chilterns AONB, an alternative being petitioned by various organisations along that section of the line.

2.1.11 It should be noted, however, that the requirements for such a gap are likely to be changed by the adoption in early 2015 of a revised TSI on Safety in Railway Tunnels, whereby the minimum safety provision at 20km intervals can be a Fire Fighting Point (FFP) able also to allow evacuation of passengers to a safe area. This FFP does not need to be directly open to the surface, and it allow safety provisions to be made in a number of different ways including through regularly spaced shafts (as in the HS2 proposal) or perhaps via an underground chamber at a convenient location for emergency access.

2.1.12 The proposed open to air Intervention Gap could become a covered FFP but, for the purposes of this study, other combinations of FFP location for the conjoined tunnels between Old Oak Common and Mantles Wood, or Wendover should the Chiltern Tunnel be extended, have not been considered. As is discussed later, this open section enables a practical arrangement for construction of a proposed tunnel and other operational benefits, therefore the potential for it to be covered is not explored further.

HS2 in the Colne Valley 6 Tunnel Feasibility Assessment

Figure 2.1: Reference Alignment and associated features

HS2 in the Colne Valley 7 Tunnel Feasibility Assessment

2.2 Colne Valley Tunnel

Tunnelling options

2.2.1 In HS2’s proposal, the 13.3km long Chilterns Tunnel is to be built from West Hyde to Mantles Wood, the 7.9km Northolt Tunnel (west) is to be built from West Ruislip to Greenpark Way and the 6.2km Northolt Tunnel (east) from Old Oak Common to Greenpark Way. In assessing the feasibility of creating a tunnel beneath the remainder of the LB Hillingdon section the following options have been considered:

° Extend the Chilterns Tunnel to West Ruislip;

° Extend the Northolt Tunnel to West Hyde;

° Introduce a new tunnel between West Hyde and West Ruislip that would form a northward extension of the Northolt Tunnel, which for the purposes of this report can be called the Colne Valley Tunnel.

2.2.2 Other combinations of tunnelling are discussed in Sect 8.

2.2.3 It is preferable to introduce a new tunnel, the Colne Valley Tunnel (CVT), between West Hyde and West Ruislip and to form this tunnel from West Hyde, where there is adequate space and good access to do so (the location of the planned railway/tunnel maintenance facility). The drive length for this tunnel is 6.6km, which is similar to the drive length from West Ruislip to Greenpark Way and, as a separate drive rather than part of a longer tunnel drive, it reduces the impact on the overall construction programme. This drive would be a chalk drive and therefore a site co-located with the drive for the Chilterns Tunnel, also in chalk, should allow for some economies of construction infrastructure.

2.2.4 Figure 2.4 below illustrates the proposed Colne Valley Tunnel solution.

Benefits

2.2.5 The primary aim of the study is to consider the extension of the already proposed Northolt Tunnel from Ickenham High Road to the west side of the Colne Valley, ideally adjacent to the M25 and the south portal for the Chiltern Tunnel.

2.2.6 A beneficial effect of extending the Northolt Tunnel westwards is that it would avoid the need for a tunnel boring machine (TBM) drive site situated close to the existing residential area west of Breakspear Road South. This construction site, including spoil handling and tunnel lining manufacture that would be in operation for 7 years 1, along with associated accommodation works such as road and major utilities diversions, will have considerable impact on local transport and amenities.

2.2.7 A TBM drive site for a Colne Valley Tunnel (CVT) and the tunnel lining manufacture/handling for an extended Northolt Tunnel should ideally be located near the M25, with a temporary access onto the M25 to allow spoil removal and material delivery. Such a temporary access is already proposed by HS2 to enable the construction of the Chiltern Tunnel and also the western end of the Colne Viaduct. The latter would be replaced by the TBM drive site.

2.2.8 The Reference Route TBM drive site for the Northolt Tunnel (west) is located in close proximity to the Chiltern Line to potentially provide a railhead for the transport of tunnel arisings by rail for disposal. This would initially appear to be a sustainable solution. However, to create this site and to form the Copthall Cutting up to 20m deep, required by the vertical alignment immediately west of the River Pinn, a considerable quantity of soil has to be moved to form a level platform on which to create the railhead. This material is proposed to be

1 ES Vol 2 CFA6 para 2.3.25

HS2 in the Colne Valley 8 Tunnel Feasibility Assessment

deposited immediately north as the ‘sustainable placement’ of material in the area known as Newyears Green.

2.2.9 The volume of material to be deposited as a result of the creation of the railhead is estimated in the HS2 Environmental Statement to be 1,600,000 cu.m taken from the Copthall and Brackenbury cuttings. The ‘Sustainable Placement Area’ (SPA 1), broadly identified in the environmental statement plans is :

° between Harvil Road and Breakspear Road South (CFA 6);

° at Newyears Green (CFA 6);

° south east of Harefield (CFA 7)

Figure 2.2: Locations of Sustainable Placement Areas

2.2.10 These areas are identified as having a capacity of 2,884,487 tonnes 2 which is equivalent to approximately 1,600,000 cubic metres. HS2 has confirmed that SPA1 will only be needed for the construction of the temporary railhead (see Appendix D, Item D.1). Despite this discrepancy in quantities, it can be concluded by this statement that if the need for this temporary railhead can be avoided the SPA will not be necessary, thus avoiding substantial ground re-profiling and soil placement. The earthworks required to form the railhead involves removal of a section of high ground approximately 1000m long, 200m wide and up to 20m deep. Transporting this material in off-road vehicles carrying 60 Tonnes, as proposed, will still require approximately 100,000 2-way vehicle movements. This excludes the earthmoving required to prepare the placement areas by stripping and stockpiling topsoil and subsoil for replacement once the excavated material has been deposited. It is also likely that access to the area bounded by Harvil Road/Breakspear Road South will need to be accessed via Harvil Road using road going vehicles. If this takes a third of the volume, the number of 2-way road lorry trips along Harvil Road required to place the material in this area alone would be about 130,000.

2 Vol 3 Route-wide Effects – Table 21

HS2 in the Colne Valley 9 Tunnel Feasibility Assessment

2.2.11 The three areas above for disposal in “sustainable placement” total approximately 60ha, to be raised by up to 3m. Where the site is natural ground it will be necessary to first remove and stockpile the topsoil and at least some of the subsoil to a depth of at least 300mm before placing the surplus material and then replacing the original soil in the correct layers. These layers of soil, estimated to total approximately 20-30,000 cubic metres, will need to be stored separately before being returned. The area south east of Harefield is also a landfill which will need remedial work before the filling is placed. This is discussed further in Section 3.

2.2.12 It is estimated that a further 500,000 cubic metres of tunnel spoil from the Northolt Tunnel West (largely London Clay) would be taken by rail for disposal elsewhere, possibly at Calvert in Buckinghamshire, a distance of about 55km on the Chiltern Line. The railhead is a temporary feature and will be removed once the construction work is completed but the land will not be returned to the original profile.

Rail alignment in tunnel

2.2.13 Analysis of the potential solution to adopting a tunnel alignment instead of the proposed viaduct of the Reference Route has shown that such a solution is possible. There are two options proposed:

° Option A - following the Reference Route horizontal alignment but set into tunnel. This is feasible although the reverse curve at each end of the viaduct is not ideal in rail operational terms. The tunnel solution also makes the inclusion of the turn-outs for the potential future Heathrow Spur, also in tunnel, more difficult.

° Option B – takes a new horizontal alignment with a single curve across the valley between straights and avoids the need for reverse curves, improving operational performance. This tunnel solution also enables the provision of turnouts for the future potential Heathrow Spur, which could be formed as part of the Phase 1 work.

2.2.14 Option B is considered as the proposal to be taken forward for further evaluation as it meets the full requirements for the delivery criteria of Phase 1 of HS2. Should the Heathrow Spur be considered unlikely to be brought forward in Phase 2, then Option A should be reconsidered. In most other respects both options have similar characteristics and any significant differences will be discussed where necessary.

2.2.15 The alignment of Option B has two variants, related to the western end:

° Option B1 - results in a deeper cutting at West Hyde and deepening of the Chiltern Tunnel Portal but a more flexible alignment for a Maintenance Loop should it be desired.

° Option B2 is also in cutting at this location but has less effect on the Chiltern Tunnel Portal and still offers a reasonable Maintenance Loop provision. The Maintenance Loop is not a specific requirement and therefore Option B2 is considered as the preferred alignment. The availability and functionality of these sidings is described in Appendix C.

2.2.16 In respect of operational criteria, the tunnel alignments avoid the short 2.5% gradient and 30m rise out of the Northolt Tunnel, by maintaining an average 0.2% gradient across the valley before rising at 1.4% and 30m to the gap between the proposed Colne Valley Tunnel and the Chiltern Tunnel. The preferred option B2 rises only 20m at 2%, which, together with a single curve between straights will be less obvious to the passenger. The design, and hence operational, speed of 320km/h will also be consistent with the Northolt Tunnel design parameters allowing a smoother journey and less energy wastage. The design speed of the Colne Valley Viaduct is 300km/h which is likely to require braking in advance and accelerating after crossing to optimise the design but does make the transit of the Colne Valley more complex and less likely to achieve efficiency in operation.

HS2 in the Colne Valley 10 Tunnel Feasibility Assessment

Ground conditions

2.2.17 A desk study has been undertaken to determine the ground conditions along the proposed route of HS2 from West Hyde through to South Ruislip. The desk study compiled from surface mapping and publically held borehole records indicates that the ground conditions underlying the route of HS2 from West Hyde to West Ruislip would comprise the Chalk, though south and west of the River Colne the Chalk is overlain by the Lambeth Group and London Clay. Relatively thin superficial deposits overlie much of the route.

2.2.18 The Chalk is characterised by its almost pure CaCO 3 content and by layers of nodules and seams of flint at intervals. The Chalk is a weak rock with variable fracturing and weathering, which may become more pronounced closer to the surface and where the cover of the Lambeth Group and London Clay has been removed, such as beneath the River Colne. The Lambeth Group is characterised by very stiff clays with beds and units of sand and silt and the London Clay by monotonous very stiff to firm grey brown clay.

2.2.19 Superficial deposits include river alluvium associated with the former courses of the River Thames and its former tributaries, glacio-fluvial deposits and river alluvium associated with current watercourses including the River Colne and River Pinn. Alluvial gravel has been extensively worked in the River Colne and the flooded former pits are now a characteristic of the landscape.

2.2.20 The River Colne is the major watercourse in the area, into which flows the River Misbourne and the River Pinn. Groundwater levels in the underlying strata are anticipated to be close to the water levels in these watercourses and rise up very gradually from them under the adjacent valley sides and high ground.

2.2.21 Immediately north of the route at Newyear’s Green the Lambeth Group was worked for sand and gravels and the resultant pits were then used for waste from unknown sources. The pits are unlined and contamination of the surrounding ground and groundwater is known and regularly monitored by LB Hillingdon.

2.2.22 Solution features are a characteristic hazard where the Chalk is overlain by a thin cover of Lambeth Group and superficial deposits at the limit of its outcrop/subcrop. The features may comprise cylindrical shaped cavities that extend from the surface to depths of up to 50m from the surface of the chalk and are naturally in-filled with materials derived from the overlying deposits.

Tunnelling Strategy

2.2.23 In developing the means of construction for the tunnel solution careful consideration has also been given to the tunnelling strategy which could be adopted and the consequent spoil handling.

2.2.24 The tunnelling distance and geology dictate that it will be preferable to adopt a strategy which allows for tunnelling in chalk through the Colne Valley and retain the principle of the Northolt Tunnel western drive in London Clay. Instead of driving the Northolt Tunnel from the portal site near Ickenham High Road however, it is proposed to drive the Northolt tunnel from a drive site and shaft situated at the western end of the existing Ruislip Rail Depot. This depot is already used by maintenance trains and forms a rail head which can be modified to transport tunnel spoil as already proposed by HS2. The site already has good access to the local road network and it is understood that the principle of this is accepted by the current owners and operators of the site, Transport for London (TfL) and London Underground Limited (LUL).

2.2.25 Therefore it is proposed that the Colne Valley Tunnel (CVT) would be driven south and eastwards from a portal situated west of the A412 at West Hyde. This area is already identified by HS2 to be used as the main Viaduct construction site, therefore the land would be subject to considerable alteration to facilitate the construction of the Chiltern Tunnel South Portal and be the drive site for the Chiltern Tunnel TBM, spoil handling and handling tunnel lining segments (either manufacture or storage).

HS2 in the Colne Valley 11 Tunnel Feasibility Assessment

2.2.26 The CVT bores would be almost entirely in water bearing chalk (only the eastern end would likely be in clay) and therefore will be almost identical to the spoil produced by the Chiltern Tunnel. This would make the combined operation of the two TBM sites complimentary and even enable shared infrastructure. The Chiltern Tunnel is about twice as long as the proposed CVT, therefore the infrastructure capacity will need to be adjusted to suit the programme and delivery but there could be economies with combined operations.

2.2.27 It is anticipated that the CVT would be driven by two TBMs working in close succession over the 6.6 km length to Ruislip Depot Vent Shaft. They would be removed from the shaft being used to drive the Northolt tunnel in a similar manner to the arrangements for removal of all the TBMs forming the Northolt tunnel (east and west) at the Greenpark Way Vent shaft.

2.2.28 The drive distances for these tunnel lengths are similar and therefore timing and handling arrangements will be compatible.

2.2.29 This solution avoids the need to remove the hill near Newyears Green and deposit the material in SPA1. Avoiding this unnecessary work and associated road and utilities diversions will be a major cost and environmental benefit.

2.2.30 An indicative programme at Appendix E indicates that the works will be no longer in time scale than the proposed scheme. The overall works timetable is potentially dictated by boring of the Chiltern Tunnel between 63 and 90 months, but the Colne Valley Viaduct is also about 70 months. The Colne Valley Tunnel Route option proposed in this study will have a maximum programme period of 71 months. However, this is a very course overview programme and the critical path elements would be programmed to ensure there is no impact on the overall procurement strategy

Summary of Benefits

2.2.31 In summary, whilst there are constraints to the delivery of a tunnel solution to cross the Colne Valley, these are not insurmountable and a tunnel would avoid the need for unnecessary excavation of soil and realignment of major overhead power lines and local roads as well as the significant disruption to the local community over a long period of time and permanent loss of amenities and land. The tunnels and vent shafts on the Northolt Tunnel from West Ruislip toward Greenpark Way are essentially as proposed for the HS2 scheme.

2.2.32 Introducing a new tunnel between West Hyde and West Ruislip will bring about the following benefits to the operation of HS2 and to LB Hillingdon:

° Straighter more direct horizontal railway alignment, including the removal of two reverse curves.

° An overall smoother and more level vertical railway alignment although some grade separation in the Ruislip Depot area has been incorporated to facilitate the provision of the future Heathrow Spur connections. Should the Spur not be required this separation could be removed.

° Consistent design, and hence operational, speed of 320 kph, instead of complex mix of 320/300/360 for tunnel/viaduct/short surface section leading into long Chiltern Tunnel with design speed of 320 kph.

° No surface railway between West Ruislip and West Hyde.

° Minimal surface works between West Ruislip and West Hyde (with the exception of a shaft site located at Harvil Rd/Highway Farm and a further shaft site at Ruislip Depot, discussed further below).

° Deletion of the River Colne viaduct.

° Deletion of a deep cutting and retaining structure at Newyears Green (Copthall Cutting).

HS2 in the Colne Valley 12 Tunnel Feasibility Assessment

° Deletion of tunnel portal at West Ruislip.

° Deletion of the major 275kV overhead powerline diversion

° Combined tunnel intervention gap and maintenance sidings/railway maintenance facility located at West Hyde, with access to both the M25 and A412. This facility would serve the Chiltern Tunnel, Colne Valley Tunnel and Northolt Tunnel.

2.2.33 Table 2.1 below summarises some key aspects associated with each of the routes

Table 2.1: Summary of key aspects of comparative routes

Aspects HS2 Reference Alignment Colne Valley Tunnel Route

Tunnel Northolt Tunnel ends at Ickenham High Continue tunnel to West Road – Hyde – 20km from Old Oak 13.1 km from Old Oak Common Common

Portals 1 at Ickenham High Road 1 at West Hyde, adjacent (West Ruislip Portal) A412

Vent Shafts in Hillingdon 1 3

Viaducts 1 0

Relative design speeds 320 kph (tunnel) / 300 kph (viaduct) 320 kph (tunnel)

Community infrastructure Ruislip Golf Course None affected Ruislip Rifle Club HOAC (incl demolition of 3 buildings) Denham Waterski Club Colne Valley Regional Park

Properties demolished 3 0

Length at Surface 7700 m 1100 km (Between A412 and M25)

Maintenance liability Weather exposed viaduct and surface Consistent maintenance infrastructure - different requirements regime with contiguous to Chiltern and Northolt tunnels at each Chiltern and Northolt tunnels side of valley

Area of Agricultural land 362.8 Ha Approx 15 Ha Disturbance (including construction areas)

No of compounds in 10 4 Hillingdon

Excavation Arisings 2,811,424 tonnes (CFA7) Approx. 900,000 tonnes

Sustainable Placement / 1,100,000 cu.m 0 Landfill (1,980,000 tonnes)

HS2 in the Colne Valley 13 Tunnel Feasibility Assessment

Figure 2.3: HS2 Reference Route

Figure 2.4: Proposed Colne Valley Tunnel

HS2 in the Colne Valley 14 Tunnel Feasibility Assessment

3 Technical Constraints - Ground Conditions

3.1 Introduction

3.1.1 The geology of the study area is shown on the geological plans and sections in the drawings at Appendix A. They are generally common for each route.

3.2 The HS2 Reference Route

3.2.1 East of the West Ruislip tunnel portal the route is fairly level and the tunnel is within the Lambeth Group and London Clay.

River Pinn valley

3.2.2 From the West Ruislip tunnel portal the route comes to the surface and then rises up onto embankment before crossing a bridge over the River Pinn and onto embankment to gain the other side. The River Pinn valley side slope is a possible zone of instability in London Clay (in the east) and, having crossed the River Pinn, it then crosses a similar zone of instability in the west. The valley side slopes typically contain relict periglacial shear zones. The soils in the side slopes tend to have very low shear strengths making them prone to land instability, even at shallow slope angles. Such soils will likely require stripping and replacing or other forms of ground treatment or piling in order that embankments have a stable construction base. It is possible that the river valley is fault controlled which would add geotechnical complexity and uncertainty to the ground conditions and stability of side slopes.

3.2.3 Bridge abutments within the valley floor will be located upon wet, compressible alluvial soils, therefore deep piled foundations are likely to be required to find suitable load bearing strata at depth.

Copthall cutting

3.2.4 The line then passes through a deep cutting (up to 20m deep) mostly in London Clay but with the track bed upon the Lambeth Group deposits in the cutting floor. This leaves the potential for cutting side slope instability in the short and longer term. Substantial slope stabilisation measures will be required or additional surface land used to reduce slope angles for improvements in stability. The potential for heave of the cutting floor will need to be considered to maintain high speed rail alignment tolerances in the medium to long term and mitigation measures employed as appropriate

River Colne valley

3.2.5 The Reference Route then crosses the Colne river valley on a viaduct up to 15m high in a horizontal curve – in doing so it crosses over a canal, river, roads and water-filled gravel pits with limited cover remaining to underlying chalk. The entire Colne valley is probably underlain by karstic chalk containing solution widened joints forming preferential pathways for groundwater flow. This dissolution weathering will extend to potential depths of up to 50m and as a consequence there will be many foundation challenges for the viaduct It is also considered likely that the form of the valley is probably controlled by faulting. Current published geology maps (e.g. Beaconsfield Sheet 255 (2005) 1:50,000 scale, British Geological Survey) and online geology mapping ( www.bgs.ac.uk ) show very few faults which is now being recognised as an under-representation of the actual situation (see 3.2.12 below)

3.2.6 Viaduct approach embankments, where they cross soft, compressible soils will be subject to the same construction base instability challenges as outlined in 3.2.2 above, increasing the earthworks depth required.

HS2 in the Colne Valley 15 Tunnel Feasibility Assessment

3.2.7 The viaduct itself will likely be supported upon deeply piled piers which will need to be constructed either within a caisson or on filled stone platforms within the valley floor lakes at each position to exclude water, as it is likely that water flows will be too large to contemplate dewatering without substantial intervention. Deep periglacial and karstic weathering will likely cause problems for piling (loss of concrete into voids, pile shaft instability affecting integrity, settlement of piles etc) unless taken down to unweathered chalk at 50-60m. It may be necessary to carry out pre-treatment grouting of the deep level chalk to improve bearing capacity ahead of piling.

3.2.8 The complex nature of these ground conditions were recognised by HS2 in an FOI response in Nov 2010 3 in that “The base cost has been uplifted by circa 20% due to the additional complexity of the viaduct foundations” . However, the actual cost of these foundations is not identified. A response to FOI request in 2014 4 provides a cost estimate for the viaduct however no breakdown of costs for the foundations is given. This latter figure is used in the cost estimates discussed in Section 6 below. It should be noted that no ground investigation has been undertaken by HS2 to inform the construction required. The ES Vol5 CFA7 Water Resources Assessment (pg 40-41) identifies the risk of pollution to the groundwater aquifer from the viaduct piers and claims it will be dealt with through selection of piling methods to avoid creating pathways. This indicates that there is still considerable uncertainty about the foundation solutions and also does not quantify the depth to which the piling might need to be taken.

3.2.9 An FOI response in June 2013 5 regarding a Colne Valley Tunnel, noted “ We consider it probable that, in order to build a tunnel, there would be additional risks of tunnelling beneath the lakes which, depending upon the techniques used during tunnel construction, might require draining areas of the lakes above the tunnel during construction”. The potential need to drain the lakes is questionable as the tunnelling technique will be no different to that required for the Chilterns Tunnel, which will also be largely within the groundwater table except at the two ends. The tunnelling solution proposed is discussed in Section 5 below.

3.2.10 Shallow level problems may include compressible alluvial soils and unstable made ground, possibly containing some materials that cause problems to piles such as reinforced concrete demolition debris or the potential to release contaminants contained within the backfills. Any lined containment systems would need to be investigated in detail and their contents analysed in case of puncture and contaminant release. There is also a risk that formerly uncharted/ unlicensed landfills are present within the valley floor which could be impacted by the works causing release of contaminants.

Tilehouse Lane cutting to Chiltern Tunnel portal (nr. West Hyde)

3.2.11 Beyond the west side of the Colne valley the surface route passes through a cutting (up to 10m or so deep) formed in chalk. However the chalk is capped with Winter Hill Gravel over Lambeth Group deposits. The interface with the chalk is commonly karstic in nature and solution pipes can be developed at various scales up to 50m depth. The intervening chalk is also generally highly weathered and of poor quality. These features and weathered chalk materials can lead to instability of the cutting side slope and along the floor of the cutting where features underlie the line. These features could lead to long term maintenance problems for a high speed line on ballasted track if not adequately identified and treated. This may involve grouting, the construction of concrete bearing slabs or excavation & replacement.

3.2.12 Beyond the cutting the line crosses a small scale valley feature on embankment before passing underground at the Chiltern Tunnel portal beside the M25. It is likely that the embankment will be built upon a deep periglacially and karstically weathered zone of chalk containing solution widened joints forming preferential pathways for groundwater flow. This

3 FOI 10/098 – The cost of mitigating the major risk to ground water resources in the Colne Valley Basin 4 FOI 14-1054 and subsequent email 23 May 2014 5 FOI 13-665 – Reasons for not opting for tunnelling under the Colne Valley.

HS2 in the Colne Valley 16 Tunnel Feasibility Assessment

will also lead to long term maintenance problems unless adequately treated using techniques such as grouting.

3.2.13 It is considered highly likely that the route will cross a series of faults that are not shown on current maps or online geology by British Geological Survey. However the Survey has begun to recognise the shortfall of faulting information as they shift their future mapping emphasis into developing 3D geological models. Recent published work by Ford et al (2008), Aldiss (2013) and Mathers et al (2014) highlight the under-representation of faulting in the wider London area as new digital structural models are developed. In recognition of the wider occurrence and significance of faulting this study into HS2 has inserted potential fault lines to explain why certain surface features like valleys are present. The positioning of such faults is subject to further investigation and ground modelling.

3.2.14 The consequence of these faults is that their existence will increase the likelihood of deeply penetrative weathering of the chalk and overlying deposits like the Lambeth Group, Where cuttings are within the Lambeth Group deposits then faulting will increase the potential for side slope instability and reduce strengths of the deposits on which embankments are to be constructed.

3.2.15 The presence of faults in cuttings in chalk will likely have increased the development of karst and because the chalk mass will be weakened by the faulting these associated effects will reduce the stability of the chalk in cuttings and also where embankments and foundations for the Colne Valley viaduct are to be built.

3.2.16 As a consequence, the faulting would add cost and risk to the surface construction works but should not present a difficulty for tunnelling at depth. The TBM will already be suitably designed to deal with weaker/stronger ground and wetter/drier ground.

3.3 Proposed tunnel route Options A and B.

3.3.1 At West Ruislip two tunnel options are proposed, Tunnel Option A (pink) which follows the same alignment as the surface HS2 Reference route (red) and Tunnel Option B (blue ) which lies further north of the HS2 Reference route and has a less pronounced bend than that of the Reference route. The tunnel boring machine (TBM) will be a pressurised chalk slurry machine, consistent with the conditions likely to be experienced both here and in the Chiltern Tunnel.

3.3.2 At West Ruislip the tunnel would emerge from the southerly dipping Lambeth Group beds and pass into the Chalk Group strata (the Seaford, Newhaven and Lewes Nodular Chalk formations). The tunnel will likely also be passing through fully saturated chalk. The Lambeth Group/Chalk interface often shows evidence of karstic weathering therefore the TBM will be designed to deal with the possible occurrence of solution cavities and flint bands.

River Pinn valley

3.3.3 Next, either tunnel option passes below the River Pinn valley at about 20m depth. It is possible that the chalk below the valley axis will be periglacially weathered and contain solution widened joints carrying enhanced groundwater flows at certain horizons. The valley feature may be fault aligned resulting in more variable and more deeply weathered chalk. The TBM will be designed to deal with chalk weathering, flints and higher water flows.

Copthall

3.3.4 The tunnel then continues through the chalk at depth below a hill before reaching the Colne Valley at around 20m or so depth below the surface. Again periglacial weathering, solution widened joints and enhanced groundwater flows are expected to be in evidence throughout this portion of the route. The Colne valley is also considered to be possibly shaped by faulting. As for 3.3.3 above the TBM will be designed to overcome the variability of the chalk ground conditions.

HS2 in the Colne Valley 17 Tunnel Feasibility Assessment

River Colne valley

3.3.5 Tunnel Option B (blue) passes below an area on the east bank of the River Colne valley which is overlain by Lambeth Group deposits with landfills on top as well as at the surface. The Lambeth Group/Chalk interface will probably exhibit karstic weathering with solution pipes present possibly to depths of up to 50m passing through the horizon containing the tunnel. Therefore overbreak through weak, collapsible zones associated with solution features is possible and may require grouting ahead to stabilise. The tunnel is generally more than 20m below the surface where the landfills are present so should not have any direct impact on them. The grouting will also serve to seal any preferential pathways for pollutants from the landfills.

3.3.6 On the west bank of the Colne Valley the tunnel route reaches the proposed north portal structure before continuing northwards to the Chiltern Tunnel South Portal and below the Chiltern Hills. At this point the proposed route level will still be below the water table. This section of route between the portals will therefore require to be water tight at the base and partly up the sides, prevention of hydraulic uplift, stability of the box structure during construction and longer term, dealing with ground conditions that are likely to include periglacially weathered chalk and solution pipes below the chalk interface with the Winter Hill Gravel and Lambeth Group deposits that may extend to the full depth of the in-ground structure. The hydraulic uplift and ground stability challenges are not unusual for in-ground structures of this nature. At the depth of the tunnel the ground conditions consist of chalk, the strength of which should restrain these deformations. Overall ground movement impacts should be negligible.

3.3.7 It is considered highly likely that the route will cross a series of faults (not widely recorded by the British Geological Survey) which may be aligned with a number of the valley axes. Fault zones may lead to enhanced weathering and softening along them and the possible formation of karstic zones in the chalk. The TBM will be designed to deal with these varying ground conditions.

3.3.8 These variations in chalk geology are not uncommon for TBM and tunnel lining design.

3.4 Groundwater impacts

Upstream uplift

3.4.1 Reference Route - Within the Colne valley care will need to be taken not to create a barrier to groundwater flow (e.g. due to the construction of the viaduct piers) that results in a lifting of ground water levels upstream from the works and depressing levels downstream. The upstream uplift could produce unwanted effects such as an increased risk of localised flooding when combined with wet weather.

3.4.2 Tunnel Options - The tunnels are positioned almost centrally within the main water bearing permeable part of the chalk aquifer. The greater permeability is likely to be nearer the surface although karstic features and jointing could make for high permeability at any depth in this zone. The barrier effect of the continuous cylinder created by a tunnel in this zone or deeper is likely to have less effect at the surface of the aquifer than the more substantial surface effects of the piers and piles, which will potentially have to be driven the full depth of this weathered zone to reach the sound chalk beneath.

Abstractions

3.4.3 There are a number of water abstraction licence sites in close proximity to the tunnel routes. As the flow of groundwater is southwards along the course of the River Colne the two abstractions north of the blue and pink tunnel routes should be unaffected by the tunnelling. However these appear to be local mineral washing abstractions and less significant. A third abstraction point lies on the west bank of the River Colne south of the tunnels and should not be affected assuming that the tunnels and any associated grouting works do not block/destroy

HS2 in the Colne Valley 18 Tunnel Feasibility Assessment

or infill any major water supply horizons utilised by the abstraction borehole. A fourth abstraction borehole appears to almost coincide with the eastern end of the Intervention Gap in-ground structure. This is also a minor abstraction and the borehole may need to be re- located to avoid destruction by the construction process or temporarily suspended in order to monitor if there are appreciable effects as a result of construction works. The works themselves might make the need for the abstraction redundant.

3.4.4 There are main public water supply abstractions at Moor Hall Rd and West Hyde. The former is situated almost equally between the two alignments being considered, whilst the latter is relatively similarly situated on the north-east side of both. No impacts to these abstractions are expected in relation to the proposed tunnelling works.

Pollution

3.4.5 Reference Route – The Viaduct will introduce a number of piers and deep piles across the valley, and hence the aquifer, and the potential impact is noted in the ES as major significant, mainly due to the risk of silt and suspended solids being introduced into the water supply. The risk of interfering with the actual flow to either PWS abstraction point is considered low as it is downstream of the main flow direction. However, the stated means of construction 6 through dewatering of cofferdams at each pier raises questions about the viability of this solution. It is unlikely that the base of a cofferdam will be sealed by sheet piles as the underlying ground is so permeable and susceptible to large fissure flow. The potential solution to this will be stone filling to above the water surface or to install a substantial concrete plug in the base of the cofferdam. The piling technique would then be either bored or driven encased piles through the base. The number of piers as well as the abutments at each end and the consequent number of piles together with the variability and uncertainty will extend the risk to the aquifer over a considerable time or over a wide front across the valley for any particular period. The risk of pollution will continue until all temporary works are removed. It is possible some temporary works may not be adequately removed.

3.4.6 Tunnel Options - The proposed tunnel boring solutions using a pressurised slurry machine will include grouting of voids as necessary behind the cutting head and shield to keep the water out of the works while the lining is set in place. The grout will be specified to set quickly on contact with water within the chalk fissures and pores and within a controlled depth. The grouting could lead to a slight increase in pH of the water but the effect of this will be limited by the setting process and dilution due to the large body of water in the aquifer, which in itself will have a slightly elevated pH from its passage through the chalk rock.

3.4.7 It has been questioned whether tunnelling would cause the water filled gravel pits to drain 7. However since the tunnel boring methods would make use of a pressure balanced shield no significant impacts on the surface water levels within the water filled gravel pits should occur. The tunnelling would create a cylindrical corridor that would exclude water from entry into the tunnel (by balancing the ground loading and hydrostatic pressure) as it was being cut by the TBM. As noted in the HS2 Information Paper D7 Tunnel Construction and Methodology, these types of TBM are planned to be used and have performed well on the Jubilee Line, HS1 and Crossrail projects. The types likely to be used are shown in Fig 3.1 below (taken from the HS2 ES Vol 1.

6 ES Vol5 CFA7 Water Resources assessment Table 9 7 FOI response 13-665 June 2013

HS2 in the Colne Valley 19 Tunnel Feasibility Assessment

Figure 3.1: Illustration of TBM types

Summary

3.4.8 In comparison to the viaduct, the tunnelling will progress in a continuous working face across the valley and at known times and locations. Any risks to the water quality at the PWS abstraction points can therefore be monitored and controlled to suit the work progress. This will provide more certainty for risk management.

3.4.9 Whilst the tunnel is designed to exclude water, construction of a viaduct will almost certainly impact the surface and groundwater regime. Overall it is considered that a tunnel at depth poses less risk to surface and groundwater flows than large scale surface construction associated with a viaduct.

HS2 in the Colne Valley 20 Tunnel Feasibility Assessment

4 Technical constraints - Rail

4.1 Introduction

4.1.1 The section of line across the Colne Valley contains key elements which dictate the solutions that meet the requirements to include provision for the possible future spurs to Heathrow at both ends of the study area. The intervening section between the two ends is designed to the line speeds of the HS2 Reference Route

4.1.2 At the design speeds proposed turnouts from the main line need to be undertaken on lengths of straight and these have dictated the alignment of Option B to accommodate the Heathrow Spur.

4.2 Heathrow Spur and potential maintenance sidings

4.2.1 There is some uncertainty as to the design standards adopted by HS2 in showing the provision for the Heathrow Spur and there is no certainty as to what turnouts HS2 actually anticipate installing . Interpretation of the HS2 drawings indicates that the layout would not provide 230 km/h (140 ~ 145 mph) on all legs of the spur, which would potentially compromise its performance.

4.2.2 In determining the tunnel alignment 'international' best practice of high speed turnouts has been employed to approximately fit the transition turnout geometry given by HS2. Regardless of the types of turnouts HS2 do eventually choose, the principles used to develop the tunnel alignment drawings would still be valid.

4.2.3 The Reference Route currently provides retaining walls in the base of the Copthall Cutting to allow future construction of the London facing turnouts. The spur itself would have to be tunnelled under both HS2 lines to complete the connection. The Birmingham facing turnouts are provided for with retaining walls and a box structure under HS2, close to and beneath the viaduct north embankment. The spur would also be tunnelled into this location.

4.2.4 This study proposes the spur connections in the form of grade separated double junctions. The principles of the arrangement are shown in the illustrations below.

4.2.5 The London facing turnouts (Figure 4.1), towards Ruislip Depot on an extended straight, are in a good location as it provides a 230 km/h junction. Other options are possible and depend on further design of the whole spur but it is preferable to adopt the Option B alignment as set out in the drawings at Appendix A. For example, with further refinement of the proposals there could be an opportunity to remove the need for the grade separation and reduce the track space requirements in the tunnel chambers, particularly if the future provision for the Heathrow Spurs is removed from the scheme.

4.2.6 The proposed vertical alignment in the vicinity of the CVT North Portal at West Hyde keeps the Birmingham facing turnouts (Figure 4.2) on the level grade or on flat planes with a shallow gradient. As mentioned above, there would be an opportunity to significantly reduce the track space requirements associated with these turnouts, if the future provision for the Heathrow Spurs is removed from the scheme.

HS2 in the Colne Valley 21 Tunnel Feasibility Assessment

Figure 4.1: London facing turnouts

PLAN

ELEVATION

Figure 4.2: Birmingham facing turnouts - Plan

HS2 in the Colne Valley 22 Tunnel Feasibility Assessment

4.2.7 Consideration has been given to the provision of a maintenance siding within the intervention gap between the Colne Valley Tunnel and the Chiltern Tunnel. Utilising the spacing of the bored tunnels, the siding could be located as a running loop between the main lines, with a spur siding to provide berthing and access for replenishment and maintenance of on-track MPV plant that would be a primary element of the tunnel and track maintenance, similar to the regime employed on High Speed One. This is indicated in Option B2 and would provide a loop siding not exceeding a 1:500 gradient capable of holding a planned maintenance train or a failed train in an emergency. This option could be provided separately from or in conjunction with any future Heathrow Spur connections .

4.2.8 FOI response 13-665 states , “More importantly, to gain the necessary depth, the tunnel would be lengthy and inevitably would then need to be continuous with the long Amersham (Chilterns) tunnel to the north” . The solution proposed in this study shows this is not the case and that the two tunnels can be constructed with a suitable gap and, in fact, beneficially with shared construction and maintenance infrastructure.

4.3 Operational Maintenance

4.3.1 The maintenance requirements resulting from the long viaduct will potentially be increased compared to a tunnel as the line will be exposed to more severe weather conditions. This section of route through the Colne Valley actually represents an atypical maintenance liability, sitting between the long sections of tunnel in the Chilterns and almost all the way to Euston. Therefore, an almost continuous tunnel route over the whole length will make maintenance regime consistent and economic. The limited exposure to open air at the intervention gap will significantly reduce general weather related maintenance issues.

HS2 in the Colne Valley 23 Tunnel Feasibility Assessment

5 Technical Constraints – Tunnels

5.1 Introduction

5.1.1 The principles of the tunnel options are dictated by the geology and the length of the tunnel drives that would be required.

5.1.2 The ground conditions over the length of the proposed Colne Valley Tunnel is dominated by Chalk for which a single type of tunnel boring machine (slurry) is suitable, similar to those required for the Chilterns Tunnel. Ground conditions east of West Ruislip change to the overlying Lambeth Group and London Clay, for which other types of tunnel boring machine are more suitable, usually an earth pressure balance machine.

5.2 Tunnel Spoil

5.2.1 The spoil arising from the proposed Colne Valley Tunnel will be received as chalk slurry at the West Hyde drive site. It is estimated that this could total approximately 1,000,000 cubic metres. This material will be identical to that produced by the Chiltern Tunnel which will be received in the same vicinity. As noted in the ES, it is intended that the spoil is first dewatered by centrifuge and then passed through plate presses to reduce the moisture content and make the material (known as ‘cake’) more suitable for transporting and incorporating into earthworks for landscape restoration or “local disposal”.

5.2.2 Processing will also make it suitable for road transport to any suitable destination, either for cement making or for backfilling of existing quarries or other voids. Whilst the transport distance and numbers of vehicles needed might be considered to add traffic to the local roads the location of this site and temporary access to the M25 mean it will quickly be on the strategic road network without affecting the minor roads when compared to the Reference Route proposals.

5.2.3 The decisions that need to be made will equally benefit decisions and infrastructure requirements for the Chiltern Tunnel spoil, with the two sites in close proximity able to share facilities more comprehensively than the completely different activities associated with the construction of the viaduct at this location. As well as the earthworks to excavate down to the track formation level the common activities will include diaphragm walling to form the portal walls and the creation of tunnel lining factory, spoil processing plant and material stockpiles. There will be common material importing and processing and shared supply lines should either tunnel require more or less resources at any one time.

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6 Impact and Cost Estimates

6.1 Introduction

6.1.1 This section considers the impacts which could result from the introduction of the proposed Colne Valley Tunnel and compares the key impacts already predicted for the Reference Route as set out in the Environmental Statement. It then sets out the estimated costs associated with the overall construction and associated mitigation measures of the Reference Route and the Tunnel Route Option B proposed in this study.

6.1.2 This is not a full environmental impact assessment but identifies the most significant elements and impacts of the proposed tunnel. The very nature of the tunnel solution does reduce the number of impacts in the locality with significant effects and therefore reduces the overall impact of the scheme through the Colne Valley and the Borough.

6.2 Significant Impacts – Construction

Reference Route

6.2.1 There are a number of clearly identifiable elements and consequent impacts of the Reference Route, which are directly related to the adoption of a surface solution, from the portal at Ickenham High Road to the northern end of the viaduct at West Hyde, adjacent to the A412, and which are avoided by the adoption of a tunnel. These can be listed as follows:

i. Construction of the West Ruislip Tunnel portal with associated headhouse at Ickenham High Road together with approach retaining walls extending over 600m to support the adjacent Chiltern Line, bridge carrying diverted public footpath and protect against the diverted Ickenham Stream.

ii. Footbridge over the line

iii. Diversion of the Ickenham Stream to River Pinn

iv. River Pinn Underbridge

v. Breakspear Road South Underbridge (online) and accommodation access road

vi. Copthall Retained structure – 200m long propped retaining wall to support buildings in an adjacent industrial estate.

vii. Heathrow Spur East Chord Retaining Walls

viii. Harvil Road Overbridges of Chiltern Line and Reference Route along with realignment of Harvil Road

ix. Moving of approximately 600,000 cu.m of soil from a section of high ground (Copthall Cutting) to form the construction railhead platform. This material is planned to be deposited on land near South Harefield, between Highway Farm and Park Lodge Farm, part of which is an unlined landfill.

x. Construction railhead on the Chiltern Line for removal of approximately 500,000 cu.m. of clay spoil from Northolt Tunnel (West) between Breakspear Road South and Harvil road. Railhead to be removed on completion of construction.

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xi. 3.4 km long Colne Valley Viaduct up to 15m high with associated abutment structures and intermediate supporting piers at approximately 20m intervals.

xii. Miscellaneous major drainage works and balancing ponds to provide adequate drainage of the surface railway

xiii. Diversion of High Pressure Gas main

xiv. 2.5 km Diversion of 275kV overhead power lines, including approximately 8 angle towers.

xv. Extensive mitigation works for ecological, landscape and flood risk impacts.

6.2.2 The majority of the above works will be accessed via either Breakspear Road South and/or Harvil Road which both lead to the B467 Swakeleys Road or other local roads before reaching the A412 and A4020 leading to the M40 Junction 1. This construction traffic will cause major local disruption to existing traffic along these roads and the surrounding area.

6.2.3 Some of the works, notably the main Colne Valley viaduct compound will be accessed from the M25 and A412.

6.2.4 Secondary work sites associated with the viaduct construction will require a temporary access causeway across the lakes. Whilst also affecting local roads these temporary works will severely disrupt if not curtail the recreational activities on the lakes, notably the Hillingdon Outdoor Activity Centre (HOAC), and, as noted previously, increase water pollution risks.

6.2.5 These works are in addition to such works as the National Grid Feeder Station and Ickenham Auto-transformer Station, accessed off Harvil Road and which will be required in the event of either solution being adopted.

Tunnel Options

6.2.6 The options presented by this study identify a feasible tunnel solution for the transit of the Colne Valley. The works required will be broadly as listed below:

i. Modification of existing maintenance railhead within Ruislip Maintenance Depot to remove tunnel spoil from Northolt tunnel (West) and either receive tunnel linings by rail precast offsite or materials for manufacture onsite.

ii. Ventilation Shaft within Ruislip Maintenance Depot incorporating the tunnel drive position for Northolt Tunnel (West) and reception position for Colne Valley Tunnel TBM. Also includes forming of London facing Heathrow Spur turnouts.

iii. Intermediate Ventilation Shaft adjacent to Harvil Road

iv. Colne Valley Tunnel North Portal at West Hyde including tunnel drive position for Colne Valley Tunnel and forming Birmingham facing Heathrow Spur turnouts.

6.2.7 The work to construct the Northolt Tunnel can be accessed from the Ruislip Depot access which connects directly to the A4180 West End Road and thence to the A40 Western Avenue and M40.

6.2.8 The work to construct the Colne Valley Tunnel, North Portal and Intervention Gap will share access arrangements already planned for construction of the Chiltern Tunnel and South Portal, using temporary accesses off the M25 as well as the A412 leading to M25 Junction 17.

6.2.9 Approximately 500,000 cu.m of chalk tunnel spoil will be removed by road to appropriate reception sites, initially with the intention that the material can be used commercially for cement making. Alternatively it could be used for the backfill and restoration of existing

HS2 in the Colne Valley 26 Tunnel Feasibility Assessment

quarries in the area suitable for receiving chalk spoil. These quarries are generally unsuited to general landfilling due to the permeability of the surrounding virgin material, but would be suitable for receiving chalk.

6.2.10 The intermediate Highway Farm Ventilation Shaft along with the National Grid Feeder Station and Ickenham Auto-transformer Station will need to be constructed by access from Harvil Road.

6.2.11 The local roads will therefore be subject to much less impact from construction traffic and for a shorter period.

6.2.12 The tunnel solution will not cause disruption to any of the community facilities, notably HOAC and Uxbridge Golf Course, and there will be no need to realign the 275kV overhead powerlines.

6.2.13 The programme effects of the tunnel solution can be considered as neutral. Where elements are potentially on the critical path appropriate action and procurement will ensure that the overall programme is not compromised. As noted in Section 3, it is expected that the tunnel solution instead of the viaduct will have less risk to programme and costs due to the ground conditions.

6.3 Significant Impacts – Operations

Reference Route

6.3.1 The operational impacts of the Reference Route are documented in the Environmental Statement and have been the subject of the consultation response submitted by London Borough of Hillingdon.

6.3.2 Apart from the permanent loss of areas of land and use of facilities described in the ES there are also ongoing impacts from noise of traffic on the surface railway and viaduct and deterioration of the viability or suitability of the remaining facilities for which mitigation is not yet identified.

6.3.3 The noise barriers proposed on the viaduct offer some mitigation but, at 3m height will result in restricted views across the valley for passengers in the trains. The effectiveness of these barriers has also been questioned and it has been suggested that the barriers should be 5m height to adequately mitigate the noise. It should also be noted that, at the operational speeds proposed, the time taken to transit this section of proposed surface line between the Northolt Tunnel and Chiltern Tunnel will be approximately 90 seconds and, on the viaduct itself, less than 45 seconds.

Tunnel options

6.3.4 In contrast, the proposed tunnel options will avoid any of these impacts, particularly loss of land, community facilities and landscape and visual impacts. The noise impacts of the tunnel will only occur at the open section near West Hyde, between the A412 and M25 which is already affected by the proposals for the Chiltern Tunnel and subjected to noise impacts from the M25.

6.3.5 Passengers will not particularly benefit from an extended open section as the transit period of 90 seconds is too short to allow adequate adjustment from artificial to natural light. Further, the pressure changes when leaving and entering the tunnels over such an interval will erode comfort levels and journey experience. Transit of the short open section at normal operating speeds will have less of an effect as the time interval will be less than 15 seconds.

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6.4 Cost estimates

6.4.1 A cost comparison has been undertaken between the HS2 Reference Route and the technically feasible Colne Valley Tunnel Option B proposed as a result of this study.

6.4.2 The costs are based largely on the information available in the November 2013 Estimate of Expense and the March 2012 Cost and Risk Model. Other cost data is taken from responses received from Freedom of Information requests. Where some elements have not been identified in these documents a budget allowance has been made drawn on experience of similar elements of work. Allowance is made for the Heathrow Spur turnouts to reflect the difference in approach to this provision.

6.4.3 The estimates exclude the cost of land or compensation for properties or businesses affected by the major surface works proposed.

6.4.4 In summary, the outcome of this comparison of costs is set out in the table below, which indicates that the adoption of a tunnel solution for HS2 to transit the Colne Valley is almost cost neutral, particularly when the cost of the impact on community facilities is taken into account.

6.4.5 The cost estimates only relate to the infrastructure and facilitating works related to the two options. No allowance has been made for the cost of property acquisitions, relocation of facilities, social costs or compensation.

6.4.6 More detail on the build-up of the costs is contained in Appendix E.

Table 6.1: Comparison of costs between HS2 and CVT Option B

Colne Valley Tunnel HS2 Reference Route Difference Option B2 £m £m £m

Potential Total £ 1,097.30 £ 1,161.33 £ 64.03

Excluding Heathrow Spur £1,035.68 £ 1,104.61 £ 68.93 turnouts

6.4.7 The cost differential between the proposed HS2 Reference Route and the tunnel solution described in this study shows that the adoption of a tunnel to transit the Colne Valley does not involve excessive additional cost and when all costs are taken into account is likely to be cost neutral whilst avoiding major impact on the borough and its residents who otherwise receive no benefit from the HS2 proposals.

6.4.8 In operational terms the alignment is suited to the speeds of 320km/hr which is nominally faster than the viaduct design speed of 300km/hr. The horizontal alignment is better and the vertical alignment of the tunnel avoids large variations in gradient, which are less severe than those proposed in the Chiltern Tunnel. Overall operational performance is likely to be similar but the consistent design speed and tunnel environment will make for a more comfortable passenger experience.

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7 Other options

7.1 General

7.1.1 This section describes other tunnel options which the study team has considered and notes why the option was not taken forward instead of the Colne Valley Tunnel proposal set out in this report. In the final paragraphs a key mitigation measure is described which is proposed if the tunnel is not adopted as the solution.

7.2 Westward extension of Northolt Tunnel

7.2.1 A key impact on the local area is identified as the extensive and prolonged construction activity which will occur at the surface between Ickenham High Road and Harvil Road. A possible mitigation would be the extension of the Northolt Tunnel westwards to Harvil Road.

7.2.2 This was considered, however, the vertical alignment and constraints associated with crossing the Colne Valley and River Pinn would result in the railway being too low as it crossed the lakes and have greater impact on the land uses in the valley with consequent significant effects. This makes a full tunnel over the whole section the best alternative option to the HS2 Reference Route.

7.2.3 Therefore a shorter tunnel extending the Northolt Tunnel westwards to beyond Newyears Green with the portal at Harvil Road would not result in a suitable solution and was not developed further.

7.3 Alignment running between Harefield and South Harefield

7.3.1 The potential of adopting an alignment for the Colne Valley Tunnel to avoid running under the landfills at Park Lodge Farm and Newyears Green was considered with an alignment running between Harefield and South Harefield.

7.3.2 Whilst this offered some benefit from the surface terrain it would result in running under many more residential dwellings in West Ruislip and therefore introducing greater concern to the community about the effects of construction and operation, particularly ground-borne vibration. The route would still have reverse curves and therefore offer no operational benefits.

7.3.3 Therefore this tunnel alignment was not considered further.

7.4 Extend the Chilterns Tunnel to West Ruislip

7.4.1 It is impractical to extend the length of the Chilterns Tunnel by relocating the point of commencement of the tunnel drives to West Ruislip, even though the ground conditions through this section comprise chalk. This is because it adds 7.7km to the drive length of the Chilterns Tunnel which is already 13km long in the HS2 scheme.

7.4.2 Furthermore, there is insufficient space at West Ruislip for a worksite to support an additional pair of tunnelling machines and boring the tunnel from the Chiltern Tunnel North Portal at Mantles Wood would impose more impacts in this locality and be unacceptable to these communities.

7.4.3 This option was not considered further.

7.5 Extend the Northolt Tunnel to West Hyde

7.5.1 Our studies indicate that the geology at the level of the tunnels changes from Chalk to the Lambeth Group at West Ruislip with London Clay further east. Different types of tunnel boring machine and spoil handling equipment are required for the Chalk and the Lambeth Group and

HS2 in the Colne Valley 29 Tunnel Feasibility Assessment

London Clay. A slurry TBM is the optimum type of machine for the chalk and an earth pressure balance TBM is the optimum type for the Lambeth Group and London Clay.

7.5.2 Whilst some interchangeability is possible over short distances, it is not efficient for the additional 7.7km length of tunnel and therefore it is also considered impractical to do this.

7.6 Required Mitigation for Reference Route

Treatment of landfills

7.6.1 Should the HS2 proposed Reference Route be adopted it will be necessary to undertake more comprehensive work to remove the contaminating material in the landfills at Newyears Green and Park Lodge Farm.

7.6.2 The proposed deposition of surplus excavated materials in the areas labelled as SPA 1 and known as Newyears Green is on top of contaminated material deposited over a number of years in previously worked sand and gravel pits. The site appears to have been selected purely on the basis of ease of access for construction traffic to avoid use of local roads. This is not considered to be a reasonable basis on which to label it sustainable placement.

7.6.3 The exact nature of the contaminating materials is not known due to a lack of records, which is typical of the period. However, it is known that a public water supply borehole in the locality is closed due to contamination of the groundwater from leachate emanating from these landfills, which do not have an engineered lining or cap. Covering these landfills with excavated materials to depths of 3 - 5m or more could have unexpected consequences on the behaviour of the landfill materials and the leachate and lead to increased and prolonged contamination which will also then be more difficult to remediate. This alone is contrary to the requirements of the Water Framework Directive which is one of the main drivers in Environmental Agency permitting, requiring that all controlled water achieve “good qualitative” status by 2015.

7.6.4 Whilst the newly placed material could act as a cap to reduce the infiltration of incident rainfall the weight of the material will compress the landfill materials potentially creating a surge of leachate into the groundwater. It could also push the leachate further into the groundwater and increase the pollution effect. It is possible the contaminating material actually intercepts the groundwater and therefore leachate is being produced by the flow of groundwater and not infiltration by rainfall. There is also no record of the potential production of landfill gas at the sites because of the current lack of a cap.

7.6.5 In any event, the effective sandwiching of this known source of contamination between the underlying chalk and associated aquifer and a significant depth of otherwise clean material will make any future remediation impossible or extremely expensive.

7.6.6 The material being placed on the SPA 1 is likely to be predominantly clays, sands and gravels from the London Clay and Lambeth Group formations forming the hill at Newyears Green being excavated. This effective cap on the landfills will also result in changes to the drainage regime of the site and will need careful consideration. The cap could also trap landfill gas and cause it to move through easier routes on the edge of the landfill and appear in currently unaffected places.

7.6.7 The “sustainable placement” of material in the proposed by HS2 is unacceptable and LBH believe that mitigation is required.

7.6.8 A considerable amount of investigation will be needed therefore to ensure that the simple placement of the surplus materials do not cause uncertain immediate or long term consequences. If deposition of excavated material is necessary in this area the only sustainable solution will be to remove the landfill materials and clean up the site before placing the clean excavated materials in the void. The landfill material will need to be taken to an appropriate facility for disposal or possibly treated on site.

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7.6.9 This will be a much more sustainable solution which leaves a lasting beneficial legacy and is the only option that should be considered. It does have the consequence of doubling the quantity of material being handled and putting more construction traffic on the road. However, the long term consequences of the ongoing pollution of a key water resource are more significant than the short term effects of this additional traffic, which demonstrates that sustainable placement needs to be considered completely and not just in one aspect.

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8 Conclusions and Recommendations

8.1 Tunnel options

8.1.1 The study has explored the options for the means of HS2 crossing the Colne Valley. It has considered the proposed HS2 scheme (Reference Route) and two further tunnel options. Consideration has been given to railway alignment, construction feasibility, environmental impacts and cost.

8.1.2 The options proposed in this report differ little in performance although Option B provides an improved alignment by reducing the reverse curves inherent in the Reference Route alignment. Furthermore, Option B enables provision of the turnouts in tunnel for the future construction of the Heathrow Spur, an important aspect of the brief. The viability of this spur and hence the need for this provision is not part of this study.

8.1.3 The study has found that:

i. A tunnel solution for crossing the Colne Valley that meets the requirements for HS2 is technically feasible;

ii. Option B enables provision of the turnouts in tunnel for the future Heathrow Spur

iii. The tunnel will have significantly fewer and much lower magnitude impacts on the environment, community, local residents and businesses; albeit with some additional local construction traffic.

iv. The passenger experience of travelling on HS2 will not be reduced by the extension of the tunnel and in fact could benefit from avoiding the discomfort of changes in air pressure when travelling into and out of tunnels over a short time interval;

v. The certainties of delivery are greater in comparison to the risks associated particularly with the foundations of the viaduct and greater mitigation measures which will be required in dealing with local ground conditions and existing landfill contamination.

vi. The costs of the tunnel would be marginally higher, but this does not take account of property or community costs.

8.1.4 Overall therefore, it can be concluded that there is a feasible tunnel solution which will allow HS2 to transit the Colne Valley in a manner which avoids the extensive work proposed on the surface, the consequent negative construction impacts over a 7 year period and the permanent operational noise and visual impacts.

8.1.5 It is recommended that Tunnel Option B should be adopted as the means of HS2 crossing the Colne Valley

8.2 Other mitigation

8.2.1 Should a tunnel across the Colne Valley not be adopted then it is essential that amongst many other controls on construction an undertaking is made to clean up the landfill at Newyears Green and Park Lodge Farm before any material is deposited in these areas designated for sustainable placement.

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REFERENCES

Ford, J.R., Burke, H., Royse, K. R. & Mathers, S. J. (2008) The 3D geology of London and the Thames Gateway: a modern approach to geological surveying and its relevance in the urban environment. Cities and their underground environment, 11 th European e-conference of International Association for Engineering Geology, Madrid, Spain, September 2008, pp15-19.

Aldiss, D. T. (2013) Under-representation of faults on geological maps of the London Region: reasons, consequences and solutions. Proceedings of the Geologists’ Association, Volume 124, pp929-945.

Mathers, S. J., Burke, H. F., Terrington, R. L., Thorpe, S., Dearden, R. A., Williamson, J. P. & Ford, J. R. (2014) A geological model of London and the Thames Valley, southeast England. Proceedings of the Geologists’ Association, Volume 125, pp373-382.

HS2 in the Colne Valley 33 Tunnel Feasibility Assessment

Appendix A Drawings

A.1 Engineering

A.1.1 30780 / 2001 / 011 – Plan of Routes

A.1.2 30780 / 2001 / 012 – Tunnel Option A : Sections

A.1.3 30780 / 2001 / 013 – Tunnel Option B1 : Sections

A.1.4 30780 / 2001 / 014 – Tunnel Option B2 : Sections

A.2 Geology

A.2.1 30780 / Geo 1 - Geology Plan

A.2.2 30780 / Geo 2 - Option A Schematic Geological Cross Section

A.2.3 30780 / Geo 3 - Option B1 Schematic Geological Cross Section

A.2.4 30780 / Geo 4 - Option B2 Schematic Geological Cross Section

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Appendix B Delivering the Colne Valley Tunnel

B.1 West Ruislip

HS2 currently propose to construct the northern part of the Northolt Tunnel from the portal at West Ruislip. A worksite will be created running alongside the northern side of the Chilterns Railway and along the southern edge of the Ruislip Golf Course between Ickenham High Road and Breakspear Road South. Within this site will be located a 600m long retaining cutting/portal structure, approximately 30m wide. The portal will be used to launch two TBMs towards Green Park Way. The length of the portal is dictated by the need to bring the railway to the surface at an appropriate gradient for railway operations and launch the TBMs/place the tunnels with sufficient cover of ground above the tunnels. Tunnelling operations would be served by the linear site, which will incorporate a conveyor to take spoil to a railhead for onward disposal by railway and a narrow gauge railway to deliver segments and sundries.

With the Colne Valley Tunnel there is no requirement for the portal at West Ruislip. However, a shaft is required to receive the TBMs from West Hyde and to launch TBMs for the Northolt Tunnel as in the HS2 scheme. This shaft could be located at the position of the West Ruislip portal (at the location of the headhouse as a permanent ventilation and access shaft is required near this location) or could be located at another location nearby that is less impactful.

Approximately 600m downline towards London lies TfL’s London Underground depot at Ruislip. The depot covers an area of approximately 10 ha and serves the Central line. There are connections at this depot onto the mainline railway and also onto the Metropolitan and Piccadilly lines. There are extensive sidings, sub-stations and also buildings. The depot also has dedicated road entrance off the A4180 West End Road leading directly to a junction on the A40.

To the south and west of the depot lies an area of farmland. The northern part of this farmland, adjacent to the Uxbridge Branch of the Metropolitan railway, is fallow.

The depot offers a good location for the West Ruislip Shaft and being located within railway land, it is screened by the depot and the railway lines around it and it is located some 50-70m from the nearest noise sensitive façade. Being industrial land, there is no change in land usage either for construction and operation. The depot provides the opportunity to utilise existing sidings or provide new dedicated sidings for spoil disposal with route options onto the rail network. There is also an established and dedicated road access.

The location of the shaft within the depot will need to consider the following:-

° A position clear of main NR and LU (Central) lines;

° Impact on existing depot operations including lines connecting the depot to the railway;

° Location clear of depot buildings;

° Provision of spoil handling and tunnel lining manufacturing and delivery;

° Proximity to a tie-in for a spur to Heathrow;

° Availability of additional land immediately to the south-west of the depot.

However, the impact of the shaft and the works can be mitigated by providing new depot facilities with the former agricultural land to the south. It is understood that TfL is considering depot expansion and these works provide TfL with the opportunity to deliver them.

There are a number of options to deliver the Colne Valley Tunnel:

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1. Re-locate the proposed alignment of HS2 to the south-west to bring it under the depot. This is a lateral shift of about 30m. This would allow any shaft to have direct vertical access onto the tunnel alignment to receive the TBMs from West Hyde and to construct the western half of the Northolt Tunnel to Green Park Way. Something similar has been achieved by the shaft at Limmo for Crossrail. The shaft can provide ventilation and access/egress and emergency facilities, if required.

2. Leave the railway alignment unchanged and construct a shaft off-line within the depot, but connect this with an adit or adits to the proposed tunnels. It is not uncommon, to be unable to provide a shaft directly over the proposed location of the tunnels, particularly where land is not available, such as in urban areas. Tunnelling for the Jubilee Line between Waterloo and Green Park was carried out from a shaft located in Jubilee Gardens next to the River Thames and connected to the running tunnels located below York Road by a 200m long access adit and 43m deep shaft. The Gotthard Base Tunnel required offset access tunnels at 3 locations along its length in addition to access from either portal, where access was considerably more difficult than at West Ruislip. At Ruislip Depot the access adit would probably need to be 30- 50 m long.

In the permanent case, the shaft would provide the same facility offered by HS2 proposed ventilation shafts.

B.2 Heathrow spur at West Ruislip

Taking HS2 underground between West Hyde and West Ruislip means that it is necessary to also locate the spurs for any proposed link to and from Heathrow underground. To do this at West Ruislip requires the construction of two tunnels big enough to accommodate the spur turnouts/junctions. It also requires the two bores on each alignment to be separated vertically to allow the tunnels to/from Heathrow to pass across the HS2 lines. Making the Heathrow Spur connections at West Ruislip then allows the portion of the Heathrow route between the turnout and the shaft to also form the access tunnel for the HS2 tunnels to Green Park Way. This can be formed in two ways either by launching the TBMs from the depot shaft and then later creating the connection cavern to meet with the tunnel from West Hyde or forming the access tunnel and connection cavern first using sprayed concrete lining prior to launching the TBMs.

Each turnout/junction tunnel would require the construction of a tapered cavern, wide enough at one end to receive a TBM from West Hyde and to allow the passage through of another TBM from the depot shaft to be launched from the tapered end. These structures are likely to be about 20m wide at their widest end and 10m wide at the taper and up to 300m long.

The access adit and caverns would probably be located in the Chalk for which groundwater control would probably be required. Similarly sized caverns have recently been constructed on Crossrail at Stepney Green requiring extensive groundwater control.

Alternatively, if the route of HS2 were shifted south-west then the junctions could possibly be made within cut-and-cover boxes within the footprint of the depot. These can be combined with the TBM launch shafts.

Importantly, the shaft or box used for the construction of HS2 can also be used at a later date for the construction of the Heathrow Spurs.

The following figures illustrate the potential arrangement at Ruislip Depot for driving Option A or Option B . Note - These are conceptual, schematic and not to scale.

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Figure B1: Option A - No Heathrow Spur

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Figure B 2: Option B – Grade separated Heathrow Spur with turnout caverns

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B.3 Tunnelling method

The Colne Valley Tunnel would be constructed within the Chalk and it would be most appropriate to do this using a slurry TBM. The principal features of a slurry TBM are the ability to pressurise the cavity formed by the TBM and provide support to ground. This is important should the chalk be found to be weathered and potentially soil-like where it underpasses the Colne valley. The slurry system provides the means of managing groundwater found within fissures within the chalk and of transporting the cut chalk back to the surface, which being a soft rock is highly susceptible to breaking down into its constituent silt parts. The slurry system allows the spoil to be pumped back to West Hyde, where it can be processed by pressing it into a ‘cake’ before onward transportation. The tunnel would be lined with pre-cast concrete segments which would be delivered into the tunnel at West Hyde. It is probable that the segments would be made at another site and delivered to West Hyde in the same way as it would need to be done for the Chilterns Tunnel. Essentially, the tunnel support systems for the Colne Valley Tunnel would mirror those for the Chilterns Tunnel and therefore there is the potential for some common facilities to be used during construction.

B.4 Spoil disposal

Chalk is a useful commodity and can be used as engineered fill; it is also a valuable commodity as it is an essential component of cement (forming 70% of the material). Once the chalk is in a slurry, transporting it via a pipeline and treating it or using at the site of its destination is one disposal option. Chalk currently being quarried in the Chilterns (at Kensworth near Dunstable) is transported via a 91.7km (57 mile) long pipeline to Rugby where it is used in cement manufacture. This facility has been doing this since the late sixties and currently consumes chalk at a rate of 4000 cu metres of slurry per day.

As a fill material, the treated chalk can be used to infill and landscape existing quarries and gravel pits in the region. There are numerous quarries and gravel pits and a detailed examination needs to be made of the available capacity for landscape recovery and restoration to adopt this option.

B.5 Sprayed concrete lining

The sequential excavation (mining) of the ground using excavators and the placement of immediate support using sprayed concrete lining (SCL is the acronym that refers to this process)

This process would be used for forming caverns outside the normal TBM bore diameter or for the creation of the Heathrow Spur turnouts and required cross passages and shafts.

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Appendix C Alignment and Track Maintenance through the Tunnels

C.1 Track Alignment, tunnel option B

The proposed track and therefore tunnel alignments follow the principles of employing curvature, gradients and transitions within the ‘normal’ criteria employed by HS2. The proposed tunnel route offers a smoother alignment without the reverse curves that are inherent in tunnel option A, which are dictated by interfaces with the surface route and therefore not a necessary constraint on a tunnel solution.

This generally applies to both horizontal and vertical alignments and without any provision for future Heathrow Spur connections these alignments would be very smooth. The provision of turnout chambers under the Ruislip Depot incorporates approximately 10 m vertical separation such that the London-bound connection passes under the main HS2 northbound (Down) tunnel with over one diameter of clearance and avoids the larger foot-print, with sweeping curves and reverse curves that would be associated with grade separation from co-planar main line tunnels.

Turnouts will provide for up to 230 km/hr facing and trailing connections to the main lines at both Ruislip and West Hyde. Care will be needed in positioning construction and access shafts, so that the access to both running tunnels can be achieved where the grade separation would make cross-passages unsuitable and cross-passages can be provided at or about the location where co-planar tracks are achieved.

At West Hyde, subject to the inclusion of any maintenance sidings, the provision for future Heathrow Spurs will be passive, as the Up connection (towards Heathrow) would climb from the main line alignment (limited to 1:500 gradient if sidings are provided) and either cross over the main lines and siding on a bridge, before entering the portal of the Heathrow spur tunnel or continue further south, entering a tunnel , which would pass over the main HS2 line tunnels, as they fall more steeply to the nadir (lowest point) under the River Colne. The location of the exit portal, coming from the northbound Heathrow Spur tunnel, would be located within the intervention gap cutting face and the track would fall towards the main line and become co- planar with that line before the switch and crossing connection.

The more detailed description of the alignment is as follows:

The vertical alignment ties into the current HS2 alignment with a 0.456% rising gradient from 18000 m, continuing to chainage 19170 m, where the grade separation to accommodate the Heathrow Spur connections begins. The Up Main enters a 40000 m radius hogging curve and then falls at a gradient of 0.33% until chainage 22150 m where a sagging curve of 40000 m radius forms the nadir. The Up Heathrow Spur passes under the Down Main running tunnel at approximately 22100 m and the southbound connection is located on the gradient on the London side of the sagging curve at approximately 21700 m.

The Down Main continues from chainage 19170 at 0.456% to a hogging curve of 40000 m radius around its summit at approximately 20000 m chainage, where the grade separation is approximately 5 m. The Down Main then falls at a gradient of 0.3% for some 480m to a sagging curve, also of 40000 m around chainage 20750 m at the South Ruislip Vent shaft and rises at 0.3% from there to approximate a summit at chainage 22300 m, passing over the Southbound Heathrow Spur at 22080.m. From this hogging curve, the gradient falls northwards at 0.3% becoming co-planar with the Up main bore at 24000 m. If necessary, to accommodate cross-passages between West Ruislip and Highway Farm shafts, these gradients (between 22300 and 24000) could both be steepened, noting that they are both falling gradients with respect to operational running.

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The vertical alignments north of Highway Farm remain co-planar and continue with average gradients of 0.2% passing under the River Colne and then climbing at 2.0% (1 in 50 ) for 200 m before entering a hogging curve into the West Hyde Intervention Gap and a 0.2% (1 in 500) to accommodate the emergency crossovers and any potential loop and maintenance sidings. The alignment then enters the Chiltern Tunnel at a slightly lower level and regains the current HS2 alignment.

C.2 Maintenance Opportunity

It can be assumed that the maintenance regime for HS2 will be largely based upon that for HS1. Within the running tunnels, one of the principal maintenance routines will be the track inspection and this can largely be carried out using video and some remote auto-recognition techniques associated with a Multi-purpose Vehicle (MPV) or track geometry measurement train. Given the predominance of tunnel track between Euston and The Chiltern Tunnel, if the CVT proposal is adopted, there would be no requirement to take ballast and sleeper supply trains, tampers or any ballast cleaning machines, into the tunnels. Therefore the requirement for substantial engineering train holding would be reduced to those trains associated with tunnel and rail inspection, grinding and rail replenishment, as required.

Potential exists to provide a maintenance facility to stable an MPV and hold inspection coaches or rail grinders, between the main HS2 lines through the West Hyde Intervention Gap. Opportunities for a long siding (up to 900 m long) were examined but the impact of a maximum 1:500 (0.2%) gradient along such a siding, would drive the Chiltern Tunnel North portal some 25 – 30 m deeper than the current proposal. However, a siding of up to 400 m train standage, plus signalling distances at both ends, could be accommodated between turnouts at both ends of the Intervention Gap, with a short spur siding at the London end to stable engineering vehicles. This would also potentially deliver the HS2 emergency crossovers and a loop siding capable of holding a 400 m train, clear of the main lines.

Such an arrangement is suggested in Option 2 for West Hyde, which would be able to accommodate the provision for Heathrow spurs, crossovers and the loop and MPV sidings, but it is only shown as an indication of the potential option available and does not constitute the main option proposed.

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Appendix D Correspondence

D.1 Sustainable Placement Areas

D.1.1 E-mail John Michealides / Ian Thynne 6 th August 2014

From: John Michaelides Date: 6 August 2014 10:43 Subject: RE: Sustainable Placement of Excavated Material To: Ian Thynne Cc: Colin Ovens

Ian

That is correct. The sustainable placement sites relate to the construction of the railhead.

Regards John

From: Ian Thynne [mailto:[email protected]] Sent: 04 August 2014 11:17 To: John Michaelides Subject: Sustainable Placement of Excavated Material

John,

I have been asked to clarify the the source of material to be used in the sustainable placement sites in Hillingdon.

I understand from our previous discussions that the placement sites were solely related to the excavation of the Harvil Road railhead (level access with the Chiltern Line). The sustainable placement sites will not take tunnel waste from either the M25 Chiltern tunnel or the Northolt/Ruislip tunnel.

Is this correct.

Kind regards

Ian Thynne Principal Sustainability Officer

direct: 01895 558 326 general: 01895 556 000

Planning Specialists London Borough of Hillingdon Civic Centre, High Street, Uxbridge Middlesex UB8 1UW

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Appendix E Cost Estimate

E.1 Introduction

The cost estimates have been prepared based on information published in relation to HS2 in the Estimate of Expense dated Jan 2013 and associated back-up data as well as the Cost and Risk Model dated March 2012.

Further cost information is used from Freedom of Information requests where specific questions have been asked and response received.

Where there is insufficient information about some of the key component of the scheme, a reasonable estimate of the associated cost for that component is included.

These costs do not include the cost of property acquisitions, relocation of facilities or wider economic and social costs.

E.2 HS2 Reference Route

The estimate of the costs for the Reference Route has been built-up from the major elements of work identified, with an allowance made for other aspects which have not been explicitly costed in the published estimates.

E.3 Proposed Colne Valley Tunnel Option B2

The costs for the tunnel option proposed utilises the same basis for estimating with the application of rates or costs for similar items of work already included in the published figures. Whilst there might be some difference between the proposals and the scope of work contained in the item referred to, this is unlikely to be significant in the overall cost figures and demonstrates the broad correlation between them.

E.4 Programme

Consideration has been given to the programme implications of the proposal, working from the programme shown in the Environmental Statement covering CFA 6, 7 and 8. This is summarised in an overview of the likely timetable for key critical path packages of work and shown in Table E2 below.

Elements have been added to that contained in the ES where appropriate to reach an equivalent stage of the Reference Route to enable rail systems to be installed.

In summary, the programme shows that the Colne Valley Tunnel itself can be constructed in a much shorter time than the viaduct and the critical elements to the programme relate to commencement of the Northolt Tunnel from Ruislip Depot. However, this is still well within the potential time to construct the 13.2 km long Chiltern Tunnel.

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Table E1 : Cost Estimates for HS2 Reference Route and Colne Valley Tunnel Alternative

HS2 Reference Route : components of Colne Valley crossing

Note: Components are listed in order along the route

Published or Cost basis Component estimated cost (Published in Estimate of Expense Jan 2013 £m unless noted otherwise)

1 A ventilation shaft at South Ruislip Item 2.3.8 £ 33.85 (2.8km from West Ruislip) 2 7.8km Northolt tunnel from the West Item 2.1.6 £ 533.16 Ruislip portal to Greenpark WayVS 3 Tunnel Systems - Northolt Tunnel £ 30.37 half Item 6.7.2 (to Greenpark Way) 4 600m long tunnel portal at West Ruislip, Item 2.2.3 incorporating a headhouse for ventilation £ 82.77 and access/egress 5 Ickenham Stream footbridge £ 2.00 budget allowance 6 600m long Ickenham Stream diversion to budget allowance £ 2.00 R Pinn 7 R Pinn underbridge £ 1.00 budget allowance 8 Breakspear Rd South Underbridge £ 5.00 budget allowance 9 min 500,000 cu.m from forming the Spoil disposal in SPA and over wide tracts £ 5.55 railhead placed in SPA 1 of land north and south of the route.

10 Turnouts/junction for future tie-in to qtr of total Retaining Walls in Country £ 30.81 Heathrow Spur - London facing South Item 3.3.3 11 Harvil Rd Overbridge (HS2 and Chiltern budget allowance £ 7.00 Line) and road realignment 12 4.3 km long surface railway formation Based on Infrastructure Rate from HS2 Cost £ 4.18 between West Ruislip and West Hyde and Risk Model March 2012 App A 13 3.4km viaduct over the River Colne with FoI 1054 and follow-up e-mail 23 May 2014. solid 1.4m high barrier on each side and Note: The extent and height of noise £ 142.00 3m noise barrier in certain locations barrier provision is unclear and should (approx 6 km total) increase. 14 600m and 250m of noise barriers 3m high£ 2.00 budget allowance 15 Tilehouse La overbridge £ 5.00 budget allowance 16 Based on Infrastructure Rate from HS2 Cost 1700m cutting 20m deep £ 23.72 and Risk Model March 2012 App A 17 Based on Infrastructure Rate from HS2 Cost 700m embankment 8m deep£ 0.93 and Risk Model March 2012 App A 18 Based on Infrastructure Rate from HS2 Cost 7.7km PW,OLE, sig and comms£ 24.15 and Risk Model March 2012 App A 19 Turnouts/junction for future tie-in to qtr of total Retaining Walls in Country £ 30.81 Heathrow Spur - Birmingham facing South Item 3.3.3 20 Balancing Ponds and drainage £ 5.00 budget allowance 21 HP Gas main diversion £ 3.00 budget allowance 22 Diversion of 275 kV O/H power lines £ 15.00 budget allowance 23 Various Utility Works £ 10.00 budget allowance 24 River Colne realignment £ 5.00 budget allowance 25 Mitigation works and planting - Colne from FoI 1054 and follow-up e-mail 23 May £ 23.00 Valley 2014 26 Mitigation works and planting - budget allowance £ 10.00 remainder of borough TOTAL£ 1,037.30 Uncommited Major additional mitigation works a Removal of contaminated material at Removal of 500,000 cu.m of contaminated Park Lodge Farm and depositon into new £ 60.00 material, transport and deposition into engineered landfill. new engineered landfill

POTENTIAL TOTAL for Reference Route£ 1,097.30

POTENTIAL TOTAL for Reference Route £ 1,035.68 (excl Heathrow Spur Turnouts)

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Colne Valley Tunnel Alternative Option B2 Note: Components are listed in order along the route

Published or Cost basis Component estimated cost (Published in Estimate of Expense Jan 2013 £m unless noted otherwise)

1 A ventilation shaft at South Ruislip as Item 2.3.8 £ 33.85 (2.8km from West Ruislip) 2 7.1 km Northolt tunnel from the Ruislip proportional to Northolt tunnel Item 2.1.6 £ 485.31 Depot to Greenpark Way 3 incl. drive and reception - similar to Vent Shaft at Ruislip Depot£ 41.42 Greenpark Way Shaft Item 2.3.6 14 This will be permanent and available for Modification of Ruislip Depot railhead£ 10.00 future use by TfL/LUL 11 Tunnel Systems - Northolt Tunnel£ 24.73 proportion to Northolt tunnel Item 6.7.2 as 4 Turnouts/junction for future tie-in to basedthey become on Item contiguous. ref 2.1.3 (SCL tunnels - £ 42.57 Heathrow Spur - London facing Victoria Road (OOC) twin track) 5 6.6 km Colne Valley Tunnel from West based on Item 2.1.7 (Chiltern tunnel 13.3 £ 416.83 Hyde to Ruislip Depot km length) 6 Ventilation shaft at Highway Farm/Harvil similar to Chalfont St Peter Shaft Item £ 17.13 Rd. 2.3.10 7 similar to Chiltern Tunnel South Portal CVT tunnel portal at West Hyde£ 23.17 Item 2.2.4 8 Turnouts/junction for future tie-in to based on Item ref 2.1.4 SCL tunnels - OOC £ 14.15 Heathrow Spur - Birmingham facing East Turn Out Cavern 9 Cutting to form Intervention Gap Based on Infrastructure Rate from HS2 Cost £ 15.35 between CVT and CT portals and Risk Model March 2012 App A 12 Tunnel Systems - Colne Valley Tunnel + proportion to Northolt tunnel Item 6.7.2 as £ 26.82 West Hyde approach they become contiguous. 10 Tilehouse La overbridge£ 5.00 budget allowance 13 transport cost only as material avaialble for CV Tunnel spoil disposal £ 5.00 commercial use

Total for CVT Option B2£ 1,161.33

diff from POTENTIAL TOTAL for HS2 £ 64.02 Reference Route TOTAL for CVT Option B2 £ 1,104.61 (excl Heathrow Spur Turnouts) diff from POTENTIAL TOTAL for Reference £ 68.92 Route (excl Heathrow Spur turnouts)

Colne Valley Tunnel Alternative Option A - Similar to Option B but excluding Heathrow Spur turnouts

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Table E2: Indicative Overview Programme

Option Activity Duration (months) Cumulative All TBM order, manufacture, delivery 19 19 months and assembly prior to drive. Construct working sites

HS2 Surface works (cuttings and 21 40 months Reference embankments) Route Northholt tunnel (7.8km) incl West 33 52 months Ruislip Portal Colne Valley Viaduct 51 70 months Tilehouse Lane overbridge and 45 64 months cutting Chiltern Tunnel – South Portal 63 82 months plus 13.2 km tunnel twin drive

Colne Ruislip Depot Compound, Vent 24 43 months Valley Shaft and adits Tunnel Route Northolt Tunnel (7.2 km) 30 73 months Tilehouse Lane overbridge and 45 64 months cutting** Colne Valley Tunnel (6.6 km) incl 27 46 months West Hyde Portal Chiltern Tunnel – South Portal 63 82 months plus 13.2 km tunnel twin drive Developed from Construction Programmes in ES (CFA 6, 7 & 8).

Longest set of works is highlighted in BOLD for each option ** this piece of work is critical for starting the Colne Valley Tunnel, but possible scope could be reduced to enable CVT portal and drive to start after initial 19 month period.

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