Tunnelling in Hillingdon

What we’ll cover today

• An overview of the area and how are the tunnels dug

• Where the tunnels will be dug and why this has changed: the tunnel is nearer to properties, but all impacts can be managed

• How this might affect you and how we’ll be managing the impacts – both during the construction of the tunnels and when the railway starts to run

• When the tunnelling will start and how long it will take

• How else we are talking to people about this subject and what happens next

How will the tunnels be dug?

Tunnel Boring Machine Overview

▪ Six pre-cast concrete segments form a ring

▪ Produced off-site facility at the Isle of Grain, Kent and delivered to the West RuislipPortal by rail

▪ Train deliveries are anticipated to be 1 per day

▪ Saves 34,000 truck movements overall

▪ Transported to the cutting head using a specialist multi-purpose vehicle

Segment Supply

We will keep you informed about our above ground proposals for tunnelling logistics

▪ Excavated material from the TBM is removed via a conveyor system

▪ Treated and prepared for reuse

▪ Material from the tunnel is being reused at West Ruislip as backfill material and on the sustainable placement areas

Excavated Material

We will keep you informed about our above ground proposals for tunnelling logistics

Where are the tunnels in your area?

Changes to the Alignment

▪ Change since the Hybrid Bill alignment

▪ Horizontal alignment has moved ‘northwards’ in some areas by approximately 12.5m

▪ Vertical alignment has changed, with some areas now approximately 2.7m shallower

▪ The “alignment for construction” is within the Limits of Deviation

▪ We are confident settlement and environmental effects arising from the “alignment for construction” can be mitigated

Changes to the Alignment

Centreline

Limits of Deviation

Limits of Deviation

Changes to the Alignment

▪ Change since the Hybrid Bill alignment

▪ Horizontal alignment has moved ‘northwards’ in some areas by approximately 12.5m

▪ Vertical alignment has changed, with some areas now approximately 2.7m shallower

▪ The “alignment for construction” is within the Limits of Deviation

▪ We are confident settlement and environmental effects arising from the “alignment for construction” can be mitigated

How is the tunnel alignment decided?

Ground Conditions

ObstructionsSegment Delivery

Existing Railway

+ + +

Limits of Deviation

EnvironmentTrain

Operability

+ +Cost

+Establishing the Rules

3 Phases of Design Evolution

Ickenham Close & Blenheim CrescentChanges since the Hybrid Bill

Ickenham Close:Approximately 2m change in the horizontal alignment

Blenheim Crescent:Approximately 4.5m change in the horizontal alignment

Alignment for Construction

Limits of Deviation

Cross Section

Measured from the top of the London Tunnel, i.e., shallowest point.

Herlwyn Avenue

Changes since the Hybrid Bill

Approximately 11-12m change in the horizontal alignment

Alignment for Construction

Limits of Deviation

Cross Section

Lawn Close, Almond Close, Cherry Close & Roundways

Changes since the Hybrid Bill

Approximately 12 to 12.5m change in the horizontal alignment

Alignment for Construction

Limits of Deviation

Cross Section

Bridgwater Road

Changes since the Hybrid Bill

Approximately 12 to 12.5m change in the horizontal alignment

Current

Limits of Deviation

Cross Section

Rabournmead Drive

Changes since the Hybrid Bill

Approximately 9.5m change in the horizontal alignment

Alignment for Construction

Limits of Deviation

Cross Section

Vertical Alignment (depth)

Approximately 21.5m

How might this impact you and what are we doing to reduce those impacts?

Tunnel Boring Machines

Best in class machinery

▪ Reduce ground settlement

▪ Reduce environmental impact

▪ High safety

▪ Far quicker than alternative forms of tunnelling

▪ High degree of precision

▪ Low manpower

Managing Settlement

MonitorAssess ProtectRecord Repair

HS2 is responsible for any damage caused to your house as a result of our works Constructing tunnels always causes small movements in the ground. Settlement is the technical

term given to the way the ground moves around an excavation after it has been dug out.

Guide to ground settlementInformation Paper C3: Ground Settlement

Ass

ess The level of

ground movement and potential effect on buildings will be determined

HS2 is responsible for any damage caused to your house as a result of our works

▪ Well established process used on other tunnelling projects such as Crossrail

▪ Conservative assessment that identifies as many properties as possible in the initial phases and then hones in on those which might be at risk

▪ Assessment concluded that residential properties in Hillingdon:▪ Category 0 (negligible damage) 37% e.g., hairline cracks.▪ Category 1 (very slight damage) 16% e.g., fine cracks easily treated,

perhaps isolated slight fractures in building, cracks in exterior bricks upon close inspection

▪ Category 2 (slight damage) 47% e.g., Cracks easily filled. Redecoration probably required. Several slight fractures inside building. Exterior cracks visible; some repointing may be required for weather‐tightness. Doors and windows may stick slightly.

Ass

ess The level of

ground movement and potential effect on buildings will be determined

HS2 is responsible for any damage caused to your house as a result of our works

Ass

ess The level of

ground movement and potential effect on buildings will be determined

HS2 is responsible for any damage caused to your house as a result of our works

▪ Well established process used on other tunnelling projects such as Crossrail

▪ Conservative assessment that identifies as many properties as possible in the initial phases and then hones in on those which might be at risk

▪ Assessment concluded that residential properties in Hillingdon:▪ Category 0 (negligible damage) 37% e.g., hairline cracks.▪ Category 1 (very slight damage) 16% e.g., fine cracks easily treated,

perhaps isolated slight fractures in building, cracks in exterior bricks upon close inspection

▪ Category 2 (slight damage) 47% e.g., Cracks easily filled. Redecoration probably required. Several slight fractures inside building. Exterior cracks visible; some repointing may be required for weather‐tightness. Doors and windows may stick slightly.

▪ Specialist monitoring equipment may be installed in your area:▪ Before: monitor the existing

ground movement▪ During: ensure movement

caused by tunnelling is as predicted

▪ After: monitor the ground until it is back to a normal rate

HS2 is responsible for any damage caused to your house as a result of our works

Mo

nit

or Specialist

equipment will be installed to monitor ground movements before, during and after construction

▪ Any property identified as experiencing 10mm or more settlement qualifies for a pre-condition survey:▪ A visual inspection of the inside and outside of a building or property

to record its condition▪ Independent surveyor▪ Photographs and notes of any defects

▪ Approximately 130 residential properties in LB Hillingdon who qualify▪ Alignment change has resulted in approximately 10% more properties

qualifying

▪ Condition surveys are conducted 3 months in advance of tunnelling

▪ We will contact those who are eligible in the near future

HS2 is responsible for any damage caused to your house as a result of our works R

eco

rd Condition surveys will be completed before construction to identify if, and what repairs are required

▪ Properties that have been identified as potentially experiencing moderate to very severe damage (Damage Category 3 to 5) may need additional protection▪ In Hillingdon no residential properties fall into these categories

▪ A mitigation strategy is set out for properties who do qualify:

▪ Requirement for any protective works or monitoring is established and designed

HS2 is responsible for any damage caused to your house as a result of our works

Pro

tect Structures that

have been identified as at risk of being damaged will be protected

Obligation to make good any damage that has occurred due to the tunnelling works

▪ If you think our work has caused damage to your building, you can let us know and we will carry out a second survey.

▪ We will compare this with the first survey and, if it shows our work has caused damage, you can claim for reasonable costs to repair the damage.

▪ You must agree these costs with us before you start the repairs.

▪ You can make a claim up to two years from the date the railway opens to the public

▪ If you are concerned about damage to your property resulting from our works, regardless of whether you qualify for a pre-condition survey, you can contact us.

HS2 is responsible for any damage caused to your house as a result of our works R

ep

air

Any queries about defect surveys or how we are managing settlement, please contact our dedicated Property team by email at property@scsrailways.co.uk or contact the HS2 Helpdesk on 08081 434 434

Noise and vibration during tunnelling

This can be perceived as:• Air-borne noiseAudible noise travelling through air, can be perceived inside or outside a building• Ground-borne vibrationPerceived as a physical sensation in the body, inside or outside of a building• Ground-borne noiseInside a building, small vibration in the ground can manifest themselves as audible noise (ground-borne noise)

Construction activities can generate physical vibration which can then travel through air and/or ground.

Noise and vibration during tunnelling

▪ HS2 completed an Environmental Impact Assessment in 2013 which set out the impacts and effects of tunnelling

▪ The Code of Construction Practice (CoCP) and Information Paper E23 set noise and vibration thresholds for effects and the actions that will be taken if thresholds are exceeded.

▪ Assessments concluded that no residential properties will be significantly affected by tunnel boring activities

▪ Any effects will be temporary and only experienced for a few days when the TBM is nearest to each individual property

▪ Assessments are being undertaken to confirm the conclusions of the previous assessments

▪ Noise and vibration monitoring will be completed along the alignment to ensure that predictions are correct and to update assessments as tunnelling progresses.

Noise and vibration during operationHave the forecast noise and vibration impacts changed?

▪ The design changes will lead to slight changes in impacts but these can be mitigated

▪ Significant change not expected

▪ No sig effects identified in Environmental Statement as a result of mitigation in the Hybrid Bill Design

▪ There are negligible impacts at the majority of properties – many of these directly above the tunnels

▪ Work continues to finalise the mitigation in the tunnels

▪ Following slides set out our approach to mitigating ground-borne noise and vibration

HS2 Policy set out in

Information Paper E21

(IPE21)

Noise and vibration during operation

What is operational ground-borne noise and vibration?

▪ Like construction, trains in tunnels can generate vibration which can spread through the ground to surrounding buildings which could result in the vibration of floors and wall walls

Operation highly unlikely

to result in levels which

could damage property

But low levels can be

perceived and can lead to annoyance

What are the effect levels?

Concept of effect levels used by World Health organisation in toxicology

SOAEL – Significant Observed Adverse Effect Level

Level above which significant adverse effects on health and quality of life occur.

LOAEL – Lowest Observed Adverse Effect Level

Level above which adverse effects on health and quality of life can be detected.

NOEL – No Observed Effect Level

Level below which no effect can be detected. In simple terms, below this level, there is no detectable effect on health and quality of life due to the noise.

Incr

ea

sin

g n

ois

e

HS2 objectives:

Design, operate and maintain to avoid SOAEL

Take all reasonable

steps to reduce below

LOAEL

What are the effect levels?

HS2 LOAEL

HS2 SOAEL

Improvement in control measures over timeImprovements in ground-borne noise from railways in tunnels with time

Gro

un

d-b

orn

e n

ois

e (

Lp

AS

Ma

x)

Negligible

Low

Medium

High

Very high

Impact

Introduction of environmental assessment process in UK

Control measures

Why have things improved over time

straighter rail alignments

resilient rail support fewer rail joints

better suspension on the trains

smoother running surfaces on the rails

improved quality of the track

Track mitigation measures

Mitigation through design and maintenance of the train and track

*Example track systems only – HS2 tracks are part of an active procurement process

Performance enhanced by engineering resilient materials into the track

▪ HS2 is committed to monitoring the performance of noise control measures throughout the life time of the railway

▪ Noise and vibration will be monitored at carefully selected locations on the route during operation

▪ Actions will be taken to investigate and correct situations where railway not performing as expected

▪ Results will be shared with Local Authorities

Monitoring of operational noise & vibration

HS2 monitoring

Policy set out in

Information Paper F4

When will the tunnels be dug?

Programme

▪ The TBM is due to be delivered to the West Ruislip Portal winter 2021

▪ Both TBMs will be launched spring / summer 2022 with a 1 month gap between the launches.

▪ Tunnelling progresses at a rate of approx. 15m/day

▪ Anticipated to complete tunnelling in 2024

▪ We will keep you informed about the progress of the TBM as it passes through Hillingdon

Programme dates are correct as of August 2021 and may be subject to change

Next StepsFurther Tunnel Boring Engagement

▪ A repeat of this webinar on 14 September

▪ Virtual 1:1s on 2 and 16 September with individual appointments for property owners. There’ll be more of these if people want them.

▪ Subsoil notices will be sent to owners of properties directly above the tunnel in September

▪ Letters to property owners explaining the location of the tunnel and how impacts will be managed

▪ Frequently Asked Questions on tunnelling to be published

▪ We will keep you informed about the progress of the TBM as it passes through Hillingdon

Other Engagement

▪ Engagement on tunnelling and earthwork logistics in the West Ruislip Area, at the end of the year, beginning of 2022

▪ Engagement on tunnel cross passages (completed after the TBM has passed)

Questions?