The Times - UK - 04.12.2021

12 Saturday December 4 2021 | the times

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working in Hong Kong for two years,

learning the art of tunnel boring, when

he was offered a job on HS2 in 2018.

Florence first dug her teeth into the

Chilterns in May. Seven months later,

she has covered about 2.4km. Seven-

teen-strong crews on board work 12-

hour shifts. At full power, she can ad-

vance up to 15.6m a day. On board is a

“canteen” room, workshop, lavatories

and two emergency shelters.

At the business end is the 10m rotat-

ing steel cutterhead with its buckets,

scrapes, knives and discs. Excavated

material is carried up a massive screw,

which removes it from the excavation

chamber, before passing out of the

TBM and the tunnel in a slurry pipe.

Behind it, the TBM also builds the

tunnel itself. Concrete segments, each

weighing 7.5 tonnes, are sucked up,

swung into place, and connected to the

previous segment. Each huge ring is

made up of seven segments, all of which

are produced on site at the south end of

the tunnel.

HS2 tunnels are considerably wider

than many older ones, partly because of

new safety regulations but also because

of the speed at which the trains will be

travelling. The tunnel entrances will al-

so have “hoods” to distribute pressure

and avoid “sonic boom”. The inside of

HS2 tunnels will have a diameter of

9.1m compared with the Channel Tun-

nel’s 7.6m or Crossrail’s 6.2m

Unlike the Channel Tunnel, where

two TBMs historically met in the mid-

dle, both Florence and Cecilia are bor-

ing northwards. Access is from HS2’s

huge South Portal, which sits just inside

the M25 motorway and covers an area

the size of 80 football pitches.

Once work is complete, the site will

be landscaped, including the creation

of 127 hectares of new chalk grassland,

woodland and wetlands. HS2 Ltd, the

government-backed company deliver-

ing the project, says 65,000 trees and

shrubs of 32 species will be planted

along with 3.5km of hedgerows.

Not that such a commitment offers

much cheer to the residents of Buck-

inghamshire who have opposed con-

struction in the Chilterns. The area’s

conservation board claims 149 mature

trees will be felled with 24 areas of

woodland affected, including nine an-

cient sites. They say 17.75 hectares of

woodland will be destroyed and more

than 13km of hedgerows.

By 2033 trains will run through the

two tunnels, heading north to Man-

chester and south to London Euston.

TIMES PHOTOGRAPHER RICHARD POHLE

Speed

Weight

It will run non-stop for 3.5 years

London bus to scale

HS2 tunnel

Channel width 9.1m

tunnel 7.6m

Crossrail

6.2m

Jubilee

line 4.4m

Length 170m (560ft)

Disc cutter

Excavated earth is pulled away

from the cutting face by a screw

conveyor

Hydraulic rams push

against the new tunnel

segments, forcing the

machine forward

A ring collects the waiting

tunnel segments, lifting

them using two arms.

It then moves into

place, and can rotate

them a full 360°

into position before

each segment is

connected together

A 10m wide cutting face

grinds through the rock,

rotating 3.2 times a minute

The earth

is mixed

with water

into slurry

and then

pumped

through

out to

the surface

Pre-cast concrete tunnel

segments travel via conveyor

belts to the front

of the macine

Erecting a tunnel

Tunnels compared

Up to 15m a day

2,000 tonnnes

The Chiltern tunnels

A

Amersham

Chiltern Tunnel

Colne Valley

viaduct

North

portal

South

M25 portal

One mile

N

London

Euston

Birmingham

East

Midlands

Parkway

Manchester

Golborne

Link

Vent shafts

Vent

shafts

HS2 trains will only take 3 minutes to pass

through the 10-mile tunnel

Up to

90m

deep

gments, lifting

g two arms.

oves into

can rotate

l 360°

on beforee

ment is

d together

N

pp

H

t

Cutting edge

Mighty machines inching HS2 ahead

Fifty metres below the Chiltern Hills,
you would be forgiven for thinking you
had arrived on the set of a sci-fi movie.
Or that you’d joined the likes of Tim
Peake for a stint on the International
Space Station.
The colossal contraption you
find, moving at the speed of a snail,
however, is Florence, a 170m tun-
nel-boring machine (TBM) that is
eating through the chalk and flint.
For three years she will work night
and day before emerging ten miles
to the north near the village of South
Heath, Buckinghamshire.
A couple of months later, Cecilia, a
second 2,000-tonne machine, will also
re-emerge from the darkness. This is
Europe’s biggest construction project
— excavating through the area of out-
standing natural beauty to create two
huge tunnels for 200mph HS2 trains.
On a cold December morning, The
Times descended — aboard a strange
wagon with a driver’s cab at both ends
— to climb aboard Florence as she
moves, 35mm a minute, through the
hills. Whatever your view of the contro-
versial new rail line, it’s hard not to be
impressed by the sheer scale of the ma-
chine and the technology being used to
build what will become one of Britain’s
longest rail tunnels.
“The biggest challenge at the mo-
ment is the logistics to keep the ma-
chine running,” says James Reilly, 29,
the senior TBM engineer. “She is work-
ing 24/7 and absolutely everything has
to be in sync. If any part of the produc-
tion fails, we’d have to stop the
machine.”
Reilly, who studied civil engineering
at Loughborough University, had been

Tunnels to carry trains

at 200mph are slowly

but surely being gouged

out below the Chilterns,

writes Ben Clatworthy

James Reilly walks through one of the two tunnels created by the boring machines he oversees. The work is fed from a vast depot at the south end where hundreds of segments to line the walls are stacked