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Farnworth

Tunnel

Engineers

Overcome

Poor Ground

Conditions

A complex tunnelling project to enable electric trains to

run between Bolton and Manchester has been delayed,

possibly until December, by exceptionally poor ground

conditions.

Network Rail engineers enlarging the 1834-built

Farnworth Tunnel ran into large swathes of sand, rather

than a firmmaterial to bore through, which pours down

into the excavated area halting progress.

It has proved impossible to safely excavate while

concurrently installing and grouting sections of tunnel

wall as was originally planned.

Engineers are now pumping resin into the ground to

firm it up before 9 m wide Fillie, the UK’s largest tunnel-

ling machine, bores through it.

For local train passengers the railway between Bolton

and Manchester will continue to operate as it has since

May.

Martin Frobisher, route managing director for

Network Rail, said:

“We first hit an area of running sand on August

14 when our engineers saw it suddenly pouring

from the working face. This has slowed progress

and created big voids, the largest of which

needed filling with around 35 tonnes of grout.

Again on August 27, sand poured into the

excavated area and our engineers had to remove

100 tonnes of material by hand.

“The nature of civil engineering, especially

deep below ground, is that you never fully know

the exact ground conditions until you start tun-

nelling or excavating. Taking soil samples acts

as a guide but is never 100% accurate because

conditions vary greatly with the amount of water

present.

“The rate of progress is very dependent

upon the conditions and we are working around

the clock to complete this as quickly as

possible.

“Our top consideration is safety. Our engi-

neers face a huge challenge. We must allow

them the time they need to tackle it safely. We

Contractors World UK & Ireland Vol 6 No 1

42

Contractors World UK & Ireland