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Contractors World UK & Ireland Vol 6 No 1

5

Emergency Wall Bracing At Dover

The Costain Kent Multifunctional

Framework (MFF) team reacted swiftly

and effectively when huge cracks ap-

peared in the sea wall next to a railway

near Dover Harbour.

All rail services between Dover and

Folkestone were cancelled when large

sink holes appeared next to the track on

Christmas Eve. Cracks in the 10 m high

sea wall appeared on Boxing Day. The

Christmas break was cancelled for 25

members of the MFF team who were

quickly mobilised to assess the situation

and formulate a plan of recovery with

Network Rail. They battled strong winds,

10 m high waves and high tides to assess

the damage and make the site safe.

Said Andy Clarke, Costain Project

Director:

“This was never going to be a quick

fix – it is a major infrastructure engineering

project that requires working inter-tidal, two

shifts per day, seven days a week. We looked at

the lessons learned when the railway line at

Dawlish was washed away by storms two years

ago. However this was always going to be a

much bigger engineering issue.”

Commented Simon Dunbar, Works Manager for the

Dover Project:

“We worked very closely and quickly with represent-

atives from Network Rail and our supply chain partners

to establish and agree plans for the project.

Two cargo ships transported the lava rock from

Norway with each boulder weighing in the region of

three to six tonnes. It takes nine days for each ship to

unload, using a 65 tonne excavator, and it then travels

back to Norway for the next load.

Over the lifetime of the project 70,000 tonnes of

quarried lava rock will be transported from Norway to

Dover.

A challenge was that the contractors can only unload

the rock at high tides when the ship rises up the quay

to the level where the excavator can move the rock to

waiting dumper trucks.

The excavator unloads each boulder on to a 30 tonne

dumper truck with flotation tyres. The trucks then trans-

port the boulders across the length of the shingle beach

and unload it. A 50 tonne excavator on the beach then

moves the boulders to create a temporary breakwater,

about 10 m in front of the failing concrete wall; this

lessens the impact of each wave before it reaches the

wall.

These rocks will be moved to form the finished rock

armour wall when the final design is in place. Currently

a fifth of the structure, which looks to be the weakest

part, is pinned back by sheet piling and limestone rock

that was moved by road over the Christmas break.

Simon Dunbar, Works Manager for the Dover Project

said:

“Each truck can carry around five to six boulders

at a time, or around 30 tonnes in weight. To

make sure that we can reinforce the structure

as safely and quickly as possible, we work 24-

hour shift patterns - weather and tides permitting

of course - so that’s a fair few trips across the

beach every day. In order to keep the

structure secure we need to shore-up

the entire length of the concrete wall

with sheet piling and lava rock, that’s

around 350 m.”

The team have also had to demolish a

footbridge, as well as carry out earthworks

to remove downward facing pressure on the

wall. The spoil and the remains of the bridge,

along with old timber sleepers and industrial

waste, were taken away for processing using

20 wagons.

[cw]

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