Contractors World UK & Ireland Vol 3 No 6 - page 15

installed. This comprised five 7.0 m exten-
sions, three 5.0 m and three 1.5 m exten-
sions, one 3.0 m section and a 1 m section.
Four hydraulic rams – one on each side
of the coffer dam - were installed to extend
the assembled frame to its final dimensions.
Lateral forces on the coffer dam were
very high due to the poor soil conditions
and the pressure exerted by up to 3 m of
water. To withstand these forces, the Mega
Brace frame was braced with a 250-tonne
capacity MP250 hydraulic strut across each
The props are generally installed at 90°
to the side of the excavation so that the
forces are directed along their length. On
this project, the struts are at 45° to the waling
beams and special end-bearings had to be
supplied to accommodate this angle.
With the props oriented across the
corners of the excavation rather than from
side to side, Mackley had more space in
which to work.
Once the frame and props were installed,
the coffer dam was excavated to its full depth
so that work could begin on the new weir.
TVO started work on the project in March
2013 and will finish this phase in December.
Work will then recommence in March
2014 as the weather improves.
Stopper Specialists
Holds Back the Tide at Medmerry
Another major project for Groundforce involves another division that supplies inflatable
pipe plugs.
Groundforce’s pipe-testing and flow control division, Stopper Specialists, has supplied
two of its large diameter Trelleborg Mega Plug inflatable pipe stoppers to contractors
working on a major new sea defence project near Selsey on the Sussex coast.
The £28 million Medmerry Managed Realignment Scheme has created new sea
defences inland from the coast to allow a new intertidal area to form on the seaward side.
The project has been
undertaken by Team Van
Oord, a joint venture
between Van Oord, Kier,
and local contractor
Mackley Construction.
Rather than trying to
hold back the sea the
chose a ‘managed
retreat’ which allows a
designated area of marsh
to flood at high tides while
being exposed during low
As a result, a 7 km of
earth embankment has
been built inland to act as
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Contractors World - UK & Ireland Vol 3 No 6
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