site and spliced together to
form the four deck structures
that were up to 34 metres in
length. But how would they
get the steelwork to site
and how would they create
enough space and solid
ground to construct the four
decks? As Matthew pointed
out the “problems kept
snowballing”.160 elephants
Once the four elements
of the superstructure were
constructed on site, they would
need to be lifted into position.
It was calculated that the
biggest lift would exceed 105
tonnes and the radius would
be more than 60 metres. This
was not work for a normal crane
and they eventually sourced a
Sarens Gottwald 1,200 tonne
crane, apparently capable of
lifting 160 elephants!
How would they get this
crane to site and how would
they ensure that it did not
sink into the spongy, sodden
ground adjacent to the river?
Well, firstly they had to create a
2km haul road using more than
10,000 tonnes of fill material.They were able to source much
of this material from three other
Network Rail sites and Scott
explained that the intention
is for the material used to be
passed on to a school project
in the vicinity. Recycling at its
best!
Once the crane was on site
and the four superstructures
constructed and ready to be
lifted in place, how would
they ensure that the crane
would be stable when the
lift commenced? To do that,
they had to construct four
sheet-piled cofferdams, ten
metres deep and six metres
square in section, and fill them
with engineering fill. These
cofferdams would be placed
so that the load from the
outriggers would be transferred
to stable ground.
Whilst the cofferdams were
being constructed, a substantial
amount of woodland needed
to be cleared to create the
workspace for the bridge
superstructure construction
and for the site offices and
accommodation, and the
sixteen weeks were ticking
away.Traction forces
At the design stage, Tony Gee
& Partners became concerned
about the ability of the breaking
and traction forces of the trains
to transfer through to the deck
to the supporting abutments.
Their solution was to include
fifty-six 100mm diameter, four-
metre-long dowels into the
design. These dowels would
need to be placed into holes in
the precast sill beams and then
drilled into the brick abutment
during the possession, after the
old decks had been removed.
Matthew had calculated that
it would take two hours using a
diamond drill for each dowel. In
a 76-hour possession, this was a
significant undertaking and the
golden rule was that there must
not be an overrun – ‘Putting
Passengers First’.
The team prepared
contingency plans which would
involve additional temporary
speed restrictions, dependent
on the number of dowels in
position. They carried out trials
and adjusted the resources with
the intention of completing
all the drilling within the
possession.70 FE ATURE