1. Project Spotlight
Conwy Tubular Railway Bridge
Kaymac Marine & Civil Engineering Ltd
Client: Birse Rail
Duration: 4 weeks- Completed April 2009
Value: £150,000.00
Conwy Tubular Railway Bridge (Underbridge No. 110), which carries the North Wales coast railway line across the River Conwy between Llandudno
Junction and the town of Conwy, was built by Robert Stephenson in 1848. The superstructure is formed from two wrought iron tubular box girders
which carry the railway lines, with masonry castellated abutments that compliment the adjacent Conwy castle. An assessment in 1899-1900
showed that the tubes were theoretically overstressed under loadings from the heaviest locomotives running at the time, and this entailed the
construction of additional piers at each end of the tubes at points of the span.
Kaymac Marine & Civil Engineering Ltd were commissioned by Birse Rail to carry out works to remove two existing inspection gantries from the
Conwy tubular railway bridge. The gantries were deemed redundant by Network Rail and required removal from both tubes. Conway Tubular
Bridge is a listed structure set within a SSSI area.
Due to access restrictions for plant and equipment on to the top of the tubular spans, it
was decided early in the project to utilise floating plant to systematically dismantle the
inspection gantries. Therefore a modular pontoon system was mobilised to site consisting
of 16 Linkflote units, which when assembled, resulted in a work barge with a deck area of
210m², complete with 2 no. 12m long spud legs and winches. Due to the high rate of tidal
flow below the bridge structure, the support vessel ‘Sabrina’, a converted landing craft
equipped with 600hp engines, was utilised to mobilise the work barge into position below
the structure.
To allow access from the work barge to the gantries, 2 no. Genie Z34/22 articulated boom
MEWP’s were mobilised from the shore to the work barge on board ‘Sabrina’. Each
MEWP had the hydraulic oil replaced with a vegetable based replacement prior to
mobilisation. The MEWP’s were then used to allow IPAF trained personnel to reach the
structures and rig 4 6.5t air hoists at both sides of each tube.
Each air hoist weighed in at 170kg, and was lifted up the outside face of each vertical
section of gantry using chain hoists. With the air hoists in position and securely rigged,
the lower underslung sections of the gantries were flame cut from the vertical elements
working from the MEWP’s. Once separated, the underslung sections were lowered onto
the deck of the work barge on the air hoists for disposal.
Before removing the side sections of the gantries, the trolleys on which they were
originally moved across the tubes were secured to their rails with cam type strops
providing 14t of down force. This was to prevent any overturning moment of the trolleys
during the dismantling process.

2. Project Spotlight
Conwy Tubular Railway Bridge
Kaymac Marine & Civil Engineering Ltd
Client: Birse Rail
Duration: 4 weeks- Completed April 2009
Value: £150,000.00
The side sections were then rigged to the air hoists and flame cut and lowered down to
the deck of the work barge for disposal. With the MEWP’s having proved successful in
providing access for the removal of the underslung and vertical sections of the gantry,
they were demobilised to allow the removal of the remaining trolley assemblies on the
top of the tubes.
To provide adequate lifting duty and radius from the work barge, a 30t telescopic crawler
crane was mobilised from the shore using ‘Sabrina’. As with the MEWP’s, the hydraulic oil
within the crane was replaced with a vegetable based alternative.
The work barge was then mobilised into position to allow the crane to access the trolley
on the downstream tube. This meant that the crane was now positioned between two
iconic listed structures, Stevenson’s Tubular Bridge and Thomas Telford’s Conwy
Suspension Bridge. Using the full extent of the 28m of crane jib, the 3t trolley was
successfully lifted off the rails, slewed between the 2 bridge structures and lowered
down onto the work barge.
The work barge was then moved upstream of the bridge structure for the final lifting
operation.
On the incoming flood tide, the crane lifted the second gantry trolley clear of the bridge
tube. The gantry section was successfully lowered into the hold of the ‘Sabrina’. The
crane was then demobilised to shore on the next suitable high tide.
The work barge was demobilised 4 days later on a night time high tide to reduce access
problems with local residents.