Work on the Mersey Gateway project has reached another milestone with the use of one more special engineering solution to complete a vital rail bridge.
The Freight Line Bridge at Widnes has been specially designed as an opti-cadre portal – also known as a pre-cast concrete tunnel.
The design was specially chosen for speed of build, short construction time and minimal disruption to the rail infrastructure, whilst providing a solution allowing traffic to pass over the top once completed.
At 99.4 metres long and 14.5 metres wide and six metres high, it’s a huge structure that has taken a high degree of engineering to construct.
The portal frame will be installed over the Garston to Timperly line which is only used for freight trains.
Hugh O’Connor, General Manager of Merseylink, said that the reason such a unique structure was specified is due to very poor ground conditions at this part of the site.
“To install the bridge a steel sheet pile wall consisting of a total of 176 driven sheet piles was installed before excavating and then constructing a foundation pile cap,” he said.
“Throughout the work the railway track was constantly surveyed using specialist fixed prisms, which allowed the position of the track to be carefully monitored.
“Deep soil mixing was also conducted on both sides of the railway to make sure the required ground settlement at the site was achieved.
“After mixing was complete, embankments were built either side of the railway track before the pre-cast concrete portal was installed.”
It is comprised of 112 base walls and 56 roof units, with the biggest unit weighing in at 51 tonnes.
The Freight Line Bridge is a fine example of modern engineering techniques, and its completion comes as Mersey Gateway engineers hit a variety of other major project milestones.
Last month the huge North Approach Viaduct structure was completed; it contains enough concrete to fill seven Olympic-sized swimming pools.