WORK on the Mersey Gateway project has reached another milestone with a unique feat of engineering.

The freight line bridge in Widnes has been specially constructed as a pre-cast concrete tunnel.

The design was 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, 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 Timperley 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.”