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Background information
A36 Skew Railway Bridge, Salisbury
Background information
Why the work was needed
The heavily skewed Victorian brick arch was built in 1850 along with the embankments and the railway line. The parapets on the existing bridge needed to be upgraded to meet the latest safety standards. The bridge not only carries road users over the railway - it also carries water mains,electricity cables, gas pipelines and a variety of telecommunications cables. Because of these services and the railway line, the options for upgrading the parapets were extremely limited.
In the last ten years there have been two accidents on Skew Bridge where road vehicles have ended up on railway property. One incident unfortunately resulted in a fatality when the driver struck the parapet wall adjacent to Brick Lane. This highlighted the need for the parapets to be upgraded.
Roads over railways
Skew Bridge crosses the Salisbury to Warminster line, where trains are permitted to travel at a top speed of 70mph. The safety of the trains is of paramount importance to the project.
To satisfy Network Rail, any works that are likely to cause safety concerns have to be carried out when the railway is closed. It is not as simple as working in the gaps between trains. Network Rail rarely allows daytime railway closures in case there are non-timetabled train movements such as freight or engineering trains. We are usually only permitted to work at night.
Progress
Before we started work the existing bridge and ground conditions were investigated as extensively as possible. Unfortunately when work started on site we discovered that the railway embankment was not as stable as first indicated and we were unable to proceed with our originalconstruction method.
Extensive piling was required in order to support the railway embankments and the road during construction. This led to a signifi cant increase in the amount of work required and hence a significant delay and increase in the number of road closures.
In addition, the site is very compact which dictates a strict method of working and sequence of operations. We are therefore unable to speed up the works or recover lost time simply by increasing staff numbers. The Health and Safety rules relating to working over railways place further restrictions on construction methods. Unfortunately high winds experienced during some of the over night road and rail closures prevented the crane from working.
The southern footbridge was slid into place in February 2004 and the final northern footbridge was slid into place in June 2004.
Statistics of the bridge
Work on the bridge has required . . .
- 2km of bored piling = the length of Southend-on-Sea pier.
- 300 tonnes of steel reinforcement = 6 Chieftain tanks.
- 5520 tonnes of concrete = 920 adult African elephants.
The cost of the project is £3million.
The footbridges has 158m of new parapets = 40 car lengths.
