Photo above: Huntworth bridge was in a poor state and could not be brought up to standard. (Bridgwater Mercury/Steve Richardson)
A lift that could change the paradigm
In the depths of the Somerset farming community is a narrow thoroughfare called Huntworth Lane. It is agricultural in style, narrow and winding, but it is an important link to schools, the M5 motorway and the town of Bridgwater for the small local communities in the area.
One of the reasons why this is such an important route is because the road crosses over the main line railway from Bristol to Exeter at Huntworth. The bridge is the original structure, built in the middle of the 19th century, consisting of three wrought-iron spans with a central span of 10.5 metres and two side spans of 10 metres. It has a single carriageway and no footpath to speak of. Due to the condition of the bridge, there is also a weight restriction of 22 tonnes imposed on it.
In 2014, Network Rail put plans in place to carry out significant steelwork repairs to bring the bridge up to EU loading standards of 40 tonnes and a £500,000 contract was let to AMCO to carry out the necessary repairs. However, subsequent examinations and assessments indicated that the condition of the bridge was such that, even with the planned repairs, the bridge would still not meet the EU standard.
Now, readers might remember the hugely disruptive floods that took place on the Somerset Levels. During that time the then Prime Minister, David Cameron, visited the area personally and promised the local community that he would invest in equipment that would increase the removal of the floodwater from the area by threefold. This would mean, of course, that new, state of the art, heavy pumping equipment would need to be imported to the area and, you know what is coming, access over Huntworth Bridge would be an essential requirement to deliver the Prime Minister’s promise.
As a consequence, a decision was taken to cancel the repair work and to reconstruct the bridge instead. An application for a 20-week road closure was submitted to Somerset County Council, although Network Rail was aware that this would not be popular with the local community as it would require a 22-mile detour.
There was another factor that had to be considered when applying for such a road closure and one that would not be easy to resolve – Somerset County Council Highways Department has a policy that no commute for school children should take longer than 40 minutes. It’s an admirable policy, one would think, but, in this case, a nightmare for the Network Rail project team. Scott Pillinger, the programme manager for the scheme, explained how this problem was resolved.
No through road!
Scott referred to a map of the area that highlighted a number of routes that could be taken that would ensure compliance with the 40-minute rule. However, when one looked closer, it was evident that some of the roads were privately owned by farmers and other land owners. Fairly intense negotiation had to be embarked upon, with twelve different interest groups representing the road owners.
As can be imagined, this became quite a challenge for Network Rail, given the options available to them, but, eventually, a solution was found that involved the installation of electronic gates and monitoring systems plus a reliable fleet of seven taxis to get children to school within the allotted time and without upsetting the road owners.
Network Rail representatives, including Scott, had to face a grilling from more than 300 residents who packed into a local village hall to discuss plans to close the main road to Bridgwater for 20 weeks. At one stage during the proceedings, the BBC, equipped with cameras and microphones, invited themselves into the meeting. It became a major communications initiative and regular newsletters were distributed throughout the project work.
So, once approval for the road closure was in place, the project team was then able to concentrate on the not-insignificant engineering issues that needed to be considered. Normally, a design would be developed that would enable the new bridge deck to be built alongside the track and lifted in with a high capacity road crane, but was this a feasible option in the back lanes of Somerset?
A detailed survey of the approach roads to the bridge was carried out and it soon became evident that it would not be possible to get a suitable road mobile crane to the site and, even if it was, the available space around the site was limited with cuttings and woodland present. In fact, there was only enough space to erect a superstructure.
Therefore, the decision was made that, after demolishing the old bridge, the team would build two new abutments and then transport individual components of the newly designed steel superstructure, which would be constructed on site alongside the railway. This would then be lifted using a rail mounted Kirow crane and positioned on the abutments. Once the superstructure was in position, reinforcement would be placed and concrete poured to form the deck of the new bridge.
The design work was carried out by Crouch Waterfall and Balfour Beatty was contracted to carry out this work as the principal contractor, with a contract value of £1.5 million. The steelwork was fabricated by Centregreat at its works in Cardiff.
This all sounds sensible and normal, but a Kirow crane had never been used to carry out this kind of lift so it was a first for Network Rail. Preparatory work began on 11 February 2019, and the new deck was installed using a Kirow crane owned by Balfour Beatty on 17 March 2019, using a 52-hour possession that was in accordance with Rules of the Route.
Although this all sounds like routine practice, the benefits of adopting this approach are quite significant.
For example, the Kirow crane arrived on site at the beginning of the 52-hour possession. When it was ready, the crane lifted the superstructure, travelled a short distance of 35 metres, then placed the steel-framed superstructure in position. This process took 55 minutes, then the crane left the site. The only preparation required was to attach the strapping from the lifting beam to the superstructure.
Compare this with using a road-going mobile crane. First, consideration would have to be given to providing adequate road access to the site. Once on site, it is more than likely that significant ground work would have to be carried out to ensure there was a stable platform for the crane. In many cases, this would probably involve the installation of concrete bases and it is also likely that substantial areas of earth would need to be moved and transported away from site.
The crane would then need to be carefully set up, inevitably commanding a significant area of land and, because the planned lift is carried out from a distance, reliable communication channels would become necessary – and they are often complex. Once ready for work, large road mobile cranes are more exposed to weather variables, especially wind and flooding, so careful weather watching is required.
Using a rail-mounted Kirow crane dramatically reduces these concerns and risks. As a consequence, there are significant financial savings. In this instance, Scott indicated that doing such work using a Kirow crane saved the project at least £200,000 and, if all the supporting issues of bringing materials to site and removing materials from site are taken into account, the savings could be more significant.
Having said that, using a rail-mounted Kirow-style crane does require precise planning. Everything has to be ready at the right time to ensure that the crane does what is required. It then must disappear out of the possession on time, ensuring hand back to traffic is as planned, with the lift completed successfully.
Superstructure design critical
The design also has to be right. The lift carried out by the crane was 22 tonnes. A walking route was incorporated into the design to ensure that quick and safe access could be obtained as soon as the superstructure was in place.
There must be thousands of Victorian overbridges throughout the rail network that will need to be replaced. In the past, there were standard bridge designs such as the Western Region Box Girder or the Z-type decks for underbridges. Is there a standard design emerging for rural overbridges like Huntworth and are they being designed with rail cranes in mind?
At Huntworth, at the time of writing this article, the superstructure was installed after five weeks and the reinforcement was in place ready to receive the concrete infill. The finished structure will consist of a new road carriageway, and a pedestrian walkway which did not exist before. In addition, a road safety audit raised concern about the approaches to the bridge, highlighting that there was no protection for the railway from road vehicles. So, as part of the project, the approaches, 25 metres either side of the bridge, now have restraints consisting of 12-metre deep piles with an integrated pile cap.
As Scott explained, it is a project that has included many challenges frequently associated with access but, as always, there is a unique element to each project that hasn’t been experienced before. This project, to help overcome these challenges, managed to adopt a methodology that could change the paradigm for renewing the ageing stock of Victorian overbridges for years to come.