Report By Colin Wheeler
As a student I worked briefly for a County Council in the department led by that County’s Surveyor and Bridgemaster who was a chartered civil engineer with many years of experience. Post-graduation working for British Rail was very different.
In one railway office I recall the working of a full-time member of staff whose sole mission was to generate income by letting contracts for the removal of the steel deck spans of redundant railway bridges usually leaving the abutments and wind walls standing. At the time the prices being paid for scrap steel significantly improved our bottom line. Detailed examination of these bridge decks often revealed serious corrosion wherever water could accumulate. Bearings, cill beams, trimmer girders, trough decks and other areas all needed close examination if the bridge’s life was to be extended.
Due to the age of these bridges their design life easily exceeded the 100 or so years with which highway engineers are well acquainted. Indeed, most if not all would have been candidates for estimated and actual cost reductions if the original designers had known how to apply “value engineering” analysis. However routine maintenance had been neglected deliberately due to budget constraints and the prioritisation of repair works to operational structures.
I also recall having to repair two ornamental stone arch bridges within the grounds of a minor stately home due to the fact that the owner of the house at the time when a certain railway was built only agreed to allow it to be built across his land if the rail company agreed to maintain the two bridges into perpetuity!
When Railtrack was set up many disused railway structures, including unused railway bridges and tunnels were initially transferred to the keeping of “British Rail Residual”. This was the method used to separate them from the operational railway. In 2013 Highways England became responsible for them. In total there is a portfolio of 3,800 bridges, tunnels and viaducts. Their website says that very rarely is demolition or infilling considered and the local authority is asked to take over the structure or others may provide a “viable new use”. Infilling of bridges they describe as “where material such as crushed rock underneath an old railway bridge makes sure it is fully supported”.
I had first-hand experience of the filling in of a number of structures but the one I best remember was a series of brick arches carrying an operational railway that had been filled in to reduce maintenance. Details of the filling were meagre, but for a few decades there had been no problems. Then the track geometry began to deteriorate, a speed restriction was imposed and we sought the cause.
From the memories of a former employee, we then discovered the inadequacy of the filling in. Having crawled into a horizontal man-sized tunnel at the top of the filled in arches embankment we discovered that only around three quarters of the depth of each arch was filled. Believing it was filled our predecessors had tried to grout up the space between the fill and each arch soffit. Generally, the set grout could be seen in the form of a near perfect cone supporting thin air! The three ring arches had deteriorated and loose brickwork with slipped bricks was easily seen. We closed the railway for some weeks, broke each arch at its springing, and filled and consolidated substantial quantities of additional filling material. The tracks were then reinstated and the problems did not recur.
Subsequently I had reason to demolish a number of redundant brick and stone bridges. A lesson had been learnt, we always broke the filled arch at both sides or by the removal of keystones and then consolidated the arch rubble and fill together to eliminate voids.
Merely filling in but leaving the arches intact will not guarantee support. But for many original railway structures especially those built in stone or brickwork (including engineering bricks) the 100-year design life does not apply. The design life of vintage rail steel structures is most often limited by fatigue considerations, with working loadings well within permitted limits. The design life of brick and stone bridges and tunnels is longer as may be judged by the number of original structures still in use. The first railway was built nearly 200 years ago.
Some time ago I recall a design consultancy business development director trying to convince me that with the number of bridges and tunnels we were responsible for, we ought to be renewing a set number each and every year. He offered to provide designers to do the job. We were standing under a splendid multi-span stone viaduct that was nearly 150 years old. I pointed to the cathedral in the city which was built 1,100 years ago to explain my lack of concern. In my experience creating a reinforced concrete saddle over weak arches is both simple and cost effective in extending the lives of such arches.
I am surprised and dismayed to learn from press reports that in May of this year a bridge at Great Musgrave in Cumbria was infilled using 1,000 tonnes of concrete and aggregate under its arches. Highways England have apparently claimed that the “infilling of the arch removes the risk of the bridge deck failing”.
The need for retrospective planning permission is now being examined despite the District Council originally stating it was not needed.
Pictures of the infilled 159 year old bridge do not look good! Given the number of Victorian innovative railway structures we have as testimony to an astonishing work of the Stephensons, Brunel and others, I concur with the use by the Historical Railways Estate Group campaigners of the description of the action taken at Great Musgrave as being “cultural vandalism”.
Photo credits: HRE Group