Causey Burn, Causey, north of Stanley, County Durham, UK
1725 - 1726, 1978 - 1981, 1988
ICE reference number
photo Jane Joyce
Causey Arch is thought to have been the largest single-span stone arch in Britain for about 30 years after it was constructed. It was built as part of the coal wagonway that ran from Tanfield to the River Tyne at Dunston, and is said to be the oldest surviving rail bridge in the world. It is a Scheduled Ancient Monument and Grade I listed building.
Once the coalfields along the banks of the River Tyne started to be depleted, people began to move mining operations further inland. This necessitated the construction of wagonways for horse-drawn wagons, used to ship the coal back to the river. Causey Arch, over the ravine of the Causey Burn, some 10km from the centre of Newcastle, is part of the line between Tanfield and the Tyne (begun in the mid 17th century). Here the wagonway was 8km long and consisted of two tracks of timber rails.
The bridge was constructed in 1725-6 by stonemason Ralph Wood (1664-1730), and opened to traffic in 1727. It cost £12,000 to build and funding came from the 'Grand Allies', a consortium of colliery owners founded in June 1726.
Wood's bridge spans 32m and is about 6.7m wide. The arch is 10.7m from springing to soffit, with an overall height of 24.4m. The timber formwork was used for its construction. It arch is flanked by broad buttresses that project 1.1m each sides. The two timber wagon tracks were made of oak and beech, with rails at a gauge of 1.2m.
The bridge, and its massive embankments, was considered an engineering marvel when it was built and was well-visited, as it today. In 1726, it was the longest single-span bridge in Britain and remained so until 1756, when a 42.7m span stone footbridge was built over the River Taff at Pontypridd in south Wales.
During the first years of its use, up to 930 horse-drawn timber wagons crossed the bridge daily in each direction — or one wagon every 20 seconds and only about 45m between each one. Between 1733 and 1738, the coal mines nearest the bridge closed. In 1739, Tanfield Colliery was destroyed by fire and closed in 1740. Landslips had also damaged the bridge approaches and by the 1770s it was used infrequently. By 1812, it was reported that the arch was "neglected and falling to ruins".
Despite the timber tracks being replaced by iron rails at some point, the wagonway/railway closed in 1962. Causey Arch passed into the care of Durham County Council, and lies within Beamish Country Park.
By 1977, the structure was in poor condition. The causeway approach had collapsed and the cliffs on which the arch stands had suffered falls. The arch soffit was spalling and mortar between the sandstone blocks had been eroded.
Repair work was carried between 1978 and 1981. Joints on the underside and edges of the arch were repointed. More than 1,200 cracked or flaking stones were core drilled and injected with epoxy resin under vacuum. The bridge was waterproofed and parapet railing installed. The eroded cliff face carrying the arch abutments was stabilised with steel rock bolts and grouting. The repairs cost £162,000.
Though the bridge was now safe, the 8.6m cliffs supporting it had horizontal overhangs of up to 2.5m in places. Concerns over the potential for further cliff falls led to reconstruction in 1988, carries out by direct labour supervised by the County Engineer.
The work consisted of casting in situ concrete 'rocks' to match the existing sandstone cliff face and support the overhangs. Each rock is plain concrete, cast against the natural rock and anchored by rock bolts, with a textured façade layer up to 500mm thick in front. Concrete mixes were adjusted with different sands and pigments to colour-match the surrounding stone. The work cost £23,000.
Contractor (1978-81): Balvac (Balfour Beatty)
"Invisible mending" by Andrew Stroud, in Concrete Quarterly, Autumn 1988, pp.26-27, British Cement Association, Slough, 1988