The Bridges of the Bishop Auckland & Weardale Railway

Introduction

By the mid-1830s, the Stockton & Darlington Railway (S&DR) was generating a healthy profit for its shareholders and was seeking to expand its sphere of influence and access to markets and goods. To this end, the company advanced a scheme to extend its mainline from Shildon north-west into Weardale.

The line (taken forward as the Bishop Auckland & Weardale Railway or BA&W) had reached as far west as Crook by 1843, eventually terminating at Eastgate in Weardale. It opened up new areas for mineral extraction, in particular deposits of coal and limestone, and connected existing mining concerns and other industries with national markets for the first time.

However, in contrast to the ‘house style’ that many railway companies, certainly in later years, applied to the bridges and tunnels they built on a new line, a study carried out by Historic England in 2019-20 as part of its Bishop Auckland Heritage Action Zone (HAZ) initiative has revealed that the BA&W applied a much more eclectic range of engineering solutions and architectural treatments.

The research programme

The Bishop Auckland study looked at eight bridges (excluding footbridges) and culverts that lie on 3 kilometres of the line between the Shildon Tunnel and just west of Bishop Auckland. The original Engineer’s Line Reference (ELR) bridge numbers for these structures were BA&W/4-12, later changed to DAE2/4-12. The study focussed on the physical evidence of each bridge’s fabric but was also informed by original engineering drawings preserved in the Network Rail Archive (NRA); it did not research the wider archives of the BA&W directly.

The bridges

The evidence of the surviving drawings (which because of COVID restrictions were seen only in facsimile, sometimes of poor-quality) suggests, unsurprisingly, that construction of the bridges happened in order from south-east to north-west as work on the line proceeded northwards from Shildon.

The plan for the first bridge after the Shildon Tunnel is entitled ‘Proposed Bridge over the Highway between South Church and Eldon’. The plan is signed and dated by the contractor; the signature is hard to read but the date is 22 April 1839. From an architectural point of view this bridge (ELR DAE2/4) is unremarkable. Its elevations are plain, each comprising a single semi-circular arch ring of simple stone voussoirs rising from an impost band at the springings and surmounted by a narrow roll moulding; the spandrels are ashlar laid in horizontal courses, although now heavily obscured by later track widenings.

As such, the design treatment appears very reminiscent of the architecturally plain and unpretentious bridges George Stephenson designed for the early S&DR (e.g. see Hummerbeck Bridge; Eric Branse-Instone's article on S&DR bridges in this issue)

The bridge is more interesting from an engineering standpoint, however, since it lies about 35 degrees skew, not at right angles, to the road over which it passes. To help resist the very different thrusts that skew bridges impose compared to bridges that cross an obstacle at 90 degrees arch rings and barrel are laid according to the helicoidal method (see above image) where the bedding joints between stones run at right angles to the bridge elevations rather than the abutment faces.

In addition, each stone in the impost bands is cut with a dog-tooth upper surface to further counteract the tendency of the arch barrel to slide over the abutments (see photograph below). No similar mitigation was applied to prevent the spandrels sliding over the arch ring, however, and there is evidence of movement here, addressed by later patching and the insertion of at least one metal tie rod and pattress plate. How quickly this movement became apparent is unknown.

Skipping over the next structure on the line (a small culvert of very simple design), the original elevations of the next bridge (DAE2/6, named ‘Shepherds’ on modern Network Rail signs) are now hidden behind extensions added later in the century when this section of line was quadrupled. No engineering drawings showing the original elevations have been traced, but the arch barrel is semi-circular and everything about the bridge speaks of simple architectural treatment very similar to DAE2/4. The bridge is a ‘regular’ arch oriented square to the rail line and did not need special engineering solutions.

The next bridge (DAE2/7, crossing a road now called Bone Mill Bank) is again some 30 degrees skew. It is, however, very different in design (see photograph below) from DAE2/4. Although the engineering drawings are undated, we know the bridge was erected between 1839 and 1842 for the railway was open to South Church station (positioned immediately before the bridge) by late 1841, and to Bishop Auckland station in 1842. In engineering terms, the design undoubtedly reflects rapid advances in the understanding of the mathematics of skew-arched bridges in the short time since DAE2/4 was built. In 1839, George Watson Buck published a treatise on what he called ‘oblique bridges’ in which he showed that semi-circular arches become unsafe where the angle of skew exceeds 25 degrees, after which it is necessary to employ a segmental arch; he also advocated stepped voussoirs to help counteract the tendency for movement at the boundary between arch ring and spandrel.

But in addition to the improved engineering solution, the bridge is also very different architecturally. All original masonry is rock-faced and margined, and that in the abutment walls features a series of diagonal and horizontal incised lines, or in the case of one stone central to the eastern abutment, a swirly cartouche (see photograph below) The impression given is that the Company was becoming increasingly proud and confident in the railway it was constructing and wanted its bridges to proclaim that fact to the communities (and potential users) through which the railway passed.

The next structure along (DAE2/8) is, in engineering terms, not a bridge but a culvert: it takes the River Gaunless through and under a high earth embankment laid to take the railway across the river valley. However, it chimes very much with the more confident, flamboyant approach to bridge-building exhibited by DAE2/7. The voussoirs forming the arch rings in both elevations are massive and have angled ends that extend a short distance into the horizontal coursing of the adjoining headwalls. Furthermore, all masonry on the elevations is rock-faced and V-grooved. The styling gives the culvert a very definite Baroque flourish (see image below), unlike anything else on the line. Its nearest comparison is probably the north portal of the Shildon Tunnel (see Howard this issue), although that cannot be described as Baroque.

The next two bridges on the line on the lead-in to Bishop Auckland are either replacements on a different site or heavily rebuilt. However, the two bridges immediately west of the town (the final ones included in the study) continue this story of experimentation in design and form.

The first of these, DAE2/11 (an overbridge taking the modern Etherley Lane across the railway) is more subdued in architectural expression than DAE2/7, but nevertheless is a fine example of its type and certainly more stylish than DAE2/4 or 6. For this reason, it was already listed at Grade II prior to the Heritage Action Zone initiative.  It is again a skew bridge (this time of three arches) and so has the helicoidal coursing, segmental arch rings and stepped voussoirs one would expect at this date (see photograph below); the voussoirs, however, are not plain but have chamfered edges creating an aesthetically very pleasing V-groove effect. According to a signature on the archive drawings, the bridge was built by the contractor, Henry Dawson or Davison (the handwriting is hard to read) in 1842-3.

Finally, bridge DAE2/12 is of a very different form altogether: a wrought-iron lenticular (lens-shaped) truss built to take a minor occupation road across the railway (Figure 8). It was already listed at Grade II* prior to the HAZ, chiefly because as stated by the noted engineering historian, Robert Rennison, it is the earliest example of its type still in use and on its original site.

But why build such a different design of bridge here ? In all probability, the BA&W deemed it unnecessary to go to the expense of a masonry structure because the bridge had only to carry farm traffic. (Nevertheless, our research has indicated the truss had to be strengthened or stiffened 20 years after construction by the addition of a second lower member or chord.

The engineering drawing for it in the NRA is instructive and may throw further light on what influenced the design choice. It is signed John Storey for the Shildon Works Company, who were in-house contractors for the S&DR. John is unknown other than as the brother of Thomas Storey who succeeded Stephenson as the S&DR’s Chief Civil Engineer in 1825. It is not clear whether John’s signature indicates that he designed the bridge or was just the draughtsman, acting perhaps on behalf of his brother (who by this time was employed by the BA&W as a consulting engineer), but what is certain is that Thomas lived at St Helen’s Auckland, not far from the lenticular truss that Stephenson had designed and constructed for the S&DR in 1823-4 to take that railway across the River Gaunless (see Branse-Instone this issue). It seems very likely, therefore, that the Storey brothers took inspiration from Stephenson’s pioneering wrought-iron truss and that DAE2/12 stands in direct line of influence from it.

Results

All in all, the research has highlighted major similarities and direct links between the first bridges on the BA&W and those George Stephenson built for the S&DR. But it has also shown how bridge design on the BA&W rapidly evolved under his immediate successors, Thomas Storey and perhaps John Harris. This was undoubtedly partly in response to advances in engineering knowledge, but also suggests the Company was becoming more confident and expressive in the architectural statements it wanted its bridges to project. The listing descriptions for the two bridges already listed have been revised accordingly. It is hoped the undesignated bridges will be considered for listing as time allows.

Further information

Buck, G W, 1839: ‘A Practical and Theoretical Essay on Oblique Bridges’, in Laxton, William (ed.) ‘On the Construction of Oblique Arches’. The Civil Engineer and Architect's Journal, Scientific and Railway Gazette, vol III, 197–8. London: Hooper, Weale, Taylor & Williams

Jecock, M 2021: ‘The Road, Rail and Parkland Bridges of Bishop Auckland, Co. Durham: as assessment of the historical and archaeological evidence’. York: Historic England Research Report Series 4-2021 

Rennison, RW, 1996: Civil Engineering Heritage: Northern England. London: Thomas Telford.

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