Twerton Wood Tunnel East Portal (MLN110903), Newbridge, Bath and North East Somerset

Summary

A railway tunnel portal in the Tudor-Gothic style, built c.1836-40 for the Great Western Railway, to the designs of Isambard Kingdom Brunel.

Description

MATERIALS: squared and coursed Pennant stone, with dressings of Bath ashlar for the voussoirs, quoins, string courses, capping stones and arrow loops.

DESCRIPTION: asymmetrical composition with an inner four-centred arch recessed within a pointed segmental arch, flanked by turrets and wing walls. The entrance consists of four concentric arches creating a complex profile: inner four-centred arch with chamfered voussoirs, set within a relieving arch of similar form, which itself is set within two concentric pointed segmental arches, the inner of which dies into the reveals of the outer at springing level. Above the arch, a string course and, above that, an embattled parapet with sloping coping stones. This central part of the portal is flanked by two turrets of octagonal plan with quoins, the north (Up side) one taller than the south (Down side) one, their lower parts battered outwards and their upper parts rising above the central parapet. At this upper level they are decorated with arrow loops, string courses, and crenellations with moulded and sloping capping stones. Turrets are flanked by short sections of plain wall with coping stones. South (Down) side of portal joined to substantial contemporary retaining wall of squared coursed Pennant stone, 340m long, up to 15m high and of curved section, connecting with the west portal of Twerton Tunnel (qv).

History

The Great Western Railway (GWR) was authorised by an Act of Parliament in 1835 to construct a line from London to Bristol. At 118 miles this was slightly longer than the other major trunk railway of its time, the London and Birmingham (112 miles) and considerably longer than other pioneering lines. Construction of the line began in 1836, using a variety of contractors and some direct labour. The first section to be completed, from London to Maidenhead Riverside (Taplow), opened in 1838, and thereafter openings followed in eight phases culminating in the completion of the whole route in 1841. Work at the Bristol end of the line had started in 1835, and the section from Bristol to Bath had opened in August 1840.

The engineering of the railway was entrusted in 1833 to Isambard Kingdom Brunel (1806-59), who was already known for his engineering projects in Bristol. More than any other railway engineer of his time he took sole responsibility for every aspect of the engineering design, from surveying the line to the detailing of buildings and structures. He sought to achieve as level a route as possible and, working from first principles, he persuaded the Directors of the GWR to adopt a broad gauge of 7ft 0¼ in rather then the standard (4ft 8½in) gauge in use on other lines. A two track broad gauge line was 30ft wide, and this determined the span of the overbridges and other structures. Except in the case of larger bridges such as Maidenhead Bridge and Gatehampton Viaduct, Brunel’s masonry bridges were not as innovative as his works in timber and iron, and his buildings followed the typical architectural idioms of his time, but together they formed integral parts of a consistently-designed pioneering railway.

Although he left no written statement concerning his design concept for the line, it can be inferred from its design and from the way it was described when opened that part of his vision was a line engineered according to picturesque principles. This influenced his selection of the route and the design of structures along it. For reasons of cost, but also because it helped blend the railway to the landscape, he used local materials for bridges and other structures, ranging from stock brick at the London end of the line, to red brick, Bath stone east of Bath and Pennant stone west of Bath. This intentional variety was remarked on by contemporaries, for instance in J.C. Bourne, 'The History and Description of the Great Western Railway' (1846). On the line from Bristol to Bath, where the track runs along the Avon valley, Brunel chose to use Tudor four-centred arches for both the over- and underbridges, and castellation for tunnel portals and viaducts. This makes it the most distinctive part of the whole route from London to Bristol, and it is also the section on which the structures have generally survived in their original form because this part of the route was not quadrupled and the Pennant stone used for most structures has lasted well.

Existing contract drawings for bridges and other structures on this section of the line carry the signature of I.K. Brunel, reflecting his involvement with every aspect of the project. The Resident Engineer was G.E. Frere (1807-87), assisted by G.T. Clark (1809-98) and Michael Lane (1802-68), but their individual contributions have not been identified.

Twerton Wood Tunnel was one of twelve tunnels built between Chippenham and Bristol. It was created c. 1836-40 under contract 3B. It is 240 m long. Contract drawings survive for the East Portal (though with some differences from the portal as executed). It is essentially unaltered since then.

The West Portal is in a similar style.

Reasons for Listing

Twerton Wood Tunnel East Portal is designated at Grade II* for the following principal reasons:
* Architectural interest: its Gothic-Revival design illustrates Isambard Kingdom Brunel's vision of engineering a line according to picturesque principle;
* Date: it is a remarkably intact structure from the pioneering first phase of railway development in England;
* Historic interest: it is constructed to a design by Isambard Kingdom Brunel who is widely regarded as one of the most important engineers and architects of the C19;
* Group value: it forms part of a sequence of Tudor-Gothic structures between Bristol and Bath, designed by Brunel in response to the to the scenic route along the Avon valley.

External Links

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