Chipping Sodbury Tunnel is a

railway tunnel Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...

that is situated on the

South Wales Main Line The South Wales Main Line (), originally known as the London, Bristol and South Wales Direct Railway or simply as the Bristol and South Wales Direct Railway, is a branch of the Great Western Main Line in Great Britain. It diverges from the co ...

in England. It runs under the

Cotswold Hills The Cotswolds ( ) is a region of central South West England, along a range of rolling hills that rise from the meadows of the upper River Thames to an escarpment above the Severn Valley and the Vale of Evesham. The area is defined by the be ...

for 4444 yards, approximately west of Badminton railway station and

Chipping Sodbury Chipping Sodbury is a market town and civil parish in the unitary authority area of South Gloucestershire, in the county of Gloucestershire, England. It is situated 13 miles (21 km) north-east of Bristol and directly east of Yate. The town ...

Yard. The tunnel was built between 1897 and 1902; it was amongst the last of the major railway tunnels to be constructed in Britain. Built to hide the line from the nearby

Badminton House Badminton House is a large country house and Grade I Listed Building in Badminton, Gloucestershire, England, which has been the principal seat of the Dukes of Beaufort since the late 17th century. The house, which has given its name to the spor ...

, a total of six

crenellated A battlement, in defensive architecture, such as that of city walls or castles, comprises a parapet (a defensive low wall between chest-height and head-height), in which gaps or indentations, which are often rectangular, occur at intervals ...

ventilation shaft In subterranean civil engineering, ventilation shafts, also known as airshafts or vent shafts, are vertical passages used in mines and tunnels to move fresh air underground, and to remove stale air. In architecture, an airshaft, also known ...

s are present. The tunnel was built with a mess room at the mid point so that maintenance crews could remain in the tunnel for the whole working day/ night. Due the tunnel passing through an underground

aquifer An aquifer is an underground layer of water-bearing material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...

, it has been particularly prone to flooding and associated closures. It was also a secondary target for

Luftwaffe The Luftwaffe () was the aerial warfare, aerial-warfare branch of the before and during World War II. German Empire, Germany's military air arms during World War I, the of the Imperial German Army, Imperial Army and the of the Imperial Ge ...

bombing during the

Second World War World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

. Numerous remedial works and improvements have been made to the tunnel throughout its service life. Such works have largely been centred around improving its drainage and other measures to reduce the occurrence of flood-related closures. A new high-capacity drainage system was installed during the 2010s. In the same decade, the tunnel was temporarily closed as part of the modernisation of the Great Western main line, for which overhead electrification equipment was installed throughout its length, enabling electric traction to traverse the tunnel.

History

The construction of Chipping Sodbury Tunnel commenced during 1897 for the South Wales and Bristol Direct Railway. It was one of the major civil engineering features of a direct 30 mile link between

Wootton Bassett Royal Wootton Bassett , formerly Wootton Bassett, is a market town and civil parish in Wiltshire, England, with a population of 13,570 at the 2021 Census. In the north of the county, it lies to the west of the town of Swindon and northeast of ...

and

Patchway Patchway is a town and civil parish in South Gloucestershire, England, situated north-north west of central Bristol. The town has become an overflow settlement for Bristol and is contiguous with Bristol's urban area, along with the nearby towns ...

, which reduced distance between

London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...

and Wales by ten miles over the previous route, as well as speeding up rail traffic by enabling trains to avoid congestion around

Bristol Bristol () is a City status in the United Kingdom, cathedral city, unitary authority area and ceremonial county in South West England, the most populous city in the region. Built around the River Avon, Bristol, River Avon, it is bordered by t ...

. The tunnel enabled the line to pass through the Cotswold Edge escarpment, which was perhaps the most challenging topological features along the new line's route. A further major factor in the tunnel's design was the nearby

country house image:Blenheim - Blenheim Palace - 20210417125239.jpg, 300px, Blenheim Palace - Oxfordshire An English country house is a large house or mansion in the English countryside. Such houses were often owned by individuals who also owned a Townhou ...

, from which it was considered important for the new railway to minimise its visual impact on its estate. According to the railway industry periodical ''Rail Engineer'', it was one of the last major railway tunnels to be constructed in Britain. The tunnel is constructed with an arch brick lining and measures some 27'6" across and 20'9" high. The

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

bricks used in the tunnel were fired at a nearby brickworks; this works used material which had been excavated as spoil from the boring process. Around 150 navvies and almost 100 railway personnel lived in the village of Sodbury during the construction effort. During 1902, the completed tunnel was opened to traffic for the first time, although the full line would not be opened in full until the following year. It slopes at a 1:300 gradient from

Badminton Badminton is a racquet sport played using racket (sports equipment), racquets to hit a shuttlecock across a net (device), net. Although it may be played with larger teams, the most common forms of the game are "singles" (with one player per s ...

falling in a westerly direction towards

. The western portal lies in the village of Old Sodbury. Above the tunnel are a series of six ventilation shafts, which were used during construction to remove soil. The places where they reach the surface are circular brick vents between and high with

crenellation A battlement, in defensive architecture, such as that of city walls or castles, comprises a parapet (a defensive low wall between chest-height and head-height), in which gaps or indentations, which are often rectangular, occur at intervals t ...

s around the top. All six are protected structures, having received Grade II

listed status In the United Kingdom, a listed building is a structure of particular architectural or historic interest deserving of special protection. Such buildings are placed on one of the four statutory lists maintained by Historic England in England, Hi ...

during the late 20th century. The brick-built east and west portals of the tunnel are similarly listed. During the

, the tunnel was a secondary target for the

bombers that regularly conducted

bombing raid Strategic bombing is a systematically organized and executed military attack from the air which can utilize strategic bombers, long- or medium-range missiles, or nuclear-armed fighter-bomber aircraft to attack targets deemed vital to the enemy' ...

s against

Filton Aerodrome Filton Airport or Filton Aerodrome was a private airport in Filton and Patchway, within South Gloucestershire, north of Bristol, England. Description The airfield was bounded by the A38 road to the east, and the former London to Avonmout ...

at neighbouring

. Up to the 1970s, as an additional safety measure to supplement the track circuits a single wire ran through the tunnel fixed at head height, the purpose being that if a train brokedown in the tunnel the driver or guard would cut the wire and so put the signals to red behind the stricken train. The tunnel passes through multiple underground water conduits and springs, which has been attributed for the tunnel's tendency towards frequent

flooding A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant concern in agriculture, civi ...

. Water has been measured entering the tunnel at rates of up to 2.5 cubic metres per second. These floods have been a common cause of closures of the tunnel, which has resulted in frequent cancellations and the diversion of passenger and freight services. Accordingly, the tunnel has been a long-standing high-priority asset for attention amongst railway maintenance staff, despite the installation of pumps and other measures to remove the water. During the 2010s, various plans were produced to improve the flooding situation, including the installation of of pipes for a new gravity drainage system. This pipe, which has an external diameter of 1.2 metres and a length of 22 meters, has a capacity of 866 litres per second, and discharges into a newly enlarged lagoon, which can to hold up to . Its installation necessitated the partial removal of an older brick culvert which carries water from the tunnel to the nearby Kingrove river. As part of the modernisation of the Great Western main line, the route through the tunnel was temporarily closed to traffic between 8 May 2017 and 19 July 2017, and again between 19 August and 15 September 2017. During these closures, the tunnel was retrofitted to fit overhead electrification equipment, which was installed along its roof via nearly 7,000 holes driven into the ceiling. This package of works also involved measures to reduce the occurrence of flooding.

Coordinates

* Western end - * Eastern end -

References

{{reflist South Wales Main Line Railway tunnels in England Tunnels completed in 1900 Rail transport in Gloucestershire Great Western Railway Tunnels in Gloucestershire Grade II listed buildings in Gloucestershire