Box, Wiltshire, UK
Isambard Kingdom Brunel
September 1836 - June 1841
ICE reference number
Box Tunnel was the last-finished and largest engineering work on Brunel's Great Western Railway, which ran between London and Bristol. At the time of its completion, it was the longest railway tunnel in existence, at almost 2.9 kilometres (1¾ miles). It remains in daily use, more than 160 years later.
Brunel had planned the 118 miles of railway so that the majority of it was either level or had gradients no steeper than 1 in 1000. Swindon was at the highest point of the line, which then fell westwards to Bath. Most of the fall was located in a section west of Wootton Bassett and a section that would include the tunnel under Box Hill, near Corsham. The section including the tunnel would lie at a gradient of 1 in 100, a steep gradient for rail. The idea of such a gradient in a rail tunnel provoked consternation and criticism from some of Brunel's contemporaries.
Box Hill was a formidable obstacle to the completion of the railway, not least because it contained a thick bed of great oolite, a type of limestone better known as Bath Stone because of its extensive use as a building material in that area.
Work on the tunnel began in September 1836, when six permanent shafts were sunk into the hill. They were 8.5m (28ft) in diameter and the deepest was 88m (290ft) from surface to rail level. They were completed by the autumn of 1837, when contracts for the excavation of the tunnel were advertised.
George Burge of Herne Bay dug the western two kilometres (1¼ miles), while two local teams, one led by Brewer of Box, the other by Lewis of Bath, did the more difficult eastern 0.8 kilometre (½ mile). One of Brunel's personal assistants, William Glennie, remained in charge of the whole work until completion, for which he was paid £150 per annum (a low sum compared with assistants later in Brunel's career).
It was a tremendous task, carried out by candlelight, and using the power of men and horses. The eastern section, which comprised the oolite, was blasted out and cut in the form of a gothic arch, and left unlined. The job was made more difficult, particularly in the wet winters, by the ingress of water through fissures in the rock. In November 1837 water overpowered the steam pump used to remove it, filled the tunnel and rose 17m (56ft) up the shafts. A second pump was installed as a result.
The western section was excavated by pick and shovel, using techniques developed in the construction of canal tunnels, and lined with brick. The excavated material was brought up the shafts in buckets, hoisted by horses at the surface. Over 30 million bricks were used. They were made a few miles away, near Chippenham, and brought by horse and cart.
Lewis and Brewer started blasting work from opposite ends. There was great anticipation about whether their two tunnels would align accurately. In fact, when the two gangs at last met, the junction was perfectly true. Brunel, who was present, was so delighted that he took a ring from his finger and gave it to the foreman.
The tunnel is completely straight, a fact that has fuelled a persistent but unconfirmed rumour that Brunel aligned it so that the rising sun would shine through it on his birthday — 9th April — every year.
However, the tunnel was not ready on schedule — it was supposed to be finished in August 1840 — so thereafter Brunel increased the workforce to 4,000 men and 300 horses, as the rest of the line was already complete. Finally, on 30th June 1841, a special train left Paddington and made the first complete rail journey to Bristol Temple Meads, in around four hours.
The completed tunnel was, and remains, 9.1m (30ft) wide, which could accommodate two of Brunel's broad-gauge lines. Its eastern end was left plain, while the west has a Classical portal, easily visible from the A4 just east of Box. It is said that in every week of the tunnel's construction a tonne of gunpowder and a tonne of candles were used, and that by its completion 100 men had died.
Rather like those who doubted Brunel's shallow arches in his bridge at Maidenhead, there were commentators who expressed concern about the solidity of the unlined part of Box Tunnel. In time, the Great Western Railway added a brick arch under some of the unlined section close to the entrance, which was more prone to frost damage. However, some of the tunnel remains unlined to this day.
"Brunel: The Life & Times of Isambard Kingdom Brunel"
by Angus R. Buchanan
Hambledon & London Ltd, 2002