Air shaft in the Kilsby Tunnel, illustrated in an 1852 railway publication.
|Operator||West Coast Main Line|
|No. of tracks||Two|
The Kilsby Tunnel is a railway tunnel on the West Coast Main Line railway in England. It is located near the village of Kilsby in Northamptonshire roughly 5 miles (8 km) south-east of Rugby and is 2,432 yards (2,224 m) long. Upon opening, Kilsby tunnel was recognised as being the longest railway tunnel in the world. As of 2018, it is the 18th longest tunnel on the British railway system.
The Kilsby Tunnel was designed and engineered by British engineer and railway pioneer Robert Stephenson as a part of the London & Birmingham Railway (L&BR). Construction work was initially performed by contractors Joseph Nowell & Sons and later by the L&BR itself, the tunnel's construction took far more time, and cost far more money, than had been anticipated. This substantial overrun has been primarily attributed to an unexpected collapse of the tunnel roof and consequential flooding, which had the effect of adding to the project's workload considerably.
The tunnel was fitted with atypically large ventilation shafts, alledgely due to a lack of experience to dictate how much ventilation would be needed for steam locomotives to safely traverse a long tunnel. Upon its opening during 1838, the tunnel was fitted a single line of track running through its length; during 1879, this was re-laid as a double-track arrangement instead. During March 1987, various elements of Kilsby Tunnel were given listed status, including both tunnel portals and its two large ventilation shafts.
During the 1830s, famed engineer and railway pioneer Robert Stephenson embarked upon the development of the London & Birmingham Railway (L&BR) (later known as the West Coast Main Line). As a result of vigerous opposition from figures, including several landowners and proprietors, within Northampton, during July 1832, the House of Lords voted to reject the original bill that would have authorised construction of the line; accordingly, Stephenson surveyed an alternative route located to the west of the town; it was this new route that featured what would be later built as Kilby Tunnel. At the time, the proposed 2,423 yard tunnel was to be the largest railway tunnel in the world. During May 1835, Joseph Nowell & Sons were awarded the contract, which was valued at £98,988, for the construction of the tunnel.
However, the construction programme soon proved to be less than straightforward. Within months of work commencing, the second of the working shafts was flooded as a result of the presence of large amounts of quicksand; trial borings into the hill had not revealed any quicksand in the vicinity, but Stephenson had already made efforts to avoid any such an encounter being made. However, similar problems had previously been encountered during the construction of the nearby Blisworth tunnel on the Grand Union Canal only a few decades earlier. The problems that were posed by the quicksand, which was eventually revealed to be quite prevent at tunnel level, were so severe that some considerations were allegedly made towards the abandonment of the shaft and restarting work afresh elsewhere; the resulting stress of the project was said to be the cause of Joseph Nowell's ill-health and death.
At the recommendation of engineer George Stephenson, Robert's father, several steam-powered pumps were installed on site; these were used to extract the excess water from the quicksand inside the tunnel; the pumping out process, which was capable of removing up to 2,000 gallons of water from a depth of 120 feet for every minute of operation, is believed to have taken as many as eight months of the project. Another measure was taken in the form of seven additional shafts, which were sunk for the purpose of installing timber cylinders for the purpose of helping to hold back the sand. During this time, multiple attempts were made to construct the tunnel's brick lining using a raft to float both men and materials into position. As a protectve measure, the lining's thickness was increased from 18 inches to in excess of two feet, straw was also used to deflect and control the ingress of water to prevent wet concrete from simply being washed away from newly placed bricks.
Perhaps the most unusual feature of the tunnel is the sheer size of its ventilation shafts, which were adapted from ten of the working shafts used during its construction. During May 1836, work started on the first of these two vast shafts, which were 132 feet deep and 20 yards in diameter; these were constructed using sequentially-dug trenches around the circumference and took over a year to reach the bottom of each shaft. Its three-foot thick walls required over one million bricks and weighed an estimate 4,034 tonnes, for aesthetic reasons, both shafts are castellated. Author Graeme Bickerdike has speculated that, while their size is excessive in regards to providing airflow, there was considerable importance placed upon overcoming public perceptions and worries over personal health due to insufficient ventilation, especially in regards to the use of steam locomotives inside lengthy tunnels. During this time, several newspapers had negatively commented on these issues, and it is likely that Stephenson would have wanted to silence critics and assuage these sentiments by visibly demonstrating how much ventilation was being provided.
Completion and subsiquent activities
On 21 June 1838, resident engineer Charles Lean laid the final brick of the tunnel, marking its completion. It took three years, and cost £320,000 to build — three times the original estimate (£23,758,000 in 2005 pounds). There had also been a relatively high accident rate in its construction, including the deaths of 26 of the 1,250 men involved. The length of time it took to build the tunnel had considerably delayed the opening of the L&BR as it comprised a vital section of the route. On 20 August 1838, the directors of the L&BR conducted the first ever rail journey between Birmingham Curzon Steet railway station and Euston railway station, London. On the way, the train briefly stopped at the tunnel so that they could marvel at the structure and meet with some of the workmen. Regular services using the tunnel commenced shortly thereafter.
Despite the fact that Kilsby Tunnel had been designed and built with the capacity for accommodating a pair of tracks, it was initially completed only with a single line of track running through its length. During early operations, the management of train movements was performed by a pair of policeman, one of which being stationed at either end of the tunnel, who would visually signal the presence of a train to one other, as only one train was allowed to enter the tunnel at a time. During June 1852, a fatal collision occurred between a ballast train and a coal train as a result of signals that were either not issued or were not received. During 1879, the original single track was replaced with a twin-line arrangement.
During March 1987, both the north and south portals of Kilsby Tunnel were Grade II* listed; furthermore, the two largest ventilation shafts were also listed, the north shaft being Grade II* listed while the south shaft was Grade II listed. During the tunnel's service life, there have been no major problems or difficulties with the structure have reportedly been experienced. During a survey conducted during the 2010s, it was found to be in a largely good condition.
During the 2010s, Kilsby Tunnel was the subject of a programme of restoration work commissioned by its owner, the state-owned rail infrastructure operator Network Rail. This maintenance activity was focused on inspecting both of the ventilation shafts, after which repairs to the brickwork of one shaft was carried out, in addition to the replacement of sections of the tunnel's lining. While unusual means of access had to be employed, in part due to the listed status of the shafts, the repairs themselves were described as being routine.
- Bickerdike, Graeme. "Stairway to heaven: shaft repairs at Kilsby tunnel." Rail Engineer, 27 April 2018.
- "Kilsby Tunnel". Spartacus Educational.
- According to Table 1 of "Archived copy" (PDF). Archived from the original (PDF) on 26 March 2009. Retrieved 2 July 2012., the RPI index in 1838 was 10.2 and had risen to 757.3 in 2005, giving a conversion factor of 74.245.
- "Kilsby Tunnel." engineering-timelines.com, Retrieved: 6 May 2018.
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