In the 1830s, Robert Stephenson developed the London & Birmingham Railway (L&BR) (later known as the West Coast Main Line).
After opposition from several landowners and proprietors in Northampton in July 1832, the House of Lords rejected the original bill to authorise construction of the line.
Stephenson surveyed an alternative route to the west of the town that included Kilsby Tunnel.
The 2,423 yard tunnel would be the world's longest railway tunnel.
In May 1835, Joseph Nowell & Sons was awarded the tunnel contract, which was valued at £98,988.

Construction proved to be less than straightforward.
Within months of work commencing, the second of the working shafts was flooded because of large amounts of quicksand not revealed by trial borings into the hill.
Similar problems had been encountered during the construction of Blisworth Tunnel on the Grand Union Canal a few decades earlier.
Problems posed by the quicksand at tunnel level were so severe that abandoning the shaft and restarting work elsewhere was considered.
Stress from the project was said to have caused Joseph Nowell's ill-health and death.

At the recommendation of George Stephenson, several steam-powered pumps were installed to extract water from the quicksand inside the tunnel.
The pumps removed up to 2,000 gallons of water from a depth of 120 feet every minute of operation and took up to eight months.
Seven more shafts were sunk to install timber cylinders to hold back the sand.
During this time, multiple attempts were made to construct the tunnel's brick lining using a raft to float men and materials into position.
As a protective measure, the lining's thickness was increased from 18 inches to in excess of two feet and straw was used to deflect and control the ingress of water to prevent wet concrete from being washed away from newly laid bricks.

An unusual feature of the tunnel is the size of its ventilation shafts, which were adapted from ten of the working shafts used during its construction.
In May 1836, work started on the first of two shafts, which were 132 feet deep and 20 yards in diameter.
The shafts were sunk 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 estimated 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, considerable importance was placed on overcoming public perceptions and worries over personal health due to insufficient ventilation, especially in regards to the use of steam locomotives inside lengthy tunnels.
Several newspapers had negatively commented on the 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.
In the 1830s, Robert Stephenson developed the London & Birmingham Railway (L&BR) (later known as the West Coast Main Line). After opposition from several landowners and proprietors in Northampton in July 1832, the House of Lords rejected the original bill to authorise construction of the line. Stephenson surveyed an alternative route to the west of the town that included Kilsby Tunnel. The 2,423 yard tunnel would be the world's longest railway tunnel. In May 1835, Joseph Nowell & Sons was awarded the tunnel contract, which was valued at £98,988.
Construction proved to be less than straightforward. Within months of work commencing, the second of the working shafts was flooded because of large amounts of quicksand not revealed by trial borings into the hill. Similar problems had been encountered during the construction of Blisworth Tunnel on the Grand Union Canal a few decades earlier. Problems posed by the quicksand at tunnel level were so severe that abandoning the shaft and restarting work elsewhere was considered. Stress from the project was said to have caused Joseph Nowell's ill-health and death. 
At the recommendation of George Stephenson, several steam-powered pumps were installed to extract water from the quicksand inside the tunnel. The pumps removed up to 2,000 gallons of water from a depth of 120 feet every minute of operation and took up to eight months. Seven more shafts were sunk to install timber cylinders to hold back the sand. During this time, multiple attempts were made to construct the tunnel's brick lining using a raft to float men and materials into position. As a protective measure, the lining's thickness was increased from 18 inches to in excess of two feet and straw was used to deflect and control the ingress of water to prevent wet concrete from being washed away from newly laid bricks.
An unusual feature of the tunnel is the size of its ventilation shafts, which were adapted from ten of the working shafts used during its construction. In May 1836, work started on the first of two shafts, which were 132 feet deep and 20 yards in diameter. The shafts were sunk 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 estimated 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, considerable importance was placed on overcoming public perceptions and worries over personal health due to insufficient ventilation, especially in regards to the use of steam locomotives inside lengthy tunnels. Several newspapers had negatively commented on the 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.
Kilsby Tunnel