Penmanshiel Tunnel is a now-disused railway tunnel near Grantshouse, Berwickshire, in the Scottish Borders region of Scotland. It was formerly part of the East Coast Main Line between Berwick-upon-Tweed and Dunbar.
The tunnel was constructed between 1845 and 1846 by contractors Ross and Mitchell, to a design by John Miller, who was the engineer to the North British Railway. Upon completion, the tunnel was inspected by the inspector-general of railways, Major-General Charles Pasley, on behalf of the Board of Trade.
The tunnel was 244 metres (267 yd) long, and carried two running lines in a single bore.
During its 134-year existence, the tunnel was the location of two incidents investigated by HM Railway Inspectorate. The first was in 1949, when a serious fire destroyed two carriages of a south-bound express from Edinburgh. Seven passengers were injured, but there were no deaths.
The second incident occurred on 17 March 1979 when, during improvement works, a length of the tunnel suddenly collapsed. Thirteen workers escaped, but two were killed. Later it was determined that it would be too dangerous and difficult to rebuild the tunnel, so it was sealed up and a new alignment was made for the railway, in a cutting to the west of the hill.
The tunnel was also affected by severe flooding in August 1948.
On 12 August 1948, 159 millimetres (6.25 in) of rain fell in the area, the total for the week being 270 mm (10.5 in). Rain falling on the Lammermuir Hills surged into the Eye Water towards Reston, and the channel could not accommodate all of the water. The flood water then backed up the tunnel and flowed to sea in the opposite direction, towards Cockburnspath. The tunnel was flooded to within 610 mm (2 ft) of the crown of the portal.
On the evening of 23 June 1949 a fire broke out in the tenth coach of an express passenger train from Edinburgh to King's Cross, about 2.5 miles (4 km) south of Cockburnspath. The train stopped somewhere near the tunnel, within one and a quarter minutes of the fire starting, but the fire spread rapidly and with such ferocity that, within seconds, the brake-composite carriage was engulfed and the fire had spread to the coach in front. Most passengers escaped by running to the guard's compartment or forwards along the corridor, but some were compelled to break the windows and jump down onto the track. One woman was seriously injured by doing this.
The train crew reacted quickly to the incident. The two coaches behind the two ablaze were uncoupled and pushed back, leaving them isolated up the line. Having drawn forward and uncoupled the two burning vehicles, the driver proceeded with the front eight coaches to Grantshouse station.
The cause of the fire was thought to be a cigarette end or lighted match dropped against a partition in the corridor, the surface of which was found to have been coated with a highly-flammable lacquer. Subsequent analysis of the lacquer indicated that it was composed of nearly 17% nitrocellulose and sustained "startling" combustion. Draughts of air from the open windows may have fanned the flames.
Despite the noxious fumes and the severity of the blaze, which reduced the two carriages to their underframes, only seven passengers were injured, with no fatalities.
The next significant event to occur at the tunnel led to its abandonment.
Work was being carried out in March 1979 to increase clearances within the tunnel, so that intermodal containers 8 ft 6 in (2.59 m) in height could be carried through it on flat wagons. This was performed by removing the existing track and ballast, digging out the floor of the tunnel by between 300 and 800 mm (12 and 31 in), and then laying new track on a concrete base at the lower level. Use of concrete base helped reduce the amount by which the floor had to be lowered. The process was judged to be safe so long as the walls of the tunnel were not undercut in the course of the works.
In order to minimise disruption to both passenger and freight services on the busy main line, it was decided that each of the two tracks through the tunnel would be renewed consecutively rather than concurrently; while one track was closed for lowering, trains could continue to run on the adjacent open track. Work was completed on the "Up" (southbound) track by 10 March 1979, and trains were then transferred to this track by the following day, to allow the "Down" (northbound) track to be modified.
Shortly before 3:45 a.m. on 17 March 1979, the duty railway works inspector noticed some small pieces of rock flaking away from the tunnel wall, 90 m (300 ft) from the southern portal. He decided that it would be wise to shore up the affected piece of the tunnel and was making his way towards the site office to arrange this when he heard the sound of the tunnel collapsing behind him.
It is estimated that approximately 20 m (66 ft) of the tunnel arch collapsed, with the resultant rockfall filling 30 m (98 ft) of the tunnel from floor to roof and burying a dumper truck and an excavator, along with the two men operating them. The 13 other people working inside the tunnel at the time of the collapse were able to escape, but despite the efforts of rescuers (including a specialised mine rescue team) it was not possible to reach the two operators or to recover their bodies.
An official HM Railway Inspectorate report was prepared by Lieutenant Colonel I. K. A. McNaughton and released on 2 August 1983. The report concluded that, without access to the collapsed portion of the tunnel, it was impossible to be certain as to the "actual cause" of the collapse.
Neither the tunnel's history, nor its condition immediately prior to commencement of the works, had given any significant cause for concern, and it was noted that workers had "paid particular attention" to the state of the tunnel walls throughout the works; "at no time" had any cracks or fractures been observed. The need to avoid undercutting the side walls during the excavation of the floor had also been observed with "great care", and a series of monitoring measurements taken periodically across the tunnel – using nails that had been machine-driven into the walls at 10-metre (33 ft) intervals especially for this purpose – had not revealed any movement. The inspectorate found that the works on site "[appeared] to have been carried out with proper care and foresight", and that there was no evidence to suggest that the side walls of tunnel had been subjected to excessive force or vibration during the upgrade works.