Penmanshiel Tunnel

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.[10] Use of concrete base helped reduce the amount by which the floor had to be lowered.[11][note 1] The process was judged to be safe so long as the walls of the tunnel were not undercut in the course of the works.[12]

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.[10]

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, approximately 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.[13]

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 totally enveloping a dumper truck and an excavator, along with the two men operating them.[14] The thirteen other people working inside the tunnel at the time of the collapse were able to escape successfully, 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.[3]

External images
South Portal of Penmanshiel Tunnel, 25 March 1979. Photograph taken from a passing vehicle eight days after the collapse.
North Portal of Penmanshiel Tunnel, 1979. Photograph taken later in 1979, showing the tunnel mouth boarded up and the approach cutting partially filled-in.

An official HM Railway Inspectorate report was prepared by Lieutenant Colonel I. K. A. McNaughton and released on 2 August 1983.[3] 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.[15]

Neither the tunnel's history, nor its condition immediately prior to commencement of the works, had given any significant cause for concern,[16] 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.[17] The need to avoid undercutting the side walls during the excavation of the floor had also been observed with "great care",[18] 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.[17] Accordingly the inspectorate found that the works on site "[appeared] to 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.[19]

Investigations into the remaining tunnel structure, particularly that adjacent to the collapsed area, did reveal inconsistencies in the tunnel's construction. A number of 'windows' cut through the brickwork by investigators showed that the crown of the arch was generally of sufficient thickness, but that this thickness tapered off through the haunches where the arch transitions into the side walls.[20] Other windows exposed cavities and voids in the rock behind the brickwork, some of which were filled with loose rock.[21] On the whole though, these findings were deemed to be inconclusive.[20][note 2] Tests conducted on samples of brickwork showed it, and the associated mortar, to be of reasonable strength; confirming observations made during the cutting of the samples, and also reports from repair works that had been conducted on the tunnel in the past.[23]

Geotechnical investigations into the surrounding hillside found evidence suggesting fracturing of the rock overlying the tunnel, but similarly this was not thought to be sufficiently definitive.[24] Only during excavation of the cutting for the bypass alignment (discussed below) did the "most revealing" piece of evidence become available: a detailed geological survey of the hill along the line of the cutting exposed an anticlinal structure of shattered and sheared rock that was found to intersect the line of the tunnel in close proximity to the area of the collapse.[25]

The report accordingly concluded that the collapse was likely to be the result of degeneration of the rock within the anticlinal structure overlying the tunnel, which progressively—but inconsistently—increased the loading on the tunnel's brick arch ring in a way that could not adequately be distributed into the surrounding hillside.[15] The existence of the anticline would almost certainly have never been confirmed without the excavation of the bypass cutting, and it was considered "most unlikely" that the "extreme complexity" of the geology could ever have been appreciated by investigation of rock exposed in the tunnel or though other routine investigatory techniques.[26]

It was further noted that the degeneration of the overlying rock had made the tunnel "dangerously unstable" for many years prior to the collapse, and that the collapse would most probably have occurred at some time or another regardless of whether or not the enlargement works had been undertaken.[27] Nonetheless, the investigation thought it likely that the works did contribute to the timing of the collapse, in that the already overloaded tunnel walls could not tolerate the slight increase in stress placed upon them by the excavation of the tunnel floor.[27]

Finally the report stated that—as the conditions leading to the collapse could not reasonably be foreseen—there were no grounds for finding any individual responsible for the accident.[28] Despite this the British Railways Board was charged in the High Court of Justiciary at Edinburgh with breaching the Health and Safety at Work etc. Act 1974 by "having failed to do all that was reasonably practical to ensure that persons in the tunnel were not exposed to the risk of personal injury by the collapse of part of the [tunnel] structure", on the basis that a full geotechnical survey—whether futile or not—had not been conducted prior to the works commencing.[29] The Board entered a guilty plea and was fined £10,000.[3]

Peter Fowler

Gordon Turnbull

Memorial plaques

As the collapsed portion of the tunnel was never excavated, the site became the final resting place of both workers who were killed in the collapse; Gordon Turnbull from Gordon, 22 miles (35 km) away, and Peter Fowler from Eyemouth. A three-sided obelisk was erected over the point where the tunnel collapsed to act as a memorial.[3] One face of the obelisk displays a cross, while each of the other two faces commemorates one of the men killed.

The memorial is adjacent to a road running over the hill and is marked on 1:50,000 and 1:25,000 scale OS maps, at grid reference NT 797670. From the maps it is also possible to determine the abandoned section of the A1 road, but the original course of the railway is not visible.

• Walker, Col. R. J. (16 January 1950). Report on the Fire which occurred in an Express Passenger Train on 23rd June, 1949, at Penmanshiel Tunnel in the Scottish Region British Railways (PDF). London: His Majesty's Stationery Office.
• Rolt, L. T. C. (1966). Red for Danger (2nd ed.). Newton Abbot: David & Charles. OCLC 897379.
• Thomas, J. (1971). Scotland: The Lowlands and the Borders. A Regional History of the Railways of Great Britain. Vol. VI (1st ed.). Newton Abbot: David & Charles. ISBN 978-0-71535-408-7. OCLC 16198685.
• Nock, O. S.; Cross, D. (1982). Main Lines Across the Border (Revised ed.). London: Ian Allan. ISBN 978-0-71101-118-2. OCLC 11622324.
• McNaughton, Lt.Col. I. K. A. (2 August 1983). Report on the Collapse of Penmanshiel Tunnel that occurred on 17th March 1979 in the Scottish Region British Railways (PDF). London: Her Majesty's Stationery Office. ISBN 0-1155-0626-8.
• Biddle, G. (1990). The Railway Surveyors: The Story of Railway Property Management 1800–1990. London: Ian Allan for the British Rail Property Board. ISBN 978-0-71101-954-6. OCLC 59852551.