Penmansheil Tunnel collapse

[52D]

I have just read the report on the Penmansheil Tunnel collapse http://www.railwaysarchive.co.uk/docume ... el1979.pdf
It makes sobering reading as the rock overlying the tunnel was by its nature unstable and could have collapsed at any time over the years. Its a miracle that it didnt collapse when a train was coming through.

[Pullman]

There is a small memorial garden on top of the tunnel roughly abover were the two workmen were killed by the roof fall. A Gordon Turner & Peter Edgar Fowler. The tunnel has been completely earthed-over at each portal. The remains of the south portal are a restful area, complete with several beehives.

Pullman

[Pullman]

Photo of the memorial Garden

[Deltic18]

If I remember correctly, the last train to go through there was 6E41 Leith South - Haverton Hill discharged anhydrous (apologies for the spelling) ammonia tanks. If it had come down on those.... well it doesn't bear thinking about! As a slight aside to that, whilst the line was shut between Bewrick and Dunbar, as we all know, a lot of services were diverted via Carlisle and Beattock. Matters were not helped when there was a landslip at Reilly Mill, just south of Durham. The Leamside branch (please reinstate it) was closed for planned maintenance (!) so everything was diverted via The Coast. That certainly upped the journey time!
Keith

[Mr Bunt]

I have just read the report on the Penmansheil Tunnel collapse http://www.railwaysarchive.co.uk/docume ... el1979.pdf
It makes sobering reading as the rock overlying the tunnel was by its nature unstable and could have collapsed at any time over the years. Its a miracle that it didnt collapse when a train was coming through.

What has always surprised me about Penmanshiel is that if it was so easy to find a new route for the line after the collapse that was all in cutting why was the tunnel ever built at all? Tunnelling is far more expensive than digging cuttings and it was private shareholders money which would have been spent on excavating it then.

A rather apocryphal tale I've heard told more than once is that the engineer involved with the original construction had never built a tunnel before and wanted to try his hand at it. His obviously poor knowledge of geology may bear the story out though.

[52A]

There was also over 100 years of development in civil engineering technigues and machinery.

[richard]

And there's going to be a point where a tunnel is cheaper (I don't know where that is in relation to Penmanshiel, mind you).

A lot of tunnels in the US have been opened up into cuttings. Usually this occurs after a collapse, landslide, or derailment. In such cases, it is probably cheaper and easier to open it up than to perform a proper tunnel repair or cut&cover job.


Richard

[52A]

I am sure that I read somewhere that during the building of the line through Penmanshiel there were difficulties with the boring of the tunnel due to the geology and that a diversion was contemplated.

[Pullman]

Yes indeed, it would seem the tunnel was hardly necessary at only 180 yards long.

Following the blockage of the tunnel, strenuous efforts were made to clear the roof-fall but all attempts proved too hazardous. A decision was made therefore in late April to by-pass the tunnel in a cutting. The serious effect of this blockage of the East Coast Main Line on passenger and freight services – a bus shuttle being operated between Berwick and Dunbar, and some trains were routed via Carlisle – required a major effort to get the railway open again. The deviation was around 1,100 yards long, but work associated with this extended over a total of 2,200 yards and involved the diversion of the A1 Trunk Road.

The consultants Mott, Hay & Anderson immediately embarked on the planning and design work necessary to enable the reopening of the line by no later than 1st October. Sir Robert McAlpine & Sons Limited began work on the site on 8th May.

The first and major work to be undertaken was the main cutting, which had, by this time, been designed. It lies a maximum 50 yards to the west of the blocked tunnel. Because its vertical depth is approximately 45 yards the slope had to be interrupted by two berms
(terraces), the upper slope being at one and a half to one and the lower at one to one.

Rock excavation was undertaken by McAlpine’s sub-contractor, Tractor Shovels and in six weeks the cutting was complete and 200,000 cu.yds. of rock and 100,000 cu.yards of ‘soft dig’ had been excavated. Much of the excavated material was used to form embankments for a previously planned realignment of the A1 trunk road and also for embankments for a temporary diversion of the A1 to suit the realignment of the railway.

The routes of the A1 diversions lay on ground that was six to eight yards deep in peat and silt, which had to be removed and dumped nearly before the embankment could be formed. The new cut slopes were landscaped and treated to the requirements of the Borders
Regional Council.

As this excavation proceeded, design work continued on the remainder of the undertaking. In order to minimise excavation in the main cutting, it was decided to build the new track four yards higher than the existing one. This necessitated the raising of over-bridge No.117 (Nellie’s Bridge) but site investigation revealed that its foundations were not strong enough to take the additional load and complete reconstruction of this bridge was therefore required.
The westward repositioning of the new line encroached on the inlet leg of the siphon carrying Pease Burn (which gained some notoriety during the 1947 floods). Thos consists of three pipes three yards in diameter and the required lowering and extension had to be undertaken with great care keeping water flowing through part of it while the remainder was being rebuilt.

Another effect of moving the railway closer to the A1 was that a sheet pile retaining wall had to be provided over a length of 150 yards. The diversion of the A1 required 25,000 cu.yds of rock to form the embankment and the construction of a three span Bailey bridge over the new railway. This work was the key factor because, until road traffic was diverted, the new railway formation could not be carried through the old A1 alignment.

Work went on around the clock and conditions varied from being 12in deep in muddy slurry in wet weather to ‘dust-bowl’ conditions in dry weather. At night the site was as bright as a city street with a total of 18 high lighting towers in use.

Eventually the A1, was rebuilt to motorway standards and crossed the railway by a bridge slightly south of the old tunnel. This bridge marks the southern end of the rail diversions, the northern end being by ‘Nellie’s Bridge’. The line reopened on 20th August when full Anglo-Scottish “Inter-City 125” HST services between London Kings Cross & Edinburgh, and Aberdeen, which had been postponed since May were inaugurated.

Tis a great shame those two men had to loose their lives in that tunnel. The entire area is now a most restful and peaceful place and the portal closest to the A1 now houses many bee-hives and plenty of yellow gorse.

Pullman