http://www.bbc.co.uk/bristol/content/articles/2007/07/06/combe_down_feature.shtml 

found this... a bit of a 'laymans view' with the usual errors ( use of the terms 'shaft' and 'tunnel', misunderstandings about the difference between temporary and permanent support, and certain elements which have become out-of-date ) but not a bad view of what's been going on here

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Very interesting... I never realised these were as extensive as they are, Be nice to see a survey of just how big they were...

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total area about 45 acres, depending on how you define it since they tend to end in indeterminate areas of quarry backfill as the stone outcrops into the hillside. There are also further areas of workings which for various reasons are not included in the project.

there have been a little less than 15km of temporary roadways constructed and at one time it was the largest working mine site in Britain ( 275 men underground ) and the largest single-location user of cement in Europe.



digressing somewhat, the best documentary I have ever seen about mining was an episode of Horizon called 'Hard Rock' dating from the early 80s, describing the then-current Carsington Reservoir tunnelling works. This was a hugely complex contract which was in part, an attempt to bypass the contentious 'Clause 12' claims for extra payment for, well, pretty much anything, which were a plague in tunnelling work at the time.

it was a substantial failure, causing more problems than it solved and suffering huge cost over-runs. It was also notable for the catastrophic failure of the dam during construction and subsequent bankruptcy of the consultant that designed it, since the claim far outstripped their PI insurance.

there are various liberties taken for the sake of making a watchable programme, and various things were not made public in such a context, but as a depiction of the contractual infighting and technical problems on a major mechanised tunnelling project it was pretty good, and the footage of the tunnelling work was very advanced for the time

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Yes I remember a couple of deaths on the Carsington tunnel... bad air or something... I remember the project being somewhat of a laughing stock around here...

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there was a good deal of uninformed nonsense talked locally about Carsington, then and since.

Like the Dinorwic machine halls which preceded it, it was a serious attempt to do something technically challenging on a large scale, it was very successful in some ways and less so in others. The dam collapse was one of the projects' less distimguished episodes, and the selection of the tunnelling machines proved unduly optimistic - one stood on its launch bridge over the A6 at Bakewell for a very long time, one was abandoned in the ground and the fourth one never assembled - while the complex grading system for grouting and excavation payment broke down under its own complexity.

Nonetheless these were real problems and represented serious, cutting-edge research at the time.



It did become rather a notorious job for poor conditions and high personnel turn-over. It broke the back of 'London John' - John Mowlem's tunnelling division - although they ultimately made a lot of money on the claims, that was years later and the main board directors had long since decided to do other things by then.

the Mowlem staff were told that they would be made redundant as the job was completed, and of course most of them left as soon as they had anywhere else to go. The latter stages of the job were carried out by a motley crew of freelancers, 'agency' staff and miscellaneous 'odds and sods' with a core of Mowlems management who had been persuaded to stay.

I spent a few unhappy weeks there before moving on 😞

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Of interest concerning the construction of the Carsington Reservoir, is the fact that it uses the the water being drained from the Wirksworth lead mines and surrounding area by one of the largest of the Derbyshire soughs i.e. the Merebrook sough (driven from 1772 to 1848 at a cost of approximately £80,000, it's total length with branches being about five miles - tradition has that it was constructed by convict labour i.e. French prisoners of war during the Napoleonic Wars). The outflow is mainly used for the public water supply by the Severn Trent Water Authority, in 1950 the average flow was 15 million gallons a day, ranging from 11 to 19 million gallons daily, and in 1961 the Water Authority was allowed to extract 11 million gallons daily. The surplus flows into the River Derwent from the sough tail (found north of Whatstandwell Bridge, up river, on the west bank of the River Derwent, just below the Holmesford Cottage Public House's car park on the A6) and adds to the volumne of the river water. However, south of Whatstandwell Bridge, again on the west bank of the River Derwent the tunnel driven by Mowlem the contractors (from memory wasn't it the original firm of contractors [Shepherd's] that went bankrupt, there were a couple or more deaths as well) goes through to the Carsington Reservoir. So in effect water drained from beneath Wirksworth is being pumped, from below the outfall of the Merebrook sough, out of the River Derwent and back into the reservoir. A good example of recycling!

Shepherd's had one of the preliminary contracts and it broke them.

Mowlem were appointed in considerable part because they were sufficiently large to stand the cash-flow if things remained a problem, and they did. Mowlem's did complete the project, but the main board directors decided that the returns represented an unacceptable commitment of company resources for an excessive period of time at an unacceptable level of risk, and closed down the tunnelling side to focus on other activities.

This is more common than you might think. The same thing happened to Lilley at the Don Valley Interceptor Sewer in the late 1970s. Mowlem actually benefitted considerably from their experience at Carsington on the second phase of this project, just about the last major tunnel project they did.

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Living at Bonsall then and just having opened my Guest House, I was very grateful to have Mowlam workmen stay at my guest house. I watched the project with interest. We had a friend who towards the end of the contract was a driver of the train in the tunnel, I think he was agency staff.

Now living near Portsmouth I find it interesting that Mowlam were once again way behind with completion date and underestimated the total cost of building the Spinnacker Tower to commemorate the Millennium!

hi Derrickman. while at carsington tunnel did you meet a guy from sandbach who worked there, remember himtelling me the conditions were worse than sewer rats habitat at times.

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