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Thames Water Ring Main


The tunnelling project which gave me the most personal pleasure was the Thames Water Ring Main contract from Merton to Battersea. If ever there was a case of snatching success from the jaws of disaster, this was it.

Work on the contract had been in progress for some months when I joined Amec as its tunnelling director. I found a contractual state of war.

The first tunnel shield had advanced about 100m in very strong clays and had become seriously bent. Amec was claiming unforeseen ground conditions. The engineer was having none of it.

A second shield of identical design was almost ready for delivery from the manufacturer. And, to top it all, the contract required Amec to drive through the Thanet Sands under Tooting Bec Common with a compressed air pressure of 1 bar against ground water pressure of 4.2 bar - a complete technical nonsense.

The position worsened. Amec was spending a fortune overcoming the shield problems, and was claiming every penny.

The engineer was not certifying and the Thanet Sands problem remained unaddressed.

I was called to a meeting with the client to try to resolve the outstanding issues. The client asked if Amec would accept a form of cost reimbursement, 'open books' of course, for the remainder of the contract. I was stunned.

Thames Water was at the time in the throes of being privatised, and it seems an unresolved financial issue of the magnitude of the dispute with Amec would be a blemish on an otherwise immaculate prospectus. What luck.

Thames' decision to adopt cost reimbursement turned out to be beneficial to both parties. The form of contract adopted was the IChemE Green Book, the first time this had been used for a tunnelling contract. All the contention on the project rapidly disappeared. The non-adversarial form of contract subsequently spread throughout much of the industry.

A special team was formed to deal with tunnelling through the Thanet Sands. It opted to use an earth pressure balance machine from the Canadian manufacturer Lovat. It was Lovat's first true EPBM, and it performed magnificently.

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