On 7 March the British Tunnelling Society held a half-day seminar titled "Lessons to be learned from recent Shotcrete Tunnelling in London Clay" providing a forum for frank discussion following the controversy of the years following the Heathrow collapse.
In a move initiated by late chairman David Wallis, the event was designed to bring attendees up to date with current thinking following the extremely bad publicity for NATM in recent years. As well as the Heathrow central area collapse, presentations covered subsequent Heathrow Express work, the Waterloo and London Bridge Jubilee Line Extension stations and the Heathrow Baggage Tunnel. Subsequent discussions extended into other underground applications of shotcrete. The main non-spercific themes were the use of instrumentation, designing for shotcrete support and insurance risk.
The atmosphere among speakers and delegates was predominently positive, mainly in recognition of cost savings achievable with shotcrete support, and the complexity of excavations that can be supported easily.
It was unfortunate that no representatives of the original NATM marketers were present to argue their case. Unlike previous meetings, the reception was likely to have been a lot more favourable provided there was evidence of recognition of past problems and their likely solutions.
Important authoritues within British tunnelling are prepared to reconsider, and indeed promote, both NATM and pre-designed shotcrete support lining in appropriate contexts.
A full report on this important meeting of the British Tunnelling Society is planned for the next issue of T&TI.
