A packed Telford Theatre at the Institution of Civil Engineers heard the BTS annual Christmas debate with regards the motion "This house believes further development of SCL for complex urban tunnels is the best way forward for our industry". The chairman for the evening, Roger Bridge, introduced Keith Bowers of London Underground who was proposing the motion, and Ross Dimmock of Normet UK who was opposing it. For many in the UK, SCL has become the default method of tunnelling to allow projects to go forward. The speakers this evening are endeavouring to convince you that their view is the best way forward.
The chairman advised the audience that the views are slightly polarised and not necessarily the views of the individuals. Then followed some technical difficulties and Ross asked if we could have the lights out so he could present in anonymity but the rapporteur thinks he will have chosen to change his name after tonight. The chairman balanced this by saying that we should appreciate that both speakers had much knowledge of the subject and therefore gives them the ability to argue either side of the case.
He went on to say that it was almost considered to give the vote to start with as to who opposed and who supported. He implored that the audience listened to what they have to say, as they know their subject well.
The Chairman then introduced the speakers: "Supporting the motion we have Keith Bowers. He is the Head of Tunnels for London Underground. He has engineering accountability for the plethora of tunnels and shafts of the world’s largest and oldest mass transit railways, as well as responsibility for new tunnel works and Crossrail too. He has his views on SCL, some of which he will elucidate tonight. "Ross Dimmock is a Director of Normet UK, a Finnish specialist tunnelling and mining company, in the last 27 years; Ross has worked exclusively on SCL projects globally and in the UK, both on the design and construction side. He too has views on SCL and we are privileged to hear these tonight."
The chair explained that the format for the evening was that each of the speakers will have 20 minutes to present their case, and have elected not to have "seconders", that is they are sure of their science. There is then a 20-minute debate and finally a five-minute summing up with a vote taken at the end to see who has won.
The meeting started with Bowers’ observation that the audience were once again gathered in the Telford Lecture theatre to discuss SCL, previously known as NATM.
Bowers then started by taking the audience on a journey, referring to a section of tunnelling history by indicating figures of two recognisable tunnelling machines, a couple of centuries apart, both under a city and both revolutionary at the time.
Bowers suggested that tunnelling evolves and that tunnelling practice changes. A parallel was drawn between SCL tunnelling and SCL tunnelling in the UK, which has occurred over the careers of some in the audience. A pause was suggested to reflect on that.
Reference was made to Channel Tunnel with its sprayed concrete for primary support, and dry mix just for temporary works purposes, all in all deemed a successful project. Similar construction, at Round Hill, was then referred to with the use of a dry mix for temporary works support and cast-in situ linings used to ensure the appropriate support. Noting this, the presenter alluded to modest issues with the permeability and around the steelwork used within the tunnel.
The presenter showed a few images that might have been construction practices of the norm then which are now not considered the good practice now: for example the operative next to the exposed face beginning to start to spray next to a cherry picker moving around behind him. The speaker asked the audience to consider that times have changed, practice had got better, as an industry got better at creating the product the client wanted, such the shotcrete technology has moved into permanent works and some fine examples were shown.
