Tunnel ring designs are getting more complex for facing new tunnel challenges, which were insurmountable 10 years ago. They require a new generation of connecting devices, gaskets, fibres and concrete mix, says Alain Preaut, CBE sales director. Having said that, moulds are not only an assembly of welded steel parts; [manufacturers] try, by their design, to bring some extra capabilities which will make the clients’ operation easier and thus more cost effective. These include faster vibration, easy cleaning and curing monitoring.
Most our technical efforts spent during the past five years have been focused on engineering and R&D issues to speed up the mould design process currently performed with 3D software. Then, we have reduced our delivery time and increased the precision of shop drawings programs involved in laser cutting and CNC machining.
In such a way, and by reducing the error factor (or margin), we have also sped up the final assembly process. Our fitters can focus on mould accuracy and tolerances instead of the mechanical performances that are guaranteed by our model and crosschecked by our R&D department. The investment in 3D laser tracking some years ago in order to control accuracy and tolerances has significantly improved lead-time and performance in the fabrication process.
Demanding
Contractors are expecting a very tight level regarding tolerances and 3D checking with 3D-laser scanners are getting more and more common. That could make the difference especially for large size moulds involved in large tunnel projects. Those expectations do not let any room for approximate skills and poor references. The legal risk involvement is also pushing our engineering survey and studies, mainly about geometrical tolerance conservation, mould deformation and stress applied to moulds during concrete pouring phase.
The German (STUVA) and British (BTS) standards are among the most exigent in terms of tolerances. Our success in these countries is the best proof of the expertise we have reached. The size of the project can be a challenge too: three double carrousels for Emisor Oriente in Mexico supplied within just 12 months, the two lots of C300 and C305 supplied the same year.
The location is also sometimes not easy, we have installed a carrousel in Russian Manchuria during winter and the same year another one in an Indian Tiger Reserve in summer.
Newer technology
We truly believe that the cast-in (‘anchored’) gasket is real progress, though the benefit does not go to CBE so much. The machining of moulds side requires a more complicated process and tooling, we do not charge this to the client.
Actually, the gasket gripping on segments is much better, the working conditions are much better for the operators who do not have to use a solvent base glue, this is also better for the environment, and the precaster is not obliged to store flammable products in his factory yard any more.
Since [the first use at] the Lee Valley project (see Tunnels International, October 2011 pp.52-54), we have supplied four other projects using this technology: Spurs National Grid in the UK, Bridlington in the UK, Blue Plains in the USA and Vélizy in France.
Carrousels
Automatic precast yards, the so-called carrousel systems, represent more than half of all CBE segment projects per year.
Automated ‘turnkey’ factories are still located in high labour cost areas but the growing demand in the BRIC group of countries, connected with high inflation are in favour of productivity gains.
It is quite usual for us to make comparative pre-studies between static and carrousel process at the quote stage. We provide also factory layout drawings, as a free service, which will help the client to make his decision.
Reputation, experience and expertise remain the key. The industrial model required by this market is now so exigent that I consider it as exclusive as long as the market player, client and competitors are reasonable: tunnel safety is involved.
Even in China, where some new and unknown companies without any references are claiming they can make moulds at half price, I am sure entering the market remains very difficult.
