A Tradition of Engineering: Schréder-Comatelec’s Undersea Adventure
A short stroll from the Champs-Élysées lies the Association Française de l'Éclairage. This august body represents the lighting manufacturers of France: in the lobby, a frieze by Raoul Dufy celebrates the genius of Edison, Kelvin and Ferrié. Upstairs, in a boardroom lined with leather-bound volumes on lighting technology of previous centuries, Christian Remande is reminiscing about an altogether less comfortable environment: the half-completed tunnel 40 metres beneath the English Channel, where he was about to see how his team’s work would fare in some of the most extreme conditions on earth.
You’re under the sea, anything is possible. You’re talking waterproofing, corrosion and extreme pressure. The luminaires would need to cope with wind speeds of up to 360km/h from passing trains.
Nothing like the channel tunnel had ever been built before, so Christian’s team of engineers had to design not just a lighting system, but a way to test it. The mission involved intense cross-channel co-operation, mathematical modelling and spraying things with high-pressure hoses. The luminaire they created was one of the company’s best sellers, lighting projects from Medellin to Monaco.
The engineering feat of the tunnel itself is remarkable enough. Named one of the Seven Wonders of the Modern World by the American Society of Civil Engineers, it reaches depths of 75m below the sea bed, is 50km long and took 11 boring machines seven (actually very interesting) years to build. In 2019, 1.6 million trucks, 2.61 million passenger cars and 11 million Eurostar passengers travelled through the tunnel1.
Schreder’s work consisted of two phases: lighting the construction of the tunnels and terminals - because there are actually three parallel routes beneath the sea, two for trains and a service tunnel between them - and creating safe, resistant, low-maintenance lighting for the finished project.
If you’ve ever wondered what the chunnel looks like inside, or how it’s lit, actor Lambert Wilson recently drove an Audi A8 through the service tunnel to launch the luxury vehicle. It’s even been traversed on a bicycle - Tour de France winner Chris Froome made it through in 55 minutes on his Pinarello Bolide time trial bike, in this collaboration with Jaguar.
But long before the engineers started testing the resilience of their latest creations, they were thinking about the light. Lighting tunnels is a particular challenge - and having heard rumours that the channel tunnel might actually happen, Schreder started thinking about how it could be done. “As soon we hear the word tunnel, we’re intrigued,” recalls Christian.
In the 1980s, they were working on a suburban rail tunnel in Massy which, crucially, had just the right type of curved wall. “We wanted to compare the relationship between how much light was coming from the luminaire, and how much was being reflected by the walls, which are curved,” he says. Like a light bulb, “the tunnel itself acts a reflector - not a very effective one, but a reflector nonetheless.”
As a company, Schreder had been obsessed with photometry, the science of measuring light, for years.
It’s not just making light, but putting it in the right place, at the right time. Anyone can sell some lamps, we sell lighting installations.
The fluorescent luminaires which were designed for the tunnel - the JVT, the MY1 and the MY2 - are still in place today, and customised to user needs. The main tunnels are only lit in emergency situations, as the trains have their own lights and drivers prefer to use them. But that part was easy compared to making them tough enough to withstand the tunnel’s environment.
In this kind of tunnel, the issue is that the clearance between the train and the walls is so thin, it’s basically a bicycle pump. As the train pushes the air in front of it, the pressure rises, and behind, the pressure drops. Think of the effect when an express train rushes past a platform - except the wind has nowhere else to go. It’s known as the piston effect and the two rail tunnels have a duct between them to allow air to flow and counter the effect. But the changes in pressure can still be as much a third more or less than normal atmospheric pressure at sea level.
Christian's team conducted mathematical studies to design luminaires that could stand up to these extreme conditions - and started puzzling over how to attach them to the walls. Brainwaves included a double-jointed protective casing for the light, chemically strengthened glass and the design of clip fasteners on the protector glass.
Schreder’s in-house laboratory then designed a tailor-made installation which enabled three tests to be performed simultaneously: one luminaire under depression, another under compression, and one being subjected to a rapid cycle of compressions and depressions - just like high-speed trains rushing past in a tunnel.
Just to be sure, though, the engineers took high-pressure hose to their prototypes. “As far as the trials are concerned,” they noted at the time “the cyclical test is clearly the most demanding and the fittings which pass this trial have no trouble in passing the high pressure hose test, even when applied directly to the sealing joint for long periods.” Having finished with the hose, it was time to rock them like a hurricane.
“The lab was very well-equipped, but we didn’t have a wind tunnel,” recalls Christian.
They ended up just over the border, working with the University of Liège and the Von Karman Institute for Fluid Dynamics in Brussels. They used mathematical modelling to scale up the wind tunnel results to replicate higher speeds in the tunnel itself. In cross-border exchange of engineering expertise that neatly mirrored the Eurotunnel itself, they got the theoretical calculations made by the University of Liège checked on the trial bench at the Imperial College London - where they proved extremely accurate.
Even when there are no trains going past, the 12,000 MY1, 7,000 MY2 and 13,000 JVT luminaires in the tunnel aren’t in the most pleasant conditions. “You’ve got iron dust coming off the rails, tiny copper particles coming down from the overhead wires, water and salt!” exclaims Christian. “That’s just the ticket for destroying aluminium.”
In order to protect the precious contents of the luminaire, they developed a double casing. “Francis Schréder and I designed it in the lobby of the Bagnolet Novotel,” recalls Christian. “We’d designed a lot of waterproof fluorescent lights, and what you needed was double-casing.” The finished item consists of aluminium frames sealed onto the ends of the luminaire, enclosed by covers with stainless-steel screws. Because everything can be measured, the International Electrotechnical Commission has a system of International Protection markings for waterproofness: the whole luminaire has a ranking of IP 67, the same as a Google Pixel 2 phone.
Indeed, Schreder’s testing rig was so impressive that another company working on the tunnel ended up using it to test stainless steel junction boxes. “When this English company saw how much work we’d done on testing the lighting, they came to us and said, ‘can we do the benchmarking in your lab?’” says Christian. After years of working together on the tunnel, there was an unprecedented level of trust between rival firms, and the technical verification was done directly between London and R-Tech, Schreder’s R&D centre in Liege.
The millions of passengers every year who sip champagne in Eurostar Business Premier, or drive their cars on to Le Shuttle to get the family holiday started take it for granted that they’re taking advantage of one of the engineering marvels of the twentieth century. But deep below sea level, the work of Schréder means that staff, drivers and passengers enjoy a tunnel lit with the most innovative techniques of the time - and technology which is still going strong more than twenty years later. Bon voyage!
Acknowledgements
Schréder would like to thank Christian Remande for taking the time to talk to us and tell us all about this fabulous adventure!
Source
1: https://www.getlinkgroup.com/en/our-group/eurotunnel/activity-and-performance/