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TLT Turbo work on Gotthard Base Tunnel – Part 2

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World Cement,

Innovative prototype developments

The special aerodynamic conditions of the 57-km tunnel deep under the mountain posed complex technical challenges. Since the trains can run at speeds of up to 250 km/hr, they generate a pressure shock in front of them and a vacuum behind them, which can cause serious problems for the giant fans. To come up with a solution, the R&D department of TLT conducted special tests early on. As a result, each fan is now being permanently monitored by a so-called stall warning unit. Stalls must be prevented at all cost. Equally dangerous is excessive impeller acceleration, the so-called windmill effect, because it may cause mechanical damage. The stall warning unit, an innovative development of the TLT engineers, measures any changes in the tunnel's air pressure ten times per second and uses the fan controller to prevent stalls by hydraulically adjusting the fan blade angles.

The logistics of moving very large and heavy components onto and into the mountain and assembling them in extremely tight spaces posed major challenges as well. In addition, schedule changes made it necessary to deliver four of the large fans to the Sedrun ventilation station in the High Alps in deepest winter. “As a rule, we had to expect snow at any time during this period in the High Alps. Fortunately, we were lucky, because we had a mild winter and almost no snow,” remembers Kuhn. The problem was that the roads in this region are designed for passenger cars, small vans and trucks with weights of no more than 28 t. The heavy trucks needed to ship the fans, however, weighed roughly 70 t. After making sure that the bridges could accommodate them, Swiss police escorted the fans to the mountain without any problems.

Coordinating more than a thousand technical interfaces

Since the tunnel shell was completed earlier than planned, its opening was pushed up by one year. As a result, all the shell equipment contractors, which included the consortium of TLT and Swiss company ABB Schweiz AG, had to perform much of their work side-by-side instead of sequentially, as had been originally planned. “The corresponding coordination and schedule management turned out to be a real challenge. Because of the complexity of the project we had to coordinate over 1000 technical interfaces in order to ensure a smooth execution,” remembers the project manager.

After the components had been successfully installed and tested, the actual commissioning could commence. To start the process, the engineers checked and documented the interaction of the system’s components and their safety compliance by conducting extensive tests, which included sending a specially rented German Rail ICE through the tunnel at a speed of 275 km/hr. “We use extensive scripts for this purpose in which virtually each action and desired reaction are described in detail. We also tested failure scenarios – automated ones and those where the operator must step in,” says Kuhn.

The special challenge facing the consortium was the fact that the fan controls are the lead controls for all components. Accordingly, each scenario has to be initiated and controlled via the TLT master computer. To explain: The Sedrun multifunction station is linked to the ventilation center via two 800-m-tall air shafts. One of these includes a large freight elevator. While this elevator moves, no fan may be in operation. This means that the controller must check whether the elevator is in its final position – top or bottom – when a ‘Start’ command is issued for a fan. If it is not, the controller must move the elevator into this position before the fan can actually commence operation.

Regular rail operations commence in late 2016

TLT initially became involved in the project as early as 2007, when a feasibility study was conducted to explore whether it is even possible to install fans with this level of performance into such small spaces. The pressure and vacuum problem caused by fast-moving trains was discussed as well. The actual bid was developed between late 2009 and August 2010. TLT won the contract in early 2011. Unlike in other tunnel projects, no standard fans could be used, but the engineers had to develop, test, install and commission prototypes. “This was a very exciting time for us in terms of the contract size as well as the related delivery and performance parameters,” says Kuhn.

The tunnel will open on June 1, 2016, when SBB as the future operator of the Gotthard Base Tunnel will commence test operations to demonstrate that passenger and freight trains can traverse the tunnel without problems and that maintenance and event management work without a hitch. If everything works as planned, the tunnel will be taken into account for the regular rail schedule starting in December 2016. For TLT, however, the project will not be over at that time. The manufacturer has already received an order for spare parts and expects to sign a five-year maintenance contract very shortly.

Adapted from press release by

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