The "longest railroad tunnel in the world" is currently being built at the Brenner Pass: Italy and Austria have been building the base tunnel, which will be 64 kilometers long, since 2007. Including all access routes, the Brenner route is set to reach a world record length of 320 kilometers. The aim is to start rail traffic in 2026: Travelers from Munich will then be able to reach the Italian city of Verona in three hours, it is said.

Albert Feißt, Head of Fluid Technology at Herrenknecht

So many superlatives require top technological performance during construction. One of the most important pieces of equipment in the construction of the route is the tunnel boring technology supplied by Herrenknecht from Schwanau on the edge of the Black Forest. Three tunnel boring machines (TBMs) are already in use on the construction site and three more will be delivered in the near future. "The TBMs are moving factories in the mountain," explains Albert Feißt, Head of Fluid Technology at Herrenknecht. "The drill head rotates and breaks through the rock. The excavated material is transported back out of the tunnel via various conveyor belts." The rock is secured with internal formwork made of segments: "A remote-controlled manipulator, the erector, is used to place prefabricated segments of reinforced concrete," says Feißt. "These segments form a ring. The annular gap between the outer diameter of the segment and the mountain is filled with pearl gravel to embed and stabilize this freshly constructed ring." A lot of compressed air is needed to convey this backfill material, which is generated and called up by the Atlas Copco compressors traveling in the trailer.

Constantly on stand-by

The tunnel boring machine that will next be delivered to the Brenner Pass is still in Schwanau at the end of 2017. This mobile factory is around 100 meters long and the diameter of the drill head is around 10 meters. Nine screw compressors supply the compressed air required by the TBM. They are positioned at the end of the plant and equipped with an intake flap control system.

Herrenknecht uses modified oil-injected screw compressors from Atlas Copco's GA series, mostly with water cooling. Five GA 55 HE and four GA 90 HE machines are installed on the "burner system". As a rule, one is sufficient to provide the base load, i.e. to supply grease and water pumps, fittings with pneumatic drives or even pneumatic screwdrivers. The other eight compressors are suddenly activated when pearl gravel has to be blown behind the segments. "On average, we only use 10 to 15 percent of the total compressed air capacity," says Feißt. "But when the capacity is called upon, it has to be available one hundred percent." The compressors, which are constantly running in standby mode, must therefore be absolutely reliable.

This TBM, designed for burner tunnel construction, is equipped with five GA 55 HE oil-injected compressors.

Especially for Herrenknecht, Atlas Copco has equipped the full-load idling compressors with mechanical volume flow control via dampers. This ensures that the air is supplied in the required quantity. "Thanks to the intake flap control, we were able to save on air receivers and thus solve a space problem," explains Feißt. Also for space reasons, the GA compressors for Herrenknecht have a more compact design than the standard series. Due to the harsh environment and the mine dust, the Atlas Copco experts have also installed heavy-duty intake filters to prevent dirt from entering the compressors. They also have a special controller for temperature management, as they are oversized in terms of performance. "We deliberately build 20 percent redundancy into all components of our TBMs, because everyone on the mountain must be able to rely on the safety and reliability of the machines used," emphasizes Feißt. Because the compressors are not regularly used to their full capacity, the oil they need for lubrication does not reach the required operating temperature. As a result, water would accumulate in the oil as it would not be separated out by the temperature. "The machines therefore have a special cooling water management system," says Feißt.

Components must be robust

The business with tunnelling machines is booming, and global urbanization is helping enormously: road, rail and water tunnels are needed in emerging countries as well as in Europe. "The focus is different every year," explains Josef Gruseck, member of Herrenknecht's Traffic Tunnelling management team. "Sometimes it's the Gotthard, then the Brenner, while major projects are underway in London, Paris or Doha. There is also a lot of construction going on in Asia." In Europe in particular, however, the investment backlog in the area of infrastructure projects is gigantic. ee