“We attach great importance to ensuring the good handling of the tunnel boring machine”

A Tuesday morning in Göschenen. Xavier von Mandach sits in his office above the northern tunnel portal. He pulls out his smartphone and uses an app to track the construction progress. It provides a wide range of real-time data about the tunnel boring machine (TBM). “Yesterday, we advanced just under 10 metres”, says von Mandach. He is responsible on behalf of ARGE secondo tubo (Implenia Switzerland Ltd. and Frutiger AG) for the main excavation from the north side.

A few meters away, 15 miners are just leaving the construction site after their shift change at 6 a.m. The new team has just begun work. There are 12 people working on the TBM at any one time, operating the many devices aboard the approximately 110-metre-long machine. Another three miners remain outside at the installation site to prepare materials to be transported into the mountain. The next shift change is scheduled for 9.30 p.m., when the third team will take over.

Depending on the rock conditions, the machine should excavate up to 20 metres of tunnel per day. At present, it is working through Aare granite. “This rock is particularly hard and abrasive, meaning we are currently managing only about eight to ten metres per day”, explains von Mandach. “The tunnel boring machine has enough power for it, but the strong vibrations require especially careful maintenance”. At the moment, the roller nits need to be replaced more frequently than is usually the case.

The two tunnel boring machines for the main excavation of the second Gotthard road tunnel were launched in February 2025. Both models were produced by Herrenknecht in Schwanau, southern Germany. They were then disassembled into individual parts and transported in about 200 shipments to Göschenen and Airolo. Both machines have a diameter of around 12.3 metres and roughly the same length. However, there are also some differences. At 2,118 tonnes, the tunnel boring machine “Paulina” in Airolo is around 300 tonnes heavier than its sister “Alessandra" in Göschenen. Accordingly, the latter machine in Göschenen is powered by 7,138 horsepower, while in Airolo 7,613 horsepower is required. Xavier von Mandach explains the differences: “We have to excavate through different layers of rock, meaning that the requirements for the two machines differ in some respects. What is more, the ordering companies are able to customise numerous elements, including the configuration of the workstations”.

Overall, excavation using tunnel boring machines today is no longer comparable with the conventional methods used in the past – including in the 1970s during the construction of the first Gotthard road tunnel. “Nowadays, progress is much faster”. However, around 18 months have to be scheduled between ordering and commissioning the machine, a process known as “ramping up”. “It is for this reason that the excavation starts later, but it is much safer than using explosives”.

The tunnel boring machine has gradually been working its way into the mountain since February. During each excavation cycle, it advances two meters. At the same time, six tubbing segments for lining the tunnel are delivered by a special vehicle. After the drilling head completes its two-metre advance, the hydraulic cylinders retract and the newly excavated tunnel section is secured using tubbing segments. Von Mandach explains: “The individual concrete elements are placed using a vacuum plate. The narrow gap between the outside of the tubbing segments and the mountain is then filled with pea gravel and mortar”. After the tunnel has been secured, the hydraulic cylinders press against the new tubbing segments and the next excavation cycle begins. At the same time as the TBM advances, the excavated rock is transported out of the tunnel on conveyor belts and fed into the material handling and logistics system.

The 12 miners per shift who work on the boring machine are spread out along its entire length. The excavation is controlled and the tubbing segments are positioned at the front. Further back on the machine, the tubbing segments are delivered and the conveyor belts and cable systems are extended. “We maintain the highest safety standards and emphasise the importance of good handling across the entire site”, explains von Mandach. The workstations aboard the machine are therefore designed for maximum efficiency. “It is important, for example, that the conveyor belt and the various cables can be mounted easily and that there is plenty of room available for injecting the pea gravel”. In addition, the conveyor belts have to be cleaned on a daily basis.

While the two tunnel boring machines still find themselves close to the tunnel portals, the excavation of the two geological fault zones is already underway several kilometres deeper inside the mountain – using conventional methods with diggers and explosives. “In spring 2026, we expect to reach the Mesozoic fault zone in the north, which should already be excavated by then”. The TBM will then pass through this section, which is around 300 metres in length. “This stretch will also be challenging, meaning we anticipate that the passage through the fault zone will take around two to three months”, estimates Xavier von Mandach. Back in his office, he is satisfied: “The initial results are positive. The TBM is running as planned and we are on schedule”. However, there is still a long way to go before breakthrough in 2027. The TBM on the north side has almost six kilometres of Gotthard massif ahead.