Gotthard Tunnel renovation, excavation on the south side: tunnel bore machine replaced by traditional excavation method using explosives over a 500 m section
The complex geological conditions on the southern side of the Gotthard require the temporary adoption of an alternative excavation method last July: the tunnel boring machine (TBM) previously used is currently being replaced, over a stretch of approximately 500 m, by the traditional technique using explosives. TBM Paulina was stopped in a controlled manner. The additional costs amount to CHF 15-20 million and the expected duration of the work is six to eight months. The Federal Roads Office (FEDRO) expects to meet the announced opening date and total budgeted costs.
In February 2025, excavation work began on the second tube of the Gotthard highway tunnel. While the tunnel boring machine (TBM) on the north side is progressing steadily, on June 23, 2025, it was necessary to stop the TBM on the south side after it had advanced approximately 190 m: the mechanized excavation method is unlikely to be effective for the next 500 m, where the partially unstable rock mass has obvious fractures and cavities. Paulina was deliberately kept operational in order to prevent it from becoming stuck in the rock and causing possible damage to the machine. The Paulina TBM is therefore not blocked or damaged in the ground. The Federal Roads Office (FEDRO) therefore conducted in-depth geognostic surveys in the affected area and, in consultation with engineers, geologists, and the contractors involved, opted to switch to an alternative excavation method.
The analyses showed that the critical areas extend over a 500 m section, which is now being excavated using traditional methods with explosives. A connecting tunnel is also being constructed, from which work is being carried out simultaneously in the opposite direction to the TBM, which is stationary at around 300 m in the direction of Göschenen. Tunnelling with Paulina will resume as soon as the challenging rock conditions encountered during blasting have been overcome.
Opening date and costs
The excavation using explosives will take approximately six to eight months and will incur additional costs of between CHF 15 and 20 million (total project costs: CHF 2.14 billion). The remaining work on the north and south sides is continuing according to plan (see construction progress). Despite the unexpected additional costs, FEDRO does not currently anticipate any impact on the planned opening date of the second tunnel (2030).
Various measures have been taken to ensure that the schedule is adhered to, including bringing forward work that is crucial to meeting the deadline. Conventional excavation work is carried out around the clock, with staff working in three shifts.
Project updates
- 27.10.2025: The connecting tunnel has been completed and the counter-excavation towards the tunnel boring machine is currently underway.