Repairing subsidence sections in the Stutzeck-Axenberg Tunnel.
Delivering a large volume of construction work in a short period under demanding conditions requires more than standard solutions. The repair of the subsidence sections in the Stutzeck-Axenberg Tunnel shows how precise planning, well-designed logistics and well-rehearsed processes can lead to success even within tight constraints.
The repair of the subsidence sections in the Stutzeck-Axenberg Tunnel between Sisikon and Flüelen was a project with exceptional requirements. A large volume of construction work was safely and successfully completed within a short period, with narrow time windows, complex conditions and high demands on planning, logistics and delivery.
The approximately 3.4-kilometre tunnel forms part of an important north-south connection in the Swiss rail network and is a key access route to the Gotthard Base Tunnels. The purpose of the work was to provide a permanent repair to several subsidence areas in the tunnel where settlement had already been identified.
A total of seven repair areas were treated as part of the project, with work progressing from one subsidence point to the next.
In the first step, the track was removed and the ballast transported away using an MFS material conveyor train. The existing concrete invert slab, rock and drainage pipe were then removed.
The concrete for the new invert was transported by rail to the respective subsidence point in the tunnel and, due to the local conditions, pumped over a distance of around 160 metres. The drainage pipe requiring renewal was concreted together with the invert.
The risk posed by water was a particular challenge during the repair. A spring at the site produced flows of up to 70 m³/h, so diversion through a temporary bypass had to function reliably at all times.
At the same time, the ballast bed and track were renewed and the track geometry restored. In total, more than one kilometre of track was renewed. The effective construction period was seven weeks.
Logistics presented one of the greatest challenges. As a large part of the construction site was located in a single-track tunnel and only limited installation areas were available, all material transport had to be organised precisely. For the most part, ballast, excavated material and construction materials could not be transported conventionally by lorry, but had to be moved to and from the construction site by rail.
Construction trains operated between the logistics locations and the tunnel worksite. Every movement of material had to be planned precisely and integrated into the available operational windows.
To meet the demanding schedule, work during the intensive construction phases was carried out predominantly in three shifts, often seven days a week. Construction work, material transport and track construction had to be coordinated precisely.
Despite the demanding conditions, the project was delivered efficiently and safely, and the specified milestones were achieved – an outcome of which everyone involved can be proud.
