Vereina Tunnel – Secure anchoring of the overhead conductor rail with SFS

Together, we tackle the challenge

Work is currently underway to install an overhead conductor rail on the tunnel ceiling. The system offers enhanced safety, particularly due to its robust construction. To avoid disrupting rail operations, the work is carried out during nighttime train breaks. The work is scheduled to be completed by November 2025.

Drilling work for the structural fastenings marks the start of the actual installation phase for the step-by-step conversion of the existing catenary system to an overhead conductor rail (OCR). Over the next two years, the 19 km tunnel, including both loading stations, will be upgraded to meet the new requirements in several stages during nightly operating breaks.

Anchoring of the overhead conductor rail

Each of the approximately 3,000 ceiling structures, which serve as support points for the overhead conductor rail, is equipped with three fastening points. A special drilling rig mounted on a low-floor car towed by a locomotive is used to drill the holes efficiently into the shotcrete ceiling using water-cooled diamond core drill bits.

Reaction cartridges (glass capsules) are used to bond the M16 threaded anchor rods, with an embedment depth of 125 mm, into the concrete shell. The anchor rods are installed using a rotary hammer drill with axial hammer rotation. During the process, the glass capsule is shattered, and its components mix. The grain and glass fragments from the capsule clean the borehole surface and roughen it. This creates a positive-locking surface bond with the cured composite material in the annular gap between the anchor rod and the borehole wall. The fischer RSB 16 reaction cartridge system is European Technical Assessed and ETA-certified as a construction product for use in diamond-drilled holes in cracked concrete substrates.

The anchor rods are made of highly corrosion-resistant stainless steel (material number 1.4529) according to corrosion resistance class 5, providing sufficient protection in chloride-containing environments. During the winter months, the car shuttle not only transports vehicles through the tunnel but also carries road salt residues from frost and de-icing agents. This creates an aggressive, salt-laden atmosphere in the tunnel. These contaminants come into contact with the anchor rods and settle on their surfaces.

Another challenge was the irregular shotcrete surface. The ceiling structures had to be mounted with spacer installation using anchor rods of varying lengths. This required up to eleven different anchor rod lengths, which we, as SFS Group Switzerland AG, manufactured in phases specifically for the tunnel and delivered directly to the construction site.

In addition to the anchoring components (reaction cartridge, anchor rod, and hex nut), wedge lock washers are also used. These special washers, rated corrosion resistance class 5, secure the threads against loosening caused by vibrations, preventing the hex nut from loosening from the anchor rod and permanently positioning the suspended ceiling structure with the overhead conductor rail.

With our contribution, you are safely on track!