Rangwee Tunnel II

This project involves building a second tunnel to connect the Glück roundabout to Rue des Scillas, south of the Luxembourg capital. Rangwee II is composed of two 2,500-ton frames, each 30m long, 13m wide and 7m high.

The structures were built side by side, at the foot of the embankment supporting the CFL railway tracks.

Each element was positioned in just two weeks using the box jacking process. The operation required blocking the CFL tracks and setting up continuous work in three shifts.

A lot of work was carried out before reaching this stage. This included:

• The excavation of a huge pit used to site-cast the elements;
• Building soldier pile walls to shore up the site-casting pit;
• The construction of a 1,300m² guide slab with a very rigorous flatness, less than 3mm of play, which was necessary to push the elements forward;
• Casting the slab and the walls of the prefabricated frames;
• Building the formwork for the slab of the frames, using a shoring tower for the whole process;
• Concreting the slab of the prefabricated frames;
• Waterproofing the slabs;
• Site-casting concrete thrust blocks so that the two frames could be jacked.

Race against time

An actual race against time began from the moment the overhead lines were deactivated. 36 hours during which our teams relayed each other continuously in three shifts. 12,000m³ of earth were excavated in order to open the way for the frames before preparing the guide slab and starting to thrust the frames using jacks.

This delicate operation took place in two stages. It began by thrusting the first element: raised by about 5cm and already in line, it reached its final location. The second frame was first pushed laterally so that it would be positioned along the right axis and then thrust forward until it was next to the first frame.

Once this stage was completed, it was necessary to backfill all around the tunnel in order to recreate the embankment and proceed with laying the tracks and signals for CFL.

The project also involved building a stormwater tank next to the new tunnel. Due to the lack of space, the structure was built at the foot of the CFL tracks using considerable shoring and a 14m deep pit.