The "Rheintalbahn," or Rhine Valley rail line, is composed of two tracks built side-by-side, to allow train traffic to flow in both directions at once. It's a crucial connector between the Rhine Valley towns of western Germany and Switzerland, and it carries a lot of freight as well as passenger traffic.

Accordingly, it was a blow to the smooth flow of goods and people when on August 12, crews working a tunnel-boring machine working on ‘Tunnel Rastatt,' a new four-kilometer-long (2.48-mile-long) rail tunnel crossing underneath the town of Rastatt, witnessed a partial cave-in of the ground above — exactly at the location where the tunnel was meant to traverse underneath the Rheintalbahn's railway tracks.

The result was that those tracks subsided by around 50 centimeters (19 inches) along around eight meters (26 feet) of their length.

Earth and water entered into the segment of tunnel under construction, causing the boring machine to get stuck. The tunnel-boring machine was not at fault; the apparent reason for the cave-in was that the ground above the route of the tunnel was, in that place, only about five meters thick, and too soft, despite an attempt to freeze the ground prior to boring.

The attempted freezing had been achieved by a relatively new method involving the sinking of a large number of pipes into the ground and circulating a very cold fluid through them at a temperature of minus 35 degrees C.   

The damage to the rail-line above the tunnel was serious enough to force closure of the Rheintalbahn rail line for nearly two months. The line is projected to re-open by October 7, if repairs go well.

The tunneling mishap demonstrated how a single mishap can cause a cascade of problems, like a row of dominoes falling over – and how in complex networks, it pays to build-in route redundancies, to avoid bottlenecks arising.

Repairs in progress

Frank Roser, a project manager overseeing the repairs, said on Thursday at a press conference in Rastatt that Deutsche Bahn would be pumping a total of 1,100 cubic meters of concrete into a trench about 100 m long and 11 m wide, in order to create a stabilizing pad underneath the Rheintalbahn rail line. A second pad will have to be built nearby, and once that's done, the section of Rheintalbahn crossing the pads will have to be rebuilt.

 "We're sticking with the October 7 date for re-opening the Rheintalbahn to rail traffic,” Roser said. "Starting at one minute after midnight on that date, the trains will be able to roll again.”

The multi-million-euro tunnel-boring machine involved in the mishap has been given up as lost, and cemented into place.

Since this means that part of the planned route of the double-tubed Tunnel Rastatt is now blocked by a huge concrete plug, engineers will have to re-route the tunnel somewhat. The tunnel was planned to be 4,270 meters long — i.e. more than four kilometers, crossing underneath the town of Rastatt — and had nearly reached completion, with about 4,000 meters already bored.

Choke points

Tunnel Rastatt is on the Rheintalbahn between the towns of Rastatt and Baden-Baden. Up to 170 freight trains normally run daily on the line. While repairs progress, the trains are being re-routed to the extent possible, but some freight has had to be put on trucks —which is more expensive, both financially and environmentally.

Rail freight experts from the European Railways Network (NEE) estimated the financial losses to goods transport companies resulting from the Rheintalbahn's interruption at about 12 million euros ($14.4 million) per week.

Critics — among them Green Party transportation policy specialist Matthias Gastel — criticized Deutsche Bahn, the operator of the line, for having neglected to ensure, ahead of time, a system of alternative routes that trains could take in case of problems arising at particular locations, such as the mishap that arose during construction of Tunnel Rastatt.

Some alternative routes that do exist were also out of operation due to unrelated maintenance or construction work. That should not have happened, according to Gastel; it was a result of uncoordinated infrastructure maintenance work-schedules within the regional rail transport nework, which left rail operators dependent on the Rheintalbahn route with too few options after the problem arose at the Tunnel Rastatt site.