One year after the incident of 12 August 2017, works are proceeding at the Rastatt Tunnel. The removal of the concrete plug in the east bore has been completed and the detailed investigation program was finished in September 2018. The evidence gathering and arbitration process agreed between the consortium Tunnel Rastatt (Hochtief and Züblin) and Deutsche Bahn to clarify the causes of the damage during tunnel driving will last until the start of 2019.
After the incident, intensive work was carried out to remedy the damage to the Rheintalbahn line and permanently stabilize the ground above the tunnel bores. Altogether about 10 500 m3 of concrete were pumped into the damaged east bore with the TBM in order to secure the line above against settlement. In order to relay the tracks of the railway line, a massive concrete slab, 270 m long and 1 m thick was poured. At the same time, grouting hoses were installed in order to be able to inject concrete in case of settlement. On 2 October 2017, trains could run on the Rheintalbahn again and the driving of the west bore was continued. After driving 3672 m, the TBM “Sibylla-Augusta” reached the shaft short of the Rheintalbahn in December 2017, where it is now waiting.
Groundwater Troughs and Sonic Boom Structure
Even if the last few metres of the tunnel bores each 4270 m long could not yet be driven, construction work is still underway. This includes the work in Niederbühl on the south groundwater trough, where divers were employed at the end of May 2018 to place the underwater concrete.
In the south, the cut-and-cover section with a length of 250 m is continuing as planned and the sonic boom structure (to avoid the so-called tunnel boom) is being constructed. At the north portal in Ötigheim, work is underway to connect the north groundwater trough to the tunnel portal. This includes about 50 m of cut-and-cover tunnel.
Removal of Concrete Plug in the East Bore
As an immediate measure under the settled section of track, a concrete plug was installed on 12 August 2017 in the tunnel, which separates the intact tunnel to the north from the damaged area. The concreted section amounted to about 160 m. At the start of February 2018, work began to remove the approx. 2000 m3 concrete plug. Temporary ballast fill is laid in the tunnel invert in order that trucks can travel along to transport material. The concrete of the plug has meanwhile been completely removed, using a tracked excavator with a special cutting attachment. Another 6 m of the concrete fill had to be removed with hammers and cutters. From here until the backup is reached, another approx. 40–50 m of concrete fill have to be removed in the tunnel bores before the difficult part of the work can start, the freeing of the concreted TBM with backup along a distance of about 90 m.
Supply and Escape Shaft
After the work to free the TBM and remove the concrete plug, an opening will be made through the tunnel roof to the surface. This shaft will serve as an escape route out of the tunnel bores (two escape routes are specified for the lining works) as well as for logistical supply to the further construction works, for example construction of the nine cross passages in the undamaged parts of the two bores. In order not to lose any more time, the permanent way is already being prepared, tracks laid and the overhead installed, wherever possible.
Extensive Drilling and Investigation Program
The Tunnel Rastatt consortium has been carrying out a drilling program together with the Deutsche Bahn since the middle of May 2018 in order to investigate the ground in more detail. At the crossing of the Rheintalbahn and in the surrounding area, altogether about 60 boreholes have been drilled with four core drills along a length of about 300 m, and nine of these will have groundwater piezometers installed. The end of the drilling program was planned for the middle to end of September 2018.
Simultaneously with the drilling, the results were evaluated. In the core store, the drill cores were examined and recorded by geologists. Samples were also taken and sent to the laboratory for evaluation. The results of the probe drilling should deliver further information about the causes of the incident. On this basis, a concept can be developed for the further driving of the west bore. The analysis of the causes will also provide the basis for further proceeding in the east bore and for the dismantling of the concreted tunnel boring machine.
Arbitration Process continues
The evidence gathering and arbitration process agreed between consortium Tunnel Rastatt and DB to clarify the causes of the incident in the tunnel in August 2017 is still underway. An end to the arbitration process with results about the reasons for the incident is not expected before the start of 2019.
The Deutsche Bahn has also drawn consequences from the incident in Rastatt and the subsequent line closure with an effect on the entire goods traffic in Europe. Internal processes have been checked, adapted and improved. An international incident management handbook has been produced in order to be able to react to an incident with uniform processes and better communication. The railway sector has set up the “round table for site management” for the optimisation of construction processes, construction communication and much more with regard to the modernisation of the railway network.
Dipl.-Ing. Roland Herr, Internationaler Freier Journalist/inernational freelance journalist, Wetzlar (Deutschland/Germany)/Bangkok (Thailand), email@example.com