German national rail infrastructure manager DB Netze has announced that construction work to complete the tunnels under the town of Rastatt will recommence in 2020, with the tunnels now due to open in 2025.
The Rastatt tunnels are a key part of the long-term plan to quadruple the entire line between Karlsruhe and the Swiss border at Basel. This is one of the busiest sections of railway anywhere in Europe, with lengthy double track sections used daily by nearly 400 trains, more than half of them freight, in 2019, according to DB.
The previous collapse of one of the tunnels underneath the existing main line on 12 August 2017 led to a seven-week closure of the line and caused major disruption to European logistics services as no alternative routes were readily available. The costs of the closure and disruption to rail users and wider industry have been estimated at up to €2 billion.
Construction of the twin bore tunnels, designed for 250km/h operation, began in 2013 using tunnel boring machines (TBMs) at shallow depths in alluvial sedimentary rocks. However, work ceased from 12 August 2017 when a landslip into the newly constructed eastern tunnel bore not only disrupted construction but severed the existing main line on the surface. A 160-metre-long section of the tunnel including the TBM was then filled with concrete to stabilize the site.
The route re-opened on 2 October 2017, after a 275-metre-long concrete slab had been laid to support the railway on top of the area that collapsed.
DB has now agreed its plans to complete the Rastatt Tunnels. The remaining 200 metres of the undamaged western bore will be completed by the ARGE Tunnel Rastatt consortium using the TBM that is already in position (having been shut down in August 2017). The existing surface main line is protected from any unexpected tunneling issues as it is on the concrete slab built in September 2017.
To permit construction of the eastern tunnel under the existing main line without danger of further disruption to the route, DB will first move a 700-metre section of the line so it follows the course of the completed western bore (on the surface) to slew it away from the construction site; approval for this has been granted by the German Federal Railway Office (EBA).
DB and ARGE Tunnel Rastatt then plan to excavate the remaining part of the eastern bore using open excavation methods (cut and cover) having first inserted concrete walls to the required depth. This will include removing the 160-metre-long concrete plug and the remains of the TBM. A concrete line trench 17 metres deep will be dug and the tunnel constructed in it before it is back filled. This work is expected to commence in 2021; DB Networks has applied for the necessary planning approvals to the EBA.
Once the two tunnel bores are completed, the surface line will be moved back above the eastern bore. Construction of remaining cross passages and entrance portals plus fit out will take until 2024. DB currently expects the Rastatt Tunnel to open in 2025 along with approach lines on either side, resulting in a four-track railway from Karlsruhe to Offenburg.
Following the 2017 accident, detailed evaluation of ground conditions, including 70 bore holes, and other factors has been underway to ascertain responsibility for the tunnel collapse and subsequent disruption to the railway line through Rastatt, which resulted in substantial financial costs for both DB and multiple private freight operators. A conciliation and arbitration process is underway to establish responsibility and financial damages, with the aim of avoiding lengthy legal action.
This article first appeared in Issue 177 of Rail Engineer, Aug/Sep 2019.
