Refurbishing the Tunnel near Niederschlema
The Schlema railway tunnel that was built from 1898 to 1900 had to be redeveloped as part of the upgrading of the line between Schwarzenberg and Zwickau. During the course of the years, the overburden above the tunnel built of natural stone masonry had grown from 6-8 to 23 m, as a dump belonging to the Wismut GmbH had been deposited on top. It was thus essential to carry out a thorough refurbishment of the 347 m long tunnel including the 2 portal zones on account of the increased strain on it, its lengthy service life of more than 100 years quite apart from extensive damage to the masonry and the drainage facilities caused by underground and surface water. The aim of the redevelopment scheme was to re-attain lasting stability of the natural stone masonry lining, targeted removal of ingressing seepage water and protection from rock-fall so that no speed limit would have to be imposed thus increasing the speed for the route to 80 km/h in Future. The tunnel was refurbished with a reinforced shotcrete shell. First of all, the entire natural stone masonry had to be exposed by removing the plaster and a sub-base created through sand blasting. A napped membrane was installed all-round in areas where only slight settlement had occurred in order to transfer seepage water. The shotcrete shell was suspended on the existing vault via reinforcement layer, which was attached to the existing masonry by means of short rock bolts. Subsequently, the roughly 13 cm thick shotcrete shell was placed using the dry spraying method. A reinforced shotcrete lining - 21 cm thick- and a 2-layer reinforcement installed in blocks were selected for sectors with major deformations that had still not subsided. Furthermore, the installation of half shells to remove underground water was also decided on. In addition, a 700 m longitudinal drainage system was set up at the side to carry the underground seepage water from the tunnel. In order to stick to the tight schedule, the individual redevelopment tasks were undertaken parallel to each other in continuous operation.
- Country: Germany
- Region: Saxony
- Tunnel utilization: Traffic
- Type of utilization: Main-line rail
- Client: DB Regio Netz, Erzgebirgbahn
- Consulting Engineer: Albrechtplan, Geotechnik Projekt
- Contractor: Max Bögl Bauunternehmung GmbH & Co. KG
- Main construction method: Refurbishment
- Lining: Shotcrete
- No. of tubes: 1
- Tunnel total length: 347 m
- Cross-section: 60 m²
- Contract Volume: € 1.2 million (Roughwork)
- Construction start/end: August 2002 to December 2002