Bochum Light Rail, Contract Section 306/Operating Track

Contract section 306 is a part of the Rhein-Ruhr Stadtbahn expansion scheme in Bochum. It starts directly next to the Bochum City Hall (Rathaus) with a roughly 130 m long cut-and-cover ramp. A reinforced concrete bridge for Line 306, which passes through the Rathaus South Station belonging to contract section E 1, adjoins the ramp at its lower end. Owing to the shallow overburden in sandy silt, the following twin-track section was driven protected by a pipe umbrella. The fork for the approx. 120 m long operating track is also located in this section. Subsequently, the 3-storey Husemannplatz underground car park, which is highly prone to Settlement, was undercut in front of the Bochum Landgericht Courts. There is also an escape way set up in this area, which links the tunnel with a 22 m deep emergency exit. The cross-section that had to be driven here amounted to around 120 m² on account of a crossover zone. Compensation grouting was applied over an area of some 2,500 m² so that the tunnel could be excavated with overburdens of less than 2 m. Towards this end, consolidating injections were first carried out via horizontal sleeve pipes. Then the building was raised in reversed proportion to the forecast settlements and undercut. Altogether the cross-section for the switching zone was executed in 3 part-cross- sections in conjunction with corresponding grouting stages. Following the completion of the first 2 part-cross-sections, a partial inner shell was installed prior to driving the final one. Two 300 and 450 m long single- track tunnel tubes follow. The southern tube undercuts the existing "A section" with overburden of approx. 1 m to that it can link up with it in the proximity of the Bochum Main Station. The task was completed without any disruptions being caused to normal services. Half of the existing, twin-track tube was demolished and widened by mining means. An access shaft was produced in advance in the junction area to enable the entire supply and disposal logistics to be undertaken. Geologically speaking, the tunnel is located in quaternary layers, occurring in the form of sands and silts, and in tertiary layers, in the form of marl with various degrees of weathering. Roughly two-thirds of the route is located beneath the natural groundwater level. A tunnel excavator was employed for driving. The tunnel was secured by means of tunnel arches, shotcrete and 1 to 2 layers of structural steel matting. Lances were also placed in friable zones. Generally speaking the invert was closed rapidly to minimise settlement. Cross-sections in excess of 40 m² were basically divided into smaller part-cross-sections. Wet shotcrete was utilised for the first time for an inner urban Underground construction scheme. Thanks to a new development, a so-called arch platform, the second working level was used with a shotcrete manipulator, lift cage and drill mast. The entire tunnel is produced as a watertight concrete structure.

• Country: Germany
• Region: North Rhine Westphalia
• Tunnel utilization: Traffic
• Type of utilization: Underground, urban and rapid transit
• Client: Bochum-Gelsenkirchener Stadtbahnverpachtungsgesellschaft des bürgerlichen Rechts (Stadtbahn GbR)
• Consulting Engineer: Zerna, Köpper & Partner, IMM- Prof. Dr.-Ing. B. Maidl Dipl.- Ing. R. MaidI, Waning Consult, CDM Jessberger
• Exanimation: Prof. Dr.-Ing. B. MaidI, Prof. Köpper
• Construction monitoring: Stadt Bochum Foundation Engineering Office
• Contractor: Beton- und Monierbau Ges. m. b. H., Heitkamp Rail GmbH
• Main construction method: Trenchless
• Type of excavation: Excavator
• Lining: Shotcrete
• No. of tubes: 1
• Tunnel total length: approx. 850 m by cut-and-cover: 130 m ramp, 21 m bridge/mining means: 140 m twin-track, roughly 900 m single-track,120 m single-track operating track; Cross-section: single-track:36 m², twin-track up to 120 m²
• Contract Volume: approx. € 23 million
• Construction start/end: October 2001 to November 2004
• Opening: 2006