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Light Rail Mühlheim, construction lot 8 / crossing river Ruhr

2,130 m of single-track running tunnel had to be driven by a shield as part of the 1.9 km long construction section 8 of Mülheim's urban railway. The overall section consisted of 2 tracks - 1,038 and 1,092 m long, with an excavating diameter of 5.90 m. The reasons for the selection of this particular route and gradients were:

  • the linking points with the existing operational line with the focal point "Hauptbahnhof" in the east and the open ramp for the tram depot connection in the west
  • the link-up with the two stations "Stadtmitte" and "Schloß Broich"
  • the undercutting of the River Ruhr taking a sufficiently thick covering layer of some 7 m and
  • the efforts to locate the tunnel section in one particular geological formation.

The tunnel tubes were driven through carboniferous clay and sand stone. The strength of the sandstone amounted to as much as 200 MN/m² given a high percentage of abrasive minerals. The groundwater table corresponded with the Ruhr's water level, so that the submersion depth amounted to a maximum of 20 m. A Mix-shield tunnel boring machine was called for and deployed as a combination of a hard rock cutting head TBM and hydro-shield with fluid supported tunnel face, as used in loose ground, in other words:

  • a cutter head fitted with disc bits and (ec)centric overcut
  • fluid-supporting of the tunnel face to ward off the groundwater
  • access to the extraction chamber via a double lock system
  • hydraulic material removal and application of a separating plant
  • monocoque segmental lining (reinforced concrete d = 35 cm) with continuous annular gap grouting.

The shield began operating in the access shaft (track 2) from a starting cavern and ended in a target shaft. The dismantled TBM was returned to the access shaft above ground, whereas the backups were transported through the finished tunnel tube (track 2). Track 2, which was driven first, produced rates of advance which amounted on average to 3.3 m/d on account of unexpectedly high wear. Through a large number of modifications and new concepts for the cutter head for the second shield run in track 1, the rate of advance was increased to 8.8 m/d. The Schloß Broich and Stadtmitte stations were created by expanding the standard section. For this purpose, 4 sections, each approx. 90 m long, were enlarged from 37.5 m² to 73.0 m² overall cross-section by drilling and blasting, after installing the segments.


  • Country: Germany
  • Region: Nordrhein-Westfalen
  • Tunnel utilization: Traffic
  • Type of utilization: Underground, urban and rapid transit
  • Client: Stadt Mülheim an der Ruhr, Stadtbahnbauamt
  • Consulting Engineer: Schlegel-Dr.-lng. Spiekermann GmbH & Co., Erdbaulaboratorium Essen
  • Contractor: Dyckerhoff & Widmann AG, Hochtief AG, Philipp Holzmann AG, Alfred Kunz GmbH & Co., Strabag Bau AG, Thyssen Schachtbau GmbH, Wayss & Freytag AG
  • Main construction method: Trenchless
  • Type of excavation: Shield machine
  • Lining: Reinforced concrete segments
  • No. of tubes: 2
  • Tunnel total length: 1,092 m, approx. 1.9 km overall length of construction Iot
  • Shield drive: 2,130 m (tracks 1 + 2)
  • Cross-section: Internal diameter 5.90 m; External diameter 6.90 m
  • Contract Volume: approx 156 million DM net
  • Construction start/end: A total of 71 months; Shield drive 19 months
  • Opening: rough state May 1994