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Main collector Leipziger Straße- Am Ringelberg

The City of Erfurt was required to lengthen a main collector for sewage by a total of 900 m within the framework of the development of a new estate, Ringelberg (with 28,000 housing units). Given the topography of the terrain, laying depths of between 6 and 20 m were necessary. Cut-and-cover could not be considered either technically or ecologically. As a result, it was decided to drive a 680 m long section by micro-tunnelling. Jacking pipes CreaDig DN 400, 2 m in length with high-grade steel sleeve from the Steinzeug GmbH, were laid. The longitudinal compressive strength of these pipes of 75 to 100 N/mm² caters for a permissible thrusting force of 1580 kN in conjunction with systems with automatic recording and control. To lay the collector, the Sonntag Baugesellschaft mbH employed an AVN 400 machine from the Herrenknecht GmbH and was able to attain an average rate of advance of 12 m per shift. The special features of the construction project were:

  • a tricky geological profile; clay and clay stone with embedded gypsum lentils (soil class 6 to 7)
  • extremely deep location: up to 20 m
  • driven lengths of up to 134 m
  • a relatively small pipe diameter DN 400
  • external temperatures ranging to -15°.

The difficult marginal conditions called for extremely careful preparations. In order to ensure that the construction measure was successfully concluded, the thrusting forces, the rolling of the bore head and the laser refraction in particular had to be taken into account. Through the use of the ELS system, the sections were driven with absolute precision. As a result, the thrusting forces during the execution of the project could be reduced to 100 kN in conjunction with the pipe material used. In order to avoid the possible rolling of the pipe column, the first pipes were connected with each other torsion-safe. In the case of major section lengths with small diameters, pronounced heat development frequently occurs in the driven column of pipes, which can lead to refraction of the laser. In order to avoid a deviation from the very outset the heated air was suctioned off at the bore head and replaced by fresh air during the entire drive. A total of 6 sections were driven, for which 3 jacking pits DN 3300 and 4 target pits DN 2600 were necessary.

 

  • Country: Germany
  • Region: Thüringen
  • Tunnel utilization: Utility
  • Type of utilization: Sewage
  • Client: Stadtverwaltung Erfurt, Tiefbauamt
  • Consulting Engineer: Deutsche Abwasser-Reinigungs-Gesellschaft mbH, Ing.-Büro für Umweltfragen
  • Contractor: Sonntag Baugesellschaft mbH
  • Main construction method: Trenchless
  • Type of excavation: Pipe jacking
  • No. of tubes: 1
  • Tunnel total length: 680 m
  • Cross-section: DN 400, ceramic
  • Contract Volume: 3.2 mill. DM
  • Construction start/end: 6 months