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Bolted segments rescue snarled pipejack Oct 2011
TunnelTalk reporting
When a 2m diameter pipejacking came up against unexpected geological conditions in Spain, it was a system of small diameter bolted and gasketed segments that rescued the situation. Claimed as the smallest inner diameter system of bolted segmental lining, the solution was designed and supplied to the contract by machine supplier Herrenknecht and its Formwork division.

Mini segmental lining in Spain

The pipejacking system was 500m into a 1,200m long wastewater tunnel for the Colector Interceptor General del Rio Nalón in Oviedo, Spain when an unexpected change in the geology to high compressive strength rock forced the tunnel construction company Eurohinca to change the lining system. When asked to provide support Herrenknecht solved the problem by reconstructing the tunnelling machine in the back-up area and delivering three sets of moulds to accommodate the change of the lining system from pipejacking to the 2,000mm i.d. (2,270mm o.d.) segmental lining alternative.
The hydraulic cylinders of the Herrenknecht push-module assembled below ground continued to provide the required thrust force along the remaining 700m.
Protected by this additional shield, segments were installed with the help of a erector installed in the minimal 2m i.d. space.
Using the Herrenknecht Formwork moulds, some 5,604 segments of 750mm wide x 135mm thick were manufactured on site by the construction crews to build trapezoidal rings of six segments per ring. Each of these segments is fitted with two curve spacers in the longitudinal joint and 12 dowels of the 'Berlin' system for secure connections.
  • Segments moulds for a small and flexible lining

    Segments moulds for a small and flexible lining

  • A 2.4m i.d. segmental lining in Melbourne

    A 2.4m i.d. segmental lining in Melbourne

Despite continued challenging geological conditions, breakthrough of the 1,200m long drive occurred successfully on October 12, 2011.
The experience illustrates that segmental lining systems for smaller diameter tunnels of 2,000mm to 2,500mm i.d. offer new possibilities. In general, pipejacking drives are limited to shorter drives due to skin friction forces and curved alignment restrictions. The segmental lining alternative allows for considerably longer drives and tight curves can be more readily accommodated. According to Herrenknecht Forwork, a segmental lining with an inner diameter of 2,000mm cab accommodate minimal curve radii of 150m and "with special measures, radii of 100m are possible." For small diameter tunnels with challenging requirements, the suggestion is that segmental lining should be included as a real alternative during the early project planning and engineering phases.
Other small diameter segmentally lined references projects by Herrenknecht Forwork include the 2.1km long x 2.4m i.d. main sewer replacement tunnel in Melbourne, Australia with a minimum radius curve of 250m; the 1,492m long x 2,280mm i.d. Galerie d'Annecy in France; and the Galerie de Choully in Switzerland with a length of 2.3km, and inner diameter of 2.5m and a minimum radius curves of 260m.
References
Palomino package for hydropower progress - TunnelTalk, Jan 2011

           

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