Successful grouting for the Zimmerberg Base Tunnel

The Zimmerberg Base Tunnel inaugurated in June 2003 is a core project of the Swiss Federal Railway (SBB) Bahn 2000 concept. Along the 780 m stretch in unconsolidated ground, under the city of Zurich, the tunnel lies within the groundwater and has only modest cover and short distances to existing buildings. The groundwater table coincides with the crown of the tunnel and the maximum overburden was 14 m at the beginning of the loose soil section, gradually decreasing to 8 m at the portal. To avoid damage to buildings, roads and lifelines, extensive precautionary construction measures had to be taken. The first 150 m long section was protected with a pipe shield consisting of 10 concrete pipes 1.55 m each. The following, approximately 100 m long construction complex had to be secured with a pre-stressed concrete girder supported by a large number of micro piles. The principal construction feature over the main tunnel was a 315 m long, continuous ceiling of 3-4 m thickness, which was created by grouting. The aim was to reduce deformation, settlement and permeability as well as to prevent loss of cover during the slurry-/mixed-shield TBM advance directly underneath the buildings at the centre of Zurich. For purposes of grouting, holes 3-23 m in length had to be drilled into the site formation from the pilot adit. From the approximately 120,000 valves of the grouting pipes, the contractor pumped injection material at a maximum pressure of 15 bar. In order to attain the greatest possible degree of pore filling, the grouting material was injected in phases, starting with the more viscous cement followed by high-flow slurry and ending with a very fluid, three-component compound. Due to the high risk, the standards were demanding and the quality assurance was of paramount importance. In order to guarantee that the quality of the grouting body could be attained a comprehensive investigation and test concept was elaborated. This encompassed the instrumental monitoring of grouting activities, opening of direct exposures and test drilling plus evaluation of grouting data. A rating system uncovered zones of weakness, which were then re-subjected to grouting. All involved parties were satisfied with the chosen construction support measures and selected procedures. In keeping with the motto ''A procedure is only as good as the method with which it can be tested'', the instrumentation and test installations, the analysis and evaluation, entailed much work and were time consuming. However, they were mandatory and decisive to ensure success. In June 2003, the tunnel was inaugurated and turned over to the owner for operation. (A). "Reprinted with permission from Elsevier". For the covering abstract see ITRD E124500.


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  • Accession Number: 01011654
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Dec 19 2005 3:23PM