About 600 M of a tunnel for the underground system being constructed in Helsinki runs through a fault between the gneiss and granite bedrock. Soil here is still overlain by silt, sand and clay of low strength. It was decided to construct a frozen shell around the workings by installing horizontal pipes. The strength of the frozen soil depends on soil type, water content, temperature, duration and intensity of load. No tensile stresses must occur in the frozen shell, and compressive stresses must not exceed the ultimate compressive strength of the frozen soil. A factor of safety of 3-5 is applied. The thickness of shell was 2.5 M, achieved by installing 35 pipes per adit. The most difficult operation was drilling for the pipes. Freon R22 was used to freeze 3600 cu M soil and 7200 cu M rock. The cooling load was about 1200 gj. Temperature was monitored by 119 sensors connected to a digital display. Displacements were measured by settlement tubes and inclinometers. Likely settlement was due to consolidation, vibration, frost heave, deformation of ice shell, thaw and deformation of the cast iron tunnel lining. Total settlement is expected to be about 200 mm.

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  • Corporate Authors:

    Svenska Vag-Och Vattenbyggaren Riksforband

    Regeringsgaten 98
    S-11139 Stockholm,   Sweden 
  • Authors:
    • Hartikainen, J
  • Publication Date: 1978

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: p. 69-74
  • Serial:
    • Vag-Och Vattenbyggaren
    • Volume: 24
    • Issue Number: 8-9
    • Publisher: Svenska Vag-Och Vattenbyggaren Riksforband
    • ISSN: 0042-2177

Subject/Index Terms

Filing Info

  • Accession Number: 00189767
  • Record Type: Publication
  • Source Agency: Swedish National Road and Transport Research Institute (VTI)
  • Files: ITRD, TRIS
  • Created Date: May 26 1979 12:00AM