Where rock is so unstable and exposed to water and frost that other safety measures will not give sufficient traffic safety, linings consisting of a rock smoothing concrete lining, a membrane and a structural concrete lining (fig. 1) should be constructed. Before constructing the lining, jobs such as blasting drainage ditches, conducting away large leakages from wall and roof (fig. 2) and tunnel cros-section control should be done. The linings are founded on concrete foundations in the sole corners which in case of unfavourable fissures ought to be bolted. The foundation is waterproofed by the membrane which is wrapped around the drain pipes. The inner concrete lining may consist of gunite or pumpable lean-mix concrete. The primary intention of this lining is to smoothen the rock surface to protect the membrance. Secondly, the inner lining establishes a rigid connection between rock and the structural lining. The structural lining is made up of high quality concrete. The purpose of this lining is to support the tunnel against high rock loads. This support is usually sufficient when the circular lining is exposed to small deformations, i.e. all cavities at the rock surface must be filled with concrete. Free span linings, e.g. at portals (fig. 3), should be reinforced and protected by means of a sand buffer. The concrete is placed behind the form by concrete pumps. The mix should contain mortar rich on fines, and coarse aggregate should be naturally rounded. The slump may be between 12-15 cm to reduce vibration to a minimum. The form is filled carefully through openings in the form wall panels (fig. 5). In the top of the form concrete should be pumped through special openings which may be sealed while filling under pressure. Alternatively the concrete may be pumped through openings in the form end. To attain a good filling of the form even in the top section of the vault expanding mortar should be added in the last batch. Even better, mortar should be injected into the voids between the two concrete linings after setting. /Author/

  • Corporate Authors:

    Norwegian Road Research Laboratory

    Postboks 8109, Gaustadalleen 25
    Oslo,   Norway 
  • Authors:
    • Larssen, T L
  • Publication Date: 1975-9


  • Norwegian

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00131566
  • Record Type: Publication
  • Report/Paper Numbers: No. 48
  • Files: TRIS
  • Created Date: May 14 1976 12:00AM