Experience has shown that geological studies for road tunnels pay off, and that it is important to supplement the investigations by drilling and borehole mapping in order to eliminate uncertain factors with respect to ground conditions. The investigations should be concluded by classifying the ground conditions and defining the rock classes on maps and sections at the tunnel level. The rock classification systems in use have many shortcomings, and a new system more suitable for Norwegian conditions is presented. Geological surveys require topographic maps, preferably in scale 11,000, and stereographic aerial photographs of the tunnel project area. The geological survey is carried out as a normal mapping of geological structures, with stress on recording structures parallel to the projected tunnel, and to advise the supposedly best crossing of joint and fault zones. Where the bedrock is covered by overburden, further investigations can be assisted by seismic measurements. If necessary, the investigations are carried on by drilling. Normal rock (percussive) drilling performed with chain fed hydraulic drilling machines may be applied to depths up to 100 m. Useful information may be obtained by continuous recording of drilling speed, mud composition and penetration difficulties. Core drilling is expensive, and should produce a continuous rock profile in good rock. Care must be taken to avoid loss of core. Where core is lost, samples of the wash water should be secured for sedimentation of material. The drill holes may supply further information if they are used for water pressure tests, borehole periscope and TV camera inspections. Such investigations may provide information on fracture widths, spacing, and orientation. Water pressure tests may provide information on the in sity location and extent of water leakage and water permeability of the bedrock. Borehole periscope inspection can define the orientation of rock boundaries and other planear structures to a depth of 34 m. In deeper holes, a borehole TV camera has to be used. ;Author;

  • Corporate Authors:

    Norwegian Road Research Laboratory

    Postboks 8109, Gaustadalleen 25
    Oslo,   Norway 
  • Authors:
    • Gronhaug, A
  • Publication Date: 1975-9


  • Norwegian

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00131557
  • Record Type: Publication
  • Report/Paper Numbers: No. 48
  • Files: TRIS
  • Created Date: May 14 1976 12:00AM