ENGINEERING GEOLOGICAL INVESTIGATIONS

Intensive investigations indicate that the rock in the area of the proposed tunnel consist mostly of interbedded sandstone, and sandstone and argillite which have been extensively weakened by weathering. The rock mass is closely jointed and many faults are present, of which the 30 m wide crush zone of the Terrace fault is the most prominent. The relatively poor rock condition throughout the site has had a significant influence on the design of the design of the tunnel and adjacent cut slopes. Geological mapping of existing exposures provided a general indication of rock condition over the site, and, together with extensive subsurface investigation work, a detailed assessment of probable construction conditions was possible. Geomechanic investigations were also carried out. The excavation of a drive the full length of the tunnel line enabled rock condition data to be recorded in detail for tunnel design. The tunnel will be excavated through rock that ranges from completely weathered, and is therefore essentially a soil, to unweathered; about a third of the length is in clayey breccia. The existing 35 deg. slopes adjacent to the north portal are formed by weathered bedrock overlain by colluvium. A retaining wall will be constructed to reduce the risk of instability that might otherwise occur in these materials because of the need for steep cuttings to obtain sufficient width for the construction of the motorway.

  • Availability:
  • Corporate Authors:

    Technical Publications Limited

    C.P.O. 3047
    Wellington,   New Zealand 
  • Authors:
    • Riddolls, B W
    • Perrin, N D
  • Publication Date: 1975-8-15

Media Info

  • Features: Figures; References;
  • Pagination: p. 221-224
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00128560
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Mar 10 1976 12:00AM