This article described the multiple headings with vacuum drainage method used to excavate the initial 150 m of the second bore of the Du Toitskloof (Huguenot) Tunnel through soft decomposed granite. A comparison was also made between this method and the ground freezing method used to excavate the soft ground section of the first bore. Details of the excavation sequence of the multiple headings was provided, as was the layout of the vacuum drains, and a description of the methods used to position them. Inspection techniques used to assess the effectiveness of the drains were also described briefly, as were details of the ground freezing method used. It was found that the ground freezing method was quicker than the method using multiple headings, giving an advance of 2 m per week as opposed to 2.5 m per week. The risks involved were also very low. By comparison the drained soft ground material was unstable and could only "stand up" for a short time. Any break-down in equipment or unexpected problems could result in collapse, requiring expensive remedial treatment. However, the comparative cost of the multiple heading and vacuum drainage was only 80% of the cost of ground freezing. (TRRL)

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  • Corporate Authors:

    South African Institute of Civil Engineers

    9 St Davids Place, Parktown, P.O. Box 62129
    Marshalltown,   South Africa 
  • Authors:
    • Matchett, J M
    • Pringle, L W
  • Publication Date: 1988-4

Media Info

  • Pagination: p. 179-183
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00493081
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD, TRIS, ATRI
  • Created Date: May 31 1990 12:00AM