SITE INVESTIGATION FOR TUNNELLING TRIALS IN CHALK

The techniques are described and the results are presented of a site investigation which consisted of several phases: preliminary investigations, a 2-stage borehole investigation, and measurements made in a 3 m diameter shaft. In addition, chalk quality encountered in the tunnel was assessed during the tunneling experiments. Measurements of the intact strength of exposed rock surfaces in the quarry, shaft and tunnel showed that RQD values were generally between 60 and 80 percent, with mean discontinuity spacing commonly between 0.07 and 0.20 m; a lower fracture spacing was observed in near-surface weathered layers. The Stage I site investigation, designed to cover the whole site, involved sinking five 131 mm diameter boreholes to depths of between 20 and 30 m and carrying out 20 resistivity depth probe surveys. The Stage II investigation carried out to examine ground conditions to be encountered during tunnelling, was concentrated along the selected tunnel line. The effectiveness of the various site investigation techniques in predicting a number of critical ground properties is evaluated, and the costs of the shaft and boreholes are compared. Predictions of ground stability are examined in the light of conditions encountered during tunnelling.

  • Corporate Authors:

    Transport and Road Research Laboratory

    Old Wokingham Road
    Crowthorne RG11 6AU, Berkshire,   England 
  • Authors:
    • Priest, J A
    • HUDSON, J A
    • Horning, J E
  • Publication Date: 1976

Media Info

  • Features: Figures; Photos; Tables;
  • Pagination: 39 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00145011
  • Record Type: Publication
  • Report/Paper Numbers: TRRL Report 730
  • Files: TRIS, ATRI
  • Created Date: Feb 1 1977 12:00AM