The article describes the use of a Schmidt hammer and grid on a tunnel face to determine the Schmidt reduction index. The index has been shown to be related to excavation rates, while increases in these rates have been attributed to the fractured state of the rock mass. The authors consider that the relationships established for four fathom mudstone should apply to most sedimentary rocks, though the values of intercepts and gradients will vary from site to site. During the investigations, seismic methods were also used to evaluate the quality of a rock mass. The use of small, ultrasonic instruments was found to be unsuitable due to attenuation characteristics of fractured rock. /TRRL/

  • Availability:
  • Corporate Authors:

    Morgan-Grampian Limited

    30 Calderwood Street
    London SE18 6QH,   England 
  • Authors:
    • Young, R P
    • FOWELL, R J
  • Publication Date: 1978-6


  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 45-48
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00189526
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Apr 12 1979 12:00AM