CROSS HOLE ACOUSTIC SURVEYING IN BASALT

The purpose of this technical note is to present preliminary results of a series of cross-hole acoustic measurements performed in a tunnel situated in a basaltic rock mass. The tunnel, at a sub-surface depth of 46 m, was excavated by conventional drill-and-blast techniques. Located well above the water table, the rock mass is characterized as dense basalt with a jointing structure of 0.15-0.36 m thick vertical columns cut by low-angle cross joints. The objectives of the test program were: first, to evaluate in situ dynamic elastic properties, and to assess their spatial variation around the opening; second, to evaluate the extent of blast damage around the opening; and third, to assess the spatial variation of jointing and fracturing around the opening. Analysis of the data included an evaluation of the velocities and frequency spectra of compressional and shear waves transmitted through the rock. The authors found that (1) the acoustic velocity and attenuation data are clearly indicative of an anisotropic, jointed rock mass, with a greater intensity of jointing in the horizontal than the vertical direction. (2) low acoustic velocities are indicative of blast damage, and of zones of intense jointing or fracturing. The same trend is seen also in the values of dynamic elastic modulus. The dynamic Poisson's ratio, however, appears to be relatively insensitive to the degree of jointing or fracturing. (3) preliminary analyses of the frequency data show that the attenuation of elastic waves is also indicative of blast damage and the intensity of jointing and fracturing. Further analyses of the frequency data are clearly required. (TRRL)

  • Availability:
  • Corporate Authors:

    Pergamon Press, Incorporated

    Headington Hill Hall
    Oxford OX30BW,    
  • Authors:
    • Rezowalli, J J
    • KING, M S
    • Myer, L R
  • Publication Date: 1984-8

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Filing Info

  • Accession Number: 00391193
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD, TRIS
  • Created Date: Mar 29 1985 12:00AM