| Abstract | Rocks are considered to bear in-herent structural discontinuities,
which includes bedding, laminations, foliation, schistosity, jointing and faulting, and these discontinuous features result in the geomechanical anisotropies of rocks. Seismic wave velocities differ as a result of the existence of anisotropic discontinuities. The velocities of compressional and shear waves in a rock may together be used to calculate
the value of Poisson's ratio, and if the density is known the value of Young's modulus may be calculated as well. By taking mica-schist as an example, experiments had been carried
out to measure seismic wave velocities by supersonic method on both laboratory test specimens and in situ outcrops in short distance. Laboratory compressional and shear wave velocities were affected by
schistosity, water content and straight openings on specimens, together with the measured densities of test specimens. Poisson' s ratio as well as Young's modulus were determined. Maximum and minimum velocities were found to be in the propagation directions parallel and perpendicular to schistosity respectively, and so do Young's moduli. By using the same equipment as that was used in the laboratory, in situ compress: Conal velocities were measured, and they were affected by
schistosity, cracks, degree of weathering and other discontinuities. velocity values showed to be the combined result of these factors. That
is to say, in situ compressional wave velocity was highly related to the degree of anisotropy.
For the laboratory test results, the ratio of the velocity in a
direction parallel to schistosity to the velocity in a direction perpendicular to schistosity, VJ../V// , was used to describe the degree of anisotropy, and the degree of anisotropy decreased with increasing water content. |