AN ULTRASONIC PROFILING INVESTIGATION ON SOME FRESH AND WEATHERED GRANITES OF HYDERABAD,INDIA*

The ultrasonic profiling method of measuring the compressional and shear wave velocities in cylindrical rock samples is extended to measurements in some weathered and fresh granite blocks collected from the Hyderabad (India) region. This possibility of the method provides a means of investigating the elastic properties of the less compact rocks, of which the near-surface formations are particularly important. In this article the important parts of the ultrasonic profiling instrument developed are described and the relevant aspects of the seismic wave fields and identification of the individual waves in the wavetrain responses to longitudinal excitation are considered. Compressional, shear and surface (Rayleigh) wave velocities in some fresh and weathered granites are detailed. The compressional velocities range from 4.8 km/s to 5.5 km/s in fresh granites and lie between 1.1 km/s and 2.5 km/s in weathered granites. Young's modulus and Poisson's ratios computed from the measured velocities are also presented. An empirical relation of the form log E= 4.27 + 2.11 log V_p between Young's modulus E and compressional velocities V_p in the fresh granites studied is deduced. The versatility of the approach is thus demonstrated.