Estimation of crack density of heat-soaked granite using ultrasonics
Ultrasonic pulse transmission studies have been carried out at room temperature conditions to examine the influence of thermally-induced cracks on dispersion and attenuation of P-waves in a set of granites in the frequency range of 0.1 MHz to 2.5 MHz. Measurements of effective velocity and frequency dependence of Q-1 have helped in estimating the density and width of thermally-induced cracks with respect to that of the unheated rock using empirical relationships based on the linear attenuation theory of dispersive body waves in cracked solids. Majority of the tests have been made on samples subjected to heat at temperatures ranging from 100 to 300°C. The time duration and temperature at which the rock specimens have been subjected to heat-soaking and cooling shall strongly influence the crack parameters as observed in the present study of ultrasonic characteristics and microscopic examination. The laboratory results suggest that velocity and attenuation measurements are useful to investigate the changes in internal structure and progressive damage of rock under thermal and thermo-mechanical stresses, with a scope for field applications during underground storage of radioactive waste, geothermal energy production etc.