Thermally induced variation of primary wave velocity in granite from Yantai: Experimental and modeling results

This work analyzes the results from experiments for studying the effect of high temperature on primary wave velocity of granite. Test samples are preheated to different temperatures (from 25° to 900 °C) and then cooled down by air. The primary wave velocity test is performed on the heated samples. Lastly, the microstructure test is carried out to study the mechanism of thermal damage and development process of micro cracks. The results show that the primary wave velocity reduces gradually while the temperature increases, i.e. the higher the heating temperature is, the faster the wave velocity reduces. Basing on the waveform, the quality factor (Q) of primary wave velocity is calculated and is decreased with the increase of heating temperature. From the thermal damage factor (D(T)) model of primary wave velocity and the measured data, the D(T) of granite samples is found to increase with heating temperature rising following the S-logistic function. Then, according to the change of microstructure, the formation mechanism of thermal damage is analyzed and the damage process of rock verified by the deterioration of mechanical parameters. For rock heated to different temperatures and then cooled down, the main reason for damage at lower temperature is dehydration and that at higher temperature is the increase of cracks which destroy the structure and weaken the bonding between particles.