Elastic Wave Attenuation Characteristics and Relevance for Rock Microstructures
We investigated elastic wave attenuation characteristics using a PCI-2 acoustic emission system. A lead-break test was employed to carry out attenuation experiments in granite, marble, red sandstone, and limestone. Because the centroid frequency variation of the red sandstone differs significantly from the other rocks, a pendulum steel ball impact test was also performed to study the attenuation characteristics of elastic waves in red sandstone. The results show that the elastic wave signal amplitude decreases with increasing propagation distance for all four rock types. In granite and red sandstone, the peak frequency of the elastic wave declines abruptly after the propagation exceeds 800 and 100 mm, respectively, and remains almost unchanged in marble and limestone. The attenuation of centroid frequency in granite, limestone, and marble shows the same trend; however, in red sandstone, when the elastic wave propagation exceeds a certain distance, the variation of centroid frequency shows an upward tendency. The main influence of elastic wave attenuation in rock is the packing state of mineral particles: less tightly packed rocks consistently have a higher attenuation coefficient. The secondary cause of attenuation is the development of structures such as joints and stratifications. More developed interior structures lead to higher attenuation coefficients. Sensor selection is also very important in rock attenuation tests. We recommend use of a wide resonant frequency sensor or sensors with different resonant frequencies along the elastic wave propagation path.