Elastic Wave Attenuation Characteristics and Relevance for Rock Microstructures
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Elastic Wave Attenuation Characteristics and Relevance for Rock Microstructures X. L. Liua*, M. S. Hana, X. B. Lia, J. H. Cuia, and Z. Liua a
School of Resources and Safety Engineering, Central South University, Changsha Hunan, 410083, China *e-mail: [email protected] Received June 4, 2019 Revised June 25, 2019 Accepted April 10, 2020
Abstract—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. Keywords: Elastic wave, attenuation coefficient, rock microstructures, frequency attenuation characteristics. DOI: 10.1134/S1062739120026674
INTRODUCTION
The energy of elastic waves is consumed by geometrical spreading, internal friction, mode conversion, and scattering during propagation. Elastic wave parameters, such as amplitude and frequency, therefore decrease with increasing propagation distance; this phenomenon is called elastic wave attenuation [1]. During elastic wave propagation in rock, mutual friction occurs along the rock particle interface that leads to the transformation of mechanical energy into heat, which is the main reason for the reduction of amplitude and frequency as the wave travels forward [2, 3]. The degree of attenuation of an elastic wave is closely related to
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