Effect of bedding planes on wave velocity and AE characteriscs of the Longmaxi shale in China.pdf

ORIGINAL PAPER Effect of bedding planes on wave velocity and AE characteristics of the Longmaxi shale in China Feng Xu1,2 Chunhe Yang1 Yintong Guo1 Lei Wang1 Zhenkun Hou3 Haoran Li4 Xiaoming Hu1,2 Tongtao Wang1 Received: 8 May 2016 /Accepted: 1 March 2017 # Saudi Society for Geosciences 2017 Abstract The experimental work described in this paper was carried out in order to discover more about the effects of bed- ding planes on wave velocity and acoustic emission (AE) characteristics of shale. Two groups of specimens, which were collected from the Longmaxi shale outcrop in Chongqing, China and cored perpendicular and parallel to the bedding planes, were tested under uniaxial compression, and the wave velocity and AE were monitored. There were obvious differ- ences in the acoustic characteristics of shale with different bedding plane orientations. The experimental results show that (1) the average increasing rates of P- and S-wave veloc- ities were 39.86 and 54.41%, respectively, for the specimen with a load perpendicular to the bedding planes (Y-0). The P-wave velocity and axial strain of specimen show a marked logarithmic relationship. However, the average increasing rates of P- and S-wave velocities were 5.44 and 10.54%, re- spectively, for the specimen with a load parallel to the bedding planes (Y-90). The good linear relationship between P-wave velocity and axial strain before failure of specimen has been built. Generally, S-wave velocity was more sensitive to axial strain than P-wave velocity. (2) AE characteristics for Y-0 showed that a few signals → quiet period → stable increase → steep increase; for Y-90: quiet period→ stable increase→ sudden increase → sharp increase. The AE energy for two groups of specimens was concentrated on low and middle of amplitudes (45-80 dB), but the proportion of amplitudes (80– 100 dB) and the total counts of AE for Y-0 was 1.95, 2.2 times as much as that for Y-90, respectively. The results preliminar- ily revealed the ef