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• Main Authors: Chih-Hong Wu, 吳志鴻
• Other Authors: Hwei-Weng Chang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/59wtc7

碩士 === 國立中央大學 === 土木工程研究所 === 94 === Abstract To realize the properties of acoustic waves propagating in soil medium, this research rely on the high sensitivity and excellent frequency response of condenser microphone to control the drop height of a steel ball dropping to the surface of sand as a sound source at the large scale soil testing pit. The purposes of this research are to investigate the propagation speed of sound, the distribution of root mean square of sound pressure and the variation of sound pressure in frequency domain in the soil medium. Finally, acoustic responses in the sand layer by dropping a steel ball on different materials were compared. From the results of experiments, it was revealed that the propagation speed of acoustic waves is about 170~220m/s and it is getting faster with depth, but the growth of speed is getting slower. Acoustic responses of dropping a steel ball onto the surface of sand layer by different drop heights make the root mean square of sound pressure attenuate with the increase of distance between sound source and microphone. The variation of root mean square of sound pressure is very large between 0~1m in horizontal direction from sound source, and very small besides 0~1m. In another aspect, frequency distributes below 300Hz and it mainly distributes below 30Hz within 1m in horizontal direction from sound source. Frequency occupy the domain of 30~300Hz and mainly occupy the domain of 30~100Hz outside of 1m from sound source. Changing the drop height of a dropping steel ball did not change the attenuation trend of root mean square of sound pressure and the frequency distribution of acoustic signals in sand. In addition, the major differences of the acoustic signals of changing the material of knocked blocks is that the change of the dominant frequency and corresponding sound pressure inside of 1m distance from sound source in horizontal direction and below 30Hz in frequency domain.