风化花岗岩声谱特征分析

岩石材料可视为声波的天然低通滤波器 ，声波在不同力学性质岩石材料中传播时 ，由于岩石对声波吸收程度不等因而高频声波滤除状况也不同。接收波中频率丰富程度与岩 石 的力学性质密切相关，岩石力学强度愈高，声谱中高频成分就愈丰富。反之，声谱中主要为 低频，高频分量因衰减而缺失。实验采用全数字化DB4型多波参数分析仪和计算机，对波形 数据进行FFT分析，通过接收谱和频率响应的特征来研究岩石的力学性质。声衰减研究可为 岩石、岩体强度和综合评价提供更多、更可靠的信息，是解决工程地质风化岩问题研究的一 种可行方法。

Study on Acoustic Spectral Characteristics of Weathered Granite

Study on weathered rocks is important in engineering geology. At present, longitudinal wave velocity is widely applied to reflect the weathering and crushing degree of rocks. However, longitudinal wave velocity is only one of the parameters of rocks, and simple velocity testing will lose much useful information. Now, some scholars are studying rock mechanics properties by other acoustic parameters, especially the acoustic attenuation index. Their important conclusion is that acoustic attenuation is more sensitive than wave velocity when reflecting the discontinuity and weathering crushing features of rock mass. Based on the viscosity acoustic absorption theory, the amplitude fades according to the law of exponential function of frequency and viscosity in the course of wave propagation. The higher the frequency is, the faster the amplitude fades. High frequency composition of wave varies with the absorption in rock materials. Degree of frequency abundance in receiving wave is closely related to properties of rock mechanics. In our experiment, the wave shape recorded by the high precision multi parameter analyzer (digital model DB4). Computer is used to analyze wave shape data with FFT in order to convert time domain signal into frequency domain signal. Then receiving spectrum and frequency response function is gained, and their frequency distribution features are applied in the study on rock mechanics. The method avoids complexity of acoustic attenuation coefficient test. Moreover, it can automatically and continuously collect test data. Study has demonstrated that the high weathered and crushed samples have only low frequency composition, and the fresh and hard ones have abundant high frequency composition. Given the same sample size and proper frequency, geometrical and diffusion attenuation can be effectively controlled, then internal friction absorption can be regarded as the main cause of test result.