Detection of shallow underground fissures by time-frequency analysis of Rayleigh waves based on wavelet transform
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Detection of shallow underground fissures by time-frequency analysis of Rayleigh waves based on wavelet transform* Shao Guang-zhou1, and Du Ting1 Abstract: Ground fissure is a geological hazard that poses a great threat to human life and, property and the environment. Therefore, it is necessary to detect shallow underground fissures effectively. In this paper, a time-frequency analysis of Rayleigh waves based on the wavelet transform is proposed to detect shallow underground fissures. The arrival time of the directed Rayleigh waves and the diffracted Rayleigh waves from the underground fissure is extracted from the time-frequency spectrum of any two traces. Furthermore, the locations of the underground fissures are calculated according to the time difference relation. Four sets of fracture models and one set of field data were used to test the effectiveness of the wavelet transform of Rayleigh waves. Moreover, the detection results of the actual data are compared with that of the high-density electrical method to further prove its detection effect. The field investigation shows that using the wavelet transform of Rayleigh waves to detect shallow underground fissures is feasible and effective. Keywords: Underground fissure, Rayleigh wave, wavelet transform
Introduction Ground fissure is a crack in surface rock and soil. It is a type of ground deformation under the action of internal and external dynamics (Peng et al., 2016). Ground fissure hazard of different degrees often happens in many parts of the world (Burbey, 2002). It pose a great threat to the living environment and human. In recent years, excessive pumping of groundwater due to the demands of the growing population and industrial development makes the frequency and severity of ground fissure disasters increase year after year (Hsieh, 1996). It has
caused serious environmental geological problems and attracted the attention of many researchers in the world. The detection of ground fissures is an interesting and difficult problem in the engineering exploration of these geological hazards. For example, in China’s northwest, a large distribution of silty loess is susceptible to soil collapse. “Soil collapse” occurs when the loess is subjected to various stresses (Li et al., 2000), which causes the fissures to be buried. Thus, this characteristic of ground fractures makes them difficult to be detected. At present, the exploration techniques mainly used include comprehensive geological survey, drilling, geochemistry methods, and geophysical methods.
Manuscript received by the Editor March 6, 2019; revised manuscript received May 6, 2020. *This research is jointly supported by the National Natural Science Foundation of China (Grant Nos. 41874123, 41004043) and fundamental research funds for the central universities (Grant Nos. 300102268401, 300102268402). 1. College of Geological Engineering and Geomatics, Chang’an University, Xi’an 710054, China ♦Corresponding author: Du Ting (Email: [email protected]) © 2020 Chinese Geophysical Society. All rights reserved.
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