Location: Watershed Physical Processes ResearchTitle: Practical techniques for enhancing the high-frequency MASW method Author
|Lu, Zhiqu - University Of Mississippi|
Submitted to: Environmental and Engineering Geoscience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2017
Publication Date: 6/1/2017
Citation: Lu, Z. 2017. Practical techniques for enhancing the high-frequency MASW method. Environmental and Engineering Geoscience. 2(I,2):197-202. doi:10.2113/JEEG22.2.197. Interpretive Summary: The author has developed a non-invasive technique called the high-frequency multi-channel analysis of surface waves (HF-MASW) to investigate soil properties in shallow depths up to several meters. It can be used to measure soil profiles and reveal surface crusting/sealing. This technique is similar to the spectral analysis of surface waves (SASW) method, but has advantages in terms of sensor placement and mode identification.
Technical Abstract: For soil exploration in the vadose zone, a high-frequency multi-channel analysis of surface waves (HF-MASW) method has been developed. In the study, several practical techniques were applied to enhance the overtone image of the HF-MASW method. They included (1) the self-adaptive MASW method using a variable sensor spacing configuration, (2) the phase-only MASW method, and (3) a nonlinear technique. To demonstrate the capability of these techniques, a HF-MASW test was conducted, which consisted of a small shaker operated in chirp mode with three gapped frequency bands and a geophone array with a variable spacing configuration. The overtone images obtained from (1) full spreadlength, (2) self-adaptive spreadlength, (3) full-spectra analysis including magnitude and phase spectra, and (4) phase-only spectrum analysis MASWs, respectively, were compared in each frequency band. The results revealed the enhanced dispersive images by the HF-MASW using the self-adaptive and phase-only with the variable spacing configuration technique. The study also demonstrated the nonlinear acoustic technique by means of harmonic generation to increase the measurable frequency range of dispersive curves. It is worthy to mention that these techniques can also be applied to the conventional NASW method using controlled seismic vibrators, such as vibroseis.