Development of a surface-wave imaging system for geotechnical applications based on distributed acoustic sensing (DAS) and ambient noise interferometry
Jonathan B Ajo-Franklin1, Thomas M Daley2, Barry M Freifeld2, David G Tang2,3, Ruxun Zhang2, Anna M Wagner4, Shan Dou5, Kevin Bjella6 and Roman Pevzner7, (1)Rice University, Earth, Environmental, and Planetary Sciences, Houston, United States, (2)Lawrence Berkeley National Laboratory, Berkeley, CA, United States, (3)University of Texas at Austin, Austin, TX, United States, (4)Cold Regions Research and Engineering Laboratory (CRREL), Fort Wainwright, AK, United States, (5)University of California Berkeley, Berkeley, CA, United States, (6)U.S. Army Cold Regions Research and Engineering Laboratory Alaska, Fairbanks, United States, (7)Curtin Univeristy, Perth, Western Australia, Australia
Abstract:
Distributed fiber-optic sensing methods have been used since the 1980’s for continuous monitoring of near-surface soil properties, typically exploiting Raman scattering to measure temperature (DTS) or stimulated Brillouin scattering to measure strain (DSS). Recent advances in high speed measurement of Rayleigh scattering has enabled distributed recording of seismic waves over long sections of fiber; this approach, referred to as distributed acoustic sensing (DAS) has the potential to allow nearly continuous monitoring of near-surface mechanical properties, a crucial target for geotechnical management of infrastructure dependent on soil strength.
We present initial results from our effort to build a real-time soil property monitoring system based on DAS; our approach employs seismic interferometry and dispersion analysis of ambient noise generated by infrastructure to provide a continuously updated model of shear modulus. Our preliminary results include an in-depth investigation of DAS fiber response in the context of active sources; this component of our study verifies classical models for the azimuthal response of straight fibers to propagating surface waves. We also explore the “noisescape” of linear infrastructure and show a usable seismic signal band of 8-40 hz at a series of sites, primarily consisting of Rayleigh waves. Finally, we present preliminary results from a DAS monitoring array installed at the Richmond Field Station near a heavily used road and compare interferometric processing of the acquired data to that generated by surface deployment of geophones.
