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Preliminary Analysis Using Surface Wave Methods To Detect Shallow Manmade Tunnels
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 21st EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Apr 2008, cp-177-00077
Abstract
Multi-channel Rayleigh wave data were acquired across a 1m diameter spillway tunnel along three parallel traverses with surface to tunnel separations of 0.90 m, 2.15 m, and 3.13 m, respectively. The data were acquired by placing a 24-channel array across the tunnel (perpendicular to the center-line of the spillway tunnel) and walking the sledge hammer source through the array starting with a far-offset of 10 m. The 4.5 Hz geophone array spacing was at 0.5 m intervals. Single shot data were analyzed to visually locate and to highlight attenuation effects associated with the tunnel. The field records were then velocity filtered in order to enhance back-scattered Rayleigh wave energy thereby allowing for visual identification of the tunnel location. The same single shot data were analyzed using the Attenuation Analysis of Rayleigh Waves (AARW) method. The intent was to demonstrate the utility of these approaches to tunnel delineation at a site where the geometry of the target and the nature of the encompassing soil was known. Electrical resistivity data was also acquired along the traverses for comparison purposes.