Non-destructive Measurement of Soil Liquefaction Density Change by Crosshole Radar Tomography, Treasure Island, California
Robert E. Kayen1, Walter A. Barnhardt1, Scott Ashford2 and Kyle Rollins3
1 USGS, 345 Middlefield Road, Menlo Park, CA 94025
2 UCSD, La Jolla, CA
3 Brigham Young University, Provo, Utah.
Computer Simulation of Earthquake Effects
Proceedings of the sessions of Geo-Denver 2000
American Society of Civil Engineers
Held August 5-8, 2000, Denver, Colorado
This abstract is reproduced by permission of the publisher, ASCE
A ground penetrating radar (GPR) experiment at the Treasure Island Test Site [TILT] was performed to non-destructively image the soil column for changes in density prior to, and following, a liquefaction event. The intervening liquefaction was achieved by controlled blasting. A geotechnical borehole radar technique was used to acquire high-resolution 2-D radar velocity data. This method of nondestructive site characterization uses radar trans-illumination surveys through the soil column and tomographic data manipulation techniques to construct radar velocity tomograms, from which averaged void ratios can be derived at 0.25 - 0.5m pixel footprints. Tomograms of void ratio were constructed through the relation between soil porosity and dielectric constant. Both pre- and post-blast tomograms were collected and indicate that liquefaction related densification occurred at the site. Volumetric strains estimated from the tomograms correlate well with the observed settlement at the site. The 2-D imagery of void ratio can serve as high-resolution data layers for numerical site response analysis.
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