Characterization of Voids and Other Subsurface Deficiencies by Geophysical Methods

2013PDFTech ReportBrandes, Horst G.University of Hawaii at Manoa. Department of Civil and Environmental EngineeringHawaii. Department of TransportationUnited States. Department of Transportation. Federal Highway AdministrationHawaii. Dept. of TransportationHawaiiUnited StatesAir voidsElectromagnetic devicesEvaluation and assessmentField studiesGeological surveyingGeophysical prospectingGround penetrating radarRefractionVoid detectionsoilseismic surveyingelectromagnetic surveyingFHWA/HI-15-5516155161Research report, 2006-2013The objective of this study was to evaluate and test a range of geophysical imaging systems for use in Hawaii\u2019s unique geological environment and range of soils. Of particular interest was the ability of these systems to identify and characterize subsurface deficiencies including cavities, loose soils, and other buried targets. The project employed ground penetrating radar (GPR), electro-magnetic (EM) surveying, and seismic refraction (SR) and reflection imaging. These techniques were used to make blind predictions of buried objects placed at various depths and locations in a long trench at each of three locations in Hawaii: Poamoho Research Station, Waimanalo Research Station and Kawaihae Harbor. Objects consisted mostly of Styrofoam shapes, but also some steel and PVC pipes. Of the three techniques, GPR was the most successful, resulting in an average of close to 50% of objects identified correctly and on the order of 20% of false predictions. The second technique in terms of success was seismic refraction, followed in a distant third place by EM. These rates should be viewed with caution since they included objects as small as 3 inches placed at depths of as much as 6 feet.104