Implementation of Down-Hole Geophysical Testing For Rock Sockets

US Transportation Collection2020PDFTech ReportHiltunen, Dennis R.Zou, JianUniversity of Florida. Dept. of Civil and Coastal EngineeringFlorida. Department of TransportationUniversity of Florida. Department of Civil and Coastal EngineeringUnited StatesAccelerometersBoreholesField testsGeological surveyingGeophonesImplementationInstrumentationPiezoelectric transducersPrototypesRocksSoftwareSolenoidsValidationDown-hole testingfull waveform inversionpiezoelectric transducersrock socketsseismic methodsBDV31-977-33Final report, November 2014-February 2020The objective of the project was to produce a prototype instrument and software analysis system for conducting geophysical characterization of subsurface conditions from within a single borehole. In Task 1, Borehole Instrument, two piezoelectric sources were constructed, the first using high frequency piezocylinders and the second using a barrel stave flextensional transducer. A third low frequency source using pneumatic solenoids was also investigated. For receivers, a system was constructed for coupling accelerometers to the wall of a borehole, and an existing 3D string of geophones was also investigated. In Task 2, Inversion Software, an analysis software was developed to create an image of the material adjacent to a borehole using the measurements from the borehole instrument and full wave inversion (FWI) technology. In Task 3, Validation Experiments, we built three lab-scale experimental models in which to test our borehole instrument. These specimens were used extensively to investigate iterations of the instrument during development. We also used the boreholes at the Newberry field site to test both the low frequency solenoid source and the barrel stave source with the 3D geophone string. Overall, we have developed a working concept for a borehole instrument and analysis software for geophysical assessment of the material surrounding a geotechnical borehole. It has been demonstrated via both the piezoelectric and pneumatic solenoid sources and the accelerometer and geophone arrays that wavefields can be generated and measurably received within a single borehole. As well, we have shown using synthetically generated waveforms that a full waveform-based analysis software can image the material surrounding a borehole. Further equipment developments and both model and laboratory tests are warranted to help validate the new procedure.96