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Services: Void/Sinkhole Delineation

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    Several different methods may be used to detect voids. The method chosen depends on a number of factors such as the depth and size of anticipated voids, reason for delineating voids, desired resolution of voids, nature of background materials or bedrock surrounding the voids, type of materials that may fill the voids (such as clay or water), depth to groundwater, size of the investigation area and sources of cultural interference in the investigation area. Spectrum commonly uses the following methods to delineate voids:


    VoidsFig2 VoidsFig1 VoidsFig3

  • Ground Penetrating Radar
  • Electrical Resistivity
  • Frequency Domain Electromagnetics
  • Seismic Reflection
  • METHODS IN ACTION


    Void Search – LOS ANGELES COUNTY, CALIFORNIA


    A geophysical investigation was conducted along two paved access roads in Los Angeles County, California where overflow of a nearby stream had caused localized flooding. Spectrum was hired to identify areas where voids beneath the paving existed or could be developing. In order to meet the objectives Spectrum used ground penetrating radar (GPR) methods.



    Spectrum collected GPR data along one-foot by one-foot orthogonal grids at each site using a Noggin Smart Cart coupled to both 500-MHz and 1000-MHz antennas. Once the data were collected the GPR-Slice 5.0® package was used to create a suite of plan-view time slice maps of GPR signal intensity (square of amplitude), each representing successively greater depths. Initial review of the data revealed six anomalies, which were then cored and used for depth and amplitude calibration. Subsequent detailed review of both amplitudes in the Slice maps and characteristic signatures in the GPR profiles identified areas of disturbed soil and voids at both sites. A geophysical interpretation map was prepared for each site, and used by the Client to identify areas requiring further investigation.

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