ABSTRACT

Soil density, porosity, elastic moduli, and the soil-water characteristic curve (SWCC) are important properties for soil characterization. However, geotechnical and laboratory tests for soil properties are costly and limited to point sampling sites. Seismic surveys can provide laterally continuous, seismic soil property values that may complement geotechnical borehole tests with less cost. We have developed a workflow to invert for soil properties and the SWCC from seismic P- and S-wave velocity-versus-depth profiles interpreted from shallow (<25m depth) unconsolidated sediments under conditions of near-full saturation (>99%). The inversion is performed by using the covariance matrix adaptation evolution strategy to search automatically for optimal input soil property values by minimizing the misfit between field-based velocity profiles and predicted velocity profiles based on the Hertz-Mindlin and Biot-Gassmann theories. The results from seismic soil property inversion are validated by comparison with geotechnical as well as laboratory results conducted independently in the same area as the seismic survey. For each seismically recognizable layer, soil types are interpreted from the inverted soil density and elasticity, aided by the SWCC to help detect thin units that are below the original seismic resolution of the field data. There is flexibility to apply our suggested workflow in future studies. For a known geologic setting, empirical relationships and other velocity prediction models could also be incorporated into the suggested workflow to improve inversion results and extract additional information in soils.

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