Cross hole measurements are a seismic technique used to determine the compressional and shear wave velocity of soil and bedrock between two boreholes. Compressional and Shear wave values can be used to calculate moduli values to evaluate the mechanical properties for the materials between the boreholes. This technique requires a minimum of two boreholes, one for an energy source, the second for the receiver (multiple receiver holes maybe used). NDT uses energy sources for Cross Hole Measurements including dynamite, blasting caps, air guns, and “packers.” Receivers are typically a tri-axial geophone containing a vertical element and two opposing horizontally orientated elements. Typically, Cross Hole Measurements measurements are made to determine the shear velocity of soils and bedrock for seismic risk analysis of structures.
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