Applying the Seismic Refraction Technique to Exploration for Transportation Facilities

The seismic refraction technique provides a simplified characterization of relatively large volumes of the subsurface in 2-dimensional (distance and depth) profiles. Compression wave (p-wave) velocities, the typical measured geologic material parameter, are a function of the moduli of the various unsaturated material masses in the subsurface profile. In saturated media, p-wave velocities are increased relative to equivalent unsaturated media. Within constraints of basic laws of physics, seismic refraction profiles are a representation of subsurface profiles as long as the p-wave velocities (material strengths) increase with depth. Soil/rock contacts or contrasts between weaker to stronger geologic material horizons can be interpreted from seismic refraction data. Preliminary subsurface profiles can be developed from this information, and characterization of subsurface profiles between geotechnical borings or test pits can be accomplished. Correlations between p-wave velocities and prediction of rock mass rippability or excavatability have been published, and correlations with other geotechnical parameters for local conditions can be compiled. ASTM D5777 provides suggested practices for seismic refraction investigations.