Engineering seismic refraction: an improved field practice and a new interpretation program, REFRACT

Abstract

Shallow seismic refraction is the principal geophysical method for engineering site investigations. The Roads and Traffic Authority of New South Wales applies the method for roadworks, chiefly in the investigation of road cuttings for design and excavation assessment. The need to obtain reliable and detailed interpreted seismic sections, particularly for intermediate layers with seismic velocities in the range 800 to 2500 m/s, has led to an improved field practice with a 3 to 5 m geophone interval and sourcepoint intervals of 10 to 15 m with offsets up to 50 m. As a result of the deficiencies of currently available interpretation software a new interactive and graphically oriented computer program called REFRACT, for IBM AT compatible computers, has been developed. A field example from a variably weathered, basaltic area demonstrates the effectiveness of the improved field and interpretation practice which is state-of-the-art for the shallow engineering refraction method in its application to roadworks.