Shear wave energy from seismic sources subjected to varying soil-coupling stresses

ABSTRACT: Modern downhole seismic cone penetration tests (SCPTs) are used in geotechnical studies to determine shear wave velocity and dynamic modulus profiles in soils. Although recommended test procedures exist for the SCPT, no standard specification is available for the source's size, type, impact energy and coupling stresses. Results of tests performed on three steel beams subjected to varying coupling stresses, as part of an ongoing research program on seismic response of SCPT sources, are presented. The test results confirm an increase in signal energy with increasing coupling stress as previously known. However, the results show that this increase occurs relatively fast and reaches a maximum at low coupling stresses between 15 kN/m2 and 28 kN/m2, irrespective of size and type of the source, for similar impact energies. One of the beams with metal blades, which were added to improve coupling, performed better than the others with smooth coupling surfaces.