M. Long, S. Donohue (University College Dublin, UCD) and P. O’Connor (APEX GeoServices, Gorey, Co. Wexford, Ireland). This paper was first published in GE’s November 2008 issue.
Geophysical techniques and, in particular, seismic methods have received considerable attention in civil engineering over recent years, their role steadily increasing to the point where they play an important part in material characterisation and engineering design. This popularity arises from recent advances in both computational power and the geophysical techniques themselves. Furthermore, many geophysical methods are noninvasive which make them well suited and cost-effective in profiling spatially and temporally.
From a geotechnical engineering perspective the most popular geophysical techniques are seismic methods, possibly because they may directly measure a mechanical property, soil or rock stiffness. This usually involves strains of 10-3 % and less. The measurement of stiffness at this magnitude of strain is important for deformation prediction, as strains associated with most soil-structure interaction problems are generally less than 0.1% (Jardine et al., 1986). It has been shown by Stokoe et al., (2004) that stiffness-strain curves for a range of materials may contain considerable error if small strain stiffness values have not been incorporated. A significant overestimation of deformation may result, which could substantially increase the cost of a project.