Abstract
• During the past decade two important parallel discoveries have taken place in geotechnical engineering which have resulted in geophysical measurements being used increasingly to provide design parameters. • Methods of measuring strain locally on laboratory samples have shown that the stress-strain behaviour of many soils and weak rocks is significantly non-linear, with very high stiffness being observed at small strains. • Field observations of ground deformations around full-scale structures, which could not be modelled using linear elastic theory, can be predicted satisfactorily if non-linear formulations (incorporating very high initial stiffness) are used. These developments have closed the gap which had been thought to exist between static and (very small strain) dynamic measurements of stiffness and have enabled meaningful stiffness parameters to be determined from seismic velocity measurements. As a result, increasing use is being made of seismic velocity measurements to ascertain the variation of stiffness with depth in the design of engineering structures. These methods require the use of one or more boreholes, which adds to the cost and time for each stiffness measurement. A relatively little used but promising method which permits the determination of a modulusdepth profile without the aid of boreholes is surface-wave geophysics. This paper describes surface-wave geophysics in terms of field techniques and, equipment and briefly reviews the range of data interpretation techniques that is currently available.