By Angela M Davis and Peter J Schultheiss, Marine Science Laboratories, University College of North Wales
This paper was first published in GE’s May 1980 issue.
The need for in situ dynamic testing of sedimentary materials, in addition to the standard static tests carried out during site investigations, has been recognised in the last few years. Knowledge of the dynamic elastic properties of a foundation material allows predictions to be made both of its response to dynamic loading (such as that imposed on the sea-floor by large oil platforms under storm conditions) and of its total strength by empirical correlations (Taylor Smith, 1975).
While seismic tests have always been available as part of any civil engineering site investigation (usually to define the thickness of the overburden and its variation), the velocity data derived when used in any diagnostic manner (to assess rock quality for instance) nearly always refer to compressional wave propagation. For a complete assessment of the dynamic properties there is a need to measure shear wave phenomena.