Simultaneous measurement of P & S wave velocities during conventional laboratory soil testing procedures

Foundations for offshore structures present a design problem resulting from two primary sources. First, the normally consolidated sea‐floor sediments are often weak and compressible compared to relatively competent terrestrial soils. Second, the technical difficulties of either obtaining relatively undisturbed sea‐floor samples or of performing in situ mechanical tests can be more problematic than with terrestrial soils. Any technique that might improve the assessment of sediment behavior is worthy of investigation. This paper describes some preliminary experiments which measure P and S velocities during conventional soil testing procedures. Computed static and dynamic moduli, measured from tests with different strain levels, have been compared, revealing that although two orders of magnitude separate the moduli, there are similarities in the way certain moduli change with increasing stress levels. It is suggested that the use of a “frame‐wave”; velocity in the calculation of dynamic moduli may reduce drastically the differences that exist between the static and dynamic moduli for saturated sediments. In this way it is thought that results from tests, such as those described in this paper, not only provide empirical correlative data for a given sediment, but may also contribute to a clearer understanding of its behavior under loading conditions.