chapter  70
Characterization of a dense deep offshore sand with CPT and shear wave velocity profiling
ByJ.G. Parra, A. Veracoechea, N. Vieira
Pages 7

In some areas of the northern South American continental shelf, 89 m below the sea floor a stratum of dense to very dense siliciclastic sand has been identified. Given the properties of the overlying soil layers, this sand is the most competent foundation strata for offshore jacket structures. The proper geomechanical characterization of this sand poses some challenges, among them: the maximum pushing capacity available in the wireline CPT system used in offshore geotechnical exploration, and the extent of the perturbed zone beneath the end of the borehole. This work describes an attempt to overcome those limitations by means of the use of shear wave velocity (Vs) profiling with a P-S logging tool, together with known correlations between Vs and CPT point resistance (qt) to generate more reliable “virtual” CPT records. A MonteCarlo simulation was performed with the objective of assessing the sensitivity of the axial capacity of the proposed foundation piles to the derived CPT records.