Accurate strength characterization of near surface seafloor soils is critical when designing and installing mat foundations and seafloor cable systems. This paper presents the results of an ongoing investigation to assess the merits of using flow penetrometer technology to aid the U.S. Navy's requirements for seafloor characterization in soft sediments. The paper presents the experiences learned from the preparation and consolidation of a large-scale clay specimen and discusses the penetration and extraction resistances measured using ball and cone penetrometers. The undrained shear strengths calculated with the cone, ball, and a vane are evaluated and compared.
Accurate strength characterization of near surface seafloor soils is critical when designing and installing mat foundations and seafloor cable systems, and when assessing the break-out force of objects embedded on the seafloor. The cone penetrometer is the most widely used tool to characterize the near surface strength of ocean bottom soils. However, cone penetrometers have limited capability when accurate determination of the shear strength of soft sediments is desired. Alternatively, full-flow penetrometers have been developed to alleviate some of the shortcomings of the cone yet still provide a continuous profile of strength with depth (Randolph, 2004; Randolph et. al., 2005). This paper presents the results of an ongoing investigation to assess the merits of using flow penetrometer technology to aid the U.S. Navy's requirements for seafloor characterization in soft sediments, and in particular to evaluate the applicability of using a ball penetrometer to determine the undrained shear strength of soft clay soils at shallow seafloor depths. Penetration and extraction resistance profiles of ball (100 cm2) and cone (10 cm2) penetrometers advanced into a laboratory prepared Kaolin specimen created in a large-scale consolidation tank are compared. Undrained shear strengths estimated from ball and cone results are compared to strengths measured from vane shear tests.
