Improved predictive model for the strength of fluidized seabed sediments with rate effect characteristics by full-scale spherical penetrometer tests

Sampling fluidized seabed surface sediments with viscous fluid characteristics is highly challenging, making in situ penetration tests essential to evaluate their strength. Unfortunately, an in situ full-flow spherical penetrometer (i.e., ball) is typically used to assess the strength via deep penetration, and research on surface penetration, extensive viscous fluid shear behavior of fluidized surface sediments, and ball-ambient water-surface sediment interaction is lacking. To address this gap, this study utilizes a computational fluid dynamics (CFD) model validated through centrifugal tests to examine the penetration of balls with free and no-slip in fluidized seabed surface sediments with the shear rate effect. This study analyzes the stress characteristics on a ball under complex conditions and proposes three phases of the penetration resistance coefficient of the ball in fluidized surface sediments. Additionally, this study quantifies the effects of various factors, such as initial undrained shear strength, rate effect, ambient water above the ball, and contact relationship between the ball and fluidized seabed surface sediment, on sediment strength evaluation. Finally, this study establishes a three-phase method to evaluate the undrained shear strength of fluidized seabed surface sediments by full-scale spherical penetrometer tests. This method calculates the surface penetration resistance coefficients as functions of the dimensionless penetration depth, providing a vital basis for acquiring the strength of fluidized seabed surface sediments.