Bearing capacity factors of T-bar from surficial to stable penetration into deep-sea sediments

Abstract

In-situ full-flow penetrometers (i.e., the ball and T-bar) have shown great advantages and promising applications in testing and evaluating the undrained shear strength of low-strength deep-sea surficial sediments with fluidization characteristics. However, compared with a ball with the same projected area, a T-bar with the advantages of smaller volume and length along the penetration direction still suffers from the lack of better understanding of the surficial penetration mechanism and a method to estimate the bearing capacity factor under the effect of ambient water. In this study, a computational fluid dynamics method, Eulerian–Eulerian two-phase flow modeling, is used to analyze a T-bar with the no slip and free slip wall boundaries penetrating deep-sea surficial sediments defined by the dynamic viscosity of a non-Newtonian fluid with shear thinning behavior under ambient water. The stress characteristics and corresponding mechanism of the entire process (i.e., surficial and deep penetration) of a T-bar penetrating deep-sea sediments from the mudline to stable penetration are revealed from the evolution of the open and trapped water cavities above the T-bar. Finally, a methodology to evaluate the undrained shear strength of deep-sea sediments tested using a T-bar with different interface contact relations is proposed, and the corresponding equations are established, providing a basis for marine engineering geology survey, engineering construction, and hazard assessment.