Identification of the sediment-water interface during field full-flow penetration tests

The undrained shear strength of marine surface sediments is critically important for both the development of marine resources and environmental protection. In situ full-flow penetration tests offer significant advantages for evaluating these surface sediments, particularly those with low strength. Accurately analyzing the strength of surface sediments during in situ full-flow penetration tests relies on correctly identifying the sediment-water interface, also known as the mudline. Unfortunately, there is currently no established method for solving this problem. This study utilizes computational fluid dynamics to conduct a numerical analysis of full-flow penetrometer probes (specifically of ball and T-bar probes) as they penetrate marine surface sediments of varying strengths and densities from different heights. By examining the variation in the dimensionless drag force coefficient of the probes in relation to the dimensionless penetration depth, the impact of the mudline on the drag force trend is systematically analyzed. Additionally, a methodology for determining the mudline location using a mudline distinguishing factor is proposed. This mudline distinguishing factor was tested during a field trial of the in situ ball full-flow penetration device in the Philippine Sea, The proposed methodology for identifying the mudline and analyzing the strength of marine surface sediments has significant value for the field.