Evaluation of undrained shear strength of surficial marine clays using ball penetration-based CFD modelling

The undrained shear strength of surficial marine clays is a significant parameter for engineering construction and geological disaster assessment. The full-flow penetration test is an effective method to evaluate marine clay strength. Currently, this method is mainly used for deep penetration, in which the stable full-flow failure state with plasticity solutions is reached; however, surficial penetration lacks a theoretical basis, and related empirical methods are still being explored, especially considering the effect of ambient water. Based on this, first, a model in the framework of computational fluid dynamics is proposed to simulate the whole penetration process of a ball penetrometer in two-phase materials (i.e., marine clay and ambient water). Furthermore, centrifugal penetration tests of two typical clay samples (i.e., South China Sea soil and kaolin clay) are used to verify the accuracy of the proposed relative motion model. Second, the characteristics of the penetration resistance factor during the whole penetration in homogenized marine clays are obtained, and the relevant mechanism is analyzed by the variation in the velocity field, volume fraction and streamline of two-phase materials. Finally, the critical depth to distinguish between surficial and stable penetration is given as 6.5 times the ball diameter; the penetration resistance factor is divided into surficial and stable penetration resistance factors, and dimensionless evaluation methods are established, which provides the basis for obtaining the strength of surficial marine clays.