This paper presents the results from numerical modeling of the keying process of plate anchors in three‐layer soft‐stiff‐soft clay deposits. Three‐dimensional large deformation finite‐element analyses were carried out, and the results were firstly validated by the centrifuge test data and the previous numerical results. The soil flow mechanism during the keying process of plate anchors was examined, and a series of parametric studies were performed to investigate the factors affecting the rotation characteristics of plate anchors with an emphasis on the presence of the interbedded stiff soil layer. The results indicate that the loss of embedment depth of plate anchors decreases with the increase of the thickness of the first soil layer when the anchor is initially located at the middle of stiff soil layer. The flow velocity of soil around the anchor that is initially embedded at the first layer and adjacent to the underlying interbedded stiff soil layer is generally larger, resulting in a smaller embedment depth loss compared with the traditional normally consolidated soil layer. The interbedded stiff soil layer affects the keying process of plate anchors embedded 1.0B above and 2.0B below the interbedded stiff soil layer (B is the width of the square plate anchors). The increase of the strength of local soil around the plate anchors leads to the increase of the embedment depth loss, but the increase of the strength of soil slightly away from the plate anchors leads to the decrease of the embedment depth loss.

In this paper, extensive resonant column tests were conducted to investigate dynamic responses of subsea sand‐silt mixtures. The effects of confining pressure, mixture ratio, curing age, and cement content were evaluated. For the test condition considered in this study, the measured damping ratio is the smallest when the ratio of subsea sand to silt is in a range of 1.5 to 2.0. Moreover, unsolidified subsea sand‐silt mixed at a ratio of 1.5 has almost the same maximum shear stiffness as the pure sand. For solidified subsea sand‐silt mixture, cement can significantly increase the dynamic shear stiffness when the curing age is less than 14 days. However, the increase of the maximum dynamic shear stiffness is negligible when the curing age is longer than 14 days. When the cement content is 2%, the damping ratio of the solidified mixtures is very close to that of the unsolidified mixture. When the cement content is higher than 4%, the damping ratio of the solidified mixtures reduces significantly. This is mainly due to hydration reactions occurring in the solidified mixtures.