Numerical investigation of caisson with pad-eye stiffener installation into nonhomogeneous clay

Caisson foundations are widely used in offshore engineering. During installation, the soil flow mechanism of stiffened caissons with local thickening at the pad-eye is still not well understood. In this study, large deformation finite element (LDFE) model is established to investigate the penetration behavior of caisson with pad-eye stiffener, where the soil flow mechanism is studied considering soil strain softening effect. The numerical model is validated by comparing with available testing data. Parametric study is then conducted to examine potential influencing factors, including the penetration depth, the geometry of stiffener, the clay shear strength, and strain softening parameters. It is found that the soil failure mechanisms and the corresponding penetration resistances of locally stiffened caisson at the pad-eye are significantly different from that of unstiffened caisson or stiffened caisson with interval rings. Two parameters, i.e. the critical rotational soil flow depth (Hr) and the limiting cavity depth (Hc) are introduced to quantitatively describe the behavior of the observed soil flow mechanisms. Based on the modeling results, a simplified flow mechanism is proposed, and approximating expressions are derived to predict the penetration resistance of the caisson for engineering design application