Analytical solution for penetration response of steel catenary riser at touchdown zone on bilinear seabed

The pipe-soil interaction at touchdown zone (TDZ) of steel catenary riser (SCR) has important influences on the penetration depth and fatigue life of pipelines. A model considering non-linearity of soil stiffness is established by using bilinear linear soil stiffness approximation of p-y curve. The model reflects the characteristics of the soil stiffness deceasing with the increase of the penetration depth of the pipelines. The differential equation for pipelines is established and the analytic expression for the penetration response of pipelines in static state is obtained based on boundary conditions. After justifying the correctness of the model, four factors that influence the penetration response of pipelines are analyzed: the shear strength of mudline, the gradient of soil shear strength, the external bending moment load and the weight of pipelines. The results show that the penetration depth of pipelines increases with the decrease of the shear strength of mudline and the gradient of the soil shear strength. And if the external bending moment load increases, the penetration depth of pipelines will increase and the maximum shear force will also increase. Due to the increase of weight of pipelines, the penetration depth of pipelines and bending moment will increase.