Time-dependent transient response of piles partially embedded in layered viscoelastic saturated cross-anisotropic soils using a fractional-order Merchant model

Abstract

A 3D analytical method is proposed for the lateral time-dependent response of monopiles partially embedded in stratified saturated viscoelastic cross-anisotropic soils under horizontal transient loads. Nevertheless, previous studies on ocean engineering have rarely considered the rheological properties of seabed materials. In this study, depending upon Biot's dynamical formulation, the linear elastic solution of the layered cross-anisotropic saturated soils due to lateral transient and vertical loads is solved using the analytical layer-element method (ALEM). The fractional-order Merchant model is adopted to describe the rheological deformation of the seabed, and the viscoelastic solution of the laminar cross-anisotropic saturated soils is derived by combining the elastic-viscoelastic transformation theory. Using the consolidation solution of the seabed as the kernel function, the pile-soil boundary problem is analyzed by the boundary element method (BEM) to obtain the BE equation of the viscoelastic saturated soils. The Timoshenko beam is employed to simulate the monopile, and based on the finite element method (FEM), the monopile is discretized into pile units to derive the FE matrix equation. Finally, the dynamic response formulation of the partially embedded offshore monopile is obtained by coupling the BE and FE equations through the coordination conditions of close contact between the Timoshenko beam and the seabed. The accuracy of the methodology is verified by comparing with the existing solutions and the numerical results from ABAQUS. And the effects of the transient load type, seabed viscosity, and pile properties on the horizontal response of partially embedded monopiles are explored.