Lateral free-field responses and kinematic interaction of monopiles to obliquely incident seismic waves in offshore engineering

Abstract This paper studies the lateral free-field response and dynamic interaction of monopiles with a partially/fully saturated porous seabed under a seawater layer, subjected to vertically and obliquely incident P and SV wave excitations. The solution of the coupled three-dimensional water-pile-soil vibration problem is developed using a rigorous semi-analytical method. Results for the free-field soil displacement and kinematic interaction factors of the pile head are obtained: the presence of water layer will increase or decrease the lateral free-field displacement for the P wave case, depending on whether the soil is fully saturated or partially saturated; the presence of water layer will have little influence, increase or decrease the lateral free-field displacement for the SV wave case, depending on the incident angle. Besides, the non-dimensional lateral kinematic interaction factors for both P wave and SV wave cases, with different water depths, are illustrated over a broad non-dimensional frequency range. Similar to the free-field responses, monopile responses can generally be amplified or reduced with the presence of a water layer, depending on the saturation degrees of soil and incident angles in P wave case and SV wave case, respectively.