This paper discusses the challenges of installing monopile offshore wind foundations in bedrock and introduces a new hybrid-monopile design as an alternative to rock-socketed monopiles. The performance of the hybridmonopile is evaluated through 1-dimension beam-spring theory and 3-dimension Finite Element analyses, with a focus on soil-foundation interaction and cyclic loading behaviour. The hybrid-monopile design is optimized and validated at two offshore sites in Korea. It is shown that optimized design can reduce required monopile penetration to avoid rock-socketed monopiles. The hybrid-monopile design shows a positive impact on reducing lateral pile displacement and rotation, particularly in soft ground conditions. The suggested 3D FE (Finite element) design approach and optimization with an additional seabed-level support structure can reliably avoid the need for rock-socketed monopiles.

This work presents an analytical method for determining vertical dynamic impedance and displacement response factor of a rigid cylindrical foundation embedded in unsaturated poroelastic soils. The foundation is assumed to be perfectly boned to its surrounding soil and its overlying half-space of unsaturated poroelastic soil, subjected to harmonic vertical loadings. The soil surrounding the circumference of the cylinder is modeled as a number of infinitely thin horizontal soil layers. Based on the Biot-type soil constitutive model, the equations governing the interaction of unsaturated soils with the cylindrical foundation are derived. Solutions are obtained by solving ordinary differential equations transformed from partial differential governing equations using the Hankel transform. The proposed solutions are verified against existing solutions of benchmark elastodynamic problems for embedded cylindrical foundations in dry and saturated soils. Using the derived solutions, several influencing parameters defining the stiffness and mass of the foundation system are examined to investigate the dynamics of the foundation interacting with it adjacent soils. It is concluded that the dynamic displacement response factor is sensitive to soil saturation. It is believed that the proposed solution should be beneficial to dynamic design with cylindrical foundations embedded in unsaturated soils.

This study explores the transverse response of bridge piers in riverbeds under a multi-hazard scenario, involving seismic actions and scoured foundations. The combined impact of scour on foundations' stability and on the dynamic stiffness of soil-foundation systems makes bridges more susceptible to earthquake damage. While previous research has extensively investigated this issue for bridges founded on piles, this work addresses the less explored but critical scenario of bridges on shallow foundations, typical of existing bridges. A comprehensive soil-foundation structure model is developed to be representative of the transverse response of multi-span and continuous girder bridges, and the effects of different scour scenarios and foundation embedment on the dynamic stiffness of the soil-foundation sub-systems are investigated through refined finite element models. Then, a parametric investigation is conducted to assess the effects of scour on the dynamic properties of the systems and, for some representative bridge prototypes, the seismic response at scoured and non-scoured conditions are compared considering real earthquakes. The research results demonstrate the significance of scour effects on the dynamic properties of the soil-foundation structure system and on the displacement demand of the bridge decks.