Subhamoy Bhattacharya

Plate–monopile hybrid foundations, as a potential alternative to monopiles, have demonstrated promising potential in enhancing load-bearing capacity and structural stability. To investigate its load transfer mechanisms and pile–soil interaction in clay, numerical models are developed under varying undrained shear strength (Su), pile diameter (D), and plate-to-pile diameter ratio (R). Through comparative analyses within different parameters configurations, the load-bearing capacity, pile deflection, bending moment and shear force distributions are systematically examined. The results indicate that: (1) Su, D and R are all positively correlated with the load-bearing capacity of the hybrid foundation, which can be expressed as the superposition of the monopile capacity and a quadratic function of R; (2) with increasing R, load transfer shifts from deep to shallow soil, accompanied by an upward pivot shift; increasing D causes a downward shift, more pronounced in weak soils; (3) for small-diameter hybrid foundation, the bending moment decreases progressively with increasing R, while for large-diameter, a stage-dependent response is observed, characterised by local moment concentration near the mudline within a certain range of R; (4) the shear force exhibits a double-peak pattern; increasing R strengthens the shallow peak and weakens the deep one, while increasing D localises the distribution near the mudline.

The plate-monopile hybrid foundation is an innovative solution developed to support increasingly larger offshore wind turbines under harsher marine conditions. However, due to its structural differences from monopile, the bearing capacity estimation model and failure mechanisms remain unclear. In this study, FEM simulations were performed to obtain the bearing capacity of the hybrid foundation for various soil parameters and foundation geometries, covering representative worldwide seabed conditions as well as current and future design parameters in the offshore wind industry. The failure envelopes of the hybrid foundation under different parameter combinations were established, and the empirical formulas for estimating the ultimate bearing capacity were derived based on extensive simulation results. The results indicated that (1) Both lateral load bearing capacity (H_R) and moment bearing capacity (M_R) were positively correlated with soil properties and foundation geometry, with consistent parameter effects. (2) The failure envelope of the hybrid foundation in the H_R-M_R plane exhibited an elliptical shape, and variations in different parameters affected the curvature of the envelope to distinct extents. (3) The applicability of the proposed bearing capacity prediction formula for the hybrid foundation incorporates both soil properties and foundation geometric parameters was quantitatively validated against previous research cases.