<p>The adoption of skirted caissons as the foundation for offshore wind turbines is gaining momentum as a promising alternative to large-diameter monopiles, which often involve high construction, manufacturing, and installation costs. This study investigates the behavior of an embedded skirted caisson subjected to monotonic horizontal and moment loading using the Fourier series aided finite element method (FSAFEM). This method analyzes horizontal, rocking, and coupled displacement modes, expressed through stiffness factors under two distinct soil–caisson interface conditions. The foundation is embedded in non-homogeneous soil, where the shear modulus varies with depth following a power law. The method’s accuracy is confirmed through comparison with other rigorous numerical solutions. A dedicated computer program is employed to perform a parametric investigation, focusing on the evolution of stiffness coefficients with changes in flexibility, slenderness ratio, and the depth-dependent soil stiffness parameter. Results are presented graphically, illustrating stiffness coefficients for three different soil stiffness profiles and two interface conditions. The range of values, bounded by those of perfectly rough and perfectly smooth interfaces, provides practical insight for estimating foundation stiffness. The study highlights how interface conditions and soil variability significantly affect the caisson’s response, offering valuable guidance for engineering design in offshore applications.</p>