<p>Installing internal bulkheads in a composite bucket foundation alters the rotational symmetry characteristic of a single-compartment bucket foundation, consequently influencing the stress distribution within the bucket and surrounding soil. During the seabed penetration of a spudcan from a jack-up wind turbine installation vessel, an angle may form between the spudcan’s axis and the axis of symmetry of the adjacent composite bucket foundation in the horizontal plane. Such a misalignment may affect load distribution and the non-uniform interaction between the foundation, soil, and spudcan, ultimately influencing the foundation’s stability. This study employs physical model tests to ascertain the trends in end resistance during spudcan penetration in sand, the extent of soil disturbance, and the backflow condition. The finite element coupled Eulerian–Lagrangian method is validated and utilized to determine the range of penetration angles that induce alterations in the maximum vertical displacement and tilt rate of the composite bucket foundation in sand. The differential contact stress distribution at the base of the bucket is analyzed, with qualitative criteria for sand backflow provided. Findings demonstrate that the maximum vertical displacement and tilt rate of the composite bucket foundation display a “wave-like” variation with the increasing spudcan penetration angle, peaking when the angle between the spudcan and bulkhead is the smallest. Stress distribution is predominantly concentrated at the base and apex of the bucket, becoming increasingly uneven as the penetration angle deviates from the foundation’s symmetry axis. The maximum stress gradually shifts to the junction of the bulkhead and bucket bottom on the side with the shortest net distance from the spudcan. Considering the in-place stability and stress state of the composite bucket foundation is therefore imperative, and particular attention should be paid to the foundation’s state when the angle between the spudcan and bulkhead is small.</p>