A method of installing an upright elongate hollow subsea foundation that is higher than it is wide, such as a suction pile. The foundation is at least partially embedded in seabed soil. A partition layer is placed within the foundation, for example by injecting a grout, supported by a plug of soil that is surrounded by the foundation. The partition layer is placed on the plug of soil at a level that is spaced from the top of the foundation by at least 20% of the height of the foundation. Above the partition layer, the interior of the foundation may be filled with water and/or a rigid body, such as a solid mass or a hollow liquid-filled tank.