Abstract: An offshore structure comprises a jacket having buoyant compartments defined by a jacket leg. A rupturable closure defines a lower end of the buoyant compartment. The rupturable closure is operable to be ruptured by a pile impacting on an upper side thereof. The rupturable closure comprises a cup-like cap having a convex under side, and a concave upper side. A plurality of circumferentially spaced, generally radially extending weakened zones in the cap are operable to define generally radially extending rupture zones when the cap is impacted by a pile on its concave upper side. The cup-like cap, when impacted by the pile, ruptures along the generally radially extending weakened zones to define a plurality of triangular cap segments. The generally triangular cap segments are pressed generally radially outwardly of the central axis of the leg toward the inner periphery of the jacket leg by the impacting pile.