A general purpose passive annular grout seal assembly is disclosed which is suitable both for offshore jacket installations with regular annular gap sizes and for offshore wind turbine structure installations with an extraordinarily large annular gap of any sizes. Grout self-sealing operation during grouting is conducted in two steps: 1) a gap reducing action enabled by a gravity differential pressure force induced tilting of a plurality of flip plates, and 2) a gravity differential pressure force induced sealing action for the remaining small gaps. This disclosed new type of grout seal can not only enhance grout seals' overall system reliability by eliminating all potential sources for harmful results known to the offshore industry, but also significantly reduce costs for fabrication, transportation, and installation of grout seals.