An expansion body for constructions like piles or anchorages located in the earth is adapted for insertion into the ground in a compact shape and expanded therein to an expanded shape. The expansion is achieved by unfolding a folded metallic casing (11) by filling it up with pressurized fluid. Each end of the elongated body is sealed by a closure comprising a socket (16, 17) with a sleeve (18, 19) encircling the near end part of the casing and a bottom plate (20, 21) with spacing means (22, 23) projecting into the inside of the casing. The sleeve (18,19) and spacing means (22, 23) define an annular space (26, 27) in which the end parts (14, 15) are kept in a folded position when the body is expanded.