A method for saturating cavities present in a mass of soil or in a body in general, comprising at least one step for at least partial filling of the cavity by introducing into the cavity a filler material in the solid state or in the fluid state and capable of setting. At least one step of saturating the cavity is then performed by introducing into the cavity a fluid synthetic substance which expands and sets by chemical reaction. The synthetic substance is adapted to generate, as a consequence of its expansion, at least the saturation of the cavity and a compaction and/or loading of the filler material introduced into the cavity in the filling step, creating an optional state of permanent tension on the walls that delimit the cavity, to the point of producing, if necessary, a deformation of the walls.