Abstract: Inverted-arch floor laid on the subsoil as foundaion of hydraulic structures are discussed. Loads acting on the structure are transmitted from the piers to the springs, then by the concordant action of the arches and piers to the subsoil. Interrelations among following factors: internal forces of arches, rotation angles of spring, vertical and horizontal displacements of springs and crowns, displacements of the base of the piers, foundation settlements, foundation reaction, characters of strctural material and soil layers, various loads including the side load, change of average temperature and temperature difference between the extrados and intrados etc. were studied. By means of equilibrium of forces and displacement compatibility of piers, arches and the subsoil, the internal forces and displacements of the inverted arch were solved. Iteration is applied to treatment of horizontal displacements of the piers and arches which are related to the friction and cohesion beneath the foundation base. New knowledge for some characteristics of this kind of structure is obtained from engineering practices and analysis.