Abstract: Disclosed is a prestressed concrete tank comprising a foundation having a generally horizontal supporting surface and a wall structure mounted on the supporting surface. The generally horizontal supporting surface is provided with at least two shear blocks which have sufficient height as to project upwardly from the top of the supporting surface. The wall structure supported by the supporting surface partially surrounds the projecting portion of the shear blocks in a fashion so as to allow for the wall structure to be sealingly supported by the supporting surface; at the same time, however, the shear blocks tend to resist shearing forces on the tank caused by backfilling, earthquakes and the like, which could cause displacement and/or rotation of the tank wall structure relative to the foundation.