Abstract: The invention relates to a block that comprises two longitudinal and vertical walls connected by hinges including two elements hinged about vertical axes. According to the invention, each of the two side walls is made of a rigid plastic material, is surrounded by a bent return oriented towards the inside, and includes, in the lower and upper longitudinal portions thereof, as well as on the vertical edge of one end thereof, respectively, a rebate oriented towards the outside, said rebate being capable, when the block is in the functional position, of covering the bent return of another block that has already been laid in order to provide a connection with said other block, independently from said block being in a same row or in an underlying row.