Abstract: A block construction for preventing the outflow of ballast along a railway which includes a slab body, a ballast-retaining wall extending upward form the slab body at a location spaced from the front and rear edges of the slab body, for retaining ballast on the laterally rearward side thereof, and a pair of spaced apart legs extending downward from the rear edge of the slab for being buried in holes in a roadbed along the railway for firmly fixing the slab relative to the ground. The slab has an upper surface forward of the retaining wall of sufficient lateral extent to provide a longitudinally extending walkway for use by railway construction and maintenance personnel.