Chalk is a porous rock which can exist in highly variable states. When excavated and recompacted, however, its engineering properties and behavior can range from those of weak rock to those of soil, depending on the proportion of ‘putty chalk’ formed as a result of breakdown of the natural material. In many chalk-rich areas of southern England, site won chalk has been successfully used for years as the structural fill in both unreinforced and reinforced soil earthwork structures. This paper presents a summary of 3 reinforced soil structures with Tensar geogrids built with site won chalk, including railway embankments for High Speed 1 (HS1) in the South of England.