This is done in the Netherlands on the polder ground. In other words it's a very specific, localized operationt...To mix various soil types ..Some soil mixtures are better than the individual layers: the Dutch soil is partly washed in from the sea, partly washed in from the rivers from the Alps, partly rotten plant material (peat) and partly virgin clay soil by damming a part of the sea and pumping out 5 meters (16 feet) of water.
Because our country is river delta mostly, soils occur in all fashions: peat on top of a clay layer, (a pool with lots of plants that rotted away over the years) sand on clay, (foreign sand washed over the clay by natural water flows) sand on peat (sand washed over peat soil)....