Vibrated stone columns in a weak peat deposit enhanced by Geogrid - 'Put a sock on it'

Economic and environmental constraints that are currently imposed on new developments encourage the utilisation of sites which due to poor ground conditions, were previously considered unsuitable. Examples of these sites include derelict land, filled ground, contaminated sediments and soft deposits. In relation to the former, the construction industry has developed several techniques that include vibrated stone columns to improve the bearing capacity of weak deposits. Inevitably limitations to the technique exist; reduced lateral restraint provided to the column from the surrounding soil can lead to excess bulging and ultimately column failure. This paper investigates the application of vibrated stone columns in conjunction with geogrid reinforcement. A series of plate loading tests were conducted on isolated stone columns installed in a soil bed consisting of peat sandwiched between two layers of sand. The load carrying capacity of the soil bed was investigated by applying load to a circular footing supported on: (a) untreated soil, (b) soil treated with an unreinforced stone column, (c) soil treated with a reinforced stone column. The work has shown that the load bearing performance of a soft deposit can be improvement by installing vibrated stone columns and that further enhancement can be obtained by reinforcing the stone column with geogrids.