1. The human factor in determining the plastic limit of cohesive soils;Ballard;Mater. Res. Stand.,1963
2. British Standards Institution 1975 Methods of test for soils for civil engineering purposes British Standard 1377: 1975 British Standards Institution, London
3. Liquid limit determination of arable topsoils using a dropcone penetrometer;Campbell;J. Soil Sci.,1975
4. The occurrence and prediction of clods in potato ridges in relation to soil physical properties;Campbell;Ibid.,1976
5. Research on the Atterberg limits of soils;Casagrande;Public Roads,1932