The Determination of Volume Change Properties in Expansive Soils

Interactive mechanistic models of expansive soil behaviour require as input data, a number of soil variables, which can describe volume change in expansive clays. Perhaps, the most useful variable is the change in volumetric or dimensional strain per unit change in soil suction. This variable, analogous to the coefficient of volume change m{v}, used in consolidation theory, has previously been defined as the 'Instability' Index. This variable is not a constant, but varies at least with stress, soil suction, direction of change, previous history. This paper describes several methods developed by the Soil Engineering Group, Division of Soils, CSIRO for determining this variable. Results for several soil profiles in the Adelaide, Melbourne and Darling Downs areas of Australia are discussed. Some comparisons with data obtained from ground movement at depth installations in the Adelaide area are also presented.