Curvature of shrinkage lines in relation to the consistency and structure of a Norwegian clay soil

Two sets of shrinkage data for a Norwegian clay Topsoil and Subsoil provided in the literature by Olsen and Haugen [Geoderma 83 (1998) 67] were re-evaluated by fitting them to the Groenevelt and Bolt [Soil Science 113 (1972) 238] constitutive shrinkage equation. The shrinkage curves were differentiated to obtain the slopes, and the slope curves were subsequently differentiated to obtain the curvatures of the shrinkage lines. The point of maximum curvature (at the dry end) of the shrinkage line was used to unambiguously separate the region of “residual” shrinkage from the region of “zero” shrinkage, and this point identified the shrinkage limit. The first inflection point on the wet side of the maximum curvature was found to correspond well with the water content at the Atterberg lower plastic limit, provided that the fitted curve matched the measured data closely at the wet end. Another point on the curvature line is suggested to correspond with the end-point of ‘structural’ shrinkage but this could not be confirmed with the limited data available.