Re-evaluation of the structural properties of some British swelling soils

The structural condition of swelling soils can be assessed from their shrinkage curves. We re-evaluated data on six British swelling soils using modem methods to model the void ratio, e, as a function of the moisture ratio, theta. The points on the e-theta curve were fitted with a constitutive shrinkage equation using an unbiased least-squares, curve-fitting program. The shrinkage curves were then differentiated to obtain their slopes, sigma(theta), which were used to calculate the overburden potentials, Omega. The slope functions were subsequently differentiated to obtain the curvatures, k(theta), from which the maximum curvature at the wet end was used to separate the structural shrinkage, S-c, from the proportional (unsaturated) shrinkage. At the point of maximum curvature, S-c and the volumetric air content, theta (ac), were calculated and found to correspond closely to those reported previously. Water retention curves were constructed and fitted using the van Genuchten equation, from which the alpha coefficient appears an important structural parameter. The structural condition of a swelling soil appears to be well described by its air content at the point of maximum curvature, its van Genuchten alpha coefficient, and a parameter describing the effect of the overburden potential.