The nature of changes in bulk density with water content in a cracking clay

Abstract

The effect of changing water content on the bulk density of undisturbed cores of a cracking clay was examined in laboratory experiments. The results were compared with the relationship between bulk density and water content established by core sampling the same soil in the field. Over the water content range measured in the field soil, the laboratory cores shrank three-dimensionally and normally. Small departures from normal shrinkage were attributed to the formation of cracks within the cores, and to the occurrence of some structural shrinkage in cores previously wet to high water contents. Swelling of cores was approximately three-dimensional, except for some unconfined swelling which occurred in the core surface. Unidimensional swelling was induced by confining dry cores to reduce the void ratio before wetting. Subsequent shrinkage was three-dimensional, indicating that the soil particles were reoriented during the unidimensional swelling phase. While the laboratory measurements showed that the soil volume changes were essentially three-dimensional and normal, the field data indicated that unidimensional shrinkage occurred at water contents greater than 0.47 g g-1. These field results were attributed to sampling inaccuracies associated with the use of a small-diameter core sampler, the actual field bulk density relationship being considered three-dimensional.