Clay—water interactions and the mechanism of soil swelling

Abstract

The examination of micropore structure in swollen systems such as wet clay soils must be preceded by removal of the enmeshed water. For such mechanically weak systems the drying process used to remove this water is of the utmost importance. This paper discusses the problem in connection with the elucidation of soil swelling mechanisms. The pore size distributions of compressed cores and natural aggregates of a clay soil have been measured over the range 2 nm–50 μm for samples which have been rapidly frozen and freeze-dried from a wide range of water potentials. These results are discussed in relation to an earlier proposal that the swelling of divalent clay systems results from the water-initiated release of stresses, accumulated as particle distortion during drying and leads to the formation of discontinuities in the soil fabric in which water is retained by surface tension forces. The observation of pores in the 1-μm range is thought to be largely an artifact from the freeze-drying process. A preliminary result based on solvent exchange and critical point drying suggests that this drying method may give a more reliable indication of the pore structure of the swollen soil.