Prediction of Swelling Potential for Compacted Clays

The possibility of damage to structures due to the swelling of clays is complicated by the problem of identifying, at the outset of an investigation, those soils likely to possess undesirable expansion characteristics. A study to develop a reliable means for predicting the potential expansion characteristics of clays from classification test data is described herein. Using test data from soils artificially prepared in the laboratory, it is shown that a well-defined relationship can be established between the percentage of clay sizes present in a soil, the activity of the clay, and the percentage of swell under a 1-psi surcharge of a sample compacted at optimum water content to maximum density in the Standard AASHO Compaction Test. The test data are used to establish charts for quantitative or qualitative evaluation of the swelling potential of compacted clays and the proposed procedure is shown to be in good agreement with expansion test data for twenty-eight soils, determined by the Bureau of Reclamation. The form of the relationship obtained is used to evaluate the usefulness of the plasticity index of a soil as a single factor for predicting swelling potential. It is shown that this parameter alone can provide as assessment of swelling potential that is probably correct to within + 35 % and it is suggested that this method of prediction might be best suited for practical purposes. The main use of the results is to identify the capability of a soil for swelling either quantitatively or qualitatively and, hence, to identify those soils requiring more detailed study, by means of swelling tests, for design purposes.