Measurement of swelling pressure: direct method versus indirect methods

Light structures including highways and railroads built over potentially expansive clay soils may suffer damage from swelling. Considerable research has been done in an attempt to characterize swelling properties of expansive soils. Although direct measurement of swelling pressure is relatively straightforward, it has not drawn much interest. The present study attempts to measure swelling pressure directly. We call experimental techniques for swelling pressure other than this direct method the indirect methods. Some indirect methods require more than one soil sample and that all samples be identical. However, natural soils may not always provide identical samples. Therefore, reconstructed identical soil samples produced from natural soils were used in the present study. For comparison, the restricted swell, swell-consolidation, double oedometer, and zero swell tests were employed as indirect methods. While the restricted swell test slightly underestimated swell pressure, swell-consolidation and zero swell tests overestimated it. The double oedometer test did not provide swell pressures correlatable with those found using the direct method. Free swell data correlated reasonably well with swell pressure data from the direct method, so an empirical form was established from which swell pressure can be easily estimated.