A novel formula for the prediction of swelling pressure of compacted expansive soils

Expansive soils have been well recognised as problematic that can pose threats to the stability of the Earth's structures due to the soils’ significant volumetric change when subject to moisture variation. In this study, a modified oedometer set-up was used to investigate the one-dimensional swelling pressure of compacted soils when subject to wetting under the constant volume constraint. Four expansive residual soils found in Auckland, New Zealand were tested. Based on the findings of two soils, a prediction formula of the swelling pressure was proposed. The formula considers not only the initial condition of the soil but also implicitly the amount of swelling minerals through the material's free swell index. The formula was validated using swelling data obtained from the other two expansive soils tested in this study and from data reported in the literature. The predicted swelling pressure was found to be reasonably close to the measured pressure, considering the range of soil expansivity in this study.