Prediction of Expansive Soil Strength Based on Micro-scale Properties

A comprehensive understanding of expansive soil behavior requires elucidation of the surface phenomena of clay particles and soil micro-structure changes. This study focuses on the influences of drying–wetting cycles on cohesion variations, and four micro-scale properties of expansive soils—fissure ratio, void ratio, specific surface area (SSA), and larger pore proportion—are measured to predict cohesion for expansive soil experienced 0–7 drying–wetting cycles. Based on each of these micro-scale properties, single linear regression analyses are used to obtain the cohesion attenuation law with cycle number. Changes in the studied four micro-factors significantly cause a discrepancy of cohesion. The fissure ratio and the SSA are the most two accurate predictor of the attenuation law for the studied soil, which are fitted by a “S” curve. The two “S” curves with lower standard error (< 1.16 kPa) perform well in predicting cohesion attenuation after different drying–wetting cycles in practical engineering. An empirical formula based on the fissure ratio and the SSA, carried out using MATLAB software, is also found to be accurate in predicting the cohesion attenuation of expansive soil. Found from the comparison with similar researches, this empirical formula caring only initial cohesion and cycle number, avoiding measuring micro-scale properties, can be simply used in the expansive soil from a particular area to predict cohesion reduction.