Abstract: The properties of expansive soil were improved by electrochemical method with hydroxyl-aluminum solution for electrolyte. The modified soil specimens were divided into three parts: part A (anode), part C (cathode), and part M (middle). Macroscopic and microscopic tests were carried out on the three parts and natural soils. Results revealed that the clay content of modified soils decreased and the silt content increased. The specific surface area and pore size decreased, which made the contact between soil particles closer, resulting in the increase of internal friction angle. Meanwhile, the water-holding capacity of soil particles reduced, indicating that the hydrophilia weakened. Moreover, the free swell of soil samples was greatly lowered. The changes in the properties are attributed to the ion exchange of [Al₁₃]⁷⁺ and the local pH changes which thin the diffused double layer and weaken the interparticle repulsion. In addition, the effects of improvement on the three parts were different due to the influence of the applied electric field on diffused double layer and the anisotropy of soil microstructure.

Key words: expansive soil, electrochemical modification, hydroxyl-aluminum, ion exchange, electrified soil particles, diffused double layer