Effect of hydration on mechanical properties and microstructure of expansive soil

The hygroscopic swelling properties of expansive soils usually present significant challenges to engineered structures. Therefore, it is of great significance to study the effect of hydration on the mechanical properties and microstructure. The influence of different initial conditions on the swelling pressure was analyzed by the three-dimensional expansion test device, and the effect of hydration on the microstructure of expansive soil was studied by the MIP method. The results show that: the swelling pressure decreases with the increase of the initial moisture content and increases with the increase of the dry density. The average swelling pressure development rate increases with increasing dry density and decreases with increasing initial moisture content. The anisotropy coefficient range of soil is 0.525–0.904. Hydration causes the collapse of macropores between the aggregates, the increase in the number of intra-aggregate pores, and the gradual decrease in total volume, and the microscopic pore structure of the specimen tends to be uniform. The dominant values corresponding to the specimen with a dry density of 1.5 cm 3 changed from 50–60 nm to 20–30 nm, and 10,000–11,000 nm to 5000–6000 nm. The dominant values corresponding to the specimen with a dry density of 1.7 cm 3 also decreased slightly. Therefore, the smaller the dry density, the greater the effect of hydration on the microstructure of the internal pores of the specimen.