Microstructure and compression characteristics of NaCl solutions saturated expansive soil

Pore water chemistry will change the intergranular force and directly affect the microstructure, the physical mechanical properties are further affected for clays. To investigate the effect of pore solution on the compressive properties and microstructure of remolded nature clay, one-dimensional compression test and mercury intrusion porosimetry (MIP) were carried out on the Ningming expansive soil which saturated with the NaCl solutions. The results show that with the increase of osmotic suction, the particles change from uniform dispersion to flocculation structure and forming intra-aggregate pore and inter-aggregate pore. Thus, the salt content specimens exhibit a double pore-size distribution. The initial void ratio of pre-consolidated sample (20 kPa) decreased with the increase of osmotic suction, leading to the increase of consolidation yield stress. However, the osmotic suction had little effect on the compression and swelling index. The permeability decreased with the increase of vertical pressure. When the vertical pressure is lower than 200 kPa, the permeability increased first and then decreased with increasing osmotic suction, but as vertical pressure is greater than 200 kPa, the effect of osmotic suction on permeability was negligible. It is found that the permeability under low pressure is controlled by the coupling effect of microstructure and density. The increase of osmotic suction leads to the increase of macropore and permeability, while permeability is decreased with the increase of density.