Effect of salt leaching on micromechanical behaviour and structure of Hachirogata clay

In the Hachirogata reclaimed area, Minamiakita County, Akita Prefecture, Japan, one of the leading agricultural production areas in the country, the agricultural production foundation and facilities are deteriorating significantly, and problems specific to low-lying reclaimed farmland, such as deterioration of water quality and differential settlement of structures, are occurring. This study investigates the effects of salt leaching on the micromechanical behaviour of highly active Hachirogata clay. A leached sample was artificially prepared using a boring sample collected from the Hachirogata reclaimed land, and a micro-indentation test was performed on both non-leached and leached samples. The results of the indentation test confirmed that the electrical conductivity (EC) of Hachirogata clay was highly correlated with cohesion, c, and that the c value dropped sharply when the EC fell below a certain threshold. Therefore, salt leaching leads to a decrease in the cohesion of clay particles by reducing the number of ions in the clay, making the clay easier to deform under load. From the results of this study, it was inferred that localised salt leaching, which changes the micromechanical behaviour of clay, is one of the factors causing ground differential settlement or slip failure. It is expected that such ground problems could be mitigated by identifying locations with low EC values, that is, weak areas in the ground, and implementing countermeasures such as ground improvement or using lightweight embankment materials in those zones.