Consolidation deformation characteristics of Hachirogata clay with salt leaching

Thick, soft alluvial clay was deposited in the Hachirogata reclaimed area in Akita Prefecture, Japan. The phenomenon of differential settlements of the irrigation structure occurring at the site lowers the function of the water supply to the irrigation channel. In this study, assuming that the differential settlement of the ground is due to salt leaching of the sediments, the effect of leaching on the physical and mechanical properties of Hachirogata clay was examined. It was confirmed that the liquid limit and plasticity index decreased due to the leaching, which indicates that the leached sample changed the flowability due to changes in the water content. From the consolidation tests, it was found that the leached clay had a delay in consolidation deformation, a decrease in permeability, and remarkable creep behaviour. According to the observations of the clay structure by scanning electron microscope, leaching caused the clay particles to change from a random arrangement to an impermeable parallel arrangement, and the resultant pore area increased. These results show that the changes in the clay structure due to leaching affect the physicochemical and mechanical properties, such as consistency limits and deformation characteristics. Therefore, it can be inferred that the occurrence of localised leaching is one of the factors that accelerates differential settlement.