2019 年 7 巻 2 号 p. 516-524
Many research works have been conducted on saturated soils under cyclic loadings. Most embankments such as fill dams, road and railway embankments are constructed by compacted unsaturated geo-materials. Nowadays, it has been more important to study the dynamic properties of unsaturated soils in geotechnical engineering. However, there have been few research works on the unsaturated soils under cyclic loadings. The main purposes of this paper are to investigate cyclic deformation properties of an unsaturated silt named DL clay, and to obtain stress-dilatancy relationships under unsaturated conditions. The stress-dilatancy relationships are expressed as the relationships between plastic strain increment ratio: dԑvp/dγp and stress ratio: q/p'. Triaxial cyclic loading tests were conducted for isotropically consolidated and unsaturated-state silt specimens under a constant net confining pressure and different suctions with three different types of cyclic shear loading applied. The stiffness of the soil increased with an increase in suctions and cyclic times. Total amount of volume reductions of the specimens decreased with an increase in suction. As the numbers of cyclic loadings and suction values increased, the amount of dilations also increased. The stress-dilatancy relationships could be formulated as linear lines and the relationships were valid under loading and unloading processes for all specimens.
