Study on water-retention and permeability characteristics of unsaturated loess under different compaction conditions

In order to explore the influence of different forming processes on the water-retention and seepage characteristics of unsaturated loess, the pressure plate apparatus is used to test the soil-water characteristic curves of three types of remolded loess specimens with different initial dry densities, including conventional remolded (layered compaction), transversely isotropic (K₀ stress state) and isotropic (isotropic stress state) conditions. The results show that there are systematic differences in the evolution of water-retention capacity and permeability of the three loess specimens: the SWCC of conventional remolded loess shifts downward with the increase of vertical stress, and the water holding capacity decreases; the SWCC of transversely isotropic loess exhibits an intersection phenomenon in the range of 50~100 kPa suction. After the intersection point, the slope of the curve decreases with the increase of vertical stress, and its water holding capacity increases. With the increase of dry density, the variation law of SWCC decline stage of isotropic loess approaches that of transversely isotropic loess. Under different vertical stresses, the sensitivity of permeability characteristics of isotropic samples to vertical stress is the highest, followed by conventional remolded samples, and the sensitivity of transverse isotropic samples is the lowest. The research results can provide useful references for related engineering applications.