Effects of density and hysteresis on hydraulic conductivity function of compacted expansive soil

The effects of density and hysteresis on the hydraulic conductivity function (HCF) of Jingmen compacted expansive soil are experimentally investigated. The saturated hydraulic conductivities over the range of void ratio from 0.476 to 1.624 are determined by the falling head permeability test. The parameters of the commonly adopted HCF model, van Genuchten-Mualem (VGM) model under six different densities and drying/wetting paths are measured by using the transient release and imbibition method (TRIM). The conclusions are drawn as follows: (1) The parameters α, n of the VGM model increase with the increase of void ratio, and their values under drying path are less than the corresponding ones under wetting path. (2) The effects of density and hysteresis on the relationship between hydraulic conductivity (k) and matric suction are significant. HCFs intersect under different densities. The value of k under lower density is larger before the intersection of HCFs, and that under higher density is larger after the intersection. The value of k under drying path is larger than that under wetting path. (3) The effects of density on the relationship between k and volumetric water content θ are significant. The value of k under higher density is smaller than that under lower density, and HCFs do not intersect under different densities. The effects of hysteresis on the relationship between k and θ are not significant. (4) One-dimensional vertical infiltration is simulated using the Hydrus with the above-mentioned parameters of VGM model. The results show that the effects of density on seepage are remarkable. But the influences of density on wetting front velocity are not monotonic. On the other hand, whether to account for hysteresis leads to significant difference of the simulated results. The empirical formulas for parameters α, n and e of VGM model under different wetting/drying paths can be used in seepage modeling to account for the effects of density and hysteresis.