Abstract
In initially dry coarse soil, it is noted that a uniform and nonponding surface water flux causes an un-table wetting front when the flux rate (q0) is less than the saturated hydraulic conductivity (Ks). To investigate the relationship between q0 and the pressure gradient with time (∂h/∂t) in the wetting layer under the condition of unstable water flow, we carried out one-dimensional infil-tration experiments by applying non-ponding water fluxes to the surface of soil packed homogeneously in an acrylic tube. We filled the tube with four different soils; sand, volcanic clay soil, loam and silt and installed microten-siometers to measure pressures in these materials. The re-sults showed that (1) negative pressure head gradients with space (∂h/∂ z) and time(∂h/∂t) appeared clearly only for sand and Eq. (1) derived by Cho et al. (2005) agreed well to the pressure measurement with time, (2) the ∂h/∂t was provided as a quadric function of q0 shown as Eq. (4) and fitted well the experimental data for sand . From this equa-tion, it was found that the smaller q0 becomes, the closer∂h/∂t approaches 0 and the flow becomes more stable. This trend could explain the experimental results of Yao and Hendrickx (1996).
