Guan'gai paishui xuebao (Dec 2021)
Saturated Soil Hydraulic Conductivity is not Constant But Varies with the Time It is Measured
Abstract
【Background and objective】 Saturated soil hydraulic conductivity (KS) is an important parameter characterizing the ability of soil to conduct water. It is often assumed to depend on soil structure and is hence constant for a given soil. The objective of this paper is to validate to what extent this common practice is valid. 【Method】 We took vertisol soil in Huaibei Plain as an example, and conducted a series of experiments using both undisturbed soil cores with bulk density 0.96 g/cm3 and repacked soil cores with bulk density in the range of 0.90 to1.30 g/cm3. For each soil core, we measured a time sequence of its saturated hydraulic conductivity (KS) using the constant-head method. 【Result】 The KS of both intact and repacked soil cores showed a rapid decrease followed by a slow increase as time elapsed from inception of the experiment. For the undisturbed soil, its initial KS was 88.4 mm/h, but reduced to 5.0 mm/h 0.98 day (the deflection point) after inception of the experiment. As time elapsed, it eventually settled at 0.8 mm/h 12.94 day after commencing the experiment. Similar pheromone was also found for the repacked soil cores, although the deflection time and the time for Ks to asymptote varied with the repacking density. In general, as the bulk density increased, the initial KS was smaller and it took less time for its KS to reach the inflection point. The KS measured at any time was negatively correlated with soil bulk density. 【Conclusion】 Contrary to what have been commonly assumed, saturated soil hydraulic conductivity does not appear to be constant but varies with the time it is measured. For the vertisol soil we studied, its hydraulic conductivity decreased first followed by an increase when time elapsed passing the deflection point though the time for the deflection to appear varied with soil bulk density.
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