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Abstract
According to the Mualem capillary model, hydraulic conductivity (HC) is integrated theoretically from the function related to soil water retention curves (SWRC). On the other hand, based on the smooth type of SWRC, the predicted HC function decreases abruptly near saturation, which often challenges the stability of numerical solutions. To improve the Mualem HC, van Genuchten’s function for SWRC was modified within the range of low matric suction. The van Genuchten-Mualem HC was then modified to integrate the proposed SWRC for each interval decomposed by a tangential curve. The analytical solutions of the modified HC were derived to prevent an abrupt decrease near saturation. The SWRC and HC data were acquired from laboratory tests for unsaturated soils sampled from five areas in Korea. The results of the HC tests were compared with the theoretical HC models using both the van Genuchten SWRCs and the modified curves. For fine grained soils, the modified model predicts a saturated HC at very small suctions. Furthermore, the modified model was shown to accurately predict the unsaturated behavior of the HC functions for Korean weathered soils.
Highlights
In variably saturated soils, the hydraulic conductivity is a crucial factor for understanding the hydrological behavior due to infiltration or evaporation
Among the various soil water retention curves (SWRCs), the van Genuchten’s model can describe the normalized hydraulic behavior successfully from two parameters and provide conductivity by a closed-form equation based on Mualem theory [3]
Small changes in the shape of the soil water retention curve near saturation can lead to significantly different results regarding the unsaturated hydraulic conductivity (HC) function based on the Mualem model
Summary
The hydraulic conductivity is a crucial factor for understanding the hydrological behavior due to infiltration or evaporation. Among the various soil water retention curves (SWRCs), the van Genuchten’s model can describe the normalized hydraulic behavior successfully from two parameters and provide conductivity by a closed-form equation based on Mualem theory [3]. Small changes in the shape of the soil water retention curve near saturation can lead to significantly different results regarding the unsaturated hydraulic conductivity (HC) function based on the Mualem model. To reduce the steepness of the HC, the original fit of the van Genuchten’s curve can be modified to a non-smooth curve at a small suction [7,12,13]. Laboratory tests on both the water retention and HC behaviors were carried out for multiple sites. The modified model reduced the slope of HC near saturation and predicted the actual HC accurately
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