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Evaluation Model of Soil Water Characteristic Curve of Red Clay Based on Dielectric Theory
WANG Hai-jun, XU Xing-qian, LI Cheng, ZHAO Xi, MA Guan-yu, MA Fang-wen
Journal of Changjiang River Scientific Research Institute ›› 2026, Vol. 43 ›› Issue (4) : 138-147.
PDF(2714 KB)
PDF(2714 KB)
Evaluation Model of Soil Water Characteristic Curve of Red Clay Based on Dielectric Theory
[Objective] The soil water characteristic curve (SWCC) can effectively reflect the relationship between soil water suction (matric potential) and water content, yet conventional testing methods pose challenges for the calibration of in situ soil hydraulic parameters. A more convenient, economical and reliable in situ testing approach is required for the rapid evaluation of in situ soil water status and hydraulic characteristics. [Methods] This study integrated soil dielectric theory with a soil water characteristic curve model and, by considering clay mineral composition, bound water, and free water, derived and established an evaluation model for the soil equivalent dielectric constant-matric suction characteristic curve (SEDCC). For model verification, remolded red clay samples with an average dry density of 1.2 g/cm3 were prepared from six regions of Yunnan Province. The prediction accuracy of the SEDCC curves for red clay across different regions was then systematically analyzed, and the feasibility of indirectly evaluating the SWCC of red clay using dielectric theory parameters of electromagnetic waves was further discussed. [Results] The results showed that the water retention characteristics of red clay were influenced by formation conditions, mineral composition, pore structure, and climatic environment, resulting in regional differences in the fitting accuracy of the Fredlund model. Volumetric water content was the key factor driving changes in matric suction and the equivalent dielectric constant. Using volumetric water content as a bridge, the equivalent dielectric constant gradually decreased as matric suction increased. By fitting the correlation between the equivalent dielectric constant and matric suction using the SEDCC model, the fitting accuracy of the SEDCC model in all regions was greater than 95%. An approximately symmetric relationship was observed between the matric suction inversion curve of red clay and the dielectric theory prediction curve. However, this relationship was still influenced by regional differences. By comparing the predicted values from the dielectric theory inversion curve with the measured values obtained by the filter paper method, it was found that the change trends of the soil water characteristic curves derived from the two were basically consistent, with an average relative error of 6.42%. [Conclusion] Therefore, the SEDCC curve proposed based on dielectric theory can fully reflect the coupling relationship between the soil equivalent dielectric constant and matric suction, indicating that the equivalent dielectric constant is a feasible indirect indicator for evaluating matric suction in red clay. Compared with traditional methods, this model is efficient, convenient, and nondestructive, and it shows potential for indirectly inverting the soil water characteristic curve using dielectric theory, thereby providing a convenient approach as well as theoretical model support and reference for the rapid and accurate detection of soil hydraulic parameters using electromagnetic wave techniques.
red clay / equivalent dielectric constant / volumetric water content / matric suction / soil water characteristic curve / soil hydraulic parameters
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