Estimation of the soil hydraulic properties and parameter characteristics of Benggang erosion in granite in southern China

Abstract

AbstractBenggang is an erosional landform that forms in granite hills due to coupled hydraulic and gravity erosion, and its unique development makes it difficult to obtain moisture characteristics through direct means. In this study, the soil moisture characteristics were investigated on the collapsing walls with different weathering degrees of two different Benggang types defined as scoop‐shaped Benggang and strip‐shaped Benggang in the typical Benggang erosion areas of southeastern Guangxi. The soil water characteristic curves (SWCCs) of the collapsing wall were measured by the centrifuge method to explore the moisture transport mechanism of Benggang development. The response of moisture characteristics to the Benggang morphology was not significant, but the soil layer changes in the collapsing wall had a significant impact. The Atterberg limits of the surface layer and laterite layer were significantly higher than those of the transition layer and sandy layer, with a liquid limit (LL) value exceeding 55%, indicating high LL clay. The Van Genuchten (VG), Gardner and Fredlund–Xing (FX) models were used to fit the SWCCs, and the results indicated that the VG model had a high fitting accuracy (R2 > 0.984), followed by the FX model (R2 > 0.943); however, the Gardner model had a low fitting accuracy (R2 > 0.891). With the change in matrix suction, the sandy layer had the maximum water release capacity, followed by the transition layer, and finally the surface layer and laterite layer. The variation in equivalent pore size distributions with soil layers showed that the micropores in the laterite layer of the two Benggangs accounted for 44.91% and 44.38% of the total porosity. The macropores of the sandy layer accounted for 35.40% and 36.84% of the total porosity. Both the unsaturated hydraulic conductivity K(θ) and water diffusivity D(θ) exhibited two abrupt changes with increasing soil volumetric water content, and K(θ) and D(θ) of the lower layers were larger than those of the upper layers. The heterogeneity of soil texture and pore conditions among different collapsing wall soil layers can significantly affect the Benggang water conditions. This study provides a database for further investigation of the Benggang development mechanism.