A Novel and Facile Method for Characterizing Shrinkage Geometry along the Granitic Soil Profile

Abstract

A simple and facile approach was proposed for measuring the anisotropic shrinkage. Subsidence was dominant for soils in the loose and aggregated structure. Horizontal shrinkage was predominant for soils with the horizontal arrangement of plate particles The shrinkage behavior of granite soils was controlled by clay content and pore structure. Soil volume change resulting from frequent drying–wetting cycles leads to severe erosion and landslides in granite regions. Limited attempts have been made to investigate the shrinkage geometry of these soils. Here, a new method was proposed for characterizing soil shrinkage behavior by testing cylindrical specimens of undisturbed granitic soils sampled separately in vertical and horizontal directions at the pedogenic layers (i.e., surface [L1], lateritic [L2 and L3], sandy [L4], and detritus [L5] layers). For L1, the coefficient of linear extensibility (COLE) was larger in the vertical than in the horizontal direction, whereas it was the opposite for L2 and L3. For L4 and L5, the COLE showed no significant differences between the two directions. A modified van Genuchten equation fitted well with the COLE curves (p < 0.01). The shrinkage potential decreased in the order of L3 > L2 > L1, L4 > L5. Subsidence was dominant for the L1 soil due to the loose‐aggregated structure, whereas cracking was dominant in the lateritic layer soils due to the horizontal arrangement of clay particles. The shrinkage geometry for L4 and L5 was largely determined by soil structure inherited from the configuration of granite rock. The shrinkage behavior of granite soils was controlled by clay content and pore structure. This new method of measuring shrinkage geometry is accurate, low cost, nondestructive, and labor saving but remains to be improved and validated on a wide range of soil types.

Influence of Benggang slope cracks on soil water regimes: Comparison of model simulation and time‐domain reflectometry

“…Therefore, this method is relatively simple and effective. This method of adding cracks to the model is possible mainly due to the low content of hydrophilic minerals in the weathered granite soil and minimal swelling when encountering water (Wei et al, 2018; Zhang & Tang, 2013). Kaolinite is the main clay mineral in weathered granite soil, with a relative content of more than 92%, followed by illite, with a relative content of 4%–8%, indicating that the wetting effect on weathered granite soil is relatively small (Wei, 2017).…”

“…The county has a typical subtropical monsoon climate with annual precipitation of approximately 1450 to 1600 mm and an annual average temperature of approximately 15.5 to 16.7 C. This rainy climate and mountainous terrain have led to the active development of collapsing gullies, and there are 1102 Benggangs in Tongcheng County. The zonal soil, derived from weathered granite and classified as an Ultisol (US Soil Taxonomy), is locally called red soil (Wei et al, 2018). In the study area, two typical Benggang slopes with complete soil profiles, TC1 and TC2, were selected (Figure A1).…”

Degradation Characteristics of Soil-Quality-Related Physical and Chemical Properties Affected by Collapsing Gully: The Case of Subtropical Hilly Region, China

“…For a better understanding of the high-steep slope of a collapsing wall and the mechanism of collapsing erosion, the engineering characteristics and preferential flows have also been investigated for the profile of the collapsing wall. Some researchers analyzed the spatial variations of shear strength and hydraulic properties in collapsing gullies and evaluated their effects on the collapsing erosion mechanism [14,[18][19][20]. Additionally, researchers have also investigated the variations of chemical composition and physical properties with soil depth in the collapsing gullies and found that the contents of gravel and sand increase while the amount of sesquioxides decreases with an increase of soil depth [21,22].…”