Abstract
The shear strength of topsoil indicates the resistance of surface land to external erosive forces and represents a key variable for inferring the extent and rate of soil erosion. However, the influence of land use on topsoil shear strength is poorly understood. This study aims to examine topsoil shear strength under different land uses in the purple-soiled region of the Three Gorges Reservoir area in China and explore the related factors that control the observed variability. Direct shear tests were performed to determine the shear strength of topsoil in terms of internal friction angle (φ) and cohesion (c) under 5 typical land use systems. The results showed that the topsoil shear stress increases with increasing shear displacement from 0 to 6 mm; thereafter, it remains relatively stable over a further increase of shear displacement from 6 to 10 mm. The shear stress–shear displacement curves display a hardening strain trend. Land use exerts a strong effect on the shear strength through differentiation of soil physicochemical properties. In general, topsoil from orchard land has the highest mean values for clay fraction, φ, and c and the lowest mean values for sand fraction and water content. The topsoil in abandoned land shows the highest mean values for bulk density and silt content. The bulk density and the clay and silt content are the main direct factors controlling the difference in shear strength of the purple topsoil. Organic matter content, total porosity, and sand content represent important indirect factors that contribute to the variability in c and φ values of the studied soils.
Highlights
Soil shear strength is defined as the maximum shear stress of soil before shear failure occurs
In forestland and sloping farmland, the purple soil has relatively low shear strength. This differs from the results of Bi et al (2006), Chen et al (2007), and Ni et al (2012, 2013), possibly because the purple soil was thin, there was significant soil erosion, and the organic matter (OM) and clay contents were lower (Zhang et al 2016), factors that lead to lower soil shear strength
This study examines shear strength under typical land uses in the Three Gorges Reservoir area and explores prevailing factors in determining the observed variances
Summary
Soil shear strength is defined as the maximum shear stress of soil before shear failure occurs. This has been widely used to evaluate soil erodibility, in particular for water erosion, and represents a key input parameter for processbased soil erosion modeling (Besalatpour et al 2012; Higuchi et al 2013; Havaee et al 2015; Singh and Thompson 2016; Khaboushan et al 2018; Zhang et al 2020). Knowledge of the surface soil shear strength is required to model runoff and soil erosion (Khalilmoghadam et al 2009). Leonard and Richard (2004) found that soil shear strength is the most useful soil property when predicting critical shear stress and runoff erosion. The study of topsoil shear strength facilitates better understanding of soil erosion mechanisms
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