Estimating soil failure due to torsion via vane shear test by varying vane diameter and soil properties

Soil–tool interaction poses an ongoing challenge to researchers, developers, and manufacturers. Numerous studies have focused on reaction forces, resistances, and associated soil failures during the penetration of tillage tools into soil or their surface movements. However, little research has been devoted to the interactions involved in the torsion failure of soil in agricultural tillage systems. To study the resistance of soil to failure due to torsion actions, this study develops a torsion-induced soil failure estimation model that is used to obtain relevant parameters based on in-situ experiments conducted in a soil bin by using soil with different physical properties (i.e., moisture content and soil density). Four vanes with various diameters but the same height (5 cm) were designed. The maximum torques at which soil failure occurred were then measured and analyzed. The results revealed a power function relationship between the soil failure due to torsion and the diameter of the vane, i.e., T = αDβ (R2 > 0.96). The dimensionless parameters α and β of the estimation model were found to be related to the soil moisture (P < 0.05) and bulk density (P < 0.05), respectively. The values of both α and β varied nonlinearly with the soil moisture content, cone index, and bulk density. It was concluded that the power function can be applied to describe the relationship between the torque and the diameter of the vane; with the measurement device performing a torsion action in the soil layer, the torque at which soil failure occurs can be estimated by using the diameter of the vane along with the moisture content of the soil and its bulk density. When the height of the vane was constant, the torsion could be predicted by using the proposed power function model at certain soil conditions.