Effect analysis of soil texture and water content on soil adhesive force based on the discrete element method

Understanding soil-metal adhesion under varying moisture and texture conditions is essential for predicting soil-tool interactions in agricultural machinery. However, despite its importance, research that directly quantifies soil adhesion and provides physically based parameters for modeling remains limited, particularly across the diverse conditions encountered in field operations. In this study, we experimentally measured soil-metal adhesion across multiple penetration speeds and integrated the results with discrete element method (DEM) simulations based on the Edinburgh Elasto-Plastic Adhesion (EEPA) model. Adhesion tests were conducted for three soil textures (sandy loam, sandy clay loam, and loam) and four water contents (10-25%) at penetration speeds of 50 and 500 mm·min⁻¹. Adhesive force increased with water content and peaked near the liquid limit (20-25%), while remaining nearly independent of penetration rate (< 5% variation). DEM calibration showed that surface energy (Δγ) is the dominant parameter governing compressive behavior, whereas the constant pull-off force (f₀) primarily controls adhesive strength. Two-way ANOVA confirmed that these mechanisms operate independently (p > 0.05). The calibrated model achieved R² ≥ 0.93 and RMSE ≤ 0.1 N across all textures, and validation at an intermediate speed of 250 mm·min⁻¹ demonstrated stable predictive performance (R² ≥ 0.93 for compression; R² ≥ 0.98 for adhesion). By linking multi-speed adhesion measurements with a physically based DEM contact model, this work establishes a robust and transferable Δγ-f₀ calibration framework for modeling soil adhesion in cohesive soils.