Subsoiler Rake and Bend Angles Optimization Using Discrete Element Modeling

Abstract

Highlights DEM soil model for cohesive frictional artificial soil. Validated elasto-plastic DEM model for shank design. DEM accurately predicted soil draft and rupture area. Shank with paraplow found to be optimal for reduced draft and increased soil rupture. ABSTRACT. Heavy machinery traffic in the Right-of-Way (ROW) of utility construction sites creates excessive subsoil compaction. Applying deep tillage using current industry-standard subsoilers in the ROW has shown limited benefits in loosening the soil. This study focuses on subsoiler-to-soil interaction, aiming to optimize shank shape designs to maximize soil rupture below the ground surface and reduce tillage energy consumption during deep-tillage operations in soils disturbed by utility construction activities. We propose a physics-based accelerated subsoiler shank optimization study by integrating simulation-driven design, discrete element modeling (DEM), standard soil testing, and soil bin validation experiments. The DEM soil model, which captures elasto-plastic behavior with a stress-dependent cohesive model, was calibrated using Design of Experiment (DOE), meta-model regression, and multi-response optimization from DEM simulations of ASABE standard cone penetration resistance and ASTM confined uniaxial compression testing of cohesive-frictional artificial soil. Validation DEM simulation of soil-to-shank interaction was performed using the calibrated DEM elasto-plastic with cohesion soil model and comparison to soil bin data on soil horizontal reaction force and soil rupture area from six geometrically scaled (1:5.63) subsoiler shanks. DEM results have good prediction accuracy, with percent relative error (PRE) of 6.9%, 10.5%, and 1.5% for confined uniaxial compression energy, maximum plate stress during confined uniaxial compression, and maximum soil penetration resistance, respectively. The DEM validation simulation of soil-to-shank interaction also showed within 10% PRE of soil horizontal reaction force (mean PRE 4%) and soil rupture area (mean PRE of 3%) across all shanks. Strong correlations were found between DEM and soil bin data for horizontal soil reaction force (R² = 0.9793) and soil rupture area (R² = 0.9966). Ranking the shanks based on minimum soil horizontal reaction force and maximum soil rupture area, a paraplow shank design (S-3, ß = 60° and a = 45°) was selected to be the optimal shank design. Geometric upscaling using a 5.63 scaling factor and DEM simulation of full-scale shanks was performed on the optimal shank shape (S-3) and two benchmark shank designs (straight shank (S-1) and raked shank (S-2)). Utilizing DEM soil-to-shank simulation using the three full-scaled (geometrically upscaled to 1:1) shanks, the paraplow shank (S-3) has better performance compared to the standard raked shank (S-2), reducing soil draft force and increasing soil rupture by 4.98% and 15.93%, respectively. This study provides valuable insights into integrating similitude principles and DEM-based design optimization of subsoiler shanks to reduce draft force and improve the efficiency of soil loosening, contributing to accelerated ground-engaging tool optimization for efficient subsoiling and promoting sustainable soil management practices. Keywords: Deep tillage, DEM, Soil compression, Soil modeling, Soil-to-tool interaction.