Modeling Soil Behaviour during Subsoiling

1. ModelingSoil Behaviour during Subsoiling Leon Fangliang Chen PhD Student Ying Chen Professor, PhD, P.Eng. Biosystems Engineering University of Manitoba

2. Introduction of subsoiling tillage • Breaking up the compacted layer to loosen the soil • Requiring high draft power and resulting in high soil disturbance • Discrete element modeling (DEM) to simulate the subsoiling process Source: www.fao.org

3. Introduction of DEM and PFC3D Discrete element method (DEM) • To study the behavior of granular material • Repeated application of Newton’s second law and a force-displacement law • More detailed study of micro-dynamics of material Particle Flow Code in 3 Dimension (PFC3D) • A commercial DEM software package • Modeling problems in solid mechanics and granular flow Source: Itasca (2003)

4. Objectives • To develop a PFC3D model to predict soil cutting forces and soil loosening • To calibrate model parameters of soil • To validate the model with field measurements

5. Model development - virtual subsoiler

6. Model development – soil parallel bond • Depicted as a cylinder of cementatious material • Envisioned as a set of elastic springs • Transmitting both force and moments • Bond breaking • Young’s modulus of the bond unknown Source: Itasca (2003)

7. Model domain

8. Model input parameters • Soil particle • Range of particle size • Particle-particle friction coefficient • Young’s modulus • Ratio of normal and shear stiffness • Bulk density • Soil box • Length, width, and height • Parallel bond between soil particles • Radius of the bond • Bond normal and shear strength • Young’s modulus (To be calibrated) • Bond stiffness ratio • Subsoiler • Soil-subsoiler friction coefficient • Subsoiler stiffness • Subsoiler travel speed • Tillage depth

9. Field measurements for model calibration and validation Field conditions: • Oakville, Manitoba, Canada • Tillage depth & speed: 300 mm, 3 km/h • Clay soil Data collection • Soil cutting pressure • Soil dry bulk density • Soil total porosity

10. Model calibration – inverse modeling • FlexiForce sensors were used to measure the soil pressure on the subsoiler and to calibrate the model Sensing circle: 4.8 mm radius Sensing area: 71 mm2

11. Model simulation Side view of the field operation Back view of the model

12. Result of the model calibration

13. Model outputs of draft forces

14. Model validation of the draft force

15. Conclusions • Successful simulation of soil behaviour with PFC3D in terms of soil-subsoiler interaction force measurements and soil porosity changes • Young’s modulus of 105 Pa for the soil bond giving the best match between the measured and predicted soil pressures • Appropriate method of simulating soil aggregates, not individual soil particles as “particles” in PFC3D when simulating agricultural clay soils

16. Future work • Simulating soil cutting forces and soil loosening resulting from the ripper at different tillage depths • Validating the simulation results against the field measurements and the universal earthmoving equation

17. Thank you for your attention!Questions?