 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 2 Source:

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 (PFC 3D )  A commercial DEM software package  Modeling problems in solid mechanics and granular flow 3 Source: Itasca (2003)

 To develop a PFC 3D model to predict soil cutting forces and soil loosening  To calibrate model parameters of soil  To validate the model with field measurements 4

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6 Source: Itasca (2003)  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

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 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 8

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 9

10 Sensing circle: 4.8 mm radius Sensing area: 71 mm 2  FlexiForce sensors were used to measure the soil pressure on the subsoiler and to calibrate the model

11 Side view of the field operation Back view of the model

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 Successful simulation of soil behaviour with PFC 3D in terms of soil-subsoiler interaction force measurements and soil porosity changes  Young’s modulus of 10 5 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 PFC 3D when simulating agricultural clay soils 15

 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 16

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