Modeling Soil Behaviour during Subsoiling

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Modeling Soil Behaviour during Subsoiling

• Leon Fangliang Chen
• PhD Student
• Ying Chen
• Professor, PhD, P.Eng.
• Biosystems Engineering
• University of Manitoba

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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
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Introduction of DEM and PFC3D

• Discrete element method (DEM)
• To study the behavior of granular material
• Repeated application of Newtons 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)
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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

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Model development - virtual subsoiler
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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
• Youngs modulus of the bond unknown

Source Itasca (2003)
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Model domain
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Model input parameters

• Soil particle
• Range of particle size
• Particle-particle friction coefficient
• Youngs 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
• Youngs modulus (To be calibrated)
• Bond stiffness ratio
• Subsoiler
• Soil-subsoiler friction coefficient
• Subsoiler stiffness
• Subsoiler travel speed
• Tillage depth

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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

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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
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Model simulation
Side view of the field operation
Back view of the model
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Result of the model calibration
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Model outputs of draft forces
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Model validation of the draft force
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Conclusions

• Successful simulation of soil behaviour with
  PFC3D in terms of soil-subsoiler interaction
  force measurements and soil porosity changes
• Youngs 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

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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

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Thank you for your attention!Questions?