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Soil compaction in three steps...

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Soil compaction in three steps...

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  1. 4a. Mechanical stresses during wheel traffic Thomas Keller1,2, Mathieu Lamandé3, Matthias Stettler4 and Per Schjønning31Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, CH-8046 Zürich, Switzerland; E-mail: thomas.keller@art.admin.ch2Swedish University of Agricultural Sciences, Department of Soil and Environment, Box 7014, SE-75007 Uppsala, Sweden3Department of Agroecology, Aarhus University, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark 4Swiss College of Agriculture, Länggasse 85, CH-3052 Zollikofen, Switzerland

  2. Contacttyre/track-soil = Upper model boundarycondition: • Contactarea • Stress distribution • Stress propagation • Stress-strain (voidratio) relationship & Mechanicalsoilstrength • Stress > Strength Compaction • Stress < Strength Elasticdeformation Soil compaction in three steps...

  3. Stress propagation in soil Kolloquium FB31 | Bodenverdichtung

  4. Modelling stress propagation • Finite element modelling (FEM) • Continuum mechanics • Elasto-plastic stress-strain relationships (e.g. Modified Cam Clay) • Can account for stress-dependent material properties • Limitations: • Description of tyre-soil contact • Parameterization • (e.g. Richards & Peth 2009, Soil & Tillage Research 102) • Analytical solutions • Simple and robust • 3-Dimensional • Limitations: • Elastic theory • (e.g. Keller & Lamandé 2010, Soil & Tillage Research 111)

  5. Modelling stress propagation • Finite element modelling (FEM) • Continuum mechanics • Elasto-plastic stress-strain relationships (e.g. Modified Cam Clay) • Can account for stress-dependent material properties • Limitations: • Description of tyre-soil contact • Parameterization • (e.g. Richards & Peth 2009, Soil & Tillage Research 102) Suitableforeasily-applicabledecisionsupporttools  Approach in Terranimo® • Analytical solutions • Simple and robust • 3-Dimensional • Limitations: • Elastic theory • (e.g. Keller & Lamandé 2010, Soil & Tillage Research 111)

  6. Stress propagation: pointload P Forelastic material (Boussinesq, 1885): y x r Ѳ σr z Boussinesq J (1885) Application des Potentiels à l’étude de l’équilibre et du Mouvement des SolidesÉlastiques. Gauthier-Villars, Paris, 30 pp.

  7. Stress propagation: pointload Soil is not fullyelastic… Therefore (Fröhlich, 1934): P y x ν = „concentrationfactor“ (empiricalfactor) r Ѳ σr z FröhlichOK (1934) DruckverteilungimBaugrunde. Springer Verlag, Wien, 178 pp.

  8. Stress propagation: Söhne‘ssummationprocedure Pi zi σz Söhne W (1953) Druckverteilung im Boden und Bodenverformung unter Schlepperreifen. Grundlagen der Landtechnik 5, 49-63.

  9. ν = Concentrationfactor Stress propagation in soil (Boussinesq, 1884; Fröhlich, 1934; Söhne, 1953) Söhne W (1953) Grundlagen der Landtechnik 5, 49-63. Boussinesq J (1885) Application des Potentiels à l’étude de l’équilibre et du Mouvement des Solides Élastiques. Gauthier-Villars, Paris, 30 pp. Fröhlich OK (1934) Druckverteilung im Baugrunde. Springer Verlag, Wien, 178 pp. Söhne W (1953) Druckverteilung im Boden und Bodenverformung unter Schlepperreifen. Grundlagen der Landtechnik 5, 49-63.

  10. Stress distribution at the tyre-soil contact affects stress propagation Simulated, using measured stress distribution Simulated, using uniform stress distribution Measured stress

  11. Stress distribution at the tyre-soil contact affects stress propagation ? But…

  12. Idea… Easily-available tyre/loading properties (e.g., tyre dimensions, tyre inflation pressure, wheel load) and information on soil condition/consistency ? Model Stress distribution

  13. Measuring stress distributionatthetyre-soilinterface 2 1 3 4 Photos: Per Schjønning

  14. Upper model boundarycondition: Model „FRIDA“ Tyre: 800/50 R34; Wheel load: 6000 kg Model ‘FRIDA’: (Keller, 2005; Schjønning et al. 2008) Contact area Stress distribution Measured Modelled Keller T (2005) A model for prediction of the contact area and the distribution of vertical stress below agricultural tyres from readily-available tyre parameters. Biosystems Engineering 92, 85-96. Schjønning P, Lamandé M, Tøgersen FA, Arvidsson J & Keller T (2008) Modelling effectsoftyreinflationpressure on the stress distributionnearthesoil-tyreinterface. Biosystems Engineering 99, 119-133.

  15. Predicting stress insoil Simulated, using measured stress distribution Simulated, using FRDIA generated stress distribution Simulated, using uniform stress distribution Measured stress

  16. Contacttyre/track-soil = Upper model boundarycondition: • Contactarea • Stress distribution • Stress propagation • Stress-strain (voidratio) relationship & Mechanicalsoilstrength • Stress > Strength Compaction • Stress < Strength Elasticdeformation Soil compaction in three steps...

  17. 6a. Stress transmissionThomas Keller1,2, Mathieu Lamandé3, Matthias Stettler4 and Per Schjønning31Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, CH-8046 Zürich, Switzerland; E-mail: thomas.keller@art.admin.ch2Swedish University of Agricultural Sciences, Department of Soil and Environment, Box 7014, SE-75007 Uppsala, Sweden3Department of Agroecology, Aarhus University, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark 4Swiss College of Agriculture, Länggasse 85, CH-3052 Zollikofen, Switzerland

  18. Stress propagation in soil: Simulation vs. measurements (typicalresult) Possible reasons (Keller & Lamandé, 2010): Upper model boundary condition is wrong Model for stress propagation is inappropriate Stress measurements are inaccurate Keller T & Lamandé M (2010) Challenges in the development of analytical soil compaction models. Soil & Tillage Research 111, 54-64.

  19. Stress propagation in soil: Simulation vs. measurements (typicalresult) FRIDA Possible reasons (Keller & Lamandé, 2010): Upper model boundary condition is wrong Model for stress propagation is inappropriate Stress measurements are inaccurate Keller T & Lamandé M (2010) Challenges in the development of analytical soil compaction models. Soil & Tillage Research 111, 54-64. We know that we are within  10% (Lamandé et al., unpublished) This cannot account for the discrepancies (Keller & Lamandé, 2010)

  20. Stress propagation in soil: Simulation vs. measurements (typicalresult) Possible reasons (Keller & Lamandé, 2010): Upper model boundary condition is wrong Model for stress propagation is inappropriate Stress measurements are inaccurate Keller T & Lamandé M (2010) Challenges in the development of analytical soil compaction models. Soil & Tillage Research 111, 54-64.

  21. Stress propagation in soil: towards a 2-layer approach A pragmatic model wouldbe: Tilledlayer(e.g. 0-0.25 m depth): no stress attenuation Subsoil: accordingto Söhne (1953)

  22. Estimation of theconcentrationfactor: Approach (i) Field measure-ments of σz Simulations of σz with different valuesforconcentrationfactor (ν). Comparison: When (atwhichν)doesthesimulatedσz fit bestthemeasuredσz (lowest RMSE)?

  23. Estimation of theconcentrationfactor: Approach (ii) ν = f (soil properties, loading) Linear regressionmodel (whichsoilproperties and loadingcharacteristicsdescribebesttheoptimizedν?)

  24. Estimation of theconcentrationfactor: Resultsfrom a preliminarystudy Regression fordatafromwheelingexperiments on sevensoils (12 -61% clay) yields: σpc [kPa] Sand [%] σpc↑  ν ↓ Sand ↑ ν ↑ Keller T, Stettler M, Arvidsson J, Lamandé M, Schjønning P, Berli M & Rydberg T (2009) Stress propagation in arablesoil: determination and estimation of theconcentrationfactor. Proc. 18th Conf. ISTRO, Izmir, Turkey, 15-19 June 2009.

  25. 6c. WP1: Soil mechanical models and pedotransfer functions

  26. Model approach • Estimation of model parameters

  27. 1. Modelling approach: a) upper model boundarycondition (i) Model ‘FRIDA’: (Keller, 2005; Schjønning et al. 2008) Contact area Stress distribution ?

  28. 1. Modelling approach: a) upper model boundary condition (ii) Easily-available tyre/loading properties (e.g., tyre dimensions, tyre inflation pressure, wheel load) and information on soil condition/consistency Empiricalmodels foreach of the FRIDA model paremeters Upper model boundary condition e.g.:  = a Ptyre + b PWheelLoad Model ‘FRIDA’: (Keller, 2005; Schjønning et al. 2008) Parameters: Contact area: l and w, n, Stress distribution: α and 

  29. 1. Modelling approach: b) stress propagation A new semi-empirical model: Tilledlayer(e.g. 0-0.25 m depth): no stress attenuation Subsoil: accordingto Söhne (1953) Compare, and selectthebestperforming model… „Classical“ one-layer model (Söhne, 1953)

  30. 1. Modelling approach: c) compressivesoilstrength Pragmatic model: CS = kx PCS where: CS = compressivestrength (kPa) PCS = precompression stress (kPa) k = empiricalfactor (-), k = 0..1

  31. Model approach • Estimation of model parameters

  32. 2. Estimation of model parameters: a) upper model boundarycondition (ii) • Data available: • Measurements from Sweden (Keller, 2005) • Measurements from Denmark (Schjønning et al., 2006, 2008; Lamandé & Schjønning, 2008; Lamandé & Schjønning, in press) • Unpublished data from Denmark [designed to study impacts of soil consistency] (Schjønning et al., unpublished) • Work to be done: • Compile data (mostly done) • Find appropriate parameter (property) to characterize soil consistency • Develop „tyre-transfer functions“ for estimation of FRIDA model parameters

  33. 2. Estimation of model parameters: b) stress propagation • Data available: • Measurements from Sweden, using load cells (Keller, 2004; Keller & Arvidsson 2004, 2006; Keller & Lamandé, 2010) • Measurements from Denmark, using load cells (Lamandé & Schjønning, 2007; Lamandé & Schjønning 1-3, in press; Keller & Lamandé, 2010) • Measurements from Switzerland, using Bolling probes (Anken et al., 1993; Zihlmann et al., 1995, Diserens & Anken, 1995; Anken et al., 2000; Gysi et al., 2001; van der Veer, 2004; Schäffer et al., 2007) • Work to be done: • Compile data (mostly done) • Correct stress readings (Berli et al., 2006; Lamandé et al., unpublished) • Simulate stress and compare with measurements  (i) best model (“2-layer” vs. “classical”), and (ii) concentration factor • Develop „pedo-transfer functions“ for estimation of the concentration factor

  34. 2. Estimation of model parameters: c) soilstrength • Data available: • Uniaxial compression from Switzerland (Weisskopf et al., unpublished), Sweden (Keller & Arvidsson, 2007; Keller et al., in press; Keller, unpublished) and Denmark (Schjønning, 1996; Schjønning & Lamandé, unpublished) • In situ stress-strain data from Sweden (Keller, 2004; Keller & Arvidsson 2004, 2006; Keller & Lamandé, 2010) and Denmark (Lamandé & Schjønning, 2007; Lamandé & Schjønning 1-3, in press; Keller & Lamandé, 2010) • Work to be done: • Merge and harmonize data (mostly done) • Agree on a proper method to obtain precompression stress • Develop „pedo-transfer functions“ for estimation of precompression stress • Find the empirical factor “k” that relates soil strength to precompression stress

  35. 7c. Structure of soil and weather data bases, Switzerland Thomas Keller1,2 and Matthias Stettler31Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, CH-8046 Zürich, Switzerland; E-mail: thomas.keller@art.admin.ch2Swedish University of Agricultural Sciences, Department of Soil and Environment, Box 7014, SE-75007 Uppsala, Sweden3Swiss College of Agriculture, Länggasse 85, CH-3052 Zollikofen, Switzerland

  36. A. Soil data • A national soildatabasedoes not exist…, but is in progress (however, tobeexpected after the end of PredICTor)… • Somecounties („Kantons“) do have GIS-basedsoilmaps ( perhapsthiscouldbeusedas a pilotstudyarea) • Best soilmap of Switzerland: „Soil suitabilitymap“ (suitabilitywithregardtoagriculturalproduction; „Bodeneignungskarte“) 1:200‘000 • Somecounties do havesoilmaps 1:5‘000 to 1:25‘000 • Problem: existingsoildata and mapsareratherdescriptive (e.g. noexactvalues of claycontent but onlyclasses)

  37. B. Meteorologicaldata • Agroscope ART hasdirectaccesstoabout 60 official (MeteoSwitzerland) weatherstations of Switzerland (hereby, datafromtheseweatherstationsaremirroredto a database on an instituteservereverynight) • The dataincludesprognosis of thecomingtwodays • Data fromthedatabasecouldbeaccessedfromTerranimo® (discussed and confirmedat a meeting in Zürich last October)

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