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Soil Compaction Models respect to critical state soil mechanics, whereby he states that the theory of critical state soil mechanics is valid for partially saturated soils, however, it should be kept simple as the total stress states have not been proven yet, but can well be used as a working hypothesis. The study by Adams and Wulfsohn (1998) showed that the critical state soil mechanics can explain agricultural soil behavior and that it is possible to identify critical state soil mechanics parameters for unsaturated soils. The critical state concept is applicable to unsaturated soils both quantitatively and qualitatively except that the critical state parameters depend on the soil moisture content according to Hettiaratchi and O’Callaghan (1980), Hettiaratchi (1987), and Kirby (1989). Additionally they found that it is reasonable to use total stress and consequently ignore soil moisture tension. Following these authors it is possible to utilize the complex critical state soil mechanics framework to describe soil compaction. An example of an empirical soil compaction model is the one developed by Adam and Erbach (1995) who empirically measure soil compaction by determining the depth to which DBD changes less than 5%. They could fit one exponential equation to the data similar to Bekker (1960) as the depth of soil compaction was not significantly affected by the water content on the silty clay loam used for their investigation. Excellent reviews of soil compaction models were done by Seig (1985) and afterwards by Defossez and Richard (2002). Both summarized and grouped the different approaches to predict soil compaction at their times. 6.1.2 Latest Soil Compaction Models Since the last reviews on soil compaction modeling by Seig (1985), Defossez and Richard (2002) and Ansorge (2005, a), Keller et al. (2007) have created a model called SOIL FLEX. It includes the soil displacement approaches of O’Sullivan et al. (1998), Bailey and Johnson (1989), and Gupta and Larsson (1982). In all the models used soil strength in- creases with strain, i.e. strain hardening applies. Gupta and Larson (1982) describe volume change with a relationship between bulk density and the logarithm of the major principal stress. Bailey and Johnson (1989) describe the natural volumetric strain in dependence of octahedral normal stress and octahedral shear stress. O’Sullivan et al. (1998) (COMPSOIL) use a critical state soil mechanics approach whereby the specific volume Ph.D. Thesis Dirk Ansorge (2007) 92
Soil Compaction Models depends on the natural logarithm of the mean normal stress. This approach is described in detail by Ansorge (2005, a). Thus in SOIL FLEX the user can choose the theoretical back- ground he wants to utilize. Stress distribution is based on Söhne (1953) with an added shear component. For stress distribution in the contact area a variety of approaches can be selected. In section 6.2 two of these predictions will be compared to results of both An- sorge (2005, a) and this study. Within SOIL FLEX this work will only consider the model COMPSOIL as this requires the least amount of parameters to be estimated while maintaining all output parameters. COMPSOIL only needs an estimation of the slope and intercept of a virgin compression line. For subsequent passes the slope of the recompression line has to be calculated. Thus overall only three parameters are needed. Gupta and Larson (1982) need similar parameters, a reference bulk density and a reference stress state on the VCL, i.e. an intercept of the VCL; and the slope of the VCL. Additionally the model of Gupta and Larson (1982) requires the slope of the bulk density vs. degree of water saturation curve and the desired degree of saturation minus the actual saturation at a reference bulk density. Thus this model requires an additional three parameters and moreover, the recompression index is equal to zero, assuming no elastic rebound, which can lead into difficulties predicting subsequent passes. The model of Bailey and Johnson (1989) requires four compactability coefficients of which two are dimensionless and two have dimensions of [kPa -1 ]. The empirical determination of this number of coefficients requires a large data set to adapt the model to a certain soil condition. Keller et al. (2007) give for each of the three models pedo- transfer functions from literature to be able to adapt each individual model to given soil conditions. However, determination of variables from pedo-transfer functions is time con- suming as it involves extended laboratory testing. Another approach concerning soil compaction models and the prediction of soil compaction was developed by Diserens and Spiess (2004) (TASC for “Tyre/Tracks and Soil Com- paction”) and is based on the principles of Etienne and Steinmann (2002) who developed a stress distribution model utilizing the approach of Newmark (1940) for stress propagation in the soil. This model is in theory and approach similar to the model from van den Akker (2004) (SOCOMO; described in detail by Ansorge 2005, a), yet it takes a different approach in both calculated pressure distribution and the occurrence of soil compaction. It merely looks at the soil pressure rather than a combined failure criteria as in SOCOMO. Ph.D. Thesis Dirk Ansorge (2007) 93
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Cranfield University School of Appl
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Abstract Ancillary experiments show
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Table of Contents TABLE OF CONTENTS
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Table of Contents 4.1.3 Analysis of
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Table of Contents 11.1.1.1 Comparis
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List of Figures and Tables Figure 3
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List of Figures and Tables Figure 1
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Nomenclature NOMENCLATURE Abbreviat
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Introduction 1 INTRODUCTION 1.1 Bac
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Introduction � Ansorge, D. and Go
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Introduction 1.2 Aim To elucidate t
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Introduction a) the soil compaction
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Experimental Methods 2.1.1.1 Test F
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Experimental Methods had been mount
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Experimental Methods track; the loa
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Experimental Methods 800/10.5/2.5 t
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Experimental Methods term. In the m
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Experimental Methods Soil Surface F
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Experimental Methods Depth (cm) 0 1
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Experimental Methods ence surface c
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Experimental Methods chine derives
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Experimental Methods depth. The dat
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Experimental Methods with water and
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Experimental Methods 2.4 Statistica
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Laboratory Studies Into Undercarria
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Page 57 and 58: Laboratory Studies Into Undercarria
Page 77 and 78: Field Study With Full Size Combine
Page 99 and 100: Alleviation of Soil Compaction Howe
Page 101 and 102: Alleviation of Soil Compaction not
Page 103 and 104: Alleviation of Soil Compaction in a
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Page 107: Soil Compaction Models sibilities t
Page 111 and 112: Soil Compaction Models Wroth (1968)
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Page 123 and 124: Soil Compaction Models ture content
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Page 127 and 128: Soil Compaction Models Predicted In
Page 129 and 130: Soil Compaction Models Depth (mm) -
Page 131 and 132: Soil Compaction Models and 13.7 % b
Page 133 and 134: Soil Compaction Models Rel. Density
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Page 137 and 138: Soil Compaction Models The approach
Page 139 and 140: Soil Compaction Models surface stay
Page 141 and 142: Soil Compaction Models This result
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Page 149 and 150: Soil Compaction Models The response
Page 151 and 152: Soil Compaction Models On medium so
Page 153 and 154: Soil Compaction Models SOILFLEX tak
Page 155 and 156: Ancillary Experiments 7 ANCILLARY E
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Ancillary Experiments In order to c
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Ancillary Experiments contrary, the
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Ancillary Experiments Figure 102: S
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Ancillary Experiments track and the
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Ancillary Experiments even when hav
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Ancillary Experiments 7.3.2 Influen
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Ancillary Experiments The results f
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Ancillary Experiments Figure 117: S
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Ancillary Experiments Contact Press
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Ancillary Experiments Figure 123: F
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Ancillary Experiments Sinkage (mm)
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Ancillary Experiments model which o
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Ancillary Experiments 7.3.5 The Inf
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Ancillary Experiments 7.3.7 Discuss
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Ancillary Experiments Terzaghi (194
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Ancillary Experiments contact area.
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Ancillary Experiments soil forward
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Conclusions � The longitudinal so
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Bibliography 10 BIBLIOGRAPHY Aboaba
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Bibliography Defossez, P., Richard,
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Bibliography Gregory, A.S.; Whalley
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Bibliography Lamande, M., Schjonnin
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Bibliography Seig, D., 1985. Soil C
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Appendix 11 APPENDIX Ph.D. Thesis D
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Appendix Figure 32: VCL sample at t
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Appendix comparison at the deepest
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Appendix Estimated Pressure (kPa) 2
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Appendix 11.1.1.2.1 SOCOMO One of t
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Appendix by Seig (1985) who showed
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Appendix Soil water content 15 % an
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Appendix Adapting critical state so
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Appendix density is obtained by add
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Appendix Table 5: Values of constan
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Appendix choice of a concentration
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Appendix 11.1.3.1 Dense/Hard and Lo
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Appendix 11.1.3.2 Stratified Soil C
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Appendix To summarize the ability t
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Appendix In the following the predi
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Appendix concentration factor of 4,
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Appendix 11.1.5.1 Confining Pressur
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Appendix Figure 24. The VCL created
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Appendix Rel. Density 2 1,9 1,8 1,7
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Appendix relation of � 1 to � 2
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Appendix Rel. Density 2 1,9 1,8 1,7
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Appendix Rel. Density 1,7 1,68 1,66
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Appendix Depth (mm) 0,0 100,0 200,0
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Appendix Figure 42: Plate in cookin
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Appendix � z � � �� k c p
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Appendix Table 8: n and k depending
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Appendix to the plate sinkage equat
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Appendix with a slight deviation fr
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Appendix Table 12: DBD values for a
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