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Soil Compaction Models The approach of Etienne and Steinmann (2002) was empirically developed using Bolling pressure probes. Soil stresses were measured at three depths and compared to the predicted results from 5 different approaches; three types of Söhne (1953) each with a different concentration factor, a combined Boussinesq and Froehlich approach, and the Newmark (1940) model. The approach by Newmark (1940) only differs by the concentration factor from Söhne (1953) as Newmark (1940) always assumes a concentration factor of 2. Stress propagation in the soil is determined using the Newmark (1940) approach as it showed the closest agreement between measured and predicted values. However, the stress decrease at the surface was larger than predicted; therefore a variable in addition to soil type and working depth was introduced determining stress decrease in the topsoil. This variable depends on the surface soil strength because stress decrease is smaller with depth for a stronger soil. This is the only input variable concerning soil conditions and is determined with a screw driver. Depending on the force necessary to push the screw driver into the soil, the soil can be qualified in soft, medium, and hard. This basic principle was extended into a model by Dieserens and Spiess (2004). It contains nearly all common agricultural and forestry tyres and tracks as input options whereby contact pressure data is stored within the model. Once the tyre or track option is selected, only load, inflation pressure, working depth, and the strength of the topsoil determined with the screwdriver test have to be entered. The model then determines the pressure distribution in the soil and states if there is a danger of subsoil compaction or not. If the pressure decreases to less than 1 MPa within the working depth, the model implies no danger of subsoil compaction, but if the pressure is higher than 1 MPa below the working depth, it assumes subsoil compaction. Additionally pressure bulbs and maximum pressure over depth curves are given. The model can compare up to four different tyre or track systems in one analysis. A great advantage of TASC is its user friendliness when compared to SOCOMO which gives similar outputs. In contrast to the models SOCOMO and TASC, COMPSOIL is able to quantify the soil density increase rather than simply stating a danger of soil compaction for given loads and inflation pressures. 6.1.3 Approaches to derive Critical State Parameters and the Influence of Water For the critical state soil mechanics model e.g. for COMPSOIL the slope and intercept of the VCL have to be determined. Following the traditional approach from Schofield and Ph.D. Thesis Dirk Ansorge (2007) 94
Soil Compaction Models Wroth (1968) critical state parameters are usually obtained from triaxial cell tests. A de- scription of the procedure can be found by Leeson and Campbell (1983). However, multiple tests are necessary which are rather time consuming. Improving this Kirby et al. (1998) derive all critical state soil mechanics parameters from one constant cell volume triaxial test. Kirby (1998) developed a further method to estimate all critical state soil mechanics parameters from shear box tests. This, however, requires multiple testing, but is less time consuming than conducting triaxial tests. Gregory et al. (2006) calculated the slope of the virgin compression line and the precom- pression stress from compression test data and show that the accuracy of the prediction of the parameters increases when the clay content increases. A totally different approach is taken by Gurtug and Sridgaran (2002), who, “out of coinci- dence” obtained compaction characteristics of soils from plastic limit tests for fine grained soils. The plastic limit test can even be reproduced if the procedure is carefully followed. However, as the following authors stated, there are differences between triaxial measurements and field conditions. Jakobsen and Dexter (1989) point out that due to the shorter loading time soil is not completely compacted in the field and consequently, the field parameters can not be readily derived from measurements in the laboratory from samples of small size. Roscoe (1970) comes to the same conclusion that the laboratory measurements do not represent real field conditions. Hence deriving a methodology to gain them from tyre passes and quantifying the difference to triaxially gained parameters is even more im- portant. Chi et al. (1993) analyse the prediction behaviour of elasto plastic models and critical state soil mechanics models and derive the conclusion that the main source of error in prediction is the variability of soil physical properties among samples. This emphasizes the advantage of an infield determination of necessary variables as sample size increases tremendously when taking the ruts of machines in consideration compared to small samples fitting into triaxial cells which can differ from each other and no true replication of field conditions is possible as stated by Roscoe (1970) and Jakobsen and Dexter (1989). The moisture content influences both, stress concept and critical state parameters. The work by Jennings and Burland (1962) indicates that it is not the total effective stress which controls the behaviour of partially saturated soils, it is rather the sum of the stress and wa- Ph.D. Thesis Dirk Ansorge (2007) 95
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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 59 and 60: 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 and 108: Soil Compaction Models sibilities t
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Page 123 and 124: Soil Compaction Models ture content
Page 125 and 126: Soil Compaction Models with four ot
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
Page 135 and 136: Soil Compaction Models VCL paramete
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 145 and 146: Soil Compaction Models σσ 1 (kPA)
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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
Page 157 and 158: Ancillary Experiments Average conta
Page 159 and 160: 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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