Compared with forces occurring in soil mechanics problems in civil engineering, the forces that are applied to soil in farming operations generally have a short duration, less than a few seconds, a small loaded area, no more than a few square decimeters, and small intensities, 10 bar being a high value. On the other hand, soil properties vary widely between those of a weak mud and a stone-like dry soil. Tillage and related applications of force to soil are practiced worldwide in farming. Tillage operations are performed on one hectare of land for every three human beings. This means that for the food production for each individual daily, something like one cubic meter of soil is stirred, or about 20 times his body weight. Theoretical knowledge of this most common human activity, which largely determines the surface shape of the fertile part of the earth, is still very limited. In this book the authors have tried to give an outline of the present state of the art. One of the starting points was a course in soil dynamics taught by the authors at the Agricultural University at Wageningen, The Netherlands. We hope to reach interested readers who have no more theoretical knowledge than high school level, as well as readers who want to go beyond the level of a third year university student. For the chapter on wheels and tires we received substantial support from F. G. J. Tijink of the Tillage Laboratory at Wageningen.

Inhalt

1 Soil Conditions.- 1.1 Strength-Determining Factors.- 1.2 Variation of Strength-Determining Factors in the Course of Time.- 1.3 Influences of Soil Type on Strength-Determining Factors.- 1.4 Soil Prepared for Laboratory Experiments.- 2 Mechanical Behavior of Soil Elements.- 2.1 General Aspects of the Mechanical Behavior of Soil Elements.- 2.1.1 Small Volume Elements Instead of Large Soil Bodies.- 2.1.2 Stress Theory.- 2.1.2.1 Stress Tensor.- 2.1.2.2 Mohr's Graphical Representation.- 2.1.2.3 Uniform Stress Distribution in Finite Soil Bodies.- 2.1.3 Strain Theory.- 2.1.4 Stress-Strain Relations.- 2.2 Elemental Treatment of Compaction.- 2.2.1 Occurrence of Compaction.- 2.2.2 Fundamentals.- 2.2.2.1 Measures of Compaction.- 2.2.2.2 General Model for Rapid Soil Compaction.- 2.2.2.3 Effects of Loading Rate, Repeated Loading, and Vibrations.- 2.2.2.4 Soil Physical Aspects.- 2.2.2.5 Slow Compression.- 2.2.3 Applications.- 2.2.3.1 Estimation of Soil Compaction by Means of Estimated Stress Distributions.- 2.2.3.2 Curve Fitting Formulas for Compression Tests.- 2.2.3.3 Håkansson's Compaction Test.- 2.2.3.4 Simulating Tire Effect by a Uni-Axial Compression Test.- 2.2.3.5 Predicting Soil Density Following Irrigation.- 2.2.3.6 Complexity of Compactibility Concept.- 2.3 Elemental Treatment of Deformation (Distortion).- 2.3.1 Occurrence of Distortional Strain.- 2.3.2 Fundamentals.- 2.3.2.1 Introduction.- 2.3.2.2 Deformation at Constant Volume.- 2.3.2.3 Distortion Combined with Compaction.- 2.3.2.4 Expansion at Breaking.- 2.3.3 Applications.- 2.3.3.1 Stress-Deformation Models.- 2.3.3.2 Determination of the Liquid Limit with a Rotary Viscosimeter.- 2.3.3.3 Distortion Combined with Compaction, Estimated Using the Flow Rule.- 2.3.3.4 Estimation of Distortion Combined with Compaction for Sand.- 2.4 Elemental Treatment of Breaking.- 2.4.1 Occurrence of Breaking.- 2.4.2 Fundamentals.- 2.4.2.1 Measures of Resistance Against Breaking.- 2.4.2.2 Shear Failure.- 2.4.2.3 Tensile Failure.- 2.4.2.4 Loading Rate and Repeated Loading Effects..- 2.4.2.5 Soil Physical Aspects of Shear Strength.- 2.4.3 Applications.- 2.4.3.1 Methods to Determine the Measures of Strength Indirectly.- 2.4.3.2 A Few Applications of the Modulus of Rupture.- 2.4.3.3 Draft Calculations Using Hypothesized Mechanisms of Rigid Soil Bodies.- 2.4.3.4 The Influence of Moisture Content at Seedbed Preparation on Plowing Resistance After Harvest.- 2.5 Elemental Treatment of Soil-Material Friction and Adherence.- 2.5.1 Occurrence.- 2.5.2 Fundamentals.- 2.5.3 Applications.- 2.5.3.1 The ?n-?1 Ratio of a Soil Element at a Soil-Material Interface.- 2.5.3.2 Attempts to Reduce Soil-Material Friction and Soil Adherence.- 3 Load Bearing and Soil Loosening Processes.- 3.1 General Aspects of Processes.- 3.1.1 Soil Tillage Processes Instead of Element Behavior..- 3.1.2 Description of the Variation of Forces and Movements in a Soil Tillage Process.- 3.1.2.1 Velocity Fields.- 3.1.2.2 Strain Fields.- 3.1.2.3 Stress Fields.- 3.1.2.4 Process Variations in Time.- 3.1.3 Basic Process Conditions.- 3.1.4 Prediction of Forces and Movements in Processes.- 3.1.4.1 Prediction Methods Mainly Based on Observations of Relationships Between Independent and Dependent Variables.- 3.1.4.2 Prediction Methods Mainly Based on Knowledge of the Mechanism of the Process Under Consideration.- 3.1.5 Types of Processes.- 3.2 Rollers, Wheels, and Tires.- 3.2.1 Occurrence.- 3.2.2 Fundamentals.- 3.2.2.1 Kinematic Aspects of Rolling Elements.- 3.2.2.2 Dynamic Aspects of Rolling Elements.- 3.2.2.3 Systems of Rollers, Wheels, and/or Tires.- 3.2.3 Applications.- 3.2.3.1 Estimating the Pull a Tire is Able to Develop.- 3.2.3.2 Estimation of the Mean Contact Stress of a Deflected Tire on a Rigid Surface.- 3.2.3.3 Estimation of the Area of Contact Between a Tire and a Rigid Surface.- 3.2.3.4 Relative Tire Deflection at Maximum Load.- 3.2.3.5 Optimal Slip Percentage.- 3.3 Penetrating Bodies (Wedges, Cones, Plates, Wires, Spheres).- 3.3.1 Occurrence.- 3.3.2 Fundamentals.- 3.3.2.1 Kinematic Aspects.- 3.3.2.2 Dynamic Aspects.- 3.3.3 Applications.- 3.3.3.1 Fitting Formulas for Plate Tests.- 3.3.3.2 Bekker's Sinkage and Rolling-Resistance Theory for Rigid Wheels.- 3.3.3.3 Correlations Between Cone Tests and Wheel Performance.- 3.3.3.4 Quick Determination of a Soil Mechanical or Physical Property.- 3.3.3.5 Determination of the Maximum Normal Stress That Has Ever Acted on a Soil Surface.- 3.3.3.6 Other Applications of Penetrometers.- 3.4 Sliding and Shearing Bodies.- 3.4.1 Occurrence.- 3.4.2 Fundamentals.- 3.4.2.1 Kinematic Aspects.- 3.4.2.2 Dynamic Aspects.- 3.4.3 Applications.- 3.4.3.1 Fitting Formulas for Shear Force-Horizontal Displacement Relationships.- 3.4.3.2 Resistance Approximations for Sliding and Shearing Bodies.- 3.4.3.3 Pull-Slip Relationships for Spaced-Link Tracks.- 3.4.3.4 Estimation of Rut Depth and/or Trim Angle of a Sled.- 3.4.3.5 Estimating c and ø Using Shear Plates or Annuli.- 3.4.3.6 Wall Friction of Cone Penetrometer Rods.- 3.5 Tracks, Cage Rollers, and Cage Wheels.- 3.5.1 Occurrence.- 3.5.1.1 Tracks.- 3.5.1.2 Cage Rollers.- 3.5.1.3 Cage Wheels.- 3.5.2 Fundamentals.- 3.5.2.1 Kinematic Aspects.- 3.5.2.2 Dynamic Aspects.- 3.5.3 Applications.- 3.5.3.1 Estimation of the Maximum Stress in the Contact Area of a Track on Soil.- 3.6 Tines.- 3.6.1 Occurrence.- 3.6.2 Fundamentals.- 3.6.2.1 Kinematic Aspects.- 3.6.2.2 Dynamic Aspects.- 3.6.3 Applications.- 3.6.3.1 The Profile of a Furrow Made by a Tine.- 3.6.3.2 Draft of Plane Blades and Tines Operating in a Saturated Clay.- 3.7 Plow Bodies.- 3.7.1 Occurrence.- 3.7.2 Fundamentals.- 3.7.2.1 Kinematic Aspects of Two-Dimensional, Curved Blade with a Small Cutting Angle and a Small Working Depth/Blade Height Ratio.- 3.7.2.2 Kinematic Aspects of Other Plow Bodies.- 3.7.2.3 Dynamic Aspects.- 3.7.3 Applications.- 3.7.3.1 Plowing Draft as Affected by Soil Moisture Content.- 3.7.3.2 Plowing Draft as Affected by Speed.- 3.7.3.3 Draft Force as Affected by Slades, Supporting Wheels, and Inclined Directions of Pull.- 3.7.3.4 Predicting Type of Intake from Unconfined Compression Tests.- Mathematical Treatment of Finite Homogeneous Strains in Two Dimensions.- References.