î4% SOIL DYNAMICS in TILLAGE AND TRACTION Agriculture Handbook No. 316 Agricultural Research Service UNITED STATES DEPARTMENT OF AGRICULTURE MBP0000263 SOIL DYNAMICS in TILLAGE AND TRACTION By WILLIAM R. GILL Soil Scientist Agricultural Engineering Research Division and Soil and Water Conservation Research Division GLEN E. VANDEN BERG Agricultural Engineer Agricultural Engineering Research Division Agricultural Research Service UNITED STATES DEPARTMENT OF AGRICULTURE Trade names are used in this publication solely to provide specific information. Mention of a trade name does not constitute a warranty of the product by the U.S. Department of Agriculture or an endorse- ment of the product to the exclusion of other products not mentioned. For sale by the Superintendent of Documents, U.S. Government Printing Office Washin^srton, D.C., 20402 - Price $1.75 (paper cover) Foreword One of the most difficult problems of research workers, teachers, and application engineers in any scientific and technical effort is to obtain all of the existing pertinent knowledge on the specific subject being investigated, taught, or applied. There are at least two approaches to the solution of this problem. One is to develop facilities for the ready retrieval of any publica- tion pertinent to the specific subject. This approach is receiving wide support, and good progress is being made by research and education institutions, professional societies, and libraries in evolving rather effective though often quite sophisticated systems of retrieving information. A second approach is to review, relate, evaluate, and assemble in one volume or set of volumes all significant facts on a specific sub- ject. This is a tedious, time-consummg activity, which requires broad understanding and great skill. However, if well done, such reviews are of great value to the scientific community. In fact, for the progress of any discipline, periodic reviews of this type are an essential supplement to even the best information retrieval system. They serve as mileposts along the highway of knowledge. SOIL DYNAMICS IN TILLAGE AND TRACTION is such a milepost. EUGENE G. MCKIBBEN, Director Agricultural Engineering Research Division Agricultural Research Service U.S. Department of Agriculture Preface Soil dynamics is defined as the branch of knowledge that con- siders the motion of soil. Soil movement results from man's attempts (1) to change prevailing soil conditions to those that are more suit- able or (2) to use soil for support and locomotion of vehicles. The scope of soil dynamics thus includes soil-machine relations in both tillage and traction. It is not restricted to agricultural soils and problems since information on basic soil behavior is universally applicable. The tremendous amount of earth construction and land forming throughout the world has made machine handling of soil increasingly important in construction, military, and mining operations. The final applications of soil dynamics knowledge may differ, but the principles are independent of application. This handbook is an attempt to convey both definitive and practical information concerning soil dynamics to persons interested in tillage and traction. The information has been brought together and de- veloped in conjunction with the research program of the National Tillage Machinery Laboratory, Auburn, Ala. This is a handbook of ideas and concepts rather than methods or procedures. The ideas stem from an attempt to w^eld a comprehen- sive organization of isolated bits of information into a coherent body of knowledge that is designated soil dynamics. An attempt has been made to be analytical as well as descriptive so that the significance of data in the literature can be established. Where possible, mathe- matical treatment has been developed in quantitative terms to express specific soil-machine relations on the assumption that these relations must obey fundamental laws. Basic forms of soil behavior such as shear failure and sliding fric- tion have been identified and quantitatively described by behavior equations. Principles by which subordinate behaviors can be isolated and quantitatively described are suggested. Definitive parameters are inherent in each basic equation that describes a soil behavior. These parameters, when identified and evaluated, provide a basis for characterizing soil with regard to its movement behavior. The feasibility of combining behavior equations into a simple soil- machine mechanics is demonstrated. The procedure by which a com- plete mechanics can be developed is described. Such a mechanics is capable of describing and predicting the action of machines in terms of performance. Criteria of performance are proposed and defined. An evaluation of these criteria provides a basis for the design of machines whose actions can be controlled and optimized. Since only rudimentary behavior equations and soil-machine me- chanics are available today, a sound theoretical basis for designing soil tillage and traction machines does not exist. In the absence of theoretical approaches, empirically established equations are proposed PREFACE as practical alternates. When properly developed, these equations will provide information for designing soil tillage and traction machines. The information will also contribute to the development of a rigorous theoretical mechanics. No attempt has been made to solve problems; rather it is estab- lished that soil dynamics provides a fundamental approach for so doing. This handbook has attempted to develop soil dynamics in depth, scope, and extent so that it defines and delineates an area of knowledge that will be a new discipline. Eesearch goals have been suggested which should provide the information required to solve most problems in soil dynamics. Acknowledgment is made to A. W. Cooper, W. F. McCreery, M. L. Nichols, C. A. Eeaves, and I. F. Eeed, who are members of the National Tillage Machinery Laboratory staff, for assistance during the preparation and review of the handbook. Special acknowledgment is made to E. G. McKibben, W. M. Carleton, L. A. Liljedahl, and S. W. McBirney of the Agricultural Engineering Eesearch Division, Beltsville, Md., for their encourage- ment and support of the project. Acknowledgment is made to technical reviewers who are not mem- bers of the National Tillage Machinery Laboratory Staff. They are : W. F. Buchele, Agricultural Engineering Department, Iowa State University ; L. O. Drew and T. H. Garner, Agricultural Engineering Department, Clemson University; J. G. Hendrick, Department of Agricultural Engineering, Auburn University; L. Johnson, Agricul- tural Engineering Department, International Eice Eesearch Insti- tute; S. Persson, Agricultural Engineering Department, Michigan State University; J. A. Weber, Department of Agricultural Engi- neering, University of Illinois; J. L. Dais, D. N. Koppes, N. Osifchm, A. G. Vedejs, G. F. Weissmann, E. N. White and W. W. Wood, members of the technical staff. Bell Telephone Laboratories. Contents 1. INTRODUCTION 1 1.1 Historical 1 1.2 Soil Dynamics 3 1.3 Research Centers 5 1.3.1 The National Tillage Machinery I^aboratory, Auburn, Ala. 6 1.3.2 The Army Mobility Research Center, Vicksburg, Miss. 7 1.3.3 The Land Locomotion Laboratory, Warren, Mich. 8 1.3.4 The National Institute of Agricultural Engineering, Silsoe, England 8 1.3.5 Institute of Fundamental Research in Agricultural Engineering, Volkenrode, Germany 10 1.3.6 Institute for Agricultural Mechanization, Konosu, Japan 11 1.3.7 Other Research Centers 11 2. DYNAMIC PROPERTIES OF SOILS 14 2.1 Introduction 14 2.2 Stress in Soil 14 2.3 Strain in Soil 17 2.4 Stress-Strain Relations __ _ Z_~ZI 20 2.5 Soil Strength '___ 22 2.6 Stress Distribution _~II_ II_ 23 2.7 Strain Distribution _ _ _ _ _~~~___I"_" ..29 2.8 Yield in Soil __ I" __"_'_ __ "_""!""" 31 2.8.1 Shear IIII—II-"_-I_-I__II_I_._"_I 32 2.8.2 Compression __ 36 2.8.3 Tension _ _ _ ~~ ___ 37 2.8.4 Plastic Flow I_ _""" _ 39 2.9 Rigid Body Soil Movement I__I_ZIII_I 39 2.9.1 Momentum ~~ "~ Z"Jl ~ 40 2.9.2 Friction IIIIIIII_IIII__I__ _ 40 2.9.3 Adhesion IIIIIII_I_ZI_"~II_I 42 2.9.4 Abrasion II_I~I~II II __"_ II 52 2.10 Dynamic Versus Static Properties ___I__I_I_ I_ I "_"_" _"_I_ 53 3. ASSESSMENT OF THE DYNAMIC PROPERTIES OF SOIL" "___ 55 3.1 Soil as a Physical System _ _ 55 3.2 Dynamic Parameters I" I I H "I QQ 3.2.1 Measuring Independent Parameters _I __~ _ _ ~~ 65 3.2.1.1 Shear __II I_~II aí 3.2.1.2 Tension IIIIIII Z.Jl.JlJl^ 74 3.2.1.3 Compression __ __ _ _ CA 3.2.1.4 Plastic Flow __"_ öQ 3.2.1.5 Friction I_ 22 3.2.1.6 Adhesion I-I-I'III _"~_'r_~~rri 89 3.2.2 Measuring Composite Parameters QQ 3.2.2.1 Penetration _ _ _ 04 3.2.2.2. Bearing Strength 3.2.2.3 Induced Strength ___ _ __ _ _ 100 3.3 Measuring Gross Dynamic Behavior 1X9 3.3.1 Rupture ~""~_ IAQ 3.3.2 Blast Erosion i}t¿ 3.3.3 Abrasion I ,XQ 3.3.4 Movement -"""IIIHIIIIIIIIIIIIIII—I—I 113 VI CONTENTS Vil 4. MECHANICS OF TILLAGE TOOLS 117 4.1 Introduction }}! 4.2 The Reaction of Soil to Tillage Tools li¿ 4.2.1 Principles for Developing a Mechanics ll» 4.2.2 The Complete Soil-Tillage Tool Mechanics 122 4.3 Mechanics of Simple Reactions 125 4.3.1 Inclined Tools 1^^ 4.3.2 Vertical Tools 1^^ 4.3.3 Cutting of Soil 14« 4.3.4 Conclusions l^jj 4.4 Soil Behavior in Simplified Systems l^Y 4.4.1 Soil-Metal Sliding 161 4.4.1.1 Measurement of Sliding Actions loi 4.4.1.2 The Sliding Path 170 4.4.1.3 Mechanics for Draft Force of Sliding Actions 171 4.4.1.4 Scouring ^— 176 4.4.2 Penetration 181 4.5 Geometry of Soil-Tool Systems 191 4.5.1 Alteration of Tool Geometry by the Formation and Adherence of Soil Bodies 192 4.5.2 Alteration of Tool Geometry Because of Wear 194 4.5.3 Soil-Tool Geometry 198 4.5.4 Orientation of the Soil-Tool System 205 4.5.5 Geometry of Interacting Tools 207 4.5.6 Conclusions 208 4.6 Mechanics of Complex Reactions 209 5.