Soil structure

About: Soil structure is a research topic. Over the lifetime, 9872 publications have been published within this topic receiving 303604 citations.

Stabilization mechanisms of soil organic matter: Implications for C-saturation of soils

Abstract: The relationship between soil structure and the ability of soil to stabilize soil organic matter (SOM) is a key element in soil C dynamics that has either been overlooked or treated in a cursory fashion when developing SOM models. The purpose of this paper is to review current knowledge of SOM dynamics within the framework of a newly proposed soil C saturation concept. Initially, we distinguish SOM that is protected against decomposition by various mechanisms from that which is not protected from decomposition. Methods of quantification and characteristics of three SOM pools defined as protected are discussed. Soil organic matter can be: (1) physically stabilized, or protected from decomposition, through microaggregation, or (2) intimate association with silt and clay particles, and (3) can be biochemically stabilized through the formation of recalcitrant SOM compounds. In addition to behavior of each SOM pool, we discuss implications of changes in land management on processes by which SOM compounds undergo protection and release. The characteristics and responses to changes in land use or land management are described for the light fraction (LF) and particulate organic matter (POM). We defined the LF and POM not occluded within microaggregates (53–250 μm sized aggregates as unprotected. Our conclusions are illustrated in a new conceptual SOM model that differs from most SOM models in that the model state variables are measurable SOM pools. We suggest that physicochemical characteristics inherent to soils define the maximum protective capacity of these pools, which limits increases in SOM (i.e. C sequestration) with increased organic residue inputs.

Fundamentals of soil behavior

Abstract: The book is intended to develop an understanding of the factors determining and controlling the engineering properties of soil, the factors controlling their magnitude, and the influences of environment and time. The two-part book contains the following chapters: Part 1 - the nature of soils; bonding, crystal structure and surface characteristics; soil mineralogy; soil formation and soil deposits; determination of soil composition; soil water; clay-water-electrolyte system; soil fabric and its measurement; Part 2 - soil behavior; soil composition and engineering properties; effective, intergranular and total stress; soil structure and its stability; fabric, structure and property relationships, volume change behavior; strength and deformation behavior; and, conduction phenomena. /TRRL/

A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics

Abstract: Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro- and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information.

Fundamentals of soil behavior

Abstract: Preface. CHAPTER 1: INTRODUCTION. 1.1 Soil Behavior in Civil and Environmental Engineering. 1.2 Scope and Organization. 1.3 Getting Started. CHAPTER 2: SOIL FORMATION. 2.1 Introduction. 2.2 The Earth's Crust. 2.3 Geologic Cycle and Geological Time. 2.4 Rock and Mineral Stability. 2.5 Weathering. 2.6 Origin of Clay Minerals and Clay Genesis. 2.7 Soil Profiles and Their Development. 2.8 Sediment Erosion, Transport, and Deposition. 2.9 Postdepositional Changes in Sediments. 2.10 Concluding Comments. Questions and Problems. CHAPTER 3: SOIL MINERALOGY. 3.1 Importance of Soil Mineralogy in Geotechnical Engineering. 3.2 Atomic Structure. 3.3 Interatomic Bonding. 3.4 Secondary Bonds. 3.5 Crystals and Their Properties. 3.6 Crystal Notation. 3.7 Factors Controlling Crystal Structures. 3.8 Silicate Crystals. 3.9 Surfaces. 3.10 Gravel, Sand, and Silt Particles. 3.11 Soil Minerals and Materials Formed by Biogenic and Geochemical Processes. 3.12 Summary of Nonclay Mineral Characteristics. 3.13 Structural Units of the Layer Silicates. 3.14 Synthesis Pattern and Classification of the Clay Minerals. 3.15 Intersheet and Interlayer Bonding in the Clay Minerals. 3.16 The 1:1 Minerals. 3.17 Smectite Minerals. 3.18 Micalike Clay Minerals. 3.19 Other Clay Minerals. 3.20 Summary of Clay Mineral Characteristics. 3.21 Determination of Soil Composition. 3.22 X-ray Diffraction Analysis. 3.23 Other Methods for Compositional Analysis. 3.24 Quantitative Estimation of Soil Components. 3.25 Concluding Comments. Questions and Problems. CHAPTER 4: SOIL COMPOSITION AND ENGINEERING PROPERTIES. 4.1 Introduction. 4.2 Approaches to the Study of Composition and Property Interrelationships. 4.3 Engineering Properties of Granular Soils. 4.4 Dominating Influence of the Clay Phase. 4.5 Atterberg Limits. 4.6 Activity. 4.7 Influences of Exchangeable Cations and pH. 4.8 Engineering Properties of Clay Minerals. 4.9 Effects of Organic Matter. 4.10 Concluding Comments. Questions and Problems. CHAPTER 5: SOIL FABRIC AND ITS MEASUREMENT. 5.1 Introduction. 5.2 Definitions of Fabrics and Fabric Elements. 5.3 Single-Grain Fabrics. 5.4 Contact Force Characterization Using Photoelasticity. 5.5 Multigrain Fabrics. 5.6 Voids and Their Distribution. 5.7 Sample Acquisition and Preparation for Fabric Analysis. 5.8 Methods for Fabric Study. 5.9 Pore Size Distribution Analysis. 5.10 Indirect Methods for Fabric Characterization. 5.11 Concluding Comments. Questions and Problems. CHAPTER 6: SOIL-WATER-CHEMICAL INTERACTIONS. 6.1 Introduction. 6.2 Nature of Ice and Water. 6.3 Influence of Dissolved Ions on Water. 6.4 Mechanisms of Soil-Water Interaction. 6.5 Structure and Properties of Adsorbed Water. 6.6 Clay-Water-Electrolyte System. 6.7 Ion Distributions in Clay-Water Systems. 6.8 Elements of Double-Layer Theory. 6.9 Influences of System Variables on the Double Layer. 6.10 Limitations of the Gouy-Chapman Diffuse Double Layer Model. 6.11 Energy and Force of Repulsion. 6.12 Long-Range Attraction. 6.13 Net Energy of Interaction. 6.14 Cation Exchange-General Considerations. 6.15 Theories for Ion Exchange. 6.16 Soil-Inorganic Chemical Interactions. 6.17 Clay-Organic Chemical Interactions. 6.18 Concluding Comments. Questions and Problems. CHAPTER 7: EFFECTIVE, INTERGRANULAR, AND TOTAL STRESS. 7.1 Introduction. 7.2 Principle of Effective Stress. 7.3 Force Distributions in a Particulate System. 7.4 Interparticle Forces. 7.5 Intergranular Pressure. 7.6 Water Pressures and Potentials. 7.7 Water Pressure Equilibrium in Soil. 7.8 Measurement of Pore Pressures in Soils. 7.9 Effective and Intergranular Pressure. 7.10 Assessment of Terzaghi's Equation. 7.11 Water-Air Interactions in Soils. 7.12 Effective Stress in Unsaturated Soils. 7.13 Concluding Comments. Questions and Problems. CHAPTER 8: SOIL DEPOSITS-THEIR FORMATION, STRUCTURE, GEOTECHNICAL PROPERTIES, AND STABILITY. 8.1 Introduction. 8.2 Structure Development. 8.3 Residual Soils. 8.4 Surficial Residual Soils and Taxonomy. 8.5 Terrestrial Deposits. 8.6 Mixed Continental and Marine Deposits. 8.7 Marine Deposits. 8.8 Chemical and Biological Deposits. 8.9 Fabric, Structure, and Property Relationships: General Considerations. 8.10 Soil Fabric and Property Anisotropy. 8.11 Sand Fabric and Liquefaction. 8.12 Sensitivity and Its Causes. 8.13 Property Interrelationships in Sensitive Clays. 8.14 Dispersive Clays. 8.15 Slaking. 8.16 Collapsing Soils and Swelling Soils. 8.17 Hard Soils and Soft Rocks. 8.18 Concluding Comments. Questions and Problems. CHAPTER 9: CONDUCTION PHENOMENA. 9.1 Introduction. 9.2 Flow Laws and Interrelationships. 9.3 Hydraulic Conductivity. 9.4 Flows Through Unsaturated Soils. 9.5 Thermal Conductivity. 9.6 Electrical Conductivity. 9.7 Diffusion. 9.8 Typical Ranges of Flow Parameters. 9.9 Simultaneous Flows of Water, Current, and Salts Through Soil-Coupled Flows. 9.10 Quantification of Coupled Flows. 9.11 Simultaneous Flows of Water, Current, and Chemicals. 9.12 Electrokinetic Phenomena. 9.13 Transport Coefficients and the Importance of Coupled Flows. 9.14 Compatibility-Effects of Chemical Flows on Properties. 9.15 Electroosmosis. 9.16 Electroosmosis Efficiency. 9.17 Consolidation by Electroosmosis. 9.18 Electrochemical Effects. 9.19 Electrokinetic Remediation. 9.20 Self-Potentials. 9.21 Thermally Driven Moisture Flows. 9.22 Ground Freezing. 9.23 Concluding Comments. Questions and Problems. CHAPTER 10: VOLUME CHANGE BEHAVIOR. 10.1 Introduction. 10.2 General Volume Change Behavior of Soils. 10.3 Preconsolidation Pressure. 10.4 Factors Controlling Resistance to Volume Change. 10.5 Physical Interactions in Volume Change. 10.6 Fabric, Structure, and Volume Change. 10.7 Osmotic Pressure and Water Adsorption Influences on Compression and Swelling. 10.8 Influences of Mineralogical Detail in Soil Expansion. 10.9 Consolidation. 10.10 Secondary Compression. 10.11 In Situ Horizontal Stress (K 0 ). 10.12 Temperature-Volume Relationships. 10.13 Concluding Comments. Questions and Problems. CHAPTER 11 STRENGTH AND DEFORMATION BEHAVIOR. 11.1 Introduction. 11.2 General Characteristics of Strength and Deformation. 11.3 Fabric, Structure, and Strength. 11.4 Friction Between Solid Surfaces. 11.5 Frictional Behavior of Minerals. 11.6 Physical Interactions Among Particles. 11.7 Critical State: A Useful Reference Condition. 11.8 Strength Parameters for Sands. 11.9 Strength Parameters for Clays. 11.10 Behavior After Peak and Strain Localization. 11.11 Residual State and Residual Strength. 11.12 Intermediate Stress Effects and Anisotropy. 11.13 Resistance to Cyclic Loading and Liquefaction. 11.14 Strength of Mixed Soils. 11.15 Cohesion. 11.16 Fracturing of Soils. 11.17 Deformation Characteristics. 11.18 Linear Elastic Stiffness. 11.19 Transition from Elastic to Plastic States. 11.20 Plastic Deformation. 11.21 Temperature Effects. 11.22 Concluding Comments. Questions and Problems. CHAPTER 12: TIME EFFECTS ON STRENGTH AND DEFORMATION. 12.1 Introduction. 12.2 General Characteristics. 12.3 Time-Dependent Deformation-Structure Interaction. 12.4 Soil Deformation as a Rate Process. 12.5 Bonding, Effective Stresses, and Strength. 12.6 Shearing Resistance as a Rate Process. 12.7 Creep and Stress Relaxation. 12.8 Rate Effects on Stress-Strain Relationships. 12.9 Modeling of Stress-Strain-Time Behavior. 12.10 Creep Rupture. 12.11 Sand Aging Effects and Their Significance. 12.12 Mechanical Processes of Aging. 12.13 Chemical Processes of Aging. 12.14 Concluding Comments. Questions and Problems. List of Symbols. References. Index.