William J. Likos is Assistant Professor of Civil and Environmental Engineering at the University of Missouri-Columbia, where he teaches courses in soil mechanics and soil behavior.

A thorough and unique introduction to the fundamental principles of unsaturated soil mechanics Through a principles-based approach, Unsaturated Soil Mechanics provides a thorough grounding in unsaturated soil mechanics principles and phenomena from three fundamental perspectives: thermodynamics, mechanics, and hydrology. In a progressive and interrelated format with logic, physical reasoning, and mathematical rigor, Unsaturated Soil Mechanics examines the fundamental principles of unsaturated soil mechanics, illustrates the application of these principles to stress and flow phenomena in unsaturated soil, and demonstrates and evaluates the measurement and modeling techniques commonly used to quantify the state and material variables required to describe these stress and flow phenomena. Unsaturated Soil Mechanics offers one focused volume uniting the microscopic physical basis and the macroscopic thermodynamic framework for pore water retention and the state of stress in unsaturated soil. Complete with extensive sample problems, this accessible text brings together the rapid advances in research in unsaturated soil mechanics, including advances in the applicability of effective stress, liquid and gas flows, and suction and hydraulic conductivity measurement. Unsaturated Soil Mechanics is an invaluable introduction to this emerging field for students in civil engineering, environmental engineering, soil science, groundwater hydrology, and geoscience, as well as an inclusive reference for professional geotechnical engineers, soil scientists, geologists, and structural engineers.

FOREWORD. PREFACE. SYMBOLS. INTRODUCTION.

1 STATE OF UNSATURATED SOIL. 1.1 Unsaturated Soil Phenomena. 1.1.1 Definition of Unsaturated Soil Mechanics. 1.1.2 Interdisciplinary Nature of Unsaturated Soil Mechanics. 1.1.3 Classification of Unsaturated Soil Phenomena. 1.2 Scope and Organization of Book. 1.2.1 Chapter Structure. 1.2.2 Geomechanics and Geo-environmental Tracks. 1.3 Unsaturated Soil in Nature and Practice. 1.3.1 Unsaturated Soil in Hydrologic Cycle. 1.3.2 Global Extent of Climatic Factors. 1.3.3 Unsaturated Zone and Soil Formation. 1.3.4 Unsaturated Soil in Engineering Practice. 1.4 Moisture, Pore Pressure, and Stress Profiles. 1.4.1 Stress in the Unsaturated State. 1.4.2 Saturated Moisture and Stress Profiles: Conceptual Illustration. 1.4.3 Unsaturated Moisture and Stress Profiles: Conceptual Illustration. 1.4.4 Illustrative Stress Analysis. 1.5 State Variables, Material Variables, and Constitutive Laws. 1.5.1 Phenomena Prediction. 1.5.2 Head as a State Variable. 1.5.3 Effective Stress as a State Variable. 1.5.4 Net Normal Stresses as State Variables. 1.6 Suction and Potential of Soil Water. 1.6.1 Total Soil Suction. 1.6.2 Pore Water Potential. 1.6.3 Units of Soil Suction. 1.6.4 Suction Regimes and the Soil-Water Characteristic Curve. Problems. I FUNDAMENTAL PRINCIPLES.

2 MATERIAL VARIABLES. 2.1 Physical Properties of Air and Water. 2.1.1 Unsaturated Soil as a Multiphase System. 2.1.2 Density of Dry Air. 2.1.3 Density of Water. 2.1.4 Viscosity of Air and Water. 2.1.5 Flow Regimes. 2.2 Partial Pressure and Relative Humidity. 2.2.1 Relative Humidity in Unsaturated Soil Mechanics. 2.2.2 Composition and Partial Pressure of Air. 2.2.3 Equilibrium between Free Water and Air. 2.2.4 Equilibrium between Pore Water and Air. 2.2.5 Relative Humidity. 2.2.6 Dew Point. 2.3 Density of Moist Air. 2.3.1 Effect of Water Vapor on Density of Air. 2.3.2 Formulation for Moist Air Density. 2.4 Surface Tension. 2.4.1 Origin of Surface Tension. 2.4.2 Pressure Drop across an Air-Water Interface. 2.5 Cavitation of Water. 2.5.1 Cavitation and Boiling. 2.5.2 Hydrostatic Atmospheric Pressure. 2.5.3 Cavitation Pressure. Problems.

3 INTERFACIAL EQUILIBRIUM. 3.1 Solubility of Air in Water. 3.1.1 Henry's Law. 3.1.2 Temperature Dependence. 3.1.3 Volumetric Coefficient of Solubility. 3.1.4 Henry's Law Constant and Volumetric Coefficient of Solubility. 3.1.5 Vapor Component Correction. 3.1.6 Mass Coefficient of Solubility. 3.2 Air-Water-Solid Interface. 3.2.1 Equilibrium between Two Water Drops. 3.2.2 Equilibrium at an Air-Water-Solid Interface. 3.2.3 Contact Angle. 3.2.4 Air-Water-Solid Interface in Unsaturated Soil. 3.3 Vapor Pressure Lowering. 3.3.1 Implications of Kelvin's Equation. 3.3.2 Derivation of Kelvin's Equation. 3.3.3 Capillary Condensation. 3.4 Soil-Water Characteristic Curve. 3.4.1 Soil Suction and Soil Water. 3.4.2 Capillary Tube Model. 3.4.3 Contacting Sphere Model. 3.4.4 Concluding Remarks. Problems.

4 CAPILLARITY. 4.1 Young-Laplace Equation. 4.1.1 Three-Dimensional Meniscus. 4.1.2 Hydrostatic Equilibrium in a Capillary Tube. 4.2 Height of Capillary Rise. 4.2.1 Capillary Rise in a Tube. 4.2.2 Capillary Finger Model. 4.2.3 Capillary Rise in Idealized Soil. 4.2.4 Capillary Rise i