Contents Preface Chapter 1 Introduction 1 1.1 Coal and Coal Measure Strata 1 1.1.1 Coal and Coal Seam Gas 1 1.1.2 Coal Measure Strata 7 1.2 Structure of Coal and Its Simplified Physical Model 13 1.2.1 Pores and Fractures in Coal 13 1.2.2 Simplified Physical Model of Coal 20 1.3 Comparison of Coal and Rock 22 1.3.1 Comparison of Structure and Strength 22 1.3.2 Comparison of Adsorption Properties 23 1.3.3 Comparison of Gas Outburst and Rock Burst Disasters 25 1.4 Research Contents of Coal Mechanics 26 1.4.1 Definition of Coal Mechanics 26 1.4.2 Development of Coal Mechanics 27 1.4.3 Structure of This Book 31 References 32 Chapter 2 Coal Formation and Metamorphism 41 2.1 Coal Forming Process 41 2.2 Coalification 43 2.2.1 Coal Diagenesis 43 2.2.2 Coal Metamorphism 43 2.3 The Maceral Composition and Metamorphic Type of Coal 44 2.3.1 The Maceral Composition of Coal 44 2.3.2 Metamorphism Types of Coal 46 2.4 Gas Generation in Coal 49 2.4.1 Gas Generation During the Biochemical Coalification Period 50 2.4.2 Gas Generation During the Coal Metamorphism Period 50 2.4.3 Coal Seam Gas Composition 53 2.4.4 Occurrence Status of Coal Seam Gas 56 2.5 Effect of Magma Intrusion on Coal Metamorphism and Gas Occurrence 59 2.5.1 Ways of Magma Intrusion into Coal Seams 59 2.5.2 Thermal Temperature Field Analysis of Magma 60 2.5.3 The Influence of Magma on Coal Metamorphism 64 2.5.4 The Influence of Magma on Gas Occurrence 65 Reference 72 Chapter 3 Basic Physical Properties and Characteristics of Coal Pores and Fractures 75 3.1 The Basic Physical Properties of Coal 75 3.1.1 Moisture of Coal 76 3.1.2 Ash in Coal 78 3.1.3 Volatiles of Coal 80 3.1.4 Density of Coal 81 3.1.5 Hardness of Coal 82 3.2 Coal Pore Features 85 3.2.1 Classification of Coal Pore 85 3.2.2 Coal Pore Characterization Methods 87 3.2.3 Pore Structure Characterization 93 3.3 Coal Fracture Features 97 3.3.1 Classification of Coal Fracture 97 3.3.2 Fracture Distribution Characteristics in Coal 97 3.4 The Matrix Characteristics of Coal 100 3.4.1 Definition of Coal Matrix 100 3.4.2 Coal Matrix Scale 101 References 104 Chapter 4 Gas Adsorption-Desorption Properties of Coal 107 4.1 Gas adsorption Properties of Coal 107 4.1.1 Gas Adsorption Mechanism in Coal 107 4.1.2 Gas Adsorption Law of Coal 108 4.1.3 Main Factors Affecting Gas Adsorption Properties of Coal 110 4.1.4 Test Methods of Gas Adsorption Properties 118 4.2 Gas Desorption Properties of Coal 123 4.2.1 Gas Desorption Mechanism 123 4.2.2 Main Factors Affecting Gas Desorption Properties 124 4.2.3 Gas Desorption Models of Coal 129 4.2.4 Test Methods of Gas Desorption Properties 132 4.2.5 Application of Gas Desorption Properties of Coal in Gas Content Determination 133 4.3 Gas Diffusion in Coal 137 4.3.1 Physical Process of Gas Diffusion in Coal 137 4.3.2 Mathematical Models of Coal Gas Diffusion 139 4.3.3 The Desorption Index of Drilling Cuttings (K1) 141 References 143 Chapter 5 Foundation of Coal Mechanics 146 5.1 Stress State 146 5.1.1 Concept of Stress 146 5.1.2 Specification of Stress State at a Point 148 5.1.3 Plane Stress State and the Mohr Stress Circle 150 5.1.4 Principal Stresses and Their Directions 153 5.2 Strain State 156 5.2.1 Displacement and Strain Concepts 156 5.2.2 Geometric Equation 158 5.2.3 Principal Strain and Volumetric Strain 160 5.3 Strength Criterion 162 5.3.1 Mohr-Coulomb Strength Criterion 162 5.3.2 Drucker-Prager Strength Criterion 164 5.3.3 Griffith’s Strength Criterion 165 5.4 The Effective Stress 166 References 168 Chapter 6 Strength and Deformation Characteristics of Coal Containing Gas 170 6.1 Mechanical Tests of Coal Containing Gas 170 6.1.1 Testing Facility and Experimental Principles 171 6.1.2 Basic Requirements for Strength Tests of Coal Containing Gas 173 6.1.3 Coal Sample Preparation Methods 174 6.2 Strength Characteristics of Coal Containing Gas 180 6.2.1 Conventional Compression Tests of Coal 180 6.2.2 Pre-peak Confining Pressure Unloading Tests of Coal Containing Gas 186 6.2.3 Analysis of the Strength Characteristics of Coal Containing Gas 190 6.3 Deformation Characteristics of Coal Containing Gas 201 6.3.1 Analysis of the Deformation Characteristics of Coal Containing Gas 201 6.3.2 Influence of Gas on Coal Deformation 207 6.4 Constitutive Equation of Coal Containing Gas 209 6.4.1 Analysis of the Constitutive Relationship Characteristics of Coal 209 6.4.2 Linear Elastic Stage 213 6.4.3 Nonlinear Elastoplastic Stage 215 6.4.4 Ideal Plastic Stage 216 6.4.5 Strain Softening Stage 216 6.5 Macroscopic Damage Features of Coal Containing Gas 216 6.6 Failure Mechanism and Strength Theory of Coal Containing Gas 220 6.6.1 C. D. Martin Fracture Strain Model 220 6.