Ballast plays a vital role in transmitting and distributing the train wheel loads to the underlying track substructure. The load-bearing capacity, safe train speed, and the levels of noise and vibration, as well as passenger comfort depend on the behaviour of ballast through particle interlocking and the corresponding deformation of this granular assembly. Attrition and breakage of ballast occur progressively under heavy and continual cyclic loading, causing track deterioration and rail misalignment affecting safety, while exacerbating the intensity of track maintenance. In the absence of realistic computational models, the track substructure is traditionally designed using mostly empirical approaches.
In this book, the authors present the detailed information on the strength, deformation, and degradation aspects of fresh and recycled ballast under monotonic, cyclic, and impact loading using innovative geotechnical testing devices. A constitutive model for ballast incorporating particle breakage is presented representing a more realistic stress–strain response. The mathematical formulations and numerical models are validated using controlled experimental simulations and fully instrumented field trials. Revised ballast gradation is described to provide greater track resiliency and extended longevity. The book also provides a detailed description of geosynthetics for substructure improvement considering track deterioration caused by particle degradation, fouling, and impeded drainage. New to this second edition are extensive discussions on subgrade soil stabilisation, causes and mechanisms of soil fluidisation (mud pumping) under cyclic loading, and preventive and remedial measures to alleviate undue instability of ballast tracks.
This book should prove most beneficial for final-year civil engineering students and for postgraduate teaching and learning. It is an ideal supplement for practising railway engineers and researchers engaged in the challenging tasks of future track design for heavier and faster trains.
Author(s): Buddhima Indraratna, Cholachat Rujikiatkamjorn, Wadud Salim
Edition: 2
Publisher: CRC Press/Balkema
Year: 2023
Language: English
Pages: 466
City: London
Cover
Half Title
Title Page
Copyright Page
Dedication
Table of Contents
Foreword
Preface
About the Authors
1 Introduction
1.1 Issues with Track Substructure
1.1.1 Fouling
1.1.2 Poor Drainage
1.1.3 Hydraulic Erosion of Ballast and Sleepers
1.1.4 Lateral Buckling
1.2 Types of Track Structure
1.3 Carbon Footprint and Track Modernisation
1.4 Scope
References
2 Track Structure and Rail Load
2.1 Types of Track Structure
2.1.1 Ballasted Track
2.1.2 Slab Track
2.2 Components of a Ballasted Track
2.2.1 Rails
2.2.2 Fastening System
2.2.3 Sleeper
2.2.4 Ballast
2.2.4.1 Functions of Ballast
2.2.4.2 Properties of Ballast
2.2.5 Subballast
2.2.6 Subgrade
2.3 Track Forces
2.3.1 Vertical Forces
2.3.1.1 Area Method
2.3.1.2 ORE Method
2.3.1.3 Equivalent Dynamic Wheel Load
2.3.1.4 Rail Stress, Speed, and Impact Factor
2.3.2 Lateral Forces
2.3.3 Longitudinal Forces
2.3.4 Impact Forces
2.4 Load Transfer Mechanism
2.5 Stress Determination
2.5.1 Odemark Method
2.5.2 Zimmermann Method
2.5.3 Trapezoidal Approximation (2:1 Method)
2.5.4 AREMA Recommendations
References
3 Factors Governing Ballast Behaviour
3.1 Particle Characteristics
3.1.1 Particle Size
3.1.2 Particle Shape
3.1.3 Surface Roughness
3.1.4 Parent Rock Strength
3.1.5 Particle Crushing Strength
3.1.6 Resistance to Attrition and Weathering
3.2 Aggregate Characteristics
3.2.1 Particle Size Distribution
3.2.2 Void Ratio (or Density)
3.2.3 Degree of Saturation
3.3 Loading Characteristics
3.3.1 Confining Pressure
3.3.2 Load History
3.3.3 Current Stress State
3.3.4 Number of Load Cycles
3.3.5 Frequency of Loading
3.3.6 Amplitude of Loading
3.4 Particle Degradation
3.4.1 Quantification of Particle Breakage
3.4.2 Factors Affecting Particle Breakage
3.4.3 Effects of Principal Stress Ratio on Particle Breakage
3.4.4 Effects of Confining Pressure on Particle Breakage
3.4.4.1 Dilatant Unstable Degradation Zone
3.4.4.2 Optimum Degradation Zone
3.4.4.3 Compressive Stable Degradation Zone
3.5 Micromechanical Aspects on Particle Angularity
References
4 State-of-the-Art Laboratory Testing and Degradation Assessment of Ballast
4.1 Monotonic Triaxial Testing
4.1.1 Large-Scale Triaxial Apparatus
4.1.2 Characteristics of Test Ballast
4.1.2.1 Source of Ballast
4.1.2.2 Properties of Fresh Ballast
4.1.2.3 Properties of Recycled Ballast
4.1.3 Preparation of Ballast Specimens
4.1.4 Test Procedure
4.2 Single-Grain Crushing Tests
4.3 Cyclic Triaxial Testing
4.3.1 Large Prismoidal Triaxial Apparatus
4.3.2 Materials Tested
4.3.2.1 Ballast, Capping, and Clay Characteristics
4.3.2.2 Characteristics of Geosynthetics
4.3.3 Preparation of Test Specimens
4.3.4 Cyclic Triaxial Testing
4.3.4.1 Magnitude of Cyclic Load
4.3.4.2 Test Procedure
4.4 Impact Testing
4.4.1 Drop-Weight Impact Testing Equipment
4.4.2 Test Instrumentation
4.4.3 Materials Tested
4.4.3.1 Ballast and Sand Characteristics
4.4.3.2 Characteristics of Shock Mat
4.4.4 Preparation of Test Specimens
4.4.5 Impact Testing Programme
4.4.5.1 Magnitude of Impact Load
4.4.5.2 Test Procedure
References
5 Behaviour of Ballast with and Without Geosynthetics and Energy-Absorbing Mats
5.1 Ballast Response Under Monotonic Loading
5.1.1 Stress – Strain Behaviour
5.1.2 Shear Strength and Stiffness
5.1.3 Particle Breakage in Triaxial Shearing
5.1.4 Critical State of Ballast
5.2 Single-Particle Crushing Strength
5.3 Ballast Response Under Cyclic Loading
5.3.1 Settlement Response
5.3.2 Strain Characteristics
5.3.3 Particle Breakage
5.4 Ballast Response Under Repeated Loading
5.5 Effect of Confining Pressure
5.6 Energy-Absorbing Materials: Shock Mats
References
6 Existing Track Deformation Models
6.1 Plastic Deformation of Ballast
6.2 Other Plastic Deformation Models
6.2.1 Critical State Model
6.2.2 Elasto-Plastic Constitutive Models
6.2.3 Bounding Surface Plasticity Models
6.3 Modelling of Particle Breakage
References
7 A Constitutive Model for Ballast
7.1 Modelling of Particle Breakage
7.1.1 Evaluation of ϕ[sub(f)] for Ballast
7.1.2 Contribution of Particle Breakage to Friction Angle
7.2 Constitutive Modelling for Monotonic Loading
7.2.1 Stress and Strain Parameters
7.2.2 Incremental Constitutive Model
7.3 Constitutive Modelling for Cyclic Loading
7.3.1 Shearing From an Anisotropic Initial Stress State
7.3.2 Cyclic Loading Model
7.3.2.1 Conceptual Model
7.3.2.2 Mathematical Model
7.4 Model Verification and Discussion
7.4.1 Numerical Method
7.4.2 Evaluation of Model Parameters
7.4.3 Model Predictions for Monotonic Loading
7.4.4 Analytical Model Compared to FEM Predictions
7.4.5 Model Predictions for Cyclic Loading
References
8 Track Drainage and Use of Geotextiles
8.1 Drainage
8.1.1 Subballast Permeability
8.1.2 Drainage Requirements
8.2 Fouling Indices
8.2.1 Fouling Index and Percentage of Fouling
8.2.2 Percentage Void Contamination
8.2.3 Relative Ballast Fouling Ratio
8.3 Geosynthetics in Rail Track
8.3.1 Types and Functions of Geosynthetics
8.4 Use of Geosynthetic Vertical Drains as a Subsurface Drainage
8.4.1 Apparatus and Test Procedure
8.4.2 Test Results and Analysis
References
9 Role of Subballast, its Drainage, and Filtration Characteristics
9.1 Subballast Selection Criteria
9.1.1 Filtration and Drainage Criteria
9.1.2 Case Studies of Subballast Selection
9.2 Empirical Studies on Granular Filtration
9.2.1 Natural Resources Conservation Service (NRCS) Method
9.2.2 Self-Filtration Method
9.3 Mathematical Formulations in Drainage and Filtration
9.3.1 Geometric and Probabilistic Modelling
9.3.2 Particle Infiltration Models
9.4 Constriction Size Distribution Model
9.4.1 Filter Compaction
9.4.2 Filter Thickness
9.4.3 Dominant Filter Constriction Size
9.4.4 Controlling Filter Constriction Size
9.4.5 Base Soil Representative Parameter
9.5 Constriction-Based Criteria for Assessing Filter Effectiveness
9.5.1 D[sub(c95)] Model
9.5.2 D[sub(c35)] Model
9.6 Implications on Design Guidelines
9.7 Steady-State Seepage Hydraulics of Porous Media
9.7.1 Development of Kozeny – Carman (KC) Equation – a Rationale
9.7.2 Formulation for the Effective Diameter
9.8 Subballast Filtration Behaviour Under Cyclic Conditions
9.8.1 Laboratory Simulations
9.8.2 Deformation Characteristics of Subballast Under Cyclic Loading
9.8.2.1 Pseudo-Static Loading
9.8.2.2 Immediate Response to Cyclic Loading
9.8.3 Strain – Porosity Relationship of Subballast Under Cyclic Loading
9.8.3.1 Pseudo-Static Loading
9.8.3.2 Increased Loading Frequency
9.8.4 Seepage Hydraulics of Subballast Under Cyclic Loading
9.8.4.1 Turbidity Measurements and Trapped Fines
9.8.4.2 Short-Term Drainage Performance
9.9 Time-Dependent Geo-Hydraulic Filtration Model for Particle Migration Under Cyclic Loading
9.9.1 Time-Based One-Dimensional Granular Filter Compression
9.9.2 Accumulation Factor
9.9.3 Mathematical Description of Porosity Reduction Due to Accumulated Fines
9.9.4 Time-Based Hydraulic Conductivity Model
References
10 Field Instrumentation for Track Performance Verification
10.1 Site Geology and Track Construction
10.1.1 Site Investigation
10.1.2 Track Construction
10.2 Field Instrumentation
10.2.1 Pressure Cells
10.2.2 Displacement Transducers
10.2.3 Settlement Pegs
10.2.4 Data Acquisition System
10.3 Data Collection
10.4 Results and Discussion
10.4.1 Vertical Deformation of Ballast Both Under Rail and Edge of Sleeper
10.4.2 Average Deformation of Ballast
10.4.3 Average Shear and Volumetric Strain of Ballast
10.4.4 In Situ Stresses Across Different Layers
10.4.5 Comparison of Current Results with Previous Literature
References
11 Discrete Element Modelling (DEM) of Ballast Densification and Breakage
11.1 Discrete Element Method and PFC[sup(2D)]
11.1.1 Calculation Cycle
11.1.2 Contact Constitutive Model
11.2 Modelling of Particle Breakage
11.3 Numerical Simulation of Monotonic and Cyclic Behaviour of Ballast Using PFC[sup(2D)]
11.3.1 Cyclic Biaxial Test Simulations
11.4 Breakage Behaviour
11.4.1 Micromechanical Investigation of Breakage
11.5 Mechanism of CF Chains Developed During Cyclic Loading
References
12 Finite Element Modelling (FEM) of Tracks and Applications to Case Studies
12.1 Use of Geocomposite Under Railway Track
12.1.1 Finite Element Analysis
12.1.2 Comparison of Field Results with FEM Predictions
12.2 Design Process for Short PVDS Under Railway Track
12.2.1 Preliminary Design
12.2.2 Comparison of Field with Numerical Predictions
References
13 Non-Destructive Testing and Track Condition Assessment
13.1 Laboratory Model Track
13.1.1 The Model Track
13.1.2 Preparation of the Ballast Sections
13.2 The GPR Method
13.2.1 Theoretical Background of GPR
13.2.2 Acquisition and Processing of GPR Data
13.3 Factors Affecting GPR
13.3.1 Influence of Antenna Frequency
13.3.2 Effect of Radar-Detectable Geotextile
13.3.3 Effect of Moisture Content
13.3.4 Applying Dielectric Permittivity to Identify the Condition of Ballast
13.4 Multichannel Analysis of Surface Wave Method
13.4.1 MASW Survey
13.4.2 Shear Properties of Clean and Fouled Ballast
13.4.3 Data Interpretation
References
14 Track Maintenance
14.1 Track Maintenance Techniques
14.1.1 Ballast Tamping
14.1.2 Stoneblowing
14.1.3 Ballast Cleaning and Ballast Renewal
14.2 Track Geotechnology and Maintenance in Cold Regions
References
15 Recommended Ballast Gradations
15.1 Australian Ballast Specifications
15.2 International Railway Ballast Grading
15.3 Gradation Effects on Settlement and Ballast Breakage
15.4 Recommended Ballast Grading
15.5 Conclusions
References
16 Bioengineering for Track Stabilisation
16.1 Introduction
16.2 Conceptual Modelling
16.2.1 Soil Suction
16.2.2 Root Distribution
16.2.3 Potential Transpiration
16.3 Verification of the Proposed Root Water Uptake Model
16.3.1 Case Study 1: Miram Village (Western Victoria, Australia)
16.3.2 Case Study 2: Milton Keynes, United Kingdom
References
17 Stabilisation of Soft Subgrade
17.1 Introduction
17.2 Failure of Subgrade
17.2.1 Mohr–Coulomb Model
17.2.2 Laboratory Tests for Determining Shear Strength Parameters
17.2.2.1 Direct Shear Test
17.2.2.2 Triaxial Test
17.2.2.3 Pore Pressure Coefficients A and B
17.2.3 Undrained Shear Strength
17.3 Soil Fluidisation (Mud Pumping)
17.4 Fluidisation of Subgrade Under Cyclic Loads
17.4.1 Roles of Cyclic Stress Ratio, Frequency, and Density
17.4.2 Stiffness Degradation
17.4.3 Upward Fine Migration
17.5 Particle Behaviour During Fluidisation
17.5.1 CFD-DEM Approach
17.5.2 Numerical Simulations
17.5.3 Undrained Cyclic Response of Saturated Subgrade
17.6 Remediation to Improve Stability
17.6.1 Addition of Plastic Fines
17.6.2 Application of Geosynthetics
17.7 Site Reconnaissance and Soil Characteristics at Mud Pumping Site
17.7.1 Descriptions of Site Investigation
17.7.2 Field Assessment
References
Appendix A: Derivation of partial derivatives of g(p, q) with respect to p and q from a first-order linear differential equation
Appendix B: Determination of model parameters from laboratory experimental results
Appendix C: A pictorial guide to track strengthening, field inspection, and instrumentation
Appendix D: Unique geotechnical and rail testing equipment
Appendix E: A circular economy perspective for track technologies – field trial at Chullora Technology Precinct
Index
