Fundamentals of Ground Improvement Engineering [1 ed.] 0415695120, 9780415695121

Table of contents :
Cover
Half Title
Title Page
Copyright Page
Table of Contents
Preface and Acknowledgments: Fundamentals of Ground Improvement Engineering
Chapter 1 Introduction to ground improvement engineering
1.1 Introduction
1.2 Improvements in soil behavior
1.2.1 Shear strength
1.2.2 Compressibility
1.2.3 Hydraulic conductivity
1.2.4 Liquefaction potential
1.2.5 Shrink/swell behavior
1.2.6 Variability
1.3 Overview of ground improvement techniques
1.3.1 Compaction: shallow methods
1.3.2 Compaction: deep methods
1.3.3 Soil mixing and injection methods
1.3.4 Stabilization and solidification
1.3.5 Grouting
1.3.6 Dewatering
1.3.7 Consolidation
1.3.8 Mechanically stabilized earth
1.3.9 In situ barriers
1.3.10 Future developments in ground improvement
1.4 Importance of construction
1.5 Problems
References
Chapter 2 Geotechnical fundamentals
2.1 Definitions
2.1.1 Water content
2.1.2 Density, unit weight, density of solids, and specific gravity
2.2 Water flow in soil
2.2.1 Darcy’s law and one-dimensional flow
2.2.2 Flownets and two-dimensional flow
2.2.3 Quantity of water flowing through soil
2.2.4 Porewater pressure with water flowing through soil
2.2.5 Uplift pressures
2.2.6 Seepage force
2.2.7 Capillary rise of groundwater
2.3 Effective stress
2.3.1 Effective stress equation
2.3.2 Importance of effective stress
2.4 Shear strength
2.4.1 The concept of soil strength
2.4.2 Laboratory evaluation of shear strength
2.4.2.1 Direct shear testing
2.4.2.2 Triaxial testing
2.4.3 Shear strength summary
2.5 Lateral earth pressures
2.5.1 Active earth pressure
2.5.2 Passive earth pressure
2.5.3 At-rest (K0) earth pressure
2.5.4 Amount of movement to develop active, passive, and at-rest earth pressures
2.6 Field investigations
2.6.1 Drilling methods
2.6.2 Sampling methods
2.6.3 In situ test methods
2.6.3.1 SPT
2.6.3.2 CPT
2.7 Problems
References
Chapter 3 Fundamentals of geosynthetics in ground improvement
3.1 Introduction
3.1.1 Geotextiles
3.1.2 Geogrids
3.1.3 Geocells
3.1.4 Geofibers
3.1.5 Historical notes
3.2 Properties of geosynthetics
3.2.1 Tensile strengths
3.2.2 Permittivity (used in drainage)
3.2.3 Transmissivity (used in drainage)
3.2.4 Pore size determination (used in filtration)
3.2.5 Interface friction (used in mechanically stabilized earth and steepened slope design)
3.2.6 Survivability and durability
3.3 Geotextile filter design
3.3.1 Introduction
3.3.2 Design procedure
3.4 Summary
3.5 Problems
References
Chapter 4 Compaction
4.1 Introduction
4.2 Theoretical underpinnings of compaction
4.3 Property improvements resulting from compaction
4.3.1 Strength
4.3.2 Compressibility
4.3.3 Hydraulic conductivity (permeability)
4.3.4 Optimizing compacted soil properties
4.4 Shallow compaction
4.4.1 Field compaction equipment
4.4.2 Construction aspects of shallow compaction
4.5 Rapid impact compaction
4.5.1 Introduction
4.5.2 Applications
4.5.3 Construction vibrations
4.6 Deep dynamic compaction
4.6.1 Introduction
4.6.2 Design considerations for dynamic compaction
4.6.3 Verification of compaction effectiveness
4.6.4 Applications of deep dynamic compaction
4.6.5 Construction vibrations
4.7 Deep vibratory methods
4.7.1 Introduction to deep vibratory methods
4.7.2 Vibrocompaction
4.7.3 Vibroreplacement
4.8 Aggregate piers
4.9 Problems
References
Chapter 5 Consolidation
5.1 Introduction
5.2 Consolidation fundamentals
5.3 Stress distribution
5.4 Design approach
5.4.1 Time rate of consolidation
5.4.2 Preloading
5.5 Speeding consolidation with vertical drains
5.5.1 Introduction
5.5.2 Consolidation with vertical drains
5.6 Additional vertical drain considerations
5.6.1 Vertical drain types
5.6.2 Effect of PVD installation patterns
5.6.3 Effect of soil disturbance (smear)
5.7 Vacuum consolidation
5.8 Combined vacuum consolidation and preloading with vertical drains
5.9 Nature’s consolidation preloading
5.10 Summary
5.11 Problems
References
Chapter 6 Soil mixing
6.1 Introduction
6.2 History of soil mixing
6.3 Definitions, types, and classifications
6.3.1 Depth of soil mixing
6.3.2 Methods of mixing reagents
6.3.3 Equipment used for soil mixing
6.3.4 Treatment patterns
6.4 Applications
6.4.1 Shear walls
6.4.2 Aerial bearing capacity improvement
6.4.3 Hydraulic cutoff walls
6.4.4 Excavation support walls
6.4.5 Environmental soil mixing
6.4.6 Geoenvironmental soil mixing
6.5 Design considerations
6.5.1 Determine project needs
6.5.2 Select target design parameters
6.5.2.1 Strength
6.5.2.2 Hydraulic conductivity
6.5.2.3 Leachability
6.5.3 Reagent addition rates
6.5.4 Reagent (binder) types and selection
6.5.5 Develop and evaluate construction objectives
6.5.6 Construction
6.5.7 Sampling
6.5.8 In situ testing
6.6 Problems
References
Chapter 7 Grouting
7.1 Introduction
7.2 History of grouting
7.2.1 History of suspension grouting
7.2.2 History of solution grouting
7.3 Grouting types and classifications
7.3.1 Suspension grouts
7.3.2 Common grout mixtures for suspension grouting
7.3.3 Neat cement grout
7.3.4 Balanced stable grout
7.3.5 Microfine or ultrafine cement grouting
7.4 Solution grouts
7.4.1 Types of solution grouts
7.5 Permeation (penetration) grouting
7.6 Fracture grouting
7.7 Compensation grouting
7.8 Void grouting
7.9 Grout properties
7.9.1 Set (gel) time
7.9.2 Stability
7.9.3 Viscosity
7.9.4 Permanence
7.9.5 Toxicity
7.10 Applications
7.11 Design considerations
7.11.1 Understanding grout physics and preliminary planning
7.11.2 Geological conditions and site investigations
7.11.3 Interaction between grout and soil/rock
7.11.4 Grout mix design
7.12 Construction
7.12.1 Pre-grouting
7.12.2 Suspension and solution grouting
7.12.3 Drill rigs
7.12.4 Mixing (batch) plants
7.12.5 Pumping systems
7.12.6 Packers
7.13 Quality control
7.13.1 Flow measurements
7.13.2 Monitoring
7.13.3 Automated Monitoring Equipment
7.14 Void grouting, a special application
7.15 Problems
References
Chapter 8 Slurry trench cutoff walls
8.1 Introduction and overview
8.1.1 Functions of slurry trench cutoff walls
8.1.2 History of slurry trench cutoff walls
8.1.3 Slurry trench cutoff walls as a ground improvement technique
8.2 SB slurry trench Cutoff Walls
8.2.1 Excavation stability
8.2.2 Slurry property measurement
8.2.3 SB backfill design
8.2.4 Excavation techniques
8.3 CB slurry trench cutoff walls
8.3.1 CB mixtures and properties
8.3.2 Role of the bentonite in CB mixtures
8.3.3 Volume change behavior
8.4 Structural slurry walls (diaphragm walls)
8.5 Problems
References
Chapter 9 Ground improvement using geosynthetics
9.1 Introduction
9.2 Geosynthetic ground improvement
9.2.1 Introduction
9.2.2 Geosynthetic types used in ground improvement
9.2.3 Geosynthetic applications in ground improvement
9.3 Properties of geosynthetics
9.3.1 Introduction
9.3.2 Tensile strength
9.3.3 Interface friction
9.3.4 Durability
9.3.5 Geotextile survivability
9.4 Road base stabilization (Corps of Engineers methods)
9.4.1 Introduction
9.4.2 Unpaved road improvement using geosynthetics
9.4.3 Paved road improvement using geosynthetics
9.4.4 Geofibers in roads
9.5 Embankments over soft ground
9.5.1 Introduction
9.5.2 Conventional construction of embankments
9.5.3 Geosynthetic usage in embankment construction
9.5.4 Design procedure
9.5.4.1 Slope stability
9.5.4.2 Sliding of soil on top of geosynthetic
9.5.4.3 Geosynthetic rupture due to sliding
9.5.4.4 Pullout of the geosynthetic
9.5.4.5 Bearing capacity
9.5.4.6 Settlement
9.5.4.7 Additional checks
9.5.5 Instrumentation
9.5.6 Construction guidance
9.5.7 Alternative procedures
9.6 Underfooting reinforcement with rolled geosynthetics
9.6.1 Introduction
9.6.2 Design procedure
9.6.3 Construction
9.7 Underfooting reinforcement with geocells
9.7.1 Introduction
9.7.2 Ultimate load calculation
9.7.3 State of practice
9.7.4 Construction advice
9.8 Underfooting reinforcement with geofibers
9.8.1 Introduction
9.8.2 Design procedure for strength increase
9.8.3 Construction advice
9.9 Soil separation
9.9.1 Introduction
9.9.2 Design procedures
9.9.3 Construction advice
9.10 Problems
References
Chapter 10 Reinforcement in walls, embankments on stiff ground, and soil nailing
10.1 Introduction
10.2 Mechanically stabilized earth walls
10.2.1 Introduction
10.2.2 Design philosophy
10.2.3 Advantages and disadvantages of MSE walls
10.2.4 Design using geosynthetics
10.2.4.1 Sliding of the reinforced mass
10.2.4.2 Reinforcement breakage
10.2.4.3 Reinforcement pullout
10.2.4.4 Other failure modes
10.2.5 Design of internal components
10.2.6 External stability
10.2.7 Typical factors of safety
10.2.8 Inclusions in the backfill
10.2.9 Drainage
10.2.10 Other considerations
10.2.11 Construction guidelines
10.3 Mechanically stabilized earth walls using metal reinforcement
10.3.1 Introduction
10.3.2 Differences between metal and geosynthetic reinforcement
10.3.3 Failure modes and typical factors of safety
10.3.4 Inclusions in the backfill
10.3.5 Construction guidelines
10.4 Reinforced soil embankments on firm foundations using geosynthetic and metal reinforcement
10.4.1 Introduction
10.4.2 Philosophy of how reinforcement for steepened slopes works
10.4.3 Engineering properties needed
10.4.4 Design notes
10.4.5 Construction procedure
10.4.6 Inclusions in the backfill
10.4.7 Internal stability: pullout and breakage, internal slope stability
10.4.8 External stability: bearing capacity, sliding, and settlement
10.4.9 Slope face stability: veneer instability, erosion control, and wrapped faces
10.4.10 Drainage
10.5 Soil nailing
10.5.1 Introduction
10.5.2 Applications
10.5.3 Applicable sites
10.5.4 Components of a soil nail system
10.5.5 Methods of installing soil nails
10.5.6 Design of soil nailed walls
10.5.6.1 Failure modes
10.5.6.2 Design calculations
10.5.7 Construction of soil nailed walls
10.5.8 Nail testing
10.5.9 Corrosion protection
10.5.10 Instrumentation
10.5.11 Launched soil nails
10.6 Problems
References
Chapter 11 Additional techniques in ground improvement
11.1 Jet grouting
11.1.1 Introduction to jet grouting
11.1.2 Environmental considerations
11.1.3 Design considerations in jet grouting
11.2 Ground freezing
11.2.1 Introduction to ground freezing
11.2.2 Fundamentals of ground freezing
11.2.3 Properties of frozen ground
11.2.4 Containment of contaminated soils
11.2.5 Limitations of ground freezing
11.2.6 Conclusions regarding ground freezing
11.3 Secant pile walls
11.4 Compaction grouting
11.4.1 Introduction and history
11.4.2 Uses
11.4.3 Design
11.4.4 Construction
11.5 Explosives in ground improvement
11.5.1 Introduction
11.5.2 Applications of explosives
11.5.3 Ground conditions favorable to explosives for compaction
11.5.4 Construction practice for compaction by explosives
11.5.5 Post explosion evaluations
11.5.6 Collateral concerns with the use of explosives
11.5.7 Case studies
11.6 Problems
References
Chapter 12 The future of ground improvement engineering
12.1 Introduction
12.2 Biogeotechnical methods for Ground improvement
12.2.1 Biocementation
12.2.2 Bioclogging to reduce hydraulic conductivity
12.2.3 Bio-methods for liquefaction mitigation
12.3 New materials for ground improvement
12.3.1 MgO cement
12.3.2 Polymers
12.3.3 Smart and self-healing materials
12.4 Technology developments in ground improvement: drones, sensors, and artificial intelligence
12.5 Equipment developments
12.6 Sustainability in ground improvement
12.6.1 Introduction to sustainable ground improvement
12.6.2 Sustainable materials
12.7 Crossover information in ground improvement
12.8 Summary of future developments in ground improvement
12.9 Problems
References
Index

Citation preview

Fundamentals of Ground Improvement Engineering

Fundamentals of Ground Improvement Engineering

Jeffrey Evans Daniel Ruffing David Elton

MATLAB ® is a trademark of The MathWorks, Inc. and is used with permission. The MathWorks does not warrant the accuracy of the text or exercises in this book. This book’s use or discussion of MATLAB ® software or related products does not constitute endorsement or sponsorship by The MathWorks of a particular pedagogical approach or particular use of the MATLAB® software. First edition published 2022 by CRC Press 2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN and by CRC Press 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742 © 2022 Jeffrey Evans, Daniel Ruffing and David Elton CRC Press is an imprint of Informa UK Limited The right of Jeffrey Evans, Daniel Ruffing and David Elton to be identified as authors of this work has been asserted by them in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. For permission to photocopy or use material electronically from this work, access www​.copyright​.com or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. For works that are not available on CCC please contact mpkbookspermissions​@ tandf​.co​​.uk Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library

Library of Congress Cataloging‑in‑Publication Data Names: Evans, Jeffrey C., author. | Elton, David J., author. | Ruffing, Daniel, author. Title: Fundamentals of ground improvement engineering / Jeffrey Evans, David Elton, Daniel Ruffing. Description: First edition. | Boca Raton : CRC Press, 2021. | Includes bibliographical references and index. Identifiers: LCCN 2021002848 (print) | LCCN 2021002849 (ebook) | ISBN 9780367419608 (hbk) | ISBN 9780415695152 (pbk) | ISBN 9780367816995 (ebk) Subjects: LCSH: Soil stabilization. Classification: LCC TA749 .E94 2021 (print) | LCC TA749 (ebook) | DDC 624.1/51363--dc23 LC record available at https://lccn.loc.gov/2021002848 LC ebook record available at https://lccn.loc.gov/2021002849 ISBN: 978-0-367-41960-8 (hbk) ISBN: 978-0-415-69515-2 (pbk) ISBN: 978-0-367-81699-5 (ebk) Typeset in Sabon by Deanta Global Publishing Services, Chennai, India

Contents

Preface and Acknowledgments: Fundamentals of Ground Improvement Engineering xv 1 Introduction to ground improvement engineering

1

1.1 Introduction 1 1.2 Improvements in soil behavior  2 1.2.1 Shear strength  3 1.2.2 Compressibility 3 1.2.3 Hydraulic conductivity  4 1.2.4 Liquefaction potential  5 1.2.5 Shrink/swell behavior  6 1.2.6 Variability 6 1.3 Overview of ground improvement techniques  8 1.3.1 Compaction: shallow methods  8 1.3.2 Compaction: deep methods  8 1.3.3 Soil mixing and injection methods  11 1.3.4 Stabilization and solidification  12 1.3.5 Grouting 13 1.3.6 Dewatering 14 1.3.7 Consolidation 15 1.3.8 Mechanically stabilized earth  15 1.3.9 In situ barriers  17 1.3.10 Future developments in ground improvement  18 1.4 Importance of construction  19 1.5 Problems 19 References 20

2 Geotechnical fundamentals

21

2.1 Definitions 21 2.1.1 Water content  22 2.1.2 Density, unit weight, density of solids, and specific gravity  23 2.2 Water flow in soil  24 2.2.1 Darcy’s law and one-dimensional flow  25 2.2.2 Flownets and two-dimensional flow  25 v

vi Contents

2.2.3 Quantity of water flowing through soil  26 2.2.4 Porewater pressure with water flowing through soil  27 2.2.5 Uplift pressures  29 2.2.6 Seepage force  29 2.2.7 Capillary rise of groundwater  30 2.3 Effective stress  31 2.3.1 Effective stress equation  31 2.3.2 Importance of effective stress  31 2.4 Shear strength  32 2.4.1 The concept of soil strength  33 2.4.2 Laboratory evaluation of shear strength  33 2.4.2.1 Direct shear testing  33 2.4.2.2 Triaxial testing  36 2.4.3 Shear strength summary  39 2.5 Lateral earth pressures  40 2.5.1 Active earth pressure  41 2.5.2 Passive earth pressure  43 2.5.3 At-rest (K0) earth pressure  44 2.5.4 Amount of movement to develop active, passive, and at-rest earth pressures  44 2.6 Field investigations  46 2.6.1 Drilling methods  46 2.6.2 Sampling methods  47 2.6.3 In situ test methods  49 2.6.3.1 SPT 49 2.6.3.2 CPT 51 2.7 Problems 52 References 56

3 Fundamentals of geosynthetics in ground improvement 3.1

3.2

3.3

Introduction   59 3.1.1 Geotextiles 59 3.1.2 Geogrids 61 3.1.3 Geocells 62 3.1.4 Geofibers   63 3.1.5 Historical notes   63 Properties of geosynthetics  64 3.2.1 Tensile strengths  64 3.2.2 Permittivity (used in drainage)  64 3.2.3 Transmissivity (used in drainage)  65 3.2.4 Pore size determination (used in filtration)  66 3.2.5 Interface friction (used in mechanically stabilized earth and steepened slope design)   67 3.2.6 Survivability and durability   67 Geotextile filter design  69 3.3.1 Introduction 69

59

Contents vii

3.3.2 Design procedure  70 3.4 Summary 77 3.5 Problems 77 References 82

4 Compaction

85

4.1 Introduction 85 4.2 Theoretical underpinnings of compaction  85 4.3 Property improvements resulting from compaction  90 4.3.1 Strength 90 4.3.2 Compressibility 90 4.3.3 Hydraulic conductivity (permeability)  90 4.3.4 Optimizing compacted soil properties  91 4.4 Shallow compaction  91 4.4.1 Field compaction equipment  91 4.4.2 Construction aspects of shallow compaction  94 4.5 Rapid impact compaction  96 4.5.1 Introduction 96 4.5.2 Applications 97 4.5.3 Construction vibrations  97 4.6 Deep dynamic compaction   98 4.6.1 Introduction 98 4.6.2 Design considerations for dynamic compaction  98 4.6.3 Verification of compaction effectiveness  100 4.6.4 Applications of deep dynamic compaction  102 4.6.5 Construction vibrations  103 4.7 Deep vibratory methods   103 4.7.1 Introduction to deep vibratory methods  103 4.7.2 Vibrocompaction 104 4.7.3 Vibroreplacement 108 4.8 Aggregate piers  112 4.9 Problems 113 References 115

5 Consolidation 5.1 5.2 5.3 5.4

5.5

5.6

Introduction 119 Consolidation fundamentals  120 Stress distribution  122 Design approach  122 5.4.1 Time rate of consolidation  124 5.4.2 Preloading 127 Speeding consolidation with vertical drains  129 5.5.1 Introduction 129 5.5.2 Consolidation with vertical drains  129 Additional vertical drain considerations  133

119

viii Contents

5.6.1 Vertical drain types  133 5.6.2 Effect of PVD installation patterns  135 5.6.3 Effect of soil disturbance (smear)  136 5.7 Vacuum consolidation  136 5.8 Combined vacuum consolidation and preloading with vertical drains  138 5.9 Nature’s consolidation preloading  138 5.10 Summary 143 5.11 Problems 143 References 145

6 Soil mixing

149

6.1 Introduction 149 6.2 History of soil mixing  150 6.3 Definitions, types, and classifications  151 6.3.1 Depth of soil mixing  152 6.3.2 Methods of mixing reagents  153 6.3.3 Equipment used for soil mixing  154 6.3.4 Treatment patterns  162 6.4 Applications 163 6.4.1 Shear walls  164 6.4.2 Aerial bearing capacity improvement  165 6.4.3 Hydraulic cutoff walls  165 6.4.4 Excavation support walls  166 6.4.5 Environmental soil mixing  168 6.4.6 Geoenvironmental soil mixing  169 6.5 Design considerations  170 6.5.1 Determine project needs  170 6.5.2 Select target design parameters  171 6.5.2.1 Strength 172 6.5.2.2 Hydraulic conductivity  175 6.5.2.3 Leachability 176 6.5.3 Reagent addition rates  176 6.5.4 Reagent (binder) types and selection  179 6.5.5 Develop and evaluate construction objectives  181 6.5.6 Construction 182 6.5.7 Sampling 185 6.5.8 In situ testing  187 6.6 Problems 187 References 189

7 Grouting 7.1 Introduction 193 7.2 History of grouting  196 7.2.1 History of suspension grouting  197 7.2.2 History of solution grouting  198

193

Contents ix

7.3

Grouting types and classifications  199 7.3.1 Suspension grouts  199 7.3.2 Common grout mixtures for suspension grouting  199 7.3.3 Neat cement grout  199 7.3.4 Balanced stable grout  200 7.3.5 Microfine or ultrafine cement grouting  201 7.4 Solution grouts  201 7.4.1 Types of solution grouts  201 7.5 Permeation (penetration) grouting  202 7.6 Fracture grouting  203 7.7 Compensation grouting  203 7.8 Void grouting  203 7.9 Grout properties  204 7.9.1 Set (gel) time  204 7.9.2 Stability 204 7.9.3 Viscosity 204 7.9.4 Permanence 205 7.9.5 Toxicity 205 7.10 Applications 206 7.11 Design considerations  207 7.11.1 Understanding grout physics and preliminary planning  207 7.11.2 Geological conditions and site investigations  212 7.11.3 Interaction between grout and soil/rock  212 7.11.4 Grout mix design  213 7.12 Construction 213 7.12.1 Pre-grouting 213 7.12.2 Suspension and solution grouting  214 7.12.3 Drill rigs  215 7.12.4 Mixing (batch) plants  218 7.12.5 Pumping systems  218 7.12.6 Packers 219 7.13 Quality control  219 7.13.1 Flow measurements  219 7.13.2 Monitoring 221 7.13.3 Automated Monitoring Equipment  221 7.14 Void grouting, a special application  222 7.15 Problems 223 References 224

8 Slurry trench cutoff walls 8.1

8.2

Introduction and overview  227 8.1.1 Functions of slurry trench cutoff walls  228 8.1.2 History of slurry trench cutoff walls  228 8.1.3 Slurry trench cutoff walls as a ground improvement technique  229 SB slurry trench Cutoff Walls  229

227

x Contents

8.2.1 Excavation stability  231 8.2.2 Slurry property measurement  236 8.2.3 SB backfill design  238 8.2.4 Excavation techniques  243 8.3 CB slurry trench cutoff walls  244 8.3.1 CB mixtures and properties  245 8.3.2 Role of the bentonite in CB mixtures  247 8.3.3 Volume change behavior  249 8.4 Structural slurry walls (diaphragm walls)  250 8.5 Problems 253 References 254

9 Ground improvement using geosynthetics 9.1 9.2

9.3

9.4

9.5

9.6

Introduction   257 Geosynthetic ground improvement  257 9.2.1 Introduction   257 9.2.2 Geosynthetic types used in ground improvement   258 9.2.3 Geosynthetic applications in ground improvement   258 Properties of geosynthetics  263 9.3.1 Introduction 263 9.3.2 Tensile strength  263 9.3.3 Interface friction   264 9.3.4 Durability   265 9.3.5 Geotextile survivability  266 Road base stabilization (Corps of Engineers methods)  266 9.4.1 Introduction   266 9.4.2 Unpaved road improvement using geosynthetics  268 9.4.3 Paved road improvement using geosynthetics  275 9.4.4 Geofibers in roads  280 Embankments over soft ground  282 9.5.1 Introduction   282 9.5.2 Conventional construction of embankments  282 9.5.3 Geosynthetic usage in embankment construction  282 9.5.4 Design procedure  283 9.5.4.1 Slope stability  283 9.5.4.2 Sliding of soil on top of geosynthetic  284 9.5.4.3 Geosynthetic rupture due to sliding  284 9.5.4.4 Pullout of the geosynthetic  285 9.5.4.5 Bearing capacity  286 9.5.4.6 Settlement 286 9.5.4.7 Additional checks  287 9.5.5 Instrumentation 287 9.5.6 Construction guidance  289 9.5.7 Alternative procedures   289 Underfooting reinforcement with rolled geosynthetics  289

257

Contents xi

9.6.1 Introduction 289 9.6.2 Design procedure  290 9.6.3 Construction 293 9.7 Underfooting reinforcement with geocells   293 9.7.1 Introduction 293 9.7.2 Ultimate load calculation  294 9.7.3 State of practice  295 9.7.4 Construction advice   295 9.8 Underfooting reinforcement with geofibers  296 9.8.1 Introduction 296 9.8.2 Design procedure for strength increase  297 9.8.3 Construction advice   297 9.9 Soil separation   298 9.9.1 Introduction   298 9.9.2 Design procedures  298 9.9.3 Construction advice  299 9.10 Problems 300 References 302

10 Reinforcement in walls, embankments on stiff ground, and soil nailing 10.1 Introduction 307 10.2 Mechanically stabilized earth walls  307 10.2.1 Introduction 307 10.2.2 Design philosophy  309 10.2.3 Advantages and disadvantages of MSE walls  309 10.2.4 Design using geosynthetics  309 10.2.4.1 Sliding of the reinforced mass  311 10.2.4.2 Reinforcement breakage  312 10.2.4.3 Reinforcement pullout  313 10.2.4.4 Other failure modes  313 10.2.5 Design of internal components  314 10.2.6 External stability  317 10.2.7 Typical factors of safety  318 10.2.8 Inclusions in the backfill  318 10.2.9 Drainage 318 10.2.10 Other considerations  319 10.2.11 Construction guidelines  319 10.3 Mechanically stabilized earth walls using metal reinforcement  320 10.3.1 Introduction 320 10.3.2 Differences between metal and geosynthetic reinforcement  321 10.3.3 Failure modes and typical factors of safety  321 10.3.4 Inclusions in the backfill  322 10.3.5 Construction guidelines  322 10.4 Reinforced soil embankments on firm foundations using geosynthetic and metal reinforcement  323

307

xii Contents

10.4.1 10.4.2 10.4.3 10.4.4 10.4.5 10.4.6 10.4.7 10.4.8 10.4.9

Introduction 323 Philosophy of how reinforcement for steepened slopes works  324 Engineering properties needed  324 Design notes  325 Construction procedure  326 Inclusions in the backfill 326 Internal stability: pullout and breakage, internal slope stability  327 External stability: bearing capacity, sliding, and settlement  327 Slope face stability: veneer instability, erosion control, and wrapped faces  328 10.4.10 Drainage  328 10.5 Soil nailing  328 10.5.1 Introduction 328 10.5.2 Applications 330 10.5.3 Applicable sites  331 10.5.4 Components of a soil nail system  332 10.5.5 Methods of installing soil nails  333 10.5.6 Design of soil nailed walls  333 10.5.6.1 Failure modes  333 10.5.6.2 Design calculations  334 10.5.7 Construction of soil nailed walls  347 10.5.8 Nail testing  349 10.5.9 Corrosion protection  349 10.5.10 Instrumentation  349 10.5.11 Launched soil nails  351 10.6 Problems 351 References 354

11 Additional techniques in ground improvement 11.1 Jet grouting  358 11.1.1 Introduction to jet grouting 358 11.1.2 Environmental considerations  360 11.1.3 Design considerations in jet grouting  362 11.2 Ground freezing  365 11.2.1 Introduction to ground freezing  365 11.2.2 Fundamentals of ground freezing  367 11.2.3 Properties of frozen ground  370 11.2.4 Containment of contaminated soils  373 11.2.5 Limitations of ground freezing  374 11.2.6 Conclusions regarding ground freezing  374 11.3 Secant pile walls  375 11.4 Compaction grouting  376 11.4.1 Introduction and history  376 11.4.2 Uses 377 11.4.3 Design 379 11.4.4 Construction 380

357

Contents xiii

11.5 Explosives in ground improvement  381 11.5.1 Introduction 381 11.5.2 Applications of explosives  381 11.5.3 Ground conditions favorable to explosives for compaction  382 11.5.4 Construction practice for compaction by explosives  382 11.5.5 Post explosion evaluations  383 11.5.6 Collateral concerns with the use of explosives  383 11.5.7 Case studies  384 11.6 Problems 384 References 385

12 The future of ground improvement engineering

389

12.1 Introduction 389 12.2 Biogeotechnical methods for Ground improvement  390 12.2.1 Biocementation 391 12.2.2 Bioclogging to reduce hydraulic conductivity  393 12.2.3 Bio-methods for liquefaction mitigation  394 12.3 New materials for ground improvement  394 12.3.1 MgO cement  395 12.3.2 Polymers 395 12.3.3 Smart and self-healing materials  395 12.4 Technology developments in ground improvement: drones, sensors, and artificial intelligence  396 12.5 Equipment developments  397 12.6 Sustainability in ground improvement  398 12.6.1 Introduction to sustainable ground improvement  398 12.6.2 Sustainable materials  399 12.7 Crossover information in ground improvement  400 12.8 Summary of future developments in ground improvement  401 12.9 Problems 401 References 401

Index 405

Preface and Acknowledgments: Fundamentals of Ground Improvement Engineering

OVERVIEW Engineers have long known that the properties of soil and rock can be improved. The modern field of ground improvement began to coalesce in the 1960s and has since grown enormously. This textbook synthesizes ground improvement literature and practice in a way that allows students to begin their studies of ground improvement engineering and helps professionals dig deeper into specific topics of relevance to their work. Fundamentals of Ground Improvement Engineering is intended to explain key topics and fundamentals of ground improvement engineering and construction for students and professionals. This book is structured to broadly introduce each topic and then delve into the details. The authors approach the topic from the balanced viewpoints of both academics and professional practice. Overall, this book provides a comprehensive introduction to the field of ground improvement to provide readers with sufficient background to understand and apply the techniques presented. It is the intention of the authors to provide the users of this book with both the current practices in ground improvement as well as the fundamental understanding of the principles to allow users to adapt to inevitable new developments in the field. Readers are expected to already have an understanding of basic geology, the fundamentals of soil mechanics, and the mathematical and natural science training that accompanies the first few years of undergraduate education in civil engineering. In order to accomplish the objectives, this book contains the following elements: • Balanced presentation of academic and practical aspects of ground improvement engineering. • Example problems with solutions and practice problems so readers can see the application of theory. • Information to meet needs in both university and professional markets. From the perspective of the student, the book provides: • A new, up-to-date, comprehensive text which blends the study of current ground improvement technologies with theoretical principles and applicable design and construction information. • Example problems with solutions, and practice problems for additional learning opportunities. • Improved ground improvement courses and offerings as faculty adopt a well-prepared textbook with instructor resources. xv

xvi Preface and Acknowledgments: Fundamentals of Ground Improvement Engineering

From the perspective of practicing professionals, the book provides: • A resource allowing practicing professionals to understand and select ground improvement techniques with confidence. • Up-to-date and thorough reference lists, enabling practicing engineers to access original materials used to evaluate alternatives and prepare designs. • Photos to enable practitioners to use this material in presentations to clients allowing improved communications about ground improvement in the engineering and industrial/commercial environments. PEDAGOGY This new book, Fundamentals of Ground Improvement Engineering, has been written for advanced undergraduate and graduate students and practicing professionals. Most topics are organized on the basis of construction methods rather than a theoretical or analytical organization. In this manner, the goals and means of construction are first presented followed by the underlying geotechnical engineering principles and design considerations. This method of presentation is adopted under the ideology that most people learn best when the material is presented from the general progressing to the specific. This book also includes thorough and up-to-date literature citations as well as an abundance of graphics including photographs, schematics, charts, and graphs. LIMITATIONS Each and every topic in this text is the subject of hundreds of technical papers published in journals, conferences, or even other textbooks. As a result, each topic could easily be the subject of a complete text. The authors encourage readers interested in a given topic to delve more deeply into the literature and citations provided in this text. ACKNOWLEDGMENTS The authors thank their supportive wives and families. Without encouragement and support on the home front, an undertaking such as this simply could not have happened. Thank you, Laurel Evans, Megan Ruffing, and Linda Elton. Bucknell University, Geo-Solutions, Inc. and retirement from full-time teaching all provide an atmosphere where the scholar can flourish. For this, the authors are grateful. The authors have enjoyed working with, and appreciate the assistance of, numerous Bucknell University students that have contributed to this work. Students who reviewed and edited various chapters include Jeff Ayers, E. J. Barben, Landon Barlow, Tim Becker, Mark Beltamello, Bradley Bentzen, Dan Bernard, Paul Bortner, Conner Briggs, Jeremy Byler, Minwoo Cho, John Conte, Michael Cortina, Kate Courtein, Loujin Daher, Akmal Daniyarov, Louis DeLuca, Ben Downing, Jonathan Eberle, Sarah Ebright, Johnna Emanuel, Jack Foley, Jake Hodges, Orman Kimbrough IV, Roger Knittle, Chris Kulish, Rich LaFredo, Muyambi Muyambi, Rachel Schaffer, Chandra Singoyi, Matthew Geiger, Jason McClain, Matthew McKeehan, Kelsey Meybin, Ryan Orbison, Brendan O’Neal, Nolan O’Shea, Michael Pontisakos, Max Pucciarello, Melissa Replogle, Kyle Rindone, Shelby Roberts, Joe Sangimino, Joseph Scalia, Brian Schultz, John Skovira, Ben Stodart, Michael Stromberg,

P reface and Acknowledgments: Fundamentals of Ground Improvement Engineering  xvii

Benjamin Summers, Brendan Swift, Dan Tischinel, Curtis Thormann, Kirsten Vaughan, Brian Ward, Nathaniel Witter, Nikki Woodward, Seungcheol Yeom, Gregory Zarski, and Tyler Zbytek. Special thanks go to Zach Schaeffer and Jeremy Derricks for their contributions. We offer apologies for students overlooked in this listing. The authors also appreciate the review and assistance of Geo-Solutions employees Ken Andromalos, Nathan Coughenour, Wendy Critchfield, and Mark Kitko for their contributions to this effort. The authors also appreciate the assistance of James Pease of McCrossin Engineering, Inc., Paul Marsden and Richard Holmes of Keller UK, Greg Stokkermans of GFL Environmental Inc., and Paul Schmall of Keller NA. Special thanks go to Jennifer A. E. Shields of Cal Poly San Luis Obispo for her work on the cover collage. Many of the figures in this text are original art created by the authors. Some were prepared with the assistance of those contributors listed above. Some photographs were provided by industry professionals as credited in the text. The authors appreciate their willingness to contribute to our efforts. Photographs and artwork not attributed to others are products of the authors and their student assistants. Lastly, the authors are appreciative of the undying patience and guidance of the publishers/editors: Tony Moore, Siobhan Poole, Scott Oakley, Gabriella Williams, and Frazer Merritt of Taylor and Francis. Jeffrey C. Evans, P. E., Professor Emeritus, Bucknell University, Lewisburg, Pennsylvania, USA Daniel G. Ruffing, P. E., Vice-President, Geo-Solutions, New Kensington, Pennsylvania, USA David J. Elton, P. E. Professor Emeritus, Auburn University, Auburn, Alabama, USA

MATLAB® is a registered trademark of The MathWorks, Inc. For product information, please contact: The MathWorks, Inc. 3 Apple Hill Drive Natick, MA 01760-2098 USA Tel: 508 647 7000 Fax: 508-647-7001 E-mail: info​@mathworks​.​com Web: www​.mathworks​.com

Chapter 1

Introduction to ground improvement engineering

1.1 INTRODUCTION Ground modification in the constructed environment is not a new idea. For instance, the method of wattle and daub has been used for thousands of years to provide tensile reinforcement to clayey materials in buildings. The process of adding straw to clay and baking it in the sun improved the strength properties of the clay creating a building material that has been used for thousands of years. In another ancient application, the Romans used timber as a base layer for roads. In modern times, inclusions (such as geogrids and geotextiles) are commonly employed for ground improvement. Similarly, the addition of lime to clay (a chemical admixture in modern terminology) has long been used to create a weak binder in stone foundations. The Roman road, Via Appia, now in modern-day Italy, is the earliest known example of the use of lime in ground improvement engineering (Berechman 2003). The terms ground improvement, ground modification, and similar terms are lexicon of the late 20th century. The first conference on the subject was “Placement and Improvement of Soil to Support Structures” and was held in Cambridge, Massachusetts, in 1968, sponsored by the Division of Soil Mechanics and Foundation Engineering of the American Society of Civil Engineers (ASCE 1968). The first comprehensive textbook on the subject was by Hausmann (1990). University courses on the subject began at about the same time. In many ways, ground improvement engineering is a relatively new field within geotechnical engineering. New developments are occurring at a rapid pace and no doubt will have occurred throughout the life of this book. Thus, this book focuses on fundamentals, enabling the user to understand and adapt to the latest ground improvement developments. How might ground modification/improvement be defined? In the proceedings on the Conference on Soil Improvement (ASCE 1978), the introduction succinctly states that one of the alternatives available when poor soil conditions are encountered is to “treat the soil to improve its properties.” Moseley and Kirsch (2004) in the second edition of their book, Ground Improvement, note that All ground improvement techniques see to improve those soil characteristics that match the desired results of a project, such as an increase in density and shear strength to aid problems of stability, the reduction of soil compressibility, influencing permeability to reduce and control groundwater flow or to increase the rate of consolidation, or to improve soil homogeneity. Schaefer et al. (2017) define ground modification as “the alteration of site foundation conditions or project earth structures to provide better performance under design and/or operational loading conditions.” For the purposes of this book, ground improvement is defined as the application of construction means and methods to improve the properties of soil. 1

2  Fundamentals of ground improvement engineering

Note that some improvements are of the first order. For example, compaction will increase the density of soil. However, density increases can lead to second order effects such as increased strength and reduced compressibility. Finally, these second order improvements can result in third order effects such as increased bearing capacity and reduced settlement and/or improved liquefaction resistance. By beginning with the fundamentals of ground improvement engineering, the text is designed to provide an understanding of both the fundamental first-order effects as well as those second- and third-order effects that are often the actual desired outcome of the application of ground improvement. As there are many definitions of ground improvement and further much gray area within each definition, the authors used this definition as a guide to define the scope of this book. Finally, for the purposes of the selection of the content in this book, the authors use the term ground improvement rather than ground modification. Ground modification is a neutral term meaning the modification could either improve or worsen the ground whereas ground improvement is unambiguous. Prior to in-depth study of ground improvement, what are the alternatives to ground improvement? Imagine a site where the subsurface conditions are not suitable for the anticipated project. While ground improvement is the option to be considered in detail in this book, what are the alternatives? Some common alternatives to the application of ground improvement include: 1. Avoid the site or area: There are many circumstances where the owner/developer has options regarding the location of the proposed facility and finding an alternative site or a different area of the same site is a viable option. 2. Remove and replace: If the unsuitable materials are limited in aerial and/or vertical extent, the best (and most economical) option may be to simply excavate the unsuitable soils and replace them with more suitable materials having more predictable properties, such as crushed stone. This is a commonly chosen alternative when a localized fill is encountered. 3. Transfer load to deeper strata: The use of deep foundations, such as piles or drilled shafts, has long been the option of choice in locations where unsuitable bearing materials are present near the ground surface. Deep foundations affect load transfer through the use of stiff structural members placed between the structure and competent bearing materials found at deeper depths. Although significantly more sophisticated today, this technique has existed for centuries with ample evidence including ancient Roman bridges supported on timber piles. 4. Design structure accordingly: Some sites and structures, in combination, may lend themselves to structural redesign to accommodate the site conditions. For instance, it may be possible to stiffen the structure to redistribute stresses within the structure and minimize differential movement. In a specific application, sinkhole prone areas such as solution-prone geologic settings, grade beams can be used to connect spread footings in order to redistribute loads in case of loss of support beneath any single footing. Likewise, structures can incorporate construction joints, allowing some differential settlement without causing distress. 1.2 IMPROVEMENTS IN SOIL BEHAVIOR Ground improvement may be viewed from the perspective of system performance. For example, it may be necessary to improve the ground to increase the allowable bearing value of a footing supported on the soils beneath a structure. From the system perspective, ground

Introduction 

3

improvement alternatives would be evaluated for their ability to increase bearing capacity and decrease settlement, i.e. increase the allowable bearing value. More precisely, the allowable bearing value can be increased by: 1. increasing the stiffness of the soil (decreases settlement), 2. increasing the shear strength of the soil (increases bearing capacity), and/or 3. decreasing soil property variability (decreases differential settlement). Densifying granular materials or consolidating cohesive materials can increase soil strength and stiffness. Using these definitions, there are many ways ground improvement can be viewed. For the purposes of understanding ground improvement, this text will focus on a fundamental understanding of the interactions between ground improvement techniques and the resulting changes in soil and/or soil system behavior. This text also provides insight into the means and methods used by contractors to implement ground improvement techniques with most of the chapters and information segmented by construction techniques. In this chapter, it is useful to articulate the improvements in soil behavior that may result from the ground improvement methods employed. These fundamental soil behavior characteristics include shear strength, compressibility, hydraulic conductivity, liquefaction potential, shrink and swell behavior, and reduction in variability in any of the aforementioned behavioral characteristics. Details of soil behavior principles related to ground improvement are provided in Chapter 2.

1.2.1 Shear strength Shear strength is a fundamental engineering property of soils that can be increased through the application of numerous ground improvement techniques. Shear strength is a measure of the soil’s ability to resist failure under the application of a load that induces shear stresses in the soil. Shear strength can be increased through ground improvement techniques that decrease the void ratio (Chapters 4, 5, and 11), and/or adding a cohesive (cementing) component (Chapter 6 and 7). There are many applications that benefit from improved shear strength including increased bearing capacity, improved slope stability, and reduced liquefaction potential. The shear strength of soils is a sophisticated concept. There are entire texts devoted solely to this topic. Unconfined compression tests (see Figure 1.1) are a common means to quantitatively judge the benefit of ground improvement efforts. For some projects, more sophisticated testing may be needed. Principles of shear strength, both drained and undrained, are reviewed in Chapter 2.

1.2.2 Compressibility Soil stiffness is a measure of the deformation of soils associated with the application of a load. Compressibility is not a unique value, since it depends on the nature of the load application and the initial stress state of the soil. The soil stiffness can be increased, i.e. decreased compressibility, through ground improvement techniques that reduce void ratio or add a cohesive or cementing component. Cohesive soil stiffness can be increased by compaction (Chapter 4) and consolidation (Chapter 5). Granular soil stiffness is generally increased by densification (Chapter 4). Cohesive and granular material compressibility can also be reduced via increasing cohesiveness through soil mixing (Chapter 6) or grouting (Chapter 7).

4  Fundamentals of ground improvement engineering

Figure 1.1 Unconfined compressive shear strength apparatus.

One of the most well-known cases of excessive deformation (aka settlement) is the campanile (bell tower) in Pisa (see Figure 1.2), aka the “Leaning Tower of Pisa.” Differential movement of the ground below the tower has been the subject of numerous studies and there have been multiple attempts to stabilize the tower. The differential movement results from non-uniform subsurface conditions and is exacerbated by the uneven load application once tilting began. In Figure 1.2, notice the cables extending outward from the left side of the tower. This photograph was taken in 1999 at which time a pulley and counterweight system were in place coupled with lead weights placed directly on the foundation acting as a counterweight employed as an emergency measure to stabilize the tower. Subsequently, ground extraction beneath the high side of the tower proved successful in arresting the movements (Burland et al. 2009). This famous landmark remains a reminder that controlling deformation and preventing strength failures are two key performance criteria for geotechnical engineering projects.

1.2.3 Hydraulic conductivity In most cases, improved ground is ground that is modified to produce a zone of reduced permeability in order to control the detrimental effects of groundwater. For example, flow beneath a dam can lead to soil particle movement (piping) and/or instability. Construction

Introduction 

5

Figure 1.2 The Leaning Tower of Pisa.

projects also frequently require construction below grade and often below the water table. In these cases, construction dewatering is needed. Ground improvement in such cases might include dewatering, installation of a low permeability vertical barrier (Chapter 8), or reduction in permeability by grouting (Chapter 7). As is often the case in practice, hydraulic conductivity and permeability are used interchangeably in this book.

1.2.4 Liquefaction potential Loose granular materials below the groundwater level can be subject to liquefaction (see Figure 1.3) upon the application of a dynamic load, such as during an earthquake. During shaking, loose granular soil deposits generally decrease in volume (i.e. loose soils densify). If these loose soils are located below the water table, drainage would be needed for the soils to actually densify. This drainage requires sufficient time, which for granular materials, is normally not a problem during static loading. However, during earthquake loading, there is insufficient time for drainage which results in an increase in porewater pressure and a reduction in the effective shear strength of the granular soil. These principles of shear strength and liquefaction potential are presented in more detail in Chapter 2. The most common mitigation of this risk is to densify the soils, which reduces their liquefaction potential. Common tools for densifying granular materials are described in Chapter 4. Other ground improvement techniques to reduce liquefaction potential include groundwater control (Chapters 7 and 8) and in situ mixing (Chapter 6).

6  Fundamentals of ground improvement engineering

Figure 1.3  Liquefaction of road foundation in New Zealand (photo courtesy National Environmental Satellite, Data, and Information Service).

1.2.5 Shrink/swell behavior Soils containing smectitic clays are subject to substantial volume changes in response to cycles of wetting and drying. The shrink/swell behavior of these expansive soils can have detrimental effects and can progressively damage a building or cause a retaining wall to fail. Figure 1.4 illustrates road damage due to expansive soils. Understanding clay mineralogy and the resulting expansive behavior (Chapter 2) prior to selecting and designing ground improvement methodologies is important. Ground improvement, through the use of admixtures and in situ mixing (Chapter 6), can minimize the propensity for these materials to change volume with wetting and drying.

1.2.6 Variability Physical and engineering properties of soils are naturally variable. At times, this variability can affect the performance of a planned structure. For example, if the compressibility varies enough from location to location, an excessive differential settlement could be expected. Ground improvement can modify the properties of subsurface materials to provide a more uniform performance. For example, consider the settlement sensitive structure shown in Figure 1.5. Here, the depth to bedrock increased in the downslope direction along the axis of the building. Overlying the bedrock were unconsolidated materials of increasing thickness

Introduction 

7

Figure 1.4 Structural damage due to expansive soils (photo courtesy of Anand Pupala).

Figure 1.5 Settlement sensitive brick structure with variable subsurface conditions.

from one end of the building to the other. Unsurprisingly, concerns with differential settlement arose and a deep foundation system was chosen for the structure (drilled shafts into pinnacled limestone). However, the chosen foundation system was very costly. This short case study serves to illustrate that, under variable site conditions, ground improvement could reduce site variability, permitting an inexpensive shallow foundation system rather than requiring an expensive deep foundation system. For this site, vibro methods (Chapter 5) could have both densified the soils and reduced variability in compressibility across the site. In cases such as this, ground improvement can prove to be significantly less costly and provide performance equivalent to a deep foundation system.

8  Fundamentals of ground improvement engineering

1.3 OVERVIEW OF GROUND IMPROVEMENT TECHNIQUES Ground improvement principles have certain fundamental mechanistic characteristics that are used to develop a classification system for ground improvement. Accordingly, this book uses four defining principles, in order of increasing complexity:

1. control of water – removal or control of groundwater, 2. mechanical modification – rearrangement of soil or water particles, 3. modification by additives – addition of chemicals and, 4. modification by inclusions or confinement – system behavior modification through rigid or flexible element inclusion or soil confinement.

Assigning a particular ground improvement technique to a particular category is imperfect since some techniques possess multiple behavioral characteristics or provide improvement via multiple principles. This results in some techniques having characteristics from more than one category. Nonetheless, such classification system is useful in understanding how particular techniques work on a fundamental level. Based upon how a given ground modification technique improves the soil, this book is structured according to Figure 1.6. Some of the important principles, engineering considerations, and construction methods that are the focus of this book are discussed further in the subsections below.

1.3.1 Compaction: shallow methods Compaction is the densification of soils at constant water content. Consolidation, in contrast, is differentiated from compaction by the decrease in water content due to the application of load to a saturated soil. Compaction (densification) is achieved through the application of mechanical energy to soil such that the air void volume is decreased, increasing soil density. Surface compaction with equipment, such as the pad foot self-propelled roller pictured in Figure 1.7, has long been used to increase strength, reduce compressibility, and reduce the permeability of soils. Examples of ground improvement techniques that use mechanical energy as the principal means to improve soil behavior include surface compaction, deep dynamic compaction, and rapid impact compaction. These are all surface applications of mechanical energy that dissipate with depth. In doing so, the mechanical energy causes a rearrangement of the soil structure into a denser configuration. Shallow (surface) methods of compaction for ground improvement are presented in Chapter 4.

1.3.2 Compaction: deep methods Occasionally, the effective depth of surface compaction is insufficient compared to the depth of material targeted for compaction. Here, deep compaction methods, which apply mechanical energy below the surface, are needed. In most cases, deep compaction methods also employ vibration and often involve the addition of stone, grout, or concrete during the process to fill the space created by the densification. Depending upon the details of the process and the contractor completing the work, various names are given to these deep methods. Such names include, but are not limited to, vibroflotation, vibrocompaction, vibroreplacement, Geopiers®, and rammed aggregate piers® (RAP). For example, Figure  1.8 shows a vibrator used for deep vibrocompaction or vibroreplacement and Figure 1.9 shows the hopper being filled with sand during a vibrocompaction project. These techniques evolved from work done over 70 years ago by the Keller Company (Kirsch and Kirsch 2016). Deep compaction techniques began to flourish in the 1950s and