FHWA_Deep_Mixing_for_Embankment_and_Foundation_Support_2013.pdf

Research, Development, and Technology Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, VA 22101-2296

Federal Highway Administration Design Manual: Deep Mixing for Embankment and Foundation Support

Publication No. FHWA-HRT-13-046 october 2013

FOREWORD

The deep mixing method (DMM) is an in situ soil treatment in which native soils or fills are blended with cementitious and/or other materials, typically referred to as binders. Compared to native soils or fills, the soil-binder composite material that is created has enhanced engineering properties such as increased strength, lower permeability, and reduced compressibility. The treated soil properties obtained by DMM reflect the characteristics of the native soil, binder characteristics, construction variables, operational parameters, curing time, and loading conditions.

The purpose of this report is to provide user-oriented DMM design and construction guidelines for the support of embankments and typical transportation-oriented foundations. The use of DMM for liquefaction mitigation and excavation support is also discussed in general terms, since these applications are often associated with DMM projects for embankments and foundations. The embankment and foundation applications addressed in this manual include embankment support (both new embankments and embankment widening), culvert support through an embankment founded on DMM, bridge abutment support, retaining wall foundations, and bridge pier support.

This manual includes guidelines required for U.S. transportation engineers to plan, design, construct, and monitor deep mixing projects for embankment and foundation support. Information includes background on the use of DMM for transportation projects in the United States; a glossary of commonly used terminology and nomenclature; a description of applications, feasibility, and flow of design and construction for DMM projects; site investigation and characterization considerations; ranges of treated soil properties and a procedure for determining treated soil strengths for design; recommended design procedures for embankment and foundation applications and a design example; a description of contract procurement vehicles and recommendations; guidance for developing plans and specifications for contract documents; guidance for developing bench-scale testing and full-scale field testing programs;

a description of means, methods, and materials for DMM; an overview of available and recommended quality control/quality assurance procedures and monitoring techniques; and typical costs and methods for estimating costs of DMM projects for comparison with alternative technologies.

Jorge E. Pagán-Ortiz Director, Office of Infrastructure Research and Development

Notice This document is distributed under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trade and manufacturers’ names appear in this report only because they are considered essential to the object of the document.

Quality Assurance Statement The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of the information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvements.

TECHNICAL REPORT DOCUMENTATION PAGE

1. Report No.

FHWA-HRT-13-046

2. Government Accession No.

3. Recipient’s Catalog No.

4. Title and Subtitle Federal Highway Administration Design Manual: Deep Mixing for Embankment and Foundation Support

5. Report Date October 2013

6. Performing Organization Code

7. Author(s) Mary Ellen C. Bruce, Ryan R. Berg, James G. Collin, George M. Filz, Masaaki Terashi, and David S. Yang

8. Performing Organization Report No.

9. Performing Organization Name and Address Geotechnica, Sa., Inc.

P.O. Box 178 Venetia, PA 15367

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-06-C-00039

12. Sponsoring Agency Name and Address Office of Transportation Management Federal Highway Administration 400 7th Street SW Washington, DC 20590

13. Type of Report and Period Covered

14. Sponsoring Agency Code

15. Supplementary Notes The Contracting Officer’s Technical Representative (COTR) was Michael Adams, HRDI-40.

16. Abstract This report provides background on deep mixing for U.S. transportation projects and provides further information on design and construction aspects. This report also includes guidelines required for U.S. transportation engineers to plan, design, construct, and monitor deep mixing projects for embankment and foundation support applications.

Considerations for secondary associated applications such as excavation support and liquefaction mitigation are also discussed.

17. Key Words Deep mixing, Design manual, Case histories, Quality control, Quality assurance, Specifications, Construction, Feasibility, Foundations, Embankments

18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161

19. Security Classif. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Pages

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized ii

SI* (MODERN METRIC) CONVERSION FACTORS

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

in inches 25.4 millimeters mm ft feet 0.305 meters m yd yards 0.914 meters m mi miles 1.61 kilometers km

AREA

in2 square inches 645.2 square millimeters mm2 ft2 square feet 0.093 square meters m2 yd2 square yard 0.836 square meters m2 ac acres 0.405 hectares ha mi2 square miles 2.59 square kilometers km2

VOLUME

fl oz fluid ounces 29.57 milliliters mL gal gallons 3.785 liters L ft3 cubic feet 0.028 cubic meters m3 yd3 cubic yards 0.765 cubic meters m3

NOTE: volumes greater than 1000 L shall be shown in m3

MASS

oz ounces 28.35 grams g lb pounds 0.454 kilograms kg T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")

TEMPERATURE (exact degrees) oF Fahrenheit 5 (F-32)/9 Celsius oC or (F-32)/1.8

ILLUMINATION

fc foot-candles 10.76 lux lx fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS lbf poundforce 4.45 newtons N lbf/in2 poundforce per square inch 6.89 kilopascals kPa

APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

mm millimeters 0.039 inches in m meters 3.28 feet ft m meters 1.09 yards yd km kilometers 0.621 miles mi

AREA

mm2 square millimeters 0.0016 square inches in2 m2 square meters 10.764 square feet ft2 m2 square meters 1.195 square yards yd2 ha hectares 2.47 acres ac km2 square kilometers 0.386 square miles mi2

VOLUME

mL milliliters 0.034 fluid ounces fl oz L liters 0.264 gallons gal m3 cubic meters 35.314 cubic feet ft3 m3 cubic meters 1.307 cubic yards yd3

MASS

g grams 0.035 ounces oz kg kilograms 2.202 pounds lb Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T

TEMPERATURE (exact degrees) oC Celsius 1.8C+32 Fahrenheit oF

ILLUMINATION

lx lux 0.0929 foot-candles fc cd/m2 candela/m2 0.2919 foot-Lamberts fl

FORCE and PRESSURE or STRESS N newtons 0.225 poundforce lbf kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for th International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. e (Revised March 2003) iii

TABLE OF CONTENTS

CHAPTER 1. INTRODUCTION TO THE DEEP MIXING METHOD IN THE

UNITED STATES

1.1 INTRODUCTION

1.2 SCOPE OF MANUAL

1.3 STUDY AND USE OF DMM BY U.S. TRANSPORTATION AGENCIES

CHAPTER 2. TERMINOLOGY

CHAPTER 3. APPLICATIONS, FEASIBILITY, AND FLOW OF DESIGN AND

CONSTRUCTION FOR DMM PROJECTS

3.1 TYPICAL DMM TRANSPORTATION APPLICATIONS

3.2 FEASIBILITY OF USING DMM

3.2.1 Advantages and Potential Limitations of DMM

3.2.2 Feasibility Evaluation for Using Deep Mixing for Transportation Projects

3.3 DESIGN AND CONSTRUCTION FLOW FOR DMM PROJECTS

3.3.1 Data Collection

3.3.2 Analysis and Design

3.3.3 Contractor Procurement

3.3.4 Construction and QC/QA

CHAPTER 4. SITE EXPLORATION PROGRAM

4.1 INTRODUCTION

4.2 PHASED APPROACH TO SITE EXPLORATION

4.2.1 Phase 1—Office Studies and Site Reconnaissance

4.2.2 Phase 2—Preliminary Field Investigations and Laboratory Testing

4.2.3 Phase 3—Detailed Field Investigations and Laboratory Testing

4.3 GENERAL SITE EXPLORATION PLANNING FOR DMM PROJECTS

4.4 IMPORTANT SITE EXPLORATION DETAILS FOR DMM PROJECTS

CHAPTER 5. TREATED SOIL PROPERTY VALUES FOR DESIGN

5.1 INTRODUCTION

5.2 PHASE RELATIONSHIPS

5.3 ENGINEERING PROPERTY VALUES FOR DMM DESIGNS

5.4 STRENGTH

5.4.1 Factors that Influence the Strength of Deep Mixed Soil

5.4.2 Effect of Total Water-to-Binder Ratio

5.4.3 Effect of Curing Time

5.4.4 Peak Unconfined Strength Versus Residual Confined Strength

5.4.5 Unconfined Compressive Strength from Laboratory-Prepared Specimens

5.4.6 Differences Between the Strength of Laboratory-Prepared Specimens and Field- Mixed Specimens

5.4.7 Unconfined Compressive Strength Specified on Previous Projects

5.4.8 Strength Variability

5.4.9 Characteristics of the Strength Envelope for Design

5.4.10 Establishing a Project-Specific Range of Unconfined Compressive Strengths

5.5 MODULUS

iv

5.6 POISSON’S RATIO

5.7 PERMEABILITY (HYDRAULIC CONDUCTIVITY)

5.8 UNIT WEIGHT

CHAPTER 6. DESIGN RECOMMENDATIONS

6.1 DESIGN OF DEEP MIXING TO SUPPORT EMBANKMENTS

6.1.1 Step 1—Establish Project Requirements

6.1.2 Step 2—Establish Representative Subsurface Conditions

6.1.3 Step 3—Establish Trial Deep Mixed Ground Property Values

6.1.4 Step 4—Establish Trial Deep Mixed Geometry

6.1.5 Step 5—Evaluate Settlement

6.1.6 Step 6—Evaluate Stability

6.1.7 Step 7—Prepare Plans and Specifications

6.1.8 Basis for Design Procedure

6.2 DESIGN CONSIDERATIONS FOR DMM SUPPORTED STRUCTURES

6.3 LIQUEFACTION MITIGATION

6.4 EXCAVATION SUPPORT

CHAPTER 7. DESIGN EXAMPLE

7.1 INTRODUCTION

7.1.1 Step 1—Establish Project Requirements

7.1.2 Step 2—Establish Representative Subsurface Conditions

7.1.3 Step 3—Establish Trial Deep Mixed Ground Property Values

7.1.4 Step 4—Establish Trial Deep Mixed Geometry

7.1.5 Step 5—Evaluate Settlement

7.1.6 Step 6—Evaluate Stability

7.1.7 Step 7—Prepare Plans and Specifications

CHAPTER 8. CONTRACTOR PROCUREMENT

8.1 RECOMMENDED CONTRACTING APPROACH

8.2 MEASUREMENT AND PAYMENT

8.3 OTHER PROCUREMENT METHODS

8.4 CONTRACTOR QUALIFICATIONS

CHAPTER 9. SPECIFICATIONS, PLANS, AND CONTRACTOR SUBMITTALS

9.1 SPECIFICATIONS

9.2 PLANS

9.3 CONTRACTOR SUBMITTALS

9.3.1 Contractor Experience Profile

9.3.2 Bench-Scale Testing Results

9.3.3 Field Validation Program Plan

9.3.4 Deep Mixing Work Plan

9.3.5 Material Certifications

9.3.6 Production Records

9.3.7 QC/QA Records

9.3.8 As-Built Field Measurement Data

v

CHAPTER 10. BENCH-SCALE TESTING AND FIELD VALIDATION PROGRAM ...107

10.1 TIMING OF PRECONSTRUCTION TESTING ACTIVITIES

10.2 BENCH-SCALE TESTING

10.2.1 Goals of Bench-Scale Testing Program

10.2.2 Bench-Scale Testing Program

10.3 FIELD VALIDATION PROGRAM (FULL-SCALE FIELD TESTING)

10.3.1 Goals of Full-Scale Field Testing

10.3.2 Full-Scale Field Testing Program

CHAPTER 11. CONSTRUCTION

11.1 CLASSIFICATION OF METHODS

11.2 WET MIXING METHODS

11.2.1 Slurry Batch Plant

11.2.2 Wet Mixing Equipment and Processes

11.2.3 WRS Methods

11.2.4 WRE Methods

11.2.5 WJE Methods

11.2.6 WVP Methods

11.3 DRY MIXING METHODS

11.3.1 Binder Injection Equipment

11.3.2 Dry Mixing Equipment and Process

11.4 OPERATIONAL CONSIDERATIONS

11.4.1 Injection Method

11.4.2 Rotation and Penetration Speeds

11.4.3 Tooling Geometry

CHAPTER 12. QC/QA

12.1 INTRODUCTION

12.2 QC

12.2.1 Role of QC Personnel

12.2.2 Bench-Scale and Field Validation (Full-Scale Field Testing) Programs

12.2.3 Deep Mixing Work Plan

12.2.4 Materials and Production Monitoring

12.2.5 QC Documentation

12.3 QA

12.3.1 Role of QA Personnel

12.3.2 Engineering Properties to be Verified for QA Purposes

12.3.3 Coring

12.3.4 Wet Grab Sampling

12.3.5 Other Verification Methods

12.3.6 Acceptance Criteria

12.3.7 Remedial Measures for Noncompliance

CHAPTER 13. COST ESTIMATING

13.1 FACTORS THAT AFFECT DMM COSTS

13.2 UNIT COSTS FOR DMM

13.3 MOBILIZATION/DEMOBILIZATION

13.4 QC/QA COSTS

vi

13.5 ENGINEERING COSTS

13.6 MEASUREMENT AND PAYMENT

APPENDIX A. LABORATORY PROCEDURE FOR MIXING, CURING,

AND STRENGTH TESTING OF TREATED SOIL SPECIMENS APPLICABLE

TO WET MIXING

EQUIPMENT AND MATERIALS

MATERIAL PREPARATION AND STORAGE PRIOR TO USE

SOIL MIXING

BINDER SLURRY MIXING

SOIL-BINDER MIXING

PLACING THE MIXTURE IN THE MOLDS

CURING

SPECIMEN PREPARATION AND TESTING

DATA REDUCTION

APPENDIX B. CALCULATIONS FOR LABORATORY PREPARATION OF

SOIL-CEMENT MIXTURES FOR APPLICATION TO WET MIXING

APPENDIX C. GUIDE CONSTRUCTION SPECIFICATION FOR DEEP MIXING

DEEP MIXING GUIDE CONSTRUCTION SPECIFICATION

PART 1—GENERAL

1.1 Scope

1.2 References

1.3 Definitions

1.4 Project Description and Performance Requirements

1.5 Qualifications of Contractor

1.6 Available Information

1.7 Construction Site Survey

1.8 Submittals

1.9 Preconstruction Meeting

PART 2—MATERIALS AND EQUIPMENT

2.1 Materials

2.2 Equipment

2.3 Products

PART 3—EXECUTION

3.1 General

3.2 Field Validation Program

3.3 Binder Preparation (Wet Method)

3.4 Locating Elements

3.5 Mixing

3.6 QC

PART 4—MEASUREMENT AND PAYMENT

APPENDIX D. TABULATED DATA FOR DMM METHODS AND EQUIPMENT

USED INTERNATIONALLY

ACKNOWLEDGMENTS

REFERENCES

vii

LIST OF FIGURES

Figure 1. Illustration. Embankment supported on DMM Figure 2. Illustration. Cut and cover culvert supported on DMM through embankment Figure 3. Illustration. Abutment supported on deep foundations and adjacent embankment supported on DMM Figure 4. Illustration. Abutment and embankment supported on DMM Figure 5. Illustration. Retaining wall supported on DMM without retained soil supported on

DMM

Figure 6. Illustration. Bridge pier supported on DMM Figure 7. Flowchart. Design and construction for DMM projects Figure 8. Illustration. Typical configuration of DMM columns for transportation applications .. 22 Figure 9. Illustration. External stability mode of failure for overturning and sliding Figure 10. Illustration. External stability mode of failure for bearing capacity Figure 11. Illustration. Internal stability mode of failure for circular sliding surface Figure 12. Illustration. Internal stability mode of failure for vertical shearing Figure 13. Illustration. Phase diagrams for dry mixing Figure 14. Illustration. Phase diagrams for wet mixing Figure 15. Equation. Specific gravity of soil solids Figure 16. Equation. Specific gravity of the binder Figure 17. Equation. Binder factor in-place Figure 18. Equation. Binder content Figure 19. Equation. Total water-to-binder ratio Figure 20. Equation. Volume ratio expressed in terms of binder factor for any degree of saturation Figure 21. Equation. Volume ratio expressed in terms of binder factor in-place for S = 1 Figure 22. Equation. Volume ratio expressed in terms of binder factor in-place for any S Figure 23. Equation. Volume ratio expressed in terms of binder content for any S Figure 24. Equation. Volume ratio expressed in terms of total-water-to-binder ratio for any S Figure 25. Equation. Binder factor expressed in terms of binder factor in-place for S = 1 Figure 26. Equation. Binder factor expressed in terms of binder factor in-place for any S Figure 27. Equation. Binder factor expressed in terms of binder content for any S Figure 28. Equation. Binder factor expressed in terms of total-water-to-binder ratio for any S Figure 29. Graph. Unconfined compressive strength versus total water-to-cement ratio for laboratory-mixed and tested specimens Figure 30. Equation. Curing factor Figure 31. Equation. Total unit weight of a saturated mixture using dry mixing Figure 32. Equation. Total unit weight of a saturated mixture using wet mixing Figure 33. Equation. Shear strength of the deep mixed ground Figure 34. Equation. Young’s modulus of deep mixed ground for wet mixing Figure 35. Equation. Young’s modulus of deep mixed ground for dry mixing Figure 36. Illustration. Typical arrangement for deep-mixed zone beneath an embankment Figure 37. Equation. Area replacement ratio beneath the central portion of an embankment Figure 38. Illustration. Definition sketch for column overlap calculations viii

Figure 39. Equation. Area replacement ratio under the side slopes of the embankment Figure 40. Equation. Chord angle expressed in radians Figure 41. Equation. Chord length Figure 42. Equation. Overlap area ratio Figure 43. Equation. Area replacement ratio of the shear walls Figure 44. Equation. Area replacement ratio beneath central portion of embankment Figure 45. Equation. Ratio of chord length to shear wall spacing Figure 46. Equation. Composite modulus Figure 47. Equation. Compression of the treated zone Figure 48. Illustration. Potential sliding surfaces and assignment of composite shear strength, sdm,center and sdm,wall Figure 49. Equation. Composite shear strength of the deep mixed zone beneath the shear walls Figure 50. Equation. Composite shear strength of the deep mixed zone beneath the central portion of the embankment Figure 51. Illustration. Definition sketch for combined overturning and bearing calculations Figure 52. Equation. Mobilized total stress cohesion intercept Figure 53. Equation. Mobilized total stress friction angle Figure 54. Equation. Mobilized effective stress cohesion intercept Figure 55. Equation. Mobilized effective stress friction angle Figure 56. Equation. Vertical force Figure 57. Equation. Effective vertical force Figure 58. Equation. Location of total resultant force Figure 59. Equation. Location of the resultant force acting on the base of the deep mixed zone Figure 60. Equation. Bearing pressure at the toe of the deep mixed shear walls using total normal stresses Figure 61. Equation. Bearing pressure at the toe of the deep mixed shear walls using effective normal stresses Figure 62. Equation. Allowable bearing pressure at the toe of the deep mixed shear walls using total normal stresses Figure 63. Equation. Allowable bearing pressure at the toe of the deep mixed shear walls using a total stress friction angle equal to zero Figure 64. Equation. Allowable bearing pressure at the toe of the deep mixed shear walls using effective normal stresses Figure 65. Equation. Allowable bearing capacity of the deep mixed ground against crushing of the deep mixed shear walls at the outside toe of the embankment Figure 66. Equation. Total lateral earth pressure Figure 67. Equation. Effective lateral earth pressure Figure 68. Illustration. Racking failure mode Figure 69. Equation. Average vertical shear stress Figure 70. Equation. Allowable vertical shear stress Figure 71. Equation. Maximum clear spacing between shear walls Figure 72. Equation. Allowable axial structural capacity of a deep mixed column Figure 73. Illustration. Plan view of soil-cement columns on BART project Figure 74. Illustration. DMM treatment plan ix

Figure 75. Illustration. Typical configuration of DMM for liquefaction mitigation Figure 76. Illustration. Example problem—embankment cross section Figure 77. Equation. Example problem—curing factor Figure 78. Equation. Example problem—shear strength of the deep mixed ground Figure 79. Equation. Example problem—determine Edm according to figure 34 Figure 80. Equation. Example problem—area replacement ratio beneath the central portion of the embankment Figure 81. Equation. Example problem—chord angle in radians Figure 82. Equation. Example problem—ratio of chord length to shear wall spacing Figure 83. Equation. Example problem—composite modulus Figure 84. Equation. Example problem—compression of the treated zone Figure 85. Equation. Example problem—composite shear strength of the deep mixed zone beneath the shear walls Figure 86. Equation. Example problem—composite shear strength of the deep mixed zone beneath the central portion of the embankment Figure 87. Illustration. Slope stability results Figure 88. Equation. Example problem—shear strength of the soft clay using total normal stresses Figure 89. Equation. Example problem—mobilized total stress friction angle of the soft clay ... 83 Figure 90. Equation. Example problem—composite shear strength of the center deep mixed zone using total normal stresses Figure 91. Equation. Example problem—composite shear strength of the embankment material using effective normal stresses Figure 92. Equation. Example problem—mobilized effective stress friction angle of the embankment material Figure 93. Equation. Example problem—mobilized effective stress friction angle of the dense sand layer Figure 94. Equation. Example problem—effective stress active lateral earth pressure coefficient Figure 95. Equation. Example problem—active force component from embankment Figure 96. Equation. Example problem—vertical distance from overturning point to line of action of active force component from embankment Figure 97. Equation. Example problem—active force component from surcharge Figure 98. Equation. Example problem—vertical distance from overturning point to line of action of active force component from surcharge Figure 99. Equation. Example problem—active force component from clay rectangle Figure 100. Equation. Example problem—vertical distance from overturning point to line of action of active force component from clay rectangle Figure 101. Equation. Example problem—active force component from clay triangle Figure 102. Equation. Example problem—vertical distance from overturning point to line of action of active force component from clay triangle Figure 103. Equation. Example problem—total active force Figure 104. Equation. Example problem—vertical distance between overturning point and total active force Figure 105. Equation. Example problem—active side shear force from the soft clay Figure 106. Equation. Example problem—passive side shear force from the soft clay x

Figure 107. Equation. Example problem—passive lateral force component from the clay rectangle Figure 108. Equation. Example problem—vertical distance from overturning point to line of action of passive force component from the clay rectangle Figure 109. Equation. Example problem—passive lateral earth force component from the clay triangle Figure 110. Equation. Example problem—vertical distance from the overturning point to the line of action of passive force component from clay triangle Figure 111. Equation. Example problem—total passive lateral earth force Figure 112. Equation. Example problem—vertical distance between the overturning point and the total passive force Figure 113. Equation. Example problem—weight of the embankment Figure 114. Equation. Example problem—location of the resultant of the embankment weight Figure 115. Equation. Example problem—weight of the deep mixed zone Figure 116. Equation. Example problem—location of the resultant of the deep mixed zone Figure 117. Equation. Example problem—total weight Figure 118. Equation. Example problem—location of the resultant of the total weight Figure 119. Equation. Example problem—resultant total vertical force Figure 120. Equation. Example problem—water force acting on the base of the deep mixed zone Figure 121. Equation. Example problem—location of water force acting on the base of the deep mixed zone Figure 122. Equation. Example problem—resultant effective vertical force Figure 123. Equation. Example problem—location of total resultant force acting on the base of the deep mixed zone Figure 124. Equation. Example problem—location of the effective resultant force acting on the base of the deep mixed zone Figure 125. Equation. Example problem—Position of resultant within the base Figure 126. Equation. Example problem—bearing pressure at the toe of the deep mixed shear walls Figure 127. Equation. Example problem—allowable bearing pressure at the toe of the deep mixed shear walls Figure 128. Equation. Example problem—at-rest lateral earth pressure coefficient Figure 129. Equation. Example problem—effective vertical stress Figure 130. Equation. Example problem—at-rest effective lateral earth pressure Figure 131. Equation. Example problem—allowable bearing capacity of deep mixed ground ... 89 Figure 132. Equation. Example problem—location of the force resultant along the base of the deep mixed zone Figure 133. Equation. Example problem—average vertical shear stress on the critical vertical plane Figure 134. Equation. Example problem—allowable vertical shear stress in the deep mixed zone Figure 135. Equation. Example problem—maximum clear spacing between shear columns Figure 136. Graph. General allocation of responsibility between owner and GC or DMM contractor based on contracting approach xi

Figure 137. Flowchart. Classification of vertical axis DMMs based on agent (W/D), penetration/mixing principle (R/J/V), and location of mixing action (S/E/P) Figure 138. Photo. Slurry batching plant for larger mixing project Figure 139. Photo. Typical WRS mixing machine Figure 140. Photo. Typical blade-based tooling for WRS mixing Figure 141. Photo. Second view of typical blade-based tooling for WRS mixing Figure 142. Photo. Typical auger-based tools for WRS methods Figure 143. Photo. WRE mixing equipment Figure 144. Photo. Typical tools used for WRE mixing Figure 145. Photo. Second view of typical tools used for WRE mixing Figure 146. Photo. CSM method cutter wheels Figure 147. Photo. Example of a WJE tool Figure 148. Photo. TRD tooling Figure 149. Photo. Second view of TRD tooling Figure 150. Photo. Typical binder delivery unit for dry mixing Figure 151. Photo. Typical mixing tool for DRE methods Figure 152. Photo. Typical mixing tool for DRE methods for peat mixing Figure 153. Photo. Horizontal mixing tool for mass soil stabilization Figure 154. Equation. BRN Figure 155. Equation. Dry unit weight expressed in terms of the total unit weight of the soil and the water content Figure 156. Equation. Dry unit weight expressed in terms of the specific gravity, water content, and degree of saturation Figure 157. Equation. Dry unit weight expressed in terms of the specific gravity and water content for saturation equal to 1 Figure 158. Equation. Degree of saturation Figure 159. Equation. Dry unit weight of slurry Figure 160. Equation. Volume of soil-cement mixture Figure 161. Equation. Weight of soil Figure 162. Equation. Weight of binder used in the slurry Figure 163. Equation. Weight of water used in the slurry Figure 164. Equation. Water-to-binder ratio of slurry Figure 165. Equation. Volume ratio of mixed soil Figure 166. Equation. As-mixed binder factor in-place for any degree of saturation Figure 167. Equation. As-mixed binder factor in-place for saturation equal to 1 Figure 168. Equation. As-mixed binder factor expressed in terms of VR and dry unit weight of slurry Figure 169. Equation. Binder content of mixed soil Figure 170. Equation. Total water-to-binder ratio of mixed soil Figure 171. Equation. Adjusted weight of slurry water xii

LIST OF TABLES

Table 1. Use of DMM for embankment and foundation applications Table 2. Summary of DMM usage for U.S. transportation projects Table 3. Relative advantages and disadvantages of DMM for general transportation project applications (adapted from FHWA) Table 4. Alternative technologies to DMM Table 5. Factors to consider in feasibility assessment for using DMM Table 6. Summary of evaluations, information, and testing considerations for highway applications of DMM Table 7. Guidelines for minimum numbers and depths of investigation points for highway applications of DMM Table 8. Definitions of deep mixing parameters Table 9. Factors affecting strength of deep mixed soil Table 10. Specified strengths for selected DMM projects Table 11. Typical design values of safety factors for design of deep mixing to support embankments Table 12. Values of fv Table 13. Values of β, c/d, and ae for selected values of e/d Table 14. Values of as,shear for selected values of e/d and d/s Table 15. Values of c/sshear for selected values of e/d and d/s Table 16. Geometric parameters necessary for design Table 17. Example problem—geometric parameters Table 18. Typical allocation of responsibilities of owner and contractor for DMM work Table 19. Suggested pay items and units of measure for DMM contract items Table 20. Typical equipment and common applications for the four general classifications of wet mixing methods Table 21. Generalized factors affecting costs of DMM projects for embankment and foundation support Table 22. Unit costs and associated general project conditions Table 23. Strength correction factors Table 24. Batch mix proportions and trend-line strengths Table 25. Allowable geometric parameters for DMM construction Table 26. Measurement and payment items for DMM contracts Table 27. Equipment, tooling, and treated soil properties for DSM and SMW techniques Table 28. Equipment, tooling, and treated soil properties for TREVIMIX Wet and Colmix techniques Table 29. Equipment, tooling, and treated soil properties for Soil Removal Technique and CDM Table 30. Equipment, tooling, and treated soil properties for SSM and in situ stabilization (ISS) auger method techniques Table 31. Equipment, tooling, and treated soil properties for RAS column method and rectangular 1 (cutting wheels) techniques Table 32. Equipment, tooling, and treated soil properties for rectangular 2 (box columns) and single auger mixing (SAM) techniques xiii

Table 33. Equipment, tooling, and treated soil properties for cementation and single axis tooling techniques Table 34. Equipment, tooling, and treated soil properties for Rotomix and CSM method techniques Table 35. Equipment, tooling, and treated soil properties for spread wing (SWING) technique Table 36. Equipment, tooling, and treated soil properties for JACSMAN and LDis techniques Table 37. Equipment, tooling, and treated soil properties for GeoJetTM and Hydramech techniques Table 38. Equipment, tooling, and treated soil properties for RAS Jet and TURBOMIX techniques Table 39. Equipment, tooling, and treated soil properties for TRD and dry jet mixing techniques Table 40. Equipment, tooling, and treated soil properties for Nordic Method and TREVIMIX DRY techniques Table 41. Equipment, tooling, and treated soil properties for MDM and dry soil mixing mass techniques Table 42. Equipment, tooling, and treated soil properties for Schnabel DMW technique xiv

LIST OF ACRONYMS

BART Bay Area Rapid Transit

BRN Blade rotation number

Caltrans California Department of Transportation

CDIT Coastal Development Institute of Technology

CDM Cement deep mixing

CDSM Cement deep soil mixing

CPT Cone penetration test

CSM Cutter soil mixing

DJM Dry jet mixing

DMM Deep mixing method

DRE Dry rotary end

DSM Deep soil mixing

ECI Early contractor involvement

FDOT Florida Department of Transportation

FHWA Federal Highway Administration

GC General contractor

GPS Global Positioning System

GWT Ground water table

ISS In situ stabilization

LPV Lake Pontchartrain and Vicinity

MassDOT Massachusetts Department of Transportation

MDM Modified deep mixing

MnDOT Minnesota Department of Transportation

PCC Portland cement concrete

PennDOT Pennsylvania Department of Transportation

PWPR Porewater pressure response ratio

QA Quality assurance

QC Quality control

RQD Rock quality designation

SPT Standard penetration test

TPF Transportation Pooled Fund xv

TRD Trench cutting and remixing deep wall method

USACE U.S. Army Corps of Engineers

VDOT Virginia Department of Transportation

WisDOT Wisconsin Department of Transportation

WJE Wet jet end

WRE Wet rotary end

WRS Wet rotary shaft

WSDOT Washington State Department of Transportation

WVP Wet vertical panel

CHAPTER 1. INTRODUCTION TO THE DEEP MIXING METHOD IN THE

UNITED STATES

1.1 INTRODUCTION

The deep mixing method (DMM) is an in situ soil treatment in which native soils or fills are blended with cementitious and/or other materials, typically referred to as binders. Compared to native soils or fills, the soil-binder composite material that is created has enhanced engineering properties such as increased strength, lower permeability, and reduced compressibility. Soils best suited to DMM include cohesive soils with high moisture contents and loose, saturated, fine granular soils. DMM has also been used successfully in a wide range of less cohesive soils and fills, but it is typically not feasible in very dense or stiff materials or in ground with obstructions such as cobbles or boulders. The treated soil properties obtained by DMM reflect the characteristics of the native soil, binder characteristics, construction variables, operational parameters, curing time, and loading conditions.

Two types of DMMs are used in the United States: wet mixing and dry mixing. Wet mixing involves injecting binders in slurry (wet) form to blend with the soil. Primarily single-auger, multi-auger, or cutter-based mixing processes are used with cement-based slurries to create isolated elements, continuous walls or blocks for large-scale foundation improvement, earth retaining systems, hydraulic barriers, and contaminant/fixation systems. Dry mixing uses binders in powder (dry) form that react with the water already present in the soil. Primarily single-auger dry mixing processes are used with lime and lime-cement mixtures to create isolated columns, panels, or blocks for soil stabilization as well as reinforcement of cohesive soils.

The generic term DMM is recommended and used within this manual. This term is inclusive of other terms such as deep soil mixing (DSM) and cement deep soil mixing (CDSM).

1.2 SCOPE OF MANUAL

In 2000 and 2001, the Federal Highway Administration (FHWA) produced a three-volume research report outlining the use of DMM for geotechnical applications.(1–3) The study focused on the applications, equipment, market conditions, and properties of treated soils produced using DMM. This study was followed by the research contributions of the National Deep Mixing Program, a Transportation Pooled Fund (TPF) Program study, TPF-5(001). TPF is a funding mechanism for State transportation departments and FHWA to pool financial and personnel resources to plan and conduct research projects of mutual interest. To increase the benefit of these efforts, FHWA commissioned the development of an unpublished literature review report as well as this design manual. The purpose of the literature review was to compile the information relevant to this report that was available from FHWA research efforts and national and international technical literature, provide background information on U.S. deep mixing for transportation projects, and identify additional sources information on design and construction methods.

The purpose of this report is to provide user-oriented DMM design and construction guidelines for the support of embankments and typical transportation-oriented foundations. The use of DMM for liquefaction mitigation and excavation support is also discussed in general terms since these applications are often associated with DMM projects for embankments and foundations.

Detailed liquefaction mitigation guidance is presented by Siddharthan and Suthahar.(4) Design guidance for excavation support is presented by Rutherford et al.(5) DMM is also frequently and successfully used to create hydraulic (seepage) cutoff walls or to remediate and/or contain environmentally hazardous materials. Seepage cutoffs and environmental applications are not addressed within the scope of this manual.

The embankment and foundation applications addressed in this manual are described in table 1 and depicted schematically in figure 1 through figure 6.

Table 1. Use of DMM for embankment and foundation applications.

Application Description

Embankment support (both new embankments and embankment widening)

Embankment supported on isolated DMM elements (single columns, multi-auger overlapping columns, or barrettes), continuous shear walls formed by overlapping elements, or fully treated blocks formed by overlapping elements

Culvert through an embankment on DMM

Cut and cover culvert supported on DMM through an embankment supported on DMM

Bridge abutment support Abutment supported on deep foundations and embankment on

DMM

Abutment and embankment supported on DMM

Retaining wall foundations

Retaining wall supported on DMM without retained soil supported on DMM

Bridge pier support Bridge pier supported on DMM; generally, DMM would be used for this application if DMM is also being used to support the bridge approaches

Figure 1. Illustration. Embankment supported on DMM.

Figure 2. Illustration. Cut and cover culvert supported on DMM through embankment.

Figure 3. Illustration. Abutment supported on deep foundations and adjacent embankment supported on DMM.

Figure 4. Illustration. Abutment and embankment supported on DMM.

Figure 5. Illustration. Retaining wall supported on DMM without retained soil supported on DMM.

Figure 6. Illustration. Bridge pier supported on DMM.

The design portion of this manual focuses on deep mixing support of embankments. In most circumstances, for DMM to be considered for structure support, DMM would also have to be used for support of the embankment. Equipment mobilization costs and other start-up costs are often too high to justify the use of DMM at structure locations alone. Design recommendations for DMM support of structures are provided in this manual, but because embankment support is generally the deciding factor, this report mainly describes embankment support.

The chapters and associated content of this report are organized as follows:

• Chapter 1: Provides the scope of the manual and background information on the use of DMM for transportation projects in the United States.

• Chapter 2: Introduces a glossary of commonly used terminology.

• Chapter 3: Describes applications, feasibility, and flow of design and construction for DMM projects.

• Chapter 4: Includes site investigation and characterization considerations.

• Chapter 5: Provides ranges of treated soil properties and a procedure for determining treated soil strengths for design.

• Chapter 6: Details recommended design procedures for embankment and foundation applications.

• Chapter 7: Provides an example illustrating the design methods.

• Chapter 8: Describes contract procurement vehicles and recommendations.

• Chapter 9: Provides guidance for developing plans and specifications for contract documents.

• Chapter 10: Includes guidance for developing bench-scale testing and full-scale field testing programs.

• Chapter 11: Provides a construction overview (i.e., means, methods, and materials for DMM).

• Chapter 12: Describes an overview of available and recommended quality control/ quality assurance (QC/QA) procedures and monitoring techniques.

• Chapter 13: Explains typical costs and methods for estimating costs of DMM projects for comparison with alternative technologies.

• Appendix A: Includes guidelines for preparing laboratory specimens for wet mixing methods.

• Appendix B: Includes guidelines for testing laboratory specimens for wet mixing methods.

• Appendix C: Provides guide specifications.

• Appendix D: Showcases tabulated data for DMM methods and equipment used internationally.

1.3 STUDY AND USE OF DMM BY U.S. TRANSPORTATION AGENCIES

Although DMM was invented in the United States in 1954, current methods mainly reflect developments made in Japan and Nordic countries over the past 40 years.(1) Until 1996, the international technical literature included many papers on the development and use of DMM.

However, most of the papers were published in Japanese and Swedish. In 1996, an international conference on grouting and deep mixing was held in Tokyo, Japan, and the official conference language was English. This conference represented the first major exposure of U.S. engineers to the extent and potential use of the various techniques included in DMM. Some types of modern DMM had been in use in the United States since 1986.(6)

In 1997, FHWA began a concerted effort to research and study DMM and its applications.

The first studies focused on gathering and summarizing information on DMM applications, equipment, and operations.(1,2) A later study focused on compiling and defining engineering characteristics of ground treated using DMM.(3)

In 1999, FHWA developed a ground improvement course and an accompanying reference manual.(7) This course covered traditional ground improvement techniques, included a module on DMM, and was offered and taught nationwide to State transportation departments. This was the first FHWA teaching vehicle that systematically introduced DMM to U.S. transportation engineers. The DMM module included applications, advantages, and potential limitations and introduced contemporary design techniques. Sufficient information was provided to allow engineers to assess the feasibility of using DMM as compared to alternative technologies.

Comprehensive design and construction details were not included. In 2003, this demonstration course was developed into a 3-day National Highway Institute course, “Ground Improvement Methods,” which is offered nationwide and internationally. The accompanying reference manuals, Ground Improvement Methods Volume I and Ground Improvement Methods Volume II, represent an update to the 2001 reference manual.(8,9)

Recognizing the need for more detailed engineering tools for practicing engineers, FHWA developed the National Deep Mixing Research Program in 2001. The program was created as a TPF Program study and was established to facilitate the advancement and implementation of DMM technology through partnered research and dissemination of international experience.(10) Researchers from the National Deep Mixing Research Program administered and developed a series of practice-oriented reports on a range of DMM topics that address various design and laboratory issues.

In addition to these efforts, numerous researchers and practitioners have contributed to the published technical literature on DMM in the United States. Many papers on U.S. DMM advances have been presented at national and international conferences. These presentations have addressed case histories, analysis of project data, equipment advancements, laboratory testing results, characterization of engineering behavior of treated soils, and development of methods for analysis and design of foundation systems incorporating DMM. Short courses and seminars have been developed and offered by U.S. professional societies and universities to promote DMM as a viable alternative to other ground improvement technologies.

Since 1991, DMM has been used successfully on over 20 large transportation projects in the United States. Project details are summarized briefly in chapter 3. However, DMM usage in the United States has been limited for a number of reasons, most notably the absence of readily accessible and user friendly design guidelines and the lack of widely accepted and effective QC/QA practices. This situation contrasts with that in the huge, active and largely transportation-driven markets in Japan and Nordic countries.

CHAPTER 2. TERMINOLOGY

Terms specific to laboratory testing, treated soil properties, design, construction, and contracting/ procurement are defined in this section. These terms are currently used and accepted by the U.S.

construction industry.

Various definitions of the same terms are often used in U.S. practice. Using a variety of terms can be misleading, and this practice has caused contractual difficulties and confusion. A single preferred term is provided for each item. Duplicate terms are shown in parenthesis following the preferred term to promote understanding, but use of the preferred term is recommended.

• Admixtures: Ingredients in the grout other than binder, bentonite, and water. Admixtures can be fluidifiers, dispersants, or retarding, plugging, or bridging agents that permit efficient use of materials and proper workability of the grout.

• Bentonite: Ultra-fine natural clay, principally comprising sodium cation montmorillonite.

• Binder: Chemically reactive material (i.e., lime, cement, gypsum, blast furnace slag, flyash, or other hardening reagents) that can be used for mixing with in situ soils to strengthen the soils and form DMM columns. Also referred to as stabilizer or reagent.

In U.S. practice, binder slurry is frequently referred to as grout or slurry.

• Binder content: Ratio of weight of dry binder to dry weight of soil to be treated.

• Binder factor: Ratio of weight of dry binder to volume of soil to be treated.

• Binder factor in-place: Ratio of weight of dry binder to volume of mixture, which is the volume of the soil to be treated plus the volume of the slurry for the wet method or the volume of the dry binder for the dry method.

• Binder slurry: Stable colloidal mixture of water, binder, and admixtures that assists in loosening the soils for effective mixing and strengthening the in situ soil upon setting.

• Blade rotation number (BRN): Total number of mixing blade rotations per meter of shaft movement. BRN has been developed to ensure uniformity of products produced by wet rotary end (WRE)/dry rotary end (DRE) systems. Refer to chapter 11 for indepth descriptions of WRE and DRE classifications. For horizontal cutter systems (e.g., cutter soil mixing (CSM)), revolutions per minute are typically reported as an indicator of mixing energy. Note that BRN is not applicable for chainsaw-type mixers (e.g., trench cutting and remixing deep wall method (TRD).

• Column: Pillar of treated soil produced in situ by a single installation process using a mixing tool, typically a rotating auger, to make a round column. A rectangular barrette produced by twin horizontal mixing shafts is also a column. See “element” and “wall,” which are related geometric terms.

• Deep mixing equipment: Deep mixing equipment with various mixing tools including single vertical shaft mixing tools, multiple vertical shaft mixing tools, horizontal rotating circular cutters, chainsaw-type cutters, etc.

• DMM: In situ ground treatment in which soil is blended with cementitious and/or other binder materials to improve strength, permeability, and/or compressibility characteristics (synonymous terms (some proprietary) include DSM, deep mixing, CDSM, and soil cement mixing).

• Dry mixing: Process of mechanical disaggregation of the soil in situ and its mixing with binders with or without fillers and admixtures in dry powder form. Binders are delivered primarily on tool retrieval.

• Element: This is an inclusive term that refers to a DMM element produced by a single stroke of the mixing tools at a single equipment location. A column produced by a single-axis machine, a set of overlapping columns produced by a single stroke of a multiple-shaft mixing tool, and a rectangular barrette produced by a mixing tool with horizontal axis rotating cutter blades are each considered an element. An element consisting of overlapping columns produced by a single stroke of a multiple-shaft mixing tool is sometimes referred to as a panel. A chainsaw-type mixing tool that travels as it mixes produces a continuous wall, which is not an element.

• Engineer: The representative of the design engineer or of the project owner (owner).

This person may either be a subconsultant to the owner or a member of the owner’s staff.

• Filler: Non-reacting materials (i.e., sand, limestone powder, etc.).

• Mix design: Ratios of soil, binder, water, and additive quantities required to meet the design requirements of the project.

• Mixing process: Mechanical disaggregation of the soil structure and dispersion of binders and fillers in the soil.

• Mixing tool: Equipment used to disaggregate the soil and distribute and mix the binder with the soil. Consists of one or several rotating units equipped with several blades, arms, and paddles with or without continuous or discontinuous flight augers, horizontal rotating cutter blades, or chainsaw-type cutters.

• Penetration (downstroke): Stage or phase of mixing process cycle in which the mixing tool is delivered to the appropriate depth (disaggregation phase) for withdrawal injection and disaggregation and mixing for penetration injection. (Not applicable for chainsaw-type mixers (TRD).)

• Penetration/retrieval speed: Vertical movement per unit time of the mixing tool during penetration or withdrawal. (Not applicable for chainsaw-type mixers (TRD).)

• Restroke: Additional penetration and withdrawal cycle of the mixing tool to increase the binder content and/or mixing energy. (Not applicable for chainsaw-type mixers (TRD).)

• Retrieval: Withdrawal of mixing tool from bottom depth to the ground surface. Binder may be injected during retrieval, which also imparts additional mixing energy.

• Rotation speed: Number of revolutions of the mixing tool per unit time.

• Soil-cement: Product of DMM consisting of a mixture of the in situ soil and binder. Also referred to as treated soil or deep mixed material.

• Strength: Dependent on application, various strengths may be used to assess the quality of deep mixed material. For design, strength usually means shear strength, but during QC/QA, strength usually means unconfined compressive strength. For clarity, the intended type of strength should always be identified when using this term.

• Stroke: One complete cycle (penetration and withdrawal) of the mixing process.

• Volume ratio: Ratio of the volume of slurry injected (in wet mixing) to the volume of soil to be treated.

• Wall: Group of overlapping elements arranged to form a continuous wall. Continuous walls can also be constructed using a chainsaw-type mixing device. Walls can be referred to as shear walls, cutoff walls, or excavation support walls, depending on the application.

A shear wall can also be referred to as a buttress.

• Water: Fresh water that is free of deleterious substances that adversely affect the strength and mixing properties of the grout and is used to…