SLOPE STABILITY ANO STABILIZATION METHODS · SLOPE STABILITY ANO STABILIZATION METHODS Second Edition LEE W. ABRAMSON Hatch Mott MacDonald Millburn, New Jersey THOMAS S. LEE Parsons,

SLOPE STABILITY ANO STABILIZATION METHODS

Second Edition

LEE W. ABRAMSON Hatch Mott MacDonald Millburn, New Jersey

THOMAS S. LEE Parsons, Brinckerhoff, Quade & Douglas San Francisco, California

SUNIL SHARMA University of Idaho Moscow, Idaho

GLENN M. BOYCE Parsons, Brinckerhoff, Quade & Douglas San Francisco, California

A Wiley-lnterscience Publication

JOHN WILEY & SONS, INC.

CONTENTS

PREFACE

ACKNOWLEDGMENTS

ABOUT THE AUTHORS

1 GENERAL SLOPE STABILITY CONCEPTS Lee W. Abramson

1.1 lntroduction l l

1.2 Aims of Slope Stability Analysis l 2

1.3 Natura] Slopes l 2

1.4 Engineered Slopes l 3

1.4.1 Embankments and Fills l 3

1.4.2 Cut Slopes l 15

1.4.3 Landfills l 18

1.4.4 Retaining Structures l 24

1.5 Landslides l 25

1.5.1 Features and Dimensions of Landslides l 25

1.5.2 Landslide Rates and Types of Movements l 29

1.6 Factors Contributing to Slope Failures l 33

1.7 Basic Concepts Applied to Slope Stability l 34

l.8 Typical Input Data for Slope Stability Analyses l 36

1.8.1 Geologie Conditions l 36

xvii

xix

xxi

1

v

vi CONTENTS

1.8.2 Site Topography l 36

1.8.3 Possible Effects of Proposed Con truction l 37

1.8.4 Materia! Properties l 39

1.8.5 Shear Strength l 42

1.8.6 Groundwater Condit ions l 48

1.8.7 Seismicity l 49

1.9 Subsurface Mode! and Back-Analysis for Slopc Stabi lity Analyses l 51

1. 1 O Conclusions l 53

References l 53

2 ENGINEERING GEOLOGY PRINCIPLES Thomas S. Lee

2.1 Introduction l 56

2.2 Types and Characteristics of Geologie Soil Deposits l 56

2.2.1 Alluvial Deposits l 57

2.2.2 Glacial Deposits l 65

2.2.3 Eolian Deposits l 65

2.2.4 Residua! Deposits l 67

2.2.5 Colluvial/Talus Deposits l 69

2.2.6 Marine Deposits l 70

2.2.7 Melanges l 71

2.2.8 Other Types of Deposits l 72

2.3 Types and Characteristics of Rocks l 73

2.3.1 Shales l 74

2.3.2 Sandstones l 75

2.3.3 Limestones and Related Carbonate Rocks l 75

2.3.4 lgneous Rocks l 75

2.3.5 Pyrocrastic Volcanic Rocks l 76

2.3.6 Metamorphic Rocks l 76

2.4 Geologie Features Associated with Slopes l 76

2.4.1 Soil/Rock Fabric l 77

2.4.2 Geologica! Structures l 77

2.4.3 Discontinuities l 78

2.4.4 Groundwater l 78

2.4.5 Ground Stresses l 79

2.4.6 Weathering l 79

2.4.7 Preex.isting Landslide Activities l 81

56

2.4.8 Clay Mineralogy l 82

2.4.9 Seismic Effects l 84

2.5 Landslides l 84 2.5.1 Landslide-Prone Occurrences l 85

2.5.2 Fundamentals of Landslides l 93 2.5.3 Useful Clues to Landslide Investigations and

Identifications l 95

References l 99

3 GROUNDWATER CONDITIONS Thomas S. Lee

3.1 lntroduction l 102 3.2 Review of Groundwater Fundamentals l 103

3.2.1 Movement of Groundwater l l 04

3.2.2 Principles of Groundwater Mechanics l 106

3.3 Site Conditions l 108 3.3.1 Groundwater Levelsl 108

3.3.2 Zones l 108

3.3.3 Aquifers l 11 1

3.3.4 Aquicludes l l I 2

3.3.5 Perched Water l 112

3.3.6 Artesian Water l 11 4

3.3.7 Springs l 114

3.4 Types of Groundwater Flow l 115

3.4.1 Runoff l 115

3.4.2 Infiltration l 117

3.4.3 Regional Flow l 118

3.5 Fluctuation of Groundwater Levels l 121

3.5.1 Rainfall l 121

3.5.2 Floods l 123

3.5.3 Snowme1t l 124

3.5.4 Sudden Drawdown l 125

3.6 Influence of Geologica! Structures on Groundwater Flows l 125

3.7 Pore Pressures l 127

3.7.1 Positive Pore Pressures l 128

3.7.2 Negative Pore Pressures l 131

3.7.3 Measurement of Pore Pressures l 133

CONTENTS vii

102

viii CONTENTS

3.8 Water Levels for Design l 138

3.8.1 Generai l 138

3.8.2 Wetting Band Approach l 139

3.9 Field ldentification and lnterpretation of Groundwater Conditions l !42

3.9.1 Field ldentification of Groundwater Conditions l !42

3.9.2 Interpretation of Groundwater Conditions l 142

3. 1 O Groundwater in Slope Stability Analysis l 144

3.1 0.1 Developing a Groundwater Mode! from the Field Data l 144

3.10.2 Groundwater Effects on Slope Stabi lity l 146 3.10.3 Groundwater in Rock l 150

3.1 l Monitoring of Groundwater Pressures l 151

3.11.1 Piezometers and Observation Wells l 151

3.11.2 Installation of Piezometers l 157

3.11.3 Fluctuating Groundwater Levels l 159

3. 12 Other Instruments-Rainfall Gages l 159

References l 159

4 GEOLOGIC SITE EXPLORATION Thomas S. Lee

4.1 lntroduction l 162

4.2 Desk Study l 166

4.2.1 Available Existing Data l 166

4.2.2 Previous Geologie Explorations l 172

4.2.3 Identification of Landslide-Prone Terrains through Topographic Expressions l 173

4.2.4 Air Photos l 175

4.3 Field Study l 183

4.3. 1 Site Reconnaissance l 183

4.4 Exploration Methods l 197

4.4. 1 Introduction l 197

4.4.2 Auger Drilling l 198

4.4.3 Rotary Wash Drilling l 200 4.4.4

4.4.5

4.4.6

4.4.7

Limitations of Auger and Rotary Wash Drilling l 203

Sampling in the Ground l 203

Large Boreholes l 204

Test Pits l 205

162

4.5 Testing Methods l 209

4.5.1 1n Situ Testing l 209

4.5.2 Geophysical Testing l 223

4.5.3 Downhole Geophysics Logging l 229

4.5.4 Mineralogy Tests l 232

4.5.5 Radiocarbon Dating l 235

4.6 Exploration Program Design l 235

4.6.1 Locations and Number of Boreholes l 235

4.6.2 Depth of Boreholes l 237

References l 238

5 LABORATORY TESTING ANO INTERPRETATION Suni/ Sharma

5.1 lntroduction l 242

5.2 Effective Stress Concepts l 243

5.3 Mohr Circle l 244 5.4 Mohr-Coulomb Failure Criterion l 245

5.4.1 Mohr-Coulomb Failure Envelope-Unsaturated Soils l 247

5.4.2 Mohr- Cou1omb Envelope in p-q Space l 249

5.5 EffectiveiTotal Stress Ana1ysis l 250

5.5.1 Factors of Safety l 252

5.6 Stress Paths l 254 5.6.1 Typical Field Stress Paths l 257

5.7 Shear Strength of Soils l 259

5.7.1 Shear Strength of Granular Soils l 260

5.7.2 Shear Strength of Fine-Grained Soi1s l 260

5.7.3 Stress-Strain Characteristics of Soils l 261

5.7.4 Discrepancies between Field and Laboratory Strengths l 263

Strength Testing l 269

CONTENTS

5.7.5

5.7.6

5.7.7

5.7.8

Selection an d Preparation of Test Samples l 271

Laboratory Test Conditions l 272

The SHANSEP Method l 274

5.7.9 Triaxial Tests l 276

5.7. l O Direct Shear Test l 283

5.7.11 Direct Simp1e Shear (DSS) Test l 287

5. 7. l 2 U nsaturated Tests l 288

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242

x CONTENTS CONTENTS xi

5.8 Pore Pressure Parameters l 291 6.7 Planar Surface Analysi l 345 5.8. 1 Skempton ·s Parameters l 291 6.7.1 Planar Surface Example l 348 5.8.2 Henkel"s Parameters l 291 6.8 Circular Surface Analysis l 349

5.9 lnterpretations of Strength Tests l 293 6.8.1 Circular Are (cf>, = 0) Method l 349 5.9.1 Triaxial Tests l 293 6.8.2 cf>, =O Example l 350 5.9.2 Direct Shear Tests l 298 6.8.3 Friction Circle Method l 350 5.9.3 Unsaturated Tests l 302 6.8.4 Ftiction Circle Example l 352 5.9.4 Selection of Design Shear Strengths l 302 6.9 Method of Slices l 353

5. 10 Other Properties l 305 6.9.1 Ordinary Method of Slices (OMS) l 358 5.10.1 Consolidation Tests l 306 6.9.2 Simplified Janbu Method l 360 5.10.2 Permeability Tests l 306 6.9.3 Simplified Bishop Method l 363 5. 10.3 Compaction Tests l 307 6.9.4 Genera1ized Limi t Equil ibrium (GLE) Method l 364 5. 10.4 Classification Tests l 308 6.9.5 Janbu's Generalized Procedure of Slices (GPS) l 367 5. 10.5 Interpretations ofCiassification Tests l 310 6.9.6 Method of Slices-An Example l 370 5.10.6 Shrinkl Swell Potenti al l 312 6.9.7 Contro( of Negative Effective Stresses l 375 5.10.7 SlakeDurability l 313 6.9.8 Comparison of Limi t Equilibrium Methods l 376 5.10.8 Collapsibi lity l 314 6.10 Selection and Use of Limit Equilibrium Methods l 378 5.10.9 Dispersivity l 315 6.10.1 Essential First Four Steps l 378 5.10. 10 Chemical Tests l 316 6.10.2 Se1ection of Analysis Method l 379 5.10.11 X-Ray Diffraction Analysis l 3 18 6.10.3 Considerations forAli Types of Analyses l 380

5. 11 Quality Control/Quality Assurance l 319 6.11 Design Charts l 380 References l 321 6.11.1 Historical Background l 381

6.11.2 Stability Charts l 381 6 SLOPE STABILITY CONCEPTS 329 6.12 Seismic Analysis l 393

Suni/ Sharma 6.12.1 Pseudostatic Method l 394

6.1 Introduction l 329 6.12.2 Newmark's Displacement Method l 396 6.2 Modes of Failure l 330 6.12.3 Accelerogram Selection for Newmark's 6.3 Factor of Safety Concepts l 332 Method l 398 6.4 Pore Water Pressures l 334 6.12.4 Computed Permanent Displacements l 399

6.4. 1 Phreatic Surface l 335 6.1 2.5 Tolerable Permanent Displacements l 408

6.4.2 Piezometric Surface l 336 6. 13 Other Factors Affecting Slope Stability Analysis l 409 6.4.3 Examp1e l 337 6.13.1 Effect ofTension Cracks on Stabi1ity Analysis l 409

6.4.4 Negative Pore Pressures l 339 6.13.2 Effects of Vegetation l 41 O 6.5 Block Analysis l 339 6.13.3 Foundation Loads on Slopes l 411

6.5.1 Example l 341 6.14 Three-Dimensiona1 Ana1ysis l 412 6.6 Infinite Slope Analysis l 343 6. 15 Rock Slope Stability l 413

6.6.1 Infinite S1opes in Dry Sand l 343 6.16 The Finite Element Method (FEM) l 415 6.6.2 Infinite Slope in c-cf> Soil wi th Seepage l 344 6.16.1 Example of FEM Analysis of Slopes l 416

xii CONTENTS

6.17 Computer Analysis l 419

6.17.1 Available ComputerPrograms l 41 9

6.18 Probabilistic Analysis of Slopes l 420 6.18.1

6.18.2

6.18.3

Sources of Uncertainty l 420

Basic Probabi1ity Concepts l 421

Re1iabi lity Index l 424

6. 18.4 Probabilistic Formulation for Slopes l 427

6.18.5 Probabilistic Analysis of Performance Function l 427

6.18.6 Quantifying Uncertainty l 436 6.18.7 Examples l 438

6. 18.8 Summary l 452

References l 454

7 SLOPE STABILIZATION METHODS Lee W Abramson

7. 1 Introduction l 462

7.2 Unloading l 463

7 .2.1 Excavation l 463

7 .2.2 Lightweight Fili l 468 7.3 Buttressing l 470

7 .3. 1 So il an d Rock Fili l 474

7.3.2 Counterberms l 474

7.3.3 Shear Keys l 475

7.3.4 Mechanically Stabil ized Embankments l 477 7.3.5 Pneusol (Tiresoil) l 480

7.4 Draioage l 482

7.4.1 Surface Drainage l 482

7.4.2 Subsurface Drainage l 483 7.5 Reioforcement l 497

7.5 .1 Soi1 Nailing l 497

7.5.2 Stone Columns l 507

7.5.3 Reticulated Micropiles l SI I

7.5.4 Geosynthetically Reioforced Slopes 1 512 7.6 Retaining Walls l 520

7.6.1 Gravity and Cantilever Retaining Wal ls l 523 7.6.2 Driven Pi1es l 523

7.6.3 Drilled Shaft Walls l 524

7.6.4 Tieback Walls l 524

462

CONTENTS xiii

7.7 Vegctation l 530

7.7.1 Generai Design Considerations l 531

7.7.2 Vegetation Specie l 537

7.7.3 Erosion Contro! Mats and Blankets l 538

7.7.4 Biotechnical Stabilization l 540

7.8 Surface Slope Protection l 54 1

7.8.1 Generai Design Considerations l 542

7.8.2 Shotcrete l 543

7.8.3 Chunam Plaster l 544

7.8.4 Masonry l 546

7.8.5 Rip-Rap l 546

7.9 Soil Hardening l 547

7.9.1 Compacted Soi 1-Cement Fili l 54 7

7.9.2 Electro-osmosis l 548

7.9.3 Thermal Treatment l 549

7.9.4 Grouting l 549

7.9.5 Lime lnjection l 550

7.9.6 Preconsolidation l 553

7.1 0 Rock Slope Stabilization Methods l 559

7.10. 1 Removal ofUnstable Rock l 559

7.10.2 Catchment l 562

7.1 0.3 Flattening of Slope l 565

7.10.4 Buttresses l 565

7.10.5 Surface Protection l 566

7.10.6 Reinforcement l 568

7.10.7 Drainage l 568

7.10.8 Use of Explosives l 571

7. 10.9 Rock Slope Stabilization Case Histories l 573

7. 11 Alternatives to Slope Stabilization l 584

7. 11.1 Complete Remova1 of Slide Zone l 585

7. 11.2 Facility Relocation l 585

7. 11.3 Bridging l 587

7. 12 Selection of Stabi lization Methods l 587

7. 12.1 Goals l 588

7. 12.2 Technical Constraints l 588

7. 12.3 Si te Constraints l 589

7. 12.4 Environmenta1 Constraints l 590

7. 12.5 Aesthetic Constraints l 590

xiv CONTENTS CONTENTS xv

7.12.6 Schedule Constraints l 590 8.6.3 Advantages and Disadvantages of TDR 7.12.7 Other Constraints l 59 ! over Inclinometers l 640 7. 12.8 Cost l 591 References l 641

7. 13 Probable Cost Analysis of Stabi lization Alternatives 1 591 7.13.1 lntroduction l 59 !

7. 13.2 Developing Alternative Schemes l 592 9 SHALLOW FAILURES 643

7. 13.3 Estimating Outcomes and Probabilities l 592 Thomas S. Lee

7. 13.4 Determining Probable Costs l 593 9.1 Introduction l 643

References l 598 9.2 Seepage Flow Mechanism due to Infiltration l 644

9.3 Mechanism of Rainfall-Induced Landslides l 645

9.4 Field Loading Conditions l 647

8 DESIGN, CONSTRUCTION, ANO MAINTENANCE 604 9.5 Correlations between Land Slides and Rainfall l 648 Glenn M. Boyce 9.5.1 Antecedent Rainfall l 650

8. 1 Introduction l 604 9.6 Rainfall Thresholds for Prediction of Shallow Failures l 651

8.2 Contract Documents l 604 9.7 Types of Soils, Hydrogeologic, and Geomorphologic

8.2. 1 Contract Drawings l 605 Features l 652

8.2.2 Specifications l 606 9.7.1 Colluvium l 652

8.2.3 Geotechnical Design Reports l 606 9.7.2 Loess l 653

8.3 Inspection during Construction l 607 9.7.3 Debris Flows l 655

8.3. 1 Inspection Guidelines l 607 9.7.4 Residua! Soils l 656

8.3.2 Quality Control/Quality Assurance l 608 9.7.5 Rapid Snowmelt l 657

8.3.3 Instrumentation l 608 9.8 Effect of Permeability of Surfìcial Stability l 657

8.3.4 Instrumentation Monitoring l 627 9.9 Standard Codes for Shallow Slope Stability l 658

8.4 lnspection following Construction l 630 9. 10 Design Practice for Shallow Slope Stability l 661

8.4.1 Introduction l 630 9.10.1 Debris Flow Hazard Mitigation l 662

8.4.2 Frequency of Inspections l 63 l 9.10.2 Design of Loess Slopes l 663

8.4.3 Technical Inspections l 632 9.11 Attending Landslide Incidents l 664

8.4.4 Engineering Inspections l 632 9.12 Sumrnary l 665

8.4.5 Inspection Reports l 632 References l 665

8.5 Maintenance l 633

8.5. 1 Access l 633 10 STABILITY OF LANDFILL SLOPES 669 8.5.2 Slope Performance Observations l 633 Lee W Abramson 8.5.3 Instruments l 637

8.5.4 Drainage l 637 10.1 Unique Nature ofLandfì lls l 669

8.5.5 Adjacent Utilities l 638 10.2 Typical Landfill Configurations l 669

8.6 Time Domain Reflectometry (TDR) l 639 10.3 Landfill Waste Engineering Properties l 675

8.6.1 Introduction l 639 10.4 Geosynthetics in Landfìlls and Engineering Properties l 679

10.4.1 Geomembranes l 680 8.6.2 Mechanics of TDR l 639 10.4.2 Geotextiles l 680

XVi CONTENTS

l 0.4.3 Geonets l 680

l 0.4.4 Geogrids l 682

l 0.4.5 Geosynthetic Clay Liners (GCLs) l 684

l 0.4.6 Engineering Properties of Geosynthetics l 685 l 0.4.7 Anchor Trenches l 686

l 0.5 Landfill Construction l 688

l 0.6 Slope Stability Considerations l 692

10.6.1 Excavation Slope Stability l 693

10.6.2 Waste Fili Stability l 696

IN DEX

l 0.6.3 Cover System Stability l 700 References l 702

703