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

ix

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