Shallow Foundations Discussions and Problem Solving by Tharwat M. Baban (KENM0008)

Shallow Foundations Discussions and Problem Solving by Tharwat M. Baban

Contents

1 Site Investigation in Relation to Analysis and Design of Foundations 1

1.1 General 1

1.2 Site Investigation 2

1.2.1 Reconnaissance 2

1.2.2 Subsurface Exploration 3

1.2.3 Laboratory Tests 4

1.2.4 Compiling Information 6

1.2.5 Final Geotechnical Report 7

2 Shallow Foundations – Introductory Chapter 76

2.1 General 76

2.2 Types of Shallow Foundations 77

2.3 Depth of Foundations 82

2.4 Foundation Performance Requirements 84

2.4.1 General 84

2.4.2 Strength Requirements 85

2.4.3 Serviceability Requirements 86

2.4.4 Constructibility Requirements 86

2.4.5 Economy Requirements 87

2.5 Sulfate and Organic Acid Attack on Concrete 87

2.5.1 Sulfate Attack 87

2.5.2 Organic Acid Attack 88

2.6 Pressures under Foundations 89

2.6.1 Contact Pressure and Contact Settlement 89

2.6.2 Contact Pressure under Eccentrically Loaded Spread Footings 92

2.7 Vertical Stresses in a Soil Mass due to Foundation Loads 95

2.7.1 General 95

2.7.2 Vertical Stress Due to a Concentrated Load 95

2.7.3 Vertical Stress Due to a Line Load 96

2.7.4 Vertical Stress Due to a Uniformly Loaded Strip Area 97

2.7.5 Vertical Stress Due to a Uniformly Loaded Circular Area 97

2.7.6 Vertical Stress Due to a Uniformly Loaded Rectangular Footing 99

2.7.7 Newmark’s Chart Method of Determining Vertical Stresses 104

2.7.8 Pressure Bulbs Method of Determining Vertical Stresses 105

2.7.9 Average Vertical Stress Due to a Loaded Rectangular Area 107

2.7.10 Westergaard’s Equations 109

3 Shallow Foundations – Settlement 144

3.1 General 144

3.2 Immediate Settlement 149

3.3 Settlement of Foundations on Coarse-grained Soils 155

3.3.1 General 155

3.3.2 Estimation of Settlements from SPT 157

3.3.3 Estimation of Settlements from CPT 161

3.4 Settlement of Foundations on Fine-grained Soils 164

3.4.1 General 164

3.4.2 Immediate Settlement of Fine-grained Soils 166

3.4.3 Consolidation Settlement 168

3.4.4 Estimation of the Rate of Consolidation Settlement 174

3.4.5 Method of Accelerating the Rate of Consolidation Settlement 175

3.4.6 Estimation of Settlements over the Construction Period 180

3.4.7 Secondary Compression 181

3.5 Settlement of Foundations on Rock 183

4 Shallow Foundations – Bearing Capacity 265

4.1 General 265

4.2 Basic Definitions 266

4.3 Gross and Net Foundation Pressures 268

4.4 Bearing Capacity Failure Mechanism for Long (Strip or Continuous) Footings 272

4.5 Bearing Capacity Equations 273

4.6 Some Considerations Concerning the Use of Bearing Capacity Equations 278

4.7 Bearing Capacity of Footings with Inclined Loads 280

4.8 Bearing Capacity of Footings with Eccentric Loads 281

4.9 Effect of Water Table on Bearing Capacity 286

4.10 Influence of Soil Compressibility on Bearing Capacity 290

4.11 Effect of Adjacent Footings on Bearing Capacity 291

4.12 Bearing Capacity of Foundations on Slopes 292

4.12.1 General 292

4.12.2 Solutions 292

4.13 Bearing Capacity of Footings on Layered Soils 296

4.13.1 General 296

4.13.2 Ultimate Bearing Capacity: Stronger Soil Underlain by Weaker Soil 298

4.13.3 Ultimate Bearing Capacity: Weaker Soil Underlain by Stronger Soil 302

4.14 Safety Factor 304

4.15 Bearing Capacity from Results of In Situ Tests 305

4.16 Uplift Capacity of Shallow Foundations 306

4.17 Some Comments and Considerations Concerning the Geotechnical Design of

Shallow Foundations 310

4.18 Bearing Capacity of Rock 312

5 Shallow Foundations – Structural Design 381

5.1 General 381

5.2 Design Loads 382

5.3 Selection of Materials 382

5.4 Structural Action of Vertically and Centrically Loaded Isolated and Continuous

(Strip) Footings 383

5.4.1 General 383

5.4.2 Flexure 383

5.4.3 Shear 388

5.4.4 Development of Reinforcement 390

5.4.5 Transfer of Force at Base of Column, Wall or Pedestal 390

5.5 Eccentrically Loaded Spread Footings 396

5.6 Pedestals 398

5.7 Pile Caps 399

5.8 Plain Concrete Spread Footings 400

5.9 Combined Footings 402

5.9.1 General 402

5.9.2 Rectangular Combined Footings 403

5.9.3 Trapezoidal Combined Footings 404

5.9.4 Strap (or Cantilever) Footings 405

5.10 Modulus of Subgrade Reaction 406

5.11 Beams on Elastic Foundations 409

5.12 Mat Foundations 413

5.12.1 General 413

5.12.2 Design Procedure for the Conventional (Rigid) Method 414

5.12.3 Design Procedure for the Approximate Flexible Method 417

5.12.4 Finite Difference Method for the Design of Mat Foundations 419

5.12.5 Modulus of Subgrade Reaction and Node Coupling of Soil Effects for Mats 421

5.12.6 Finite Element Method for the Design of Mat Foundations 424

5.12.7 Finite Grid Method for the Design of Mat Foundations 426

6 Eurocode Standards and the Design of Spread Foundations 649

6.1 General 649

6.2 Basis of Design Irrespective of the Material of Construction 651

6.2.1 Introduction 651

6.2.2 Terms and Definitions 652

6.2.3 Requirements 655

6.2.4 Quality Management 657

6.2.5 Principles of Limit States Design 657

6.3 Design of Spread Foundations 664

6.3.1 Introduction 664

6.3.2 Geotechnical Categories 665

6.3.3 Limit States 666

6.3.4 Geotechnical Design 667

6.3.5 Structural Design 677

Shallow Foundations Discussions and Problem