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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Written by a leader on the subject, Introduction to Geotechnical Engineering is first introductory geotechnical engineering textbook to cover both saturated and unsaturated soil mechanics. Destined to become the next leading text in the field, this book presents a new approach to teaching the subject, based on fundamentals of unsaturated soils, and extending the description of applications of soil mechanics to a wide variety of topics. This groundbreaking work features a number of topics typically left out of undergraduate geotechnical courses.
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Seitenzahl: 1945
Veröffentlichungsjahr: 2013
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Table of Contents
Title Page
Copyright
Acknowledgments
Chapter 1: Introduction
1.1 Why This Book?
1.2 Geotechnical Engineering
1.3 The Past and the Future
1.4 Some Recent and Notable Projects
1.5 Failures May Occur
1.6 Our Work Is Buried
1.7 Geotechnical Engineering Can Be Fun
1.8 Units
Problems
Chapter 2: Engineering Geology
2.1 Definition
2.2 The Earth
2.3 Geologic Time
2.4 Rocks
2.5 Soils
2.6 Geologic Features
2.7 Geologic Maps
2.8 Groundwater
Problems
Chapter 3: Soil Components and Weight-Volume Parameters
3.1 Particles, Liquid, and Gas
3.2 Particle Size, Shape, and Color
3.3 Composition of Gravel, Sand, and Silt Particles
3.4 Composition of Clay and Silt Particles
3.5 Particle Behavior
3.6 Soil Structure
3.7 Three-Phase Diagram
3.8 Weight-Volume Parameters
3.9 Measurement of the Weight-Volume Parameters
3.10 Solving a Weight-Volume Problem
Problems
Chapter 4: Soil Classification
4.1 Sieve Analysis
4.2 Hydrometer Analysis
4.3 Atterberg Limits and Other Limits
4.4 Classification Parameters
4.5 Engineering Significance of Classification Parameters and Plasticity Chart
4.6 Unified Soil Classification System
Problems
Chapter 5: Rocks
5.1 Rock Groups and Identification
5.2 Rock Mass vs. Rock Substance
5.3 Rock Discontinuities
5.4 Rock Index Properties
5.5 Rock Engineering Properties
5.6 Rock Mass Rating
5.7 Rock Engineering Problems
5.8 Permafrost
Problems
Chapter 6: Site Investigation, Drilling, and Sampling
6.1 General
6.2 Preliminary Site Investigation
6.3 Number and Depth of Borings and In Situ Tests
6.4 Drilling
6.5 Sampling
6.6 Groundwater Level
6.7 Field Identification and Boring Logs
6.8 Soil Names
6.9 Offshore Site Investigations
Problems
Chapter 7: In Situ Tests
7.1 Standard Penetration Test
7.2 Cone Penetration Test
7.3 Pressuremeter Test
7.4 Dilatometer Test
7.5 Vane Shear Test
7.6 Borehole Shear Test
7.7 Plate Load Test
7.8 California Bearing Ratio Test
7.9 Pocket Penetrometer and Torvane Tests
7.10 Pocket Erodometer Test
7.11 Compaction Control Tests
7.12 Hydraulic Conductivity Field Tests
7.13 Offshore In Situ Tests
Problems
Chapter 8: Elements of Geophysics
8.1 General
8.2 Seismic Techniques
8.3 Electrical Resistivity Techniques
8.4 Electromagnetic Methods
8.5 Remote Sensing Techniques
Problems
Chapter 9: Laboratory Tests
9.1 General
9.2 Measurements
9.3 Compaction Test: Dry Unit Weight
9.4 Compaction Test: Soil Modulus
9.5 Consolidation Test
9.6 Swell Test
9.7 Shrink Test
9.8 Collapse Test
9.9 Direct Shear Test
9.10 Simple Shear Test
9.11 Unconfined Compression Test
9.12 Triaxial Test
9.13 Resonant Column Test
9.14 Lab Vane Test
9.15 Soil Water Retention Curve (Soil Water Characteristic Curve) Test
9.16 Constant Head Permeameter Test
9.17 Falling Head Permeameter Test for Saturated Soils
9.18 Wetting Front Test for Unsaturated Soils
9.19 Air Permeability Test for Unsaturated Soils
9.20 Erosion Test
Problems
Chapter 10: Stresses, Effective Stress, Water Stress, Air Stress, and Strains
10.1 General
10.2 Stress Vector, Normal Stress, Shear Stress, and Stress Tensor
10.3 Sign Convention for Stresses and Strains
10.4 Calculating Stresses on Any Plane: Equilibrium Equations for Two-Dimensional Analysis
10.5 Calculating Stresses on Any Plane: Mohr Circle for Two-Dimensional Analysis
10.6 Mohr Circle in Three Dimensions
10.7 Stress Invariants
10.8 Displacements
10.9 Normal Strain, Shear Strain, and Strain Tensor
10.10 Cylindrical Coordinates and Spherical Coordinates
10.11 Stress-Strain Curves
10.12 Stresses in the Three Soil Phases
10.13 Effective Stress (Unsaturated Soils)
10.14 Effective Stress (Saturated Soils)
10.15 Area Ratio Factors and
10.16 Water Stress Profiles
10.17 Water Tension and Suction
10.18 Precision on Water Content and Water Tension
10.19 Stress Profile at Rest in Unsaturated Soils
10.20 Soil Water Retention Curve
10.21 Independent Stress State Variables
Problems
Chapter 11: Problem-Solving Methods
11.1 General
11.2 Drawing to Scale as a First Step
11.3 Primary Laws
11.4 Continuum Mechanics Methods
11.5 Numerical Simulation Methods
11.6 Probability and Risk Analysis
11.7 Regression Analysis
11.8 Artificial Neural Network Method
11.9 Dimensional Analysis
11.10 Similitude Laws for Experimental Simulations
11.11 Types of Analyses (Drained-Undrained, Effective Stress-Total Stress, Short-Term-Long-Term)
Problems
Chapter 12: Soil Constitutive Models
12.1 Elasticity
12.2 Linear Viscoelasticity
12.3 Plasticity
12.4 Common Models
Problems
Chapter 13: Flow of Fluid and Gas Through Soils
13.1 General
13.2 Flow of Water in a Saturated Soil
13.3 Flow of Water and Air in Unsaturated Soil
Problems
Chapter 14: Deformation Properties
14.1 Modulus of Deformation: General
14.2 Modulus: Which One?
14.3 Modulus: Influence of State Factors
14.4 Modulus: Influence of Loading Factor
14.5 Modulus: Differences Between Fields of Application
14.6 Modulus, Modulus of Subgrade Reaction, and Stiffness
14.7 Common Values of Young's Modulus and Poisson's Ratio
14.8 Correlations with Other Tests
14.9 Modulus: A Comprehensive Model
14.10 Initial Tangent Modulus Go or Gmax
14.11 Reduction of Gmax with Strain: The G/Gmax Curve
14.12 Preconsolidation Pressure and Overconsolidation Ratio from Consolidation Test
14.13 Compression Index, Recompression Index, and Secondary Compression Index from Consolidation Test
14.14 Time Effect from Consolidation Test
14.15 Modulus, Time Effect, and Cyclic Effect from Pressuremeter Test
14.16 Resilient Modulus for Pavements
14.17 Unsaturated Soils: Effect of Drying and Wetting on the Modulus
14.18 Shrink-Swell Deformation Behavior, Shrink-Swell Modulus
14.19 Collapse Deformation Behavior
Problems
Chapter 15: Shear Strength Properties
15.1 General
15.2 Basic Experiments
15.3 Stress-Strain Curve, Water Stress Response, and Stress Path
15.4 Shear Strength Envelope
15.5 Unsaturated Soils
15.6 Experimental Determination of Shear Strength (Lab Tests, In Situ Tests)
15.7 Estimating Effective Stress Shear Strength Parameters
15.8 Undrained Shear Strength of Saturated Fine-Grained Soils
15.9 The Ratio su/σov′ and the SHANSEP Method
15.10 Undrained Shear Strength for Unsaturated Soils
15.11 Pore-Pressure Parameters A and B
15.12 Estimating Undrained Shear Strength Values
15.13 Residual Strength Parameters and Sensitivity
15.14 Strength Profiles
15.15 Types of Analyses
15.16 Transformation from Effective Stress Solution to Undrained Strength Solution
Problems
Chapter 16: Thermodynamics for Soil Problems
16.1 General
16.2 Definitions
16.3 Constitutive and Fundamental Laws
16.4 Heat Conduction Theory
16.5 Axisymmetric Heat Propagation
16.6 Thermal Properties of Soils
16.7 Multilayer Systems
16.8 Applications
16.9 Frozen Soils
Problems
Chapter 17: Shallow Foundations
17.1 Definitions
17.2 Case History
17.3 Definitions and Design Strategy
17.4 Limit States, Load and Resistance Factors, and Factor of Safety
17.5 General Behavior
17.6 Ultimate Bearing Capacity
17.7 Load Settlement Curve Approach
17.8 Settlement
17.9 Shrink-Swell Movement
17.10 Foundations on Shrink-Swell Soils
17.11 Tolerable Movements
17.12 Large Mat Foundations
Problems
Chapter 18: Deep Foundations
18.1 Different Types of Deep Foundations
18.2 Design Strategy
18.3 Pile Installation
18.4 Vertical Load: Single Pile
18.5 Vertical Load: Pile Group
18.6 Downdrag
18.7 Piles in Shrink-Swell Soils
18.8 Horizontal Load and Moment: Single Pile
18.9 Horizontal Load and Moment: Pile Group
18.10 Combined Piled Raft Foundation
Problems
Chapter 19: Slope Stability
19.1 General
19.2 Design Approach
19.3 Infinite Slopes
19.4 Seepage Force in Stability Analysis
19.5 Plane Surfaces
19.6 Block Analysis
19.7 Slopes with Water in Tensile Cracks
19.8 Chart Methods
19.9 Method of Slices
19.10 Water Stress for Slope Stability
19.11 Types of Analyses
19.12 Progressive Failure in Strain-Softening Soils
19.13 Shallow Slide Failures in Compacted Unsaturated Embankments
19.14 Reinforced Slopes
19.15 Probabilistic Approach
19.16 Three-Dimensional Circular Failure Analysis
19.17 Finite Element Analysis
19.18 Seismic Slope Analysis
19.19 Monitoring
19.20 Repair Methods
Problems
Chapter 20: Compaction
20.1 General
20.2 Compaction Laboratory Tests
20.3 Compaction Field Tests
20.4 Compaction and Soil Type
20.5 Intelligent Roller Compaction
20.6 Impact Roller Compaction
20.7 Dynamic or Drop-Weight Compaction
Problems
Chapter 21: Retaining Walls
21.1 Different Types (Top-Down, Bottom-Up)
21.2 Active, At Rest, Passive Earth Pressure, and Associated Displacement
21.3 Earth Pressure Theories
21.4 Special Case: Undrained Behavior of Fine-Grained Soils
21.5 At-Rest Earth Pressure
21.6 Earth Pressure Due to Compaction
21.7 Earth Pressures in Shrink-Swell Soils
21.8 Displacements
21.9 Gravity Walls
21.10 Mechanically Stabilized Earth Walls
21.11 Cantilever Top-Down Walls
21.12 Anchored Walls and Strutted Walls
21.13 Soil Nail Walls
21.14 Special Case: Trench
Problems
Chapter 22: Earthquake Geoengineering
22.1 Background
22.2 Earthquake Magnitude
22.3 Wave Propagation
22.4 Dynamic Soil Properties
22.5 Ground Motion
22.6 Seismic Hazard Analysis
22.7 Ground Response Analysis
22.8 Design Parameters
22.9 Liquefaction
22.10 Seismic Slope Stability
22.11 Seismic Design of Retaining Walls
22.12 Seismic Design of Foundations
Problems
Chapter 23: Erosion of Soils and Scour Problems
23.1 The Erosion Phenomenon
23.2 Erosion Models
23.3 Measuring the Erosion Function
23.4 Soil Erosion Categories
23.5 Rock Erosion
23.6 Water Velocity
23.7 Geometry of the Obstacle
23.8 Bridge Scour
23.9 River Meandering
23.10 Levee Overtopping
23.11 Countermeasures for Erosion Protection
23.12 Internal Erosion of Earth Dams
Problems
Chapter 24: Geoenvironmental Engineering
24.1 Introduction
24.2 Types of Wastes and Contaminants
24.3 Laws and Regulations
24.4 Geochemistry Background
24.5 Contamination
24.6 Remediation
24.7 Landfills
24.8 Future Considerations
Problems
Chapter 25: Geosynthetics
25.1 General
25.2 Types of Geosynthetics
25.3 Properties of Geosynthetics
25.4 Design for Separation
25.5 Design of Liners and Covers
25.6 Design for Reinforcement
25.7 Design for Filtration and Drainage
25.8 Design for Erosion Control
25.9 Other Design Applications
Problems
Chapter 26: Soil Improvement
26.1 Overview
26.2 Soil Improvement without Admixture in Coarse-Grained Soils
26.3 Soil Improvement without Admixture in Fine-Grained Soils
26.4 Soil Improvement with Replacement
26.5 Soil Improvement with Grouting and Admixtures
26.6 Soil Improvement with Inclusions
26.8 Selection of Soil Improvement Method
Problems
Chapter 27: Technical Communications
27.1 General
27.2 E-Mails
27.3 Letters
27.4 Geotechnical Reports
27.5 Theses and Dissertations
27.6 Visual Aids for Reports
27.7 Phone Calls
27.8 Meetings
27.9 Presentations and PowerPoint Slides
27.10 Media Interaction
27.11 Ethical Behavior
27.12 Professional Societies
27.13 Rules for a Successful Career
References
Index
Cover image: © Art Koenig, Photographer/Artist
Cover design: Wiley
This book is printed on acid-free paper.
Copyright © 2013 by John Wiley & Sons, Inc. All rights reserved
Published by John Wiley & Sons, Inc., Hoboken, New Jersey
Published simultaneously in Canada
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Library of Congress Cataloging-in-Publication Data:
Briaud, J.-L.
Introduction to geotechnical engineering : unsaturated and saturated soils / Jean-Louis Briaud.
pages cm
“Published simultaneously in Canada“—Title page verso.
Includes bibliographical references and index.
ISBN 978-0-470-94856-9 (cloth : acid-free paper); 978-1-118-41574-0 (ebk.); 978-1-118-41826-0 (ebk.)
1. Geotechnical engineering–Textbooks. 2. Soil
mechanics–Textbooks. I. Title.
TA705.B75 2013
624–dc23
2013004684
Acknowledgments
One of the greatest joys in writing this book was working as a team with all my PhD students. From 2010 to 2013, they contributed tremendously to making this book possible. The leader of the team was Ghassan Akrouch. I thank them all very sincerely for their magnificent help. The beautiful memories of our work together on this huge project will be with me as a source of strength and friendship forever.
Ghassan Akrouch (Lebanon)
Alireza Mirdamadi (Iran)
Deeyvid Saez (Panama)
Mojdeh Asadollahipajouh (Iran)
Congpu Yao (China)
Stacey Tucker (USA)
Negin Yousefpour (Iran)
Oswaldo Bravo (Peru)
DoHyun Kim (Korea)
Axel Montalvo (Puerto Rico)
Gang Bi (China)
Mohsen Madhavi (Iran)
Seung Jae Oh (Korea)
Seok Gyu Kim (Korea)
Mohammad Aghahadi (Iran)
Yasser Koohi (Iran)
Carlos Fuentes (Mexico)
My colleagues also provided advice on many topics:
Marcelo Sanchez (Texas A&M University)
Don Murff (Exxon)
Jose Roesset (Texas A&M University)
Giovanna Biscontin (Texas A&M University)
Chuck Aubeny (Texas A&M University)
Zenon Medina Cetina (Texas A&M University)
Vincent Drnevich (Purdue)
Chris Mathewson (Texas A&M University)
One person stands out as a major helper in this book project by her dedication to the task and her relentless denial of the impossible: my assistant Theresa Taeger, who took care of the hundreds of illustration permission requests in record time.
I also want to thank all those who share their knowledge and intellectual property online. Without the Internet as a background resource, this work would have taken much longer.
Chapter 1
Introduction
1.1 Why This Book?
“Things should be made as simple as possible but not a bit simpler than that.”
Albert Einstein (Safir and Safire 1982)
Finding the Einstein threshold of optimum simplicity was a constant goal for the author when writing this book (Figure 1.1).
Figure 1.1 Einstein threshold of optimum simplicity.
(Photo by Ferdinand Schmutzer)
The first driving force for writing it was the coming of age of unsaturated soil mechanics: There was a need to introduce geotechnical engineering as dealing with true three-phase soils while treating saturated soil as a special case, rather than the other way around. The second driving force was to cover as many geotechnical engineering topics as reasonably possible in an introductory book, to show the vast domain covered by geotechnical engineering and its important contributions to society. Dams, bridges, buildings, pavements, landfills, tunnels, and many other infrastructure elements involve geotechnical engineering. The intended audience is anyone who is starting in the field of geotechnical engineering, including university students.
1.2 Geotechnical Engineering
Geotechnical engineering is a young (∼100 years) professional field dealing with soils within a few hundred meters of a planet's surface for the purpose of civil engineering structures. For geotechnical engineers, soils can be defined as loosely bound to unbound, naturally occurring materials that cover the top few hundred meters of a planet. In contrast, rock is a strongly bound, naturally occurring material found within similar depths or deeper. At the boundary between soils and rocks are intermediate geo-materials. The classification tests and the range of properties described in this book help to distinguish between these three types of naturally occurring materials.
Geotechnical engineers must make decisions in the best interest of the public with respect to safety and economy. Their decisions are related to topics such as:
Foundations
Slopes
Retaining walls
Dams
Landfills
Tunnels
These structures or projects are subjected to loads, which include:
Loads from a structure
Weight of a slope
Push on a retaining wall
Environmental loads such as waves, wind, rivers, earthquakes, floods, droughts, and chemical changes, among others
Note that current practice is based on testing an extremely small portion of the soil or rock present in the project area. A typical soil investigation might involve testing 0.001% of the soil that will provide the foundation support for the structure. Yet, on the basis of this extremely limited data, the geotechnical engineer must predict the behavior of the entire mass of soil. This is why geotechnical engineering is a very difficult discipline.
1.3 The Past and the Future
While it is commonly agreed that geotechnical engineering started with the work of Karl Terzaghi at the beginning of the 20th century, history is rich in instances where soils and soils-related engineering played an important role in the evolution of humankind (Kerisel 1985; Peck 1985; Skempton 1985). In prehistoric times (before 3000 bc), soil was used as a building material. In ancient times (3000-300 bc), roads, canals, and bridges were very important to warriors. In Roman times (300 bc-300 ad), structures started to become larger and foundations could no longer be ignored. The Middle Ages (ad 300-1400) were mainly a period of war, in which structures became even heavier, including castles and cathedrals with very thick walls. Severe settlements and instabilities were experienced. The Tower of Pisa was started in 1174 and completed in 1370. The Renaissance (ad 1400-1650) was a period of enormous development in the arts, and several great artists proved to be great engineers as well. This was the case of Leonardo da Vinci and more particularly Michelangelo. Modern times (ad 1650-1900) saw significant engineering development, with a shift from military engineering to civil engineering. In 1776, Charles Coulomb developed his earth pressure theory, followed in 1855 by Henry Darcy and his seepage law. In 1857, William Rankine proposed his own earth pressure theory, closely followed by Carl Culman and his graphical earth pressure solution. In 1882, Otto Mohr presented his stress theory and the famous Mohr circle, and in 1885 Joseph Boussinesq provided the solution to an important elasticity problem for soils. From 1900 to 2000 was the true period of development of modern geotechnical engineering, with the publication of Karl Terzaghi's book Erdbaumechanik (in 1925), which was soon translated into English; new editions were co-authored with Ralph Peck beginning in 1948. The progress over the past 50 years has been stunning, with advances in the understanding of fundamental soil behavior and associated soil models (e.g., unsaturated soils), numerical simulations made possible by the computer revolution, the development of large machines (e.g., drill rigs for bored piles), and a number of ingenious ideas (e.g., reinforced earth walls).
Geotechnical engineering has transcended the ages because all structures built on or in a planet have to rest on a soil or rock surface; as a result, the geotechnical engineer is here to stay and will continue to be a very important part of humanity's evolution. The Tower of Pisa is one of the most famous examples of a project that did not go as planned, mostly because of the limited knowledge extant some 900 years ago. Today designing a proper foundation for the Tower of Pisa is a very simple exercise, because of our progress. One cannot help but project another 900 years ahead and wonder what progress will have been made. Will we have:
complete nonintrusive site investigation of the entire soil volume?
automated four-dimensional (4D) computer-generated design by voice recognition and based on a target risk?
tiny and easily installed instruments to monitor geotechnical structures?
unmanned robotic machines working at great depth?
significant development of the underground?
extension of projects into the sea?
soil structure interaction extended to thermal and magnetic engineering?
failures down to a minimum?
expert systems to optimize repair of defective geotechnical engineering projects?
geospace engineering of other planets?
geotechnical engineers with advanced engineering judgment taught in universities?
no more lawyers, because of the drastic increase in project reliability?
1.4 Some Recent and Notable Projects
Among some notable geotechnical engineering projects and developments are the underpinning of the foundation of the Washington Monument in 1878 (Figure 1.2; Briaud et al. 2009); the Panama Canal (1913) and its slope stability problems (Figure 1.3; Marcuson 2001); the Tower of Pisa (1310) and its foundation repair in 1990 (Figure 1.4; Jamiolkowski 2001); the locks and dams on the Mississippi River and their gigantic deep foundations (Figure 1.5); and airports built offshore, as in the case of the Tokyo Haneda airport runway extension (Figure 1.6). Among the most significant milestones in the progress of geotechnical engineering are the discovery of the effective stress principle in saturated and then unsaturated soil mechanics; the development of laboratory testing and in situ testing to obtain fundamental soil properties; the combination of soil models with numerical methods to simulate three-dimensional behavior; the advent of geo-synthetics and of reinforced soil, which is to geotechnical engineering what reinforced concrete is to structural engineering; and the development of instruments to monitor full-scale behavior of geotechnical engineering structures.
Figure 1.2 The Washington Monument.
Figure 1.3 Culebra cut of the Panama Canal, 1913.
(a: Courtesy of Fernando Alvarado; b: Courtesy of United States Geological Survey)
Figure 1.4 The Tower of Pisa and its successful repair in 1995.
(c: Courtesy of Dr. Gianluca De Felice (General Secretary), Opera Primaziale Pisana.)
Figure 1.5 Lock and Dam 26 on the Mississippi River in 1990.
(a: Courtesy of United States Army Corps of Engineers, b: Courtesy of Thomas F. Wolff, St. Louis District Corps of Engineers, 1981. c: Courtesy of Missouri Department of Transportation.)
Figure 1.6 Extension of the Tokyo Haneda airport in 2010.
(Courtesy of Kanto Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism, Japan.)
1.5 Failures May Occur
Failures do occur. The fact remains that it is not possible to design geotechnical engineering structures that will have zero probability of failure. This is because any calculation is associated with some uncertainty; because the geotechnical engineering profession's knowledge, despite having made great strides, is still incomplete in many respects; because human beings are not error free; and because the engineer designs the geotechnical engineering structure for conditions that do not include extremely unlikely events such as an asteroid hitting the structure at the same time as an earthquake, a hurricane, and a 100-year flood during rush hour.
Nevertheless, geotechnical engineers learn a lot from failures, because thorough analysis of what happened often points out weaknesses and needed improvement in our approaches. Some of the most notable geotechnical engineering failures have been the Transcona silo bearing capacity failure in 1913 (Figure 1.7), the Teton dam seepage failure in 1976 (Figure 1.8), and the failure of some of the New Orleans levees during Hurricane Katrina in 2005 (Figure 1.9).
Figure 1.7 Transcona silo bearing capacity failure and repair (1913).
(Courtesy of the Canadian Geotechnical Society.)
Figure 1.8 Teton Dam seepage failure (1976)
(Photos by Mrs. Eunice Olson. Courtesy of Arthur G. Sylvester.)
Figure 1.9 New Orleans levee failures during the Katrina hurricane in 2005.
(Courtesy of United States Army Corps of Engineers.)
1.6 Our Work Is Buried
As Terzaghi is said to have noted, there is no glory in foundations. Indeed, most of our work is buried (Figure 1.10). For example, everyone knows the Eiffel Tower in Paris, but very few know about its foundation (Figure 1.11; Lemoine 2006). The foundation was built by excavating down to the water level about deep—but the soil at that depth was not strong enough to support the weight of the Tower, so digging continued. Because of the water coming from the River Seine, the deepening of the excavation had to be done using pressurized caissons (upside-down coffee cans, big ones!) so that the air pressure could balance the water pressure and keep it out of the excavation. Workers got into these caissons (Figure 1.12) and worked literally under pressure until they reached a depth where the soil was strong enough to support the Tower (about on the side closest to the river and about on the side away from the river).
Figure 1.10 A rendition of the geotechnical engineering world.
(Courtesy of Hayward Baker Inc., Geotechnical Contractor.)
Figure 1.11 The Eiffel Tower foundation plan.
Figure 1.12 The Eiffel Tower foundation.
(Photos b, c: Courtesy of the Musée d'Orsay, Paris.)
1.7 Geotechnical Engineering Can Be Fun
Geotechnical engineering can be fun and entertaining, as the book by Elton (1999; Figure 1.13) on geo-magic demonstrates. Such phenomena as the magic sand (watch this movie: www.stevespanglerscience.com/product/1331?gclid=CNiW1uu-aICFc9J2godZwuiwg), water going uphill, the surprisingly strong sand pile (Figure 1.13), the swelling clay pie (Figure 1.13), and the suddenly very stiff glove full of sand will puzzle the uninitiated. Geotechnical engineering is seldom boring; indeed: the complexity of soil deposits and soil behavior can always surprise us with unanticipated results. The best geotechnical engineering work will always include considerations regarding geology, proper site characterization, sound fundamental soil mechanics principles, advanced knowledge of all the tools available, keen observation, and engineering judgment. The fact that geotechnical engineering is so complex makes this field an unending discovery process, which keeps the interest of its adepts over their lifetimes.
Figure 1.13 Soil magic.
(Courtesy of David J. Elton.)
1.8 Units
In engineering, a number without units is usually worthless and often dangerous. On this planet, the unit system most commonly used in geotechnical engineering is the System International or SI system. In the SI system, the unit of mass is the kilogram (kg), which is defined as the mass of a platinum-iridium international prototype kept at the International Bureau of Weights and Measures in Paris, France. On Earth, the kilogram-mass weighs about the same as 10 small apples. The unit of length is the meter, defined as the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second. A meter is about the length of a big step for an average human. The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium . Watches and clocks often have a hand ticking off the seconds. The unit of temperature is the Kelvin, defined as 1/273.16 of the difference in temperature between the absolute zero and the triple point of water. The degree Celsius (C) is also commonly used; it has the same magnitude as the degree Kelvin but starts at for the freezing point of water and uses for the boiling point of water. There are seven fundamental units in a unit system, but these four (kg, m, s, K) are the most commonly used in geotechnical engineering. The other fundamental units in the SI system are the mole (substance), the candela (light), and the ampere (electricity).
Other geotechnical engineering units are derived from these fundamental units. The unit of force is the Newton, which is the force required to accelerate a mass of to .
1.1
This force is about the weight of a small apple. Humans typically weigh between 600 and . Most often the kilo-Newton (kN) is used rather than the Newton. The kilogram force is the weight of one kilogram mass. On Earth, the equation is:
1.2
The unit of stress is the kN/m2, also called kilo-Pascal (kPa); there is about under your feet when you stand on both feet. Note that a kilogram force is the weight of a kilogram mass and depends on what planet you are on and even where you are on Earth. Other units are shown in a table at the beginning of this book.
Accepted multiples of units, also called SI prefixes, are:
terra
giga
mega
kilo
milli
micro
nano
pico
(An angstrom is meter.)
Problems
1.1 How would you decide if you have reached the threshold of optimum simplicity?
1.2 What was achieved by underpinning the Washington Monument foundation from a square foundation to a square ring, as shown in Figure 1.2?
1.3 How would you go about deciding if the slopes of the Panama Canal are too steep?
1.4 What major geotechnical engineering problems come to mind for the extension of the Tokyo Airport?
1.5 Write a step-by-step procedure for the up-righting of the Transcona Silo.
1.6 For the Eiffel Tower, calculate the average pressure under the foundation elements.
Figure 1.1s Foundation of the Eiffel Tower.
1.7 For the Tower of Pisa, calculate the pressure under the foundation, given that the foundation is a ring with a outside diameter and a inside diameter. Compare this pressure to the pressure obtained for the Eiffel Tower in problem 1.6.
Figure 1.2s Tower of Pisa foundation.
1.8 Calculate the pressure under your feet.
Figure 1.3s Feet geometry.
1.9 What do you think caused the failure of the Teton Dam? What do you think might have avoided this problem?
1.10 Explain the magic behind Figures 1.13d and 1.13e.
1.11 Are the following equations correct?
1.12 What is the relationship between a kilopascal (kPa) and a pound per square foot (psf)? What is the net pressure in psf under the Eiffel Tower foundation?
which is much larger than the pressure due to the tower alone. Indeed, the weight of all the foundation elements is a lot more than the weight of the tower.
Figure 1.1s Foundation of the Eiffel Tower.
Figure 1.3s Feet geometry.
Chapter 2
Engineering Geology
This chapter is intended to give readers a general overview of engineering geology. More detailed information should be sought in textbooks and other publications (Waltham 1994; Bell 2007).
2.1 Definition
Geology is to geotechnical engineering what history is to humankind. It is the history of the Earth's crust. Engineering geology is the application of the science of geology to geotechnical engineering in particular and engineering in general. The same way we learn from history to avoid repeating mistakes in the future, we learn from engineering geology to improve geotechnical engineering for better design of future structures. Engineering geology gives the geotechnical engineer a large-scale, qualitative picture of the site conditions. This picture is essential to the geotechnical engineer and must always be obtained as a first step in any geotechnical engineering project.
2.2 The Earth
The age of the universe and of the Earth is a matter of debate. The most popular scientific views are that the universe started with a “big bang” some 15 billion years ago and that the Earth (Figure 2.1) began to be formed some 4.5 billion years ago (Dalrymple 1994), when a cloud of interstellar matter was disturbed, possibly by the explosion of a nearby star. Gravitational forces in this flat, spinning cloud caused its constituent material to coalesce at different distances from the Sun, depending on their mass density, and eventually to form planets. The Earth ended up with mostly iron at its center and silicates at the surface.
Figure 2.1 The Earth.
(Courtesy of NOAA-NASA GOES Project.)
The Earth has a radius of approximately 6400 km (Jefferis 2008). The first layer, known as the crust (Figure 2.2), is about 100 km thick and is made of plates of hard silica rocks. The next layer, called the mantle, is some 2800 km thick and made of hot plastic iron silicates. The core is the third and last layer; it has a radius of 3500 km and is largely made of molten iron.
Figure 2.2 Earth temperature, pressure, and density.
Early on, the planet was very hot and all earth materials were melted like they are on the Sun today. The cooling process started right away and has been progressing ever since. The present temperature gradient, shown in Figure 2.2, represents an average increase in temperature with depth of 15 degrees Celsius per kilometer in the crust, although the overall average is only 1 degree Celsius per kilometer. The gravity field is governed by the acceleration due to gravity ( on the average). This gravity field generates an increase in stress versus depth, which leads to an enormous pressure at the center of the Earth of about 340 GPa. The Earth's magnetic field is created by magma movement in the core and varies between 30 and 60 microteslas; it is strongest near the poles, which act as the two ends of the Earth dipole.
The Earth is a dynamic medium that changes and evolves through major events such as plate tectonics and earthquakes. The rock plates (about 100 km thick) that “float” on the semiliquid and liquid layers below accumulate strains at various locations where they run into each other. When the stress buildup is released abruptly, the result is an earthquake. Earthquakes and other movements allow the plates to move slowly (centimeters per year) yet significantly over millions of years. For example, on today's world map South America still looks like it could fit together with Africa—because in the distant past they were in fact joined (Figure 2.3).
Figure 2.3 South America and Africa fit.
(Courtesy of John Harvey.)
2.3 Geologic Time
Geologic time is a scale dividing the age of the earth (4600 million years) into 5 eras (Figure 2.4): Precambrian (4600 million years ago [MYA] to 570 MYA), Paleozoic (570 MYA to 245 MYA), Mesozoic (245 MYA to 65 MYA), Tertiary (65 MYA to 2 MYA), and Quaternary (2 MYA to the present) (Harland et al. 1989). Each era is subdivided into periods and then into epochs (Figure 2.5). The Quaternary era, for example, is divided into the Pleistocene period and the Holocene or Recent period.
Figure 2.4 Geologic time (eras).
Figure 2.5 Geologic time (periods and epochs).
Typically, the older the earth material, the stronger it is. The last Ice Age occurred about 10,000 years ago at the beginning of the Holocene period. Glaciers, some of them 100 meters thick, covered the earth from the North Pole down to about the 40th parallel (St. Louis in the USA) and preloaded the soil. Because of this very heavy preloading, called overconsolidation or OC, those soil types (e.g., till) are very stiff and strong and do not settle much under load, but may erode quickly (as in the Schoharie Creek bridge failure disaster in 1987). When the glaciers melted, the soil surface rebounded; in some places this movement is still ongoing at a rate of about 10 mm per year.
2.4 Rocks
The Earth crust is 95% silica—and when silica cools, it hardens. This cooling creates the first kind of rocks: igneous rocks. Igneous rocks (e.g., granite, basalt, gneiss) are created by the crystallization of magma. Sedimentary rocks (e.g., sandstone, limestone, clay shales) are made of erosional debris on the Earth surface which was typically granular and recemented; they are created by wind erosion and water erosion, and are recemented by long-term high pressure or by chemical agents such as calcium. Metamorphic rocks (e.g., schist, slate) are rocks that have been altered by heat and/or pressure. The strength of rocks varies greatly, from 10 times stronger than concrete (granite) to 10 times weaker than concrete (sandstone). Older rocks are typically stronger than younger rocks. Figure 2.6 shows some of the main rock types.
Figure 2.6 Main categories of rocks.
(Courtesy of EDUCAT Publishers)
2.5 Soils
Soils are created by the exposure of rocks to the weather. This weathering can be physical (wetting/drying, thermal expansion, frost shatter) or chemical (solution, oxidation, hydrolysis). The elementary components of rocks and soils are minerals such as quartz and montmorillonite. Some minerals are easier to break down (montmorillonite) than others (quartz). As a result, the coarse-grained soils (sand, gravel) tend to be made of stable minerals such as quartz, whereas the fine-grained soils (silt and clay) tend to be made of less stable minerals such as montmorillonite. Organic soils may contain a significant amount of organic matter (wood, leaves, plants) mixed with the minerals, or may be made entirely of organic matter, such as the peat often found at the edges of swamps. Figure 2.7 shows some of those soils categories. Note that what the geotechnical engineer calls soil may be called rock by the engineering geologist; this can create confusion during discussion and interpretation.
Figure 2.7 Main soil categories (crushed rock, gravel, sand, silt, clay).
2.6 Geologic Features
The ability to recognize geologic features helps one to assess how the material at the site may be distributed. These features (Waltham 1994; Bell 2007) include geologic structures (faults, synclines, anticlines), floodplains and river deposits (alluviums, meander migration), glacial deposits (glacial tills and boulders left behind by a glacier), arid landforms (dunes, collapsible soils, shrink-swell soils), and coastal processes (shoreline erosion, sea-level changes).
The following list identifies some of the most common and important geological features that can affect geotechnical engineering projects.
Faults (Figure 2.8) are fractures in a rock mass that has experienced movement. They can lead to differences in elevation at the ground surface, differential erosion, contrasting visual appearance, and weaker bearing capacity of the fault material compared to the parent rock.
Outcrops show up at the ground surface when the rock layers are inclined. The area on the ground surface associated with an outcrop depends on the thickness of the layer and its dip or angle with the horizontal.
Escarpments are asymmetric hills formed when an outcrop is eroded unevenly or when the edge of rock layers is not flat. A cliff is an extreme case of an escarpment.
Folds (Figure 2.9) are created when rock layers are curved or bent by earth crust movement. Synclines are concave features (valleys), whereas anticlines are convex features (hills). Folds are best seen on escarpments.
Inliers and outliers are the result of erosion. Older rocks are typically below younger rocks. When an anticline erodes, the old rock appears at the surface between two zones of younger rocks (inlier). When a syncline erodes, it can lead to the reverse situation (outlier).
Figure 2.8 Example of rock fault.
(Courtesy of USGS U.S. Geological Survey.)
Figure 2.9 Example of anticline-syncline combination.
(Photo by R. W. Schlische.)
Karst is the underground landscape created when limestone is eroded or dissolved by groundwater. This process leads to holes in the limestone, called sinkholes, which can range from 1 meter to more than 100 meters in size and may become apparent while drilling during the site investigation (Figure 2.10).
Subsidence refers to settlement of the ground surface over large areas (in the order of square kilometers). Subsidence can be caused by pumping water out of the ground for irrigation or drinking purposes (Houston, Mexico City), pumping oil, digging large tunnels and mines, the presence of sinkholes, melting of the permafrost, and wetting of certain soils that collapse in the presence of water (called collapsible soils).
Meander migration occurs because rivers are dynamic features that change their contours by lateral erosion, particularly around bends or meanders. The soil forming the bank on the outside of the meander is eroded and is sent to the inside of the meander by the helical current of the river as it takes the meander turn. The inside of the meander then forms a sand bar (Figure 2.11).
Figure 2.10 Examples of sinkholes.
(Left: Courtesy of R.E. Wallace, United States Geological Survey, USA,; Right: Courtesy of International Association of Certified Home Inspectors, Inc.)
Figure 2.11 Example of meander migration.
Figure 2.12 Example of an alluvial fan.
(Courtesy of Mike Norton.)
Flood plain deposits occur when rivers experience flooding and the water spills over from the main channel into the floodplain. The main channel is a high-energy deposition environment, and only coarse-grained soils heavy enough not to be transported away are found there. In contrast, floodplains are a low-energy deposition environment where fine-grained soils are typically found. Floodplains and main channels can end up being buried or abandoned as the river migrates laterally and vertically. Abandoned floodplains are called river terraces.
Alluvium and alluvial fans are soil deposits transported to the bottom of a steep slope by the erosion of a river flowing down that steep slope (Figure 2.12).
Colluvial fans are deposits that form by gravity at the bottom of steep slopes when the slope fails.
Dunes are wind-blown sediments that accumulate over time to form a hill.
Permafrost is a zone of soil that remains frozen year round.
2.7 Geologic Maps
Geologic maps are very useful to the geotechnical engineer when evaluating the large-scale soil and rock environment to be dealt with in a project. These maps typically have a scale from 1:10,000 to 1:100,000 and show the base rock or geologic unit and major geologic features such as faults. Each rock area of a certain age is given a different color (Figure 2.13); soil is usually not shown on those maps. These maps can provide useful information regarding groundwater and hydrogeology, landslide hazards, sinkhole susceptibility, earthquakes, collapsible soils, flood hazards, and karst topography. Remember that what the geotechnical engineer calls soil may be called rock by the engineering geologist; to avoid confusion during discussion and interpretation, it is best to clarify the terminology.
Figure 2.13 Example of geologic map.
(Courtesy of National Park Service, NPS.)
2.8 Groundwater
Another important contribution of engineering geology to geotechnical engineering is a better understanding of how the groundwater is organized at a large scale. This field involves aquifer conditions, permeability of the rocks, and weather patterns (Winter et al. 1999). If you drill a hole in the ground, at some point you are likely to come to a depth where there is water. This water is called groundwater and it comes from infiltration from rain, rivers, springs, and the ocean. It may be stationary or flow slowly underground. If you go very deep (about 3 km or more), you will get to a point where there is no more water and the rocks are dry. The groundwater table (Figure 2.14) is the surface of the water within the soil or rock where the water stress is equal to the atmospheric pressure (zero gauge pressure). Under natural conditions and in the common case, the groundwater table is close to being flat.
Figure 2.14 Groundwater.
The phreatic surface, also called the piezometric surface, is the level to which the water would rise in a tube connected to the point considered in the soil mass. Most of the time, the groundwater table and the phreatic surface are the same. In some cases, though, they are different: artesian pressure refers to the case where the pressure in the water at some depth below the groundwater table is higher than the pressure created by a column of water equal in height to the distance between the point considered and the groundwater table. This can occur when a less permeable clay layer lies on top of a more permeable sand layer connected to a higher water source (Figure 2.14). Indeed, if you were to drill a hole through the soil down to a zone with artesian pressure, the water would rise above the level of the ground surface and could gush out into a spring (Figure 2.15).
Figure 2.15 Example of flow due to artesian pressure.
(Courtesy of USGS U.S. Geological Survey.)
Perched water is a zone of water in the soil where the water appears at a certain depth in a boring and then disappears at a deeper depth; it acts as a pocket of water in the ground. Aquifers are typically deeper reservoirs of water that are supplied by surrounding water through a relatively porous rock. Aquifers are often pumped for human consumption. Their depletion can create kilometers-wide zones of settlement called subsidence, and in some instances the settlement can reach several meters in depth.
In geotechnical engineering, it is very important to know where the groundwater table is located, as it often affects many aspects of the project. Furthermore, it is important to identify irregularities in groundwater, such as artesian pressure or perched water.
Problems
2.1 Calculate the pressure at the center of the Earth.
2.2 Calculate the temperature at the center of the Earth
2.3 What is the depth of interest for most geotechnical engineering projects?
2.4 List the Tertiary and Quaternary epochs.
2.5 What happened about 10,000 years ago on the Earth? What are some of the consequences for soil and rock behavior today?
2.6 What are the three main categories of rocks, and what is the origin of each category?
2.7 What are the four main categories of soil sizes? How were each of these soils generated?
2.8 What engineering geology features can you look for when you visit a site for a geotechnical engineering project?
2.9 How can geologic maps be useful to the geotechnical engineer?
2.10 Define the following terms: groundwater level, perched water, phreatic surface, aquifer.
where G is the gravitational constant
Figure 2.1s Parameters definition.
Chapter 3
Soil Components and Weight-Volume Parameters
3.1 Particles, Liquid, and Gas
Soils are made of particles, gas (most often air), and fluid (most often water). Particles are also called grains. The space between the particles makes up the voids sometimes also called pores. If the voids are completely filled with air, the soil is called dry. If the voids are completely filled with water, the soil is called saturated. If the soil is filled partly with air and partly with water, the soil is called unsaturated. Figure 3.1 shows a soil sample and its graphical representation (the three-phase diagram discussed later in this chapter).
Figure 3.1 Three-phase diagram representation.
Note that in some cases, there is a subtle distinction between saying that a soil is dry and saying that a soil has no water. If a small sample of wet soft clay is left in the sun or in a low-humidity laboratory, it will become “dry” after a while and at the same time much stronger than when it was wet. This “dry” clay still has a tiny bit of water firmly bound between the particles. This water is in tension and sucks the particles together through a phenomenon called suction (explained in Chapter 10 on effective stress). This suction is responsible for the increase in strength of the clay. If the dried clay is ground into individual particles and placed in an oven at 100°C, then it will have no water and no strength. Thus, it becomes important to make a distinction between dried and no water; for example, a dried clay is a hard block of soil whereas a clay with no water may simply be a dry powder.
