Geotechnical Problem Solving E-Book

John C. Lommler

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 637

Veröffentlichungsjahr: 2012

Beschreibung

Devised with a focus on problem solving, Geotechnical Problem Solving bridges the gap between geotechnical and soil mechanics material covered in university Civil Engineering courses and the advanced topics required for practicing Civil, Structural and Geotechnical engineers. By giving newly qualified engineers the information needed to apply their extensive theoretical knowledge, and informing more established practitioners of the latest developments, this book enables readers to consider how to confidently approach problems having thought through the various options available. Where various competing solutions are proposed, the author systematically leads through each option, weighing up the benefits and drawbacks of each, to ensure the reader can approach and solve real-world problems in a similar manner The scope of material covered includes a range of geotechnical topics, such as soil classification, soil stresses and strength and soil self-weight settlement. Shallow and deep foundations are analyzed, including special articles on laterally loaded piles, retaining structures including MSE and Tieback walls, slope and trench stability for natural, cut and fill slopes, geotechnical uncertainty, and geotechnical LRFD (Load and Resistance Factor Design).

Leseprobe

Contents

Cover

Title Page

Copyright

Preface

1: General Topics

1.1: How to Use this Book

1.2: You Have to See it to Solve it

1.2.1 Introduction to Problem Solving

1.2.2 Advanced and Expert Practice

1.2.3 Theories Can Be Wrong…

1.2.4 Seeing is Better than Not Seeing …

1.2.5 Why is Standard Engineering Practice Changing?

1.2.6 An Example of Increasing Complexity of Standard Practice …

1.2.7 Helping You See …

1.3: My Approach to Modern Geotechnical Engineering Practice – An Overview

1.3.1 Introduction

1.3.2 Summary of Problem-Solving Approach

1.3.3 Geotechnical Overview and Approach

1.3.4 What Do I Do? Answer: The Graded Approach

1.3.5 Geotechnical Investigations for $15 per Foot

1.3.6 Geotechnical Problems

1.3.7 Bearing Capacity

1.3.8 Summary

1.3.9 Additional Material

1.4: Mistakes or Errors

1.4.1 Mistakes

1.4.2 Errors

1.4.3 Mistakes and Errors – Closing Remarks

2: Geotechnical Topics

2.1: Soil Classification – Why Do we Have it?

2.1.1 Introduction to Soil Classification

2.1.2 Soil Properties Suggested by Classification Tests

2.1.3 Examples of Soil Classification Problems

2.1.4 A Word about Units and Normalization

2.1.5 Soil Classification – Concluding Remarks

2.1.6 Additional Reading Material

2.2: Soil Stresses and Strains

2.2.1 Introduction to Soil Stresses

2.2.2 Isotropic and Linearly Elastic versus Anisotropic and Non-Linearly Elastic

2.2.3 Anisotropic Materials and Anisotropic Stresses

2.2.4 Soil Strains

2.2.5 Additional General Information on Soil Stresses and Strains

2.2.6 Additional Specific Information on Stresses and Strains

2.3: Soil Shear Strength

2.3.1 Introduction to Soil Shear Strength

2.3.2 Soil Cohesion and Friction

2.3.3 Soil Shear Strength

2.3.4 Additional Soil Shear Strength Information – General

2.3.5 Additional Information and Second-Order Terms

2.3.6 Additional Information – Non-Linear Failure Envelopes

2.4: Shear Strength Testing – What is Wrong with the Direct Shear Test?

2.4.1 Introduction to Direct Shear Testing

2.4.2 Direct Shear Rotation of Principle Stresses

2.4.3 Use of the Direct Shear Test to Determine Internal Friction Angle,

2.4.4 The Direct Shear Test – Details

2.4.5 How Can the Direct Shear Test Go Wrong?

2.4.6 Evaluating Results of Direct Shear Tests

2.4.7 Concluding Remarks about the Direct Shear Test

2.5: What is the Steady State Line?

2.5.1 Introduction to the Steady State Line

2.5.2 Hydrostatic Stresses and Volume Changes

2.5.3 Shearing Stresses and Volume Changes

2.5.4 Clays – SSL versus CSL

2.6: Static Equilibrium and Limit States

2.6.1 Introduction to Static Equilibrium and Limit States

2.6.2 What Are Limit States?

2.6.3 Competition between Rankine and Coulomb Equations

2.7: Unsaturated Soils

2.7.1 Introduction to Unsaturated Soils

2.7.2 Unsaturated Soil Mechanics – Soil Suction and Soil Tension

2.7.3 Analysis of Unsaturated Soils

2.7.4 Expansive and Collapsible Soils

2.7.5 Depth of Wetting

2.7.6 The Soil Water Characteristic Curve

2.7.7 Additional Study of Unsaturated Soils

3: Foundations

3.1: Settlements of Clays

Introduction

3.1.1 A Brief Geotechnical History and Overview of Clay Settlement

3.1.2 Time Rate of Consolidation Issues

3.1.3 Time Rate of Consolidation Corrections – The Asaoka Method

3.1.4 A Few Lessons Learned from Field Measurements of Settlement

3.1.5 Closing Remarks on Clay Settlement Calculations

3.2: Settlement of Sands

3.2.1 Introduction

3.2.2 Settlement of Sands – General

3.2.3 The Granular Soil Identification Problem

3.2.4 Identification of Loose Granular Soils

3.2.5 Identification of Dense Granular Soils

3.2.6 Analyzing the Sand Settlement Problem

3.2.7 Janbu Method of Settlement Calculation

3.2.8 Estimating Settlements – Why Did We Over-Estimate the Settlement?

3.2.9 Additional Sand Settlement Information – Specific

3.3: Self-Weight Settlement of Sandy Soils

3.3.1 Introduction to Collapsible Soils

3.3.2 Soil with a Metastable Collapsible Structure

3.3.3 Collapse Settlement of Dry Loose Sandy Soil with a Stable Structure

3.3.4 Standard Laboratory Testing of Collapsible Soils

3.4: Bearing Capacity of Shallow Foundations

3.4.1 Background and History of Bearing Capacity

3.4.2 Allowable Bearing Pressure

3.4.3 How Structural Engineers Use Allowable Bearing Pressures

3.4.4 Advanced Bearing Capacity Material

3.5: Load Capacity of Deep Foundations

3.5.1 Deep Foundations – What Are They?

3.5.2 Allowable Load Capacity of Deep Foundations

3.5.3 Case Histories and Full-Scale Load Tests

3.6: Laterally Loaded Piles and Shafts

3.6.1 Introduction of Laterally Loaded Piles and Shafts

3.6.2 L-Pile Program Use – A Few Pointers

3.6.3 L-Pile Soil Input Parameters

3.6.4 Lateral Pile/Shaft Group Reduction Factors

4: Retaining Structures – Lateral Loads

4.1: Lateral Earth Pressure

4.1.1 Lateral Earth Pressure Introduction

4.1.2 Lateral Earth Pressure – The Problem

4.1.3 Coulomb Earth Pressure Equations

4.1.4 Rankine Earth Pressure Equations

4.1.5 Including Cohesion into Active and Passive Earth Pressures

4.1.6 Equivalent Fluid Pressure

4.1.7 Lateral Earth Pressures for Wet Soil versus Submerged Soil

4.1.8 Friction between Retained Fill and Wall – Curved Failure Surfaces

4.1.9 Seismic Earth Pressure

4.1.10 Suggested Further Reading

4.2: Retaining Walls – Gravity, Cantilevered, MSE, Sheet Piles, and Soldier Piles

4.2.1 Introduction to Retaining Walls

4.2.2 Design of Gravity Retaining Walls

4.2.3 Issues with Static Equilibrium Analyses of Walls

4.2.4 Design of Cantilevered Retaining Walls

4.2.5 Design of MSE Retaining Walls

4.2.6 Design of Sheet-Pile Walls

4.2.7 Design of Soldier-Pile Walls

4.2.8 What Kind of Wall Would You Use Here?

4.3: Tieback Walls

4.3.1 Introduction to Tieback Walls

4.3.2 Retaining Structures with One Row of Tiebacks

4.3.3 Retaining Structures with Multiple Rows of Tiebacks

5: Geotechnical LRFD

5.1: Reliability, Uncertainty, and Geo-Statistics

5.1.1 Introduction – Why Not Just Pick the Best Number?

5.1.2 How Do we Know that Our Designs Are Safe?

5.1.3 What is Reliability and How is it Used in Design?

5.1.4 Certainty and Uncertainty

5.1.5 Factors of Safety and Reliability

5.2: Geotechnical Load and Resistance Factor Design

5.2.1 Limit State Design – General

5.2.2 Let's Stop and Think about this for a Moment

5.2.3 Geotechnical LRFD Design

5.3: LRFD Spread Footings

5.3.1 LRFD and ASD Spread Footing Analyses – An Overview

5.3.2 A Spread Footing LRFD Design Approach

5.3.3 Development of Spread Footing Load-Settlement Curves

5.3.4 Development of a Spread Footing Service and Strength Resistance Chart

5.3.5 Other Spread Footing LRFD Considerations – Eccentricity and Sliding

5.4: LRFD Pile Foundations

5.4.1 LRFD Piles – Overview

5.4.2 Geotechnical LRFD Codes for Piles and Drilled Shafts

5.4.3 Development of a Driven-Pile Axial Strength Resistance Chart

5.4.4 Development of a Driven-Pile Axial Service Resistance Chart

5.5: LRFD Drilled-Shaft Foundations

5.5.1 LRFD Drilled Shafts – Overview

5.5.2 Development of a Drilled-Shaft Axial Strength Resistance Chart

5.5.3 Development of a Drilled-Shaft Axial Service Resistance Chart

5.5.4 Drilled-Shaft Load-Settlement Curves

5.6: LRFD Slope Stability

5.6.1 Introduction

5.6.2 Slope Stability by the Beam Analogy Method

5.6.3 Slope Stability – ASD and LRFD Analysis Methods

5.6.4 Three Basic Slope-stability Problem Types

5.6.5 Closing Thoughts on LRFD Slope-Stability Analyses

6: Closing

6.1: The Big Picture

6.1.1 How Do Geotechnical Engineers Miss the Big Picture?

6.1.2 The Big Picture – What a Soils Engineer Should Know about the Geologic Setting before Going to the Job Site

6.1.3 Bedrock

6.1.4 Structural Problems

6.1.5 Previous Land Usage

6.1.6 Paleo Channels

6.1.7 Jerry's Closing Comment and a Thought from Ralph Peck

6.2: V and V and Balance

6.2.1 Have Hand Calculations Died?

6.2.2 What about the Graded Approach and Balance?

6.3: The Biggest Problem

6.3.1 What is the Biggest Problem?

6.3.2 How do We Solve the Biggest Problem?

6.4: Topics Left for Later

6.4.1 Geotechnical Engineering Topics are Endless

6.4.2 Closing

Index

This edition first published 2012 © 2012 John Wiley & Sons, Ltd

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Library of Congress Cataloging-in-Publication Data

Lommler, John C. Geotechnical problem solving / John C. Lommler. p. cm. Includes bibliographical references and index. ISBN 978-1-119-99297-4 (hardback) 1. Engineering geology. 2. Soil mechanics. 3. Soil-structure interaction. I. Title. TA705.L64 2012 624.1′51–dc23 2011044002

A catalogue record for this book is available from the British Library.

Preface

7 December 2007, 6:19 am

For several years, my friend Ralph Peck has been gently encouraging me to participate more actively in the geotechnical engineering community and to write a book. A few weeks ago he told me about starting to write his famous book, Soil Mechanics in Engineering Practice. The day he started to write was December 7, 1941, better known as “Pearl Harbor Day.” Talk about hard times to write a book! Ralph told me it took seven years to write that first book and that it was impossible, or nearly impossible, to finish, but worth the effort.

I suggested to Ralph that at 61 years old, I am past my prime for writing, and that in 1948 at the age of 36, when “Terzaghi and Peck” was published, he was in his prime. Ralph pointed out that although he was 36, Terzaghi was 65 years old, and that the old gentleman wrote papers and books until the day he died at age 80.

Although Ralph is too much of a gentleman to say it directly, he does suggest by comparison to his generation, that my generation of geotechnical engineers took the money, kept information proprietary, and did not share our experience with the engineering community at large. I guess (alright I know) that Dr. Peck is right, and so this book is my first serious attempt at sharing with you the practicing engineer.

For his example, and his encouragement, we all owe a great debt of gratitude to Ralph B. Peck, thanks Ralph.

John C. Lommler, Ph.D., P.E. Sandia Park, New Mexico

1

General Topics

1.1

How to Use this Book

I want you the reader to be a good, if not great, problem solver. Problem solving is what engineers do, and it represents your value to society. When a client or employer pays for an engineer’s services, they are purchasing a solution to their problems. Often this process is called designing, investigating or analyzing, but in the end it all comes down to solving a problem or a series of problems.

Engineering problems involving geotechnical issues are difficult to solve, primarily because geotechnical parameters are difficult to measure, difficult to characterize and difficult to analyze. Some of the geotechnical difficulty comes from spatial variability in a large volume of soil on a building site. Some of the geotechnical problem is due to correlating field and/or laboratory measurements to the soil parameters required for analysis, and some of the problem is associated with limitations of analysis methods. I want to help you figure out how to solve geotechnical problems, and I want you to enjoy the problem-solving process.

I want to be your personal mentor, and if you have a mentor, I want to help them mentor you. If you are a student, I want you to start thinking about what is required to become a practicing engineer and to start now to develop the problem-solving tools you need.

Right from the start, I want you to accept the fact that you will never be able to include all of the physical processes involved in natural systems in your model of reality. You have to simplify real-world problems by use of models that have a few essential parameters, or, to use mathematical terminology, you need to limit the number of variables included in your models (equations). Later, in Section 1.2, I will discuss and explain the phenomenon of increasing complexity. Let’s just say for now that you will need to know how to adjust the number of variables considered in your problem-solving efforts to fit the needs of your particular problem.

Speaking of adjustment of the number of variables considered in your engineering problems brings me to a rather thorny engineering management problem that frequently arises between problem-solving engineers and project managers. Before starting to work on the solution of an engineering problem, there needs to be agreement between the engineer and the manager on the level of detail and complexity to be included in the planned analyses. If the project manager thinks that the problem at hand is a simple issue, and you perform a highly complex analysis without informing the project manager, he or she will be unpleasantly surprised. There is going to be an issue over your charging excessive analysis hours to the project manager’s budget. Fights over man-hour budgets for engineering analysis tasks versus the actual number of man-hours expended to solve the problem are quite common in consulting engineering practice these days. Matching the complexity of an engineering investigation and analysis to the requirements of the problem is called applying the “graded approach .” I will give you more information about the graded approach to problem solving in Section 1.3.4, and don’t worry, we will include a discussion of how to handle surprises requiring more work than was initially anticipated.

Unlike most engineering/technical books that you have used, the presentation given here is conversational and personal from me to you. I want to give you practical advice on solving geotechnical problems and give you keys to the use of material that may not have been included in your college work. This “advanced” geotechnical material may be familiar to you, or it may be new; in either case, I want to help you understand the underlying assumptions and limitations of various geotechnical problem-solving techniques. You may not agree with my preferred choices of analytical methods. I would be surprised and a bit suspicious if you did agree with me on everything presented. It is alright to disagree, but we have to agree to base our disagreements on logic and interpretation of physical principles, not on arbitrary preferences. You may conclude that the available data and problem requirements need a more intensive analysis than I suggest is required. That’s fine; if you need to do more detailed analysis work to feel comfortable with the solution, it’s your choice. Just be ready to defend your man-hour charges with your boss, project manager, or client, or come in early or stay late and do the extra work on your own time. Having confidence in your solution to an engineering problem gives a sense of self-satisfaction. Remember that increasing your problem-solving skills increases your personal worth. Please do not think of extra work as giving “the company” something for nothing, consider it as money in your personal problem-solving account. It is your engineering career, not theirs.

During the early part of my career, I was a structural engineer. It was common in an earlier time for geotechnical engineer s to start their careers as structural engineers. My friend Ralph Peck was a famous geotechnical engineer who started as a structural engineer. He had a Ph.D. in structural engineering and no formal degrees in geotechnical engineering. I converted to geotechnical engineering during my graduate studies to help me understand how settlement-induced load redistributions in a structure could lead to structural failure. By the time my Masters degree studies were completed, I was hooked on geotechnical engineering. When I started working as a consulting geotechnical engineer, it quickly became quite clear to me that my structural engineering work had not been a waste. Knowledge of structural engineering helped me communicate with my structural clients because I knew what they needed from their geotechnical consultant. I have included material in this book to help geotechnical engineers understand what structural engineers need for their work, and I’ve tried to clarify geotechnical engineering topics to structural engineers so they can better communicate their project requirements to geotechnical engineers.

I have included what I consider to be important topics on selection and interpretation of soil laboratory tests, on analyses of shallow and deep foundations, retaining structures, slope stability, behavior of unsaturated soils including collapsible and expansive soils, and geotechnical Load and Resistance Factor Design (LRFD) topics, to name a few. I want you the reader to develop problem-solving tools for each of these geotechnical problems. We will start you with simpler standard practice approaches in each article, and work up to the advanced material. I’ll give you examples of standard practice analysis methods including their assumptions and limitations. I don’t want you to pick a standard practice approach for solving your problem if it doesn’t fit the requirements of your problem! Advanced problem-solving methods are often required to deal with problems that have additional complexity. I do not believe that so-called advanced geotechnical material is only for Ph.Ds. I am convinced that if you graduated from college with a degree in engineering (or science and mathematics), you can use all of the material covered in this book.

In each section of this book, I will give suggested references and include a “Further Reading” section that provides materials for your study and consideration. At the end of each section, I will include a list of the references discussed in the section. I hope you will forgive me, but I do not like to repeat figures and equations from other books. Some equations and discussions are essential and I cannot avoid repeating them, but hopefully with added insights. Over the years I have grown weary of seeing the same material repeated and repeated over and over. I will refer you to the books where these materials are covered, and I hope you will take the opportunity to grow your geotechnical reference library.

It is my goal to help you understand the “how” and “why” of each topic, and to give you tools to use to solve problems that are not always included in text books, but are present in the real world. My advice is that you do not need a geotechnical engineering “cookbook.” What you need is an understanding of geotechnical principles so that you can use them as tools to solve your engineering problems.

1.2

You Have to See it to Solve it

1.2.1 Introduction to Problem Solving

A question that I am asked by students and 60 year old engineers alike goes something like this, “Why is geotechnical engineering and engineering in general so difficult? When are the codes and requirements going to be simplified like they were in the good old days?” Give me a chance, and I’ll answer these questions, but I need to build my case for the answer.

Did you ever notice that there is one person in the group that almost always disagrees with your opinion, conclusion, report, presentation, problem solution, etc? Sometimes they start by saying, “I’m just a Devil’s Advocate here, but ….” Personally, I don’t want to give the Devil or his attorneys the credit for this phenomena, I believe that skepticism is a natural human trait that at least 10 to 15% of your students, clients, or associates will possess at any given moment. No matter how hard you try to convince these people that you have considered all of the important problem variables, they always seem to come up with new variables for consideration. How do they always manage to complicate your work?

I have come to believe (but cannot prove) that all problems in engineering have at least 10 to 15 variables that could be measured, analyzed, and used in their solution. The ideal or perfect solution to a given problem is a function that considers the impacts and interactions of all of these 10 to 15 variables. This hypothetical perfect solution considers all of the theoretical complexity involved. The engineering profession accepts two to three of these variables as the primary variables required in analysis and design. Analysis based on these two or three variables is referred to as standard practice, see Figure 1.2.1 below.

Figure 1.2.1 Engineering standard practice versus complete problem solution

After removing the primary two to three variables from the solution set, the remaining seven to 13 variables are not considered to be standard practice , and I will call them second-order term s. These second-order terms may not often have a great impact on any given problem, but sometimes they do have significance. When second-order terms are important to the solution of an experienced engineer’s problem, and when he or she has a feel for the magnitude of the impact of these terms is referred to as “experience” or “engineering judgment.”

Thinking of an engineering problem as a number line of issues or variables, such as Figure 1.2.1, helps us to see an aerial view of the problem landscape. On the left end of the scale, say from one to three are the engineering design issues that make up standard practice. Let’s assume that standard practice includes 60 to 70% of the weighted factors of significance . The 30 to 40% that standard practice is off the mark is covered by standard factors such as factors of safety, load factors, resistance factors, and so on. Presumably, standard practice suggests that if you are 60% correct and use a factor of safety of 3.0, or if you are 70% correct and use a factor of safety of 2.5, you should safely bound your problem.

On the right end of the scale in Figure 1.2.1, three issues from the remaining seven to 13 are commonly selected engineering research issues. These second-order terms on the right end of the scale are the habitation of university researchers and professors seeking research funding. If you want to get the problem solved, the design completed, stay in budget and meet your client’s schedule, then you need to stay with the “engineering standard practice analyses” end of the problem scale. If you want a research topic, and you don’t want to cover the same old ground of standard practice variables, then you need to select a second-order variable for study that may prove to be more significant than is currently understood. And finally, if you want to argue with others at conferences and monthly technical meetings, as many skeptics do (and you know who you are), please feel free to bring up issues from the portion of the problem scale that is not considered by standard practice or by current mainline researchers.

1.2.2 Advanced and Expert Practice

Imagine that a client like a national laboratory, government agency, or high-tech project owner wants you to analyze something out of the ordinary. The measurements, analysis tools and advanced theories required involve something that is not covered by standard design practice. This type of engineering work is often referred to as advanced practice or expert practice. You can see from Figure 1.2.2 that standard practice is bounded by advanced and expert practice. These high-tech practices may be the standard of practice in some other parts of the United States or in other continents outside North America, such as in Europe or Asia. The point is that the definition of standard practice varies from place to place, and it varies with time.

Figure 1.2.2 Advanced practice, expert practice, and research topics

After a natural disaster like Hurricane Katrina in New Orleans on 29 August 2005 or a major failure like the I-35W bridge collapse in Minneapolis on 1 August 2007, standard practice often expands rapidly to deal with issues uncovered during forensic analyses.

1.2.3 Theories Can Be Wrong…

You may say, “Standard practice or the accepted notion of what variables are important can be wrong. What about Albert Einstein and his proof that the standard idea of ether as the element that fills space was wrong?” You have a point, just like those skeptics I’m talking about.

Albert Einstein is famous for his attack on the concept of ether as the substance that fills space and transmits light. The concept of ether was an accepted principle of physics in the nineteenth century. Ralph Peck and I read the Einstein biography by Walter Isaacson (Isaacson, 2007) shortly after it came out in 2007. Ralph’s eyesight was failing at the time, so he had a reader named Nida read the book to him. I recommended the book to my mother, a retired accounting professor from Kent State University. Nida and my mother commented on the parts of the Isaacson book that illustrated how human and fragile Dr. Einstein was in his personal and family relationships.

Ralph and I were drawn to the sections of Isaacson’s book that illustrated how Einstein solved problems and developed theories. Ralph commented that Einstein solved problems by visualizing the solution. Einstein used analogies such as an elevator, a train, or a spacecraft traveling at the speed of light to frame problems and suggest their solutions. Ralph also pointed out that Einstein’s physics journal papers were short and directly to the point, a trait that Ralph admired and strived to accomplish in his own work. I was taken by the contrast of Einstein’s early work where he visualized problems, and his later work where he focused on mathematical formulations. Einstein accomplished a large amount of highly significant work when he relied on visual models or analogies to help guide his theories, and after 30+ years of work he never came up with a solution to the Unified Field Theory problem, although he formulated endless equations that appeared promising but failed.

Theories may be wrong, but we have to prove them wrong. Clearly seeing the issues involved seems to be the best guide to working through a complex problem.

1.2.4 Seeing is Better than Not Seeing …

My point in all of this is that you need a simple, visual model to understand and solve engineering problems. Focusing on two or three primary variables, as is the custom in standard design practice helps clarify the solution model because most people can see things in two or three dimensions. Clarifying the complex problem of changing engineering practice was my intention in showing “Problem Solutions” and “Standard Practice” and numerous potential variables in Figure 1.2.1 as a one-dimensional number line.

For those few of you who are experts and can see problems in five- or six- dimensional space, and have the mathematical tools to solve equations in these spaces, consider your selves blessed. It’s up to you to reconfigure these complex problems in ways that are easy for the rest of us to see. We have to see a problem clearly to solve the problem.

1.2.5 Why is Standard Engineering Practice Changing?

The concept of seeing problems clearly brings me to a question that seems to be on many engineers’ minds these days. Why does engineering practice seem to be becoming more and more complicated? To help you see this problem and predict the answer to this question, please refer to Figure 1.2.3.

Figure 1.2.3 Growth of standard practice requirements

As time goes on, more and more clients become involved in designs that require solutions to complex problems and require application of advanced engineering practice. Infrastructure failures, such as the failure of levees in New Orleans and the collapse of the World Trade Center towers in New York, raises questions about the variables and principles used in standard engineering design practice. These problems become topics for funded university research. As university research into these advanced topics is published and made available to the engineering community through technical journals and conference proceedings, more and more engineers and clients want to work at a higher level. Computer programs are written that incorporate advanced topics, and everyone wants to have the latest and greatest computer modeling tools. The result of all of this pressure to do more is that standard practice expands to cover advanced practice, as illustrated in Figure 1.2.3. The amount of engineering analysis work increases, the cost and effort increases, and the complexity increases as we consider first three, then four, and then five or more variables in the problem solution. When asked if engineering practice will ever get easier, like in the good old days, my answer is no!

1.2.6 An Example of Increasing Complexity of Standard Practice …

As an example of how the engineering design process becomes more complex, consider paving design, which is an interaction problem between traffic, pavement, aggregate base, soil subgrade , drainage and weather. Let’s say that a local university professor gets funding from the State Department of Transportation to do research on the standard problem of paving design. Say, for instance, that paving in their State is failing prematurely. Standard practice indicates that performance of paving depends on climate, traffic volume, wheel loads, and paving-base-subgrade strength. The premature paving failures could be related to excessive traffic, overweight vehicles, severe winters, or inadequate strength of a portion of the paving section.

But then one day an engineer from the Department of Transportation drives down a roadway in the State and notices that rainfall water is soaking into and seeping out of the paving. As he drives along, the Department engineer starts to think that maybe water in the paving section is the real problem behind premature paving failures. After the engineer convinces his colleagues, the Department puts out a supplemental request for paving research on the topic of the effect of water in the paving section. The local university professor researching paving performance submits a proposal to further his study to include the affects of water in the paving section. His new paving proposal is accepted and research into the permeability of pavement and the affects of water on paving is funded, conducted, reported, and guess what, it does affect the life span of the paving section. As a result of findings of this research, the State Department of Transportation requires that two more variables related to paving permeability and paving saturation’s affect on paving life be included in all standard paving designs. Referring to Figure 1.2.3 above, note that addition of a fifth and a sixth variable into the paving standard design practice increases the amount of work required and as a result increases the design complexity. In this way, the scope of standard practice increases and the work required increases, but likely the budget to do this additional work is not increased. From this analogy, I suggest that increasing complexity is to be expected. As time goes on, the size of the circle representing standard practice in Figure 1.2.3 will become larger and larger, and the ability of most engineers to see the impact and interaction of the design variables will be clouded. An engineer I know told me that he is working with an EPA standard contaminate transport model that has 23 input parameters. How’s that for increased complexity!

1.2.7 Helping You See …

This book is designed to help you see each geotechnical problem clearly, so you can solve your problem. The discussions of each geotechnical problem are presented in a sequence from basic principles of standard practice to more complicated advanced practice issues. For those of you interested in advanced topics, a reference section is included with each problem discussion. These references to advanced material are included for those who have the need to dig into the body of available information.

To help you see concepts, analogies will be used. Don’t worry that we’re already introducing complexity; the definition used here for an analogy is a simple example that is similar to or has the same physical principles as the more complex problem. These simple analogies give you a visual key to help see the concept in your mind. An example of a simple analogy is the concept of frictional resistance in a granular soil, which is like a sliding wooden block on a table. At low strains the soil’s frictional resistance or friction angle is higher, which is like static friction of the block on the table. At higher strains the soil’s frictional resistance or friction angle is lower, which is like sliding friction of the block on the table.

We are going to discuss problem solutions from simple to complex, but how do you know which problem solution method to use on your problem. How do you decide when to use a simple, quick method or a highly complex, sophisticated method? How do you adjust the number of problem variables to fit your clients’ scope and budget and still solve the problem? The answer is you need to understand and use the “graded approach.” What is the graded approach? It’s just a case of good old common sense, check out Section 1.3.4 for the answer to this question.

Please remember two things: (1) geotechnical engineering is not physics, we use constitutive equations that are based on tests that are designed to solve specific problems. Our tests and equations are not “laws of physics;” (2) whether it is geotechnical engineering, physics, accounting or everyday life … to solve it you have to see it. What do you see in Figure 1.2.4?

Figure 1.2.4 Would you expect to find expansive soil in a nearby boring?

Reference

Isaacson, W. (2007) Einstein, His Life and Universe, Simon & Schuster, New York, 675 pages.

1.3

My Approach to Modern Geotechnical Engineering Practice – An Overview

1.3.1 Introduction

This book is intended to bridge the gap between geotechnical material covered in university civil engineering course work and the geotechnical topics required for practicing civil, structural, and geotechnical engineers to solve real world problems. Over the past decade or so there has been a tug of war between competing groups for the size and content of curricula included in undergraduate civil engineering programs. Several groups, the American Society of Civil Engineers comes to mind, have adopted programs requiring a Masters degree or an additional 30 credit hours of specialized training beyond the bachelor’s degree to qualify for a professional engineering license. Will these additional training requirements discourage potential engineering students from entering the profession? Maybe it will. The fact remains that additional knowledge and skills beyond the bachelor’s degree and even beyond a Professional Engineer’s License are required to become a fully competent senior engineer.

For a long time, I’ve had the idea for a book to explain practical geotechnical problem solving to practicing engineers. My basic thought was to discuss alternate analysis methods and approaches. I’m not embarrassed to admit that I have struggled for years with many geotechnical topics, conflicts between competing theories of soil mechanics, and issues of increasing complexity, as discussed in Section 1.2. Having a mentor to help you through these geotechnical topics is a good thing, a very good thing.