The Engineering of Foundations, Slopes and Retaining Structures

Rodrigo Salgado

• Publisher: CRC Press
• Year: 2022
• ISBN:
  9781351818360
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

The Engineering of Foundations, Slopes and Retaining Structures rigorously covers the construction, analysis, and design of shallow and deep foundations, as well as retaining structures and slopes. It includes complete coverage of soil mechanics and site investigations.

This new edition is a well-designed balance of theory and practice, emphasizing conceptual understanding and design applications. It contains illustrations, applications, and hands-on examples that continue across chapters. Soil mechanics is examined with full explanation of drained versus undrained loading, friction and dilatancy as sources of shear strength, phase transformation, development of peak effective stress ratios, and critical-state and residual shear strength. The design and execution of site investigations is evaluated with complete discussion of the CPT and SPT. Additional topics include the construction, settlement and bearing capacity of shallow foundations, as well as the installation, ultimate resistance and settlement of deep foundations. Both traditional knowledge and methods and approaches based on recent progress are available. Analysis and design of retaining structures and slopes, such as the use of slope stability software stability calculations, is included.

The book is ideal for advanced undergraduate students, graduate students and practicing engineers and researchers.

Chapter 1 The world of foundation engineering

DOI: 10.1201/b22079-1

Technology moves so rapidly that the challenges and problems of tomorrow are certain to be different than those of today, and it is probable that most of tomorrow’s problems will come as surprises, since our ability to predict the future is very poor. I believe that the best way to adapt is to have a thorough mastery of first principles, as these never change and can always be applied to new problems.

James K. Mitchell

A profession can be broadly understood as a type of work done using specialized knowledge or skills acquired by attending and getting a degree from a higher education institution and by lifelong learning. The “first principles” that Prof. Mitchell refers to, in an engineering context, are most often scientific principles – science being one of the cornerstones of engineering. Additionally, every profession has its own language and its own set of rules, which the effective professional knows well. In this chapter, we will examine the current practice in geotechnical and foundation engineering. We will start by defining what is meant by geotechnical and foundation engineering and then go on to discuss the education and licensing processes a geotechnical engineer must go through to practice the profession in its plenitude. We follow that with a brief discussion of the geotechnical and foundation engineering industries. The discussion is pursued in the context of the “global economy,” which to a considerable extent has become a reality. In the paradigm of the global economy, barriers to trade, including engineering services, weaken considerably, forcing the engineer to deal with technical, cultural, legal, and language issues that could be safely ignored in the past. This chapter concludes with a discussion of units, which are needed in any engineering calculation.

1.1 The geotechnical engineering industry

1.1.1 Geotechnical engineering, foundation engineering, and geotechnical and foundation engineering problems

Engineering is the creative use of experience, empirical methods, and engineering science to solve engineering problems. Engineering involves the search for solutions to problems that require significant technical and scientific knowledge and that change the environment in some way or make new things possible. For example, a civil engineer may be interested in connecting one bank of a river to the other, while a chemical engineer may be interested in the manufacturing of a certain chemical in industrial scale.

An engineering problem is subjected to a number of constraints arising mainly due to economic and environmental reasons. More formally, an engineering problem may be defined in a general way as the need or wish to change something from a current state A to a new state B in the most economical fashion, under safe conditions, with minimum or no harm to the environment. Additional requirements arising out of legal and aesthetic issues also need to be fulfilled. Fortunately, there are also a number of tools available to the engineer that facilitate achieving an optimal design solution: engineering science, empirical rules, and experimental techniques.

Geotechnical engineering is the engineering of problems involving the ground. Geotechnical engineers work on the analysis, design, and construction of dams, soil and rock slopes, tunnels through soil or rock, and foundations for various types of structures. Foundation engineers are called upon to determine the best way of transferring to the ground the loads from structures (such as buildings, warehouses, and bridges), machines, highway signs, and a variety of other sources. Therefore, we may define foundation engineering as the body of knowledge that enables solution of problems involving the safe and economical transfer of structural loads to the ground. A foundation engineer would design the foundation elements themselves, but, in the United States, structural engineers typically do this, using the information or data provided to them by geotechnical engineers.

Foundations may take many different configurations, being most generally classified as shallow (covered in Chapters 8–11) or deep (covered in Chapters 12–15). The most common types of shallow foundations are concrete footings, typically built of reinforced concrete in shallow excavations with plan areas most often in the 1–10 m² range. Piles are the most common type of deep foundations. These are slender structural elements made of wood, steel, or concrete that, in onshore applications, have diameters ranging from 0.1 m to in excess of one meter and lengths ranging from a few to many tens of meters.¹ Foundation engineers are also called upon to safely and economically design and build retaining structures of all kinds. Construction dewatering and excavations are also often part of foundation works. Reinforced concrete design of foundations and retaining structures is often done by a structural engineer; in such cases, the best results are obtained when the structural and foundation engineers work in close cooperation.

The term geotechnical engineering has a more general meaning than foundation engineering, as the subject encompasses a broader spectrum of soil or rock problems, including geoenvironmental problems such as landfill design, waste containment, and groundwater cleanup.

As discussed in the previous paragraph, the design and analysis of slopes and retaining structures are an integral part of foundation engineering, but are seen more generally as well. In urban areas, where space is restricted, retaining structures allow the construction of underground facilities, such as parking garages, underground shopping malls, and subway stations. Although more incidental to foundation works, slope instability failures must also be prevented. In foundation works, temporary excavations are sometimes planned in such a way as to leave temporary soil slopes to support the excavation walls. Another situation where slope stability becomes an issue is when the building or structure is located in a hilly or mountainous area, in which a well-designed foundation will serve no purpose if the structure is founded on a potential sliding soil or rock mass. More broadly, slopes occur as part of road embankments, soil or rock cuts for various projects, and in dam projects.

1.1.2 Geotechnical engineering as a profession

It is useful to identify what distinguishes a profession from other occupations. The following excerpt from a New York Court of Appeals judgment (In re Estate of Julius Freeman, 355 N.Y. S.2d 336, 1974) provides an excellent summary of the distinctions²: “A profession is not a business. It is distinguished by the requirements of extensive formal training and learning, admission to practice by a qualifying licensure examination, a code of ethics imposing standards qualitatively and extensively beyond those that prevail or are tolerated in the marketplace, a system for discipline of its members for violation of the code of ethics, a duty to subordinate financial reward to social responsibility, and, notably, an obligation on its members, even in nonprofessional matters, to conduct themselves as members of a learned, disciplined, and honorable occupation.”

¹ In offshore applications, piles can have diameters of several meters and lengths in excess of 100 m. ² This appeared in a column by Arthur Schwartz in Engineering Times, Vol. 25, No. 6, June 2003.

1.1.3 Education and professional licensing

Geotechnical and foundation engineers are, with some exceptions, first and foremost civil engineers. In the United States, civil engineering programs normally last 4 years. In other countries, programs may last 5 or even 6 years and typically require a thesis or project report at the end of the program. Students interested in geotechnical engineering or foundation engineering, particularly if graduating from a 4-year program, would benefit tremendously from obtaining a master’s degree in geotechnical engineering after completion of the undergraduate program.

In many countries, a graduate of a civil engineering program is automatically licensed to practice engineering, sign plans, and supervise the work of other engineers. However, this is not true in the United States, where engineering programs vary in size, scope, and duration, and a system of licensure has been in place for a long time to ensure the quality of engineering work. Licenses to practice engineering are granted by professional engineering state boards. The licensing is a four-step process. The first requires obtaining a civil engineering degree (preferably from an institution accredited by the Accreditation Board for Engineering and Technology [ABET]). The second step is the taking of a fundamental engineering exam focusing on engineering science. Anyone who passes the exam (formerly known as the EIT exam, now known as the Fundamentals of Engineering or FE exam) becomes an engineer intern (EI) or, equivalently, and engineer in training (EIT). The EI then completes a number of years of actual professional experience. This number varies from state to state and is longer for engineers whose degrees are not from an ABET-accredited institution. Years spent on graduate studies count toward the required number of years of experience up to a limit. After satisfying the years of experience requirement, the engineer is entitled to take the professional engineer exam. Those who pass this exam become professional engineers in the state in which they take the exam. Professional engineers are held legally accountable for the work they do or supervise, as well as for any plans or documents to which they affix their seal. Professional engineers should only pract...