INTRODUCTION: SOIL GEOTECHNICAL ENGINEERING 1 (SOIL MECHANICS)

Introduction
For engineering purposes, soil is defined as the uncemented aggregate of mineral grains and decayed organic matter
(solid particles) with liquid and gas in the empty spaces between the solid particles. Soil is used as a construction
material in various civil engineering projects, and it supports structural foundations. Thus, civil engineers must study
the properties of soil, such as its origin, grain-size distribution, ability to drain water, compressibility, shear strength,
and load-bearing capacity.
Soil mechanics is the branch of science that deals with the study of the physical properties of soil and the behavior of
soil masses subjected to various types of forces.

Soils engineering is the application of the principles of soil mechanics to practical problems.

Geotechnical engineering is the subdiscipline of civil engineering that involves natural materials found close to the
surface of the earth. It includes the application of the principles of soil mechanics and rock mechanics to the design of
foundations, retaining structures, and earth structures

Geotechnical Engineering Prior to the 18th Century

The record of a person’s first use of soil as a construction material is lost in antiquity.
In true engineering terms, the understanding of geotechnical engineering as it is
known today began early in the 18 th century (Skempton, 1985). For years, the art of
geotechnical engineering was based on only past experiences through a succession
of experimentation without any real scientific character. Based on those
experimentations, many structures were built—some of which have crumbled, while
others are still standing.
Recorded history tells us that ancient civilizations flourished along the banks
of rivers, such as the Nile (Egypt), the Tigris and Euphrates (Mesopotamia), the
Huang Ho (Yellow River, China), and the Indus (India). Dykes dating back to about
2000 B.C. were built in the basin of the Indus to protect the town of Mohenjo Dara (in
what became Pakistan after 1947). During the Chan dynasty in China (1120
B.C.to249B.C.) many dykes were built for irrigation purposes. There is no evidence
that measures were taken to stabilize the foundations or check erosion caused by
floods (Kerisel, 1985). Ancient Greek civilization used isolated pad footings and strip-
and-raft foundations for building structures. Beginning around 2750 B.C., the five most
important pyramids were built in Egypt in a period of less than a century (Saqqarah,
Meidum, Dahshur South and North, and Cheops). This posed formidable challenges
regarding foundations, stability of slopes, and construction of underground chambers.
With the arrival of Buddhism in China during the Eastern Han dynasty in 68
A.D., thousands of pagodas were built. Many of these structures were
constructed on silt and soft clay layers. In some cases the foundation
pressure exceeded the load-bearing capacity of the soil and thereby caused
extensive structural damage.
One of the most famous examples of problems related to soil-bearing
capacity in the construction of structures prior to the 18 th century is the
Leaning Tower of Pisa in Italy. (See Figure 1.1) Construction of the tower
began in 1173 A.D. when the Republic of Pisa was flourishing and continued
in various stages for over 200 years. The structure weighs about 15,700
metric tons and is supported by a circular base having a diameter of 20 m (66
ft). The tower has tilted in the past to the east, north, west and, finally, to the
south. Recent investigations showed that a weak clay layer exists at a depth
of about 11 m(36 ft) below the ground surface compression, which caused
the tower to tilt. It became more than 5 m (16.5 ft) out of plumb with the 54 m
(179 ft) height. The tower was closed in 1990 because it was feared that it
would either fall over or collapse. It recently has been stabilized by excavating
soil from under the north side of the tower. About 70 metric tons of earth was
removed in 41 separate extractions that spanned the width of the tower. As
the ground gradually settled to fill the resulting space, the tilt of the tower
eased. The tower now leans 5 degrees. The half-degree change is not
noticeable, but it makes the structure considerably more stable. Figure 1.2 is

PREPARED BY: ENGR. HESSA G. AZUL 1

Reference: Fundamentals of Geotechnical Engineering
By: Braja M. Das
INTRODUCTION: SOIL GEOTECHNICAL ENGINEERING 1 (SOIL MECHANICS)

an example of a similar problem. The towers shown in Figure 1.2 are located in Bologna, Italy, and they were built in
the 12th century. The tower on the left is usually referred to as the Garisenda Tower. It is 48 m (157 ft) in height and
has tilted severely.
After encountering several foundation-related problems during construction over centuries past, engineers
and scientists began to address the properties and behaviors of soils in a more methodical manner starting in the
early part of the 18th century. Based on the emphasis and the nature of study in the area of geotechnical engineering,
the time span extending from 1700 to 1927 can be divided into four major periods (Skempton, 1985):

1. Pre-classical (1700 to 1776 A.D.)

2. Classical soil mechanics—Phase I (1776 to 1856 A.D.)
3. Classical soil mechanics—Phase II (1856 to 1910 A.D.)
4. Modern soil mechanics (1910 to 1927 A.D.)

Preclassical Period of Soil Mechanics (1700 –1776)

This period concentrated on studies relating to natural slope and unit weights of various types of soils, as well as the
semiempirical earth pressure theories. In 1717 a French royal engineer, Henri Gautier (1660 –1737), studied the
natural slopes of soils when tipped in a heap for formulating the design procedures of retaining walls. The natural
slope is what we now refer to as the angle of repose. According to this study, the natural slope of clean dry sand and
ordinary earth were 31and 45, respectively. Also, the unit weight of clean dry sand and ordinary earth were
recommended to be 18.1 kN/m3 (115 lb/ft3) and 13.4 kN/m3), respectively. No test results on clay were reported. In
1729, Bernard Forest de Belidor (1671–1761) published a textbook for military and civil engineers in France. In the
book, he proposed a theory for lateral earth pressure on retaining walls that was a follow-up to Gautier’s (1717)
original study. He also specified a soil classification system in the manner shown in the following table.

The first laboratory model test results on a 76-mm-high (3 in.) retaining wall built with sand backfill were
reported in 1746 by a French engineer, Francois Gadroy (1705–1759), who observed the existence of slip planes in
the soil at failure. Gadroy’s study was later summarized by J. J. Mayniel in 1808.

Classical Soil Mechanics—Phase I (1776 –1856)

During this period, most of the developments in the area of geotechnical engineering came from engineers and
scientists in France. In the preclassical period, practically all theoretical considerations used in calculating lateral earth
pressure on retaining walls were based on an arbitrarily based failure surface in soil. In his famous paper presented in
1776, French scientist Charles Augustin Coulomb (1736 –1806) used the principles of calculus for maxima and
minima to determine the true position of the sliding surface in soil behind a retaining wall. In this analysis, Coulomb
used the laws of friction and cohesion for solid bodies. In 1820, special cases of Coulomb’s work were studied by
French engineer Jacques Frederic Francais (1775 –1833) and by French applied mechanics professor Claude Louis
Marie Henri Navier (1785 –1836). These special cases related to inclined backfills and backfills supporting surcharge.
In 1840, Jean Victor Poncelet (1788–1867), an army engineer and professor of mechanics, extended Coulomb’s
theory by providing a graphical method for determining the magnitude of lateral earth pressure on vertical and inclined
retaining walls with arbitrarily broken polygonal ground surfaces. Poncelet was also the first to use the symbol f for soil
friction angle. He also provided the first ultimate bearing-capacity theory for shallow foundations. In 1846 Alexandre
Collin (1808–1890), an engineer, provided the details for deep slips in clay slopes, cutting, and embankments. Collin
theorized that in all cases the failure takes place when the mobilized cohesion exceeds the existing cohesion of the
soil. He also observed that the actual failure surfaces could be approximated as arcs of cycloids.

PREPARED BY: ENGR. HESSA G. AZUL 2

Reference: Fundamentals of Geotechnical Engineering
By: Braja M. Das
INTRODUCTION: SOIL GEOTECHNICAL ENGINEERING 1 (SOIL MECHANICS)

The end of Phase I of the classical soil mechanics period is generally marked by the year (1857) of the first
publication by William John Macquorn Rankine (1820 – 1872), a professor of civil engineering at the University of
Glasgow. This study provided a notable theory on earth pressure and equilibrium of earth masses. Rankine’s theory is
a simplification of Coulomb’s theory.

Classical Soil Mechanics—Phase II (1856 –1910)

Several experimental results from laboratory tests on sand appeared in the literature in this phase. One of the earliest
and most important publications is one by French engineer Henri Philibert Gaspard Darcy (1803–1858). In 1856, he
published a study on the permeability of sand filters. Based on those tests, Darcy defined the term coefficient of
permeability (or hydraulic conductivity) of soil, a very useful parameter in geotechnical engineering to this day.
Sir George Howard Darwin (1845–1912), a professor of astronomy, conducted laboratory tests to determine
the overturning moment on a hinged wall retaining sand in loose and dense states of compaction. Another noteworthy
contribution, which was published in 1885 by Joseph Valentin Boussinesq (1842–1929), was the development of the
theory of stress distribution under loaded bearing areas in a homogeneous, semiinfinite, elastic, and isotropic medium.
In 1887, Osborne Reynolds (1842 –1912) demonstrated the phenomenon of dilatency in sand.

Modern Soil Mechanics (1910 –1927)

In this period, results of research conducted on clays were published in which the fundamental properties and
parameters of clay were established.

Geotechnical Engineering after 1927

The publication of Erdbaumechanik auf Bodenphysikalisher
Grundlage by Karl Terzaghi in 1925 gave birth to a new era in the
development of soil mechanics. Karl Terzaghi is known as the
father of modern soil mechanics, and rightfully so. Terzaghi
(Figure 1.3) was born on October 2, 1883 in Prague, which was
then the capital of the Austrian province of Bohemia. In 1904 he
graduated from the Technische Hochschule in Graz, Austria, with
an undergraduate degree in mechanical engineering. After
graduation he served one year in the Austrian army. Following his
army service, Terzaghi studied one more year, concentrating on
geological subjects. In January 1912, he received the degree of
Doctor of Technical Sciences from his alma mater in Graz. In
1916, he accepted a teaching position at the Imperial School of
Engineers in Istanbul. After the end of World War I, he accepted a
lectureship at the American Robert College in Istanbul (1918 –
1925). There he began his research work on the behavior of soils
and settlement of clays and on the failure due to piping in sand
under dams. The publication Erdbaumechanik is primarily the
result of this research.
In 1925, Terzaghi accepted a visiting lectureship at
Massachusetts Institute of Technology, where he worked until
1929. During that time, he became recognized as the leader of the
new branch of civil engineering called soil mechanics. In October
1929, he returned to Europe to accept a professorship at the
Technical University of Vienna, which soon became the nucleus for civil engineers interested in soil mechanics. In
1939, he returned to the United States to become a professor at Harvard University.
The first conference of the International Society of Soil Mechanics and Foundation Engineering (ISSMFE) was
held at Harvard University in 1936 with Karl Terzaghi presiding. It was through the inspiration and guidance of
Terzaghi over the preceding quarter-century that papers were brought to that conference covering a wide range of
topics, such as shear strength, effective stress, in situ testing, Dutch cone penetrometer, centrifuge testing,
consolidation settlement, elastic stress distribution, preloading for soil improvement, frost action, expansive clays,
arching theory of earth pressure, soil dynamics, and earthquakes. For the next quarter-century, Terzaghi was the
guiding spirit in the development of soil mechanics and geotechnical engineering throughout the world. To that effect,
in 1985, Ralph Peck (Figure 1.4) wrote that “few people during Terzaghi’s lifetime would have disagreed that he was
not only the guiding spirit in soil mechanics, but that he was the clearing house for research and application
throughout the world. Within the next few years he would be engaged on projects on every continent save Australia

PREPARED BY: ENGR. HESSA G. AZUL 3

Reference: Fundamentals of Geotechnical Engineering
By: Braja M. Das
INTRODUCTION: SOIL GEOTECHNICAL ENGINEERING 1 (SOIL MECHANICS)

and Antarctica.” Peck continued with, “Hence, even today, one can hardly
improve on his contemporary assessments of the state of soil mechanics as
expressed in his summary papers and presidential addresses.” In 1939,
Terzaghi delivered the 45th James Forrest Lecture at the Institution of Civil
Engineers, London. His lecture was entitled “Soil Mechanics—A New Chapter in
Engineering Science.” In it, he proclaimed that most of the foundation failures
that occurred were no longer “acts of God.”

PREPARED BY: ENGR. HESSA G. AZUL 4

Reference: Fundamentals of Geotechnical Engineering
By: Braja M. Das