CE-113 Module 1: Introduction to Geotechnical Engineering PDF

S MO INTRODUCTION TO GEOTECHNICAL ENGINEERING RA SOIL  is defined as the uncemented aggregate of mineral grains and decayed organic...

S MO INTRODUCTION TO GEOTECHNICAL ENGINEERING RA SOIL  is defined as the uncemented aggregate of mineral grains and decayed organic N. matter (solid particles) with liquid and gas in the empty spaces between the solid particles. O YN  is used as a construction material in various civil engineering projects, and it supports structural foundations. Thus, civil engineers must study the properties RE of soil, such as its origin, grain-size distribution, ability to drain water, compressibility, shear strength, and load-bearing capacity. GR EN SOIL MECHANICS S MO  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. RA SOILS ENGINEERING N.  is the application of the principles of soil mechanics to practical problems. O GEOTECHNICAL ENGINEERING YN RE  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 GR soil mechanics and rock mechanics to the design of foundations, retaining structures, and earth structures. EN  S GEOTECHNICAL ENGINEERING PRIOR TO THE 18TH CENTURY MO The record of a person’s first use of soil as a construction material is lost in RA antiquity. In true engineering terms, the understanding of geotechnical engineering as it is known today began early in the 18th century. For years, the art of N. 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 O crumbled, while others are still standing. YN RE 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). GR  Dykes dating back to about 2000 B.C. were built in the basin of the Indus to EN protect the town of Mohenjo Dara (in what became Pakistan after 1947).  During the Chan dynasty in China (1120 B.C. to 249 B.C.) many dykes were S built for irrigation purposes. There is no evidence that measures were taken to MO stabilize the foundations or check erosion caused by floods. RA  Ancient Greek civilization used isolated pad footings and strip-and-raft foundations for building structures.  Beginning around 2700 B.C., several pyramids were built in Egypt, most of N. which were built as tombs for the country’s Pharaohs and their consorts during the Old and Middle Kingdom periods. As of 2008, a total of 138 pyramids have O been discovered in Egypt. The construction of the pyramids posed formidable YN challenges regarding foundations, stability of slopes, and construction of underground chambers. RE  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 GR pressure exceeded the load-bearing capacity of the soil and thereby caused EN extensive structural damage. One of the most famous examples of problems related to soil-bearing capacity in S the construction of structures prior to the 18th century is the Leaning Tower of MO Pisa in Italy. Construction of the tower began in 1173 A.D. when the Republic of RA 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. The tower has tilted in the past to the east, north, west, N. and, finally, to the south. Recent investigations showed that a weak clay layer existed at a depth of about 11 m below the ground surface compression of which O caused the tower to tilt. It became more than 5 m out of plumb with the 54 m YN 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 RE north side of the tower. About 70 metric tons of earth were 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. GR The half-degree change is not noticeable, but it makes the structure considerably EN more stable. Another example of a similar problem are the towers located in Bologna, Italy, and S they were built in the 12th century. The Garisenda Tower is 48 m in height and MO weighs about 4210 metric tons. It has tilted about 4 degrees. The Asinelli Tower, RA which is 97 m high and weighs 7300 metric tons has tilted about 1.3 degrees. After encountering several foundation-related problems during construction over centuries past, engineers and scientists began to address the properties and N. behaviors of soils in a more methodical manner starting in the early part of the 18th century. O YN 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 RE major periods: 1. Preclassical (1700 to 1776 A.D.) GR 2. Classical soil mechanics—Phase I (1776 to 1856 A.D.) 3. Classical soil mechanics—Phase II (1856 to 1910 A.D.) EN 4. Modern soil mechanics (1910 to 1927 A.D.) Brief descriptions of some significant developments during each of these four S periods are presented below. MO 1. PRECLASSICAL PERIOD OF SOIL MECHANICS (1700–1776) RA This period concentrated on studies relating to natural slope and unit weights of N. 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 O slopes of soils when tipped in a heap for formulating the design procedures of YN retaining walls. The natural slope is what we now refer to as the angle of repose. RE 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 ⁄ and 13.4 ⁄ (85 ⁄ ), respectively. No GR test results on clay were reported. EN In 1729, Bernard Forest de Belidor (1671–1761) published a textbook for military S and civil engineers in France. In the book, he proposed a theory for lateral earth MO pressure on retaining walls that was a follow-up to Gautier’s (1717) original study. RA He also specified a soil classification system in the manner shown in the following table. N. O YN RE GR EN  S The first laboratory model test results on a 76-mm-high retaining wall built with MO 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. RA Gadroy’s study was later summarized by J. J. Mayniel in 1808. Another notable contribution during this period is that by the French engineer N. Jean Rodolphe Perronet (1708–1794), who studied slope stability around 1769 and distinguished between intact ground and fills. O YN 2. CLASSICAL SOIL MECHANICS—PHASE I (1776–1856) RE During this period, most of the developments in the area of geotechnical engineering came from engineers and scientists in France. In the preclassical GR period, practically all theoretical considerations used in calculating lateral earth pressure on retaining walls were based on an arbitrarily based failure surface in EN soil. In his famous paper presented in 1776, French scientist Charles Augustin S Coulomb (1736–1806) used the principles of calculus for maxima and minima to MO determine the true position of the sliding surface in soil behind a retaining wall. In RA this analysis, Coulomb used the laws of friction and cohesion for solid bodies. In 1840, Jean Victor Poncelet (1788–1867), an army engineer and professor of N. 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 O YN also the first to use the symbol f for soil friction angle. He also provided the first ultimate bearing-capacity theory for shallow foundations. RE 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 GR (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 EN masses. Rankine’s theory is a simplification of Coulomb’s theory.  S 3. CLASSICAL SOIL MECHANICS—PHASE II (1856–1910) MO Several experimental results from laboratory tests on sand appeared RA in the literature in this phase. One of the earliest and most important publications is one by N. French engineer Henri Philibert Gaspard Darcy (1803–1858). In 1856, he published a study on the permeability of sand filters. Based on O those tests, Darcy defined the term coefficient of permeability (or YN hydraulic conductivity) of soil, a very useful parameter in geotechnical engineering to this day. RE Sir George Howard Darwin (1845–1912), a professor of astronomy, GR conducted laboratory tests to determine the overturning moment on a hinged wall retaining sand in loose and dense states of compaction. EN Another noteworthy contribution, which was published in 1885 by Joseph S Valentin Boussinesq (1842–1929), was the development of the theory of MO stress distribution under loaded bearing areas in a homogeneous, semi- infinite, elastic, and isotropic medium. RA In 1887, Osborne Reynolds (1842–1912) demonstrated the phenomenon of dilatancy in sand. 4. MODERN SOIL MECHANICS (1910–1927) N. In this period, results of research conducted on clays were published in O which the fundamental properties and parameters of clay were established. YN Around 1908, Albert Mauritz Atterberg (1846–1916), a Swedish chemist and RE soil scientist, defined clay-size fractions as the percentage by weight of particles smaller than 2 microns in size. He realized the important role of clay particles in a soil and the plasticity thereof. In 1911, he GR explained the consistency of cohesive soils by defining liquid, plastic, and shrinkage limits. He also defined the plasticity index as the EN difference between liquid limit and plastic limit. In October 1909, the 17-m-high earth dam at Charmes, France, S failed. It was built between 1902 and 1906. A French engineer, Jean MO Fontard (1884–1962), carried out investigations to determine the RA cause of failure. In that context, he conducted undrained double- shear tests on clay specimens (0.77 m2 in area and 200 mm thick) under constant vertical stress to determine their shear strength N. parameters. The times for failure of these specimens were between 10 to 20 minutes. O YN Arthur Langley Bell (1874–1956), a civil engineer from England, worked on the design and construction of the outer seawall at Rosyth Dockyard. Based RE on his work, he developed relationships for lateral pressure and resistance in clay as well as bearing capacity of shallow foundations in clay. He also used shear-box tests to measure the undrained shear strength GR of undisturbed clay specimens. EN Wolmar Fellenius (1876–1957), an engineer from Sweden, developed the S stability analysis of saturated clay slopes (that is, Φ = 0 condition) MO with the assumption that the critical surface of sliding is the arc of a circle. These were elaborated upon in his papers published in 1918 and RA 1926. The paper published in 1926 gave correct numerical solutions for the stability numbers of circular slip surfaces passing through the toe N. of the slope. Karl Terzaghi (1883–1963) of Austria developed the theory of O consolidation for clays as we know today. The theory was developed when YN Terzaghi was teaching at the American Robert College in Istanbul, Turkey. His study spanned a five-year period from 1919 to 1924. Five different RE clay soils were used. The liquid limit of those soils ranged between 36 and 67, and the plasticity index was in the range of 18 to 38. The consolidation theory was published in Terzaghi’s celebrated book GR Erdbaumechanik in 1925. EN GEOTECHNICAL ENGINEERING AFTER 1927 S The publication of Erdbaumechanik auf Bodenphysikalisher MO Grundlage by Karl Terzaghi in 1925 gave birth to a new era in the development of soil mechanics. Karl Terzaghi is known as “the RA father of modern soil mechanics”. In 1925, Terzaghi accepted a visiting lectureship at Massachusetts Institute of Technology, N. where he worked until 1929. During that time, he became recognized as the leader of the new branch of civil engineering called soil mechanics. For the next quarter-century, Terzaghi was the guiding O spirit in the development of soil mechanics and geotechnical YN engineering throughout the world. To that effect, in 1985, Ralph RE Peck 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 GR application throughout the world. Within the next few years, he would be engaged on projects on every continent save Australia and EN Antarctica.” Peck continued with, “Hence, even today, one can hardly improve S on his contemporary assessments of the state of soil mechanics MO as expressed in his summary papers and presidential addresses.” In 1939, Terzaghi delivered the 45th James Forrest Lecture at RA the Institution of Civil Engineers, London. His lecture was entitled “Soil Mechanics—A New Chapter in Engineering Science.” N. In it, he proclaimed that most of the foundation failures that occurred were no longer “acts of God.” From 1939 to 1943, Dr. Peck worked as an assistant to Karl O Terzaghi. Ralph B. Peck was an American civil engineer who YN invented a controversial construction technique that would be RE used on some of the modern engineering wonders of the world, including the Channel Tunnel. Known as “the godfather of soil mechanics,” he was directly responsible for a succession of GR celebrated tunneling and earth dam projects that pushed the boundaries of what was believed to be impossible. EN