Principles of Geotechnical Engineering FIFTH EDITION
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Principles of Geotechnical Engineering FIFTH EDITION
BRAJA M. DAS California State University, Sacramento
Australia • Canada • Mexico • Singapore • Spain • United Kingdom • United States
Principles of Geotechnical Engineering, Sixth Edition by Braja M. Das Associate Vice-President and Editorial Director: Evelyn Veitch Publisher: Chris Carson Sales and Marketing Manager: John More Developmental Editor: Kamilah Reid Burrell Permissions Coordinator: Vicki Gould
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1 Geotechnical Engineering— A Historical Perspective
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.
1.1
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 18th 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. to 249 B.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, 1
2
Chapter 1
Geotechnical Engineering—A Historical Perspective
Figure 1.1 Leaning Tower of Pisa, Italy
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 18th 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,
1.1
Geotechnical Engineering Prior to the 18th Century
3
Figure 1.2 Tilting of Garisenda Tower (left) in Bologna, Italy
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 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. The half-degree change is not noticeable, but it makes the structure considerably more stable. Figure 1.2 is 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
4
Chapter 1
Geotechnical Engineering—A Historical Perspective
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. 2. 3. 4.
Pre-classical (1700 to 1776 A.D.) Classical soil mechanics—Phase I (1776 to 1856 A.D.) Classical soil mechanics—Phase II (1856 to 1910 A.D.) Modern soil mechanics (1910 to 1927 A.D.)
Brief descriptions of some significant developments during each of these four periods are discussed below.
1.2
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 (see Chapter 11) of clean dry sand and ordinary earth were 31 and 45, respectively. Also, the unit weight of clean dry sand (see Chapter 3) and ordinary earth were recommended to be 18.1 kN/m3 (115 lb/ft3) and 13.4 kN/m3 (85 lb/ft3), 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 (see Chapter 12) 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. (See Chapters 3 and 4.) Unit weight Classification
Rock
kN/m3
—
lb/ft3
—
Firm or hard sand Compressible sand
16.7 to 18.4
106 to 117
Ordinary earth (as found in dry locations) Soft earth (primarily silt) Clay
13.4 16.0 18.9
85 102 120
—
—
Peat
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. (See Chapter 12.) Gadroy’s study was later summarized by J. J. Mayniel in 1808.
1.4
1.3
Classical Soil Mechanics—Phase II (1856 –1910)
5
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 (see Chapter 12). 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 (see Chapter 11). He also provided the first ultimate bearing-capacity theory for shallow foundations (see Chapter 15). In 1846 Alexandre Collin (1808 –1890), an engineer, provided the details for deep slips in clay slopes, cutting, and embankments (see Chapter 14). 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. 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 (see Chapter 12). Rankine’s theory is a simplification of Coulomb’s theory.
1.4
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 (see Chapter 6). 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 (see Chapter 9). In 1887, Osborne Reynolds (1842 –1912) demonstrated the phenomenon of dilatency in sand.
6
Chapter 1
Geotechnical Engineering—A Historical Perspective Table 1.1 Important Studies on Clays (1910 –1927)
1.5
Investigator
Year
Topic
Albert Mauritz Atterberg (1846 –1916), Sweden
1911
Jean Frontard (1884 –1962), France
1914
Arthur Langtry Bell (1874 –1956), England
1915
Wolmar Fellenius (1876 –1957), Sweden Karl Terzaghi (1883 –1963), Austria
1918, 1926 1925
Consistency of soil, that is, liquid, plastic, and shrinkage properties (Chapter 3) Double shear tests (undrained) in clay under constant vertical load (Chapter 11) Lateral pressure and resistance of clay (Chapter 12); bearing capacity of clay (Chapter 15); and shear-box tests for measuring undrained shear strength using undisturbed specimens (Chapter 11) Slip-circle analysis of saturated clay slopes (Chapter 14) Theory of consolidation for clays (Chapter 10)
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. The most notable publications are given in Table 1.1.
1.6
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 (see Chapter 10) and on the failure due to piping in sand under dams (see Chapter 8). The publication Erdbaumechanik is primarily the result of this research. In 1925, Terzaghi accepted a visiting lectureship at Massachusetts Institute of
1.6
Geotechnical Engineering after 1927
7
Figure 1.3 Karl Terzaghi (1883 –1963) (Photo courtesy of Ralph B. Peck)
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 (Chapter 11), effective stress (Chapter 8), in situ testing (Chapter 17), Dutch cone penetrometer (Chapter 17), centrifuge testing, consolidation settlement (Chapter 10), elastic stress distribution (Chapter 9), preloading for soil improvement, frost action, expansive clays, arching theory of earth pressure, soil dynamics, and earthquakes. For the next quarter-century, Terzaghi
8
Chapter 1
Geotechnical Engineering—A Historical Perspective
Figure 1.4 Ralph B. Peck
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 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.” Following are some highlights in the development of soil mechanics and geotechnical engineering that evolved after the first conference of the ISSMFE in 1936: •
Publication of the book Theoretical Soil Mechanics by Karl Terzaghi in 1943 (Wiley, New York);
1.6
• • • • • • •
Geotechnical Engineering after 1927
9
Publication of the book Soil Mechanics in Engineering Practice by Karl Terzaghi and Ralph Peck in 1948 (Wiley, New York); Publication of the book Fundamentals of Soil Mechanics by Donald W. Taylor in 1948 (Wiley, New York); Start of the publication of Geotechnique, the international journal of soil mechanics in 1948 in England; Presentation of the paper on f 0 concept for clays by A. W. Skempton in 1948 (see Chapter 11); Publication of A. W. Skempton’s paper on A and B pore water pressure parameters in 1954 (see Chapter 11); Publication of the book The Measurement of Soil Properties in the Triaxial Test by A. W. Bishop and B. J. Henkel in 1957 (Arnold, London); ASCE’s Research Conference on Shear Strength of Cohesive Soils held in Boulder, Colorado, in 1960.
Since the early days, the profession of geotechnical engineering has come a long way and has matured. It is now an established branch of civil engineering, and thousands of civil engineers declare geotechnical engineering to be their preferred area of speciality. Since the first conference in 1936, except for a brief interruption during World War II, the ISSMFE conferences have been held at four-year intervals. In 1997, the ISSMFE was changed to ISSMGE (International Society of Soil Mechanics and Geotechnical Engineering) to reflect its true scope. These international conferences have been instrumental for exchange of information regarding new developments and ongoing research activities in geotechnical engineering. Table 1.2 gives the location and year in which each conference of ISSMFE /ISSMGE was held, and Table 1.3 gives a list of all of the presidents of the society. In 1997, a total of 30 technical committees of ISSMGE was in place. The names of these technical committees are given in Table 1.4. Table 1.2 Details of ISSMFE (1936 –1997) and ISSMGE (1997–present) Conferences Conference
Location
Year
I II III IV V VI VII VIII IX X XI XII XIII XIV XV XVI
Harvard University, Boston, U.S.A. Rotterdam, the Netherlands Zurich, Switzerland London, England Paris, France Montreal, Canada Mexico City, Mexico Moscow, U.S.S.R. Tokyo, Japan Stockholm, Sweden San Francisco, U.S.A. Rio de Janeiro, Brazil New Delhi, India Hamburg, Germany Istanbul, Turkey Osaka, Japan
1936 1948 1953 1957 1961 1965 1969 1973 1977 1981 1985 1989 1994 1997 2001 2005
Table 1.3 Presidents of ISSMFE (1936 –1997) and ISSMGE (1997–present) Conferences Year
President
1936 –1957 1957–1961 1961–1965 1965 –1969 1969 –1973 1973 –1977 1977–1981 1981–1985 1985 –1989 1989 –1994 1994 –1997 1997–2001 2001–2005
K. Terzaghi (U. S. A.) A. W. Skempton (U. K.) A. Casagrande (U. S. A.) L. Bjerrum (Norway) R. B. Peck (U. S. A.) J. Kerisel (France) M. Fukuoka (Japan) V. F. B. deMello (Brazil) B. B. Broms (Singapore) N. R. Morgenstern (Canada) M. Jamiolkowski (Italy) K. Ishihara (Japan) W. F. Van Impe (Belgium)
Table 1.4 ISSMGE Technical Committees for 1997–2001 (based on Ishihara, 1999) Committee number
Committee name
TC-1 TC-2 TC-3 TC-4 TC-5 TC-6 TC-7 TC-8 TC-9 TC-10 TC-11 TC-12 TC-14 TC-15 TC-16 TC-17 TC-18 TC-19 TC-20 TC-22 TC-23 TC-24 TC-25 TC-26 TC-28 TC-29 TC-30 TC-31 TC-32 TC-33 TC-34
Instrumentation for Geotechnical Monitoring Centrifuge Testing Geotechnics of Pavements and Rail Tracks Earthquake Geotechnical Engineering Environmental Geotechnics Unsaturated Soils Tailing Dams Frost Geosynthetics and Earth Reinforcement Geophysical Site Characterization Landslides Validation of Computer Simulation Offshore Geotechnical Engineering Peat and Organic Soils Ground Property Characterization from In-situ Testing Ground Improvement Pile Foundations Preservation of Historic Sites Professional Practice Indurated Soils and Soft Rocks Limit State Design Geotechnical Engineering Soil Sampling, Evaluation and Interpretation Tropical and Residual Soils Calcareous Sediments Underground Construction in Soft Ground Stress-Strain Testing of Geomaterials in the Laboratory Coastal Geotechnical Engineering Education in Geotechnical Engineering Risk Assessment and Management Scour of Foundations Deformation of Earth Materials
References
11
References ATTERBERG, A. M. (1911). “Über die physikalische Bodenuntersuchung, und über die Plastizität de Tone,” International Mitteilungen für Bodenkunde, Verlag für Fachliteratur. G.m.b.H. Berlin, Vol. 1, 10 – 43. BELIDOR, B. F. (1729). La Science des Ingenieurs dans la Conduite des Travaux de Fortification et D’Architecture Civil, Jombert, Paris. BELL, A. L. (1915). “The Lateral Pressure and Resistance of Clay, and Supporting Power of Clay Foundations,” Min. Proceeding of Institute of Civil Engineers, Vol. 199, 233 –272. BISHOP, A. W. and HENKEL, B. J. (1957). The Measurement of Soil Properties in the Triaxial Test, Arnold, London. BOUSSINESQ, J. V. (1885). Application des Potentiels â L’Etude de L’Équilibre et du Mouvement des Solides Élastiques, Gauthier-Villars, Paris. COLLIN, A. (1846). Recherches Expérimentales sur les Glissements Spontanés des Terrains Argileux Accompagnées de Considérations sur Quelques Principes de la Mécanique Terrestre, Carilian-Goeury, Paris. COULOMB, C. A. (1776). “Essai sur une Application des Règles de Maximis et Minimis à Quelques Problèmes de Statique Relatifs à L’Architecture,” Mèmoires de la Mathèmatique et de Phisique, présentés à l’Académie Royale des Sciences, par divers savans, et lûs dans sés Assemblées, De L’Imprimerie Royale, Paris, Vol. 7, Annee 1793, 343 –382. DARCY, H. P. G. (1856). Les Fontaines Publiques de la Ville de Dijon, Dalmont, Paris. DARWIN, G. H. (1883). “On the Horizontal Thrust of a Mass of Sand,” Proceedings, Institute of Civil Engineers, London, Vol. 71, 350 –378. FELLENIUS, W. (1918). “Kaj-och Jordrasen I Göteborg,” Teknisk Tidskrift. Vol. 48, 17–19. FRANCAIS, J. F. (1820). “Recherches sur la Poussée de Terres sur la Forme et Dimensions des Revêtments et sur la Talus D’Excavation,” Mémorial de L’Officier du Génie, Paris, Vol. IV, 157–206. FRONTARD, J. (1914). “Notice sur L’Accident de la Digue de Charmes,” Anns. Ponts et Chaussées 9 th Ser., Vol. 23, 173 –292. GADROY, F. (1746). Mémoire sur la Poussée des Terres, summarized by Mayniel, 1808. GAUTIER, H. (1717). Dissertation sur L’Epaisseur des Culées des Ponts . . . sur L’Effort et al Pesanteur des Arches . . . et sur les Profiles de Maconnerie qui Doivent Supporter des Chaussées, des Terrasses, et des Remparts. Cailleau, Paris. ISHIHARA, K. (1999). Personal communication. KERISEL, J. (1985). “The History of Geotechnical Engineering up until 1700,” Proceedings, XI International Conference on Soil Mechanics and Foundation Engineering, San Francisco, Golden Jubilee Volume, A. A. Balkema, 3 –93. MAYNIEL, J. J. (1808). Traité Experimentale, Analytique et Pratique de la Poussé des Terres. Colas, Paris. NAVIER, C. L. M. (1839). Leçons sur L’Application de la Mécanique à L’Establissement des Constructions et des Machines, 2nd ed., Paris. PECK, R. B. (1985). “The Last Sixty Years,” Proceedings, XI International Conference on Soil Mechanics and Foundation Engineering, San Francisco, Golden Jubilee Volume, A. A. Balkema, 123 –133. PONCELET, J. V. (1840). Mémoire sur la Stabilité des Revêtments et de seurs Fondations, Bachelier, Paris. RANKINE, W. J. M. (1857). “On the Stability of Loose Earth,” Philosophical Transactions, Royal Society, Vol. 147, London. REYNOLDS, O. (1887). “Experiments Showing Dilatency, a Property of Granular Material Possibly Connected to Gravitation,” Proceedings, Royal Society, London, Vol. 11, 354 – 363.
12
Chapter 1
Geotechnical Engineering—A Historical Perspective SKEMPTON, A. W. (1948). “The f 0 Analysis of Stability and Its Theoretical Basis,” Proceedings, II International Conference on Soil Mechanics and Foundation Engineering, Rotterdam, Vol. 1, 72 –78. SKEMPTON, A. W. (1954). “The Pore Pressure Coefficients A and B,” Geotechnique, Vol. 4, 143 –147. SKEMPTON, A. W. (1985). “A History of Soil Properties, 1717–1927,” Proceedings, XI International Conference on Soil Mechanics and Foundation Engineering, San Francisco, Golden Jubilee Volume, A. A. Balkema, 95 –121. TAYLOR, D. W. (1948). Fundamentals of Soil Mechanics, John Wiley, New York. TERZAGHI, K. (1925). Erdbaumechanik auf Bodenphysikalisher Grundlage, Deuticke, Vienna. TERZAGHI, K. (1939). “Soil Mechanics—A New Chapter in Engineering Science,” Institute of Civil Engineers Journal, London, Vol. 12, No. 7, 106 –142. TERZAGHI, K. (1943). Theoretical Soil Mechanics, John Wiley, New York. TERZAGHI, K., and PECK, R. B. (1948). Soil Mechanics in Engineering Practice, John Wiley, New York.
Origin of Soil and Grain Size I n g c n e r a l .s o i l sa r c l ' o r r n c db v w c a t l " r c r i nogf r o c k s .T h e p h y s i c a lp r o p e r t i e sc l l a s o i l a r c d i c l a t c d p r i n l a r i l y b y t h e m i n c r a l st h a t c o n s t i t u t ct h e s o i l p l r t i c l e s a n d . h c n c c , thc rock I'rorr which it is dcrivccl.This chaptcr proviclcsan outline of the reck cvclc a n c lt h c o r i g i n o l ' s o i l a n c lt h c g r a i n - s i z cd i s t r i b u t i o no f p a r t i c l c si n a s g i l l r r r s s .
2.1
Rock Cycle and the Origin of Soil T h c n l i n c r a l g r a i n st h a t l i l r r n t h e s o l i c lp h a s co l ' a s o i l a g g r c g i l t ca r c t h c p r o d u c t 1 ; l r o c k w c a t h e r i n c . ' l ' l r cs i z c t l l ' t h c i n d i v i c l u agl r a i n sv a r i c s< l v c ra w i c l er a n g c .M a n y o f t h c p h y s i c a lp r o p c r t i c so l ' s t t i l a r c c l i c t a l c cbl y t h e s i z e .s h a p c ,a n c lc h c m i c l l c o m p e s i t i t l no l ' t h c g r a i n s .' f o b c t t c r u n d c r s t a n dt h c s cl a c t o r s .o n c m u s t b c I ' a m i l i a rw i t h t h e b a s i ct y p c s o l ' r o c k t h a t l o r n ' rt h c c a r t h ' . sc r u s t , t h c * r c k - l i r r r r i ' g m i ' c r a l s . a n d t h e w c i r t h c r i n gp t ' ( ) c c \ \ . On thc basisol their ntttclcol'origin, rocks car'rbc cliviclecl into three basictypes: il4trcrttt's, scdintentury,artdrtretumorphit'.F igurc 2. I showsa cliagramof the fclrmalion 'fhis c y c l co l ' d i l l c r e n t t y p e so l ' r o c k a n d t h c p r o c e s s c as s s o c i a t e w c li t h t h e m . iscallecl L h er o c ' kc v c l c .B r i e l ' d i s c u s s i o nosl ' c a c h c l e m c n t o l ' t h c r o c k c v c l c f o l l o w . lgneous Rock Igncous rocks are forr.ncdby thc solidilication of n.roltenmullnlu cjectcd from deep within the earth'.smantle. Al'ter cjection by either,Ttssure erttption or vttlt.LtrtiL crupI i o r i ,s o m c o f t h e r n c l l t e nm a g m ac o o l so n t h e s u r f a c co f t h e e a r t h .S o m e t i m e sm a g m a ceiisesits mobility below thc carthlssurlacc and cclolsto form intrusiveigneousrocks that are calledplutons. Intrusive rocks krrmeclin the past may be exposcdat the surface as a result of the continuous processo1'erosionof the materials that once covcred them. 'rhe typcs of igneousrock ftrrmed by the cooling of magma depend on factors such as the composition of the magma and the rate ol cooling associatedwith it. After conductingseverallaboratory tests,Bowen (1922)was ablc to cxplain the relation of the rate of magma cooling to the formation of different types of rock. This explanation - known as Bowen'sreaclittnprinciple* describesthe sequenceby which new
13
14
Chapter 2
Origin of Soil and Grain Size
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"
i , t ; ' " ' bt l r ,
Figure 2.7 Rock cyclc
Crystallization lt highcr tomperaturc
[ - o w c rr e s i s t a n c e 1 ow e a t h c r i n g
(potussiumI'eldspar.t
I
V Muscovitc ( w h i t er n i c a ) H i g h e rr c s i s t a n c e to weathering
Figure 2.2 Bowcn'.sreaction serles
I
t Quartz
Crystallization at lower temperature
2.1 Rock Cycleand the Origin of Soit
15
Table2' 1 compositionof MineralsShownin Bowcn! ReactionScries Composition Olivine Augite Hornblende Biotite (black mica) plasiocrrrsc{ calcium .lc,lclsp.r Isofl1x6lcldsPar Orthoclase (potassiumfeldspar) Muscovite (white mica) Quartz
(Mg. Fe),SiOa Ca. Na(Mg. Fc, Al)(Al. Si2Oo) Cornplcx i'erromagnesiansilicateof Ca.Na. Mg, Ti, and Al K(Mg. Fe)lAlsiroro(OH)r Cla(AllSi,O*) Na(AlSi3O5) K(AlSirOs) KAlrSirOro(OH)r
sior
mlnerals are formed as magma cools.T'ht:mincral crystalsgrow larger anclsome ol' t h e m s e t t l e .T h e c r y s t a l st h a t r e m a i n s u s p e n c l c iM
Once the percent fincr for each sieveis calculated(step 5), the calculationsare plotted on semilogarithmicgraph paper (Figure 2.15) with percent finer as the ordinate (arithmetic scale) and sieve opening size as the abscissa(logarithmic scale). distrihution curveThis plot is referred to as the particle-siz,e Hydrometer
Analysis
Hydrometer analysis is based on the principle of sedimentation of soil grains in water. When a soil specimen is dispersed in water, the particles settle at different velocities, depending on their shape,size,and weight, and the viscosity of the water.
2.5 MechanicatAnalysis of Soil
Figure 2.14 A set of sievcslbr a test in thc laborarorv
E
l 0.5 particle size (rnnr)_ log scale
Figure 2.15 Particle-size distributioncurve
31
32
Chapter 2
Origin of Soil and Grain Size For simplicity,it is assumedthat all the soil particles are spheresand that the velocity of soil particles can be expressedby Stokes' law, according to which
u: where u : p, : p,,,: 4 : D :
p, - p1n pz
r8T
(2.r)
velocity density of soil particles dcnsity of water viscosityof water diameter of soil particles
Thus,from Eq. (2.l),
(2.2)
D : Dislancc whcre r Time Note that
L t P,:
G,P,,,
(2.3)
Thus. combining Eqs. (2.2) and (2.3) gives
(2.4) I l ' t h e u n i t so f 4 a r e ( g ' s e c ) / c m 2p,, , ,i s i n g i c m r ,L i s i n c m , t i s i n m i n , a n d D i s i n m m , thelr
D(_TI'): l0
()r
-ttr'r [(e.r".y.ff] T llc )
',1 ( C , - l ) 1 , , , . 1 g / c mV /(ni'n) \ 60
fL. D : Vt-r " 3(\" ..-tl,V ; Assume p,,.to bc approximately cqual to 1 g/cm3,so that
D(mm):6
L (cm) r (min)
/7 5\
where
3oa
(G, - 1)
(2.6)
2.5 Mechanical Analvsis of Soil
33
Table2.6 Valuesof K tiom Eq. (2.6),' Temperature
('c) 16 77 18 l9 20 21 22 L-)
24 25 26 27 28 29 30
c. 2.45
0.01510 0.01511 0.01492 0.01474 0.014,56 0.01438 0.01421 0.01404 0.013u8 0.01372 0.013.57 0.01342 0.01327 0.01312 0.01298
2.60
0.01-505 0.014rJ6 0.0146l 0.01449 0.01431 0.01414 0.01397 0.013[iI 0.01 36-5 0.01349 0.01334 0.0l3l9 0.01304 0.01290 0.01276
0.01481 0.01462 0.01443 0.01425 0.0140n 0 . 013 91 0.01374 0.0I 1.513 0.01342 0.01327 0.01312 0.0t29'/ 0.012133 0.01269 0.012-56
0.014-57 0.01439 0.01421 0.01403 0 . 0 I3 8 6 0.01 369 0.01353 0.0I337 0.0I321 0.01306 0.01291 0.01277 0.01261 0.01249 0.01236
2.70
0.0143.5 0.01 417 0.0I399 0 . 01 3 u 2 0.0I 36-s 0.01 348 0.01 332 0.013t7 0.01 301 0.012116 0.0t272 0.0I2.sti o.ol244 0.01230 0.01217
0.0141,1 0.01 396 0.0I 378 0 . 0 1 316 0.01344 0 . 0I 3 2 8 0.01 3 12 0.01297 0.01 2u2 0.01267 0.0t253 0.0I 239 0.01225 0.01212 0.01199
2.75
0.01394 0.01376 0.01 359 0.01342 0.01 325 0.01309 0.0t294 0.0t279 0.01264 0.01249 0.0123-5 0.01221 0.0t201J 0 . 0 11 9 - s 0.01ltt2
2.80
0.0137 4 0.01356 0.01 339 0.01323 0.01 307 0.01291 0.01276 0.0t261 0.01246 0.0t232 0.0121t3 0.01204 0.01191 0 . 0 11 7 u 0.01t69
"AfterASTM (1999)
Note that the value of K is a function of G, and 4, which are depenclenton the temperature of the test. Table 2.6 givesthc variation o1'K with the test tempcrature and the specificgravity of soil solids. ln the laboratory, the hydrometcr test is concluctcclin a sedimentationcylinder usually with 50 g of oven-dricclsample. Sometimes 100-gsamplescan also be u s e d .T h e s e d i m e n t a t i o nc y l i n d c r i s 4 - 5 7m m ( 1 8 i n . ) h i g h a n d 6 3 . , 5m m ( 2 . - 5i n . ) i n d i ameter. It is marked for a volume of 1000ml. Sodium hexametaphosphateis generafly used as the dispersingugent.The volumc of the clispersedsoil suspensionis inc r e a s e dt o 1 0 0 0m l b y a d d i n gd i s t i l l e dw a t e r .F i g u r e2 . 1 6s h o w sa n A S T M l 5 2 H t v p e of hydrometer. When a hydrometer is placed in the soil suspensionat a time t, measuredfrom the start of sedimentationit measuresthe specificgravity in the vicinity of its bulb at a depth L (Figure 2.17).The specificgravity is a function of the amount of soil particles present per unit volume of suspensionat that depth. Also, at a time r, the soil particlesin suspensionat a depth L will have a diameter smaller than D as calculated in Eq. (2.,5).The larger particles would have settred beyond the zone of measurement. Hydrometers are designedto give the amount of soil, in grams, that is still in suspension.They are calibrated for soils that have a specificgravity, G., of 2.65;for soils of other specificgravity,a correction must be made. By knowing the amount of soil in suspension.L, and /, we can calculatethe percentageof soil by weight finer than a given diameter.Note that L is the depth measured from the surface of the water to the center of gravity of the hydrometer bulb at which the density of the suspensionis measured.The value of L will changewith time /. Hydrometer analysisis effective for separating soil fractions down to a size of
Chapter 2
Origin of Soil and Grain Size
I
i I
I
L l
L
j 6 0
L1
Figure 2.16 A S T M l 5 2 H h y d r o n r c t er ( c ( ) u r t c s )t r l S o i l t c s t .I n c . . L a k c B t u l l ' .I l l i n o i s )
Figure 2.17 Definition o1/- in hydrometertest
about 0.-5pm. The value of L (cm) 1or the ASTM l52H hydrometer can be given by t h c e x p r e s s i o n( s e eF i g u r e2 . 1 7 )
L : L r+. ( t ,+ )
(2.1)
where L, : distancealong the stem of the hydrometer from the top of the bulb to the mark for a hydrometer reading (cm) L, : length of the hydrometer bulb : 14 cm I/a : volume of the hydromcter bulb : 67 cml -A : cross-sectionalarea of the sedimentationcylinder : 27.8 cm2 The value of l,, is 10.-5cm for a reading of R : 0 and 2.3 cm for a reading of R : 50. Hence, for any reading R,
Lr : 10.5-
r r 0.5- 2.3) : 10.5- 0.164R(cm)
-R
2.5
Mechanical Analysis of Soit
35
Table 2.7 Variation of L with Hyclrometer Reading ASTM 152H Hvdrometer Hydrometer reading, fl
U I 2 3 4 5 6 7 8 r)
l0 ll t2 l3 t4 l5 l6 T7 l8 l9 20 2l 22 L-) 1 /,1
25 26 27 213 29 30
I (cml
16.3 16.1 i6.0 l-5.tt 1.5.6 1.5.5 l -5.3 15.2 15.0 14.8 I4.l 14..5 1,1.3 14.2 r4.0 l3.tt t3.7 I3.-5 I -).-)
13.2 13.0 t2.9 12.7 12.-5 12.4 t2.2 12.0 I1.9 t1.7 I l.-s I1.4
Hydrometer reading, fr
31 33 -)4
3-5 36 37 38 39 40 4l 42 4-1
44 45 46 41 4tt 49 50 .)l
52 1.1
-s4
5-5 -56 57
-5u -s9 60
L (cml
tI.z
l l.l 10.9 I0.7 10.6 10.4 to.2 I0.l 9.9 9.7 9.6 L).4
9.2 9 .1 8.9 ti.tt 6.6 8.4
u.3
,1.I 7.9 7.8 1.6 7.4
1.1 7.0 6.tt b.o 6.-5
Thus, from Ecl. (2.1),
- 67\ L- to..s lsaqn+l/ to,zv 0.164R 2(14 -.n): where R : hydrometer reading corrected for "the meniscus.
(2.8)
on the basisof Eq. (2.8), the variations of L with the hydrometer readinss R are given in Table 2.7. In many instances,the results of sieve analysisand hydrometer analysis for finer fractions for a given soil are combined on one graph, iuch as the one shown in Figure 2.18.When these resultsare combined, a discontinuity generally occursin the range where they overlap. This discontinuity occurs UecausJsoil particles are generally irregular in shape.Sieve analysisgives thc intermediate diminsions of a
36
Chapter 2
Origin of Soil and Grain Size Unified classification Silt and clay
Sand
100
Sieve no. l0
16
Hydroneter analysis
Sieveanalysis 30 40 60 100 200
o Sieveanalysis t Hydrorneteranalysis
tsoo d
+r,
(,
'5
2 I 0s
0(x)2 000r l],1,,.1i'.,il,i.,'",,,,\'#"t""""t
and hydrometeranalysis distributioncurvc- sicveanalysis Figure2.18 Parlicle-size particlet hydrometer analysisgivesthe diametcr of an equivtllentsphere that would s c t t l ea t t h e s a m c r a t c a s t h e s o i l p a r t i c l c .
2.6
Particle'Size Distribution Curve A particle-sizeclistribution curve can be used to determine the following four par a m e t e r sf o r a g i v c n s o i l ( F i g u r c 2 . 1 9 ) : l. 8.fl'ectivesiz,e(D11):This parameter is the diameter in the particle-sizcdistribution curve correspondingto l0% Iiner. The effectivesize of a granular soil is a good measureto estimatethe hydraulic conductivity and drainage t h r o u g hs o i l . (C,,): This parameter is defincd as 2. IJniformity ctte.ft'icient
c, ..tt : le Dn
es)
where D66: diameter correspondingto 60% finer' 3. Coefficient of gradation (C ,): This parameter is defined as
..:#;
D4"
(2.10)
2.6 Particle-Size Distribution Curve
80 75 b 6 0 E g
ol +o 30 25 20 t0
(,
l0
5
|
0.-5
P a r t i c l es i z c( m n r ) Figure
2.19
Detinition
of D7., Dnu. Dtr l)2., and D1,,
Sorting coefficient(s,,):This parameter is another measureof uniformitv and is generally encounteredin geologic works and expressedas
6; S ,: ,V r ^
(2.r1)
The sorting coefficientis not frequently used as a parameter by geotechnical engineers. The percentagesof gravel,sand,silt, and clay-sizeparticlespresentin a soil can be obtained from the particle-sizedistribution curve. As an example,we will use the particle-sizedistribution curve shown in Figure 2. lg to determine the gravel, sand, silt, and clay-sizeparticles as follows (according to the Unified Soil Classification System- seeTable 2.3): Size (mm)
76.2 4.75 0.075
lo tiner
100 100 62 U
1 0 0- 1 0 0 : 0 % g r a v e l 1 0 0- 6 2 : 3 8 %s a n d 62 - 0: 620/osllt and clay
The particle-sizedistributioncurve showsnot only the rangeof particle sizes presentin a soil,but alsothe type of distributionof various-size pirticlei. Suchtypes of distributionsare demonstratedin Figure2.20.CurveI representsa type of soii in
38
Chapter 2
Origin of Soil and Grain Size 100
H 6i) E b 4 0
o
20
2
|
0.-5
0.2
0.|
0.05 0.02 0.0|
0.005
Ptniclc diamcter (nllr)
Figure 2.20 Dilferent typesol pirrticle-sizcdistributioncurves which most of the soil grains zrrcthe same size. This is called poorly gradad soll. Curve II representsa soil in which the particle sizesare distributed over a wide range, termed well grtrtled.A well-gracledsoil hasa uniformity coefficientgreaterthan about 4 for gravclsand 6 for sands,and zrcoefficicntofgradation bctween 1 and 3 (for gravels and sands).A soil might havea combinationof two or morc uniformly graded frac'Ihis type ol'soil is tcrmed gap grudcd. tions. Curve lll reprcsentssuch a soil.
Example2.1 calculationsand Followingare the resultsof a sieveanalysis.Make the necessary draw a particle-sizedistributioncurve. U.S. sieve size
Mass of soil retained on each sieve {gl
4 10 20 40 60 80 100 200
Pan
Solution itr"hff.*i"g
tablecannowbe prepared.
0 40 60 89 140 tzt
21.0 56 T2
2.6 Particle-Size Distribution Curve
u.s.
Opening {mm}
sieve (1)
{2t
A T
4. tJ
10 20 40 60 80 100 200 Pan
2^00 0.850 0.425 0.250 0.180 0.150 0.075
Mass retained on each sieve (gl
{3}
0 40 60 89 140 \22 270 56 I2
0 0+ 40:40 40+60=100 100+89:189 189+I40-329 329+122-451 45I+210=661 661+56=717 7 1 7+ 1 2 : 7 2 9: 2 M
. > M - col.4 x 1oo:Z*U 2M
Cumulative mass retained above each sieve (gt {4)
* ,uo
729
The particle-sizedistributioncurveis shownin Fisure 2.21. 100
b6() E
I
+tl
t0
(,
t0
= fl.15 n.'t,t 1)111
5
3
I 0..5 0.3 Particlcsizc(mrn)
Figure 2.21 Particle-size distribution curve
Example2.2 For the particle-sizedistributioncurveshownin Figure2.21,determine e. Dro,D.ro, and Doo b. Uniformity coefficient,C, c. Coefficientof gradation,C.
Percent finero
t5)
100 94.5 86.3 74,1 54.9 3E.1 9.3 1.7 0
39
40
Chapter 2
Origin of Soil and Grain Size
$olution a. From Figwe2.27, Dro : 0'15mm D3s: 0.17mm D6r,: 0.27mm
b . c , D^,, , : n :O27: n s -tt . _
'':#o*:#ffib-o'71 For the particle-sizedistributioncurve shownin Figure2'21, determinethe percentagesof gravel,sand,silt, and clay-sizeparticlespresent.Use the Unified Soil ClassificationSystem. Solution From Figure2.27,wecan preparethe followingtable. Size (mml
76.2 4.75 0.075
2.7
% finer,
l[]3,=
100* 100= 0o/oEravel sand 100* 1.7 * 98.3olo 1.7 - 0 = l.7o/osilt and clay
Particle Shape T'hc shape of particles present in a soil massis equally as important as the particlesizc distribution becauseit has significantinfluence on the physical properties of a given soil. However, not much attention is paid to particle shapebecauseit is more difhcult to meersure.The particle shape can generally be divided into three major categories: l. Bulky 2. Flaky 3. Needle shaped BuLky particles are mostly formed by mechanical weathering of rock and minerals. Geologists use such terms as angular, subangular' rounded, and subrounded
2.7 Particle Shape
41
Figure2.22 Eleclrttnmicrograplr ol'sontcIinc subar-rgular quartzsand and subroundccl
t o d e s c r i b et h e s h a p e so f b u l k y p a r t i c l e s .F i g u r e 2 . 2 2 s h o w s a s c a n l i n s c l e c t r o n micrograph of some subangularancl subroundeclquartz sarrd.'l-hc ungtiluritv,A, is dcfincd as
o :
AM$9 t9'dillolggMtt
a'd edscs
Radius ol'the maximu- inr.titre.t rph"t.
(2.12)
The sphericityoi bulky particles is defineclas
__ D, .tL whcre Q, - equivalent diameter of the particle I/ - volume of particle L,, : length of particle
( 2 .r3 ) 6V T
Flaky purticleshave very low sphericity- usually 0.01 or less.Thesc particles are predominantly clay minerals. Needle-shapedparticles are much less common than thc other two oarticle types. Examples of soils containing needle-shapedparticlesarc some coral deposits and attapulgite clays.
42
Chapter 2
2.8
Origin of Soil and Grain Size
Summary In this chapter, we discussedthe rock cycle, the origin of soil by weathering, the particle-sizedistribution in a soil mass,the shape of particles,and clay minerals. Some important points include the following: 1. Rocks can be classifiedinto three basic categories:(a) igneous,(b) sedimentary, and (c) metamorphic. 2. Soils are formed by chemical and mechanicalweathering of rocks. 3. Based on the size of the soil particles,soil can be classifiedas gravel,sand, silt, or clay. 4. Clays are mostly flake-shapedmicroscopicand submicroscopicparticles of mica, clay minerals,and other minerals. 5. Clay minerals are complex aluminum silicatesthat develop plasticity when mixed with a limited amount of water. 6. Mechanical analysisis a processfor determining the size range of particles present in a soil mass.Sieveanalysisand hydrometer analysisare two tests used in the mcchanicalanalysisof soil.
Problems 2.1 2.2 2.3
: 0.21 mm, and D',, : 0.16 mm, calculate For a soil with Do,,: 0.42 mm, D11y thc uniformity coefficientand the coeflicientof gradation. : 0.27mm' Dj1,: 0.41 Rcpeat Problem 2.1 with the following values:D 111 mm, and 1),,,,: 0.lll mm. Following arc the resultsof a sievc analysis:
no. U.s. sieve 4 l0 20 40 60 100 200 Pan
2.4
tn""'"h'liff:",Ti' t
) 18.5 53.2 90..s 81.8 92.2 58.5 26.5
a. Determine the percent finer than each sieve size and plot a grain-size distribution curve. from the grain-sizedistribution curve. b. Determine Dy,, D.u. and D611 C,,. coeflicient c. Calculate the uniformity gradation, C-. of d. Calculate the coefficient results of a sieve analysis. following 2.3 with the Repeat Problem
Problems U.S.sieve no.
1 l0 20 4t) 60 100 200 Pan
Mass of soil retained on each sieve (g)
0 41.2 5.5.1 80.t) 9l.6 60.-s 3-5.6 21.5
Repeat Problem 2.3 with the following resultsfor a sieveanalysis. U.S.sieveno. 4 6 l0 20 40 60 l(x) 200 Pan
Massof soil retained on eachsieve(gl 0 (., 20.1 19.5 2I0.-5 135.6 22.7 I .5.-5 l-1.-)
Thc particle-sizecharacteristicsof a soil are given in this table. Draw the p a r t i c l e - s i z ed i s t r i b u t i o nc u r v c .
2.7
Size(mm)
Percent finer
('t.425 0.033 0.018 0.0I 0.(x)62 0.0035 0.001r.i 0.00I
l(x) 90 t30 7o 60 50 40 35
Determinc the percentagesof gravel,sand, silt, and clay: a. According to the USDA system. b. According to the AASHTO system. Repeat Problem 2.6 with the following data: Size(mm) Percent finer 0.425 0.1 0.052 0.02 0.01 0.004 0.001
r00 92 84 62 46 JL
22
Chapter 2
Origin of Soil and Grain Size 2.8
2.9
Repeat Problem 2.6 with the following values: Size(mm)
finer Percent
0.425 0.1 0.04 0.02 0.01 0.002 0.001
100 19 57 48 40 35 33
Repeat Problem 2.6 with the following data: Size(mm)
finer Percent
0.425 0.07 0.046 0.034 0.026 0.019 0.014 0.009 0.(x)54 0 . ( x )9t
100 90 80 70 60 -50 40 30 20 l0
2.10 A hydromcter test has the following results:G, : 2.'7, tempcrature of water : 24"C. and l, : 9.2 cm at 60 minutes after the start of sedimentation.(See Figure 2.17.)What is the diameter D of the smallest-sizeparticles that have settled beyond the zone of measurementat that time (that is, r : 60 min) / 2 . l l R e p e a tP r o b l e m 2 . 1 0w i t h t h e f o l l o w i n gv a l u e s :G , : 2 . 7 5 , t e m p e r a t u r eo f watcr : 23"C. t : 100 min. and L : 12.ucm.
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