Geotechnical Engineering - Module 1 Notes

Introduction

  • Soil Definition:
    • Uncemented aggregate of mineral grains and decayed organic matter.
    • Contains liquid and gas in the empty spaces between solid particles.
    • Used as construction material and supports structural foundations.

Soil Mechanics

  • Definition:
    • Branch of science studying the physical properties of soil.
    • Studies the behavior of soil masses subjected to various forces.

Soil Engineering vs. Geotechnical Engineering

  • Soil Engineering:
    • Application of soil mechanics principles to practical problems.
  • Geotechnical Engineering:
    • Subdiscipline of civil engineering dealing with natural materials near the Earth's surface.
    • Applies soil and rock mechanics to design foundations, retaining structures, and earth structures.

Geotechnical Engineering Prior to the 18th Century

  • Before the 18th century, geotechnical engineering relied on past experiences and experimentation without scientific character.
  • Egypt:
    • Construction of the Pyramid of Giza posed challenges related to foundations, slope stability, and underground chambers.
  • China:
    • Construction of thousands of pagodas following the arrival of Buddhism during the Eastern Han dynasty.
    • Pagodas were built on silt and soft clay layers.
    • Foundation pressure exceeded the soil's load-bearing capacity, leading to structural damage.
  • Italy:
    • The Leaning Tower of Pisa is a famous example of soil-bearing capacity problems.
    • The tower weighs 15,700 metric tons and is supported by a circular base with a 20 m diameter.
    • A weak clay layer existed about 11 m below the ground surface, leading to compression and tilting.
    • The tower leans more than 5 m out of plumb with a height of 54 m.
    • Stabilization was achieved by excavating soil from under the north side of the tower.
    • 70 metric tons of earth were removed in 41 separate extractions across the tower's width.
    • The tower now leans at 5 degrees.

Development of Soil Mechanics (18th Century Onward)

  • Engineers and scientists began a methodical approach to soil properties and behaviors in the early 18th century.
  • Four major periods:
    • Preclassical (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.)

Preclassical Period of Soil Mechanics (1700 - 1776)

  • Concentrated on studies related to natural slope, unit weights of soils, and semi-empirical earth pressure theories.
  • Henri Gautier (1660 - 1737)
    • French royal engineer.
    • Studied natural slopes of soils when tipped in a heap for retaining wall design procedures.
    • Natural slope is now referred to as the angle of repose.
    • Clean dry sand: natural slope = 31°, unit weight = 18.1kNm318.1 \frac{kN}{m^3}
    • Ordinary earth: natural slope = 45°, unit weight = 13.4kNm313.4 \frac{kN}{m^3}
  • Bernard Forest de Belidor (1671 - 1761)
    • Proposed theory of lateral earth pressure on retaining walls.
    • Specified a soil classification system.
    • Classification and Unit Weight:
      • Rock: 16.7 to 18.4kNm318.4 \frac{kN}{m^3}
      • Firm or hard sand: 16.0kNm316.0 \frac{kN}{m^3}
      • Compressible sand: 13.4kNm313.4 \frac{kN}{m^3}
      • Ordinary earth (dry): 18.9kNm318.9 \frac{kN}{m^3}
      • Soft earth (silt): (No Unit Weight Mentioned)
      • Clay:
      • Peat: (No Unit Weight Mentioned)
  • Francois Gadroy (1705 - 1759)
    • Observed the existence of slip planes in soil at failure.
  • J. J. Mayniel
    • Summarized Gadroy's study in 1808.
  • Jean Rodolphe Perronet (1708-1794)
    • Studied slope stability around 1769.
    • Distinguished between intact ground and fills.

Classical Soil Mechanics - Phase I (1776 - 1856)

  • Charles Augustin Coulomb (1736 - 1806)
    • Used calculus principles for maxima and minima to determine the true position of the sliding surface in soil behind a retaining wall.
    • Used laws of friction and cohesion for solid bodies.
  • Gaspard Clair Marie Riche de Prony (1755 - 1839)
    • Included Coulomb's theory in his textbook Nouvelle Architecture Hydraulique (Vol. 1).
  • Jacques Frederic Francais (1775 - 1833) and Claude Louis Marie Henri Navier (1785-1836)
    • Addressed special cases related to inclined backfills and backfills supporting surcharge.
  • Jean Victor Poncelet (1788 - 1867)
    • Extended Coulomb's theory with a graphical method for determining lateral earth pressure on vertical and inclined retaining walls with arbitrarily broken polygonal ground surfaces.
    • First to use the symbol φ for soil friction angle.
    • Developed the first ultimate bearing-capacity theory for shallow foundations.
  • Alexandre Collin (1808-1890)
    • Provided details for deep slips in clay slopes, cuttings, and embankments.
    • Theorized that failure occurs when mobilized cohesion exceeds the existing cohesion of the soil.
    • Observed that actual failure surfaces could be approximated as arcs of cycloids.
  • William John Macquorn Rankine (1820-1872)
    • Developed 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)

  • Henri Philibert Gaspard Darcy (1803 - 1858)
    • Published a study on the permeability of sand filters.
    • Defined the term coefficient of permeability (hydraulic conductivity) of soil.
  • Joseph Valentin Boussinesq (1842 - 1929)
    • Developed the theory of stress distribution under loaded bearing areas in a homogenous, semi-infinite, elastic, and isotropic medium in 1885.
  • Osborne Reynolds (1842-1912)
    • Demonstrated the phenomenon of dilatancy in sand.
  • John Clibborn (1847-1938) and John Stuart Beresford (1845-1925)
    • Studied the flow of water through sand beds and uplift pressure.

Modern Soil Mechanics (1910-1927)

  • Albert Mauritz Atterberg (1846-1916)
    • Defined clay-size fractions as the percentage by weight of particles smaller than 2 microns in size.
    • Emphasized the important role of clay particles in soil and plasticity.
    • Explained the consistency of cohesive soils by defining liquid, plastic, and shrinkage limits.
    • Defined plasticity index as the difference between liquid limit and plastic limit.
  • Jean Fontard (1884 - 1962)
    • Investigated the failure of the 17-m high earth dam at Charmes, France.
    • Conducted undrained vertical double-shear tests on clay specimens (0.77 m² in area and 200 mm thick) under constant vertical stress to determine their shear strength parameters.
  • Arthur Langley Bell (1874-1956)
    • Worked on the design and construction of the outer seawall at Rosyth Dockyard.
    • Developed relationships for lateral pressure and resistance in clay, as well as bearing capacity of shallow foundations in clay.
    • Used shear-box tests to measure the undrained shear strength of undisturbed clay specimens.
  • Wolmar Fellenius (1876 - 1957)
    • Developed the stability analysis of saturated clay slopes (ϕ\phi = 0) with the assumption that the critical surface of sliding is the arc of a circle.
    • His published work gave correct numerical solutions for the stability numbers of circular slip surfaces passing through the toe of the slope.
  • Karl Terzaghi (1883 - 1963)
    • Developed the theory of consolidation for clays.
    • Used five different clay soils in his study with liquid limit ranging between 36 and 67, and the plasticity index in the range of 18 to 38.
    • His consolidation theory was published in his celebrated book Erdbaumechanik in 1925.

Geotechnical Engineering After 1927

  • Karl Terzaghi (1883-1963)
    • The publication of Erdbaumechanik auf Bodenphysikalisher Grundlage marked a new era in soil mechanics.
    • Considered the Father of Modern Soil Mechanics.
    • Born on October 2, 1883, in Prague.
    • Graduated from Technische Hochschule in Graz, Austria, with a mechanical engineering degree.
    • Served one year in the Austrian army.
    • Studied geological subjects for one year.
    • Received the degree of Doctor of Technical Sciences.
    • Accepted a teaching position at the Imperial School of Engineers in Istanbul.
    • After WWI, accepted a lectureship at the American Robert College in Istanbul.
    • Began research on the behavior of soils and settlement of clays and on failure due to piping in sand under dams.
    • Accepted a visiting lectureship at MIT.
    • Recognized as the leader of the new branch of civil engineering called soil mechanics.
    • Became a professor at the Technical University of Vienna.
    • 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.

End of Era

  • Ralph B. Peck
    • Considered the last of the early giants of geotechnical engineering.
    • Passed away on February 18, 2008, at the age of 95.
    • Born on June 23, 1912.
    • Received BS and PhD degrees in 1934 and 1937 from Rensselaer Polytechnic Institute.
    • Worked as an assistant to Karl Terzaghi.
    • Professor of foundation engineering.