Geotechnical Engineering

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


  The application of the principles of soil mechanics to practical problems
• Soil mechanics


  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
• Soil mechanics is systematized in its modern form by Karl Von Terzaghi, who is regarded as the "Father of Modern Soil Mechanics"
• Terzaghi's definition of soil mechanics

  The application of the laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles produced by the mechanical and chemical disintegration of rocks, regardless of whether or not they contain an admixture of organic constituents
• Rock mechanics


  Concerned with the engineering mechanics and properties of rock, usually but not necessarily the bed rock
• Historical development of geotechnical engineering

  • Dikes dating back to about 2000 B.C. built in the basin of the Indus to protect the town of Mohenjo Dara
  • Dykes built for irrigation purposes during the Chan Dynasty in China (1120 B.C. to 249 B.C.)
  • Ancient Greek civilization used isolated pad footings and strip-and-raft foundations for building structures
  • The five most important pyramids built in Egypt in a period of less than a century (Saqqarah, Meidum, Dahshur South and North, and Cheops)
  • Leaning Tower of Pisa in Italy, a structure that weighs about 15,700 metric tons and is supported by a circular base having a diameter of 20 m, has tilted in the past to the east, north, west and finally to the south, now leaning 5 degrees
  • Garisenda Tower and Asinelli Tower in Bologna, Italy, similar problem like the Leaning Tower of Pisa, built in the 12th century, Garisenda Tower is 48 m in height and weighs about 4210 metric tons, it has tilted about 4 degrees, Asinelli Tower is 97 m high and weighs 7300 metric tons, it has tilted about 1.3 degrees
• Historical developments in soil mechanics and geotechnical engineering

  • In 1717, a French royal engineer, Henri Gautier, studied the natural slopes of soils when tipped in a heap for formulating the design procedures of retaining walls
  • In 1729, Bernard Forest de Belidor proposed a theory for lateral earth pressure on retaining walls that was a follow-up to Gautier's (1717) original study, and specified a soil classification system
  • In 1840, Jean Victor Poncelet 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
  • In 1776, French scientist Charles Augustin Coulomb 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 1856, Henri Philibert Gaspard Darcy published a study on the permeability of sand filters and defined the term coefficient of permeability (or hydraulic conductivity) of soil
  • Sir George Howard Darwin conducted laboratory tests to determine the overturning moment on a hinged wall retaining sand in loose and dense states of compaction
  • In 1887, Osborne Reynolds demonstrated the phenomenon of dilatency in sand
  • Albert Mauritz Atterberg defined clay-size fractions as the percentage by weight of particles smaller than 2 microns in size
• Soil is the relatively loose mass of mineral and organic materials and sediments found above the bedrock, which can be relatively easily broken down into its constituent mineral or organic particles
• Rock can be defined as a compact, semi-hard to hard mass of natural mineral or organic material
• 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
• Darcy (1803–1858) published a study on the permeability of sand filters in 1856 and defined the term coefficient of permeability (or hydraulic conductivity) of soil
• Darwin (1845–1912) conducted laboratory tests to determine the overturning moment on a hinged wall retaining sand in loose and dense states of compaction
• Reynolds (1842–1912) demonstrated the phenomenon of dilatency in sand in 1887
• Atterberg (1846–1916) defined clay-size fractions as the percentage by weight of particles smaller than 2 microns in size
• Soil


  The relatively loose mass of mineral and organic materials and sediments found above the bedrock, which can be relatively easily broken down into its constituent mineral or organic particles
• Rock


  A compact, semi-hard to hard mass of natural material composed of one or more minerals
• Types of rocks based on mode of formation

  • Igneous
  • Sedimentary
  • Metamorphic
• Igneous rocks


  • granite, basalt, dolerite, andesite, gabbro, syenite, porphyry
• Sedimentary rocks


  • limestone, sandstone, mudstone, shale, conglomerate
• Metamorphic rocks


  • marble, quartzite, slate, schist
• Mineral


  A natural inorganic substance of a definite structure and chemical composition
• The specific gravity of most rock and soil forming minerals varies from 2.50 (some feldspars) and 2.65 (quartz) to 3.5 (augite or olivine)
• Gypsum has a smaller value of 2.3 and salt (NaCl) has 2.1
• Some iron minerals may have higher values, for instance, magnetite has 5.2
• Soil formation


  1. Weathering of rocks and minerals

  2. Mechanical weathering

  3. Chemical weathering
• Mechanical weathering


  Breaking down of rocks to smaller particles due to agents like freezing water, temperature changes, abrasion by moving water or glaciers
• Chemical weathering


  Changes in the composition of rocks by decomposing the parent minerals and transforming them into new compounds like clay, silica, carbonates, iron oxides
• Oxidation


  Oxidation of metals like iron to form hydroxides and oxides, giving a reddish-brown coloration and weakening the rock
• Carbonation


  Reaction of rock material with carbon dioxide in the presence of water, affecting limestones
• Hydration


  Rigid attachment of H+ and OH- ions to the atoms and molecules of a mineral, causing physical stresses within the rock
• Leaching


  Washing out of water-soluble salts from the soil by percolating water
• Types of soil based on origin

  • Residual soils
  • Transported soils
• Names of some soils used in practice

  • Marl
  • Hardpan
  • Caliche
  • Peat
  • Loam
  • Loess
• Marl


  A mixture of calcareous sands, clays, or loam
• Hardpan


  A relatively hard, densely cemented soil layer, like rock, that does not soften when wet
• Caliche


  An admixture of clay, sand, and gravel cemented by calcium carbonate deposited from ground water
• Peat


  A fibrous aggregate of finer fragments of decayed vegetable matter, very compressible
• Loam


  A mixture of sand, silt and clay