Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials.
It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It also relies on knowledge of geology, hydrology, geophysics, and other related sciences. Geotechnical (rock) engineering is a subdiscipline of geological engineering.
In addition to civil engineering, geotechnical engineering also has applications in military, mining, petroleum, coastal engineering, and offshore construction.
The fields of geotechnical engineering and engineering geology have knowledge areas that overlap. However, while geotechnical engineering is a specialty of civil engineering, engineering geology is a specialty of geology.
They share the same principles of soil mechanics and rock mechanics, but differ in the application.
Humans have historically used soil as a material for flood control, irrigation purposes, burial sites, building foundations, and construction materials for buildings.
Early activities were linked to irrigation and flood control, as demonstrated by traces of dykes, dams, and canals dating back to at least 2000 BCE that were found in ancient Egypt, ancient Mesopotamia, and the Fertile Crescent, as well as around the early settlements of Mohenjo Daro and Harappa in the Indus valley.
As cities expanded, structures were erected and supported by formalized foundations. The ancient Greeks notably constructed pad footings and strip-and-raft foundations. Until the 18th century, however, no theoretical basis for soil design had been developed, and the discipline was more of an art than a science, relying on experience.
Several foundation-related engineering problems, such as the Leaning Tower of Pisa, prompted scientists to begin taking a more scientific-based approach to examining the subsurface.
The earliest advances occurred in the development of earth pressure theories for the construction of retaining walls. Henri Gautier, a French Royal Engineer, recognized the "natural slope" of different soils in 1717, an idea later known as the soil's angle of repose. A rudimentary soil classification system was also developed based on a material's unit weight, which is no longer considered a good indication of soil
The application of the principles of mechanics to soils was documented as early as 1773 when Charles Coulomb (a physicist, engineer, and army captain) developed improved methods to determine the earth pressures against military ramparts.
Coulomb observed that, at failure, a distinct slip plane would form behind a sliding retaining wall and he suggested that the maximum shear stress on the slip plane, for design purposes, was the sum of the soil cohesion and friction tan, where is the normal stress on the slip plane and is the friction angle of the soil.
By combining Coulomb's theory with Christian Otto Mohr's 2D stress state, the theory became known as Mohr-Coulomb theory.
Although it is now recognized that precise determination of cohesion is impossible because is not a fundamental soil property, the Mohr-Coulomb theory is still used in practice today.
In the 19th century, Henry Darcy developed what is now known as Darcy's Law, describing the flow of fluids in a porous media. Joseph Boussinesq (a mathematician and physicist) developed theories of stress distribution in elastic solids that proved useful for estimating stresses at depth in the ground.
William Rankine, an engineer and physicist, developed an alternative to Coulomb's earth pressure theory. Albert Atterberg developed the clay consistency indices that are still used today for soil classification.
In 1885, Osborne Reynolds recognized that shearing causes volumetric dilation of dense materials and contraction of loose granular materials.
Modern geotechnical engineering is said to have begun in 1925 with the publication of Erdbaumechanik by Karl Terzaghi (a mechanical engineer and geologist). Considered by many to be the father of modern soil mechanics and geotechnical engineering, Terzaghi developed the principle of effective stress, and demonstrated that the shear strength of soil is controlled by effective stress.
Terzaghi also developed the framework for theories of bearing capacity of foundations, and the theory for prediction of the rate of settlement of clay layers due to consolidation.
Afterwards, Maurice Biot fully developed the three-dimensional soil consolidation theory, extending the one-dimensional model previously developed by Terzaghi to more general hypotheses and introducing the set of basic equations of Poroelasticity.
In 1960, Alec Skempton carried out an extensive review of the available formulations and experimental data in the literature about the effective stress validity in soil, concrete, and rock in order to reject some of these expressions, as well as clarify what expression was appropriate according to several working hypotheses, such as stress-strain or strength behavior, saturated or non-saturated media, and rock/concrete or soil behavior.
In his 1948 book, Donald Taylor recognized that the interlocking and dilation of densely packed particles contributed to the peak strength of the soil. The interrelationships between the volume change behavior (dilation, contraction, and consolidation) and shearing behavior were all connected via the theory of plasticity using critical state soil mechanics by Roscoe, Schofield, and Wroth with the publication of "On the Yielding of Soils" in 1958.
Critical state soil mechanics is the basis for many contemporary advanced constitutive models describing the behavior of soil.
Geotechnical centrifuge modeling is a method of testing physical scale models of geotechnical problems.
The use of a centrifuge enhances the similarity of the scale model tests involving soil because the strength and stiffness of soil is very sensitive to the confining pressure.
The centrifugal acceleration allows a researcher to obtain large (prototype-scale) stresses in small physical models. Soil mechanics
A phase diagram of soil indicating the weights and volumes of air, soil, water, and voids. Main articles: Soil mechanics and Rock mechanics
In geotechnical engineering, soils are considered a three-phase material composed of rock or mineral particles, water, and air. The voids of soil, the spaces in between mineral particles, contain water and air.
The engineering properties of soils are affected by four main factors: the predominant size of the mineral particles, the type of mineral particles, the grain size distribution, and the relative quantities of minerals, water, and air present in the soil matrix. Fine particles (fines) are defined as particles less than 0.075 mm in diameter.
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