Geotechnical engineering: Difference between revisions

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[[File:slope 2d plain.svg|thumb|A typical cross-section of a slope used in two-dimensional analyses.]]

'''Geotechnical engineering''', also known as '''geotechnics''', is the branch of [[civil engineering]] concerned with the engineering behavior of [[earth materials]]. It uses the principles of [[soil mechanics]] and [[rock mechanics]] forto the solution ofsolve its respective [[engineering]] problems. It also relies on knowledge of [[geology]], [[hydrology]], [[geophysics]], and other related sciences. Geotechnical (rock) engineering is a subdiscipline of [[civil engineering]].

In addition to [[civilGeotechnical engineering]], geotechnical engineering also has applications in [[military engineer|militaryengineering]], [[mining engineering|mining]], [[petroleum engineering|petroleum]], [[coastal engineering]], and [[offshore construction]]. The fields of geotechnical engineering and [[engineering geology]] have overlapping 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.

==History==

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 dykesDykes, [[dam]]s, and [[canal]]s dating back to at least 2000 BCEBCE—found thatin wereparts found inof ancient [[Egypt]], ancient [[Mesopotamia]], and the [[Fertile Crescent]], as well as aroundand the early settlements of [[Mohenjo-daro|Mohenjo Daro]] and Harappa in the [[Indus valley]]—provide evidence for early activities linked to [[irrigation]] and [[flood control]]. 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.<ref name=das>{{cite book | last = Das | first = Braja | title = Principles of Geotechnical Engineering | publisher = Thomson Learning | year = 2006}}</ref>

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 [[lateral earth pressure|earth pressure]] theories for the construction of [[retaining walls]]. Henri Gautier, a French Royalroyal Engineerengineer, recognized the "natural slope" of different soils in 1717, an idea later known as the soil's [[angle of repose]]. AAround the same time, 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 type.<ref name=das/><ref name=budhu>{{cite book | last = Budhu | first = Muni | title = Soil Mechanics and Foundations | publisher = John Wiley & Sons, Inc | year = 2007 | isbn = 978-0-471-43117-6}}</ref>

The application of the principles of [[mechanics]] to soils was documented as early as 1773 when [[Charles-Augustin de Coulomb|Charles Coulomb]], a physicist, engineer, and army captainengineer, 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, <math>c</math>, and friction <math>\sigma\,\!</math> <math> \tan(\phi\,\!)</math>, where <math>\sigma\,\!</math> is the normal stress on the slip plane and <math>\phi\,\!</math> is the friction angle of the soil. By combining Coulomb's theory with [[Christian Otto Mohr]]'s [[Mohr's circle|2D stress state]], the theory became known as [[Mohr-Coulomb theory]]. Although it is now recognized that precise determination of cohesion is impossible because <math>c</math> is not a fundamental soil property, the Mohr-Coulomb theory is still used in practice today.<ref name="schofield">Disturbed soil properties and geotechnical design, Schofield, Andrew N., Thomas Telford, 2006. {{ISBN|0-7277-2982-9}}</ref> 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 medium|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 [[Atterberg limits|clay consistency]] indices that are still used today for soil classification.<ref name=das/><ref name=budhu/> In 1885, [[Osborne Reynolds]] recognized that shearing causes volumetric dilation of dense materials and contraction of loose [[granular material]]s.

Modern geotechnical engineering is said to have begun in 1925 with the publication of ''Erdbaumechanik'' by [[Karl Terzaghi|Karl von Terzaghi]], a mechanical engineer and geologist. Considered by many to be the father of modern soil mechanics and geotechnical engineering, [[Karl von Terzaghi|Terzaghi]] developed the principle of effective [[Stress (mechanics)|stress]], and demonstrated that the [[Shear strength (soil)|shear strength]] of soil is controlled by effective stress.<ref>{{cite journal |last1=Guerriero V. |first1=Mazzoli S. |title=Theory of Effective Stress in Soil and Rock and Implications for Fracturing Processes: A Review |journal=Geosciences |date=2021 |volume=11 |issue=3 |page=119 |doi=10.3390/geosciences11030119|bibcode=2021Geosc..11..119G |doi-access=free }}</ref> 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 (soil)|consolidation]].<ref name=das/><ref name=schofield/><ref name="Lambe and Whitman">Soil Mechanics, Lambe, T.William and Whitman, Robert V., Massachusetts Institute of Technology, John Wiley & Sons., 1969. {{ISBN|0-471-51192-7}}</ref> 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 his 1948 book, Donald Taylor recognized that the interlocking and dilation of densely packed particles contributed to the peak strength of the soil. Roscoe, Schofield, and Wroth, with the publication of ''On the Yielding of Soils'' in 1958, established the interrelationships between the volume change behavior (dilation, contraction, and consolidation) and shearing behavior with the theory of [[plasticity (physics)|plasticity]] using critical state soil mechanics. [[Critical state soil mechanics]] is the basis for many contemporary advanced [[constitutive model]]s describing the behavior of soil.<ref name="Wood">Soil Behavior and Critical State Soil Mechanics, Wood, David Muir, Cambridge University Press, 1990. {{ISBN|0-521-33782-8}}</ref>

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 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 expressionexpressions waswere 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.

Roscoe, Schofield, and Wroth, with the publication of ''On the Yielding of Soils'' in 1958, established the interrelationships between the volume change behavior (dilation, contraction, and consolidation) and shearing behavior with the theory of [[plasticity (physics)|plasticity]] using critical state soil mechanics. [[Critical state soil mechanics]] is the basis for many contemporary advanced [[constitutive model]]s describing the behavior of soil.<ref name="Wood">Soil Behavior and Critical State Soil Mechanics, Wood, David Muir, Cambridge University Press, 1990. {{ISBN|0-521-33782-8}}</ref>

[[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 are very sensitive to the confining [[pressure]]. The [[Centrifugal force|centrifugal acceleration]] allows a researcher to obtain large (prototype-scale) stresses in small physical models.

== Geotechnical investigation ==

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[[Exploration geophysics|Geophysical exploration]] is also sometimes used. Geophysical techniques used for subsurface exploration include measurement of [[seismic waves]] (pressure, shear, and [[Rayleigh waves]]), surface-wave methods and/or downhole methods, and [[Prospecting|electromagnetic surveys]] (magnetometer, [[Electrical resistivity and conductivity|resistivity]], and [[ground-penetrating radar]]).

[[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 are very sensitive to the confining [[pressure]]. The [[Centrifugal force|centrifugal acceleration]] allows a researcher to obtain large (prototype-scale) stresses in small physical models.

== Foundations ==