Geotechnical engineering: Difference between revisions

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{{Use American English|date=July 2023}}

{{short description|Scientific study of earth materials in engineering problems}}[[Image:Boston CAT Project-construction view from air.jpeg|thumb|upright=1.15|[[Boston]]'s [[Big Dig]] presented geotechnical challenges in an urban environment.]]

[[File:Precastconcreteretainingwall.tif|thumb|Precast concrete retaining wall]]

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

'''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]] to solve its [[engineering]] problems. It also relies on knowledge of [[geology]], [[hydrology]], [[geophysics]], and other related sciences.

Geotechnical engineering has applications in [[military engineering]], [[mining engineering]], [[petroleum engineering]], [[coastal engineering]], and [[offshore construction]]. The fields of geotechnical engineering and [[engineering geology]] have overlapping knowledge areas. However, while geotechnical engineering is a specialty of [[civil engineering]], engineering geology is a specialty of [[geology]].

==History==

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{{Main|Geotechnical investigation}}

Geotechnical engineers investigate and determinatedetermine the properties of subsurface conditions and materials. They also design corresponding [[Earthworks (engineering)|earthworks]] and [[Retaining wall|retaining structures]], [[tunnel]]s, and structure [[foundation (engineering)|foundations]], and may supervise and evaluate sites, which may further involve site monitoring as well as the risk assessment and mitigation of [[natural hazard]]s.<ref name="TerzaghiPeckMesri">Terzaghi, K., Peck, R.B. and Mesri, G. (1996), ''Soil Mechanics in Engineering Practice'' 3rd Ed., John Wiley & Sons, Inc. {{ISBN|0-471-08658-4}}</ref><ref name="HoltzKovacs">Holtz, R. and Kovacs, W. (1981), ''An Introduction to Geotechnical Engineering'', Prentice-Hall, Inc. {{ISBN|0-13-484394-0}}</ref>

Geotechnical engineers and engineering geologists perform geotechnical investigations to obtain information on the [[Physical property|physical properties]] of soil and rock underlying, and adjacent to, a site to design earthworks and foundations for proposed structures and for the repair of distress to earthworks and structures caused by subsurface conditions. Geotechnical investigations involve both surface and subsurface exploration of a site, often including subsurface sampling and laboratory testing of retrieved soil samples retrieved. Sometimes, [[Exploration geophysics|geophysical methods]] are also used to obtain data, which include measurement of [[seismic waves]] (pressure, shear, and [[Rayleigh waves]]), surface-wave methods and downhole methods, and [[Prospecting|electromagnetic surveys]] (magnetometer, [[Electrical resistivity and conductivity|resistivity]], and [[ground-penetrating radar]]). [[Electrical resistivity tomography|Electrical tomography]] can be used to survey soil and rock properties and existing underground infrastructure in construction projects.<ref>Deep Scan Tech (2023): [https://www.deepscantech.com/news/deep-scan-tech-uncovers-hidden-structures-at-the-site-of-denmarks-tallest-building.html Deep Scan Tech uncovers hidden structures at the site of Denmark's tallest building].</ref>

Surface [[exploration]] can include on-foot surveys, [[geologicgeological map]]ping, [[Exploration geophysics|geophysical methods]], and [[photogrammetry]]. GeologicGeological mapping and interpretation of [[geomorphology]] are typically completed in consultation with a [[geologist]] or [[engineering geologist]]. Subsurface exploration usually involves in-situ testing (for example, the [[standard penetration test]] and [[cone penetration test]]). The digging of test pits and trenching (particularly for locating [[Fault (geology)|faults]] and [[landslide|slide planes]]) may also be used to learn about soil conditions at depth. Large-diameter borings are rarely used due to safety concerns and expense. Still, butthey are sometimes used to allow a geologist or engineer to be lowered into the borehole for direct visual and manual examination of the soil and rock [[stratigraphy]].

A variety ofVarious [[Geotechnical investigation#Soil sampling|soil samplers]] existsexist to meet the needs of different engineering projects. The [[standard penetration test]], which uses a thick-walled split spoon sampler, is the most common way to collect disturbed samples. Piston samplers, employing a thin-walled tube, are most commonly used forto the collection ofcollect less disturbed samples. More advanced methods, such as the Sherbrooke block sampler, are superior, but expensive. Coring frozen ground provides high-quality undisturbed samples from any ground conditions, such as fill, sand, [[moraine]], and rock fracture zones.<ref name="Coring frozen ground">{{cite web | url=https://www.geofrost.no/en/ground-investigations/#Undisturbed%20samples | title=Geofrost Coring | publisher=GEOFROST | access-date=20 November 2020}}</ref>

[[Geotechnical centrifuge modeling]] is another 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 thesoil's strength and [[stiffness]] of soil are very sensitivesusceptible to the confining [[pressure]]. The [[Centrifugal force|centrifugal acceleration]] allows a researcher to obtain large (prototype-scale) stresses in small physical models.

=== Foundation design ===

{{Main|Foundation (engineering)}}

The foundation of a structure's infrastructure transmits loads from the structure to the earth. Geotechnical [[engineer]]s design foundations based on the load characteristics of the structure and the properties of the soils and [[bedrock]] at the site. In generalGenerally, geotechnical engineers first estimate the magnitude and ___location of loads to be supported, before developing an investigation plan to explore the subsurface and also determiningdetermine the necessary soil parameters through field and lab testing. Following whichthis, they may begin the design of an engineering foundation. The primary considerations for a geotechnical engineer in foundation design are [[bearing capacity]], settlement, and ground movement beneath the foundations.<ref name="Han 2015">{{Cite book |last=Han |first=Jie |title=Principles and Practice of Ground Improvement |publisher=Wiley |year=2015 |isbn=9781118421307}}</ref>

=== Earthworks ===

[[Image:Seabees compactor roller.jpg|thumb|A [[compactor]]/[[road roller|roller]] operated by U.S. Navy Seabees]]

{{See also|Earthworks (engineering)}}Geotechnical engineers are also involved in the planning and execution of [[Earthworks (engineering)|earthworks]], which include ground improvement,<ref name="Han 2015" /> slope stabilisationstabilization, and stopeslope stability analysis.

====Ground improvement====

Various geotechnical engineering methods can be used for ground improvement, including reinforcement [[geosynthetics]] such as geocells and geogrids, which disperse loads over a larger area, increasing the soil's load-bearing capacity of soil. Through these methods, geotechnical engineers can reduce direct and long-term costs.<ref>{{cite book | title=Ground Improvement Technologies and Case Histories | publisher=Research Publishing Services | author=RAJU, V. R. | id=Ground Improvement – Principles And Applications In Asia | year=2010 | ___location=Singapore | pages=809 | isbn=978-981-08-3124-0}}</ref>

====Slope stabilization====

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{{Main|Slope stability}}

Geotechnical engineers can analyseanalyze and improve theslope stability of slopes using engineering methods. Slope stability is determined by the balance of [[shear stress]] and [[shear strength (soil)|shear strength]]. A previously stable slope may be initially affected by various factors, making the slopeit unstable. Nonetheless, geotechnical engineers can design and implement engineered slopes to increase stability.

=====Slope stability analysis=====

{{Main|Slope stability analysis}}

Stability analysis is needed for theto design of engineered slopes and for estimatingestimate the risk of slope failure in natural or designed slopes by determining the conditions under which the topmost mass of soil will slip relative to the base of soil and lead to slope failure.<ref>{{cite book|last=Pariseau|first=William G.|title=Design analysis in rock mechanics|year=2011|publisher=CRC Press}}</ref> If the interface between the mass and the base of a slope has a complex geometry, slope stability analysis is difficult and [[Numerical analysis|numerical solution]] methods are required. Typically, the interface's exact geometry of the interface is not knownunknown, and a simplified interface geometry is assumed. Finite slopes require three-dimensional models to be analyzed, so most slopes are analyzed assuming that they are infinitely wide and can be represented by two-dimensional models.

== GeosyntheticsSub-disciplines ==

=== Geosynthetics ===

{{Main|Geosynthetics}}

[[Image:Geocollage.JPG|thumb|upright=1.15|A collage of geosynthetic products.]]

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[[Geosynthetics]] are a type of plastic [[polymer]] products used in geotechnical engineering that improve engineering performance while reducing costs. This includes [[geotextiles]], [[geogrids]], [[geomembranes]], [[geocells]], and [[geocomposites]]. The synthetic nature of the products make them suitable for use in the ground where high levels of durability are required. Their main functions include [[drainage]], [[filtration]], reinforcement, separation, and containment.

Geosynthetics are available in a wide range of forms and materials, each to suit a slightly different end-use, although they are frequently used together. Some reinforcement geosynthetics, such as geogrids and more recently, [[cellular confinement]] systems, have shown to improve bearing capacity, modulus factors and soil stiffness and strength.<ref>Hegde, A.M. and Palsule P.S. (2020), Performance of Geosynthetics Reinforced Subgrade Subjected to Repeated Vehicle Loads: Experimental and Numerical Studies. Front. Built Environ. 6:15. https://www.frontiersin.org/articles/10.3389/fbuil.2020.00015/full.</ref> These products have a wide range of applications and are currently used in many civil and geotechnical engineering applications including roads, airfields, railroads, [[Embankment (earthworks)|embankments]], piled embankments, retaining structures, [[reservoir]]s, canals, dams, [[landfill]]s, bank protection and coastal engineering.<ref>{{Cite book |last=Koerner |first=Robert, M. |title=Designing with Geosynthetics |publisher=Xlibris |year=2012 |isbn=9781462882892 |edition=6th Edition, Vol. 1}}</ref>

=== Offshore ===

{{Main|Offshore geotechnical engineering}}

[[File: Offshore platforms.jpg|thumb|Platforms offshore Mexico.]]

''Offshore'' (or ''marine'') ''geotechnical engineering'' is concerned with foundation design for human-made structures in the [[sea]], away from the [[coast]]line (in opposition to ''onshore'' or ''nearshore'' engineering). [[Oil platform]]s, [[artificial island]]s and [[submarine pipeline]]s are examples of such structures.<ref name="Dean">Dean, E.T.R. (2010). Offshore Geotechnical Engineering – Principles and Practice. Thomas Telford, Reston, VA, 520 p.</ref> [[Oil platform]]s, [[artificial island]]s and [[submarine pipeline]]s are examples of such structures.

There are a number of significant differences between onshore and offshore geotechnical engineering.<ref name="Dean" /><ref name="Randolph&Gourvenec">Randolph, M. and [[Susan Gourvenec|Gourvenec, S.]], 2011. Offshore geotechnical engineering. Spon Press, N.Y., 550 p.</ref> Notably, site investigation and ground improvement (on the seabed) and site investigation are more expensive,; the offshore structures are exposed to a wider range of [[geohazard]]s,; and the environmental and financial consequences are higher in case of failure. Offshore structures are exposed to various environmental loads, notably [[wind]], [[wind wave|wave]]s and [[Ocean current|currents]]. These phenomena may affect the integrity or the serviceability of the structure and its foundation during its operational lifespan – theyand need to be taken into account in offshore design.

In [[subsea]] geotechnical engineering, seabed materials are considered a two-phase material composed of 1) rock or [[mineral]] particles and 2) water.<ref name="Das">Das, B.M., 2010. Principles of geotechnical engineering. Cengage Learning, Stamford, 666 p.</ref><ref name="Atkinson">Atkinson, J., 2007. The mechanics of soils and foundations. Taylor & Francis, N.Y., 442 p.</ref> Structures may be fixed in place in the seabed—as is the case for [[pier]]s, [[jettyjetties]]s and fixed-bottom wind turbines—or maybemay comprise a floating structure that remains roughly fixed relative to its geotechnical anchor point. Undersea mooring of human-engineered floating structures include a large number of [[Offshore drilling rig|offshore oil and gas platforms]] and, since 2008, a few [[floating wind turbine]]s. Two common types of engineered design for anchoring floating structures include [[Tension-leg platform|tension-leg]] and [[catenary]] [[Mooring (watercraft)|loose mooring]] systems.<ref name="Tensionmit200710">

leg mooring systems have vertical tethers under tension providing large restoring [[Moment of inertia|moments]] in pitch and roll. [[Catenary]] mooring systems provide station keeping for an offshore structure, yet provide little stiffness at low tensions."<ref name=mit200710>

[http://web.mit.edu/flowlab/pdf/Floating_Offshore_Wind_Turbines.pdf Floating Offshore Wind Turbines: Responses in a Sea state – Pareto Optimal Designs and Economic Assessment], P. Sclavounos et al., October 2007.</ref>

==Observational method==

InFirst geotechnicalproposed engineering,by during[[Karl theTerzaghi]] constructionand oflater earthdiscussed structuresin (damsa andpaper tunnelsby for[[Ralph example)Brazelton Peck|Ralph B. Peck]], the '''observational method''' is a continuous, managed, and integrated process of design, construction control, monitoring, and review, enablingwhich appropriate, previously-definedenables modifications to be incorporated during (orand after) construction. All these aspects must be demonstrably robust. The objectivemethod isaims to achieve a greater overall economy, without compromising [[safety]] by creating designs based on the most probable conditions rather than the most unfavorable.<ref>Nicholson, D, Tse, C and Penny, C. (1999). The Observational Method in ground engineering – principles and applications. Report 185, CIRIA, London.</ref> Using the observational method, gaps in available information are filled by measurements and investigation, which aid in assessing the behavior of the structure during [[construction]], which in turn can be modified per the findings. The method was described by Peck as "learn-as-you-go".<ref name="peck">Peck, R.B (1969). Advantages and limitations of the observational method in applied soil mechanics, Geotechnique, 19, No. 1, pp. 171–187.</ref>

The observational method may be described as follows:<ref name="peck" />

The observational method was proposed by [[Karl Terzaghi]] and discussed in a paper by [[Ralph Brazelton Peck|Ralph B. Peck]] (1969). This was in an effort to reduce the costs during construction incurred by designing earth structures based on the most-unfavorable assumptions (in other words, geological conditions, soil engineering properties, and so on). Instead, the [[design]] is based on the most-probable conditions rather than the most unfavorable. Gaps in the available information are filled by observations: geotechnical-instrumentation measurements (for example, [[inclinometer]]s and [[piezometer]]s) and geotechnical site investigation (for example, [[borehole]] drilling and a [[Cone penetration test|CPT]]). These observations aid in assessing the behavior of the structure during [[construction]], which can then be modified in accordance with the findings. The method may be described as "learn-as-you-go".<ref name=peck>Peck, R.B (1969). Advantages and limitations of the observational method in applied soil mechanics, Geotechnique, 19, No. 1, pp. 171-187.</ref>

*Exploration# General exploration sufficient to establish the generalrough nature, pattern, and properties of the [[Deposition (geology)|deposits]] (not necessarily in detail).

The observational method may be described as follows:

*#Assessment of the most probable conditions, and the most unfavorable conceivable deviations from these conditions. Geology plays a major role.

*Exploration sufficient to establish the general nature, pattern, and properties of the [[Deposition (geology)|deposits]] (not necessarily in detail).

#Creating the design based on a working hypothesis of behavior anticipated under the most probable conditions.

*Assessment of the most probable conditions, and the most unfavorable conceivable deviations from these conditions. Geology plays a major role.

*Creating#Selection theof design,quantities basedto onbe aobserved workingas hypothesisconstruction ofproceeds behaviorand calculating their anticipated values based on the working hypothesis under the most-probable unfavorable conditions.

*#Selection, (in advance), of a course of action or design modification for every foreseeable significant deviation of the observational findings from those predicted based on the working [[hypothesis]].

*Selection of quantities to be observed as construction proceeds, and calculation of their anticipated values based on the working hypothesis.

*#Measurement of quantities to be observed and evaluation of actual conditions.

*Calculation of values of the same quantities under the most unfavorable conditions compatible with the available data concerning subsurface conditions.

*#Design modification in accordance withper actual conditions

*Selection (in advance) of a course of action or design modification for every foreseeable significant deviation of the observational findings from those predicted based on the working [[hypothesis]].

*Measurement of quantities to be observed and evaluation of actual conditions.

*Design modification in accordance with actual conditions

The observational method is suitable for construction that has already begun when an unexpected development occurs, or when a failure or [[accident]] threatenslooms or has already occurredhappened.<ref name=peck/> The methodIt is not suitableunsuitable for projects whose design cannot be altered during construction.<ref name="peck" />

The most serious blunder in applying the observational method is failing to select (in advance) an appropriate course of action for all foreseeable deviations (disclosed by observation) from those assumed in the design. The engineer must devise solutions to all problems which could arise under the least favorable conditions. If he or she cannot solve these hypothetical problems (even if the probability of their occurrence is very low), he or she must revert to a design based on the least-favorable conditions.<ref name=peck/>

== See also ==

{{Portal inline|Engineering}}

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* [[Civil engineering]]

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* [[Land reclamation]]

* [[Landfill]]

* [[List of publications in geology#Geotechnical engineering|List of publications in geotechnical engineering]]

* [[Mechanically stabilized earth]]

* [[Offshore geotechnical engineering]]

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* [[Soil science]]

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==Notes==

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* Bates and Jackson, 1980, Glossary of Geology: American Geological Institute.

* Krynine and Judd, 1957, Principles of Engineering Geology and Geotechnics: McGraw-Hill, New York.

* Pierfranco Ventura, Fondazioni, Modellazioni: Verifiche Statiche e Sismiche Strutture-Terreni, vol. I, Milano Hoepli, 2019, pp.770, ISBN 978-88203-8644-3

* Pierfranco Ventura, Fondazioni, Applicazioni: Verifiche Statiche e Sismiche Strutture-Terreni, vol. II, , Milano, Hoepli, 2019, pp.749,ISBN 978-88-203-8645-0 https://www.hoeplieditore.it/hoepli-catalogo/articolo/fondazioni-modellazioni-pierfrancventura/9788820386443/1451

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*[http://www.swedgeo.se/templates/SGIStandardPage____184.aspx?epslanguage=EN Worldwide Geotechnical Literature Database]

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