Geotechnical engineering: Difference between revisions

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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 stabilization, 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 analyze 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.

== Sub-disciplines ==

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==Observational method==

First proposed by [[Karl Terzaghi]] and later discussed in a paper by [[Ralph Brazelton Peck|Ralph B. Peck]], the observational method is a managed process of construction control, monitoring, and review, which enables modifications to be incorporated during and after construction. The method aims 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. 171-187171–187.</ref>

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

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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.

* Ventura, Pierfranco, 2019Ventura, Fondazioni, Volume 1, Modellazioni: staticheVerifiche Statiche e sismicheSismiche Strutture-Terreni, Hoeplivol. 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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