Geotechnical engineering: Difference between revisions

Revision as of 20:05, 28 March 2023

Revision as of 08:44, 1 April 2023

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== Geotechnical investigation ==

{{Main|Geotechnical investigation}}

The tasks of a geotechnical engineer comprise the investigation of subsurface conditionssubsurf and materials; the determination of the relevant physical, mechanical, and chemical properties of these materials; the design of [[Earthworks (engineering)|earthworks]] and retaining structures (including [[dam]]s, [[Embankment (transportation)|embankments]], sanitary landfills, deposits of [[hazardous waste]]), [[tunnel]]s, and structure [[foundation (engineering)|foundations]]; the monitoring of site conditions, earthwork, and foundation construction; the evaluation of the [[Slope stability|stability of natural slopes]] and man-made soil deposits; the assessment of the risks posed by site conditions; and the prediction, prevention, and mitigation of damage caused by [[natural hazard]]s (such as [[avalanche]]s, [[mud flow]]s, [[landslide]]s, [[rockslide]]s, [[sinkhole]]s, and [[volcanic eruptions]]).<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 sometimes 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. A geotechnical investigation will include surface exploration and subsurface exploration of a site. Sometimes, [[Exploration geophysics|geophysical methods]] are used to obtain data about sites. Subsurface exploration usually involves in-situ testing (two common examples of in-situ tests are the [[standard penetration test]] and [[cone penetration test]]). In addition site investigation will often include subsurface sampling and laboratory testing of the soil samples retrieved. 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, but 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]].noyhi

A variety of [[Geotechnical investigation#Soil sampling|soil samplers]] exists to meet the needs of different engineering projects. The [[standard penetration test]] (SPT), 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 for the collection of less disturbed samples. More advanced methods, such as the Sherbrooke block sampler, are superior, but even more 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>

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[[Atterberg limits]] tests, [[water content]] measurements, and [[Grain (unit)|grain]] size analysis, for example, may be performed on disturbed samples obtained from thick-walled [[Geotechnical investigation#Soil sampling|soil samplers]]. Properties such as shear strength, stiffness, [[hydraulic conductivity]], and coefficient of [[Consolidation (soil)|consolidation]] may be significantly altered by sample disturbance. To measure these properties in the laboratory, high-quality sampling is required. Common tests to measure strength and stiffness include the [[Triaxial shear tests|triaxial shear]] and unconfined compression test. These can all be done through a third party testing company such as [https://www.intertek.com/building/geotechnical-engineering/ Intertek].

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Surface [[exploration]] can include [[geologic map]]ping, [[Exploration geophysics|geophysical methods]], and [[photogrammetry]]; or it can be as simple as an engineer walking around to observe the physical conditions at the site. Geologic mapping and interpretation of [[geomorphology]] are typically completed in consultation with a [[geologist]] or [[engineering geologist]].

[[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]]).