Geotechnical engineering: Difference between revisions

Revision as of 14:06, 7 April 2023

Revision as of 00:56, 13 June 2023

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

== Soil mechanics ==

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{{Main|Soil mechanics}}

Some of the important properties of soils that are used by geotechnical engineers to analyze site conditions and design earthworks, retaining structures, and foundations are:<ref name=HoltzKovacs/>

; [[Specific weight|Specific weight or Unit Weight]]: The cumulative weight of the solid particles, water, and air of the unit volume of soil. Note that the air phase is often assumed to be weightless.

; [[Porosity]]: The ratio of the volume of voids (containing air, water, or other fluids) in the soil to the total volume of the soil. Porosity is mathematically related to void ratio as shown below<ref name="nptel_Void">{{cite web | url=http://nptel.ac.in/courses/105103097/web/chap2final/s3.htm | title=Void Ratio | publisher=NPTEL | access-date=24 August 2015}}</ref>

<math>

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; [[Compressibility]]: The rate of change of volume with effective stress. If the pores are filled with water, then the water must be squeezed out of the pores to allow volumetric compression of the soil; this process is called consolidation.

; [[Shear strength (soil)|Shear strength]]: The maximum [[shear stress]] that can be applied in a soil mass without causing shear failure.<ref name="nptel_S">{{cite web | url=http://nptel.ac.in/courses/105103097/web/chap9final/s1.htm | title=Shear strength | publisher=NPTEL | access-date=24 August 2015}}</ref>

; [[Atterberg Limits]]: [[Atterberg limits#Liquid limit|Liquid limit]], [[Atterberg limits#Plastic limit|Plastic limit]], and [[Atterberg limits#Shrinkage limit|Shrinkage limit]]. These indices are used for the estimation of other engineering properties and for [[soil classification]].

== Geotechnical investigation ==

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The tasks of a geotechnical engineer include the following: the investigation of subsurface conditions 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]].

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>

[[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.

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# Medium / Heavy-duty percussion [[drilling]] winches.

# Heavy-duty rotary diamond core drill machine.

# Light -duty geo machine.

# Manual [[winch]]es with tripod.

# Dynamic cone penetration test machine.