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| | == それが機能し、あなたはそれ == |
| [[Image:Boston CAT Project-construction view from air.jpeg|thumb|right|200px|[[Boston]]'s [[Big Dig (Boston, Massachusetts)|Big Dig]] presented geotechnical challenges in an urban environment.]]
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| '''Geotechnical engineering''' is the branch of [[civil engineering]] concerned with the engineering behavior of [[earth materials]]. Geotechnical engineering is important in [[civil engineering]], but is also used by [[military engineer|military]], [[mining engineering|mining]], [[petroleum engineering|petroleum]], or any other engineering concerned with construction on or in the ground. Geotechnical engineering usually uses principles of [[soil mechanics]] and [[rock mechanics]] to investigate subsurface conditions and materials; determine the relevant physical/mechanical and chemical properties of these materials; evaluate [[Slope stability|stability of natural slopes]] and man-made soil deposits; assess risks posed by site conditions; design [[Earthworks (engineering)|earthworks]] and structure [[foundation (engineering)|foundations]]; and monitor site conditions, earthwork and foundation construction.<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>
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| A typical geotechnical engineering project begins with a review of project needs to define the required material properties. Then follows a site investigation of [[soil]], rock, fault distribution and [[bedrock]] properties on and below an area of interest to determine their engineering properties including how they will interact with, on or in a proposed [[construction]]. Site investigations are needed to gain an understanding of the area in or on which the engineering will take place. Investigations can include the assessment of the risk to humans, property and the environment from natural hazards such as [[earthquakes]], [[landslides]], [[sinkholes]], [[soil liquefaction]], [[debris flow]]s and [[rockfall]]s.
| | 「約束のディレクターを邪魔する方法を調整するのではない当分のための副所長オフ、または仕事？ [http://www.dmwai.com/webalizer/kate-spade-3.html 財布 kate spade] '：道路<br>「簡単にそれを取る、何のミッション、難しさ、それはあなたが恐れてミッションが存在せず、ゆっくりとあなたを見つける：副所長は、警察官が、これは植物に練習し许平秋行うには何を持っているかわからない、彼は徐Pingqiuを見て、徐Pingqiuは微笑んで言ったオフ<br>それが機能し、あなたはそれ。の外出のためにじっと座ってする必要があります。 [http://www.dmwai.com/webalizer/kate-spade-1.html ケイトスペード 財布 店舗] '<br>仕事の<br>ハンドオーバは、唯一のような足のような2つのチェック、ガードの内側から外にわずか10分で同行にロードされた衣服の小さな袋を言及する寮で、この場所では犯罪よりも個以上の月を過ごしており、今彼は、拷問が実際に蹴っていないが、1日8時間、気密集会室でロックされ、アルコールを飲むではなく、喫煙をし、ゴシップしないように許可されていませんが、またさりげなく呼び出すことはできません、ほとんどの、拷問が何であるかを知っている拷問、フィールド全体面積は時折、男性、ワイヤ·スパロウに落ち、彼は深く懐疑的、異性愛を見ていない [http://www.dmwai.com/webalizer/kate-spade-8.html 財布 ケイトスペード]。<br>これに耐えることができるhuanhangrn、自然が再生するために家を出るしようとしている、または都市にされ、彼は、彼は追い出されていたほとんどを知っていた |
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| Ground Improvement refers to a technique that improves the engineering properties of the soil mass treated. Usually, the properties that are modified are shear strength, stiffness and permeability. Ground improvement has developed into a sophisticated tool to support foundations for a wide variety of structures. Properly applied, i.e. after giving due consideration to the nature of the ground being improved and the type and sensitivity of the structures being built, ground improvement often reduces direct costs and saves time.<ref>{{cite book | title=Ground Improvement Technologies and Case Histories | publisher=Research Publishing Services | author=RAJU, V. R. | authorlink=Ground Improvement — Principles And Applications In Asia | year=2010 | location=Singapore | pages=809 | isbn=978-981-08-3124-0}}</ref>
| | == お互いに耳の後 == |
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| A geotechnical engineer then determines and designs the type of foundations, earthworks, and/or pavement subgrades required for the intended man-made structures to be built. Foundations are designed and constructed for structures of various sizes such as high-rise buildings, [[bridge]]s, medium to large commercial buildings, and smaller structures where the soil conditions do not allow code-based design.
| | 私たちの新しいポイントにはるかに。 [http://www.dmwai.com/webalizer/kate-spade-11.html ケイトスペードのバッグ] 「私は罪Coushangが来た。<br>「あなたがドロップすることができ、ボスにまあ、......有望な未来を。 [http://www.dmwai.com/webalizer/kate-spade-6.html ケイトスペード 財布 セール] '<br>馬の所有者は、二人の男の肩を叩いて、それぞれが賞を示すためにタバコを作った [http://www.dmwai.com/webalizer/kate-spade-11.html kate spade マザーズバッグ]。<br>お互いに耳の後<br>煙は、二人の男が颯爽と進み出た、とうなずき：「ボスをお願いします。 [http://www.dmwai.com/webalizer/kate-spade-2.html ケイトスペード 財布 新作] '<br>これは、新聞や雑誌を読んで、あなたはお茶を飲むことができ、ラウンジにゲストを喜ばせるためにあるhuanhangrn、人々は1が、ここに行く車の中で行く、洗浄、色に加えて、洗浄、ワックス、デュオは発汗してくださいカーン、ドアにフル10分、など光沢のある車、誤って罪とマウスルックに渡ってちらっと男、両方乱暴にお世辞の安い笑いで、彼はまた、約笑いを面白がった、見て二つの大きなショートパンツ、サンダル、生きるための裸の上半身の疲れ発汗、容易に200ドル紙幣を掘る、二つのねじれを意味し、私は罪と人はマウスを得た。<br><br>「ヨーヨーヨーヨー......陰上司は、それは......できない [http://www.dmwai.com/webalizer/kate-spade-12.html ケイトスペード 財布 値段] '馬主神経質、駆け上がった、ヒントはより多くのお金を払って洗車よりも、正当化することはできない。<br><br>「光 |
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| Foundations built for above-ground structures include shallow and deep foundations. Retaining structures include earth-filled [[dams]] and retaining walls. Earthworks include [[Embankment (transportation)|embankments]], [[tunnel]]s, [[levee|dikes and levees]], [[Channel (geography)|channels]], [[reservoir]]s, deposition of [[hazardous waste]] and sanitary [[landfills]].
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| Geotechnical engineering is also related to [[coastal engineering|coastal]] and [[Offshore construction|ocean engineering]]. Coastal engineering can involve the design and construction of [[wharves]], [[marina]]s, and [[jetties]]. Ocean engineering can involve foundation and anchor systems for [[offshore construction|offshore structures]] such as [[oil platforms]].
| | <li>[http://www.nobuzushi.com/freecgi/treebbs.cgi http://www.nobuzushi.com/freecgi/treebbs.cgi]</li> |
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| The fields of geotechnical engineering and [[engineering geology]] are closely related, and have large areas of overlap. However, the field of geotechnical engineering is a specialty of [[engineering]], where the field of engineering geology is a specialty of [[geology]].
| | <li>[http://www.cdilovegym.cn/plus/feedback.php?aid=274 http://www.cdilovegym.cn/plus/feedback.php?aid=274]</li> |
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| ==History==
| | <li>[http://www.auto-s.co.jp/cgi/t2bbs.cgi http://www.auto-s.co.jp/cgi/t2bbs.cgi]</li> |
| Humans have historically used soil as a material for flood control, irrigation purposes, burial sites, building foundations, and as construction material for buildings. First activities were linked to irrigation and flood control, as demonstrated by traces of dykes, dams, and canals dating back to at least 2000 BCE that were found in ancient [[Egypt]], ancient [[Mesopotamia]] and the [[Fertile Crescent]], as well as around the early settlements of [[Mohenjo Daro]] and Harappa in the [[Indus valley]]. As the cities expanded, structures were erected supported by formalized foundations; [[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 past experience.<ref name=das>{{cite book | last = Das | first = Braja | title = Principles of Geotechnical Engineering | publisher = Thomson Learning | year = 2006}}</ref>
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| 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 Royal Engineer, recognized the "natural slope" of different soils in 1717, an idea later known as the soil's [[angle of repose]]. 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>
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| 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 Captain) 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,<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.
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| In the 19th century [[Henry Darcy]] developed what is now known as [[Darcy's Law]] describing the flow of fluids in 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/> [[Osborne Reynolds]] recognized in 1885 that shearing causes volumetric dilation of dense and contraction of loose granular materials.
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| Modern geotechnical engineering is said to have begun in 1925 with the publication of ''Erdbaumechanik'' by [[Karl Terzaghi]] (a mechanical engineer and geologist). Considered by many to be the father of modern soil mechanics and geotechnical engineering, Terzaghi developed the principle of effective stress, and demonstrated that the shear strength of soil is controlled by effective stress. 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> In his 1948 book, Donald Taylor recognized that interlocking and dilation of densely packed particles contributed to the peak strength of a soil. The interrelationships between volume change behavior (dilation, contraction, and consolidation) and shearing behavior were all connected via the theory of [[plasticity (physics)|plasticity]] using [[critical state soil mechanics]] by Roscoe, Schofield, and Wroth with the publication of "On the Yielding of Soils" in 1958. [[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>
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| [[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 is very sensitive to the confining pressure. The centrifugal acceleration allows a researcher to obtain large (prototype-scale) stresses in small physical models.
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| ==Practicing engineers==
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| Geotechnical engineers are typically graduates of a four-year civil engineering program and often hold a [[masters degree]]. In the USA, geotechnical engineers are typically licensed and regulated as Professional Engineers (PEs) in most states; currently only [[California]] and [[Oregon]] have licensed geotechnical engineering specialties. State governments will typically license engineers who have graduated from an [[ABET]] accredited school, passed the [http://www.ncees.org/Exams/FE_exam.php Fundamentals of Engineering] examination, completed several years of work experience under the supervision of a licensed Professional Engineer, and passed the [[Professional Engineering]] examination.<ref>{{cite web |url=http://www.ncees.org/licensure/licensure_for_engineers/#how |title=Licensure for Engineers |accessdate=2006-12-11}}</ref>
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| == Soil mechanics ==
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| [[File:Soil-phase-diagram.svg|thumb|A phase diagram of soil indicating the weights and volumes of air, soil, water, and voids.]]
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| {{Main|Soil mechanics|Rock mechanics}}
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| In geotechnical engineering, soils are considered a three-phase material composed of: rock or [[mineral]] particles, water and air. The voids of a soil, the spaces in between mineral particles, contain the water and air.
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| The engineering properties of soils are affected by four main factors: the predominant size of the mineral particles, the type of mineral particles, the grain size distribution, and the relative quantities of mineral, water and air present in the soil matrix. Fine particles (fines) are defined as particles less than 0.075 mm in diameter.
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| ===Soil properties===
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| {{Main|Soil mechanics}}
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| 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/>
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| ; [[Specific weight|Unit Weight]]: Total unit weight: Cumulative weight of the solid particles, water and air in the material per unit volume. Note that the air phase is often assumed to be weightless.
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| ; [[Porosity]]: Ratio of the volume of voids (containing air, water, or other fluids) in a soil to the total volume of the soil. A porosity of 0 implies that there are no voids in the soil.
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| ; [[Void ratio]]: is the ratio of the volume of voids to the volume of solid particles in a soil. Void ratio is mathematically related to the porosity.
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| ; [[Permeability (fluid)|Permeability]]: A measure of the ability of water to flow through the soil, expressed in units of velocity.
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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.
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| ; [[Shear strength (soil)|Shear strength]]: The [[shear stress]] that will cause shear failure.
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| ; [[Atterberg Limits]]: [[Liquid limit]], [[plastic limit]], and shrinkage limit. These indices are used for estimation of other engineering properties and for [[soil classification]].
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| == Geotechnical investigation ==
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| {{Unreferenced section|date=September 2010}}
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| {{Main|Geotechnical investigation}}
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| Geotechnical engineers perform geotechnical investigations to obtain information on the physical properties of soil and rock underlying (and sometimes adjacent to) a site to design earthworks and foundations for proposed structures, and for 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.
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| A variety of [[Geotechnical investigation#Soil sampling|soil samplers]] exist 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 ground freezing and the Sherbrooke block sampler, are superior, but even more expensive.
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| [[Atterberg limits]] tests, [[water content]] measurements, and 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 the strength and stiffness include the [[Triaxial shear tests|triaxial shear]] and unconfined compression test.
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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 is typically completed in consultation with a [[geologist]] or [[engineering geologist]].
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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 electromagnetic surveys (magnetometer, resistivity, and [[ground-penetrating radar]]).
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| == Foundations ==
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| {{Unreferenced section|date=September 2010}}
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| {{Main|Foundation (engineering)}}
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| A building's foundation transmits loads from buildings and other structures to the earth. Geotechnical engineers design foundations based on the load characteristics of the structure and the properties of the soils and/or bedrock at the site. In general, geotechnical engineers:
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| # Estimate the magnitude and location of the loads to be supported;
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| # Develop an investigation plan to [[geotechnical investigation|explore the subsurface]];
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| # Determine necessary soil parameters through field and lab testing (e.g., [[consolidation (soil)|consolidation test]], [[triaxial shear test]], vane shear test, [[standard penetration test]]);
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| # Design the foundation in the safest and most economical manner.
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| The primary considerations for foundation support are [[bearing capacity]], settlement, and ground movement beneath the foundations. Bearing capacity is the ability of the site soils to support the loads imposed by buildings or structures. Settlement occurs under all foundations in all soil conditions, though lightly loaded structures or rock sites may experience negligible settlements. For heavier structures or softer sites, both overall settlement relative to unbuilt areas or neighboring buildings, and differential settlement under a single structure, can be concerns. Of particular concern is settlement which occurs over time, as immediate settlement can usually be compensated for during construction. Ground movement beneath a structure's foundations can occur due to shrinkage or swell of expansive soils due to climatic changes, frost expansion of soil, melting of permafrost, slope instability, or other causes.{{Citation needed|date=March 2011}} All these factors must be considered during design of foundations.
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| Many building codes specify basic foundation design parameters for simple conditions, frequently varying by jurisdiction, but such design techniques are normally limited to certain types of construction and certain types of sites, and are frequently very conservative.{{Citation needed|date=March 2011}}
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| In areas of shallow bedrock, most foundations may bear directly on bedrock; in other areas, the soil may provide sufficient strength for the support of structures. In areas of deeper bedrock with soft overlying soils, deep foundations are used to support structures directly on the bedrock; in areas where bedrock is not economically available, stiff "bearing layers" are used to support deep foundations instead.
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| ===Shallow foundations===
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| {{Unreferenced section|date=September 2010}}
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| {{Main|Shallow foundation}}
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| [[Image:Slab on grade.JPG|thumb|right|Example of a slab-on-grade foundation.]]
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| Shallow foundations are a type of foundation that transfers building load to the very near the surface, rather than to a subsurface layer. Shallow foundations typically have a depth to width ratio of less than 1.
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| ====Footings====
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| Footings (often called "spread footings" because they spread the load) are structural elements which transfer structure loads to the ground by direct areal contact. Footings can be isolated footings for point or column loads, or strip footings for wall or other long (line) loads. Footings are normally constructed from [[reinforced concrete]] cast directly onto the soil, and are typically embedded into the ground to penetrate through the zone of frost movement and/or to obtain additional bearing capacity.
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| ====Slab foundations====
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| A variant on spread footings is to have the entire structure bear on a single slab of concrete underlying the entire area of the structure. Slabs must be thick enough to provide sufficient rigidity to spread the bearing loads somewhat uniformly, and to minimize differential settlement across the foundation. In some cases, flexure is allowed and the building is constructed to tolerate small movements of the foundation instead. For small structures, like single-family houses, the slab may be less than 300 mm thick; for larger structures, the foundation slab may be several meters thick.
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| Slab foundations can be either [[slab-on-grade foundation]]s or embedded foundations, typically in buildings with basements. Slab-on-grade foundations must be designed to allow for potential ground movement due to changing soil conditions.
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| ===Deep foundations===
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| {{Unreferenced section|date=September 2010}}
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| [[Image:PileDriving.jpg|thumb|right|150px|[[Pile driver|Piledriving]] for a bridge in [[Napa, California]].]]
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| {{Main|Deep foundations}}
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| Deep foundations are used for structures or heavy loads when shallow foundations cannot provide adequate capacity, due to size and structural limitations. They may also be used to transfer building loads past weak or compressible soil layers. While shallow foundations rely solely on the [[bearing capacity]] of the soil beneath them, deep foundations can rely on end bearing resistance, frictional resistance along their length, or both in developing the required capacity. Geotechnical engineers use specialized tools, such as the [[cone penetration test]], to estimate the amount of skin and end bearing resistance available in the subsurface.
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| There are many types of deep foundations including [[Deep foundation|piles]], drilled shafts, [[caisson (engineering)|caissons]], piers, and earth stabilized columns. Large buildings such as [[skyscraper]]s typically require deep foundations. For example, the [[Jin Mao Tower]] in [[China]] uses tubular steel piles about 1m (3.3 feet) driven to a depth of 83.5m (274 feet) to support its weight.
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| In buildings that are constructed and found to undergo settlement, [[underpinning]] piles can be used to stabilise the existing building.{{Citation needed|date=March 2011}}
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| There are three ways to place piles for a deep foundation. They can be driven, drilled, or installed by use of an auger. Driven piles are extended to their necessary depths with the application of external energy in the same way a nail is hammered. There are four typical hammers used to drive such piles: drop hammers, diesel hammers, hydraulic hammers, and air hammers. Drop hammers simply drop a heavy weight onto the pile to drive it, while diesel hammers use a single cylinder diesel engine to force piles through the Earth. Similarly, hydraulic and air hammers supply energy to piles through hydraulic and air forces. Energy imparted from a hammer head varies with type of hammer chosen, and can be as high as a million foot pounds for large scale diesel hammers, a very common hammer head used in practice. Piles are made of a variety of material including steel, timber, and concrete. Drilled piles are created by first drilling a hole to the appropriate depth, and filling it with concrete. Drilled piles can typically carry more load than driven piles, simply due to a larger diameter pile. The auger method of pile installation is similar to drilled pile installation, but concrete is pumped into the hole as the auger is being removed.<ref name="Coduto, et al 2011">{{cite book|last=Coduto, et al|first=Donald|title=Geotechnical Engineering Principles and Practices|year=2011|publisher=Pearson Higher Education|location=New Jersey|isbn=9780132368681}}</ref>
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| == Lateral earth support structures ==
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| {{Unreferenced section|date=September 2010}}
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| {{Main|Retaining wall}}
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| A retaining wall is a structure that holds back earth. Retaining walls stabilize soil and rock from downslope movement or erosion and provide support for vertical or near-vertical grade changes. Cofferdams and bulkheads, structures to hold back water, are sometimes also considered retaining walls.
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| The primary geotechnical concern in design and installation of retaining walls is that the retained material is attempting to move forward and downslope due to gravity. This creates [[lateral earth pressure theory|soil pressure]] behind the wall, which can be analysed based on the angle of internal friction (φ) and the cohesive strength (c) of the material and the amount of allowable movement of the wall. This pressure is smallest at the top and increases toward the bottom in a manner similar to hydraulic pressure, and tends to push the wall forward and overturn it. [[Groundwater]] behind the wall that is not dissipated by a drainage system causes an additional horizontal hydraulic pressure on the wall.
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| ===Gravity Walls===
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| Gravity walls depend on the size and weight of the wall mass to resist pressures from behind. Gravity walls will often have a slight setback, or batter, to improve wall stability. For short, landscaping walls, gravity walls made from dry-stacked (mortarless) stone or segmental concrete units (masonry units) are commonly used.
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| Earlier in the 20th century, taller retaining walls were often gravity walls made from large masses of concrete or stone. Today, taller retaining walls are increasingly built as composite gravity walls such as: geosynthetic or steel-reinforced backfill soil with precast facing; gabions (stacked steel wire baskets filled with rocks), crib walls (cells built up log cabin style from precast concrete or timber and filled with soil or free draining gravel) or soil-nailed walls (soil reinforced in place with steel and concrete rods).
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| For '''reinforced-soil gravity walls''', the soil reinforcement is placed in horizontal layers throughout the height of the wall. Commonly, the soil reinforcement is '''geogrid''', a high-strength polymer mesh, that provide tensile strength to hold soil together. The wall face is often of precast, segmental concrete units that can tolerate some differential movement. The reinforced soil's mass, along with the facing, becomes the gravity wall. The reinforced mass must be built large enough to retain the pressures from the soil behind it. Gravity walls usually must be a minimum of 30 to 40 percent as deep (thick) as the height of the wall, and may have to be larger if there is a slope or surcharge on the wall.
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| ===Cantilever walls===
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| Prior to the introduction of modern reinforced-soil gravity walls, cantilevered walls were the most common type of taller retaining wall. Cantilevered walls are made from a relatively thin stem of steel-reinforced, cast-in-place concrete or mortared masonry (often in the shape of an inverted T). These walls cantilever loads (like a beam) to a large, structural footing; converting horizontal pressures from behind the wall to vertical pressures on the ground below. Sometimes cantilevered walls are buttressed on the front, or include a counterfort on the back, to improve their stability against high loads. Buttresses are short [[wing wall]]s at right angles to the main trend of the wall. These walls require rigid concrete footings below seasonal frost depth. This type of wall uses much less material than a traditional gravity wall.
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| Cantilever walls resist lateral pressures by friction at the base of the wall and/or '''passive earth pressure''', the tendency of the soil to resist lateral movement.
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| Basements are a form of cantilever walls, but the forces on the basement walls are greater than on conventional walls because the basement wall is not free to move.
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| ===Excavation shoring===
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| {{Unreferenced section|date=September 2010}}
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| Shoring of temporary excavations frequently requires a wall design which does not extend laterally beyond the wall, so shoring extends below the planned base of the excavation. Common methods of shoring are the use of '''sheet piles''' or '''soldier beams and lagging'''. Sheet piles are a form of driven piling using thin interlocking sheets of steel to obtain a continuous barrier in the ground, and are driven prior to excavation. Soldier beams are constructed of wide flange steel H sections spaced about 2–3 m apart, driven prior to excavation. As the excavation proceeds, horizontal timber or steel sheeting (lagging) is inserted behind the H pile flanges.
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| In some cases, the lateral support which can be provided by the shoring wall alone is insufficient to resist the planned lateral loads; in this case additional support is provided by walers or tie-backs. Walers are structural elements which connect across the excavation so that the loads from the soil on either side of the excavation are used to resist each other, or which transfer horizontal loads from the shoring wall to the base of the excavation. Tie-backs are steel tendons drilled into the face of the wall which extend beyond the soil which is applying pressure to the wall, to provide additional lateral resistance to the wall.
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| == Earth structures ==
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| [[Image:Seabees compactor roller.jpg|thumb|A [[compactor]]/[[road roller|roller]] operated by U.S. Navy Seabees]]
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| {{See also|Earthworks (engineering)}}
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| ===Compaction===
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| [[Soil compaction|Compaction]] is the process by which the strength and stiffness of soil may be increased and permeability may be decreased. Fill placement work often has specifications requiring a specific degree of compaction, or alternatively, specific properties of the compacted soil. In-situ soils can be compacted either by excavation and recompaction, or by methods such as [[deep dynamic compaction]], [[vibrocompaction]], or [[compaction grouting]].
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| ==Slope stability==
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| {{Unreferenced section|date=September 2010}}
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| [[Image:Slopslump2.jpg|thumb|250px|right|Simple slope slip section.]]
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| {{Main|Slope stability|Slope stability analysis}}
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| Slope stability is the analysis of soil covered slopes and its potential to undergo [[mass wasting|movement]]. Stability is determined by the balance of [[shear stress]] and [[shear strength (soil)|shear strength]]. A previously stable slope may be initially affected by preparatory factors, making the slope conditionally unstable. Triggering factors of a [[slope failure]] can be climatic events can then make a slope actively unstable, leading to mass movements. Mass movements can be caused by increases in shear stress, such as loading, lateral pressure, and transient forces. Alternatively, shear strength may be decreased by weathering, changes in [[pore water pressure]], and organic material.
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| Several modes of failure for earth slopes include falls, topples, slides, and flows. In slopes with coarse grained soil or rocks, falls typically occur as the rapid descent of rocks and other loose slope material. A slope topples when a large column of soil tilts over its vertical axis at failure. Typical slope stability analysis considers sliding failures, categorized mainly as rotational slides or translational slides. As implied by the name, rotational slides fail along a generally curved surface, while translational slides fail along a more planar surface. A slope failing as a flow would resemble a fluid flowing downhill.
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| Analysis:
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| Geotechnical engineers consider two types of slopes when analyzing stability, finite and infinite slopes. Most slopes are analyzed in the 20th and 21st century using principles pertaining to the limit equilibrium concept. This method analyzes a finite or infinite slope as if it were about to fail along its sliding failure surface. Equilibrium stresses are calculated along the failure plane, and compared to the soils shear strength as determined by Terzaghi’s shear strength equation. Stability is ultimately decided by a factor of safety equal to the ratio of shear strength to the equilibrium stresses along the failure surface. A factor of safety greater than one generally implies a stable slope, failure of which should not occur assuming the slope is undisturbed. A factor of safety of 1.5 is acceptably safe in practice.
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| The analysis of an infinite slope is made possible by several engineering assumptions: The failure surface is planar and infinitely long, it is parallel to the above ground slope, and the soil composing the medium in question is homogenous and isotropic, meaning the same throughout. The assumption of an isotropic soil medium includes that the groundwater table, if present, is parallel to the failure surface, and thus the ground surface above.
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| Swedish Slip Circle Method of Analysis:
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| The Swedish Slip Circle method is used in slope analysis under the assumption that the friction angle of the soil is equal to zero. This simplifies the factor of safety calculation in the way it affects the soil’s shear strength parameter. Terzaghi concludes that shear strength is equal to the soil cohesion value added to the product of the effective stress and the tangent of the soils friction angle. When friction angle is considered to be zero, the effective stress term goes to zero, thus equating the shear strength to the cohesion parameter of the given soil. The Swedish slip circle method assumes literally a circular failure plane, and analyzes stress and strength parameters using circular geometry and statics. The moment caused by the internal driving forces of a slope is compared to the moment cause by forces resisting slope failure. If resisting forces are greater than driving forces, the slope is assumed stable.
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| Ordinary Method of Slices:
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| The method of slices is another analysis method for determination of slope stability. The Swedish slip circle method only accounts for soil with a friction angle equal to zero; therefore, the method of slices is needed for soils having a friction angle greater than zero. The ordinary method of slices, commonly referred to as OMS, neglects the equal and opposite forces on any given soil slice. This allows for a simple static equilibrium calculation, considering only soil weight, along with shear and normal stresses along the failure plane.
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| Modified Bishop’s Method of Analysis:
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| The Modified Bishop’s method for analyzing slope stability is slightly different than the ordinary method of slices in its assumptions regarding side forces on each slice considered. Instead of assuming equal and opposite side forces, the Modified Bishop’s Method considers these forces equal to zero. Such an assumption improves accuracy in factor of safety calculations.
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| Spencer’s Method:
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| Spencer’s Method of analysis requires a computer program capable of cyclic algorithms, but makes slope stability analysis easier. It is not as accurate as the Modified Bishop’s method, but is acceptably accurate in engineering practices.<ref name="Coduto, et al 2011"/>
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| == Offshore geotechnical engineering ==
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| {{Main|Offshore geotechnical engineering}}
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| [[File:Offshore platforms.jpg|thumb|Platforms offshore Mexico.]]
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| ''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'').<ref name="Dean">Dean, E.T.R. (2010). Offshore Geotechnical Engineering - Principles and Practice. Thomas Telford, Reston, VA, U.S.A., 520 p.</ref> [[Oil platform]]s, [[artificial island]]s and [[submarine pipeline]]s are examples of such structures. There are number of significant differences between onshore and offshore geotechnical engineering.<ref name="Dean"/><ref name="Randolph&Gourvenec">Randolph, M. and Gourvenec, S., 2011. Offshore geotechnical engineering. Spon Press, N.Y., 550 p.</ref> Notably, 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 – they need to be taken into account in offshore design.
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| 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, Stamfort, U.S.A., 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, [[jetty]]s and fixed-bottom wind turbines—or may be a floating structure that remain 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. "Tension
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| 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>
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| [http://web.mit.edu/flowlab/pdf/Floating_Offshore_Wind_Turbines.pdf Floating Offshore Wind Turbines: Responses in a Seastate -- Pareto Optimal Designs and Economic Assessment], P. Sclavounos et al, October 2007.</ref>
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| ==Geosynthetics== | |
| {{Unreferenced section|date=September 2010}}
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| [[Image:Geocollage.JPG|thumb|right|230px|A collage of geosynthetic products.]]
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| {{Main|Geosynthetics}}
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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. These products have a wide range of applications and are currently used in many civil and geotechnical engineering applications including: roads, airfields, railroads, embankments, piled embankments, retaining structures, reservoirs, canals, dams, landfills, bank protection and coastal engineering.<ref>Koerner, R. M. (2012) Designing with geosynthetics, 6th Edition, Xlibris Corporation, USA</ref>
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| == See also ==
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| {{Portal|Engineering}}
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| * [[Civil engineering]]
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| * [[Deep Foundations Institute]]
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| * [[Effective stress]]
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| * [[Geology]]
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| ** [[Engineering geology]]
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| ** [[Rock mass classifications]]
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| ** [[Seismology]]
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| * [[Geoprofessions]]
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| * [[International Society for Soil Mechanics and Geotechnical Engineering]]
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| * [[Karl von Terzaghi]]
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| * [[Land reclamation]]
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| * [[Landfill]]
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| * [[List of publications in geology#Geotechnical engineering|List of publications in geotechnical engineering]]
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| * [[Mechanically stabilized earth]]
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| * [[Observational method (geotechnics)]]
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| * [[Offshore geotechnical engineering]]
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| * [[Sediment control]]
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| * [[Soil mechanics]]
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| * [[Soil physics]]
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| * [[Soil science]]
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| ==Notes==
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| {{Reflist|2}}
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| ==References==
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| {{Col-begin}}
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| {{Col-2}}
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| <div style="font-size: 85%">
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| *Holtz, R. and Kovacs, W. (1981), ''An Introduction to Geotechnical Engineering'', Prentice-Hall, Inc. ISBN 0-13-484394-0
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| *Bowles, J. (1988), ''Foundation Analysis and Design'', McGraw-Hill Publishing Company. ISBN 0-07-006776-7
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| *Cedergren, Harry R. (1977), ''Seepage, Drainage, and Flow Nets'', Wiley. ISBN 0-471-14179-8
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| *Kramer, Steven L. (1996), ''Geotechnical Earthquake Engineering'', Prentice-Hall, Inc. ISBN 0-13-374943-6
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| *Freeze, R.A. & Cherry, J.A., (1979), ''Groundwater'', Prentice-Hall. ISBN 0-13-365312-9
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| *Lunne, T. & Long, M.,(2006), ''Review of long seabed samplers and criteria for new sampler design'', Marine Geology, Vol 226, p. 145-165
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| *Mitchell, James K. & Soga, K. (2005), ''Fundamentals of Soil Behavior'' 3rd ed., John Wiley & Sons, Inc. ISBN 978-0-471-46302-3
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| *Rajapakse, Ruwan., (2005), "Pile Design ans Construction", 2005. ISBN 0-9728657-1-3
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| </div> | |
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| {{Col-2}}
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| <div style="font-size: 85%">
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| *Fang, H.-Y. and Daniels, J. (2005) ''Introductory Geotechnical Engineering : an environmental perspective'', Taylor & Francis. ISBN 0-415-30402-4
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| *[http://www.vulcanhammer.net/geotechnical/dm7_01.pdf NAVFAC (Naval Facilities Engineering Command) (1986) ''Design Manual 7.01, Soil Mechanics''], US Government Printing Office
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| *[http://www.vulcanhammer.net/geotechnical/dm7_02.pdf NAVFAC (Naval Facilities Engineering Command) (1986) ''Design Manual 7.02, Foundations and Earth Structures''], US Government Printing Office
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| *NAVFAC (Naval Facilities Engineering Command) (1983) ''Design Manual 7.03, Soil Dynamics, Deep Stabilization and Special Geotechnical Construction'', US Government Printing Office
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| *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
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| *Santamarina, J.C., Klein, K.A., & Fam, M.A. (2001), "Soils and Waves: Particulate Materials Behavior, Characterization and Process Monitoring", Wiley, ISBN 978-0-471-49058-6
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| *Firuziaan, M. and Estorff, O., (2002), "Simulation of the Dynamic Behavior of Bedding-Foundation-Soil in the Time Domain", Springer Verlag.
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| </div> | |
| {{Col-end}}
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| {{Geotechnical engineering}}
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| {{Technology}}
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| {{DEFAULTSORT:Geotechnical Engineering}}
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| [[Category:Geotechnical engineering| ]]
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| [[Category:Geology]]
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| [[Category:Civil engineering]]
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