1.
Erg Chebbi
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Erg Chebbi is one of Moroccos two Saharan ergs – large seas of dunes formed by wind-blown sand. The other is Erg Chigaga near Mhamid, the nearest sizable town is Erfoud, about 60 kilometers further north. Although rainfall is very brief and uncommon, in 2006 flooding adjacent to the dunes destroyed many buildings, Merzouga The local tourist center, is located near the edge of the dunes. A number of companies offer trips from Merzouga and into the desert, taking tourists on overnight trips several kilometres into the erg. During the warmest part of the year, Moroccans come to Erg Chebbi to be buried neck-deep in the hot sand for a few minutes at a time and this is considered to be a treatment for rheumatism. Aeolian processes Blowout List of ergs •→ Safari Camel tripcamel-trek Media related to Erg Chebbi at Wikimedia Commons Erg Chebbi – Location map
2.
Force
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In physics, a force is any interaction that, when unopposed, will change the motion of an object. In other words, a force can cause an object with mass to change its velocity, force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity and it is measured in the SI unit of newtons and represented by the symbol F. The original form of Newtons second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time. In an extended body, each part usually applies forces on the adjacent parts, such internal mechanical stresses cause no accelation of that body as the forces balance one another. Pressure, the distribution of small forces applied over an area of a body, is a simple type of stress that if unbalanced can cause the body to accelerate. Stress usually causes deformation of materials, or flow in fluids. In part this was due to an understanding of the sometimes non-obvious force of friction. A fundamental error was the belief that a force is required to maintain motion, most of the previous misunderstandings about motion and force were eventually corrected by Galileo Galilei and Sir Isaac Newton. With his mathematical insight, Sir Isaac Newton formulated laws of motion that were not improved-on for nearly three hundred years, the Standard Model predicts that exchanged particles called gauge bosons are the fundamental means by which forces are emitted and absorbed. Only four main interactions are known, in order of decreasing strength, they are, strong, electromagnetic, weak, high-energy particle physics observations made during the 1970s and 1980s confirmed that the weak and electromagnetic forces are expressions of a more fundamental electroweak interaction. Since antiquity the concept of force has been recognized as integral to the functioning of each of the simple machines. The mechanical advantage given by a machine allowed for less force to be used in exchange for that force acting over a greater distance for the same amount of work. Analysis of the characteristics of forces ultimately culminated in the work of Archimedes who was famous for formulating a treatment of buoyant forces inherent in fluids. Aristotle provided a discussion of the concept of a force as an integral part of Aristotelian cosmology. In Aristotles view, the sphere contained four elements that come to rest at different natural places therein. Aristotle believed that objects on Earth, those composed mostly of the elements earth and water, to be in their natural place on the ground. He distinguished between the tendency of objects to find their natural place, which led to natural motion, and unnatural or forced motion
3.
Particle
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A particle is a minute fragment or quantity of matter. In the physical sciences, a particle is a small localized object to which can be ascribed several physical or chemical properties such as volume or mass. Particles can also be used to create models of even larger objects depending on their density. The term particle is rather general in meaning, and is refined as needed by various scientific fields, something that is composed of particles may be referred to as being particulate. However, the particulate is most frequently used to refer to pollutants in the Earths atmosphere. The concept of particles is particularly useful when modelling nature, as the treatment of many phenomena can be complex. It can be used to make simplifying assumptions concerning the processes involved, francis Sears and Mark Zemansky, in University Physics, give the example of calculating the landing location and speed of a baseball thrown in the air. The treatment of large numbers of particles is the realm of statistical physics, the term particle is usually applied differently to three classes of sizes. The term macroscopic particle, usually refers to particles much larger than atoms and these are usually abstracted as point-like particles, or even invisible. This is even though they have volumes, shapes, structures, examples of macroscopic particles would include powder, dust, sand, pieces of debris during a car accident, or even objects as big as the stars of a galaxy. Another type, microscopic particles usually refers to particles of sizes ranging from atoms to molecules, such as carbon dioxide, nanoparticles and these particles are studied in chemistry, as well as atomic and molecular physics. The smallest of particles are the particles, which refer to particles smaller than atoms. These particles are studied in particle physics, because of their extremely small size, the study of microscopic and subatomic particles fall in the realm of quantum mechanics. Particles can also be classified according to composition, composite particles refer to particles that have composition – that is particles which are made of other particles. For example, an atom is made of six protons, eight neutrons. By contrast, elementary particles refer to particles that are not made of other particles, according to our current understanding of the world, only a very small number of these exist, such as the leptons, quarks or gluons. However it is possible some of these might turn up to be composite particles after all. While composite particles can very often be considered point-like, elementary particles are truly punctual, both elementary and composite particles, are known to undergo particle decay
4.
Sand
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Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than gravel and coarser than silt, Sand can also refer to a textural class of soil or soil type, i. e. a soil containing more than 85% sand-sized particles by mass. The second most common type of sand is calcium carbonate, for example aragonite, for example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean. Sand is a non renewable resource over human timescales, and sand suitable for making concrete is in high demand, in terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm to 2 mm. An individual particle in this size is termed a sand grain. Sand grains are between gravel and silt, a 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. A1938 specification of the United States Department of Agriculture was 0.05 mm. Sand feels gritty when rubbed between the fingers. ISO14688 grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size, very fine sand, fine sand, medium sand, coarse sand, and very coarse sand. These sizes are based on the Krumbein phi scale, where size in Φ = -log2D, on this scale, for sand the value of Φ varies from −1 to +4, with the divisions between sub-categories at whole numbers. The composition of sand is highly variable, depending on the local rock sources. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, arkose is a sand or sandstone with considerable feldspar content, derived from weathering and erosion of a granitic rock outcrop. Some sands contain magnetite, chlorite, glauconite or gypsum, Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic with a high olivine content, many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color. Sand deposits in some areas contain garnets and other resistant minerals, the study of individual grains can reveal much historical information as to the origin and kind of transport of the grain. Quartz sand that is weathered from granite or gneiss quartz crystals will be angular. It is called grus in geology or sharp sand in the trade where it is preferred for concrete. Sand that is transported long distances by water or wind will be rounded, people who collect sand as a hobby are known as arenophiles
5.
Soil
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Soil is a mixture of minerals, organic matter, gases, liquids, and countless organisms that together support life on Earth. Soil is called the Skin of the Earth and interfaces with the lithosphere, the hydrosphere, the atmosphere, the term pedolith, used commonly to refer to the soil, literally translates ground stone. Soil consists of a phase of minerals and organic matter, as well as a porous phase that holds gases. Accordingly, soils are often treated as a system of solids, liquids. Soil is a product of the influence of climate, relief, organisms, Soil continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness soil has been considered as an ecosystem by soil ecologists. Most soils have a dry bulk density between 1.1 and 1.6 g/cm3, while the particle density is much higher. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, Soil science has two basic branches of study, edaphology and pedology. Edaphology is concerned with the influence of soils on living things, pedology is focused on the formation, description, and classification of soils in their natural environment. In engineering terms, soil is referred to as regolith, or loose material that lies above the solid geology. Soil is commonly referred to as earth or dirt, technically, as soil resources serve as a basis for food security, the international community advocates its sustainable and responsible use through different types of soil governance. Soil is a component of the Earths ecosystem. The worlds ecosystems are impacted in far-reaching ways by the carried out in the soil, from ozone depletion and global warming, to rainforest destruction. Following the atmosphere, the soil is the next largest carbon reservoir on Earth, as the planet warms, soils will add carbon dioxide to the atmosphere due to its increased biological activity at higher temperatures. Thus, soil carbon losses likely have a positive feedback response to global warming. Since soil has a range of available niches and habitats. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial, Soil has a mean prokaryotic density of roughly 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter of seawater. Since plant roots need oxygen, ventilation is an important characteristic of soil and this ventilation can be accomplished via networks of interconnected soil pores, which also absorb and hold rainwater making it readily available for plant uptake
6.
Gravel
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Gravel /ˈɡrævəl/ is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel is categorized by the Udden-Wentworth scale into granular gravel and pebble gravel, one cubic metre of gravel typically weighs about 1,800 kg. Gravel is an important commercial product, with a number of applications, many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or tarmac, both sand and small gravel are also important for the manufacture of concrete. Large gravel deposits are a geological feature, being formed as a result of the weathering. The action of rivers and waves tends to pile up gravel in large accumulations and this can sometimes result in gravel becoming compacted and concreted into the sedimentary rock called conglomerate. Where natural gravel deposits are insufficient for human purposes, gravel is often produced by quarrying and crushing hard-wearing rocks, such as sandstone, limestone, quarries where gravel is extracted are known as gravel pits. Southern England possesses particularly large concentrations of them due to the deposition of gravel in the region during the Ice Ages. As of 2006, the United States is the leading producer and consumer of gravel. The word gravel comes from the Breton language, adding the -el suffix in Breton denotes the component parts of something larger. Thus gravel means the stones which make up such a beach on the coast. Many dictionaries ignore the Breton language, citing Old French gravele or gravelle, Gravel often has the meaning a mixture of different size pieces of stone mixed with sand and possibly some clay. American English also allows small stones without sand mixed in also known as crushed stone, types of gravel include, Bank gravel, naturally deposited gravel intermixed with sand or clay found in and next to rivers and streams. Also known as Bank run or River run, bench gravel, a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level. Creek rock, this is rounded, semi-polished stones, potentially of a wide range of types. It is also used as concrete aggregate and less often as a paving surface. Crushed stone, rock crushed and graded by screens and then mixed to a blend of stones and fines and it is widely used as a surfacing for roads and driveways, sometimes with tar applied over it. Crushed stone may be made from granite, limestone, dolomite, also known as crusher run, DGA QP, and shoulder stone
7.
Coin
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A coin is a small, flat, round piece of metal or plastic used primarily as a medium of exchange or legal tender. They are standardized in weight, and produced in quantities at a mint in order to facilitate trade. They are most often issued by a government, Coins are usually metal or alloy, or sometimes made of synthetic materials. Coins made of metal are stored in large quantities as bullion coins. Other coins are used as money in transactions, circulating alongside banknotes. Usually the highest value coin in circulation is less than the lowest-value note. In the last hundred years, the value of circulation coins has occasionally been lower than the value of the metal they contain. Exceptions to the rule of face value being higher than content value also occur for some bullion coins made of copper, silver, or gold, while the Eagle, Maple Leaf, and Sovereign coins have nominal face values, the Krugerrand does not. The first coins were developed independently in Iron Age Anatolia and Archaic Greece, India, Coins spread rapidly in the 6th and 5th centuries BCE, throughout Greece and Persia, and further to the Balkans. Standardized Roman currency was used throughout the Roman Empire, important Roman gold and silver coins were continued into the Middle Ages. Fiat money first arose in medieval China, with the paper money. Early paper money was introduced in Europe in the later Middle Ages, the penny was minted as a silver coin until the 17th century. The first circulating United States coins were cents, produced in 1793, Coins were an evolution of currency systems of the Late Bronze Age, where standard-sized ingots, and tokens such as knife money, were used to store and transfer value. In the late Chinese Bronze Age, standardized cast tokens were made and these were replicas in bronze of earlier Chinese currency, cowrie shells, so they were named Bronze Shell. According to Aristotle and Pollux, the first issuer of coins was Hermodike of Kyme The earliest coins are associated with Iron Age Anatolia. Early electrum coins were not standardized in weight, and in their earliest stage may have been ritual objects, such as badges or medals, issued by priests. The first Lydian coins were made of electrum, a naturally occurring alloy of silver, most of the early Lydian coins include no writing, only an image of a symbolic animal. Anatolian Artemis was the Πὀτνια Θηρῶν, whose symbol was the stag, a small percentage of early Lydian/Greek coins have a legend
8.
Liquid
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A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a constant volume independent of pressure. As such, it is one of the four states of matter. A liquid is made up of tiny vibrating particles of matter, such as atoms, water is, by far, the most common liquid on Earth. Like a gas, a liquid is able to flow and take the shape of a container, most liquids resist compression, although others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, a distinctive property of the liquid state is surface tension, leading to wetting phenomena. The density of a liquid is usually close to that of a solid, therefore, liquid and solid are both termed condensed matter. On the other hand, as liquids and gases share the ability to flow, although liquid water is abundant on Earth, this state of matter is actually the least common in the known universe, because liquids require a relatively narrow temperature/pressure range to exist. Most known matter in the universe is in form as interstellar clouds or in plasma form within stars. Liquid is one of the four states of matter, with the others being solid, gas. Unlike a solid, the molecules in a liquid have a greater freedom to move. The forces that bind the molecules together in a solid are only temporary in a liquid, a liquid, like a gas, displays the properties of a fluid. A liquid can flow, assume the shape of a container, if liquid is placed in a bag, it can be squeezed into any shape. These properties make a suitable for applications such as hydraulics. Liquid particles are bound firmly but not rigidly and they are able to move around one another freely, resulting in a limited degree of particle mobility. As the temperature increases, the vibrations of the molecules causes distances between the molecules to increase. When a liquid reaches its point, the cohesive forces that bind the molecules closely together break. If the temperature is decreased, the distances between the molecules become smaller, only two elements are liquid at standard conditions for temperature and pressure, mercury and bromine. Four more elements have melting points slightly above room temperature, francium, caesium, gallium and rubidium, metal alloys that are liquid at room temperature include NaK, a sodium-potassium metal alloy, galinstan, a fusible alloy liquid, and some amalgams
9.
Friction
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Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction, Dry friction resists relative lateral motion of two surfaces in contact. Dry friction is subdivided into static friction between non-moving surfaces, and kinetic friction between moving surfaces, fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces, skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. Internal friction is the force resisting motion between the making up a solid material while it undergoes deformation. When surfaces in contact move relative to other, the friction between the two surfaces converts kinetic energy into thermal energy. This property can have consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Kinetic energy is converted to thermal energy whenever motion with friction occurs, another important consequence of many types of friction can be wear, which may lead to performance degradation and/or damage to components. Friction is a component of the science of tribology, Friction is not itself a fundamental force. Dry friction arises from a combination of adhesion, surface roughness, surface deformation. The complexity of interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis. Friction is a non-conservative force - work done against friction is path dependent, in the presence of friction, some energy is always lost in the form of heat. Thus mechanical energy is not conserved, the Greeks, including Aristotle, Vitruvius, and Pliny the Elder, were interested in the cause and mitigation of friction. They were aware of differences between static and kinetic friction with Themistius stating in 350 A. D. that it is easier to further the motion of a moving body than to move a body at rest. The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology and these laws were rediscovered by Guillaume Amontons in 1699. Amontons presented the nature of friction in terms of surface irregularities, the understanding of friction was further developed by Charles-Augustin de Coulomb. Coulomb further considered the influence of sliding velocity, temperature and humidity, the distinction between static and dynamic friction is made in Coulombs friction law, although this distinction was already drawn by Johann Andreas von Segner in 1758. Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, in Leslies view, friction should be seen as a time-dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before
10.
Slope stability
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Slope stability is the potential of soil covered slopes to withstand and undergo movement. Stability is determined by the balance of stress and shear strength. A previously stable slope may be affected by preparatory factors. Triggering factors of a failure can be climatic events which can then make a slope actively unstable. Mass movements can be caused by increase in stress, such as loading, lateral pressure. Alternatively, shear strength may be decreased by weathering, changes in water pressure. Slope stability investigation, analysis, and design mitigation is typically completed by geologists, engineering geologists, as seen in Figure 1, earthen slopes can develop a cut-spherical weakness area. The probability of this happening can be calculated in advance using a simple 2-D circular analysis package, a primary difficulty with analysis is locating the most-probable slip plane for any given situation. Many landslides have only been analyzed after the fact, more recently slope stability radar technology has been employed, particularly in the mining industry, to gather real time data and assist in pro-actively determining the likelihood of slope failure. Real life failures in naturally deposited mixed soils are not necessarily circular, nevertheless, failures in pure clay can be quite close to circular. This is combined with increased soil weight due to the added groundwater, a shrinkage crack at the top of the slip may also fill with rain water, pushing the slip forward. At the other extreme, slab-shaped slips on hillsides can remove a layer of soil from the top of the underlying bedrock, again, this is usually initiated by heavy rain, sometimes combined with increased loading from new buildings or removal of support at the toe. Stability can thus be improved by installing drainage paths to reduce the destabilising forces. Once the slip has occurred, however, a weakness along the slip circle remains, Slope stability issues can be seen with almost any walk down a ravine in an urban setting. An example is shown in Figure 3, where a river is eroding the toe of a slope, and there is a swimming pool near the top of the slope. If the toe is eroded too far, or the swimming pool begins to leak, the forces driving a slope failure will exceed those resisting failure, if the forces available to resist movement are greater than the forces driving movement, the slope is considered stable. A factor of safety is calculated by dividing the forces resisting movement by the forces driving movement, discontinuity layout optimization Mass wasting Mohr-Coulomb theory Slope stability analysis Slope stability radar Coduto, Donald P. Geotechnical Engineering, Principles and Practices. ISBN 0-13-576380-0 Fredlund, D. G. H. Rahardjo, unsaturated Soil Mechanics in Engineering Practice
11.
Soil liquefaction
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In soil mechanics the term liquefied was first used by Allen Hazen in reference to the 1918 failure of the Calaveras Dam in California. The phenomenon is most often observed in saturated, loose, sandy soils and this is because a loose sand has a tendency to compress when a load is applied, dense sands by contrast tend to expand in volume or dilate. If the soil is saturated by water, a condition that exists when the soil is below the ground water table or sea level. In response to the soil compressing, this increases in pressure. These contacts between grains are the means by which the weight from buildings and overlying soil layers are transferred from the surface to layers of soil or rock at greater depths. This loss of soil structure causes it to all of its strength. Although the effects of liquefaction have been understood, it was more thoroughly brought to the attention of engineers after the 1964 Niigata earthquake and 1964 Alaska earthquake. It was also a factor in the destruction in San Franciscos Marina District during the 1989 Loma Prieta earthquake. A state of soil liquefaction occurs when the stress of soil is reduced to essentially zero. This may be initiated by either monotonic loading or cyclic loading, in both cases a soil in a saturated loose state, and one which may generate significant pore water pressure on a change in load are the most likely to liquefy. As pore water pressure rises a progressive loss of strength of the soil occurs as effective stress is reduced and it is more likely to occur in sandy or non-plastic silty soils, but may in rare cases occur in gravels and clays. A flow failure may initiate if the strength of the soil is reduced below the required to maintain equilibrium of a slope or footing of a building for instance. This can occur due to loading or cyclic loading, and can be sudden. A historical example is the Aberfan disaster, casagrande referred to this type of phenomena as flow liquefaction although a state of zero effective stress is not required for this to occur. The term cyclic refers to the occurrence of a state of soil when large shear strains have accumulated in response to cyclic loading. A typical reference strain for the occurrence of zero effective stress is 5% double amplitude shear strain. This is a soil test based definition, usually performed via cyclic triaxial, cyclic direct simple shear and these tests are performed to determine a soils resistance to liquefaction by observing the number of cycles of loading at a particular shear stress amplitude before it fails. Failure here is defined by the shear strain criteria
12.
Earthquake
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An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earths lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to people around. The seismicity or seismic activity of an area refers to the frequency, type, Earthquakes are measured using measurements from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe and these two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly imperceptible or weak and magnitude 7 and over potentially cause damage over larger areas. The largest earthquakes in historic times have been of magnitude slightly over 9, intensity of shaking is measured on the modified Mercalli scale. The shallower an earthquake, the damage to structures it causes. At the Earths surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground, when the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity, in its most general sense, the word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of faults, but also by other events such as volcanic activity, landslides, mine blasts. An earthquakes point of rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter, tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to a form of stick-slip behavior, once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the portion of the fault. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface and this process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of a total energy is radiated as seismic energy. Most of the energy is used to power the earthquake fracture growth or is converted into heat generated by friction
13.
Stress (physics)
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For example, when a solid vertical bar is supporting a weight, each particle in the bar pushes on the particles immediately below it. When a liquid is in a container under pressure, each particle gets pushed against by all the surrounding particles. The container walls and the pressure-inducing surface push against them in reaction and these macroscopic forces are actually the net result of a very large number of intermolecular forces and collisions between the particles in those molecules. Strain inside a material may arise by various mechanisms, such as stress as applied by external forces to the material or to its surface. Any strain of a material generates an internal elastic stress, analogous to the reaction force of a spring. In liquids and gases, only deformations that change the volume generate persistent elastic stress, however, if the deformation is gradually changing with time, even in fluids there will usually be some viscous stress, opposing that change. Elastic and viscous stresses are usually combined under the mechanical stress. Significant stress may exist even when deformation is negligible or non-existent, stress may exist in the absence of external forces, such built-in stress is important, for example, in prestressed concrete and tempered glass. Stress may also be imposed on a material without the application of net forces, for example by changes in temperature or chemical composition, stress that exceeds certain strength limits of the material will result in permanent deformation or even change its crystal structure and chemical composition. In some branches of engineering, the stress is occasionally used in a looser sense as a synonym of internal force. For example, in the analysis of trusses, it may refer to the total traction or compression force acting on a beam, since ancient times humans have been consciously aware of stress inside materials. Until the 17th century the understanding of stress was largely intuitive and empirical, with those tools, Augustin-Louis Cauchy was able to give the first rigorous and general mathematical model for stress in a homogeneous medium. Cauchy observed that the force across a surface was a linear function of its normal vector, and, moreover. The understanding of stress in liquids started with Newton, who provided a formula for friction forces in parallel laminar flow. Stress is defined as the force across a small boundary per unit area of that boundary, following the basic premises of continuum mechanics, stress is a macroscopic concept. In a fluid at rest the force is perpendicular to the surface, in a solid, or in a flow of viscous liquid, the force F may not be perpendicular to S, hence the stress across a surface must be regarded a vector quantity, not a scalar. Moreover, the direction and magnitude depend on the orientation of S. Thus the stress state of the material must be described by a tensor, called the stress tensor, with respect to any chosen coordinate system, the Cauchy stress tensor can be represented as a symmetric matrix of 3×3 real numbers
14.
Pore water pressure
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Pore water pressure refers to the pressure of groundwater held within a soil or rock, in gaps between particles. Pore water pressures in below the level are measured in piezometers. The vertical pore water pressure distribution in aquifers can generally be assumed to be close to hydrostatic, in the unsaturated zone, the pore pressure is determined by capillarity and is also referred to as tension, suction, or matric pressure. Pore water pressures under unsaturated conditions are measured in with tensiometers, tensiometers operate by allowing the pore water to come into equilibrium with a reference pressure indicator through a permeable ceramic cup placed in contact with the soil. Pore water pressure is vital in calculating the stress state in the soil mechanics. Hydrostatic water pressure, resulting from the weight of material above the point measured, osmotic pressure, inhomogeneous aggregation of ion concentrations, which causes a force in water particles as they attract by the molecular laws of attraction. Adsorption pressure, attraction of surrounding soil particles to one another by adsorbed water films, the buoyancy effects of water have a large impact on certain soil properties, such as the effective stress present at any point in a soil medium. Consider an arbitrary point five meters below the ground surface, in dry soil, particles at this point experience a total overhead stress equal to the depth underground, multiplied by the specific weight of the soil.81 kN/m^3. This parameter is called the stress of the soil, basically equal to the difference in a soils total stress. The pore water pressure is essential in differentiating a soils total stress from its effective stress, a correct representation of stress in soil is necessary for accurate field calculations in a variety of engineering trades. The static pressure of groundwater at a specific depth, piezometers often employ electronic pressure transducers to provide data. The United States Bureau of Reclamation has a standard for monitoring water pressure in a mass with piezometers. It sites ASTM D4750, Standard Test Method for Determining Subsurface Liquid Levels in a Borehole or Monitoring Well, at any point above the water table, in the vadose zone, the effective stress is approximately equal to the total stress, as proven by Terzaghis principle. Realistically, the stress is greater than the total stress. This is primarily due to the tension of pore water in voids throughout the vadose zone causing a suction effect on surrounding particles. This capillary action is the movement of water through the vadose zone. The height of rise is inversely proportional to the diameter of void space in contact with water. Therefore, the smaller the space, the higher water will rise due to tension forces
15.
Quartz
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Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly chiral, both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks. The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties, the cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
16.
Density
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The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume, ρ = m V, where ρ is the density, m is the mass, and V is the volume. In some cases, density is defined as its weight per unit volume. For a pure substance the density has the numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity, osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser. Thus a relative density less than one means that the floats in water. The density of a material varies with temperature and pressure and this variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object, increasing the temperature of a substance decreases its density by increasing its volume. In most materials, heating the bottom of a results in convection of the heat from the bottom to the top. This causes it to rise relative to more dense unheated material, the reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is a property in that increasing the amount of a substance does not increase its density. Archimedes knew that the irregularly shaped wreath could be crushed into a cube whose volume could be calculated easily and compared with the mass, upon this discovery, he leapt from his bath and ran naked through the streets shouting, Eureka. As a result, the term eureka entered common parlance and is used today to indicate a moment of enlightenment, the story first appeared in written form in Vitruvius books of architecture, two centuries after it supposedly took place. Some scholars have doubted the accuracy of this tale, saying among other things that the method would have required precise measurements that would have been difficult to make at the time, from the equation for density, mass density has units of mass divided by volume. As there are units of mass and volume covering many different magnitudes there are a large number of units for mass density in use. The SI unit of kilogram per metre and the cgs unit of gram per cubic centimetre are probably the most commonly used units for density.1,000 kg/m3 equals 1 g/cm3. In industry, other larger or smaller units of mass and or volume are often more practical, see below for a list of some of the most common units of density
17.
Beaker (glassware)
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A beaker is a simple container for stirring, mixing and heating liquids commonly used in many laboratories. Beakers are generally cylindrical in shape, with a flat bottom, most also have a small spout to aid pouring as shown in the picture. Beakers are available in a range of sizes, from one millilitre up to several litres. Standard or low-form beakers typically have a height about 1.4 times the diameter, the common low form with a spout was devised by John Joseph Griffin and is therefore sometimes called a Griffin beaker. In short, low form beakers are likely to be used in some way when performing just about any chemical experiment, tall-form beakers have a height about twice their diameter. These are sometimes called Berzelius beakers and are used for titration. Flat beakers are often called crystallizers because most are used to perform crystallization and these beakers usually do not have a flat scale. A beaker is distinguished from a flask by having straight rather than sloping sides, the exception to this definition is a slightly conical-sided beaker called a Philips beaker. Beakers are commonly made of glass, but can also be in metal or certain plastics, a common use for polypropylene beakers is gamma spectral analysis of liquid and solid samples. Beakers are often graduated, that is, marked on the side with lines indicating the volume contained, most beakers are accurate to within ~10%. The presence of a means that the beaker cannot have a lid. However, when in use, beakers may be covered by a glass to prevent contamination or loss of the contents. Alternatively, a beaker may be covered with another larger beaker that has been inverted, though a watch glass is preferable
18.
Buoyancy
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In science, buoyancy or upthrust, is an upward force exerted by a fluid that opposes the weight of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid, thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object and this pressure difference results in a net upwards force on the object. For this reason, an object whose density is greater than that of the fluid in which it is submerged tends to sink, If the object is either less dense than the liquid or is shaped appropriately, the force can keep the object afloat. This can occur only in a reference frame, which either has a gravitational field or is accelerating due to a force other than gravity defining a downward direction. In a situation of fluid statics, the net upward force is equal to the magnitude of the weight of fluid displaced by the body. The center of buoyancy of an object is the centroid of the volume of fluid. Archimedes principle is named after Archimedes of Syracuse, who first discovered this law in 212 B. C, more tersely, Buoyancy = weight of displaced fluid. The weight of the fluid is directly proportional to the volume of the displaced fluid. Thus, among completely submerged objects with equal masses, objects with greater volume have greater buoyancy and this is also known as upthrust. Suppose a rocks weight is measured as 10 newtons when suspended by a string in a vacuum with gravity acting upon it, suppose that when the rock is lowered into water, it displaces water of weight 3 newtons. The force it exerts on the string from which it hangs would be 10 newtons minus the 3 newtons of buoyancy force,10 −3 =7 newtons. Buoyancy reduces the apparent weight of objects that have sunk completely to the sea floor and it is generally easier to lift an object up through the water than it is to pull it out of the water. The density of the object relative to the density of the fluid can easily be calculated without measuring any volumes. Density of object density of fluid = weight weight − apparent immersed weight Example, If you drop wood into water, Example, A helium balloon in a moving car. During a period of increasing speed, the air mass inside the car moves in the direction opposite to the cars acceleration, the balloon is also pulled this way. However, because the balloon is buoyant relative to the air, it ends up being pushed out of the way, If the car slows down, the same balloon will begin to drift backward. For the same reason, as the car goes round a curve and this is the equation to calculate the pressure inside a fluid in equilibrium
19.
Hydrostatics
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Fluid statics or hydrostatics is the branch of fluid mechanics that studies incompressible fluids at rest. It encompasses the study of the conditions under which fluids are at rest in stable equilibrium as opposed to fluid dynamics, hydrostatics are categorized as a part of the fluid statics, which is the study of all fluids, incompressible or not, at rest. Hydrostatics is fundamental to hydraulics, the engineering of equipment for storing, transporting and using fluids and it is also relevant to geophysics and astrophysics, to meteorology, to medicine, and many other fields. Some principles of hydrostatics have been known in an empirical and intuitive sense since antiquity, by the builders of boats, cisterns, aqueducts and fountains. Archimedes is credited with the discovery of Archimedes Principle, which relates the force on an object that is submerged in a fluid to the weight of fluid displaced by the object. The fair cup or Pythagorean cup, which dates from about the 6th century BC, is a technology whose invention is credited to the Greek mathematician. It was used as a learning tool, the cup consists of a line carved into the interior of the cup, and a small vertical pipe in the center of the cup that leads to the bottom. The height of this pipe is the same as the line carved into the interior of the cup, the cup may be filled to the line without any fluid passing into the pipe in the center of the cup. However, when the amount of fluid exceeds this fill line, due to the drag that molecules exert on one another, the cup will be emptied. Herons fountain is a device invented by Heron of Alexandria that consists of a jet of fluid being fed by a reservoir of fluid. The fountain is constructed in such a way that the height of the jet exceeds the height of the fluid in the reservoir, the device consisted of an opening and two containers arranged one above the other. The intermediate pot, which was sealed, was filled with fluid, trapped air inside the vessels induces a jet of water out of a nozzle, emptying all water from the intermediate reservoir. Pascal made contributions to developments in both hydrostatics and hydrodynamics, due to the fundamental nature of fluids, a fluid cannot remain at rest under the presence of a shear stress. However, fluids can exert pressure normal to any contacting surface, if a point in the fluid is thought of as an infinitesimally small cube, then it follows from the principles of equilibrium that the pressure on every side of this unit of fluid must be equal. If this were not the case, the fluid would move in the direction of the resulting force, thus, the pressure on a fluid at rest is isotropic, i. e. it acts with equal magnitude in all directions. This characteristic allows fluids to transmit force through the length of pipes or tubes, i. e. a force applied to a fluid in a pipe is transmitted, via the fluid, to the other end of the pipe. This principle was first formulated, in an extended form, by Blaise Pascal. In a fluid at rest, all frictional and inertial stresses vanish, when this condition of V =0 is applied to the Navier-Stokes equation, the gradient of pressure becomes a function of body forces only
20.
Darcy's law
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Darcys law is an equation that describes the flow of a fluid through a porous medium. The law was formulated by Henry Darcy based on the results of experiments on the flow of water through beds of sand, forming the basis of hydrogeology, although Darcys law was determined experimentally by Darcy, it has since been derived from the Navier-Stokes equations via homogenization. It is analogous to Fouriers law in the field of heat conduction, Ohms law in the field of electrical networks, or Ficks law in diffusion theory. Morris Muskat first refined Darcys equation for single phase flow by including viscosity in the single equation of Darcy. The generalized multiphase flow equations of Muskat et alios provide the foundation for reservoir engineering that exists to this day. The above equation for single phase flow is the equation for absolute permeability. The negative sign is needed because fluid flows from high pressure to low pressure, note that the elevation head must be taken into account if the inlet and outlet are at different elevations. If the change in pressure is negative, then the flow will be in the x direction. There have been proposals for a constitutive equation for absolute permeability. Dividing both sides of the equation by the area and using more general notation leads q = − κ μ ∇ p, where q is the flux and ∇p is the pressure gradient vector. This value of flux, often referred to as the Darcy flux or Darcy velocity, is not the velocity which the fluid traveling through the pores is experiencing, the fluid velocity is related to the Darcy flux by the porosity. The flux is divided by porosity to account for the fact only a fraction of the total formation volume is available for flow. The fluid velocity would be the velocity a conservative tracer would experience if carried by the fluid through the formation, a graphical illustration of the use of the steady-state groundwater flow equation is in the construction of flownets, to quantify the amount of groundwater flowing under a dam. Darcys law is valid for slow, viscous flow, fortunately. Typically any flow with a Reynolds number less than one is clearly laminar, experimental tests have shown that flow regimes with Reynolds numbers up to 10 may still be Darcian, as in the case of groundwater flow. For stationary, creeping, incompressible flow, i. e. In isotropic porous media the off-diagonal elements in the permeability tensor are zero, κij =0 for i ≠ j and the elements are identical, κii = κ. The above equation is an equation for single phase fluid flow in a porous medium
21.
Quicksand
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Quicksand is a colloid hydrogel consisting of fine granular material, and water. Quicksand forms in saturated loose sand when the sand is suddenly agitated, when water in the sand cannot escape, it creates a liquefied soil that loses strength and cannot support weight. Quicksand can form in standing water or in upwards flowing water, in the case of upwards flowing water, seepage forces oppose the force of gravity and suspend the soil particles. The saturated sediment may appear quite solid until a change in pressure or shock initiates liquefaction. This causes the sand to form a suspension and lose strength, the cushioning of water gives quicksand, and other liquefied sediments, a spongy, fluidlike texture. Objects in liquefied sand sink to the level at which the weight of the object is equal to the weight of the displaced soil/water mix, liquefaction is a special case of quicksand. In this case, sudden earthquake forces immediately increase the pressure of shallow groundwater. The saturated liquefied soil loses strength, causing buildings or other objects on surface to sink or fall. Quicksand is a shear thinning non-Newtonian fluid, when undisturbed, it appears to be solid. Someone stepping on it will start to sink, to move within the quicksand, a person or object must apply sufficient pressure on the compacted sand to re-introduce enough water to liquefy it. The forces required to do this are large, to remove a foot from quicksand at a speed of 0.01 m/s would require the same amount of force as that needed to lift a medium-sized car. Contrary to popular belief, quicksand itself is harmless, a human or animal is unlikely to sink entirely into quicksand, Quicksand has a density of about 2 grams per milliliter, whereas the density of the human body is only about 1 gram per milliliter. At that level of density, sinking in quicksand is impossible, descending about up to the waist is possible, but not any further. Even objects with a higher density than quicksand will float on it—until they move, aluminum, for example, has a density of about 2.7 grams per milliliter, but a piece of aluminum will float on top of quicksand until motion causes the sand to liquefy. Continued or panicked movement, however, may cause a person in quicksand to sink deeper, leading to belief that quicksand is dangerous. Since it increasingly impairs movement, this, then, can lead to a situation where other such as weather exposure, dehydration, hypothermia. Quicksand may be escaped by slow movement of the legs in order to increase viscosity of the fluid, Quicksand may be found on riverbanks, near lakes, in marshes, or near the coast. People falling into quicksand or a substance is a trope of adventure fiction
22.
Gravity
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Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible
23.
Geotechnical engineering
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Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. A typical geotechnical engineering project begins with a review of project needs to define the material properties. Site investigations are needed to gain an understanding of the area in or on which the engineering will take place, 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 built for above-ground structures include shallow and deep foundations, retaining structures include earth-filled dams and retaining walls. Earthworks include embankments, tunnels, dikes and levees, channels, reservoirs, deposition of hazardous waste, Geotechnical engineering is also related to coastal and ocean engineering. Coastal engineering can involve the design and construction of wharves, marinas, ocean engineering can involve foundation and anchor systems for offshore structures such as oil platforms. The fields of engineering and engineering geology are closely related. However, the field of engineering is a specialty of engineering. Humans have historically used soil as a material for flood control, irrigation purposes, burial sites, building foundations, 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 basis for soil design had been developed. Several foundation-related engineering problems, such as the Leaning Tower of Pisa, the earliest advances occurred in the development of earth pressure theories for the construction of retaining walls. Henri Gautier, a French Royal Engineer, recognized the natural slope of different soils in 1717, a rudimentary soil classification system was also developed based on a materials unit weight, which is no longer considered a good indication of soil type. The application of the principles of mechanics to soils was documented as early as 1773 when Charles Coulomb developed improved methods to determine the pressures against military ramparts. By combining Coulombs theory with Christian Otto Mohrs 2D stress state, although it is now recognized that precise determination of cohesion is impossible because c is not a fundamental soil property, the Mohr-Coulomb theory is still used in practice today. In the 19th century Henry Darcy developed what is now known as Darcys Law describing the flow of fluids in porous media, albert Atterberg developed the clay consistency indices that are still used today for soil classification. Osborne Reynolds recognized in 1885 that shearing causes volumetric dilation of dense, modern geotechnical engineering is said to have begun in 1925 with the publication of Erdbaumechanik by Karl Terzaghi. Terzaghi also developed the framework for theories of bearing capacity of foundations, in his 1948 book, Donald Taylor recognized that interlocking and dilation of densely packed particles contributed to the peak strength of a soil. Critical state soil mechanics is the basis for many contemporary advanced constitutive models describing the behavior of soil, Geotechnical centrifuge modeling is a method of testing physical scale models of geotechnical problems
24.
Engineering geology
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Engineering geologists provide geological and geotechnical recommendations, analysis, and design associated with human development and various types of structures. The principal objective of the engineering geologist is the protection of life, the practice of engineering geology is also very closely related to the practice of geological engineering and geotechnical engineering. If there is a difference in the content of the disciplines, the first book titled Engineering Geology was published in 1880 by William Penning. The first American engineering geology textbook was written in 1914 by Ries, in 1925, Karl Terzaghi, an Austrian trained engineer and geologist, published the first text in Soil Mechanics. Terzaghi is known as the parent of soil mechanics, but also had great interest in geology, in 1929, Terzaghi, along with Redlich and Kampe, published their own Engineering Geology text. The need for geologist on engineering works gained worldwide attention in 1928 with the failure of the St. Francis Dam in California and these two aspects of the engineering geologists education provides them with a unique ability to understand and mitigate for hazards associated with earth-structure interactions. Soil mechanics is a discipline that applies principles of engineering mechanics, e. g. kinematics, dynamics, fluid mechanics, the fundamental processes are all related to the behaviour of porous media. Together, soil and rock mechanics are the basis for solving many engineering geology problems, an engineering geology report describes the objectives, methodology, references cited, tests performed, findings and recommendations for development and detailed design of engineering works. Engineering geologists also provide data on topographic maps, aerial photographs, geologic maps, Geographic Information System maps. Brock,1923, The Education of a Geologist, Economic Geology, v.18, bates and Jackson,1980, Glossary of Geology, American Geological Institute. Theory of Linear Poroelasticity with Applications to Geomechanics and Hydrogeology, Princeton Press, foundations of Engineering Geology, 2nd Edition, Taylor & Francis
25.
Groundwater-related subsidence
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One estimate has 80% of serious land subsidence problems associated with the excessive extraction of groundwater, making it a growing problem throughout the world. Groundwater is considered to be one of the last free resources, as anyone who can afford to drill, however, as seen in the figure, the act of pumping draws down the free surface of the groundwater table, and can affect a large region. Thus, the extraction of groundwater becomes a tragedy of the commons, the hot desert areas of the world are requiring more and more water for growing populations and agriculture. In the San Joaquin Valley of the United States, groundwater pumping for crops has gone on for generations and this has resulted in the entire valley sinking an extraordinary amount, as shown in the figure. It has been argued there is little consequence to subsidence in a wide, flat, agricultural basin. However, no large-scale change due to subsidence of the magnitude seen in the San Joaquin Valley is likely to be some negative impact. Other regions of the world, such as New Orleans and Bangkok, are now subject to flooding due to subsidence associated with groundwater removal. Total settlement, and therefore the potential impacts of the settlement, can only be determined by surveys, not all groundwater-related subsidence is benign. In Mexico City, the buildings interact with the settlement, and cause cracking, tilting, in many places, large sinkholes open up, as well as surface cavities. Damage from Hurricane Katrina was exacerbated due to sinking, associated with groundwater withdrawal. The cause of the surface changes associated with this phenomenon are fairly well known. As shown in the USGS figure, aquifers are frequently associated with layers of silt or clay. As the groundwater is pumped out, the effective stress changes, precipitating consolidation, thus, the total volume of the silts and clays is reduced, resulting in the lowering of the surface. The damage at the surface is greater if there is differential settlement, or large-scale features. The only known method to prevent this condition is by pumping less groundwater, attempts are being made to directly recharge aquifers but this is still a preliminary effort. Subsidence Land subsidence UNESCO Working Group on Land Subsidence
26.
Wayback Machine
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The Internet Archive launched the Wayback Machine in October 2001. It was set up by Brewster Kahle and Bruce Gilliat, and is maintained with content from Alexa Internet, the service enables users to see archived versions of web pages across time, which the archive calls a three dimensional index. Since 1996, the Wayback Machine has been archiving cached pages of websites onto its large cluster of Linux nodes and it revisits sites every few weeks or months and archives a new version. Sites can also be captured on the fly by visitors who enter the sites URL into a search box, the intent is to capture and archive content that otherwise would be lost whenever a site is changed or closed down. The overall vision of the machines creators is to archive the entire Internet, the name Wayback Machine was chosen as a reference to the WABAC machine, a time-traveling device used by the characters Mr. Peabody and Sherman in The Rocky and Bullwinkle Show, an animated cartoon. These crawlers also respect the robots exclusion standard for websites whose owners opt for them not to appear in search results or be cached, to overcome inconsistencies in partially cached websites, Archive-It. Information had been kept on digital tape for five years, with Kahle occasionally allowing researchers, when the archive reached its fifth anniversary, it was unveiled and opened to the public in a ceremony at the University of California, Berkeley. Snapshots usually become more than six months after they are archived or, in some cases, even later. The frequency of snapshots is variable, so not all tracked website updates are recorded, Sometimes there are intervals of several weeks or years between snapshots. After August 2008 sites had to be listed on the Open Directory in order to be included. As of 2009, the Wayback Machine contained approximately three petabytes of data and was growing at a rate of 100 terabytes each month, the growth rate reported in 2003 was 12 terabytes/month, the data is stored on PetaBox rack systems manufactured by Capricorn Technologies. In 2009, the Internet Archive migrated its customized storage architecture to Sun Open Storage, in 2011 a new, improved version of the Wayback Machine, with an updated interface and fresher index of archived content, was made available for public testing. The index driving the classic Wayback Machine only has a bit of material past 2008. In January 2013, the company announced a ground-breaking milestone of 240 billion URLs, in October 2013, the company announced the Save a Page feature which allows any Internet user to archive the contents of a URL. This became a threat of abuse by the service for hosting malicious binaries, as of December 2014, the Wayback Machine contained almost nine petabytes of data and was growing at a rate of about 20 terabytes each week. Between October 2013 and March 2015 the websites global Alexa rank changed from 162 to 208, in a 2009 case, Netbula, LLC v. Chordiant Software Inc. defendant Chordiant filed a motion to compel Netbula to disable the robots. Netbula objected to the motion on the ground that defendants were asking to alter Netbulas website, in an October 2004 case, Telewizja Polska USA, Inc. v. Echostar Satellite, No.02 C3293,65 Fed. 673, a litigant attempted to use the Wayback Machine archives as a source of admissible evidence, Telewizja Polska is the provider of TVP Polonia and EchoStar operates the Dish Network
27.
Geotechnical investigation
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This type of investigation is called a site investigation. A geotechnical investigation will include surface exploration and subsurface exploration of a site, sometimes, geophysical methods are used to obtain data about sites. Subsurface exploration usually involves soil sampling and laboratory tests of the soil samples retrieved, to obtain information about the soil conditions below the surface, some form of subsurface exploration is required. Methods of observing the soils below the surface, obtaining samples, and determining physical properties of the soils and rocks include test pits, trenching, boring, borings come in two main varieties, large-diameter and small-diameter. Small-diameter borings are frequently used to allow a geologist or engineer to examine soil or rock cuttings or to samples at depth using soil samplers. Soil samples are often categorized as being disturbed or undisturbed, however. Offshore soil collection introduces many difficult variables, in shallow water, work can be done off a barge. In deeper water a ship will be required, deepwater soil samplers are normally variants of Kullenberg-type samplers, a modification on a basic gravity corer using a piston. Seabed samplers are available, which push the collection tube slowly into the soil. Soil samples are taken using a variety of samplers, some provide only disturbed samples, samples can be obtained by digging out soil from the site. Samples taken this way are disturbed samples, trial Pits are relatively small hand or machine excavated tranches used to determine groundwater levels and take disturbed samples from. This sampler typically consists of a cylinder with a cutting edge attached to a rod. The sampler is advanced by a combination of rotation and downward force, samples taken this way are disturbed samples. A method of sampling using an auger as a corkscrew, the auger is screwed into the ground then lifted out. Soil is retained on the blades of the auger and kept for testing, the soil sampled this way is considered disturbed. Utilized in the Standard Test Method for Standard Penetration Test and Split-Barrel Sampling of Soils and this sampler is typically an 18-30 long,2.0 outside diameter hollow tube split in half lengthwise. A hardened metal drive shoe with a 1.375 opening is attached to the end. It is driven into the ground with a 140-pound hammer falling 30, the blow counts required to advance the sampler a total of 18 are counted and reported
28.
Cone penetration test
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The cone penetration or cone penetrometer test is a method used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. It was initially developed in the 1950s at the Dutch Laboratory for Soil Mechanics in Delft to investigate soft soils, based on this history it has also been called the Dutch cone test. Today, the CPT is one of the most used and accepted methods for soil investigation worldwide. The test method consists of pushing an instrumented cone, with the tip facing down, the early applications of CPT mainly determined the soil geotechnical property of bearing capacity. The original cone penetrometers involved simple mechanical measurements of the total resistance to pushing a tool with a conical tip into the soil. Different methods were employed to separate the total measured resistance into components generated by the conical tip, a friction sleeve was added to quantify this component of the friction and aid in determining soil cohesive strength in the 1960s. Electronic measurements began in 1948 and improved further in the early 1970s, most modern electronic CPT cones now also employ a pressure transducer with a filter to gather pore water pressure data. The filter is located either on the cone tip, immediately behind the cone tip or behind the friction sleeve. Pore water pressure data aids determining stratigraphy and is used to correct tip friction values for those effects. CPT testing which also gathers this data is called CPTU testing. CPT and CPTU testing equipment generally advances the cone using hydraulic rams mounted on either a heavily ballasted vehicle or using screwed-in anchors as a counter-force. One advantage of CPT over the Standard Penetration Test is a continuous profile of soil parameters, with data recorded at intervals typically of 20 cm. In addition to the mechanical and electronic cones, a variety of other CPT-deployed tools have developed over the years to provide additional subsurface information. One common tool advanced during CPT testing is a set to gather seismic shear wave. This data helps determine the shear modulus and Poissons ratio at intervals through the column for soil liquefaction analysis. Engineers use the wave velocity and shear modulus to determine the soils behavior under low-strain. An additional CPT deployed tool used in Britain, Netherlands, Germany, Belgium and this is used to attempt to ensure that tests, boreholes, and piles, do not encounter unexploded ordnance or duds. The magnetometer in the cone detects ferrous materials of 50 kg or larger within a radius of up to about 2 m distance from the probe depending on the material, orientation, CPT for geotechnical applications was standardized in 1986 by ASTM Standard D3441
29.
Standard penetration test
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The standard penetration test is an in-situ dynamic penetration test designed to provide information on the geotechnical engineering properties of soil. The test procedure is described in ISO 22476-3, ASTM D1586, the test uses a thick-walled sample tube, with an outside diameter of 50.8 mm and an inside diameter of 35 mm, and a length of around 650 mm. This is driven into the ground at the bottom of a borehole by blows from a hammer with a mass of 63.5 kg falling through a distance of 760 mm. The sample tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm up to a depth of 450 mm is recorded. The sum of the number of blows required for the second, in cases where 50 blows are insufficient to advance it through a 150 mm interval the penetration after 50 blows is recorded. The blow count provides an indication of the density of the ground, detailed procedure can be found on Geotechdata. info database. The main purpose of the test is to provide an indication of the density of granular deposits, such as sands. The great merit of the test, and the reason for its widespread use is that it is simple. If the samples are found to be disturbed, it may be necessary to use a different method for measuring strength like the plate test. When the test is carried out in granular soils below groundwater level, in certain circumstances, it can be useful to continue driving the sampler beyond the distance specified, adding further drilling rods as necessary. Soils in arid areas, such as the Western United States and this condition will often increase the standard penetration value. The SPT is used to provide results for empirical determination of a sand layers susceptibility to soil liquefaction, based on research performed by Harry Seed, despite its many flaws, it is usual practice to correlate SPT results with soil properties relevant for geotechnical engineering design. Standard Penetration Test blow counts do not represent a physical property of the soil. There exist multiple correlations, none of which are of high quality
30.
Water well
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A water well is an excavation or structure created in the ground by digging, driving, boring, or drilling to access groundwater in underground aquifers. The well water is drawn by a pump, or using containers, such as buckets, placing a lining in the well shaft helps create stability and linings of wood or wickerwork date back at least as far as the Iron Age. Wells have been sunk by hand digging as is the case in rural developing areas. These wells are inexpensive and low-tech as they use mostly manual labour, a more modern method called caissoning uses pre-cast reinforced concrete well rings that are lowered into the hole. Deeper wells can be excavated by hand drilling methods or machine drilling, using a bit in a borehole, drilled wells are usually cased with a factory-made pipe composed of steel or plastic. Drilled wells can access water at greater depths than dug wells. A collector well can be constructed adjacent to a lake or stream with water percolating through the intervening material. The site of a well can be selected by a hydrogeologist, Water may be pumped or hand drawn. Impurities from the surface can easily reach shallow sources and contamination of the supply by pathogens or chemical contaminants needs to be avoided, Well water typically contains more minerals in solution than surface water and may require treatment before being potable. Soil salination can occur as the water falls and the surrounding soil begins to dry out. Another environmental problem is the potential for methane to seep into the water, hand-dug wells are excavations with diameters large enough to accommodate one or more people with shovels digging down to below the water table. The excavation is braced horizontally to avoid landslide or erosion endangering the people digging, a more modern method called caissoning uses reinforced concrete or plain concrete pre-cast well rings that are lowered into the hole. A well-digging team digs under a ring and the well column slowly sinks into the aquifer. Hand-dug wells are inexpensive and low tech as they use mostly manual labour to access groundwater in rural locations in developing countries and they may be built with a high degree of community participation, or by local entrepreneurs who specialize in hand-dug wells. They have been excavated to 60 metres. They have low operational and maintenance costs, in part because water can be extracted by hand bailing, without a pump. The water is coming from an aquifer or groundwater, and can be easily deepened. The yield of existing hand dug wells may be improved by deepening or introducing vertical tunnels or perforated pipes, drawbacks to hand-dug wells are numerous
31.
Piezometer
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A piezometer is designed to measure static pressures, and thus differs from a pitot tube by not being pointed into the fluid flow. Observation wells give some information on the level in a formation. Electrical pressure transducers of several types can be read automatically, making data acquisition more convenient, the first piezometers in geotechnical engineering were open wells or standpipes installed into an aquifer. A Casagrande piezometer will typically have a casing down to the depth of interest. The casing is sealed into the drillhole with clay, bentonite or concrete to prevent surface water from contaminating the groundwater supply. In an unconfined aquifer, the level in the piezometer would not be exactly coincident with the water table. In a confined aquifer under artesian conditions, the level in the piezometer indicates the pressure in the aquifer. Piezometer wells can be smaller in diameter than production wells. Piezometers in durable casings can be buried or pushed into the ground to measure the pressure at the point of installation. The pressure gauges can be vibrating-wire, pneumatic, or strain-gauge in operation, converting pressure into an electrical signal
32.
Borehole
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A borehole is a narrow shaft bored in the ground, either vertically or horizontally. g. in Carbon capture and storage. This includes holes advanced to collect samples, water samples or rock cores, to advance in situ sampling equipment. Samples collected from boreholes are often tested in a laboratory to determine their physical properties, typically, a borehole used as a water well is completed by installing a vertical pipe and well screen to keep the borehole from caving. This also helps prevent surface contaminants from entering the borehole and protects any installed pump from drawing in sand, oil and natural gas wells are completed in a similar, albeit usually more complex, manner. As detailed in proxy, borehole temperature measurements at a series of different depths can be inverted to help estimate historic surface temperatures. Clusters of small-diameter boreholes equipped with heat exhangers made of plastic PEX pipe can be used to heat or cold between opposing seasons in a mass of native rock. The technique is called seasonal thermal energy storage, media that can be used for this technique range from gravel to bedrock. There can be a few to several hundred boreholes, and in practice, Borehole drilling has a long history. Han Dynasty China used deep borehole drilling for mining and other projects, chinese borehole sites could reach as deep as 600 m. The practice of logging in boreholes dates to 1927, for the French Pechelbronn oil field. For many years, the world’s deepest borehole was the Kola Superdeep Borehole, from 2011 until August 2012 the record was held by the 12, 345-metre long Sakhalin-I Odoptu OP-11 Well, offshore the Russian island Sakhalin. The Chayvo Z-44 extended-reach well took the title of the worlds longest borehole on 27 August 2012, z-44s total measured depth is 12,376 m. However, ERD wells are more shallow than Kola Superdeep Borehole, drillers may sink a borehole using a drilling rig or a hand-operated rig. The machinery and techniques to advance a borehole vary considerably according to manufacturer, geological conditions, for offshore drilling floating units or platforms supported by the seafloor are used for the drilling rig. Askam Borehole in Pennsylvania Borehole thermal energy storage Deep borehole disposal Hole opener Kola Superdeep Borehole Vertical seismic profile
33.
Atterberg limits
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The Atterberg limits are a basic measure of the critical water contents of a fine-grained soil, its shrinkage limit, plastic limit, and liquid limit. As a dry, clayey soil takes on increasing amounts of water, it undergoes changes in behavior. Depending on the content of the soil, it may appear in four states, solid, semi-solid, plastic. In each state, the consistency and behavior of a soil is different, thus, the boundary between each state can be defined based on a change in the soils behavior. The Atterberg limits can be used to distinguish between silt and clay, and it can distinguish different types of silts and clays. These limits were created by Albert Atterberg, a Swedish agriculturist and they were later refined by Arthur Casagrande. These distinctions in soil are used in assessing the soils that are to have built on. Soils when wet retain water and some expand in volume, the amount of expansion is related to the ability of the soil to take in water and its structural make-up. These tests are used on clayey or silty soils since these are the soils that expand. Clays and silts react with the water and thus change sizes and have varying shear strengths, as a hard, rigid solid in the dry state, soil becomes a crumbly semisolid when a certain moisture content, termed the shrinkage limit, is reached. If it is a soil, this soil will also begin to swell in volume as this moisture content is exceeded. Increasing the water content beyond the soils plastic limit will transform it into a malleable, plastic mass, the soil will remain in this plastic state until its liquid limit is exceeded, which causes it to transform into a viscous liquid that flows when jarred. The shrinkage limit is the content where further loss of moisture will not result in any more volume reduction. The test to determine the limit is ASTM International D4943. The shrinkage limit is less commonly used than the liquid. The plastic limit is determined by rolling out a thread of the portion of a soil on a flat. The procedure is defined in ASTM Standard D4318, if the soil is at a moisture content where its behavior is plastic, this thread will retain its shape down to a very narrow diameter. The sample can then be remolded and the test repeated, as the moisture content falls due to evaporation, the thread will begin to break apart at larger diameters
34.
Hydrometer
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A hydrometer or areometer is an instrument that measures the specific gravity of liquids—the ratio of the density of the liquid to the density of water. A hydrometer is usually made of glass, and consists of a cylindrical stem, the liquid to test is poured into a tall container, often a graduated cylinder, and the hydrometer is gently lowered into the liquid until it floats freely. The point at which the surface of the liquid touches the stem of the hydrometer correlates to specific gravity, Hydrometers usually contain a scale inside the stem, so that the person using it can read specific gravity. A variety of scales exist for different contexts, principle Operation of the hydrometer is based on that a solid suspended in a fluid is buoyed by a force equal to the weight of the fluid displaced by the submerged part of the suspended solid. Thus, the lower the density of the substance, the farther the hydrometer sinks, thus, it is based on the principle of floatation. An early description of a hydrometer appears in a letter from Synesius of Cyrene to the Greek scholar Hypatia of Alexandria, in Synesius fifteenth letter, he requests Hypatia to make a hydrometer for him. Hypatia is given credit for inventing the hydrometer sometime in the late 4th century or early 5th century, the instrument in question is a cylindrical tube, which has the shape of a flute and is about the same size. It has notches in a line, by means of which we are able to test the weight of the waters. A cone forms a lid at one of the extremities, closely fitted to the tube, the cone and the tube have one base only. Whenever you place the tube in water, it remains erect and you can then count the notches at your ease, and in this way ascertain the weight of the water. According to the Encyclopedia of the History of Arabic Science, it was used by Abū Rayhān al-Bīrūnī in the 11th century and it later appeared again in the work of Jacques Alexandre César Charles in the 18th century. In low-density liquids such as kerosene, gasoline, and alcohol, the hydrometer sinks deeper, and in high-density liquids such as brine, milk, and acids it doesnt sink so far. In many industries a set of hydrometers is used — covering specific gravity ranges of 1. 0–0.95,0. 95–0.9 etc. — to provide precise measurements. Modern hydrometers usually measure specific gravity but different scales were used in certain industries, examples include, API gravity, universally used worldwide by the petroleum industry. A lactometer is used to check purity of cows milk, the specific gravity of milk does not give a conclusive indication of its composition since milk contains a variety of substances that are either heavier or lighter than water. Additional tests for fat content are necessary to determine overall composition, the instrument is graduated into a hundred parts. Milk is poured in and allowed to stand until the cream has formed, the device works on the principle of Archimedes principle that a solid suspended in a fluid is buoyed by a force equal to the weight of the fluid displaced. If the milk sample is pure, then the lactometer floats on it and if it is adulterated or impure, an alcoholmeter is a hydrometer that indicates the alcoholic strength of liquids
35.
Proctor compaction test
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The Proctor compaction test is a laboratory method of experimentally determining the optimal moisture content at which a given soil type will become most dense and achieve its maximum dry density. The term Proctor is in honor of R. R. Proctor and his original test is most commonly referred to as the standard Proctor compaction test, later on, his test was updated to create the modified Proctor compaction test. These laboratory tests generally consist of compacting soil at known moisture content into a mold of standard dimensions using a compactive effort of controlled magnitude. The soil is compacted into the mold to a certain amount of equal layers. This process is repeated for various moisture contents and the dry densities are determined for each. The graphical relationship of the dry density to moisture content is then plotted to establish the compaction curve, the maximum dry density is finally obtained from the peak point of the compaction curve and its corresponding moisture content, also known as the optimal moisture content. Currently, the procedures and equipment details for the standard Proctor compaction test is designated by ASTM D698, also, the modified Proctor compaction test is designated by ASTM D1557 and AASHTO T180. Proctors fascination with geotechnical engineering began when taking his undergraduate studies at University of California and he was interested in the publications of Sir Alec Skempton and his ideas on in situ behavior of natural clays. Skempton formulated concepts and porous water coefficients that are widely used today. Ghayttha found that in an environment, the soil could be compacted to the point where the air could be completely removed. From this, the dry density could be determined by measuring the weight of the soil before and after compaction, calculating the moisture content. Ralph R. Proctor went on to teach at the University of Arkansas, in 1958, the modified Proctor compaction test was developed as an ASTM standard. A higher and more relevant compaction standard was necessary, there were larger and heavier compaction equipment, like large vibratory compactors and heavier steam rollers. This equipment could produce higher dry densities in soils along with greater stability and these improved properties allowed for the transport of far heavier truck loads over roads and highways. During the 1970s and early 1980s the modified Proctor test became widely used as a modern replacement for the standard Proctor test. Compaction can be defined as the densification of soil by the removal of air. The energy exerted by compaction forces the soil to fill available voids, because a wide range of particles are needed in order to fill all available voids, well-graded soils tend to compact better than poorly graded soils. The degree of compaction of a soil can be measured by its dry unit weight, when water is added to the soil, it functions as a softening agent on the soil particles, causing them to slide between one another more easily
36.
Sieve analysis
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A sieve analysis is a practice or procedure used to assess the particle size distribution of a granular material. The size distribution is often of importance to the way the material performs in use. Being such a technique of particle sizing, it is probably the most common. A gradation test is performed on a sample of aggregate in a laboratory, a typical sieve analysis involves a nested column of sieves with wire mesh cloth. See the separate Mesh page for details of sieve sizing, a representative weighed sample is poured into the top sieve which has the largest screen openings. Each lower sieve in the column has smaller openings than the one above, at the base is a round pan, called the receiver. The column is placed in a mechanical shaker. The shaker shakes the column, usually for some fixed amount of time, after the shaking is complete the material on each sieve is weighed. The weight of the sample of each sieve is then divided by the weight to give a percentage retained on each sieve. The size of the particle on each sieve is then analysed to get a cut-off point or specific size range. The results of this test are provided in form to identify the type of gradation of the aggregate. The entire nest is then agitated, and the material whose diameter is smaller than the opening pass through the sieves. After the aggregate reaches the pan, the amount of material retained in each sieve is then weighed, in order to perform the test, a sufficient sample of the aggregate must be obtained from the source. To prepare the sample, the aggregate should be mixed thoroughly, the total weight of the sample is also required. The results are presented in a graph of percent passing versus the sieve size, on the graph the sieve size scale is logarithmic. To find the percent of aggregate passing through each sieve, first find the percent retained in each sieve, the next step is to find the cumulative percent of aggregate retained in each sieve. To do so, add up the amount of aggregate that is retained in each sieve. The cumulative percent passing of the aggregate is found by subtracting the percent retained from 100%, %Cumulative Passing = 100% - %Cumulative Retained
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Hydraulic conductivity
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Hydraulic conductivity, symbolically represented as K, is a property of vascular plants, soils and rocks, that describes the ease with which a fluid can move through pore spaces or fractures. It depends on the permeability of the material, the degree of saturation. Saturated hydraulic conductivity, Ksat, describes water movement through saturated media, by definition, hydraulic conductivity is the ratio of velocity to hydraulic gradient indicating permeability of porous media.0 and 1.5, with an average value of 1.0. A. F. Salarashayeri & M. Siosemarde give C as usually taken between 1.0 and 1.5, with D in mm and K in cm/s. There are relatively simple and inexpensive laboratory tests that may be run to determine the conductivity of a soil, constant-head method. The constant-head method is used on granular soil. This procedure allows water to move through the soil under a steady state head condition while the quantity of flowing through the soil specimen is measured over a period of time. The water is allowed to flow through the soil without adding any water. The advantage to the method is that it can be used for both fine-grained and coarse-grained soils. When the water table is shallow, the method, a slug test. The method was developed by Hooghoudt in The Netherlands and introduced in the US by Van Bavel en Kirkham, the picture shows a large variation of K -values measured with the augerhole method in an area of 100 ha. The ratio between the highest and lowest values is 25, the cumulative frequency distribution is lognormal and was made with the CumFreq program. The transmissivity is a measure of how water can be transmitted horizontally. Transmissivity should not be confused with the similar word transmittance used in optics, an aquifer may consist of n soil layers. Expressing K i in m/day and d i in m, the transmissivity T i is found in units m2/day. The total transmissivity T t of the aquifer is, T t = ∑ T i where ∑ signifies the summation over all layers i =1,2,3, ⋯, n, the transmissivity of an aquifer can be determined from pumping tests. Influence of the water table When a soil layer is above the table, it is not saturated. When the soil layer is entirely below the table, its saturated thickness corresponds to the thickness of the soil layer itself
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Water content
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Water content or moisture content is the quantity of water contained in a material, such as soil, rock, ceramics, crops, or wood. Water content is used in a range of scientific and technical areas, and is expressed as a ratio. It can be given on a volumetric or mass basis, gravimetric water content is expressed by mass as follows, u = m w m where m w is the mass of water and m is the mass of the substance. Values of Sw can range from 0 to 1, in reality, Sw never reaches 0 or 1 - these are idealizations for engineering use. Water content can be measured using a known volume of the material. In wood drying, this is an important concept, other methods that determine water content of a sample include chemical titrations, determining mass loss on heating, or after freeze drying. In the food industry the Dean-Stark method is commonly used. There are several methods available that can approximate in situ soil water content. Geophysical sensors are used to monitor soil moisture continuously in agricultural. Satellite microwave remote sensing is used to estimate soil moisture based on the large contrast between the properties of wet and dry soil. The microwave radiation is not sensitive to atmospheric variables, and can penetrate through clouds, also, microwave signal can penetrate, to a certain extent, the vegetation canopy and retrieve information from ground surface. The data from remote sensing satellite such as, WindSat, AMSR-E, RADARSAT, ERS-1-2. Moisture may be present as adsorbed moisture at internal surfaces and as capillary condensed water in small pores, at low relative humidities, moisture consists mainly of adsorbed water. At higher relative humidities, liquid water becomes more and more important, in wood-based materials, however, almost all water is adsorbed at humidities below 98% RH. The method used to water content may affect whether water present in this form is accounted for. For a better indication of free and bound water, the activity of a material should be considered. Water molecules may also be present in materials closely associated with molecules, as water of crystallization. In soil science, hydrology and agricultural sciences, water content has an important role for groundwater recharge, agriculture, many recent scientific research efforts have aimed toward a predictive-understanding of water content over space and time.1 in gravel and 0.3 in peat
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Clay
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Clay is a fine-grained natural rock or soil material that combines one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to water content and become hard, brittle. Depending on the content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red. Although many naturally occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size, silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. There is, however, some overlap in size and other physical properties. The distinction between silt and clay varies by discipline, geologists and soil scientists usually consider the separation to occur at a particle size of 2 µm, sedimentologists often use 4–5 μm, and colloid chemists use 1 μm. Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils Atterberg limits, ISO14688 grades clay particles as being smaller than 2 μm and silt particles as being larger. These solvents, usually acidic, migrate through the rock after leaching through upper weathered layers. In addition to the process, some clay minerals are formed through hydrothermal activity. There are two types of deposits, primary and secondary. Primary clays form as residual deposits in soil and remain at the site of formation, secondary clays are clays that have been transported from their original location by water erosion and deposited in a new sedimentary deposit. Clay deposits are associated with very low energy depositional environments such as large lakes. Depending on the source, there are three or four main groups of clays, kaolinite, montmorillonite-smectite, illite, and chlorite. Chlorites are not always considered to be a clay, sometimes being classified as a group within the phyllosilicates. There are approximately 30 different types of clays in these categories. Varve is clay with visible annual layers, which are formed by deposition of those layers and are marked by differences in erosion. This type of deposit is common in glacial lakes
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Silt
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Silt is granular material of a size between sand and clay, whose mineral origin is quartz and feldspar. Silt may occur as a soil or as sediment mixed in suspension with water in a body of such as a river. It may also exist as soil deposited at the bottom of a water body, Silt has a moderate specific area with a typically non-sticky, plastic feel. Silt usually has a floury feel when dry, and a slippery feel when wet, Silt can be visually observed with a hand lens. Silt is created by a variety of physical processes capable of splitting the generally sand-sized quartz crystals of primary rocks by exploiting deficiencies in their lattice and these involve chemical weathering of rock and regolith, and a number of physical weathering processes such as frost shattering and haloclasty. The main process is abrasion through transport, including fluvial comminution, aeolian attrition and it is in semi-arid environments that substantial quantities of silt are produced. Silt is sometimes known as rock flour or stone dust, especially produced by glacial action. Mineralogically, silt is composed mainly of quartz and feldspar, sedimentary rock composed mainly of silt is known as siltstone. Liquefaction created by an earthquake is silt suspended in water that is hydrodynamically forced up from below ground level. In the Udden–Wentworth scale, silt particles range between 0.0039 and 0.0625 mm, larger than clay but smaller than sand particles, ISO14688 grades silts between 0.002 mm and 0.063 mm. In actuality, silt is chemically distinct from clay, and unlike clay, grains of silt are approximately the size in all dimensions, furthermore. Clays are formed from thin plate-shaped particles held together by electrostatic forces, according to the U. S. Department of Agriculture Soil Texture Classification system, the sand-silt distinction is made at the 0.05 mm particle size. The USDA system has been adopted by the Food and Agriculture Organization, in the Unified Soil Classification System and the AASHTO Soil Classification system, the sand-silt distinction is made at the 0.075 mm particle size. Silts and clays are distinguished mechanically by their plasticity, Silt is easily transported in water or other liquid and is fine enough to be carried long distances by air in the form of dust. Thick deposits of silty material resulting from deposition by aeolian processes are called loess. Silt and clay contribute to turbidity in water, Silt is transported by streams or by water currents in the ocean. When silt appears as a pollutant in water the phenomenon is known as siltation, Silt, deposited by annual floods along the Nile River, created the rich, fertile soil that sustained the Ancient Egyptian civilization. In south east Bangladesh, in the Noakhali district, cross dams were built in the 1960s whereby silt gradually started forming new land called chars, the district of Noakhali has gained more than 28 square miles of land in the past 50 years
41.
Peat
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Peat, also called turf, is an accumulation of partially decayed vegetation or organic matter that is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem is the most efficient carbon sink on the planet because peatland plants capture the CO2 which is released from the peat. Sphagnum moss is one of the most common components in peat, soils that contain mostly peat are known as histosols. Peat forms in wetland conditions, where flooding obstructs flows of oxygen from the atmosphere, Peatlands, particularly bogs, are the most important source of peat. That said, other less common types, including fens, pocosins. Landscapes covered in peat are home to specific kinds of plants including Sphagnum moss, ericaceous shrubs, because organic matter accumulates over thousands of years, peat deposits also provide records of past vegetation and climates stored in plant remains like pollen. This allows humans to reconstruct past environments and study changes in land use. Peat is harvested as an important source of fuel in certain parts of the world, by volume, there are about 4 trillion cubic metres of peat in the world, covering a total of around 2% of the global land area, containing about 8 billion terajoules of energy. Over time, the formation of peat is often the first step in the formation of other fossil fuels such as coal. This is also the commonly used in the peat industry. At 106 g CO2/MJ, the carbon dioxide emission intensity of peat is higher than that of coal and natural gas, lastly, peat fires have been responsible for large public health disasters including the 1997 Southeast Asian haze. Peat forms when plant material does not fully decay in acidic and anaerobic conditions and it is composed mainly of wetland vegetation, principally bog plants including mosses, sedges, and shrubs. As it accumulates, the peat holds water and this slowly creates wetter conditions that allow the area of wetland to expand. Peatland features can include ponds, ridges, and raised bogs, most modern peat bogs formed 12,000 years ago in high latitudes after the glaciers retreated at the end of the last ice age. Peat usually accumulates slowly at the rate of about a millimetre per year, using Carbon-dating, scientists found that Peat in peatlands started forming 360 million years ago based on it currently containing 550 Gt of carbon. Peat material is either fibric, hemic, or sapric, fibric peats are the least decomposed and consist of intact fiber. Hemic peats are partially decomposed and sapric are the most decomposed, Phragmites peat is one composed of reed grass, Phragmites australis, and other grasses. It is denser than other types of peat
