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43-509: The Gezira (which means "island") is particularly suited to irrigation because the soil slopes away from the Blue Nile and water therefore naturally runs through the irrigation canals by gravity. The soil has a high clay content which keeps down losses from seepage . Reginald Wingate , the British governor-general of Sudan, originally envisaged the farmers growing wheat but this was abandoned as

86-479: A close collaborator of Karl Terzaghi (both pioneers of soil mechanics ). Distinctions in soils are used in assessing soil which is to have a structure built on them. Soils when wet retain water, and some expand in volume ( smectite clay). The amount of expansion is related to the ability of the soil to take in water and its structural make-up (the type of minerals present: clay , silt , or sand ). These tests are mainly used on clayey or silty soils since these are

129-575: A gel of orthosilicic acid ).) The clay minerals formed depend on the composition of the source rock and the climate. Acid weathering of feldspar -rich rock, such as granite , in warm climates tends to produce kaolin. Weathering of the same kind of rock under alkaline conditions produces illite . Smectite forms by weathering of igneous rock under alkaline conditions, while gibbsite forms by intense weathering of other clay minerals. There are two types of clay deposits: primary and secondary. Primary clays form as residual deposits in soil and remain at

172-836: A great capacity to take up water, and they increase greatly in volume when they do so. When dried, they shrink back to their original volume. This produces distinctive textures, such as mudcracks or "popcorn" texture, in clay deposits. Soils containing swelling clay minerals (such as bentonite ) pose a considerable challenge for civil engineering, because swelling clay can break foundations of buildings and ruin road beds. Clay minerals most commonly form by prolonged chemical weathering of silicate-bearing rocks. They can also form locally from hydrothermal activity. Chemical weathering takes place largely by acid hydrolysis due to low concentrations of carbonic acid , dissolved in rainwater or released by plant roots. The acid breaks bonds between aluminium and oxygen, releasing other metal ions and silica (as

215-402: A major challenge in civil engineering . The defining mechanical property of clay is its plasticity when wet and its ability to harden when dried or fired. Clays show a broad range of water content within which they are highly plastic, from a minimum water content (called the plastic limit ) where the clay is just moist enough to mould, to a maximum water content (called the liquid limit) where

258-443: A rate of 120 blows per minute, during which the groove closes up gradually as a result of the impact. The number of blows for the groove to close is recorded. The moisture content at which it takes 25 drops of the cup to cause the groove to close over a distance of 12.7 millimetres (0.50 in) is defined as the liquid limit. The test is normally run at several moisture contents, and the moisture content which requires 25 blows to close

301-429: A reddish or brownish colour from small amounts of iron oxide . Clays develop plasticity when wet but can be hardened through firing . Clay is the longest-known ceramic material. Prehistoric humans discovered the useful properties of clay and used it for making pottery . Some of the earliest pottery shards have been dated to around 14,000 BCE, and clay tablets were the first known writing medium. Clay

344-452: Is Armenian bole , which is used to soothe an upset stomach. Some animals such as parrots and pigs ingest clay for similar reasons. Kaolin clay and attapulgite have been used as anti-diarrheal medicines. Clay as the defining ingredient of loam is one of the oldest building materials on Earth , among other ancient, naturally occurring geologic materials such as stone and organic materials like wood. Between one-half and two-thirds of

387-441: Is a measure of the plasticity of soil. The plasticity index is the size of the range of water contents where the soil exhibits plastic properties. The PI is the difference between the liquid and plastic limits (PI = LL-PL). Soils with a high PI tend to be clay, those with a lower PI tend to be silt, and those with a PI of 0 (non-plastic) tend to have little or no silt or clay. Soil descriptions based on PI: The liquidity index (LI)

430-620: Is a unique type of marine clay indigenous to the glaciated terrains of Norway , North America , Northern Ireland , and Sweden . It is a highly sensitive clay, prone to liquefaction , and has been involved in several deadly landslides . Modelling clay is used in art and handicraft for sculpting . Clays are used for making pottery , both utilitarian and decorative, and construction products, such as bricks, walls, and floor tiles. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware, stoneware, and porcelain. Prehistoric humans discovered

473-505: Is also a close relationship between the limits and properties of soil, such as compressibility , permeability , and strength . This is thought to be very useful because as limit determination is relatively simple, it is more difficult to determine these other properties. Thus, the Atterberg limits are used to identify the soil's classification and allow for empirical correlations for some other engineering properties. The plasticity index (PI)

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516-459: Is clay with visible annual layers that are formed by seasonal deposition of those layers and are marked by differences in erosion and organic content. This type of deposit is common in former glacial lakes . When fine sediments are delivered into the calm waters of these glacial lake basins away from the shoreline, they settle to the lake bed. The resulting seasonal layering is preserved in an even distribution of clay sediment banding. Quick clay

559-406: Is considered non-plastic if a thread cannot be rolled out down to 3.2 mm at any moisture possible. The liquid limit (LL) is conceptually defined as the water content at which the behavior of a clayey soil changes from the plastic state to the liquid state. However, the transition from plastic to liquid behavior is gradual over a range of water contents, and the shear strength of the soil

602-674: Is important to soil fertility. Clay is a common component of sedimentary rock . Shale is formed largely from clay and is the most common of sedimentary rocks. However, most clay deposits are impure. Many naturally occurring deposits include both silts and clay. Clays are distinguished from other fine-grained soils by differences in size and mineralogy. 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 particle size and other physical properties. The distinction between silt and clay varies by discipline. Geologists and soil scientists usually consider

645-420: Is known as the flow curve. The equation for flow curve is: W = - I f Log N + C Where 'I f is the slope of flow curve and is termed as "Flow Index" The shearing strength of clay at the plastic limit is a measure of its toughness. It is the ratio of the plasticity index to the flow index. It gives us an idea of the shear strength of the soil. The activity of soil is the ratio of the plasticity index to

688-435: Is not actually zero at the liquid limit. The precise definition of the liquid limit is based on standard test procedures described below. Atterberg's original liquid limit test involved mixing a pat of clay in a round-bottomed porcelain bowl of 10–12 cm diameter. A groove was cut through the pat of clay with a spatula, and the bowl was then struck many times against the palm of one hand. Casagrande subsequently standardized

731-496: Is the water content where further loss of moisture will not result in more volume reduction. The test to determine the shrinkage limit is ASTM International D4943. The shrinkage limit is much less commonly used than the liquid and plastic limits. The plastic limit (PL) is determined by rolling out a thread of the fine portion of a soil on a flat, non-porous surface. The procedure is defined in ASTM Standard D ;4318. If

774-512: Is used in many industrial processes, such as paper making, cement production, and chemical filtering . Bentonite clay is widely used as a mold binder in the manufacture of sand castings . Clay is a common filler used in polymer nanocomposites . It can reduce the cost of the composite, as well as impart modified behavior: increased stiffness , decreased permeability , decreased electrical conductivity , etc. Traditional uses of clay as medicine go back to prehistoric times. An example

817-886: Is used in many modern industrial processes, such as paper making, cement production, and chemical filtering . Between one-half and two-thirds of the world's population live or work in buildings made with clay, often baked into brick, as an essential part of its load-bearing structure. Clay is a very common substance. Shale , formed largely from clay, is the most common sedimentary rock. Although many naturally occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts , which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. Mixtures of sand , silt and less than 40% clay are called loam . Soils high in swelling clays ( expansive clay ), which are clay minerals that readily expand in volume when they absorb water, are

860-412: Is used to scale the natural water content of a soil sample to the limit. It can be calculated as a ratio of the difference between natural water content, plastic limit, and liquid limit: LI=(W-PL)/(LL-PL), where W is the natural water content. The consistency index (Ic) indicates a soil's consistency (firmness). It is calculated as CI = (LL-W)/(LL-PL) , where W is the existing water content. The soil at

903-403: The apparatus (by incorporating a crank-rotated cam mechanism to standardize the dropping action) and the procedures to make the measurement more repeatable. Soil is placed into the metal cup (Casagrande cup) portion of the device and a groove is made down at its center with a standardized tool of 2 millimetres (0.079 in) width. The cup is repeatedly dropped 10 mm onto a hard rubber base at

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946-538: The boundary between each state can be defined based on a change in the soil's behavior. The Atterberg limits can be used to distinguish between silt and clay and to distinguish between different types of silts and clays. The water content at which soil changes from one state to the other is known as consistency limits, or Atterberg's limit. These limits were created by Albert Atterberg , a Swedish chemist and agronomist , in 1911. They were later refined by Arthur Casagrande , an Austrian geotechnical engineer and

989-415: The cohesion that makes it plastic. In kaolinite clay, the bonding between plates is provided by a film of water molecules that hydrogen bond the plates together. The bonds are weak enough to allow the plates to slip past each other when the clay is being moulded, but strong enough to hold the plates in place and allow the moulded clay to retain its shape after it is moulded. When the clay is dried, most of

1032-482: The colonial authorities thought that a better cash crop was needed. When it was discovered that Egyptian-type long staple cotton could be grown, this was welcomed as a better choice as it would also provide a raw material for the British textile industry. Cotton was first grown in the area in 1904. After many experiments with irrigation, 24 square kilometres (9.3 sq mi) was put under cultivation in 1914. After

1075-578: The cone penetrometer test. It is based on the measurement of penetration into the soil of a standardized stainless steel cone of specific apex angle, length and mass. Although the Casagrande test is widely used across North America, the fall cone test is much more prevalent in Europe and elsewhere due to being less dependent on the operator in determining the liquid limit. Advantages over Casagrande Method The values of these limits are used in several ways. There

1118-516: The first known writing medium. Clay was chosen due to the local material being easy to work with and widely available. Scribes wrote on the tablets by inscribing them with a script known as cuneiform , using a blunt reed called a stylus , which effectively produced the wedge shaped markings of their writing. After being written on, clay tablets could be reworked into fresh tablets and reused if needed, or fired to make them permanent records. Purpose-made clay balls were used as sling ammunition . Clay

1161-426: The groove is interpolated from the test results. The liquid limit test is defined by ASTM standard test method D 4318. The test method also allows running the test at one moisture content where 20 to 30 blows are required to close the groove; then a correction factor is applied to obtain the liquid limit from the moisture content. Another method for measuring the liquid limit is the fall cone test , also called

1204-467: The liquid limit will have a consistency index of 0, the soil at the plastic limit will have a consistency index of 1, and if W > LL, Ic is negative. That means the soil is in the liquid state. Moreover, the sum of the Liquidity index and Consistency index is equal to 1 (one) The curve obtained from the graph of water content against the log of blows while determining the liquid limit is almost straight and

1247-591: The lowest Nile flood for 200 years, the Sennar Dam was constructed on the Blue Nile to provide a reservoir of water. This dam was completed in 1925 and is about 3 kilometres (1.9 mi) long. The Gezira Scheme was initially financed by the Sudan Plantations Syndicate in London and later the British government guaranteed capital to develop it. The Sudan Gezira Board took over from private enterprise in 1950 and

1290-404: The material. The clay mineral kaolinite is transformed into a non-clay material, metakaolin , which remains rigid and hard if moistened again. Further firing through the stoneware and porcelain stages further recrystallizes the metakaolin into yet stronger minerals such as mullite . The tiny size and plate form of clay particles gives clay minerals a high surface area. In some clay minerals,

1333-724: The moulded clay is just dry enough to hold its shape. The plastic limit of kaolinite clay ranges from about 36% to 40% and its liquid limit ranges from about 58% to 72%. High-quality clay is also tough, as measured by the amount of mechanical work required to roll a sample of clay flat. Its toughness reflects a high degree of internal cohesion. Clay has a high content of clay minerals that give it its plasticity. Clay minerals are hydrous aluminium phyllosilicate minerals , composed of aluminium and silicon ions bonded into tiny, thin plates by interconnecting oxygen and hydroxide ions. These plates are tough but flexible, and in moist clay, they adhere to each other. The resulting aggregates give clay

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1376-467: The plates carry a negative electrical charge that is balanced by a surrounding layer of positive ions ( cations ), such as sodium, potassium, or calcium. If the clay is mixed with a solution containing other cations, these can swap places with the cations in the layer around the clay particles, which gives clays a high capacity for ion exchange . The chemistry of clay minerals, including their capacity to retain nutrient cations such as potassium and ammonium,

1419-497: The removal of heavy metals from waste water and air purification. Atterberg limits 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 . Depending on its water content , soil may appear in one of four states: solid, semi-solid, plastic and liquid. In each state, the consistency and behavior of soil are different, and consequently so are its engineering properties. Thus,

1462-696: The separation to occur at a particle size of 2 μm (clays being finer than silts), sedimentologists often use 4–5 μm, and colloid chemists use 1 μm. Clay-size particles and clay minerals are not the same, despite a degree of overlap in their respective definitions. Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' Atterberg limits . ISO 14688 grades clay particles as being smaller than 2 μm and silt particles as being larger. Mixtures of sand , silt and less than 40% clay are called loam . Some clay minerals (such as smectite ) are described as swelling clay minerals, because they have

1505-841: 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. Secondary clay deposits are typically associated with very low energy depositional environments such as large lakes and marine basins. The main groups of clays include kaolinite , montmorillonite - smectite , and illite . Chlorite , vermiculite , talc , and pyrophyllite are sometimes also classified as clay minerals. There are approximately 30 different types of "pure" clays in these categories, but most "natural" clay deposits are mixtures of these different types, along with other weathered minerals. Clay minerals in clays are most easily identified using X-ray diffraction rather than chemical or physical tests. Varve (or varved clay )

1548-447: 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. The plastic limit is defined as the gravimetric moisture content where the thread breaks apart at a diameter of 3.2 mm (about 1/8 inch). A soil

1591-439: The soils which expand and shrink when the moisture content varies. Clays and silts interact with water and thus change sizes and have varying shear strengths . Thus these tests are used widely in the preliminary stages of designing any structure to ensure that the soil will have the correct amount of shear strength and not too much change in volume as it expands and shrinks with different moisture contents. The shrinkage limit (SL)

1634-542: The useful properties of clay. Some of the earliest pottery shards recovered are from central Honshu , Japan . They are associated with the Jōmon culture, and recovered deposits have been dated to around 14,000 BCE. Cooking pots, art objects, dishware, smoking pipes , and even musical instruments such as the ocarina can all be shaped from clay before being fired. Ancient peoples in Mesopotamia adopted clay tablets as

1677-426: The water molecules are removed, and the plates hydrogen bond directly to each other, so that the dried clay is rigid but still fragile. If the clay is moistened again, it will once more become plastic. When the clay is fired to the earthenware stage, a dehydration reaction removes additional water from the clay, causing clay plates to irreversibly adhere to each other via stronger covalent bonding , which strengthens

1720-493: The world's population, in both traditional societies as well as developed countries, still live or work in buildings made with clay, often baked into brick, as an essential part of their load-bearing structure. Also a primary ingredient in many natural building techniques, clay is used to create adobe , cob , cordwood , and structures and building elements such as wattle and daub , clay plaster, clay render case, clay floors and clay paints and ceramic building material . Clay

1763-689: Was chaired by Arthur Gaitskell . Farmers cooperated with the Sudanese government and the Gezira Board. This network of canals and ditches was 4,300 kilometres (2,700 mi) long, and with the completion in the early 1960s of the Manaqil Extension on the western side of the Gezira Scheme, by 2008 the irrigated area covered 8,800 square kilometres (3,400 sq mi), about half the country's total land under irrigation. The main crop grown in this region

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1806-438: Was still cotton. 14°30′N 33°10′E  /  14.500°N 33.167°E  / 14.500; 33.167 Clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite , Al 2 Si 2 O 5 ( OH ) 4 ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impurities, such as

1849-461: Was used as a mortar in brick chimneys and stone walls where protected from water. Clay, relatively impermeable to water, is also used where natural seals are needed, such as in pond linings, the cores of dams , or as a barrier in landfills against toxic seepage (lining the landfill, preferably in combination with geotextiles ). Studies in the early 21st century have investigated clay's absorption capacities in various applications, such as

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