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64-552: The Géotechnique lecture is an biennial lecture on the topic of soil mechanics , organised by the British Geotechnical Association named after its major scientific journal Géotechnique . This should not be confused with the annual BGA Rankine Lecture . Soil mechanics This article describes the genesis and composition of soil, the distinction between pore water pressure and inter-granular effective stress , capillary action of fluids in

128-577: A x {\displaystyle e_{max}} is the "maximum void ratio" corresponding to a very loose state, e m i n {\displaystyle e_{min}} is the "minimum void ratio" corresponding to a very dense state and e {\displaystyle e} is the in situ void ratio. Methods used to calculate relative density are defined in ASTM D4254-00(2006). Thus if D r = 100 % {\displaystyle D_{r}=100\%}

192-575: 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

256-836: 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

320-402: 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

384-430: A mixture of gravel and fine sand, with no coarse sand, the sample may be gap graded . Uniformly graded and gap graded soils are both considered to be poorly graded . There are many methods for measuring particle-size distribution . The two traditional methods are sieve analysis and hydrometer analysis. The size distribution of gravel and sand particles are typically measured using sieve analysis. The formal procedure

448-415: A mixture of particles of different size, shape and mineralogy. Because the size of the particles obviously has a significant effect on the soil behavior, the grain size and grain size distribution are used to classify soils. The grain size distribution describes the relative proportions of particles of various sizes. The grain size is often visualized in a cumulative distribution graph which, for example, plots

512-417: A relatively large specific surface area. The specific surface area (SSA) is defined as the ratio of the surface area of particles to the mass of the particles. Clay minerals typically have specific surface areas in the range of 10 to 1,000 square meters per gram of solid. Due to the large surface area available for chemical, electrostatic, and van der Waals interaction, the mechanical behavior of clay minerals

576-422: A river bed. Wind blown soil deposits ( aeolian soils) also tend to be sorted according to their grain size. Erosion at the base of glaciers is powerful enough to pick up large rocks and boulders as well as soil; soils dropped by melting ice can be a well graded mixture of widely varying particle sizes. Gravity on its own may also carry particles down from the top of a mountain to make a pile of soil and boulders at

640-579: A small but non-negligible amount of fines (5–12%) may be given a dual classification such as SW-SC . Clays and Silts, often called 'fine-grained soils', are classified according to their Atterberg limits ; the most commonly used Atterberg limits are the Liquid Limit (denoted by LL or w l {\displaystyle w_{l}} ), Plastic Limit (denoted by PL or w p {\displaystyle w_{p}} ), and Shrinkage Limit (denoted by SL ). The Liquid Limit

704-414: A soil. As the transitions from one state to another are gradual, the tests have adopted arbitrary definitions to determine the boundaries of the states. The liquid limit is determined by measuring the water content for which a groove closes after 25 blows in a standard test. Alternatively, a fall cone test apparatus may be used to measure the liquid limit. The undrained shear strength of remolded soil at

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768-437: A variety of colours from impurities, such as 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

832-419: A variety of parameters used to describe the relative proportions of air, water and solid in a soil. This section defines these parameters and some of their interrelationships. The basic notation is as follows: V a {\displaystyle V_{a}} , V w {\displaystyle V_{w}} , and V s {\displaystyle V_{s}} represent

896-452: 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

960-546: Is quartz , also called silica , which has the chemical name silicon dioxide. The reason that feldspar is most common in rocks but silica is more prevalent in soils is that feldspar is much more soluble than silica. Silt , Sand , and Gravel are basically little pieces of broken rocks . According to the Unified Soil Classification System , silt particle sizes are in the range of 0.002 mm to 0.075 mm and sand particles have sizes in

1024-405: Is a common example of a residual soil. The common mechanisms of transport are the actions of gravity, ice, water, and wind. Wind blown soils include dune sands and loess . Water carries particles of different size depending on the speed of the water, thus soils transported by water are graded according to their size. Silt and clay may settle out in a lake, and gravel and sand collect at the bottom of

1088-620: 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

1152-459: 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

1216-543: Is defined as the difference between the Liquid Limit and the Plastic Limit of the specimen; it is an indicator of how much water the soil particles in the specimen can absorb, and correlates with many engineering properties like permeability, compressibility, shear strength and others. Generally, the clay having high plasticity have lower permeability and also they are also difficult to be compacted. According to

1280-417: Is defined as the size for which 10% of the particle mass consists of finer particles. Sands and gravels that possess a wide range of particle sizes with a smooth distribution of particle sizes are called well graded soils. If the soil particles in a sample are predominantly in a relatively narrow range of sizes, the sample is uniformly graded . If a soil sample has distinct gaps in the gradation curve, e.g.,

1344-541: Is described in ASTM D6913-04(2009). A stack of sieves with accurately dimensioned holes between a mesh of wires is used to separate the particles into size bins. A known volume of dried soil, with clods broken down to individual particles, is put into the top of a stack of sieves arranged from coarse to fine. The stack of sieves is shaken for a standard period of time so that the particles are sorted into size bins. This method works reasonably well for particles in

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1408-413: Is determined primarily by their Atterberg limits , not by their grain size. If it is important to determine the grain size distribution of fine-grained soils, the hydrometer test may be performed. In the hydrometer tests, the soil particles are mixed with water and shaken to produce a dilute suspension in a glass cylinder, and then the cylinder is left to sit. A hydrometer is used to measure the density of

1472-674: 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

1536-524: 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

1600-474: Is the ratio of the volume of voids to the volume of solids: Porosity , n {\displaystyle n} , is the ratio of volume of voids to the total volume, and is related to the void ratio: Degree of saturation , S {\displaystyle S} , is the ratio of the volume of water to the volume of voids: From the above definitions, some useful relationships can be derived by use of basic algebra. Geotechnical engineers classify

1664-405: Is the water content at which the soil behavior transitions from a plastic solid to a liquid. The Plastic Limit is the water content at which the soil behavior transitions from that of a plastic solid to a brittle solid. The Shrinkage Limit corresponds to a water content below which the soil will not shrink as it dries. The consistency of fine grained soil varies in proportional to the water content in

1728-512: 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

1792-412: Is very sensitive to the amount of pore fluid available and the type and amount of dissolved ions in the pore fluid. The minerals of soils are predominantly formed by atoms of oxygen, silicon, hydrogen, and aluminum, organized in various crystalline forms. These elements along with calcium, sodium, potassium, magnesium, and carbon constitute over 99 per cent of the solid mass of soils. Soils consist of

1856-480: The Unified Soil Classification System (USCS), silts and clays are classified by plotting the values of their plasticity index and liquid limit on a plasticity chart. The A-Line on the chart separates clays (given the USCS symbol C ) from silts (given the symbol M ). LL=50% separates high plasticity soils (given the modifier symbol H ) from low plasticity soils (given the modifier symbol L ). A soil that plots above

1920-497: The Unified Soil Classification System , a #4 sieve (4 openings per inch) having 4.75 mm opening size separates sand from gravel and a #200 sieve with an 0.075 mm opening separates sand from silt and clay. According to the British standard, 0.063 mm is the boundary between sand and silt, and 2 mm is the boundary between sand and gravel. The classification of fine-grained soils, i.e., soils that are finer than sand,

1984-443: The soil pore spaces, soil classification , seepage and permeability , time dependent change of volume due to squeezing water out of tiny pore spaces, also known as consolidation , shear strength and stiffness of soils. The shear strength of soils is primarily derived from friction between the particles and interlocking, which are very sensitive to the effective stress. The article concludes with some examples of applications of

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2048-538: The A-line and has LL>50% would, for example, be classified as CH . Other possible classifications of silts and clays are ML , CL and MH . If the Atterberg limits plot in the"hatched" region on the graph near the origin, the soils are given the dual classification 'CL-ML'. The effects of the water content on the strength of saturated remolded soils can be quantified by the use of the liquidity index , LI : When

2112-446: The LI is 1, remolded soil is at the liquid limit and it has an undrained shear strength of about 2 kPa. When the soil is at the plastic limit , the LI is 0 and the undrained shear strength is about 200 kPa. The density of sands (cohesionless soils) is often characterized by the relative density, D r {\displaystyle D_{r}} where: e m

2176-429: The USCS, gravels (given the symbol G ) and sands (given the symbol S ) are classified according to their grain size distribution. For the USCS, gravels may be given the classification symbol GW (well-graded gravel), GP (poorly graded gravel), GM (gravel with a large amount of silt), or GC (gravel with a large amount of clay). Likewise sands may be classified as being SW , SP , SM or SC . Sands and gravels with

2240-614: The arrangement of particles in a load carrying framework as well as the pore size and pore fluid distributions. Engineering geologists also classify soils based on their genesis and depositional history. In the US and other countries, the Unified Soil Classification System (USCS) is often used for soil classification. Other classification systems include the British Standard BS 5930 and the AASHTO soil classification system. In

2304-420: The base; soil deposits transported by gravity are called colluvium . The mechanism of transport also has a major effect on the particle shape. For example, low velocity grinding in a river bed will produce rounded particles. Freshly fractured colluvium particles often have a very angular shape. Silts, sands and gravels are classified by their size, and hence they may consist of a variety of minerals. Owing to

2368-415: 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

2432-525: The density of the mixture minus the density of water is useful if the soil is submerged under water: where ρ w {\displaystyle \rho _{w}} is the density of water Water Content , w {\displaystyle w} is the ratio of mass of water to mass of solid. It is easily measured by weighing a sample of the soil, drying it out in an oven and re-weighing. Standard procedures are described by ASTM. Void ratio , e {\displaystyle e} ,

2496-462: The density of the mixture, i.e., the total mass of air, water, solids divided by the total volume of air water and solids (the mass of air is assumed to be zero for practical purposes): Dry Density , ρ d {\displaystyle \rho _{d}} , is the mass of solids divided by the total volume of air water and solids: Buoyant Density , ρ ′ {\displaystyle \rho '} , defined as

2560-399: The first known writing medium. Clay 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,

2624-516: 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

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2688-475: The geologic cycle by becoming igneous rock. Physical weathering includes temperature effects, freeze and thaw of water in cracks, rain, wind, impact and other mechanisms. Chemical weathering includes dissolution of matter composing a rock and precipitation in the form of another mineral. Clay minerals, for example can be formed by weathering of feldspar , which is the most common mineral present in igneous rock. The most common mineral constituent of silt and sand

2752-414: The liquid limit is approximately 2 kPa. The Plastic Limit is the water content below which it is not possible to roll by hand the soil into 3 mm diameter cylinders. The soil cracks or breaks up as it is rolled down to this diameter. Remolded soil at the plastic limit is quite stiff, having an undrained shear strength of the order of about 200 kPa. The Plasticity Index of a particular soil specimen

2816-641: The mass, M, by the acceleration due to gravity, g; e.g., W s = M s g {\displaystyle W_{s}=M_{s}g} Specific Gravity is the ratio of the density of one material compared to the density of pure water ( ρ w = 1 g / c m 3 {\displaystyle \rho _{w}=1g/cm^{3}} ). Specific gravity of solids , G s = ρ s ρ w {\displaystyle G_{s}={\frac {\rho _{s}}{\rho _{w}}}} Note that specific weight , conventionally denoted by

2880-433: The masses of air, water and solids in a soil mixture; ρ a {\displaystyle \rho _{a}} , ρ w {\displaystyle \rho _{w}} , and ρ s {\displaystyle \rho _{s}} represent the densities of the constituents (air, water and solids) in a soil mixture; Note that the weights, W, can be obtained by multiplying

2944-404: 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,

3008-724: 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

3072-454: The percentage of particles finer than a given size as a function of size. The median grain size, D 50 {\displaystyle D_{50}} , is the size for which 50% of the particle mass consists of finer particles. Soil behavior, especially the hydraulic conductivity , tends to be dominated by the smaller particles, hence, the term "effective size", denoted by D 10 {\displaystyle D_{10}} ,

3136-467: 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,

3200-705: The principles of soil mechanics such as slope stability, lateral earth pressure on retaining walls, and bearing capacity of foundations. The primary mechanism of soil creation is the weathering of rock. All rock types ( igneous rock , metamorphic rock and sedimentary rock ) may be broken down into small particles to create soil. Weathering mechanisms are physical weathering, chemical weathering, and biological weathering Human activities such as excavation, blasting, and waste disposal, may also create soil. Over geologic time, deeply buried soils may be altered by pressure and temperature to become metamorphic or sedimentary rock, and if melted and solidified again, they would complete

3264-447: The range of 0.075 mm to 4.75 mm. Gravel particles are broken pieces of rock in the size range 4.75 mm to 100 mm. Particles larger than gravel are called cobbles and boulders. Soil deposits are affected by the mechanism of transport and deposition to their location. Soils that are not transported are called residual soils —they exist at the same location as the rock from which they were generated. Decomposed granite

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3328-401: The sand and gravel size range. Fine particles tend to stick to each other, and hence the sieving process is not an effective method. If there are a lot of fines (silt and clay) present in the soil it may be necessary to run water through the sieves to wash the coarse particles and clods through. A variety of sieve sizes are available. The boundary between sand and silt is arbitrary. According to

3392-447: The sand or gravel is very dense, and if D r = 0 % {\displaystyle D_{r}=0\%} the soil is extremely loose and unstable. 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

3456-696: 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

3520-841: 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 )

3584-409: The soil particle types by performing tests on disturbed (dried, passed through sieves, and remolded) samples of the soil. This provides information about the characteristics of the soil grains themselves. Classification of the types of grains present in a soil does not account for important effects of the structure or fabric of the soil, terms that describe compactness of the particles and patterns in

3648-584: The stability of quartz compared to other rock minerals, quartz is the most common constituent of sand and silt. Mica, and feldspar are other common minerals present in sands and silts. The mineral constituents of gravel may be more similar to that of the parent rock. The common clay minerals are montmorillonite or smectite , illite , and kaolinite or kaolin. These minerals tend to form in sheet or plate like structures, with length typically ranging between 10  m and 4x10  m and thickness typically ranging between 10  m and 2x10  m, and they have

3712-624: The suspension as a function of time. Clay particles may take several hours to settle past the depth of measurement of the hydrometer. Sand particles may take less than a second. Stokes' law provides the theoretical basis to calculate the relationship between sedimentation velocity and particle size. ASTM provides the detailed procedures for performing the Hydrometer test. Clay particles can be sufficiently small that they never settle because they are kept in suspension by Brownian motion , in which case they may be classified as colloids . There are

3776-406: The symbol γ {\displaystyle \gamma } may be obtained by multiplying the density ( ρ {\displaystyle \rho } ) of a material by the acceleration due to gravity, g {\displaystyle g} . Density , Bulk Density , or Wet Density , ρ {\displaystyle \rho } , are different names for

3840-548: 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

3904-525: The volumes of air, water and solids in a soil mixture; W a {\displaystyle W_{a}} , W w {\displaystyle W_{w}} , and W s {\displaystyle W_{s}} represent the weights of air, water and solids in a soil mixture; M a {\displaystyle M_{a}} , M w {\displaystyle M_{w}} , and M s {\displaystyle M_{s}} represent

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3968-426: 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

4032-493: 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

4096-461: 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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