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G1-Lecture11-Clays

G1-Lecture11-Clays - CEGCEG-4011 Geotechnical Engineering I...

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CEG CEG-4011 Geotechnical Engineering I 4011 Geotechnical Engineering I Lecture #11 Clays Their Properties and Behavior © L. Prieto-Portar, 2009
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Why do clays expand and contract by over 500% and cause so much damage?
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What makes clays such interesting and dangerous soils for foundations? This simple experiment shows the range of strength for a single clay sample.
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The Origins of Soils from Igneous Minerals. The vast majority of soils emerge from seven families of minerals, listed below in a simplified format. Minerals Chemical Name Form Hardness 1. SILICA SiO 2 Quartz crystalline 7 Chert cryptocrystalline Flint Chalcedony 2. FELDSPAR K-silicate Orthoclase 6 Na-silicate Microcline Ca-silicate Plagioclase 3. MICA K-silicate Muscovite 2.5 Fe-silicate Biotite 4. FERROMAGNESIAN Augite, Hornblend, Olivene IRON OXIDES Limonite, Magnetite 5. CARBONATES CaCO 3 Calcite, Aragonite CaMg (CO 3 ) 2 Dolomite Chalk, Gypsum 6. CLAYS Kaolinite, Illite, Montmorillonite 7. LIFE PRODUCTS Cellulose, organics, man-made garbage
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Quartz (amethyst) at top is the silica dioxide's crystalline form. Chalcedony silica (at left) is a cryptocrystalline form of the silica dioxide.
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Orthoclase feldspar. Biotite mica.
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Microcline feldspar at left, and Augite (iron ore) at right.
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Magnetite (iron ore).
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Dolomite (calcium magnesium carbonate)
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Diamond is the hardest material on Earth with a hardness = 10.
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The term clay refers to a number of earthy materials that are composed of minerals rich in alumina, silica and water. Clay is not a single mineral, but a number of minerals. When most clays are wet, they become "plastic" meaning they can be formed and molded into shapes. When they are "fired" (exposed to very high temperatures), the water is driven off and they become as hard as stone. Clay is easily found all over the world. As a result, nearly all civilizations have used some form of clay for everything from bricks to pottery to tablets for recording business transactions. The clay minerals are a part of a general but important group within the phyllosilicates that contain large percentages of water trapped between the silicate sheets, which also include the rocks serpentine, pyrophyllite, talc, mica and chlorite. Most clays are chemically and structurally analogous to other phyllosilicates but contain varying amounts of water and allow more substitution of their cations.
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Physical characteristics that define this group: 1)They can absorb water or lose water from simple humidity changes. 2) When water is absorbed, clays will often expand as the water fills the spaces between the stacked silicate layers. 3) Due to the absorption of water, the specific gravity of clays is highly variable and is lowered with increased water content. 4) Clays tend to form from weathering and secondary sedimentary processes with only a few examples of clays forming in primary igneous or metamorphic environments.
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