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Clay Minerals and Soil Structure Outline 10 11 12 Clay Minerals Identification of Clay Minerals Specific Surface (Ss) Interaction of Water and Clay Minerals Interaction of Clay Particles Soil Structure and Fabric Soil Fabric-Natural Soil Soil Fabric-Clay Soils Soil Fabrics-Granular Soils Loess Suggested Homework References Clay Minerals (c)2001 Brooks/Cole, a division of Thomson Learning, Inc Thomson Learning™ is a trademark used herein under license Figure 2.2 Bowen’s reaction series Figure 2.3A Mechanical erosion due to ocean waves and wind at Yehliu, Taiwan (c)2001 Brooks/Cole, a division of Thomson Learning, Inc Thomson Learning™ is a trademark used herein under license (c)2001 Brooks/Cole, a division of Thomson Learning, Inc Thomson Learning™ is a trademark used herein under license Figure 2.3B (cont.) Mechanical erosion due to ocean waves and wind at Yehliu, Taiwan Figure 2.3C (cont.) Mechanical erosion due to ocean waves and wind at Yehliu, Taiwan (c)2001 Brooks/Cole, a division of Thomson Learning, Inc Thomson Learning™ is a trademark used herein under license (c)2001 Brooks/Cole, a division of Thomson Learning, Inc Thomson Learning™ is a trademark used herein under license Figure 2.3 D (cont.) Mechanical erosion due to ocean waves and wind at Yehliu, Taiwan (c)2001 Brooks/Cole, a division of Thomson Learning, Inc Thomson Learning™ is a trademark used herein under license Figure 2.3E (cont.) Mechanical erosion due to ocean waves and wind at Yehliu, Taiwan Figure 2.7 Scanning electron micrograph of a kaolinite specimen (courtesy of U.S Geological Survey) 8.4 Fabric of Natural Clay Soils (Cont.) Domains and clusters with micropores 1.Domain 2.Cluster 3.Ped 4.Silt grain 5.Micropore 6.Macropore Yong and Sheeran (1973) (from Holtz and Kovacs, 1981) Enlargement 82 8.4 Fabric of Natural Clay Soils (cont.) • Macrostructure, including the stratigraphy of fine-grained soil deposits, has an important influence on soil behavior in engineering practice Joints, fissures, silt and sand seams, root holes, varves, and other defects often control the engineering behavior of the entire soils mass • The microstructure reflects the depositional history and environment of the deposit, its weathering history (both chemical and physical), (From Holtz and Kovacs, 1981) and stress history Clay particle Water 83 Soil Fabrics-Granular Soils 84 9.1 Packing Loose packing Dense packing Holtz and Kovacs, 1981 Honeycombed fabric •Meta-stable structure •Loose fabric •Liquefaction •Sand boil 85 9.1 Packing (Cont.)-Sand Boil Loose sand Kramer, 1996 86 9.1 Packing (Cont.) “Contrary to popular belief, it is not possible to drown in quicksand, unless you really work at it, because the density of quicksand is much greater than that of water Since you can almost float in water, you should easily be able to float in quicksand “(from Holtz and Kovacs, 1981) Help! 87 9.2 Load Transfer Loading The black particles carry most of load The remaining particles prevent the buckling of the loadcarrying chains (From Santamarina et al., 2001) 88 9.3 The Relative Density (Dr) The relative density Dr is used to characterize the density of natural granular soil e max − e Dr = ×100% e max − e γ d max γ d − γ d = × ×100% γd γ d max − γ d The relative density of a natural soil deposit very strongly affects its engineering behavior Consequently, it is important to conduct laboratory tests on samples of the sand at the same relative density as in the field ( from Holtz and Kovacs, 1981) (compaction) (Lambe and Whitman, 1979) 89 Derivation Dr = = e max − e ×100% e max − e γ d max γ − γ d × d ×100% γd γ d max − γ d 90 9.3 The Relative Density (Dr) (Cont.) “The relative density (or void ratio) alone is not sufficient to characterize the engineering properties of granular soils” (Holtz and Kovacs, 1981) Two soils with the same relative density (or void ratio) may contain very different pore sizes That is, the pore size distribution probably is a better parameter to correlate with the engineering properties (Santamarina et al., 2001) : Holtz and Kovacs, 1981 91 10 Loess 92 Loess • Loess is a type of aeolian soils, and the particles are predominantly silt-size The soil structure is mainly stabilized by (1) the capillary force and (2) light cementation arising from the salt and fines (e.g clay) precipitation around the contacts (Holtz and Kovacs, 1981; Santamarina, 2001) Capillary force Cementation • After loess is submerged, collapse of the soil structure occurs due to loss of suction and cementation Why? Capillary force cementation The interaction between water and salts and clay 93 11 Suggested Homework Read Chapter Problem 4-1, 4-3, 4-4, 4-5, 4-6, 4-8(interesting) 94 12 References Main References: Holtz, R.D and Kovacs, W.D (1981) An Introduction to Geotechnical Engineering, Prentice Hall (Chapter 4) Mitchell, J.K (1993) Fundamentals of Soil Behavior, 2nd edition, John Wiley & Sons (Chapter 3) Others: Israelachvili, J (1991) Intermolecular and Surface Forces, 2nd edition, Academic Press Kramer, S.L (1996) Geotechnical Earthquake Engineering, Prentice Hall Lambe, T.W and Whitman, R.V (1979) Soil Mechanics, SI Version, John Wiley & Sons Santamarina, J.C., Klein, K.A and Fam, M.A (2001) Soils and Waves, John Wiley & Sons Van Olphen, H (1991) An Introduction to Clay Colloid Chemistry Reprint edition, Krieger Publishing Company Velde, B (1995) Origin and Mineralogy of Clays Springer Xanthakos, P.P (1991) Surry Walls as Structural Systems, 2nd Edition, McGraw-Hill, Inc 95 Figure 2.5 Atomic structure of kaolinite (after Grim, 1959) (c)2001 Brooks/Cole, a division of Thomson Learning, Inc Thomson Learning™ is a trademark used herein under license [...]... is transformed into kaolinite Feldspar + hydrogen ions+water → clay (kaolinite) + cations, dissolved silica 2KAlSi3O8+2H+ +H2O → Al2Si2O5(OH )4 + 2K+ +4SiO2 •Note that the hydrogen ion displaces the cations 11 1.1 Origin of Clay Minerals (Cont.) • The alternation of feldspar into kaolinite is very common in the decomposed granite • The clay minerals are common in the filling materials of joints and faults... Kovacs, 1981) 14 1.2 Basic Unit-Summary Mitchell, 1993 15 1.3 Synthesis Mitchell, 1993 Noncrystall ine clay -allophane 16 1 .4 1:1 Minerals-Kaolinite Basal spacing is 7.2 Å layer • Si4Al4O10(OH)8 Platy shape • The bonding between layers are van der Waals forces and hydrogen bonds (strong bonding) Trovey, 1971 ( from Mitchell, 1993) 17 µm • There is no interlayer swelling • Width: 0.1~ 4 m, Thickness:... (after Grim 1959 1.7 Chain Structure Clay Minerals Attapulgite • They have lathlike or threadlike morphologies • The particle diameters are from 50 to 100 Å and the length is up to 4 to 5 µm • Attapulgite is useful as a drilling mud in saline environment due to its high stability 4. 7 µm Trovey, 1971 ( from Mitchell, 1993) 27 1.8 Mixed Layer Clays • Different types of clay minerals have similar structures... engineering practice (expansive clay) 5 µm (Holtz and Kovacs, 1981) • Width: 1 or 2 µm, Thickness: 10 Å~1/100 width 19 1.5 2:1 Minerals-Illite (mica-like minerals) • Si8(Al,Mg, shape potassium Fe )4~ 6O20(OH )4 (K,H2O)2 Flaky • The basic structure is very similar to the mica, so it is sometimes referred to as hydrous mica Illite is the chief constituent in many shales K • Some of the Si4+ in the tetrahedral sheet... are van der Waals forces and hydrogen bonds (strong bonding) Trovey, 1971 ( from Mitchell, 1993) 17 µm • There is no interlayer swelling • Width: 0.1~ 4 m, Thickness: 0.05~2 µm 17 1 .4 1:1 Minerals-Halloysite • Si4Al4O10(OH)8·4H2O • A single layer of water between unit layers • The basal spacing is 10.1 Å for hydrated halloysite and 7.2 Å for dehydrated halloysite • If the temperature is over 50 °C or...1.1 Origin of Clay Minerals “The contact of rocks and water produces clays, either at or near the surface of the earth” (from Velde, 1995) Rock +Water → Clay For example, The CO2 gas can dissolve in water and form carbonic acid, which will become hydrogen ions H+ and bicarbonate ions,... 1993) 2 µm • There is no interlayer swelling • Tubular shape while it is hydrated 18 1.5 2:1 Minerals-Montmorillonite (Theoretical • Si8Al4O20(OH )4 nH2O unsubstituted) Film-like shape • There is extensive isomorphous substitution for silicon and aluminum by other cations, which results in charge deficiencies of clay particles • n·H2O and cations exist between unit layers, and the basal spacing is from... that interstratification of layers of different clay minerals can be observed • In general, the mixed layer clays are composed of interstratification of expanded water-bearing layers and non-water-bearing layers Montmorillonite-illite is most common, and chlorite-vermiculite and chlorite-montmorillonite are often found (Mitchell, 1993) 28 1.9 Noncrystalline Clay Materials Allophane Allophane is X-ray amorphous... irregular spherical particles with diameters of 3.5 to 5.0 nm 29 2 Identification of Clay Minerals 30 2.1 X-ray diffraction Mitchell, 1993 • The distance of atomic planes d can be determined based on the Bragg’s equation BC+CD = nλ, nλ = 2d·sinθ, d = nλ/2 sinθ where n is an integer and λ is the wavelength • Different clays minerals have various basal spacing (atomic planes) For example, the basing spacing... 1 2 Electron microscopy Specific surface (Ss) 3 4 Cation exchange capacity (cec) Plasticity chart 34 2.3 Other Methods (Cont.) 5 Potassium determination Well-organized 10Å illite layers contain 9% ~ 10 % K2O 6 Thermogravimetric analysis It is based on changes in weight caused by loss of water or CO2 or gain in oxygen Sometimes, you cannot identify clay minerals only based on one method 35 3 Specific
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