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The+clay+minerals+2007

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  • 1. Introduction to Soil Engineering D. A. Cameron 2007
  • 2. Staff CIVIL ENGINEERING Dr. Don Cameron [email_address] P2-35 ph 8302 3128
  • 3. Reference
    • Barnes, G E
    • “ Soil Mechanics, Principles and Practice,” MacMillan Press
    • Civil Engineering students will need this text in 3 rd year
  • 4. The engineering behaviour of soil
    • How soils are formed
    • The basic units which form soil material
    • Engineering concepts of sand, silt and clay
    • The Unified Soil Classification System
    • Stress in soil, total and effective
    • Water flow in saturated soils
    • Erosion, scour or piping
    • Physical improvement of soil (“compaction”)
    • Terminology
  • 5. Origins of Soils
    • Residual
    • Alluvial
    • Aeolian = wind blown
    • Glacial
    • Marine
    • Lacustrine
    • Organic
  • 6. Mountains Lakes, estuaries, deltas Ocean River valleys Coastline G B, ‘C’ G S C, O (organic) M = silts Water Transport and Soil Development
  • 7. Soil from Rocks = Residual
    • SAND - quartz, silica
    • SILT - finer quartz & silica (8:4:2)
    • CLAY - clay minerals (from weathered feldspar & mica )
      • very fine “clay” particles
  • 8. Particle Interactions
    • Coarse soils v. Fine soils
    • [sand and gravel] v. [silt and clay]
    • STRENGTH DERIVED FROM
    • Friction, interlock v.
    • physico-chemical interaction
  • 9. Clean Sand - under the microscope 1 mm = 1000  m angular particles from quarry
  • 10. Fine - Grained Soils
    • Cohesion
    • “ Apparent” cohesion  “apparent” tensile strength,
    • arising from
    • electrostatic forces
    • ( are stronger, the finer the particle)
  • 11. Molecular Structure of the Clay Minerals Lecture 1 Civil Engineering Practice
  • 12.
    • http://pubpages.unh.edu/~harter/crystal.htm#
    • Phyllosilicates
    • are the clay “building blocks”
    •  Tetrahedrons & Octahedrons
    • Clays form from weathering and secondary sedimentary processes
    • Clays are usually mixed
      • other clays
      • microscopic crystals of carbonates, feldspars, micas and quartz
  • 13. 1. The Tetrahedron Unit
    • Silica, Si 4+
    • forms a tetrahedron
    • with 4 x O 2-
    • Has a nett -ve charge of 4-
  • 14. 1. Silica Tetrahedron Unit 8 - , 4 +
  • 15. Tetrahedral sheets
    • Formed by sharing of O 2- between units
    • Corner O 2- shared, creating the sheet
    • Nett –ve charge at top of tetrahedral sheets!
  • 16. Sharing
  • 17. 2. The Aluminium Octahedral Unit
    • Al 3+ with six O 2-
    • Each oxygen ion is left
    • with 1.5 –ve charge
  • 18. Aluminium Octahedra
  • 19. Octahedral sheets
    • Octahedral sheets formed by each oxygen being bonded to two Al ions
    • Each O ion left with one –ve charge
    • IF charge satisfied by hydrogen ions,
    • the Gibbsite mineral is formed
  • 20. Sharing
  • 21. The Kaolinite CLAY Mineral
    • Top oxygen ions in Silica sheet bonded to Aluminium sheet
    • – “ 1:1 clay mineral”
    • Each top oxygen ion shared by 2 Al and 1 O ion
    • This unit = “a clay micelle ”
    • (approx. 0.7 nm thick and 10 x10 nm)
  • 22. Kaolinite micelle Gibbsite layer Silicate layer
  • 23. Kaolinite clay mineral
    • … consists of stacks of micelles
    • Usually hydrogen bonds micelles together:
    • a strong bond
    • stable clay mineral
  • 24. Kaolinite Hydrogen bonding Micelle
  • 25. Kaolinite
  • 26. 2:1 Clay Minerals “ The Mica Group”
    • 3 sheets , 2 silica tetrahedra,
    • 1 aluminium octahedron = a micelle
    • Many different clay minerals occur with this basic unit
    • e.g. “ Illite” (Adelaide clays) and “Montmorillonite” (basaltic clays)
  • 27. Smectite ( includes montmorillonite )
  • 28.
    • Clay mineral 1x10 -7 m
    2. Clay mineral stack 0.1x10 -6 m 3. Aggregate 1 to 4x10 -5 m
    • Clod 0.1 mm = 1x10 -4 m?
  • 29. Properties of the clay minerals
    • When mixed with a little water, clays become “ plastic” i.e. are able to be mo u lded
    • SO, moisture affects clay soil engineering properties
  • 30. Properties of the clay minerals
    • Can absorb or lose water between the silicate sheets
      • negative charge attracts H 2 O
    • When water is absorbed, clays may
    • Expand !
      • water in spaces between stacked layers
      • Montmorillonite most expandable
      • Kaolinite the least
  • 31. Illite v Montmorillonite Different forms of bonding between these minerals
    • Illite - main component of shales and other argillaceous rocks
      • - s tacks keyed together by K +
      • - nett negative charge
      • Montmorillonite
      • - s tacks keyed together by Na ++ or Ca ++
      • and H 2 O
      • - greater nett negative charge
  • 32. Clay Minerals – capacity for water
    • i) Kaolinite (China clay) Water absorption, approximately 90%
    • ii) Montmorillonite (Bentonite, Smectite) Water absorption, approximately 300 - 700%
    • iii) Illite Intermediate water absorption
  • 33. “ Specific surface” = grain area/grain mass
  • 34. The influence of charges
    • “ The greater the surface area, the greater the charge ”
      • the greater the affinity for water
      • some water strongly adsorbed in a very thin layer
      • other water “free” in the soil “pores”
      • Electrostatic forces give rise to COHESION in soils with clay minerals
  • 35. Uses of Kaolinite
      • C eramics (China clay)
      • Filler for paint, rubber & plastics
      • G lossy paper production
  • 36. Uses of Montmorillonite The “ Smectite ” group
      • facial powder (talc)
      • filler for paints & rubbers
      • an electrical, heat & acid resistant porcelain
      • plasticizer in mo u lding sands
      • drilling muds
      • repairing leaking farm dams
  • 37. In Summary
    • The basic building blocks of clays are small
    • Si, O, H and Al are the chief ingredients
    • Tetrahedral & octahedral sheets possible
    • Different combinations of sheets form the basic micelles of clay minerals
    • Clay mineral properties vary due to the nature of bonding of the sheets between micelles
  • 38. Revision
    • What is a clay micelle ?
    • Describe how a 1:1 clay mineral is formed
    • How does the Mica group of clay minerals differ from the 1:1 clay minerals?