The+clay+minerals+2007

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The+clay+minerals+2007

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

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