1. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 1 Introduction to Soil Engineering D. A. Cameron 2007

2. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 2 Staff CIVIL ENGINEERING Dr. Don Cameron donald.cameron@unisa.edu.au P2-35 ph 8302 3128

3. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 3 Reference Barnes, G E “Soil Mechanics, Principles and Practice,” MacMillan Press Civil Engineering students will need this text in 3 rd year

4. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 4 The engineering behaviour of soil 1.How soils are formed 2.The basic units which form soil material 3.Engineering concepts of sand, silt and clay 4.The Unified Soil Classification System 5.Stress in soil, total and effective 6.Water flow in saturated soils 7.Erosion, scour or piping 8.Physical improvement of soil (“compaction”) 9.Terminology

5. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 5 Origins of Soils Residual Alluvial Aeolian = wind blown Glacial Marine Lacustrine Organic

6. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 9 Clean Sand - under the microscope 1 mm = 1000  m angular particles from quarry

10. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 10 Fine - Grained Soils Cohesion “Apparent” cohesion  “apparent” tensile strength, arising from electrostatic forces ( are stronger, the finer the particle)

11. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 11 Molecular Structure of the Clay Minerals Lecture 1 Civil Engineering Practice

12. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 13 1. The Tetrahedron Unit Silica, Si 4+ forms a tetrahedron with 4 x O 2- Has a nett -ve charge of 4-

14. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 14 1. Silica Tetrahedron Unit 8-, 4+8-, 4+

15. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 16 Sharing

17. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 17 2. The Aluminium Octahedral Unit Al 3+ with six O 2- Each oxygen ion is left with 1.5 –ve charge

18. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 18 Aluminium Octahedra

19. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 20 Sharing

21. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 22 Kaolinite micelle Gibbsite layer Silicate layer

23. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 23 Kaolinite clay mineral …consists of stacks of micelles Usually hydrogen bonds micelles together:  a strong bond  stable clay mineral

24. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 24 Kaolinite Hydrogen bonding Micelle

25. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 25 Kaolinite

26. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 27 Smectite ( includes montmorillonite )

28. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 28 2. Clay mineral stack 0.1x10 -6 m 1.Clay mineral 1x10 -7 m 3. Aggregate 1 to 4x10 -5 m 4.Clod 0.1 mm = 1x10 -4 m?

29. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 29 Properties of the clay minerals When mixed with a little water, clays become “plastic” i.e. are able to be moulded SO, moisture affects clay soil engineering properties

30. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 31 Illite v Montmorillonite Different forms of bonding between these minerals Illite - main component of shales and other argillaceous rocks - stacks keyed together by K + - nett negative charge Montmorillonite - stacks keyed together by Na ++ or Ca ++ and H 2 O - greater nett negative charge

32. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 33 “Specific surface” = grain area/grain mass

34. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 35 Uses of Kaolinite  Ceramics (China clay)  Filler for paint, rubber & plastics  Glossy paper production

36. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 36 Uses of Montmorillonite The “Smectite” group  facial powder (talc)  filler for paints & rubbers  an electrical, heat & acid resistant porcelain  plasticizer in moulding sands  drilling muds  repairing leaking farm dams

37. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 37 In Summary 1.The basic building blocks of clays are small 2.Si, O, H and Al are the chief ingredients 3.Tetrahedral & octahedral sheets possible 4.Different combinations of sheets form the basic micelles of clay minerals 5.Clay mineral properties vary due to the nature of bonding of the sheets between micelles

38. DIVISION OF INFORMATION TECHNOLOGY, ENGINEERING AND THE ENVIRONMENT 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?