2. What is compaction? A simple ground improvement technique, where the soil is densified through external compactive effort. + water = Compactive effort

4. Why compact soils? Increases strength Decreases permeability Reduces settlement Reduces shrinkage Applications: Roads Foundations Embankments Dams Aircraft runways Parking areas Paving Retaining walls Rammed earth structures Etc. etc.

5. Theory: Ralph R. Proctor (circa 1933) related compaction to four variables: Dry density Moisture content Compactive effort Soil type Laboratory tests Mould (standard dimensions) Hammer (standard cross-section area, weight, drop) Method (standard number of layers and number of drops for each layer) Mositure content

6. Compaction Curve Water content Dry density (  d ) optimum water content  d, max Soil grains densely packed - good strength and stiffness - low permeability

7. Compaction Curve What happens to the relative quantities of the three phases with addition of water? Water content Dry density (  d ) soil water air difficult to expel all air lowest void ratio and highest dry density at optimum w

8. Zero Air Void Curve All compaction points should lie to the left of ZAV curve - corresponds to 100% saturation Water content Dry density (  d ) Zero air void curve (S=100%) S<100% S>100% (impossible)

9. Effect of Compactive Effort Increasing compactive effort results in: E1E1 E 2 (>E 1 ) Lower optimum water content Higher maximum dry density Water content Dry density (  d )

10. Compaction and Clay Fabric Higher water content or higher compactive effort gives more dispersed fabric. more dispersed fabric Water content Dry density (  d )

11. Line of Optimum Water content Dry density (  d ) Compaction curves for different efforts Line of optimum

12. Laboratory Compaction Test - to obtain the compaction curve and define the optimum water content and maximum dry density for a specific compactive effort. hammer Standard Proctor: Modified Proctor: 3 layers 25 blows per layer 5 layers 25 blows per layer 2.7 kg hammer 300 mm drop 4.9 kg hammer 450 mm drop 1000 ml compaction mould

13. Compaction Control -a systematic exercise where you check at regular intervals whether the compaction was done to specifications. e.g., 1 test per 1000 m 3 of compacted soil Minimum dry density Range of water content Field measurements (of  d ) obtained using sand cone nuclear density meter

22. simple stress (Axial stress) Stress (Pascal) = Force (Newton) Area (square metre) Mass x gravity Area Reaction force

23. Soil mechanics: stress Stress due to the weight of soil above  v =  h  v = vertical stress (kPa)  = unit weight of soil (kN/m 3 ) h  = depth (m) 33 33 22 22 Horizontal stresses Stress ellipsiod

24. Soil mechanics: stress Stress due to the weight of soil above  v =  h 33 33 22 22 Horizontal stresses  v = vertical stress (kPa)  = unit weight of soil (kN/m 3 ) h  = depth (m)

25. Circular failure surface due to shearing of the soil Soil mechanics: stress & strain

26. Barham River valley Apollo Bay 1987 Moorabool River valley Gheringhap 2001

27. shear stress Normal stress (  ) Shear stress (  ) Coulomb Equation  = c +  tan   = shear stress c = cohesion  = normal stress  = angle of shearing resistance Charles-Augustin de Coulomb 1736 - 1806

28. shear stress The groundwater in the pore spaces creates an uplift pressure – the pore water pressure – to the shear plane. The pore water pressure relates to the pressure head caused by the weight of water and rock above Water table The normal stress (  )is countered by the pore water pressure (u) and the result (  – u) is called the effective stress (  ’)  u Mohr - Coulomb Equation  = c’ +  ’ tan  ’  = shear stress c’ = effective cohesion  ’ = effective stress  ’ = effective angle of shearing resistance

29. Slope mechanics: rainfall as a trigger of instability Pore water pressure time Rainfall event Water table Raising the watertable increases the pore-water pressure and reduces the effective stress, which in turn lowers the soil’s shear strength and causes a shear failure

30. Soil mechanics: stress Stress due to the weight of soil above  v =  h  v = vertical stress (kPa)  = unit weight of soil (kN/m 3 ) h  = distance (m) 33 33 22 22 Horizontal stresses Stress ellipsiod

31. Soil mechanics: strain Strain is the change in shape caused by the application of stress

32. Kinds of strain Strain ellipsoid Oblate (  1 >  2 =  3 ) Prolate (  1 =  2 >  3 ) Triaxial (  1 >  2 >  3 )

33. Introduction to Consolidation When a saturated clay is loaded externally, saturated clay GL the water is squeezed out of the clay over a long time (due to low permeability of the clay).

34. This leads to settlements occurring over a long time, which could be several years. time settlement Soil Consolidation

35. In granular soils… Granular soils are freely drained, and thus the settlement is instantaneous. time settlement

36. Laboratory testing consolidation