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Phase of soil (Complete Soil Mech. Undestanding Pakage: ABHAY)

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Complete Soil Mech. Undestanding Pakage: ABHAY)

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Phase of soil (Complete Soil Mech. Undestanding Pakage: ABHAY)

  1. 1. Phase Relations N. Sivakugan Duration: 6 min 31 s SIVA 1
  2. 2. Copyright©2001 Objectives To compute the masses (or weights) and volumes of the three different phases. Va Ma=0 air water soil Vs SIVA 2 Mw Ms Mt Vw Vv Vt Phase Diagram Notation M = mass or weight V = volume s = soil grains w = water a = air v = voids t = total
  3. 3. Copyright©2001 Definitions Water content (w) is a measure of the water present in the soil. Va Ma=0 air water soil Vs W M X 100% SIVA 3 Mw Ms Mt Vw Vv Vt Phase Diagram S w = M Expressed as percentage. Range = 0 – 100+%.
  4. 4. Copyright©2001 Definitions Void ratio (e) is a measure of the void volume. Va Ma=0 air water soil Vs V V SIVA 4 Mw Ms Mt Vw Vv Vt Phase Diagram S e = V
  5. 5. Copyright©2001 Definitions Porosity (n) is also a measure of the void volume, expressed as a percentage. Va Ma=0 air water soil Vs n = V X 100% V V SIVA 5 Mw Ms Mt Vw Vv Vt Phase Diagram T Theoretical range: 0 – 100%
  6. 6. Copyright©2001 Definitions Degree of saturation (S) is the percentage of the void volume filled by water. Va Ma=0 air water soil Vs S = V W V X 100% SIVA 6 Mw Ms Mt Vw Vv Vt Phase Diagram V Range: 0 – 100% Dr y Saturate d
  7. 7. Copyright©2001 A Simple Example SIVA 7 air water soil In this illustration, e = 1 n = 50% S = 50%
  8. 8. Copyright©2001 Definitions Bulk density (rm) is the density of the soil in the current state. Va Ma=0 air water soil Vs T r = M m V SIVA 8 Mw Ms Mt Vw Vv Vt Phase Diagram T Units: t/m3, g/ml, kg/m3
  9. 9. Copyright©2001 Definitions Saturated density (rsat) is the density of the soil when the voids are filled with water. Submerged density (r’) is the effective density of the soil when it is submerged. r’ = rsat - rw SIVA 9
  10. 10. Copyright©2001 Definitions Dry density (rd) is the density of the soil in dry state. Va Ma=0 air water soil Vs S r = M d V SIVA 10 Mw Ms Mt Vw Vv Vt Phase Diagram T Units: t/m3, g/ml, kg/m3
  11. 11. Copyright©2001 Definitions Bulk, saturated, dry and submerged unit weights (g) are defined in a similar manner. Here, use weight (kN) instead of mass (kg). g = rg N/m3 kg/m3 m/s2 Specific gravity of the soil grains (Gs) typically varies between 2.6 and 2.8. SIVA 11
  12. 12. Copyright©2001 Phase Relations Consider a fraction of the soil where Vs = 1. SIVA air Se water Serw soil 1 Gsrw e Phase Diagram The other volumes can be obtained from the previous definitions. Mass = Density x Volume volumes masses The masses can be obtained from:
  13. 13. Copyright©2001 Phase Relations From the previous definitions, Serw Se soil w = M W = Se G n V V SIVA 13 air water 1 Gsrw e Phase Diagram S S M e e V T + = = 1
  14. 14. Copyright©2001 Phase Relations Serw Se soil r = M T = + r m e r = M T = + r sat e r M S r d e SIVA 14 air water 1 Gsrw e Phase Diagram W S T G Se V + 1 W S T G e V + 1 W S T G V + = = 1
  15. 15. Copyright©2001 Try not to memorise the equations. Understand the definitions, and develop the relations from the phase diagram with VS = 1; Assume GS (2.6-2.8) when not given; Do not mix densities and unit weights; Soil grains are incompressible. Their mass and volume remain the same at any void ratio. SIVA 15
  16. 16. Copyright©2001 A Suggestion.. If you can remember one thing in phase relations, that should be .. air water SerSe w 1 Gsrw e soil SIVA 16
  17. 17. Copyright©2001 Testing Times… State whether the following are true or false? (a) Dry density is greater than submerged density (b) In unsaturated soils, water content is always less than 100%. (c) Larger the void ratio, larger the porosity. SIVA 17 True False True

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