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Phase Relations

This article explains the computation of masses, volumes, and properties of soil phases like air, water, and soil grains. It provides definitions and examples of water content, void ratio, porosity, degree of saturation, and bulk density.

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Phase Relations

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  1. Phase Relations N. Sivakugan Duration: 6 min 31 s

  2. Va Ma=0 air Vv Vw water Mw Vt Mt soil Vs Ms Objectives To compute the masses (or weights) and volumes of the three different phases. NotationM = mass or weight V = volume s = soil grains w = water a = airv = voidst = total Phase Diagram

  3. Va Ma=0 air Vv Vw water Mw Mt Vt soil Vs Ms Definitions Water content (w) is a measure of the water present in the soil. X 100% Expressed as percentage. Range = 0 – 100+%. Phase Diagram

  4. Va Ma=0 air Vv Vw water Mw Mt Vt soil Vs Ms Definitions Void ratio (e) is a measure of the void volume. Phase Diagram

  5. Va Ma=0 air Vv Vw water Mw Mt Vt soil Vs Ms Definitions Porosity (n) is also a measure of the void volume, expressed as a percentage. X 100% Theoretical range: 0 – 100% Phase Diagram

  6. Va Ma=0 air Vv Vw water Mw Mt Vt soil Vs Ms Definitions Degree of saturation (S) is the percentage of the void volume filled by water. X 100% Range: 0 – 100% Dry Saturated Phase Diagram

  7. air water soil A Simple Example In this illustration, e = 1 n = 50% S = 50%

  8. Va Ma=0 air Vv Vw water Mw Mt Vt soil Vs Ms Definitions Bulk density (m) is the density of the soil in the current state. Units: t/m3, g/ml, kg/m3 Phase Diagram

  9. Definitions Saturated density (sat) is the density of the soil when the voids are filled with water. Submerged density (’) is the effective density of the soil when it is submerged. ’ = sat - w

  10. Va Ma=0 air Vv Vw water Mw Mt Vt soil Vs Ms Definitions Dry density (d) is the density of the soil in dry state. Units: t/m3, g/ml, kg/m3 Phase Diagram

  11. N/m3 kg/m3 m/s2 Definitions Bulk, saturated, dry and submerged unit weights () are defined in a similar manner. Here, use weight (kN) instead of mass (kg).  = g Specific gravity of the soil grains (Gs) typically varies between 2.6 and 2.8.

  12. air e Se water Sew soil 1 Gsw Phase Relations The other volumes can be obtained from the previous definitions. Consider a fraction of the soil where Vs = 1. The masses can be obtained from: Mass = Density x Volume volumes masses Phase Diagram

  13. air e Se water Sew soil 1 Gsw Phase Relations From the previous definitions, Phase Diagram

  14. air e Se water Sew soil 1 Gsw Phase Relations Phase Diagram

  15. 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.

  16. air water e Se Sew soil Gsw 1 A Suggestion.. If you can remember one thing in phase relations, that should be ..

  17. Testing Times… State whether the following are true or false? (a) Dry density is greater than submerged density True (b) In unsaturated soils, water content is always less than 100%. False (c) Larger the void ratio, larger the porosity. True

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