2.1 Physical Properties of Soil (Three Phase System)
S.No Point Description
1. Definition Soil is a three-phase system composed of solid particles, water, and air.
Soil's behaviour depends on how these three phases interact. It can be
2. Explanation
fully saturated (no air) or dry (no water).
Helps in understanding soil strength, permeability, and compaction
3. Purpose
characteristics.
4. Advantages Simplifies complex soil behaviour into a manageable model for analysis.
5. Disadvantages Assumes ideal behaviour, may not account for microstructure.
6. Classification/Types Saturated, partially saturated, dry soils based on water/air content.
Volume of soil (V) = Volume of solids (Vs) + Volume of water (Vw) +
7. Working/Process
Volume of air (Va).
8. Suitability Applicable in geotechnical investigations, construction, and foundations.
9. Principle Volume-mass relationships based on phase separation.
10. Objectives To determine key parameters like porosity, void ratio, unit weights, etc.
Used in soil mechanics, field compaction, permeability, and strength
11. Uses/Applications
analysis.
12. Location Subsurface investigations, bore logs, site testing.
13. Situation When designing embankments, foundations, dams, etc.
14. Cost/Economy Low-cost conceptual model, commonly used in all soil analysis.
15. Limitations Cannot represent complex mineral interactions or clay-water chemistry.
16. Remedial Measures Use advanced models (e.g., soil-structure interaction) if needed.
17. Curative Measures Field validation of assumptions.
- Total Volume, V = Va + Vw + Vs
- Void Ratio (e) = Vv/Vs
18. Equations
- Porosity (n) = Vv/V x 100
- Degree of Saturation (S) = Vw/Vv x 100
19. IS or Other Codes IS 2720 Part 2 (Methods of test for soils)
20. Sketch/Figure
21. Examples Used in dry density test, permeability analysis, slope stability assessment.
,2.1 Continued: Water Content & Unit Weights of Soil
A. Water Content (Moisture Content)
S.No Point Description
Water content (w) is the ratio of the weight of water to the weight of dry
1. Definition
soil.
Indicates the amount of water present in a soil sample, expressed as a
2. Explanation
percentage.
3. Purpose To assess soil behaviour such as compaction, strength, and permeability.
4. Advantages Helps in estimating optimum moisture content for compaction.
5. Disadvantages Not suitable alone for clayey soils without Atterberg limits.
6. Classification/Types Natural, optimum, and residual water contents.
7. Working/Process Determined by oven-drying method (as per IS 2720 Part 2).
8. Suitability Useful in earthwork, dams, highways, and embankments.
9. Principle Based on evaporation of water from the sample at 105–110°C.
10. Objectives Evaluate soil dryness/saturation for structural decisions.
11. Uses/Applications Compaction control, bearing capacity evaluation, shrinkage control.
12. Location Used in lab testing for subgrade and embankment soils.
13. Situation Where soil’s water content impacts construction stability.
14. Cost/Economy Very low cost using simple oven method.
15. Limitations Long drying time (~24 hours), can't use on organic soils.
16. Remedial Measures Use rapid moisture meters if needed.
17. Curative Measures Re-test with standard temperature.
18. Equations w=WwWs×100w = \frac{W_w}{W_s} \times 100w=WsWw×100%
19. IS or Other Codes IS 2720 Part 2
20. Sketch/Figure
21. Examples 15% water content in clay = high plasticity.
,B. Unit Weights of Soil
S.No Point Description
1. Definition Unit weight is the weight of soil per unit volume (kN/m³).
2. Explanation It helps in understanding load-bearing capacity and design loads.
3. Purpose To compute stresses in soil mass and for earthwork estimation.
4. Advantages Essential for structural design and geotechnical analysis.
5. Disadvantages Need multiple field/lab methods for accurate result.
Bulk unit weight (γ), dry (γd), saturated (γsat), submerged (γsub), unit
6. Classification/Types
weight of solids (γs).
Determined using core cutter (IS 2720 Part 29) or sand replacement
7. Working/Process
method (IS 2720 Part 28).
8. Suitability Useful in retaining wall, foundation, and dam design.
9. Principle Based on mass/volume relationship of soil solids and voids.
10. Objectives Evaluate soil compaction and stability.
11. Uses/Applications Earth dam design, foundation load analysis.
12. Location Lab or field tests.
13. Situation Construction over soft or variable soil profiles.
14. Cost/Economy Core cutter is cheaper; sand replacement more accurate but costlier.
15. Limitations Core cutter not suitable for coarse-grained soil.
16. Remedial Measures Use sand replacement or nuclear methods.
17. Curative Measures Calibrate equipment, dry sample properly.
- γ=WVγ = \frac{W}{V}γ=VW
- γd=WsVγ_d = \frac{W_s}{V}γd=VWs
18. Equations
- γsat=WsatVγ_{sat} = \frac{W_{sat}}{V}γsat=VWsat
- γsub=γsat−γwγ_{sub} = γ_{sat} - γ_wγsub=γsat−γw
19. IS or Other Codes IS 2720 Part 28, 29
20. Sketch/Figure
21. Examples γbulk = 18.5 kN/m³, γdry = 15.8 kN/m³, γsub = 9.8 kN/m³
, 2.2 Determination of Index Properties of Soil
A. Determination of Water Content by Oven-Drying Method (IS 2720 Part 2)
S.No Point Description
It is the process of measuring the water content (moisture content) of soil
1. Definition
by oven drying at 105–110°C.
Water is evaporated from the soil sample, and the loss in weight is used
2. Explanation
to calculate water content.
To assess moisture in the soil which influences strength, compaction,
3. Purpose
permeability, etc.
4. Advantages Accurate and standardized.
5. Disadvantages Time-consuming (~24 hours), not suitable for organic soils.
6. Classification/Types Rapid moisture tester, infrared drying, oven-drying.
7. Suitability Suitable for all inorganic soils.
8. Working Principle Based on mass difference before and after drying.
9. Limitation Can't be used for soils with organic matter or gypsum.
10. Objective Get accurate water content for engineering purposes.
11. Applications Road construction, compaction control.
12. Test Location Laboratory.
13. Real-life Use Deciding OMC in highways.
14. Cost Low cost – basic oven and weighing balance.
15. Errors Incomplete drying, loss of fines.
16. Precautions Keep oven temperature constant; use airtight containers.
17. IS Code IS 2720 Part 2
18. Equation w=WwWs×100w = \frac{W_w}{W_s} \times 100w=WsWw×100%
19. Sketch
20. Sample Clay soil with 22% moisture.
21. Conclusion Reliable method for standard testing.
S.No Point Description
1. Definition Soil is a three-phase system composed of solid particles, water, and air.
Soil's behaviour depends on how these three phases interact. It can be
2. Explanation
fully saturated (no air) or dry (no water).
Helps in understanding soil strength, permeability, and compaction
3. Purpose
characteristics.
4. Advantages Simplifies complex soil behaviour into a manageable model for analysis.
5. Disadvantages Assumes ideal behaviour, may not account for microstructure.
6. Classification/Types Saturated, partially saturated, dry soils based on water/air content.
Volume of soil (V) = Volume of solids (Vs) + Volume of water (Vw) +
7. Working/Process
Volume of air (Va).
8. Suitability Applicable in geotechnical investigations, construction, and foundations.
9. Principle Volume-mass relationships based on phase separation.
10. Objectives To determine key parameters like porosity, void ratio, unit weights, etc.
Used in soil mechanics, field compaction, permeability, and strength
11. Uses/Applications
analysis.
12. Location Subsurface investigations, bore logs, site testing.
13. Situation When designing embankments, foundations, dams, etc.
14. Cost/Economy Low-cost conceptual model, commonly used in all soil analysis.
15. Limitations Cannot represent complex mineral interactions or clay-water chemistry.
16. Remedial Measures Use advanced models (e.g., soil-structure interaction) if needed.
17. Curative Measures Field validation of assumptions.
- Total Volume, V = Va + Vw + Vs
- Void Ratio (e) = Vv/Vs
18. Equations
- Porosity (n) = Vv/V x 100
- Degree of Saturation (S) = Vw/Vv x 100
19. IS or Other Codes IS 2720 Part 2 (Methods of test for soils)
20. Sketch/Figure
21. Examples Used in dry density test, permeability analysis, slope stability assessment.
,2.1 Continued: Water Content & Unit Weights of Soil
A. Water Content (Moisture Content)
S.No Point Description
Water content (w) is the ratio of the weight of water to the weight of dry
1. Definition
soil.
Indicates the amount of water present in a soil sample, expressed as a
2. Explanation
percentage.
3. Purpose To assess soil behaviour such as compaction, strength, and permeability.
4. Advantages Helps in estimating optimum moisture content for compaction.
5. Disadvantages Not suitable alone for clayey soils without Atterberg limits.
6. Classification/Types Natural, optimum, and residual water contents.
7. Working/Process Determined by oven-drying method (as per IS 2720 Part 2).
8. Suitability Useful in earthwork, dams, highways, and embankments.
9. Principle Based on evaporation of water from the sample at 105–110°C.
10. Objectives Evaluate soil dryness/saturation for structural decisions.
11. Uses/Applications Compaction control, bearing capacity evaluation, shrinkage control.
12. Location Used in lab testing for subgrade and embankment soils.
13. Situation Where soil’s water content impacts construction stability.
14. Cost/Economy Very low cost using simple oven method.
15. Limitations Long drying time (~24 hours), can't use on organic soils.
16. Remedial Measures Use rapid moisture meters if needed.
17. Curative Measures Re-test with standard temperature.
18. Equations w=WwWs×100w = \frac{W_w}{W_s} \times 100w=WsWw×100%
19. IS or Other Codes IS 2720 Part 2
20. Sketch/Figure
21. Examples 15% water content in clay = high plasticity.
,B. Unit Weights of Soil
S.No Point Description
1. Definition Unit weight is the weight of soil per unit volume (kN/m³).
2. Explanation It helps in understanding load-bearing capacity and design loads.
3. Purpose To compute stresses in soil mass and for earthwork estimation.
4. Advantages Essential for structural design and geotechnical analysis.
5. Disadvantages Need multiple field/lab methods for accurate result.
Bulk unit weight (γ), dry (γd), saturated (γsat), submerged (γsub), unit
6. Classification/Types
weight of solids (γs).
Determined using core cutter (IS 2720 Part 29) or sand replacement
7. Working/Process
method (IS 2720 Part 28).
8. Suitability Useful in retaining wall, foundation, and dam design.
9. Principle Based on mass/volume relationship of soil solids and voids.
10. Objectives Evaluate soil compaction and stability.
11. Uses/Applications Earth dam design, foundation load analysis.
12. Location Lab or field tests.
13. Situation Construction over soft or variable soil profiles.
14. Cost/Economy Core cutter is cheaper; sand replacement more accurate but costlier.
15. Limitations Core cutter not suitable for coarse-grained soil.
16. Remedial Measures Use sand replacement or nuclear methods.
17. Curative Measures Calibrate equipment, dry sample properly.
- γ=WVγ = \frac{W}{V}γ=VW
- γd=WsVγ_d = \frac{W_s}{V}γd=VWs
18. Equations
- γsat=WsatVγ_{sat} = \frac{W_{sat}}{V}γsat=VWsat
- γsub=γsat−γwγ_{sub} = γ_{sat} - γ_wγsub=γsat−γw
19. IS or Other Codes IS 2720 Part 28, 29
20. Sketch/Figure
21. Examples γbulk = 18.5 kN/m³, γdry = 15.8 kN/m³, γsub = 9.8 kN/m³
, 2.2 Determination of Index Properties of Soil
A. Determination of Water Content by Oven-Drying Method (IS 2720 Part 2)
S.No Point Description
It is the process of measuring the water content (moisture content) of soil
1. Definition
by oven drying at 105–110°C.
Water is evaporated from the soil sample, and the loss in weight is used
2. Explanation
to calculate water content.
To assess moisture in the soil which influences strength, compaction,
3. Purpose
permeability, etc.
4. Advantages Accurate and standardized.
5. Disadvantages Time-consuming (~24 hours), not suitable for organic soils.
6. Classification/Types Rapid moisture tester, infrared drying, oven-drying.
7. Suitability Suitable for all inorganic soils.
8. Working Principle Based on mass difference before and after drying.
9. Limitation Can't be used for soils with organic matter or gypsum.
10. Objective Get accurate water content for engineering purposes.
11. Applications Road construction, compaction control.
12. Test Location Laboratory.
13. Real-life Use Deciding OMC in highways.
14. Cost Low cost – basic oven and weighing balance.
15. Errors Incomplete drying, loss of fines.
16. Precautions Keep oven temperature constant; use airtight containers.
17. IS Code IS 2720 Part 2
18. Equation w=WwWs×100w = \frac{W_w}{W_s} \times 100w=WsWw×100%
19. Sketch
20. Sample Clay soil with 22% moisture.
21. Conclusion Reliable method for standard testing.
