Index Properties of Soil.pdf
- 1. GEOTECHNICAL ENGINEERING PHYSICAL & INDEX PROPERTIES OF SOIL PREPARED BY GOURHARI BISWAS
- 2. INDEX PROPERTIES OF SOILS • Index properties are the simple physical properties of the soils, which are used for identification and classification of soils for various engineering applications. • They indicate a qualitative behaviour of soil when subjected to various types of load. • To determine index properties simple tests are required. These tests are called classification tests. The soils are classified and identified based on index properties. • Engineering properties of soils are those properties which can be used for quantifying the Engineering behaviour of soils.
- 3. Different Index Properties They can be listed as given below: 1.Water content 2.Specific gravity 3.Grain size distribution 4.Plasticity properties popularly known as Atterberg limits (Liquid limit, Plastic limit and Shrinkage limit) and their indices like plasticity Index, Liquidity Index, Consistency Index, Shrinkage Index. 5.In-situ density 6.Relative density • Void ratio, porosity, degree of saturation, are not properties of soils, but state parameters indicating the in- situ state of soil.
- 4. Different Engineering Properties of Soil 1.Shear strength (Cohesion intercept and angle of internal friction) 2.Compressibility characteristics (compression index and coefficient of compressibility) 3.Permeability (Coefficient of Hydraulic conductivity) 4.Compaction characteristics (Optimum moisture content and Maximum Dry Unit weight) 5.Swell/Collapse potential
- 5. PHASE DIAGRAM OF SOIL • Soil is not a coherent solid material like steel and concrete, but is a particulate/granular material. Soils, as they exist in nature, consist of solid particles (mineral grains, rock fragments) with water and air in the voids between the particles. The water and air contents are readily changed by changes in ambient conditions and location. • As the relative proportions of the three phases vary in any soil deposit, it is useful to consider a soil model which will represent these phases distinctly and properly quantify the amount of each phase.
- 6. Phase Diagrams A schematic diagram of the three-phase system is shown in terms of weight and volume symbols respectively for soil solids, water, and air. The weight of air can be neglected. The soil model is given dimensional values for the solid, water and air components. Total volume, V = Vs + Vw + Vv
- 7. Phase Diagram for Fully Saturated and Dry Soil A phase diagram of soil indicating the masses and volumes of air, solid, water, and voids.
- 8. Inter Relationship For the purpose of engineering analysis and design, it is necessary to express relations between the weights and the volumes of the three phases. The various relations can be grouped into: • Volume relations • Weight relations • Inter-relations
- 9. VOLUME RELATIONS As the amounts of both water and air are variable, the volume of solids is taken as the reference quantity. Thus, several relational volumetric quantities may be defined. The following are the basic volume relations: 1. Void ratio (e) is the ratio of the volume of voids (Vv) to the volume of soil solids (Vs), and is expressed as a decimal. 2. Porosity (n) is the ratio of the volume of voids to the total volume of soil (V ), and is expressed as a percentage.
- 10. Inter relation between Void ratio and Porosity Void ratio and porosity are inter-related to each other as follows: 1/n=V/Vv= (Vv+vs)/Vv 1/n= 1+ (1/e) = (1+e)/e n=e/ (1+e) …….(a) 1/e= (1/n)-1= (1-n)/n e=n/ (1-n)………. (b) • In equations (a) and (b), the porosity should be expressed as a ratio and not percentage. • The porosity can not be smaller than 0, and can not be greater than 1. The void ratio can be greater than 1.
- 11. Degree of saturation • The pores of a soil may contain water and air. To describe the ratio of these two the degree of saturation S is introduced. The degree of saturation is the ratio of the volume of water to the volume of voids. It is denoted by ‘S’. • S=Vw/Vv • The degree of saturation is generally expressed as a percentage. It is equal to zero when the soil is absolutely dry and 100% when the soil is fully saturated. • For a dry soil, S = 0%, and for a fully saturated soil, S = 100%.
- 12. Air Content and Percent Air Voids Air content (ac) is the ratio of the volume of air (Va) to the volume of voids. Also, na=n ac
- 13. WEIGHT RELATIONS Density is a measure of the quantity of mass in a unit volume of material. Unit weight is a measure of the weight of a unit volume of material. Both can be used interchangeably. The units of density are ton/m3, kg/m3 or g/cm3. The following are the basic weight relations: 1. Water content, which is also called moisture content, is the quantity of water contained in a material, such as soil. Water content is denoted by small letter w. Here weight of water is Ww and weight of solids is Ws. Its value is 0% for dry soil and its magnitude can exceed 100%.
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- 15. INTER RELATIONS • It is important to quantify the state of a soil immediately after receiving in the laboratory and prior to commencing other tests. The water content and unit weight are particularly important, since they may change during transportation and storage. • Some physical state properties are calculated following the practical measurement of others. For example, dry unit weight can be determined from bulk unit weight and water content. The following are some inter-relations:
- 16. Inter Relations
- 17. VOLUME-MASS RELATIONSHIPS 1. BULK MASS DENSITY : The bulk mass density (ρ) is defined as the total mass (M) per unit volume (V) , ρ=M/V 2. DRY MASS DENSITY : The dry mass density (ρd) is defined as the mass of solids per unit total volume , ρd= Ms/V 3. SATURATED MASS DENSITY : The saturated mass density (ρsat) is the bulk density of the soil when it is fully saturated. ρsat= Msat/V
- 18. contd... 4. SUBMERGED MASS DENSITY : When the soil exists below water, it is in a submerged condition. The submerged mass density (ρ’) of the soil is defined as the submerged mass per unit total volume. ρ’= Msub/V 5.MASS DENSITY OF SOLIDS :The mass density of solids (ρs) is equal to the ratio of the mass of solids to the volume of solids ρs=Ms/Vs
- 19. VOLUME-WEIGHT RELATIONSHIPS 1.BULK UNIT WEIGHT (γ)= W/V 2.DRY UNIT WEIGHT (γd) = Ws/V 3.SATURATED UNIT WEIGHT (γsat) = Wsat/V 4.SUBMERGED UNIT WEIGHT (γsub or γ’) = Wsub/V 5.UNIT WEIGHT OF SOIL SOLIDS (γs) = Ws/Vs
- 20. SPECIFIC GRAVITY OF SOLIDS • The specific gravity of soil particles (G) is defined as the ratio of the mass of a given volume of solids to the mass of an equal volume of water at 4°C. • G = ρs/ρw • The mass density of water ρw at 4°C is 1gm/ml, 1000 kg/m3 or 1 Mg/m3
- 22. Relative Density/Density Index It is a ratio of difference between maximum void ratio and natural void ratio to the difference between maximum void ratio and minimum void ratio expressed in percentage.