# [Capsule] Phase relation of soils | Civil Engineering Capsule for SSC, ESE, GATE, AE/AEE for any Govt. CE Job Preparations.

### Topic: Phase relation of soils

• Total volume, V = Vs + Vw + Vv
• Soils can be partially saturated (with both air and water present), or be fully saturated (no air content) or be perfectly dry (no water content).
• In a saturated soil or a dry soil, the three-phase system thus reduces to two phases only.
• 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.
• Porosity (n) is the ratio of the volume of voids to the total volume of soil (V ), and is expressed as a percentage.
• Void ratio and porosity are inter-related to each other.
• The volume of water (Vw) in a soil can vary between zero (i.e. a dry soil) and the volume of voids. This can be expressed as the degree of saturation (S) in percentage.
• For a dry soil, S = 0%, and for a fully saturated soil, S = 100%.

• Air content (ac) is the ratio of the volume of air (Va) to the volume of voids.
• Percentage air voids (na) is the ratio of the volume of air to the total volume.
• The ratio of the mass of water present to the mass of solid particles is called the water content (w), or sometimes the moisture content.
• The mass of solid particles is usually expressed in terms of their particle unit weight or specific gravity (Gs) of the soil grain solids.
• For most inorganic soils, the value of Gs lies between 2.60 and 2.80. The presence of organic material reduces the value of Gs.
• Dry unit weight is a measure of the amount of solid particles per unit volume.
• Bulk unit weight is a measure of the amount of solid particles plus water per unit volume.
• Saturated unit weight is equal to the bulk density when the total voids is filled up with water.
• Buoyant unit weight or submerged unit weight is the effective mass per unit volume when the soil is submerged below standing water or below the ground water table.

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