How to Determine the Atterberg Limits

The Atterberg limits, created by swedish chemist Albert Atterberg, are the moisture content, in percent, at which the soil changes state. They are defined as: Plastic Limit (solid to plastic) Liquid Limit (plastic to liquid) Some textbooks often refer to a third Atterberg limit, the “shrinkage limit” which defines the boundary between “solid” and a […]

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How to Calculate Relative Density

Relative Density is the ratio of the density of a substance to a specified reference density. Where: Dr = Relative Density (dimensionless) ρs = bulk density of soil (kg/m3 or lb/ft3) ρref = bulk density of reference (kg/m3 or lb/ft3) Often, the reference density is that of water, 62.4 lbs/ft3 or 1000 kg/m3. Alternatively, the […]

How to Calculate Specific Gravity

Specific Gravity is the ratio of the density of a soil to the density of water. Where: SG = Specific Gravity (dimensionless) ρs = bulk density of soil (kg/m3 or lb/ft3) ρw = bulk density of water (kg/m3 or lb/ft3) = 1000 kg/m3 (62.4 lb/ft3) Specific Gravity of Various Substances Substance Specific Gravity Water 1.0 […]

How to Calculate Bulk Density

Bulk density, also called soil density, is the ratio of the total mass of a soil to the total volume. Where: ρ = bulk density (kg/m3 or lb/ft3) mt = Total mass (kg or lbs) mw = Mass of water (kg or lbs) ms = Mass of solids (kg or lbs) Vt = Total Volume […]

How to Calculate Degree of Saturation

The degree of saturation is the ratio of the volume of water in a soil to the volume of voids. Where: S = Degree of Saturation Vw = Volume of water (m3 or ft3) Vv = Volume of voids (m3 or ft3) Vg = Volume of air (m3 or ft3) The degree of saturation is […]

How to Calculate Soil Porosity

The soil porosity, also called the void fraction, is the ratio of the volume of voids (open spaces, i.e. air and water) in a soil to the total volume. Where: Vv = Volume of voids (m3 or ft3) Vt = Total Volume (m3 or ft3) Vg = Volume of air (m3 or ft3) Vw = […]

What is the Plastic Limit?

The plastic limit is defined as the moisture content at which a soil becomes plastic. It is the boundary between a soil’s solid and plastic states. ASTM D4318 is the standard test procedure for determining the plastic limit. Of course, a soil doesn’t go from solid to plastic all at once, but the standard test […]