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 […]

## How to Calculate Relative Density

Relative Density is the ratio of the density of a substance to a specified reference density. $latex D_r = \frac{\rho_s}{\rho_{ref}}&s=2$ 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 […]

## How to Calculate Specific Gravity

Specific Gravity is the ratio of the density of a soil to the density of water. $latex SG = \frac{\rho_s}{\rho_w}&s=2$ 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 […]

## 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. $latex \rho = \frac{m_t}{V_t}\newline\newline =\frac{m_w + m_s}{V_g + V_w + V_s}&s=2$ Where: ρ = bulk density (kg/m3 or lb/ft3) mt = Total mass (kg or lbs) mw = Mass of water (kg or lbs) ms […]

## 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. $latex S = \frac{V_w}{V_v}\times 100\%\newline\newline =\frac{V_w}{V_g + V_w}\times 100\%&s=2$ Where: S = Degree of Saturation Vw = Volume of water (m3 or ft3) Vv = Volume of voids (m3 or ft3) Vg = Volume of […]

## 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. $latex n = \frac{V_v}{V_t}\newline\newline =\frac{V_g + V_w}{V_g + V_w + V_s}&s=2$ Where: Vv = Volume of voids (m3 or ft3) Vt = Total Volume (m3 or […]

## 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 […]