What Is Soil Cohesion?

Soil cohesion, as applied to soil mechanics, is the force that resists separation of soil particles along a fracture plane. Cohesion is usually due to the interlocking of grains and cementation by clay and other materials. Its magnitude is determined by the bonding forces between soil particles, which can be very complex. Clayey and silty soils usually exhibit greater cohesion than sandy or gravelly soils.

Cohesion is one of the two fundamental shear strength components of soil, the other being soil friction, which is the frictional resistance to slip, slide or roll along a fracture plane. The strength of soil, which resists its rupture, is determined by the combination of cohesion and soil friction.

Soil cohesion is measured in a variety of ways. One common method is using the direct shear test, which measures the shear strength required to separate two soil samples along a shear surface. Another method is the unconfined compression test, which measures the force required to compress a cylindrical soil specimen to failure.