Coulomb’s law of shear strength :
This law of shear strength was presented in 1773. The Shear strength of the soil is basically composed of two major components:
The inter granular friction is in directly proportional to the normal stress acting on shear surface. Which means that if inter granular friction increases the normal stress acting on the shear surface also increases. On the other hand the cohesion is dependent on the type of the soil, size of the soil grains and the packing of the soil grains and on the suction properties of the soil.
Coulomb in 1773 governed the shearing strength of the soil by a straight line equation in Coulomb’s law of shear strength:
C = apparent cohesion
σ = the normal stress
φ = the angle of internal friction or shearing resistance of the soil.
When this equation was put forward in 1773, the concept of effective stress even then was not introduced.