Definition of Shear Strength of Soil
The shear stress produced in a loaded soil mass tends to deform the soil mass by tearing it into the blocks, causing the movement of one block over the other along the failure plane. But this tendency of shear failure is resisted by the inherent resistance of the soil mass, called shear strength of the soil.
Therefore, the shear strength of soil can be defined as the inherent resistance of the soil against deformation due to the action of shear stress. Shear strength of the soil is constituted basically of the following components:
1. The structural resistance to displacement of the soil because of the interlocking of the particles.
2. The friction between the individual soil particles at their contact points.
3. Cohesion or adhesion between the surfaces of the soil particles.
Factor affecting the shear strength of soil
Shear strength of soil influenced by the following factors:
a) Cohesion i.e. the mutual attraction of soil particles.
b) Internal friction i.e. the resistance of soil particles in sliding over each other. It depends upon the angle of internal friction.
c) The resistance by increasing viscosity of pore water and negative pore pressure.
d) Structural Formation or the resistance offered by the mechanically interlocked particles during their dislocation.
Coarse-grained soils are cohesionless and the shear strength of such soil is mainly due to their property of internal friction. Fine-grained soils are free from internal friction and the shear strength of fine-grained soil is mainly due to cohesion. In mixed soil, The shear strength of soil is due to the presence of both properties like internal friction and cohesion.