Introduction
The consequences of exceeding the shear strength[1] of soils in civil engineering are seen in foundation failures, landslides, etc.
Definition : Sources of Shear Strength
The shear strength of a soil primarily arises from three sources:
Resistance due to particle interlocking.
Frictional resistance between individual soil grains, which can include sliding friction, rolling friction, or both.
Adhesion between soil particles, known as "cohesion."
Granular soils (e.g., sands) derive their shear strength from the first two sources, while cohesive soils (e.g., clays) rely on the second and third sources. Highly plastic clays may derive their shear strength solely from cohesion.