What is the difference between cohesive and cohesionless soil?
Cohesion as the word itself denotes, is the attraction between particles of same type/origin/nature . Hence cohesive soil is a type of soil where there is inter-particular attraction.
This adds to the shear strength of the soil.The main feature of such soil types are that their particles are very fine and they are governed by the surface forces rather than by their self weight.
Clay is a very good example for a cohesive soil. In pure cohesive soils, the friction between particles will not occur and hence their shear strength will be contributed by only cohesive force and not by internal friction. The angle of internal friction will not come into play here.
Non-cohesive soil as the name indicates do not have cohesive forces. They are comparatively coarser particles with self weight governing their behaviour. The particles have internal friction and their shear strength depends upon the angle of internal friction between particles. Sand is a typical example. Exclusively non-cohesive soils will have zero cohesion.
Now you must know that majority of the natural soil deposits do not come under the above categories. They are mostly C-φ soils. That means they have both cohesive forces and frictional forces contributing to their shear strength.These are the difference between cohesive and cohesionless soil.