Considering
(i) The structural resistance to displacement of the soil
(ii) Frictional resistance between the individual soil particles
(iii) Cohesion between the surface of the soil particles. The Shear strength of a soil basically made up of these statements

Explanation:

• Shear strength is the ability of soil to resist sliding along internal surfaces when subjected to stress.

• It is fundamental for the stability of slopes, foundations, retaining walls, and earthworks.

The shear strength of soil is composed of three main components:

(i) Structural resistance to displacement

• Comes from the soil’s internal structure or fabric.

• This involves the way soil particles are arranged and interlocked.

• Stronger packing or structure offers more resistance against movement or failure.

(ii) Frictional resistance between individual soil particles

• Arises due to the roughness and angularity of particles (especially in coarse-grained soils like sand and gravel).

• Larger, angular particles generate more friction, enhancing shear strength.

• Dominant component in cohesionless soils.

(iii) Cohesion between the surface of soil particles

• Occurs mainly in fine-grained soils (like clays).

• Due to electrochemical attraction, cementation, or water menisci.

• Allows soil to "stick together," even without frictional resistance.

• Plays a major role in undrained conditions or saturated clays.

 Additional Information

Factors Affecting Shear Strength of Soil

• Granular soils (sand and gravel) mainly derive their shear strength from internal friction between particles.

• Cohesive soils (clays) gain strength from cohesion (electrochemical attractions) and internal friction.

• Silty soils behave in between; they may show some cohesion but are highly sensitive to water.

• Water affects pore water pressure within the soil.

• High pore water pressure reduces effective stress, thus reducing shear strength.

• In well-drained conditions (drained shear), water drains out and soil can resist shear better.

• In undrained conditions (rapid loading or poor drainage), pore pressure builds up and shear strength decreases, especially in clays.

• If loading is applied slowly, water has time to drain out (drained behavior), leading to higher shear strength.

• If loading is rapid (such as during earthquakes or quick construction), the soil behaves undrained and pore pressures may increase, causing a drop in shear strength.