Even when the normal forces are reduced to zero, some part of shear strength is still left on the soil. This strength is due to:

Explanation:

True Cohesion:

• Refers to the inherent bonding strength between soil particles, primarily due to molecular or chemical forces (such as electrostatic forces in clay).

• This cohesion exists even without normal stress.

• It provides shear strength in soils, particularly fine-grained soils like clay, even when normal forces are reduced to zero.

• Correct answer: True cohesion is the reason some shear strength remains in the soil even when normal forces are zero.

Additional Information

Interlocking Friction:

• Refers to the resistance to sliding between irregularly shaped particles, such as in coarse-grained soils like gravel.

• Interlocking friction depends on the normal force to create friction between particles.

• When normal forces are reduced to zero, interlocking friction doesn't significantly contribute to shear strength because it's tied to the pressure between the particles.

Sliding Friction:

• Refers to the frictional force that resists the sliding of two surfaces over one another.

• In soils, sliding friction is usually governed by the normal force, as the frictional resistance increases with greater normal stress.

• Like interlocking friction, sliding friction decreases or is eliminated when normal forces are reduced to zero, so it doesn't contribute to the shear strength in that case.

Apparent Cohesion:

• Occurs in unsaturated soils, where water creates a capillary bond between particles. This bond provides some strength even without normal forces.

• Apparent cohesion is often temporary and depends on factors like soil moisture and surface tension.

• While it can provide shear strength when normal forces are reduced, it's not the primary reason for shear strength when there is no normal force, especially in dry or fully saturated soils.