Shear Strength of Soil Quiz

Shear Strength of Soils

• Shear strength is the resistance along a plane that passes between or along particle surfaces, but not through the particles.
• It's one of the most important characteristics of soils.

Types of Soils w.r.t. Shear Strength

• Cohesive soils: e.g., clayey soil, which possesses a bonding among particles.
• Cohesionless soils: e.g., sand, which has only friction factors among particles.

Components of Shear Resistance of Soils

• Friction resistance: developed due to friction that creates among particles under the applied stress, consisting of:
  • Friction due to sliding of particles.
  • Friction due to rolling of particles.
  • Friction due to interlocking.
• Cohesion force: a force developed in clayey soils only among particles, which comes from bonding.

Mohr-Coulomb Theory

• The relation between shear strength and friction and cohesion as per Mohr-Coulomb law: S = τ = c + σn*tanυ.
• Where: S = shear strength of soil, c = cohesion of soil, υ = angle internal friction, σn = normal stress act on soil.

Stresses on Soil

• Normal stress (σ): a stress that acts perpendicular to a plane.
• Shear stress (τ): a stress that acts parallel to a plane.
• The state of stress at a point can be defined by nine components of stresses.
• There are three planes at right angles where only normal stresses acting, called principal planes.

Principal Stresses and Planes

• Principal stresses: σ1, σ2, σ3, acting on major, intermediate, and minor principal planes, respectively, where shear stresses = 0.

Factors Affecting Shear Strength of Soils

• Water content.
• Type and amount of loads (static or dynamic).
• Soil structures and disturbance effects.

Importance of Shear Strength in Soil Study

• Stability of slopes (e.g., hills slides, cuts, embankments, earth dams).
• Ultimate bearing capacity of a soil for foundation design.
• Lateral pressure against retaining walls, sheeting, or bracing.
• Friction developed by piles.