Angle of internal friction

Definition

The angle of internal friction is a measure of the shear strength of soil, which describes the resistance to sliding or deformation when stress is applied. This angle plays a critical role in understanding how soil behaves under load, influencing calculations related to stability, bearing capacity, and settlement. Higher values indicate better soil strength and stability, while lower values suggest weaker soil that may be more susceptible to failure.

5 Must Know Facts For Your Next Test

1. The angle of internal friction is typically denoted by the Greek letter phi (φ) and is expressed in degrees.
2. It can be determined experimentally using triaxial tests or direct shear tests, which measure how soil reacts when subjected to different stresses.
3. In Rankine's and Coulomb's earth pressure theories, the angle of internal friction is crucial for calculating lateral earth pressures acting on retaining structures.
4. The angle of internal friction can vary significantly depending on factors such as soil type, moisture content, and density.
5. In geotechnical engineering, knowing the angle of internal friction helps engineers design foundations and slopes to prevent failures due to instability.

Review Questions

• How does the angle of internal friction influence the stability of slopes and foundations in geotechnical engineering?
  • The angle of internal friction is a key factor in determining the shear strength of soils, which directly affects slope stability and foundation design. Higher angles indicate that soils can resist sliding forces better, making it less likely for slopes to fail or foundations to settle. Engineers use this angle in calculations to ensure that structures are safe and stable under various loading conditions.
• Discuss how Rankine's and Coulomb's earth pressure theories utilize the angle of internal friction in predicting earth pressures.
  • Both Rankine's and Coulomb's earth pressure theories incorporate the angle of internal friction to calculate lateral earth pressures on retaining walls and other structures. In Rankine's theory, the angle helps define the conditions for active and passive earth pressure states, while Coulomb’s theory considers both cohesion and internal friction for more complex scenarios. The angle is essential for ensuring accurate predictions of forces acting on structures, which is crucial for design safety.
• Evaluate how changes in moisture content affect the angle of internal friction and what implications this has for construction projects.
  • Changes in moisture content can significantly affect the angle of internal friction, often leading to reduced shear strength when soils become saturated. This reduction can increase the risk of slope failure or settlement issues in construction projects. Engineers must account for varying moisture conditions during design and site assessments, as ignoring these changes could lead to unsafe conditions or costly failures post-construction.

Related terms

Cohesion: Cohesion is the property of soil that describes the intermolecular forces that hold the particles together, contributing to the overall strength of the soil.

Shear Strength: Shear strength refers to the maximum resistance of a soil to shearing forces, which is influenced by both cohesion and the angle of internal friction.

Effective Stress: Effective stress is the concept that describes how much of the total stress applied to a soil mass is effective in supporting load, considering pore water pressure in saturated soils.