1. What is the Angle of Internal Friction?

Definition: The angle of internal friction (φ) is a measure of a material's shear strength, representing the angle between the normal force and resultant force when the material begins to fail.

Purpose: It's crucial in geotechnical engineering for analyzing soil stability, slope failure, and foundation design.

2. How Does the Formula Work?

The calculator uses the formula:

Where:

• \( \phi \) — Angle of internal friction (degrees)
• \( \mu \) — Coefficient of friction (dimensionless)

Explanation: The arctangent function converts the friction coefficient (ratio of shear to normal stress) into an angle.

3. Importance in Engineering

Details: This angle helps determine:

• Slope stability and maximum safe angles
• Bearing capacity of soils
• Lateral earth pressures on retaining structures
• Shear strength of granular materials

4. Using the Calculator

Tips: Enter the coefficient of friction (typically 0-1 for most soils). The value must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical μ value for soils?
A: Common ranges: Sand (0.4-0.6), Gravel (0.5-0.8), Clay (0.2-0.4).

Q2: How is μ determined experimentally?
A: Through direct shear tests or triaxial compression tests in geotechnical labs.

Q3: What's the difference between φ and μ?
A: μ is the coefficient (ratio), while φ is the angle representation of the same shear strength property.

Q4: Can φ exceed 45°?
A: Yes, for very rough or angular particles, φ can reach 50° or more.

Q5: How does moisture affect φ?
A: For granular soils, moisture has little effect. For clays, it significantly reduces φ.