1. What is Active Earth Pressure Coefficient?

The Active Earth Pressure Coefficient (Ka) is a dimensionless parameter used in geotechnical engineering to calculate the lateral earth pressure exerted by soil on a retaining wall when the wall moves away from the soil mass.

2. How Does the Calculator Work?

The calculator uses Rankine's formula for active earth pressure:

Where:

• \( K_a \) — Active earth pressure coefficient
• \( \phi \) — Angle of internal friction of soil (degrees)

Explanation: The formula shows that Ka decreases as the angle of internal friction increases, meaning more stable soils exert less pressure on retaining structures.

3. Importance of Ka Calculation

Details: Accurate calculation of Ka is essential for designing safe and economical retaining walls, sheet pile walls, and other earth-retaining structures.

4. Using the Calculator

Tips: Enter the angle of internal friction in degrees (typically between 25°-40° for most soils). The value must be between 0 and 45 degrees.

5. Frequently Asked Questions (FAQ)

Q1: What is the range of typical Ka values?
A: For common soils, Ka typically ranges from 0.20 to 0.40, depending on the soil type and friction angle.

Q2: What's the difference between active and passive earth pressure?
A: Active pressure occurs when the wall moves away from the soil (smaller coefficient), while passive pressure occurs when the wall moves into the soil (larger coefficient).

Q3: Does this formula account for cohesion?
A: No, this is Rankine's formula for cohesionless soils. For cohesive soils, additional terms are needed.

Q4: What are typical φ values for different soils?
A: Loose sand: 28°-30°, dense sand: 35°-40°, stiff clay: 20°-25°, gravel: 35°-45°.

Q5: When is Coulomb's theory used instead of Rankine's?
A: Coulomb's theory is used when wall friction and sloping backfill are significant factors.