1. What is the Coefficient of Earth Pressure?

The coefficient of earth pressure (K) represents the ratio of horizontal to vertical stress in soil. The active earth pressure coefficient (K_a) is used when a retaining wall moves away from the soil, causing the soil to expand and reduce lateral pressure.

2. How Does the Calculator Work?

The calculator uses the active earth pressure coefficient formula:

Where:

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

Explanation: The equation shows that as the angle of internal friction increases, the active earth pressure coefficient decreases, resulting in lower lateral earth pressure.

3. Importance of Earth Pressure Calculation

Details: Calculating earth pressure coefficients is essential for designing retaining walls, sheet pile walls, basement walls, and other earth-retaining structures to ensure stability and safety.

4. Using the Calculator

Tips: Enter the angle of internal friction in degrees (typically between 25°-45° for common soils). The value must be between 0 and 90 degrees.

5. Frequently Asked Questions (FAQ)

Q1: What is the range of K_a values?
A: For typical soils (φ = 25°-45°), K_a ranges from about 0.58 to 0.29. Lower values indicate less lateral pressure.

Q2: How does this differ from passive earth pressure?
A: Passive earth pressure (K_p = 1 + sinφ) occurs when a wall moves into the soil, causing compression and higher pressure.

Q3: What factors affect the angle of internal friction?
A: Soil type (sand has higher φ than clay), density, moisture content, and particle shape/size all influence φ.

Q4: When is this simplified formula not appropriate?
A: For cohesive soils (clays), sloping backfill, or when wall friction is significant, more complex methods are needed.

Q5: How is this used in retaining wall design?
A: K_a helps calculate the total lateral force on the wall, which is used to check stability against sliding and overturning.