1. What is the Active Pressure Coefficient?

The Active Pressure Coefficient (K_a) is a dimensionless parameter used in geotechnical engineering to calculate the lateral earth pressure exerted by soil in its active state. It represents the ratio of horizontal to vertical stress when a soil mass is allowed to expand laterally.

2. How Does the Calculator Work?

The calculator uses the Active Pressure Coefficient equation:

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 pressure coefficient decreases, resulting in lower lateral earth pressures.

3. Importance of K_a Calculation

Details: Accurate calculation of K_a is essential for designing retaining walls, sheet pile walls, and other earth-retaining structures to ensure stability against soil pressure.

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 typical range for K_a?
A: For common soils with φ between 25°-45°, K_a typically ranges from 0.41 to 0.17.

Q2: How does K_a differ from K_p?
A: K_a is for active pressure (soil expanding), while K_p (passive coefficient) is for soil being compressed, calculated as (1 + sinφ)/(1 - sinφ).

Q3: What factors affect φ value?
A: Soil type (sand, clay), density, moisture content, and compaction affect the angle of internal friction.

Q4: Can this be used for cohesive soils?
A: The equation is primarily for cohesionless soils. For cohesive soils, additional terms accounting for cohesion are needed.

Q5: What about wall friction angle?
A: This is the basic Rankine theory which assumes smooth wall. For rough walls, Coulomb's theory with wall friction should be used.