What is Earth Pressure?

Earth pressure is the lateral force exerted by soil against a structure, typically a retaining wall or foundation. Understanding these forces is critical in geotechnical engineering to ensure the stability and safety of civil infrastructure. Depending on the movement of the wall relative to the soil mass, earth pressure is categorized into three states: at-rest, active, and passive.

Active vs. Passive Earth Pressure

Active Earth Pressure (Ka): This occurs when the retaining wall moves away from the soil. The soil expands laterally, and its internal strength is mobilized to resist the movement. Rankine’s theory provides a coefficient (Ka) to determine this pressure, which is generally the lowest force exerted by the soil.

Passive Earth Pressure (Kp): This occurs when the wall is pushed into the soil mass. The soil is compressed, and the resistance offered by the soil mass is much higher than the active state. This is often used in designing anchors or calculating the resistance provided by soil in front of a toe of a wall.

How to Use the Earth Pressure Calculator

To calculate the lateral forces accurately, follow these steps:

1. Enter the Unit Weight (γ) of the soil, which represents its density.
2. Input the Height (H) of the retaining structure.
3. Provide the Angle of Internal Friction (φ), which reflects the shear strength of the soil.
4. Include the Cohesion (c) value if the soil is clayey or has cohesive properties.
5. Click "Calculate" to see the coefficients (Ka, Kp) and the total resultant forces per unit length of the wall.

Frequently Asked Questions

Q: What is Rankine's Theory?
A: Rankine's theory assumes that the soil is homogeneous, isotropic, and has a horizontal surface. It provides a simple method to calculate lateral pressure based on the friction angle of the soil.

Q: How does cohesion affect earth pressure?
A: Cohesion reduces active pressure (it helps the soil stand up) and increases passive pressure (it adds to the resistance against the wall).