What Is the Culmann Active Lateral Earth Pressure Calculator?
Culmann active earth pressure theory models a planar failure wedge sliding along an inclined slip surface behind a retaining structure.
It accounts for both internal soil friction and interface friction along the rough back face of the wall.
How Does the Culmann Active Lateral Earth Pressure Calculator Work?
When the retaining wall yields slightly away from the backfill, soil shear strength is mobilized.
The active thrust Pa acts at an angle delta to the normal of the wall back face at H/3 above the base.
The horizontal component causes base sliding and overturning moments about the wall toe.
Culmann Active Lateral Earth Pressure Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Calculates Coulomb active lateral earth pressure coefficient and total thrust per unit run of retaining wall.
How to Use the Culmann Active Lateral Earth Pressure Calculator
- Enter the vertical wall height in meters and backfill unit weight in kN/m3.
- Specify soil internal friction angle and wall interface friction angle.
- Enter the ground slope angle behind the wall.
Step-by-Step Example Calculation
Culmann Earth Pressure Standard Case
Input Values:
Understanding Your Result
Active coefficient Ka reflects the proportion of vertical overburden converted to horizontal thrust.
Total active thrust indicates the resultant force vector per linear meter of wall.
Overturning moment provides the destabilizing torque that footing self-weight must counterbalance.
Factors That Affect the Result
- Backfill slope: Sloping backfill dramatically increases Ka and the total thrust on the wall.
- Wall friction delta: Interfacial roughness reduces the horizontal component of lateral thrust.
- Soil drainage: Un-drained hydrostatic water pressure can double the total lateral load.
When Should You Use This Calculator?
- Structural sizing of reinforced concrete cantilever, gravity, and MSE retaining walls.
- Evaluating geotechnical sliding, overturning, and bearing stability.
Assumptions & Limitations
- Assumes cohesionless granular backfill (c = 0) yielding active plastic equilibrium.
- Requires sufficient wall lateral deflection (approx. 0.001 to 0.004 H) to mobilize active state.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Analytical formulation of Coulomb-Culmann wedge equilibrium for vertical planar walls.