Soil Bearing Capacity Calculator
Calculation Results
Ultimate Bearing Capacity (qᵤ): 0 kN/m²
Allowable Bearing Capacity (qₐ): 0 kN/m²
What is Soil Bearing Capacity?
Soil bearing capacity is the maximum contact pressure that a soil can support without undergoing shear failure or excessive settlement. In civil engineering and geotechnical design, determining this capacity is the first and most critical step before constructing any foundation. Whether you are building a small residential home or a massive industrial complex, the soil must be able to withstand the load applied by the structure.
Understanding Terzaghi’s Formula
This calculator utilizes Terzaghi's bearing capacity theory for shallow foundations. The formula accounts for three primary components of soil resistance: cohesion (c), the weight of the soil above the foundation level (surcharge), and the weight of the soil within the failure zone below the foundation. The general equation is expressed as:
qᵤ = c·N꜀ + q·Nᵦ + 0.5·γ·B·Nᵧ
Where N꜀, Nᵦ, and Nᵧ are dimensionless bearing capacity factors that depend solely on the angle of internal friction (φ). The factor q represents the surcharge pressure at the foundation level (γ × Df).
How to Use This Calculator
To use the soil bearing capacity calculator with steps, follow these instructions:
- Cohesion (c): Enter the shear strength of the soil (typically 0 for dry sand, higher for clay).
- Unit Weight (γ): Provide the density of the soil in kN/m³.
- Depth (Df): The vertical distance from the ground surface to the bottom of the footing.
- Width (B): The shortest dimension of the footing base.
- Internal Friction Angle (φ): The resistance of soil particles to sliding against each other.
- Factor of Safety (FS): Usually ranges from 2.5 to 3.0 to ensure a safety margin against soil failure.
Frequently Asked Questions
Q: Why is a Factor of Safety necessary?
A: Soils are natural materials with inherent variability. A Factor of Safety (FS) accounts for uncertainties in soil testing and potential loading variations, ensuring the foundation never reaches its ultimate failure point.
Q: Does the water table affect bearing capacity?
A: Yes. High water tables can significantly reduce soil bearing capacity by reducing the effective unit weight of the soil. This calculator assumes dry or drained conditions.