Foundation Depth Calculator
Calculate the minimum foundation depth using Rankine's theory based on bearing capacity, soil weight, and friction angle.
How to Use the Foundation Depth Calculator
- Enter the required bearing capacity in kPa.
- Enter the soil unit weight (typically 18–20 kN/m³).
- Enter the soil friction angle in degrees.
- Click Calculate for the minimum foundation depth.
Use Cases
- •Determining foundation embedment depth.
- •Comparing soil types for foundation design.
- •Geotechnical preliminary analysis.
- •Civil engineering coursework.
Formula
D = (q / γ) × ((1 − sin φ) / (1 + sin φ))², where q is bearing capacity, γ is soil unit weight, φ is friction angle.
Frequently Asked Questions
What is Rankine's formula?
Rankine's formula estimates the minimum depth at which a foundation must be placed to achieve the required bearing capacity.
What is the friction angle?
The internal friction angle (φ) describes how soil particles interlock. Sand: 30–45°. Clay: 0–20°.
Why is there a minimum of 0.3 m?
Foundations should always be at least 300 mm below the surface to avoid disturbance.