Depth of Footing given Bearing Capacity Factor and Width of Footing Calculator

Depth of Footing Formula:

\[ D = \frac{q_{nf} - (C_s \times N_c + 0.5 \times \gamma \times B \times N_\gamma)}{\gamma \times (N_q - 1)} \]

Net Ultimate Bearing Capacity:

Cohesion of Soil:

Bearing Capacity Factor (Cohesion):

Unit Weight of Soil:

N/m³

Width of Footing:

Bearing Capacity Factor (Unit Weight):

Bearing Capacity Factor (Surcharge):

Depth of Footing (m):

1. What is Depth of Footing Calculator?

Definition: This calculator determines the required depth of a footing based on soil properties and bearing capacity factors.

Purpose: It helps civil engineers and construction professionals design stable foundations that can support structural loads.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ D = \frac{q_{nf} - (C_s \times N_c + 0.5 \times \gamma \times B \times N_\gamma)}{\gamma \times (N_q - 1)} \]

Where:

\( D \) — Depth of footing (meters)
\( q_{nf} \) — Net ultimate bearing capacity (Pascals)
\( C_s \) — Cohesion of soil (Pascals)
\( N_c \) — Bearing capacity factor for cohesion
\( \gamma \) — Unit weight of soil (N/m³)
\( B \) — Width of footing (meters)
\( N_\gamma \) — Bearing capacity factor for unit weight
\( N_q \) — Bearing capacity factor for surcharge

Explanation: The formula calculates the required footing depth to prevent shear failure based on soil mechanics principles.

3. Importance of Footing Depth Calculation

Details: Proper footing depth ensures structural stability, prevents settlement, and accounts for soil bearing capacity.

4. Using the Calculator

Tips: Enter all required parameters. Bearing capacity factors typically have ±5% variability. Ensure Nq > 1 for valid results.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for bearing capacity factors?
A: Nc ≈ 9, Nγ ≈ 1.6, Nq ≈ 2.01 for many soils, but consult geotechnical reports for specific values.

Q2: How do I determine net ultimate bearing capacity?
A: This is typically determined through geotechnical testing of soil samples.

Q3: What if my soil has no cohesion (Cs=0)?
A: The calculator works for cohesive (clay) and cohesionless (sand) soils. Just enter 0 for Cs if no cohesion.

Q4: Why is Nq-1 in the denominator?
A: This accounts for the surcharge effect of soil above footing level in the bearing capacity equation.

Q5: What units should I use?
A: Use consistent SI units: Pascals for pressure, meters for dimensions, and N/m³ for unit weight.