Safe Bearing Capacity given Depth and Width of Footing Calculator

Safe Bearing Capacity Formula:

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

Cohesion of Soil (C_s):

Bearing Capacity Factor (N_c):

Unit Weight of Soil (γ):

N/m³

Depth of Footing (D):

Bearing Capacity Factor (N_q):

Width of Footing (B):

Bearing Capacity Factor (N_γ):

Factor of Safety (F_s):

Safe Bearing Capacity (q_sa): Pa

1. What is Safe Bearing Capacity?

Definition: Safe Bearing Capacity is the maximum pressure which the soil can carry safely without risk of shear failure.

Purpose: It helps engineers determine the appropriate foundation size and type for structures.

2. How Does the Calculator Work?

The calculator uses the formula:

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

Where:

\( q_{sa} \) — Safe bearing capacity (Pa)
\( C_s \) — Cohesion of soil (Pa)
\( N_c \) — Bearing capacity factor dependent on cohesion (±5%)
\( \gamma \) — Unit weight of soil (N/m³)
\( D \) — Depth of footing (m)
\( N_q \) — Bearing capacity factor dependent on surcharge (±5%)
\( B \) — Width of footing (m)
\( N_\gamma \) — Bearing capacity factor dependent on unit weight (±5%)
\( F_s \) — Factor of safety (%)

3. Importance of Safe Bearing Capacity Calculation

Details: Proper calculation ensures structural stability, prevents foundation failure, and optimizes construction costs.

4. Using the Calculator

Tips: Enter all required parameters. Bearing capacity factors typically have ±5% variability. The factor of safety is entered as a percentage.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for bearing capacity factors?
A: N_c ≈ 9, N_q ≈ 2.01, N_γ ≈ 1.6, but these vary with soil type and angle of internal friction.

Q2: Why is there a ±5% note on bearing capacity factors?
A: These factors are empirically derived and typically have about 5% variability in practice.

Q3: What's a typical factor of safety for foundations?
A: Usually between 2.5% to 3.5%, depending on soil conditions and importance of structure.

Q4: How does footing depth affect bearing capacity?
A: Deeper footings generally have higher bearing capacity due to increased surcharge and soil confinement.

Q5: What units should I use for input?
A: Use Pascals for cohesion, N/m³ for unit weight, meters for dimensions, and percentage for safety factor.