Bearing Capacity for Square Footing Calculator

Bearing Capacity Formula for Square Footing:

\[ q_{square} = (1.3 \times C \times N_c) + (\sigma' \times N_q) + (0.5 \times \gamma \times B \times N_\gamma \times 0.8) \]

Cohesion (C):

Bearing Capacity Factor (N_c):

Effective Surcharge (σ'):

Bearing Capacity Factor (N_q):

Unit Weight of Soil (γ):

N/m³

Width of Footing (B):

Bearing Capacity Factor (N_γ):

Bearing Capacity (q_square): Pa

1. What is Bearing Capacity for Square Footing?

Definition: The bearing capacity for square footing is the maximum load per unit area that the soil can support without experiencing shear failure when subjected to load applied by a square footing.

Purpose: It helps civil engineers and construction professionals design safe foundations that won't fail under applied loads.

2. How Does the Calculator Work?

The calculator uses Terzaghi's bearing capacity formula modified for square footings:

\[ q_{square} = (1.3 \times C \times N_c) + (\sigma' \times N_q) + (0.5 \times \gamma \times B \times N_\gamma \times 0.8) \]

Where:

\( q_{square} \) — Bearing capacity (Pa)
\( C \) — Cohesion of soil (Pa)
\( N_c \) — Bearing capacity factor dependent on cohesion (±5%)
\( \sigma' \) — Effective surcharge (Pa)
\( N_q \) — Bearing capacity factor dependent on surcharge (±5%)
\( \gamma \) — Unit weight of soil (N/m³)
\( B \) — Width of footing (m)
\( N_\gamma \) — Bearing capacity factor dependent on unit weight (±5%)

3. Importance of Bearing Capacity Calculation

Details: Proper bearing capacity estimation prevents foundation failures, ensures structural stability, and helps optimize foundation design.

4. Using the Calculator

Tips: Enter all required parameters. The bearing capacity factors have ±5% uncertainty. All values must be ≥ 0, with factors > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why are there different bearing capacity factors?
A: Each factor (N_c, N_q, N_γ) accounts for different soil properties (cohesion, surcharge, unit weight respectively).

Q2: What's the significance of the ±5% on factors?
A: This represents the typical uncertainty in these empirical factors due to soil variability.

Q3: How do I determine the bearing capacity factors?
A: They're typically determined from soil friction angle using established tables or formulas.

Q4: Why is the formula different for square footings?
A: The 1.3 and 0.8 factors account for the different shape compared to continuous footings.

Q5: What safety factors should I apply?
A: Typical safety factors range from 2.5-3.0 for bearing capacity calculations.