Ultimate Bearing Capacity for Rectangular Footing Calculator

Ultimate Bearing Capacity Formula:

\[ q_{fc} = \frac{(C \times N_c) \times (1 + 0.3 \times \frac{B}{L}) + (\sigma_s \times N_q) + (0.4 \times \gamma \times B \times N_\gamma)}{±5\%} \]

Cohesion in Soil (C):

kPa

Bearing Capacity Factor (Nc):

Width of Footing (B):

Length of Footing (L):

Effective Surcharge (σₛ):

kPa

Bearing Capacity Factor (Nq):

Unit Weight of Soil (γ):

kN/m³

Bearing Capacity Factor (Nγ):

Ultimate Bearing Capacity (kPa):

Range (±5%):

1. What is Ultimate Bearing Capacity for Rectangular Footing?

Definition: The ultimate bearing capacity is the maximum pressure that a rectangular footing can sustain before shear failure occurs in the supporting soil.

Purpose: This calculation is essential for foundation design to ensure structural stability and prevent soil failure.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ q_{fc} = (C \times N_c) \times (1 + 0.3 \times \frac{B}{L}) + (\sigma_s \times N_q) + (0.4 \times \gamma \times B \times N_\gamma) \]

Where:

\( q_{fc} \) — Ultimate bearing capacity (kPa)
\( C \) — Cohesion of soil (kPa)
\( N_c \) — Bearing capacity factor for cohesion
\( B \) — Width of footing (m)
\( L \) — Length of footing (m)
\( \sigma_s \) — Effective surcharge (kPa)
\( N_q \) — Bearing capacity factor for surcharge
\( \gamma \) — Unit weight of soil (kN/m³)
\( N_\gamma \) — Bearing capacity factor for unit weight

3. Importance of Bearing Capacity Calculation

Details: Proper calculation ensures foundation stability, prevents excessive settlement, and maintains structural integrity.

4. Using the Calculator

Tips: Enter all required parameters. The calculator provides results with ±5% accuracy range to account for soil variability.

5. Frequently Asked Questions (FAQ)

Q1: Why is there a ±5% range in the results?
A: This accounts for natural variability in soil properties and measurement uncertainties.

Q2: What are typical values for bearing capacity factors?
A: Default values are provided (Nc=9, Nq=2.01, Nγ=1.6) but should be adjusted based on soil conditions.

Q3: How does footing shape affect the calculation?
A: The (1 + 0.3 × B/L) term accounts for rectangular footing shape effects.

Q4: What units should be used?
A: Consistent SI units are required (kPa for stresses, m for dimensions, kN/m³ for unit weight).

Q5: When should I consult a geotechnical engineer?
A: Always consult a professional for critical structures or complex soil conditions.