Bearing Capacity of Cohesive Soil for Square Footing Calculator

Ultimate Bearing Capacity Formula:

\[ q_f = (C \times N_c) \times (1 + 0.3 \times \frac{B}{L}) + \sigma_s \]

Cohesion in Soil (C):

kPa

Bearing Capacity Factor (N_c):

Width of Footing (B):

Length of Footing (L):

Effective Surcharge (σ_s):

kPa

Ultimate Bearing Capacity (q_f): kPa

1. What is Bearing Capacity of Cohesive Soil?

Definition: The ultimate bearing capacity is the maximum pressure that soil can withstand before shear failure occurs.

Purpose: This calculator helps geotechnical engineers determine the load-bearing capacity of cohesive soils for square footings.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ q_f = (C \times N_c) \times (1 + 0.3 \times \frac{B}{L}) + \sigma_s \]

Where:

\( q_f \) — Ultimate bearing capacity (kPa)
\( C \) — Cohesion in soil (kPa)
\( N_c \) — Bearing capacity factor (typically 9 for cohesive soils)
\( B \) — Width of footing (m)
\( L \) — Length of footing (m)
\( \sigma_s \) — Effective surcharge (kPa)

Explanation: The formula combines soil cohesion, footing dimensions, and surcharge to determine maximum load capacity.

3. Importance of Bearing Capacity Calculation

Details: Proper calculation ensures foundation stability, prevents settlement issues, and guarantees structural safety.

4. Using the Calculator

Tips: Enter soil cohesion, bearing capacity factor (default 9±5%), footing dimensions, and surcharge pressure. All values must be ≥ 0.

5. Frequently Asked Questions (FAQ)

Q1: What is typical N_c value for cohesive soils?
A: For cohesive soils, N_c is typically 9, but can range from 5.14 to 9 depending on soil conditions.

Q2: Why is the width/length ratio important?
A: The B/L ratio accounts for the shape effect on bearing capacity (1.0 for square footings, lower for rectangular).

Q3: What if my footing is perfectly square?
A: For square footings (B = L), the term (1 + 0.3*(B/L)) simplifies to 1.3.

Q4: How is effective surcharge determined?
A: It's the vertical stress from soil or other loads above foundation level (γ × depth).

Q5: Should I apply a safety factor?
A: Yes, divide the ultimate capacity by 2.5-3.0 for allowable bearing capacity in design.