Effective Surcharge given Square Footing and Bearing Capacity Calculator

Effective Surcharge Formula for Square Footing:

\[ \sigma_{square} = \frac{q_f - (1.3 \times C \times N_c + 0.5 \times \gamma \times B \times N_\gamma \times 0.8)}{N_q} \]

Ultimate Bearing Capacity (qf):

Cohesion (C):

Bearing Capacity Factor (Nc):

Unit Weight of Soil (γ):

N/m³

Width of Footing (B):

Bearing Capacity Factor (Nγ):

Bearing Capacity Factor (Nq):

Effective Surcharge (σsquare): Pa

1. What is Effective Surcharge for Square Footing?

Definition: Effective surcharge is the additional pressure exerted on the soil due to external loads distributed over a square footing.

Purpose: It helps geotechnical engineers determine the additional load-bearing capacity required for foundations.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ \sigma_{square} = \frac{q_f - (1.3 \times C \times N_c + 0.5 \times \gamma \times B \times N_\gamma \times 0.8)}{N_q} \]

Where:

\( \sigma_{square} \) — Effective surcharge (Pa)
\( q_f \) — Ultimate bearing capacity (Pa)
\( C \) — Cohesion of soil (Pa)
\( N_c \) — Bearing capacity factor dependent on cohesion
\( \gamma \) — Unit weight of soil (N/m³)
\( B \) — Width of footing (m)
\( N_\gamma \) — Bearing capacity factor dependent on unit weight
\( N_q \) — Bearing capacity factor dependent on surcharge

3. Importance of Effective Surcharge Calculation

Details: Proper calculation ensures foundation stability, prevents settlement issues, and optimizes material usage in construction projects.

4. Using the Calculator

Tips: Enter all required parameters with appropriate units. The bearing capacity factors include ±5% uncertainty ranges.

5. Frequently Asked Questions (FAQ)

Q1: Why are bearing capacity factors given with ±5%?
A: The ±5% accounts for natural variability in soil properties and empirical determination of these factors.

Q2: What's a typical value for cohesion (C)?
A: Cohesion varies widely: 0 for pure sand, 10-100 kPa for clay, and 0-10 kPa for silt.

Q3: How do I determine the ultimate bearing capacity?
A: It's typically determined through geotechnical testing or estimated from soil properties.

Q4: What if my footing isn't square?
A: Different shape factors apply for rectangular or circular footings.

Q5: How does water table affect the calculation?
A: Submerged unit weight should be used if water table is above footing base.