Cohesion of Soil given Square Footing and Bearing Capacity Calculator

Cohesion of Soil Formula:

\[ C_{sq} = \frac{q_f - (\sigma' \times N_q + 0.5 \times \gamma \times B \times N_\gamma \times 0.8)}{1.3 \times N_c} \]

Ultimate Bearing Capacity (qf):

Effective Surcharge (σ'):

Bearing Capacity Factor (Nq):

Unit Weight of Soil (γ):

N/m³

Width of Footing (B):

Bearing Capacity Factor (Nγ):

Bearing Capacity Factor (Nc):

Cohesion of Soil (Csq): Pa

1. What is Cohesion of Soil given Square Footing?

Definition: This calculator determines the cohesion of soil for square footings based on bearing capacity theory.

Purpose: It helps geotechnical engineers and construction professionals assess soil strength for foundation design.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ C_{sq} = \frac{q_f - (\sigma' \times N_q + 0.5 \times \gamma \times B \times N_\gamma \times 0.8)}{1.3 \times N_c} \]

Where:

\( C_{sq} \) — Cohesion of soil for square footing (Pa)
\( q_f \) — Ultimate bearing capacity (Pa)
\( \sigma' \) — Effective surcharge (Pa)
\( N_q, N_\gamma, N_c \) — Bearing capacity factors (±5%)
\( \gamma \) — Unit weight of soil (N/m³)
\( B \) — Width of footing (m)

Explanation: The formula calculates soil cohesion by accounting for bearing capacity contributions from surcharge, soil weight, and footing geometry.

3. Importance of Soil Cohesion Calculation

Details: Proper cohesion estimation ensures foundation stability, prevents settlement, and helps in selecting appropriate construction techniques.

4. Using the Calculator

Tips: Enter all required parameters. Bearing capacity factors typically have ±5% variability. All values must be > 0 except surcharge which can be 0.

5. Frequently Asked Questions (FAQ)

Q1: What is cohesion in soil mechanics?
A: Cohesion is the component of shear strength in soils that is independent of interparticle friction.

Q2: Why 0.8 factor in the formula?
A: The 0.8 factor accounts for shape correction for square footings in the bearing capacity equation.

Q3: How to determine bearing capacity factors?
A: They depend on soil friction angle and are typically obtained from geotechnical tables or correlations.

Q4: What's a typical range for soil cohesion?
A: Cohesion varies widely: 0-10 kPa for loose sands, 10-100 kPa for stiff clays, higher for cemented soils.

Q5: When would effective surcharge be zero?
A: When there's no additional load at the ground surface adjacent to the foundation.