Bearing Capacity for Local Shear Failure given Depth of Footing Calculator

Ultimate Bearing Capacity Formula:

\[ qf = \left(\frac{2}{3} \times Cs \times Nc\right) + \left(\gamma \times D \times Nq\right) + \left(0.5 \times \gamma \times B \times N\gamma\right) \]

Cohesion of Soil (Cs):

Bearing Capacity Factor (Nc):

Unit Weight of Soil (γ):

N/m³

Depth of Footing (D):

Bearing Capacity Factor (Nq):

Width of Footing (B):

Bearing Capacity Factor (Nγ):

Ultimate Bearing Capacity (qf):

1. What is Bearing Capacity for Local Shear Failure?

Definition: This calculator determines the ultimate bearing capacity of soil for local shear failure conditions, considering the depth of footing and soil properties.

Purpose: It helps geotechnical engineers and foundation designers assess the soil's capacity to support loads without experiencing local shear failure.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ qf = \left(\frac{2}{3} \times Cs \times Nc\right) + \left(\gamma \times D \times Nq\right) + \left(0.5 \times \gamma \times B \times N\gamma\right) \]

Where:

\( qf \) — Ultimate bearing capacity (Pa)
\( Cs \) — Cohesion of soil (Pa)
\( Nc \) — Bearing capacity factor for cohesion (±5%)
\( \gamma \) — Unit weight of soil (N/m³)
\( D \) — Depth of footing (m)
\( Nq \) — Bearing capacity factor for surcharge (±5%)
\( B \) — Width of footing (m)
\( N\gamma \) — Bearing capacity factor for unit weight (±5%)

Explanation: The formula combines three components: cohesion term, surcharge term, and unit weight term to calculate the total bearing capacity.

3. Importance of Bearing Capacity Calculation

Details: Proper bearing capacity estimation ensures foundation stability, prevents settlement issues, and maintains structural integrity.

4. Using the Calculator

Tips: Enter all required parameters. The bearing capacity factors (Nc, Nq, Nγ) typically have ±5% variability. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is local shear failure?
A: Local shear failure occurs when the soil beneath a footing fails in a limited zone, with some soil still providing resistance.

Q2: Why use 2/3 of cohesion for local shear?
A: The 2/3 factor accounts for reduced shear strength in local failure conditions compared to general shear failure.

Q3: How do I determine bearing capacity factors?
A: Factors depend on soil friction angle. Use standard geotechnical tables or our Bearing Capacity Factors Calculator.

Q4: What's a typical unit weight for soil?
A: Common values range from 16,000-20,000 N/m³ for most soils, but this varies with soil type and moisture.

Q5: How does footing depth affect capacity?
A: Deeper footings generally have higher capacity due to increased surcharge from overlying soil.