Cohesion of Soil for Local Shear Failure given Depth of Footing Calculator

Cohesion of Soil Formula:

\[ C = \frac{q_{fc} - ((\gamma \times D_{footing} \times N_q) + (0.5 \times \gamma \times B \times N_\gamma))}{(2/3) \times N_c} \]

Ultimate Bearing Capacity (kPa):

kPa

Unit Weight of Soil:

kN/m³

Depth of Footing:

Bearing Capacity Factor (Nq):

Width of Footing:

Bearing Capacity Factor (Nγ):

Bearing Capacity Factor (Nc):

Cohesion in Soil (kPa):

1. What is Cohesion of Soil for Local Shear Failure?

Definition: This calculator determines the cohesion of soil when local shear failure occurs, considering the footing depth and other soil parameters.

Purpose: It helps geotechnical engineers assess soil stability and design appropriate foundations to prevent local shear failure.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ C = \frac{q_{fc} - ((\gamma \times D_{footing} \times N_q) + (0.5 \times \gamma \times B \times N_\gamma))}{(2/3) \times N_c} \]

Where:

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

Explanation: The formula calculates soil cohesion by accounting for the bearing capacity components from surcharge, soil weight, and cohesion.

3. Importance of Cohesion Calculation

Details: Proper cohesion estimation helps prevent foundation failures, ensures structural stability, and optimizes foundation design.

4. Using the Calculator

Tips: Enter all required parameters with positive values. Bearing capacity factors typically have ±5% uncertainty.

5. Frequently Asked Questions (FAQ)

Q1: What is local shear failure?
A: It occurs when soil fails only beneath the foundation while the surrounding soil remains intact.

Q2: How do I determine bearing capacity factors?
A: They depend on soil friction angle; use standard geotechnical tables or equations.

Q3: Why is cohesion important in foundation design?
A: Cohesion contributes significantly to soil shear strength, especially in clayey soils.

Q4: What units should I use?
A: Use consistent units: kN/m³ for unit weight, meters for dimensions, and kPa for pressure/stress.

Q5: How accurate is this calculation?
A: Accuracy depends on input parameters. Bearing capacity factors typically have ±5% uncertainty.