1. What is Cohesion of Soil for Purely Cohesive Soil?

Definition: This calculator determines the cohesion of purely cohesive soil based on ultimate bearing capacity, unit weight of soil, and depth of footing.

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

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( C_s \) — Cohesion of Soil (Pascal)
• \( q_f \) — Ultimate Bearing Capacity (Pascal)
• \( \gamma \) — Unit Weight of Soil (N/m³)
• \( D \) — Depth of Footing (m)

Explanation: The formula calculates soil cohesion by accounting for the bearing capacity minus the effect of soil weight at a given depth, divided by the Terzaghi bearing capacity factor.

3. Importance of Soil Cohesion Calculation

Details: Accurate cohesion values are critical for determining foundation stability, slope stability, and earth pressure calculations.

4. Using the Calculator

Tips: Enter the ultimate bearing capacity, unit weight of soil, and depth of footing. All values must be > 0. Results include ±5% tolerance.

5. Frequently Asked Questions (FAQ)

Q1: What is purely cohesive soil?
A: Purely cohesive soil (clay) derives its shear strength primarily from cohesion rather than internal friction.

Q2: Why is the 5.7 factor used?
A: This is Terzaghi's bearing capacity factor (Nc) for continuous footings in purely cohesive soil.

Q3: What units should I use?
A: Consistent SI units: Pascals for pressure, N/m³ for unit weight, and meters for depth.

Q4: How accurate is this calculation?
A: Results are theoretical estimates with ±5% tolerance; field tests provide more accurate values.

Q5: When would I need this calculation?
A: For foundation design in clay soils, slope stability analysis, or when laboratory test data isn't available.

Cohesion of Soil Calculator© - All Rights Reserved 2025