1. What is Shear Strength of Cohesionless Soil?

Definition: Shear strength is the maximum resistance of cohesionless soil (like sand or gravel) to shear stresses before failure occurs.

Purpose: This calculator helps geotechnical engineers and construction professionals determine the shear strength of granular soils for foundation design and slope stability analysis.

2. How Does the Calculator Work?

The calculator uses the Mohr-Coulomb failure criterion for cohesionless soils:

Where:

• \( \tau_s \) — Shear strength (MPa)
• \( \sigma_{nm} \) — Normal stress on failure plane (MPa)
• \( \phi \) — Angle of internal friction (degrees)

Explanation: The shear strength is directly proportional to the normal stress and increases with the tangent of the friction angle.

3. Importance of Shear Strength Calculation

Details: Accurate shear strength estimation is crucial for designing stable foundations, retaining walls, and slopes in cohesionless soils.

4. Using the Calculator

Tips: Enter the normal stress in MPa, friction angle in degrees (typically 30-40° for sands), and allowable variation percentage (default ±5%).

5. Frequently Asked Questions (FAQ)

Q1: What is angle of internal friction?
A: It's a measure of a soil's shear strength, representing the friction between soil particles under normal stress.

Q2: Why is there no cohesion term?
A: This calculator is for cohesionless soils (like sand) where cohesion (c) is zero. For cohesive soils, use \( \tau_s = c + \sigma_{nm} \tan(\phi) \).

Q3: What's a typical friction angle for sand?
A: Loose sand: 28-34°, Medium dense: 32-36°, Dense sand: 36-45°.

Q4: What does the variation percentage mean?
A: It accounts for uncertainty in soil properties, showing the possible range of shear strength values.

Q5: How is normal stress determined?
A: It's calculated from the overburden pressure at the depth of interest, considering unit weight and depth.

Shear Strength of Cohesionless Soil Calculator© - All Rights Reserved 2025