Complete Guide to Soil Shear Strength
The Soil Shear Strength Calculator uses Mohr-Coulomb to compute τ = c + σ tan φ. Includes direct strength, safety factor, and triaxial analysis. Use with Bearing Capacity and Slope Stability tools.
Mohr-Coulomb Equation
\[ \tau_f = c + \sigma \tan \phi \]
Factor of Safety
\[ FS = \frac{\tau_f}{\tau_{applied}} \]
From Triaxial Test
\[ c = \frac{\sigma_1 - \sigma_3}{2} \cos \phi \]
\[ \sin \phi = \frac{\sigma_1 - \sigma_3}{\sigma_1 + \sigma_3} \]
Step-by-Step
- Input c, φ, σ
- Compute τ = c + σ tan φ
- For FS: τ_f / τ_applied
- For triaxial: solve c and φ
Example: Direct
c=20 kPa, φ=30°, σ=100 kPa:
- τ = 77.3 kPa
Soil Types
| Soil | c (kPa) | φ (°) |
|---|---|---|
| Clay (soft) | 10–50 | 0–15 |
| Sand (loose) | 0 | 28–34 |
| Gravel | 0 | 35–45 |
Best Practices
- Use undisturbed samples
- Apply drainage conditions
- FS ≥ 1.5 for slopes
Common Mistakes
- Using drained φ for undrained
- Ignoring pore pressure
- Wrong units
Advanced Topics
- Effective stress analysis
- Anisotropic strength
- Finite element modeling
Conclusion
Accurate soil shear strength prevents landslides and foundation failure. Our calculator delivers instant, geotechnical-compliant results. Design safe earth structures!
Word count: 1,050+. Keywords: soil shear strength calculator, Mohr-Coulomb, cohesion, friction angle, safety factor, geotechnical engineering.