Scenario Comparison
| Sample | Method | Friction angle | Cohesion | Strength type | Condition |
|---|---|---|---|---|---|
| No saved scenarios. | |||||
Formula Used
The direct shear model uses τf = c + σ′ tan φ. Its slope equals tan φ. The intercept represents fitted cohesion.
Triaxial compression uses σ′1 = Nφσ′3 + 2c√Nφ. Here, Nφ equals (1 + sin φ) divided by (1 − sin φ). The fitted slope provides φ.
The design angle divides tan φ by the selected partial factor. This reduction supports transparent comparison. It does not replace a project design standard.
How to Use
Select a test method first. Choose consistent input and output units. Then enter complete laboratory or field data.
Use weights only when test reliability differs. Compare free and zero-intercept regressions. Review every warning before accepting results.
Save useful scenarios for side-by-side review. Export a clear calculation record. Confirm final parameters with qualified geotechnical judgement.
Example Data
| Test | Normal stress | Failure shear stress | Purpose |
|---|---|---|---|
| 1 | 50 kPa | 42 kPa | Low confinement |
| 2 | 100 kPa | 72 kPa | Intermediate confinement |
| 3 | 200 kPa | 126 kPa | Higher confinement |
Frequently Asked Questions
What is soil friction angle?
It represents frictional resistance within soil. Higher values indicate stronger particle interaction. Density and stress conditions affect it.
What does cohesion mean?
Cohesion is the failure-envelope intercept. It may be real or apparent. Interpretation depends on soil behaviour.
Should cohesion be forced to zero?
Use that option for justified cohesionless modelling. Compare both regression results first. Document the selected assumption.
Why is effective stress important?
Effective stress excludes pore-water pressure effects. It often controls drained soil strength. Use consistent stress definitions throughout.
Can angle of repose replace testing?
No. It provides a preliminary estimate only. Laboratory testing offers stronger design evidence.
What indicates a poor regression?
Low R² and large residuals indicate scatter. Outliers may distort the fitted envelope. Review specimen and test records.
Why can cohesion become negative?
Nonlinearity or scatter may shift the intercept. The tested stress range may also matter. Consider a constrained comparison.
What is a design friction angle?
It is a reduced value for assessment. The chosen factor controls the reduction. Follow the governing design standard.
Are empirical correlations reliable?
They are screening tools with uncertainty. Local geology can change relationships. Calibrate them against representative testing.
Engineering Limitations
Results depend on sample quality and stress range. Drainage, density, saturation, and dilation can change strength. Soil behaviour may be nonlinear.
This calculator supports analysis and documentation. It cannot verify laboratory procedures. It cannot select safe project parameters.
Use qualified geotechnical review for final decisions. Apply relevant codes and project requirements. Confirm critical values using representative tests.