Calculated Results
Primary settlement, stress path, consolidation timing, and staged settlement trend.
Settlement Versus Time
Awaiting calculationComputed Notes
| Time | U (%) | Settlement (mm) |
|---|
Input Data
Use consistent soil parameters. The calculator supports normally consolidated, overconsolidated, and optional secondary compression checks.
Example Data Table
This sample illustrates a moderately compressible clay layer under a new surface load.
| Parameter | Example Value | Unit | Comment |
|---|---|---|---|
| Layer thickness, H | 6.0 | m | Compressible clay thickness |
| Initial void ratio, e₀ | 0.92 | — | Measured from lab data |
| Compression index, Cc | 0.30 | — | Virgin compression slope |
| Recompression index, Cr | 0.05 | — | Stress range below σ′p |
| Initial effective stress, σ′₀ | 110 | kPa | Before new loading |
| Stress increment, Δσ | 80 | kPa | Fill or footing influence |
| Preconsolidation stress, σ′p | 150 | kPa | Overconsolidated threshold |
| Expected primary settlement | 117.4 | mm | Approximate sample output |
Formula Used
Primary consolidation settlement
Normally consolidated: S = H × [Cc / (1 + e₀)] × log₁₀[(σ′₀ + Δσ) / σ′₀]
Overconsolidated: use Cr below σ′p and Cc above σ′p. The calculator automatically splits the stress path where required.
Time factor relationship
t = Tv × Hdr² / Cv
Hdr is the drainage path. Use H/2 for double drainage and H for single drainage.
Average degree of consolidation
The chart uses the Terzaghi one-dimensional series solution to estimate U over time, then multiplies U by primary settlement.
Secondary compression
When enabled: Ss = [Cα × H / (1 + e)] × log₁₀(t / t₁), applied after the selected reference time.
How to Use This Calculator
- Enter the compressible layer thickness, void ratio, and soil indices from consolidation test data.
- Add the initial effective stress, proposed stress increase, and preconsolidation stress.
- Select the consolidation coefficient unit and choose single or double drainage.
- Set the target degree of consolidation and analysis horizon for the chart.
- Enable secondary compression only when creep settlement needs checking.
- Press calculate to display summary results above the form, then export the report as CSV or PDF.
FAQs
1. What does this calculator estimate?
It estimates primary consolidation settlement, average consolidation over time, target settlement timing, final void ratio, and optional secondary compression for a one-dimensional loading case.
2. When should I use Cc instead of Cr?
Use Cr when the final effective stress stays below preconsolidation stress. Use Cc for virgin compression beyond preconsolidation. The calculator handles mixed stress paths automatically.
3. Why does drainage condition matter?
Drainage condition changes the drainage path length. Shorter paths accelerate consolidation, reducing the time needed to reach the same average degree of consolidation.
4. Can I use this for layered soils?
Yes, but calculate each layer separately using representative parameters, then sum the settlements. This file models one compressible layer at a time.
5. What unit should I use for Cv?
Enter Cv in the selected unit. The tool converts it internally so settlement timing stays consistent with the chosen analysis horizon.
6. Does this include immediate settlement?
No. It focuses on consolidation behavior. Immediate or elastic settlement should be evaluated separately and added when the project requires total settlement checks.
7. When is secondary compression useful?
It is useful for organic soils, soft clays, and long service periods where post-primary creep may continue after pore pressure dissipation substantially finishes.
8. Is the chart suitable for design reports?
Yes. It is useful for screening, concept design, and report appendices. Final design should still rely on verified lab data and project-specific geotechnical judgment.