Input Data
Example Data Table
| Item | Example Value |
|---|---|
| Layer thickness, H | 6.0 m |
| Initial void ratio, e₀ | 0.95 |
| Initial effective stress, σ′₀ | 120 kPa |
| Stress increase, Δσ′ | 80 kPa |
| Preconsolidation stress, σ′pc | 150 kPa |
| Compression index, Cc | 0.32 |
| Recompression index, Cr | 0.06 |
| Coefficient of consolidation, Cv | 0.015 m²/day |
| Drainage condition | Double drainage |
| Elapsed time for current check | 365 days |
Formula Used
1) Primary Consolidation Settlement
Normally consolidated or yielded clay:
S = H / (1 + e₀) × Cc × log₁₀[(σ′₀ + Δσ′) / σ′₀]
Overconsolidated clay, recompression only:
S = H / (1 + e₀) × Cr × log₁₀[(σ′₀ + Δσ′) / σ′₀]
Overconsolidated clay crossing preconsolidation stress:
S = H / (1 + e₀) × [Cr × log₁₀(σ′pc / σ′₀) + Cc × log₁₀((σ′₀ + Δσ′) / σ′pc)]
2) Time Rate of Consolidation
Tv = Cv × t / Hdr²
where Hdr = H for single drainage and Hdr = H / 2 for double drainage.
3) Average Degree of Consolidation
The calculator uses the Terzaghi series solution:
U = 1 − Σ [8 / (π²(2m+1)²)] × exp{−[(2m+1)²π²Tv]/4}
4) Settlement at Time t
S(t) = U × S_primary
5) Secondary Compression
S_secondary = Cα × H / (1 + e_end) × log₁₀(t₂ / t₁)
These equations are typically used for saturated fine-grained soils where one-dimensional consolidation assumptions are acceptable.
How to Use This Calculator
- Enter the clay layer thickness and initial void ratio.
- Provide the initial effective stress at the layer center.
- Enter the estimated stress increase caused by the structure or fill.
- Input the preconsolidation stress to distinguish OC and NC behavior.
- Fill in compression index, recompression index, and consolidation coefficient.
- Select single or double drainage based on field drainage conditions.
- Enter elapsed time to estimate settlement already developed.
- Set a target consolidation percentage to estimate the required time.
- Enable secondary compression when long-term creep is important.
- Click the calculate button and review the summary, table, and curve.
FAQs
1) What does this calculator estimate?
It estimates one-dimensional consolidation settlement in compressible soils. It also evaluates settlement progression with time, degree of consolidation, drainage effects, and optional secondary compression for long-term performance checks.
2) When should I use Cc and Cr together?
Use both when the soil is overconsolidated and the final effective stress exceeds preconsolidation stress. The calculator applies recompression up to σ′pc and virgin compression beyond it.
3) Why is drainage type important?
Drainage type changes the drainage path length. A shorter path means faster dissipation of excess pore pressure, so double drainage reaches the same consolidation level sooner than single drainage.
4) What unit should Cv use here?
This file assumes Cv is entered in square meters per day. If your data is in another time unit, convert it first so the plotted times and reported consolidation times remain correct.
5) Does the calculator include immediate settlement?
No. This version focuses on consolidation and optional secondary compression. Immediate or elastic settlement should be checked separately and added when total foundation movement is needed.
6) How should I choose the stress increase?
Use a representative increase in effective vertical stress at the center of the compressible layer. Many engineers obtain it from stress distribution methods, layered analysis, or software-based foundation models.
7) What does the plotted curve show?
The graph shows settlement growth with time. Primary, secondary, and total settlement lines help you compare short-term development against long-term creep behavior in a clear visual form.
8) Is this suitable for final design without judgment?
No. It is a strong calculation aid, but field variability, drainage boundaries, staged loading, smear effects, and sample disturbance still require engineering review before final design decisions.