How to use the Consolidation Settlement Calculator
- 1. Enter the clay layerThickness, initial void ratio, compression index and clay type.
- 2. Enter the stressesEffective stress and stress increase at mid-depth, and drainage condition.
- 3. Get settlement and timeFinal settlement, change in void ratio and time for each degree of consolidation.
Settlement formulas
Normally consolidated clay: Sc = Cc · H/(1 + e₀) · log(σf/σ₀), where σf = σ₀ + Δσ at mid-depth.
Over-consolidated clay: if σf ≤ σc, Sc = Cs · H/(1 + e₀) · log(σf/σ₀). If σf > σc, add both parts: Cs · H/(1 + e₀) · log(σc/σ₀) + Cc · H/(1 + e₀) · log(σf/σc).
Time: t = Tv · Hd²/cv, where Hd is half the thickness for double drainage and the full thickness for single drainage. Tv = (π/4)U² for U ≤ 60%, and Tv = 1.781 − 0.933 log(100 − U%) above 60%.
Worked example and exam tips
A 4 m clay layer with e₀ = 0.9, Cc = 0.3, σ₀ = 100 kN/m² and Δσ = 50 kN/m²: Sc = 0.3 × 4/1.9 × log(1.5) = 0.111 m (111 mm). With double drainage, Hd = 2 m; for cv = 2 m²/year, 90% consolidation (Tv = 0.848) takes 0.848 × 4/2 = 1.7 years.
- Use stresses at the middle of the clay layer. For thick layers, split into sub-layers.
- If Cc is not given, Skempton's Cc ≈ 0.009(LL − 10) is a common estimate.
- Remember: Tv for 50% is 0.197 and for 90% is 0.848. These come up in almost every exam.
Frequently asked questions
What is the compression index Cc?
Cc is the slope of the void ratio vs log effective stress curve in the virgin compression range. A higher Cc means more compressible clay.
What is the drainage path for double drainage?
When water can drain from both the top and bottom of the clay, the longest path is half the thickness, so Hd = H/2.
Does this include immediate and secondary settlement?
No. It gives primary consolidation settlement only. Immediate (elastic) and secondary compression must be added separately.
Is this calculator free?
Yes. You fill a short form once to see your result, and other Uncodemy tools then open without the form. Everything is calculated in your browser and nothing you type is uploaded.