What is primary consolidation settlement?

Primary consolidation settlement is the gradual compression of a saturated soil layer as excess pore water pressure dissipates under an applied load. It is governed by Terzaghi's 1-D consolidation theory and calculated as Sc = (Cc × H) / (1+e0) × log10((σ0' + Δσ) / σ0').

What is the difference between Cc and Cs?

Cc (compression index) governs settlement when effective stress exceeds the preconsolidation pressure σp' (normally consolidated range). Cs (swell or recompression index) is used when effective stress stays below σp' (overconsolidated range). Cs is typically 5–10 times smaller than Cc.

How do I determine if my soil is overconsolidated?

Compare the initial effective stress σ0' with the preconsolidation pressure σp'. If σp' > σ0', the soil is overconsolidated. The overconsolidation ratio (OCR) = σp' / σ0'. An OCR of 1 means normally consolidated.

What influence factor Iw should I use for elastic settlement?

Iw depends on footing shape and flexibility. Common values: flexible square ≈ 0.82, rigid square ≈ 0.82, flexible rectangle (L/B=2) ≈ 1.06, flexible rectangle (L/B=5) ≈ 1.43. For a quick estimate, use Iw = 1.0.

Does this include secondary compression (creep)?

No. This tool computes primary consolidation settlement only. Secondary compression occurs after primary consolidation and requires the secondary compression index Cα and time estimates, which are not included here.

Settlement Calculator

Name: Settlement Calculator
Availability: InStock
Author: Nham Vu

Enter soil layer properties and foundation stress to instantly compute primary consolidation settlement (Sc) using Cc and e0, with overconsolidation and elastic settlement support.

Soil & Load Parameters

Consolidation Condition

Layer thickness H (m)

Initial void ratio e0

Typical: 0.5–1.5 for clays.

Compression index Cc

Typical: 0.2–0.5 for soft to medium clay.

Initial effective stress σ0' (kPa)

Stress increase Δσ (kPa)

Net vertical stress increase at mid-layer.

Include elastic (immediate) settlement

Enter soil parameters, then click Calculate.

Summary

Enter soil layer properties and foundation stress to instantly compute primary consolidation settlement (Sc) using Cc and e0, with overconsolidation and elastic settlement support.

How it works

Enter the soil layer thickness H (m) and initial void ratio e0.
Enter the compression index Cc and, if the soil is overconsolidated, the swell index Cs.
Enter the initial effective vertical stress σ0' (kPa) and stress increase Δσ (kPa).
For overconsolidated soils, enter the preconsolidation pressure σp' (kPa).
Optionally enable elastic settlement and enter foundation width B, applied stress q, elastic modulus Es, Poisson's ratio ν, and influence factor Iw.
Click Calculate to see primary consolidation settlement Sc and, if enabled, immediate settlement Si.

Use cases

Estimating total settlement of foundations on soft clay layers.
Distinguishing normally consolidated from overconsolidated soil behavior in design.
Checking settlement predictions against allowable limits in building codes.
Teaching Terzaghi 1-D consolidation theory interactively.
Verifying hand calculations during geotechnical coursework or professional practice.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu