Consolidation Settlement Calculator

Estimate primary consolidation settlement of a normally consolidated clay layer using the compression index method: enter CⲜ, initial void ratio, layer thickness, and the initial and added effective stresses at mid-layer.

Educational / preliminary estimating tool. Results use published correlations and idealized assumptions (homogeneous soil, no groundwater effects unless stated). They are not a substitute for a site-specific investigation and design by a licensed geotechnical engineer.

Consolidation Parameters

Compression Index C_c

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Initial Void Ratio e₀

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Layer Thickness H

Initial Effective Stress σ′₀

psf

Stress Increase Δσ

psf

Enter consolidation properties and stresses to estimate settlement.

The equation

S_c = C_c·H ÷ (1 + e₀) × log₁₀((σ′₀ + Δσ) ÷ σ′₀)

Evaluate stresses at the mid-depth of the compressible layer. C_c comes from an oedometer test, or preliminary correlations like C_c ≈ 0.009(LL − 10) for normally consolidated clays (Terzaghi & Peck). For thick layers, better accuracy comes from splitting the layer into sublayers and summing — stresses and void ratios vary with depth.

Scope and what’s not included

This computes primary consolidation of a normally consolidated layer. Overconsolidated soils recompress along C_r (roughly 5–10× stiffer) until the preconsolidation pressure is exceeded, so applying C_c from the start overstates settlement. Immediate (elastic) settlement and long-term secondary compression (creep) are separate components, and the time for consolidation to occur is a separate calculation entirely (c_v, drainage path).

Frequently Asked Questions

How much settlement is acceptable?

Common serviceability limits are about 1 inch (25 mm) total for isolated footings and around L/300 for angular distortion between columns — but the tolerable value is structure-specific.

What is a typical compression index Cc?

Silty clays often run 0.2–0.5; soft, high-plasticity clays 0.5–1.0 or higher. The correlation Cc ≈ 0.009(LL − 10) gives a first estimate from the liquid limit.

How long does consolidation settlement take?

It depends on the layer’s drainage path and coefficient of consolidation — from months in thin, doubly drained layers to decades in thick clay deposits. This calculator gives magnitude, not time-rate.