Terzaghi 1D Consolidation Calculator
Geotechnical foundation mechanics: Calculate ultimate 1D consolidation settlement (S_c), degree of consolidation (U_v), and settlement time dissipation (t_50, t_90).
Clay Layer & Stress Profile
Settlement Magnitude & Rate
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Frequently Asked Questions
Why does primary consolidation settlement in clay take years or decades?
Unlike coarse sand and gravel which drain pore water almost instantaneously, cohesive clays have microscopic pore channels and extremely low hydraulic permeability (k ~ 10⁻⁸ to 10⁻¹¹ m/s). When external building loads are applied, the stress is initially carried by excess pore water pressure. Dissipating this trapped water through the low-permeability clay matrix takes years, causing slow, long-term foundation settlement.
Why does double drainage shorten consolidation time by fourfold compared to single drainage?
Consolidation time scales with the square of the maximum drainage path length (t ∝ d_drain²). For a clay layer with pervious sand both above and below (double drainage), the furthest a water droplet must travel is half the layer thickness (d = H/2). If the base is impervious bedrock (single drainage), water must travel the entire thickness (d = H). Because (H)² / (H/2)² = 4, single drainage takes exactly four times longer to consolidate.
What is the Preconsolidation Stress (σ'p) and Overconsolidation Ratio (OCR)?
The preconsolidation stress (σ'p) is the maximum effective vertical stress that a soil layer has ever experienced in its geological history (e.g. from glaciers or eroded overburden). The OCR = σ'p / σ'v0. If OCR = 1.0, the soil is Normally Consolidated and settles along the steep virgin compression curve (Cc). If OCR > 1.0, the soil is Overconsolidated and settles along the much flatter, stiffer recompression curve (Cr ≈ 10% of Cc).