Estimation of Compressibility and Consolidation Characteristics of Lightly Overconsolidated Soils from In-Situ Time Settlement Plots.-Paper

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The study presents a method for estimating the compressibility and radial consolidation characteristics of lightly overconsolidated (LOC) soils from in-situ time–settlement data. Rather than relying on laboratory tests of samples assumed to represent an entire deposit, the approach back-analyzes settlement measurements at different depths. Compression indices are calculated for soil sublayers under overconsolidation ratios (OCRs) from 1.0 to 2.0, assuming a swell-to-compression index ratio of 0.1. The coefficient of radial consolidation, Cvr, is estimated using Asaoka plots and Barron’s radial-drainage theory.<br /><br />The method is applied to the soft clay deposit at Suvarnabhumi International Airport in Bangkok, where preloading and prefabricated vertical drains were used. Results show that the compression index increases with OCR when settlement is held constant. The increase varies by depth: for example, it is reported as 27% in the 0–2 m sublayer and 315% in the 12–15 m sublayer as OCR rises from 1 to 2. Estimated Cvr values for different sublayers range from 0.67 to 1.27 m²/year.<br /><br />Comparisons using linear and nonlinear consolidation theories indicate that changes in Asaoka-plot slope with OCR are generally small, suggesting that Cvr is not significantly affected by light overconsolidation. The study concludes that accounting for LOC conditions can provide more representative in-situ parameter estimates, and that predicted settlements may be lower than estimates based on assuming normally consolidated soil.

Keywords

lightly overconsolidated soils

compressibility

radial consolidation

in-situ settlement data

compression index

overconsolidation ratio

coefficient of radial consolidation

Asaoka plot

Barron theory

prefabricated vertical drains