Prediction of movement in expansive clays
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The movement of expansive soils is usually due to a change of suction near the soil surface. The properties of the soil that govern the amount and rate of movement are the suction compression index, and the unsaturated permeability and diffusivity. Methods of using these to determine suction and heave (or shrinkage) profiles with depth are outlined. Methods of estimating these properties using simple laboratory tests, namely Atterberg limits, water content, dry density, porosity, sieve analysis, and hydrometer analysis are presented. Differential movement governs the design of slabs-on-ground, highway and airport pavements and canal linings, which are themselves controlled by the edge moisture variation distance. Graphs of the edge moisture variation distance as it changes with the unsaturated diffusivity and the Thornthwaite Moisture Index are presented for both the center lift and edge lift distortion modes. The values were computed using a coupled unsaturated moisture flow and elasticity finite element program which had been calibrated to match reasonably well the measured suctions in an extensive field study involving several pavement sites in a number of different climatic zones in Texas.
Geotechnical Special Publication
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