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Résumé :
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Direct measurement of a permeability function, k(ψ) (where ψ = suction), of an unsaturated soil is often tedious and time-consuming. Thus, researchers have proposed various semiempirical predictive methods to determine k(ψ) indirectly from a soil-water characteristic curve (SWCC) or a particle-size distribution. Also, stress effects on k(ψ) are generally not considered. To explore any stress effect on k(ψ), a new 1-m-high stress-controllable soil column is developed to measure stress-dependent SWCC (SDSWCC) and k(ψ) of soils directly. The objectives of this paper are to investigate the effects of (1) two stress-state variables (matric suction and net normal stress) and (2) a drying-wetting cycle on both SDSWCC and k(ψ) of a compacted decomposed silty clay. Each compacted soil column is subjected to an evaporation-ponding cycle under various vertical net normal stresses. The variations of pore-water pressure and volumetric water content (VWC, θw) profiles with time are measured instantaneously. The k(ψ) is hence determined by using the instantaneous profile method. At a given average vertical net normal stress, the measured k(ψ) exhibits a remarkable hysteresis loop, whereas the k(θw) seems to be less hysteretic. The effects of the vertical net normal stress appear to be more pronounced than that of the drying-wetting cycle on k(θw). As average vertical net normal stress is increased from 4 to 78 kPa, the measured permeability decreases by up to two orders of magnitude at a given VWC.
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