Variation of the intrinsic permeability of expansive clays upon saturation

摘要

The intrinsic permeability of compacted bentonite has been determined on samples saturated and unsaturated, using different techniques but, in all the cases, keeping the volume of the specimen constant. The saturated hydraulic conductivity of compacted bentonite has been measured for a variety of void ratios, which has allowed the determination of an exponential relationship between permeability and void ratio. In parallel, the permeability to nitrogen gas has also been measured in specimens of compacted bentonite with different void ratio and degree of saturation. It has been observed that, for a given void ratio, the value of intrinsic permeability obtained when the measurement is done with water in the saturated sample, is much lower than that obtained when the measurement is performed with gas in the unsaturated sample. This behaviour is a consequence of the variation of the structure of the bentonite as a function of the degree of saturation. As the degree of saturation increases, the clay particles swell and fill the big pores among aggregates, thus causing the decrease of the average pore size, and consequently, the decrease of the intrinsic permeability, although the total porosity remains the same.