EXPERIMENTAL-STUDY OF FRAGIPANS FORMATION IN SOILS - ROLE OF BOTH CLAY DISPERSION AND WETTING-DRYING CYCLES

There is considerable literature about fragipans but their origin is s till under discussion. In the laboratory, we investigated silt-clay fa brics which were obtained by mixing a sill fraction with either air-dr ied clay forming clayey aggregates or wet clay as a paste. The results from scanning electron microscopy and porosity analysis were used to study the formation of fragipans. Our results suggest that fragipans o riginate from successive wetting and drying cycles. Each wetting perio d would favour the dispersion of clay particles within the soil matrix and each drying period would favour its reorganization into coatings over the skeleton grains and wall-shaped bridges between these grains. The prevalence of these processes makes possible the formation of fra gipans under varied climatic conditions. (C) Acadimie des sciences/Els evier, Paris.