Abstract: In order to investigate the unsaturated hydraulic properties of wide grading gravelly soil which will be conducted as the protective layer of the geotextile clay liners geomembrane (GCLs/GM) lining in a landfill composite liners under drying-wetting cycles, the parameters of SWCC for the gravel soil were measured by using pressure plate extractors; and the four dehydration SWCCs with 0-3 drying-wetting cycles were fitted by using the equations of van Genuchte and Fredlund with 3 parameters. The results show that the wide grading gravelly soil dehydrate rapidly in low suction within 0-100 kPa, and the variation of moisture content gradually decreases when the suction is located on 400 kPa with the increase of drying-wetting cycles; the saturated water content presents convex function but the residual moisture content gradually reduces and smooths under drying-wetting cycles; there is little difference between both the models, and van Genuchte is slightly better than the model of Fredlund with 3 parameters. In addition, the experimental results were compared with clay and bentonite soils from existing literatures. It is suggested that wide grading gravelly soil, as a protective layer of the anti-seepage lining of landfill, is more conducive to the moisture and hydration of GCLs.

Key words: wide grading gravelly soil, drying-wetting cycles, SWCC, model simulating, composite liners of landfill