Clay membrane made of natural high plasticity clay: Leachate migration due to advection and diffusion

Niels Foged, Jens Baumann

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    Leachate containment in Denmark has through years been regulated by the DIF Recommendation for Sanitary Landfill Liners (DS/R 466). It states natural clay deposits may be used for membrane material provided the membrane and drainage system may contain at least 95% of all leachate created throughout the lifetime of the landfill. Presently, the recommendation is under revision partly because this clause was considered not to be sufficient to secure drink water quality in underlying aquifers - a necessary containment of at least 99% is foreseen. The revision should consequently take into account advective ion transport as well as diffusion.Clay prospection for clays rich in smectite has revealed large deposits of Tertiary clay of very high plasticity in the area around Rødbyhavn on the Danish island Lolland. The natural clay contains 60 to 75% smectite, dominantly as a sodium-type. The clay material has been evaluated using standardised methods related to mineralogy, classification, compaction and permeability, and initial studies of diffusion properties have been carried out. Furthermore, at a test site the construction methods for establishing a 0.15 to 0.3m thick clay membrane have been tested successfully. At natural watercontent w = 40 to 45% it is possible to establish a homogeneous membrane with hydraulic conductivity k <5 E-12 m/s giving an extreme low transport by advection. The hydraulic conductivity measured in oedometer tests used for establishing swell and deformation properties showed to be very dependent on the stress level. It varies from k = E-11 to 2 E-13 m/s at vertical stresses from 5 to 4800 kPa and is clearly related to a reduced effective porosity diminishing with stress. Preliminary diffusion tests indicate a similar influence on the effective diffusion coefficient being much lower than anticipated using the total porosity. These properties are of major importance to the future use of clay membranes for containment of hazardous waste. In order to explain these properties microstrutural investigations were initiated to establish boundary conditions for evaluation of relevant transport processes.Consequently, this clay material may be used as raw material to be compacted for membrane purposes in a natural wet condition using high compaction effort comparable to Modified proctor energy. It fulfils the requirements that are presently proposed in the new Danish Recommendation for Landfills and a number of other applications that are foreseen for clay embedment of hazardous waste.
    Original languageEnglish
    Title of host publicationProceedings of the Symposium on Microstructural modelling og natural and artifically prepared clay soils with special emphasis on the use of clays for waste isolation
    Place of PublicationLund
    PublisherRoland Pusch
    Publication date1998
    Publication statusPublished - 1998
    EventWorkshop on Microstructural modelling of natural and artificially prepared clay soils with special emphasis on the use of clays for waste insulation - Lund, Sweden
    Duration: 1 Jan 19981 Jan 1998


    WorkshopWorkshop on Microstructural modelling of natural and artificially prepared clay soils with special emphasis on the use of clays for waste insulation
    OtherNo exact date found.

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