Landfilling

Capping system for shielding of hazardous waste stored underground

The project participants developed a multi-link geotechnical sealing segment that prevents ingress of moisture to hazardous waste stored underground. The capping structure's operating principle is based on a granular layer that distributes fluids homogeneously between two seal segments by means of capillary rising, thus breaking up advancing moisture fronts.

Summary

The project's aim was to develop a multi-link capping system that protects hazardous waste in subterranean storage from non-homogeneous moisture progression and thus reliably shields it from the biosphere. To this end, a geotechnical barrier of bentonite acting as a seal segment (SS) and a cohesion-less material to equalise hydraulic potential (e.g. fine sand) between two seal segments was used. Any locally penetrating fluid is distributed across the equipotential segment (ES) and forms a new homogeneous potential surface. Accordingly, the ES must display a high suction power to establish a significant capillary rising and break-up of advancing moisture fronts. It must also display a high draining power. As part of the project, riser and stack tests are performed to examine the moisture distribution, rising speed, effect of salinity and the correlation between ES and SS during capillary rising. Parallel to the barrier system's layers, sensors are installed in the ES to measure the progression of the moisture front and the pressure.
Results:

  • Pillar tests with halite lye show that no salt is released during transport through the mineral mixture. A slight chromatography effect is discernible only at the pillar's base.
  • The carbonate content, which affects rising, remains constant throughout the pillar.
  • By streaming salt lye through the calcium- and magnesium bearing montmorillonite in the bentonite Calcigel, the montmorillonite is transformed into smectite.
  • In a chute test, the SS was weakened for trial purposes. At these locations, a preferential flow can be measured and the ES's effect is confirmed. The ES reliably breaks up the lye front and distributes it across the ES's cross-section through the capillaries.
  • Contact with the moisture from the ES does not result in adsorption or deposition of salt from the lye on the SS.  
  • The presented capping system seals chutes, runs and blast holes.

More Project Informations

Project title: Verschlusssystem mit Äquipotenzialsegmenten für die untertägige Entsorgung (UTD und ELA) gefährlicher Abfälle zur Sicherstellung der homogenen Befeuchtung der Dichtelemente und zur Verbesserung der Langzeitstabilität

Project number: 02C0922

Project period: 2002 - 2009

Project region: Germany (Baden-Württemberg)

Project contact:

Frau Dr. Datcheva
Herr Prof. Dr.-Ing. Kudla

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Source: German National Library of Science and Technology Hannover (TIB)