PELLET MIXTURES IN ISOLATION BARRIERS
Granular mixtures made of high-density pellets of bentonite are being evaluated as an alternative buffer material for waste isolation. Ease of handling is an often-mentioned advantage. The paper describes the experimental program performed to characterize the hydromechanical behaviour of compacted pellets mixtures. Grain size distribution was adjusted to a maximum pellet size compatible with the specimens dimensions. Dry densities of statically compacted specimens varied in most of the cases in the range: 1.3 to 1.5 Mg/m3. Pellets had a very high dry density, close to 2 Mg/m3. The outstanding characteristic of these mixtures is its discontinuous porosity. Pore sizes of the compacted pellets vary around 10 run. However the inter-pellet size of the pores is four to five orders of magnitude higher. This double porosity and the highly expansive nature of the pellets controlled all the hydraulic and mechanical properties of the mixture. Tests performed include infiltration tests using different water injection rates and mechanisms of water transfer (in liquid and vapour phases), suction controlled oedometer tests and swelling pressure tests. The interpretation of some of the tests performed required backanalysis procedures using a HydroMechanical (HM) computer code. Material response was studied within the framework of the elastoplastic constitutive model proposed by Alonso et al. (1990)(Barcelona Basic Model, BBM). Parameters for the model were identified and also a set of hydraulic laws necessary to perform coupled HM analysis. a large scale in situ test (the EB test in Mont Tern, Switzerland) is described and analyzed. Rock barrier parameters were adjusted on the basis of available tests. The test excavation, barrier emplacement and forced hydration was simulated by means of the CODE_BRIGHT program. The comparison between measurements and computed results include data on relative humidity in the rock and the buffer, swelling pressures and displacements.
bentonite laboratory tests laboratory equipment partial saturation suction granular mizture in situ test hydro-mechanical model nuclear waste disposal ezcavation disturbed zone
E.E. Alonso C. Hoffmann E. Romero
Universitat Politecnica de Catalunya, Barcelona, Spain Formerly at Universitat Politecnica de Catalunya, Barcelona, Spain
国际会议
上海
英文
1-22
2009-08-24（万方平台首次上网日期，不代表论文的发表时间）