Design and construction of a large-scale sand-bentonite seal in the Meuse/Haute Marne underground research laboratory : NSC experiment

Abstract : During the excavation of a shaft or drift, the rock properties around the underground openings could be altered due to the level of the ratio in situ stresses over strength of the rock. And even in some case, the rock mass could be fractured. One concern regarding waste disposal is that the associated disturbance and damage created in this area around these excavations might change the favorable properties of such formations and thus negatively impact the repository performance. To limit radionuclides migration along drifts and through the EDZ, seals will be implemented in drifts and shafts. These seals will be composed of swelling clay (mainly bentonite) core in between two concrete plugs. After natural hydration from the surrounding rock mass, the bentonite will swell and apply radial pressure against the drift wall. In this context, ANDRA designs a large scale sealing experiment which is called NSC (French acronym for Noyau de SCellement) The main objective is to back analyze the equivalent permeability of the seal in place in order to check the efficiency of such seal. Before to reach this ambitious goal, numerous output will be provided by this experiment on the effect of the hydration of the seal: evolution of the permeability (at the interface seal/claystone and in the surrounding rock mainly the damaged zone), the pressure build up on the concrete plug. The experiment is not a demonstration of the seal emplacement technique. Lot of sensors has to be installed in the seal and around it and results have to obtain over a reasonable timescale. That implies that properties and emplacement of the seal could not be fully representative of the forecast seal.
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R. de la Vaissiere, N. Conil, J. Morel, F. Leveau, C. Gatabin, et al.. Design and construction of a large-scale sand-bentonite seal in the Meuse/Haute Marne underground research laboratory : NSC experiment. International conference on the performance of engineered barriers, Feb 2014, Hanovre, Germany. pp.133-135. ⟨ineris-01862255⟩

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