Centrifuge model tests on clay based engineered barriers subjected to differential settlements

The objective of this paper is to investigate the influence of thickness of the clay barrier and overburden pressure on the integrity of the clay barrier, which is provided in the cover system of low low-level radioactive waste disposal sites. A series of centrifuge tests were performed on model clay barrier subjected to continuous differential settlement at 40 g. The model clay barrier material has been selected in such a way that it envelopes the material characteristics of the clay barriers. The model clay barriers were moist-compacted on the wet side of its optimum moisture content. The performance of the clay barrier as an effective hydraulic barrier was monitored throughout the deformation process and attempts have been made to arrive at strain distribution along the top surface of clay barrier with the help of marker based digital image analysis. A 1.2 m thick clay barrier with a nominal overburden pressure of the order of 12.5 kPa was found to experience multiple cracking extending up to its full depth; whereas with overburden pressure of the order of 25 kPa, it was observed to have suppression of cracks. A catastrophic nature of water breakthrough was registered for a 0.6 m thick clay barrier with an overburden equal to that of a closure system of a low-level radioactive waste disposal site, once settlement ratio attains 0.6. This indicates that provision of thickness of clay barrier equal to 0.6 m may not be adequate.

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