摘要(英) |
The multiple barriers design is the main concept for radioactive waste repository system. These barriers (host rock, backfill, buffer, …) are the isolators that help to prevent the poisonous chemical leak to biosphere. Therefore, the barriers components must be robust and durable. Backfill is an important component of the barriers system and thus it need to meet some rigorous requirements about strength, swelling potential and low hydraulic conductivity to ensure the human being safety.
This study investigated the engineering and mechanical properties of mixtures by sand and bentonite with different ratio. Two bentonites (MX-80 and K-V1) and seven bentonite contents (30%, 40%, 50%, 60%, 70%, 80% and 90%) were tested to investigate the effect of the mixture content on the mechanical properties of backfill material. Compressive strength and elastic modulus were obtained by unconfined compression test. During the testing, it was found that the sample preparation technique has a considerable effect on the uniformity of sample, the more bentonite content of mixed material the more influence on its strength. In order to apply the loading on the sample uniformly, the preparation methods were tried in four ways: one-way loading, two-way loading, up and down turning, layer-by-layer compression.
Through the experiment program some conclusions can be draw. Firstly, the use of two-way loading preparation method could produce a more uniform specimen. Secondly, for K-V1 based mixture the maximal unconfined strength is reached where the ratio of bentonite is 50%. However, the highest strength of MX-80 based mixture archived where the ratio of bentonite is 60%. Second, comparing two mixture types where the ratio of bentonite over 60% the MX-80 based mixture has a larger strength than K-V1 based material and vice versa, where the ratio of bentonite lower than 60% the K-V1 based mixture has a higher strength.
Keywords: Bentonite, Backfill, Compressive strength, Elastic modulus
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