| Summary: | 碩士 === 國立中央大學 === 土木工程學系 === 86 === Radioactive wastes are required to be isolated from the
environment to prevent possible contamination. The disposal
concept presently being considered is "deep geological
disposal". In an underground disposal site, the radioactive
wastes are encapsulated in containers surrounded by a buffer
material and the excavation backfilled with a mixture of clay
and aggregate. The study aims at creating an appropriate
composition of the backfill material with satisfactory
performance and characterizing the engineering properties of
backfill material for an underground radioactive waste disposal
site. Synthetic clays with plasticity index of 74, 145, and 214
were mixed with crushed Andesite-aggregate having top sizes of
25.4 and 19.1mm. The theory of proportioning developed by Fuller
for maximum density gradation curves was followed. In order to
meet the stringent requirements of backfill material, a series
of tests including moisture-density relationship, hydraulic
conductivity, load-bearing capacity, free-swell, swelling
pressure, and thermal conductivity were conducted on clay-
aggregate mixtures to evaluate the physical properties of
backfill material.The results indicate that the maximum
aggregate size should be limited to 25.4mm to prevent possible
segregation. To ensure low permeability and reasonable bearing
strength and swelling pressure, clay content in the backfill
should be higher than 10% and less than 30%, and the plasticity
index of the clay is recommended to be around 145. The swelling
pressure and free swell increase with clay contend and the
plasticity index of the clay. The swelling pressure of backfill
material depends greatly on the clay content. The thermal
conductivity shows a tendency to decrease as the clay content
and the plasticity index of the clay is increased.
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