Physical properties of backfill materials for radioactive waste disposal site

• Main Authors: Yeh, Tzuoo Ren, 葉佐仁
• Other Authors: Huang Wei Hsing
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/79686675899027956105

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.