回填材料為多重障壁的主要安全貢獻因子之一，而膨潤土為回填材料之主要原料，本研究以不同種類之膨潤土(KV-1膨潤土、MX-80 膨潤土)以1:1混合矽砂作為主要研究對象，以夯實法製作成低放射性廢棄物處置場使用之回填材料。首先以改良式夯實試驗，取得不同膨潤土混合矽砂之回填材料的最大乾密度以及最佳含水量，然後以其最大乾密度與最佳含水量來製作回填材料試體，進行直接剪力試驗、定體積回脹壓力試驗、水力傳導度試驗，及自由回脹試驗。 膨潤土與砂混合料修正夯實試驗中，兩種回填材料皆出現典型的 夯實曲線，且KV-1膨潤土與砂混合料最大乾密度較MX-80膨潤土與砂混合料大。兩種膨潤土材料的定體積回脹壓力歷時曲線皆有出現些微的雙峰曲線，但與純膨潤土定體積回脹歷時曲線相較其雙峰現象較不明顯。而本研究中兩種膨潤土與砂混合料之水力傳導度皆與純膨潤土相當接近，可見膨潤土與砂混合後仍能維持回填材料所需之低水力傳導度，並可改善回填材料之工作性。直接剪力試驗中，KV-1膨潤土與砂混合料之抗剪強度高於MX-80 膨潤土，主要原因是因其最大乾密度較大所致，KV-1膨潤土與砂混合料之孔隙比較低，膨潤土有效乾密度較高，故試體緊密程度較高，因此其剪力強度較高。 ;This Backfill serves as a component of the multiple engineered barriers for isolation of low-level radioactive wastes in a repository. The backfill material is a mixture of bentonite and sand. With a high swelling potential, bentonite is expected to serve the sealing function, while the crushed sand improves the workability of the mixture. This study aims at the investigation on the backfill that is made by using compaction method. KV-1 bentonite and MX-80 bentonite are used in this research. The backfill material was prepared by mixing 50% of bentonite with 50% of silica sand to produce sand-bentonite mixture. Two kinds of bentonite, MX-80 and Kunigel V1 (KV-1) bentonite, were investigated in this study. Modified proctor compaction test was conducted to determine the optimal moisture content and maximum dry unit weight of backfill material. Specimens of backfill material prepared according to the result of modified proctor compaction test were evaluated for swelling pressure, hydraulic conductivity, swelling strain, and direct shear test. Modified proctor compaction test results show that the two bentonite-sand mixtures exhibited typical compaction curve. The maximum dry density of KV-1 bentonite-sand mixture is higher than MX-80 bentonite-sand mixture. The swelling curves of the two bentonite-sand mixtures show two-peak curve, but are less significant than that of the 100% bentonite. The swelling pressure of MX-80 bentonite-sand mixture is higher than KV-1 bentonite-sand mixture since the Montmorillonite content of MX-80 bentonite is higher than that of KV-1 bentonite. In this study, the hydraulic conductivity of the KV-1 bentonite-sand mixture and the MX-80 bentonite-sand mixture was found to be quite close to that of pure bentonite. This indicates that the incorporation of silica sand to bentonite does not affect the low hydraulic conductivity feature of bentonite, while improving the workability of bentonite significantly. In the direct shear test, it was found that the shear strength of the KV-1 bentonite-sand mixture is higher than MX-80 bentonite-sand mixture. This is because the effective dry density of KV-1 bentonite in the mixture is higher than that of MX-80 bentonite in the mixture.
