國際間採用多重障壁的設計理念並推崇以膨潤土作為放射性廢棄物最終處置的基質材料,達到阻絕放射性物質遠離生物圈的目的。本研究為探討混合型緩衝材料於低放射性廢棄物最終處置場之工程特性,透過進行實驗室測試,模擬現地可能發生之情況。當處置場中的緩衝材料受到水-力學 (H-C) 耦合效應的影響,由處置窖自重以及其他設施所產生的壓力,而造成處置窖位移,並利用ABAQUS有限元素法進行潛變行為之數值模擬分析。 本研究以美國懷俄明州MX-80膨潤土與日本K-V1膨潤土,並混合30 %苗栗地區石英砂為緩衝材料。首先透過修正式夯實試驗,取得不同膨潤土混合石英砂之緩衝材料的最大乾單位重與最佳含水量,依照修正式夯實試驗結果之最佳含水量調配試體的初始含水量,採用黏土有效密度控制,以靜態壓實法製備緩衝材料,進行回脹壓力、水力傳導係數與力學強度評估,最後針對飽和緩衝材料進行等應力直剪試驗,求取潛變參數。 本研究結果分為兩個部份,第一部分為實驗成果顯示:(1)以石英砂取代30 %的膨潤土後,其回脹壓力與阻水性能皆可滿足瑞典SKB高放相關安全功能需求;(2)等應力控制直剪顯示,施加愈高的應力位準,潛變初始發生時間將有提早的現象;(3)單向度壓縮試驗顯示,當施加正向應力達1.6 MPa時,MX-80混合材料於黏土有效密度1600 kg/m3的變形行為至後期會有微幅膨脹的現象。第二部分為數值模擬成果:以等應力控制直剪實驗求取潛變參數A、α、m,而時間次序m值愈大代表具有較高的潛變特性,當B100純膨潤土以部分石英砂進行重量取代後 (B70-S30),由原先m值-0.905、-0.904降低至 (-0.935、-0.933),說明砂顆粒的骨架結構可能會提升力學穩定性,影響微觀結構的調整時間。本研究採用Drucker-Prager潛變模式,經由ABAQUS模擬分析結果顯示,混合型緩衝材料預計在20年內將達到飽和狀態,而潛變行為所造成的垂直位移量,長期而言向上推擠引致的變形僅13、15 mm,應不會對低放處置設施造成危害;但是當混合型緩衝材料達飽和後,因回脹壓力的增加,將造成處置窖有向上運動的行為。 ;Many countries consider the multiple barriers system as a feasible way for the final nuclear disposal. Bentonite has been preferred as a primary buffering material for the disposal of low-level nuclear waste. In order to realize the engineering properties of mixed buffer material, this study use laboratory tests to simulate the situation of the in-situ repository. The low-level nuclear waste disposal facility components are affected by hydrological (H) and mechanical (M) coupling processes simultaneously. Bentonite-sand mixtures as buffer material affected by H-M coupling effects, needs to keep the vault physically stable to avoid damage from displacements initiated by the weight of the vault and stresses exerted by other components of the multiple barriers system.Then, the finite element program ABAQUS was then employed to carry out the numerical simulation of the creep behavior. MX-80 bentonite and K-V1 bentonite are used as raw clay materials in this study. These clays are mixed with Miaoli area silica sand to produce the buffer material. The buffer material was prepared by mixing 30 % of silica sand from 70 % of MX-80 bentonite and K-V1 bentonite. Modified proctor compaction test were conducted to determine the maximum dry unit weight and optimum moisture content of buffer material. Specimens of buffer material prepared according to the modified proctor compaction test were evaluated for swelling potential, hydraulic conductivity, and mechanical strength. Finally, using the constant stress direct shear test carried out for the saturated buffer material to obtains the creep parameters. The first part of results from laboratory tests shows that (1) Mixtures with 30 % of silica sand and 70 % of MX-80 / K-V1 bentonites, satisfy safety requirements of SKB. (2) Results of the constant stress direct shear test shows that, the earlier the initial occurrence of creep happened as applied higher stress level. (3) One-dimensional compression tests shows that, the deformation behaiviors of MX-80 bentonite-sand mixtures at clay effective density of 1600 kg/m3 will be slightly expaned in anaphase as applied to normal stress 1.6 MPa. The second part is the numerical simulation results revealing the creep parameters obtained from constant stress direct shear tests. Parameters of A and α were the extrapolation of the relationship between (γ_0 ) ? and Dr, and the slope of the relationship between (γ_0 ) ? and Dr, respectively, and Dr is stress-dependent constant. The m values is a significantly factor in the evaluation of creep behaviors, and it can explian the phenomenon that the strain rates decreased with time and represent more prominent creep behavior as its vaules are much bigger. This study used the Drucker-Prager creep model in the numerical simulation. The instantaneous displacements caused by vault weight, and the results of simulation K-V1 bentonite-sand mixtures have higher displacements compared to MX-80. In the model tests, the mixed buffer material was predicted to be fully saturated in 20 years. The displacements due to creep behavior were found at the interface of buffer and backfill affected by the swelling pressure after saturation.