高放射性廢棄物處置後，其衰變熱與放射性會持續釋出而影響近場環境，而海水入侵也是瀕海處置場首要分析的重要情節。以具潛力的台灣日興土與美國懷俄明州膨潤土(BH膨潤土)為試驗材料，探索膨潤土在深層地質處置場中工程性質與微觀組織為本文研究軸心。模擬近場環境因子下的回脹行為，模擬的因子包括衰變熱、地下水入侵等緩衝材料可能遭遇的近場環境變化。再以穿透式電子顯微鏡(TEM)觀察經過加熱程序後達最終回脹量下的膨潤土，進行對基本結構特徵之鑑別為目的之研究。此外，並以X-RAY繞射方法來鑑定黏土礦物的組成。 試驗結果顯示：(1)日興土與美國土回脹量皆隨乾燥受熱時程增加而下降，然而美國土下降程度較緩和，而日興土在受熱達6個月後回脹量明顯下降約50?60%。(2) 日興土與美國土回脹壓力試驗結果與自由回脹應變量結果，兩者間趨勢極為相近，皆隨受熱時程增加而遞減。而日興土之下降趨勢同樣較明顯。受熱達6個月後回脹壓力降幅約30%。(3)日興土在飽和狀態下，水力傳導係數隨樣本受熱時程增加而有增加的趨勢，其水力傳導係數在受熱6個月後約為2.5×10-8(cm/s)。(4) X-RAY繞射分析結果顯示，本研究之日興土其黏土礦物中以伊利石的相對含量最豐，約佔50?60%左右；次多是綠泥石相對含量約為20%；蒙脫石的含量則低於10%以下。(5)藉由程式的計算所得到之孔隙百分比，可得知美國土在未受熱與受熱3個月後，回脹後之微觀孔隙率略微上升。經由本實驗所得孔隙率小幅增加大約2?3%，變化不大。 In a high-level radioactive waste deposal site, the decay heat produced from the wastes will cause the near field temperature to increase. And then the repository is subjected to groundwater intrusion. The present study adopted Zhisin clay and Wyoming Black Hills (BH) bentonite as potential buffer material. The theme work focused on the swelling property and evolution of micro-structure while these two bentonites were under the deep geologic repository. Using the transmission electronic microscope (TEM) to observe the bentonite which was heated and reached the swelling amount; moreover processing to fingerprint the essential frame as the purpose of this research. And further; we adopt X-RAY powder diffraction analysis to identify the composition of the clay mineral. The results indicated: (1) the free swelling of both Zhisin clay and BH bentonite decreased as the heating duration increased, and the decrease in swelling is low for BH bentonite and much higher for Zhisin clay, with a total reduction of 50-60 percent as Zhisin clay has been heated at 100℃ for 6 months; (2) the development in swelling pressure for Zhisin clay and BH bentonite is similar and the swelling pressure for the 2 clays declined after heating, and again, the decrease in swelling pressure was also more pronounced for Zhisin clay; (3) the hydraulic conductivity of Zhisin clay increased after heated of the bentonite for a period of 6 months; (4) X-ray diffraction results showed that the clay mineral of Zhisin clay was found to be most rich in illite and ranged around 50-60 percent, and the secondary clay mineral was Chlorite having about 20 percent; the content of montmorillonite was found to be less than 10 percent; (5) using the image analysis techniques, the porosity of bentonite was determined from specimens taken before and after swelling. The porosity increased slightly (2-3 percent) after the heating procedure.