對放射性廢棄物最終處置場的地下通道關閉時，國際上建議利用皂土與現場母岩碎石混合物為回填材。要求重點在利用皂土遇水膨脹自癒特性，也應具低回脹壓力與高導熱性質，因此於皂土中添加適當比例的顆粒材料是必要的。目前回填材之研究較多集中在皂土與碎石使用比例上，最被推薦的配比是：30%皂土與70%碎石。但事實上，同一碎石比例或級配下，也可能有不同的碎石排列情況、碎石顆粒間留下皂土填塞的空間，以致回脹行為均將有所不同。故本研究目的在探究這70%碎石的級配型態，對回填材回脹行為之影響。 研究成果顯示，即使固定皂土－碎石使用比例的條件下，選用添加的碎石級配型態或碎石粒徑範圍，仍會影響皂土－碎石回填材內部所餘留空隙分佈均勻性及皂土與碎石的接觸狀況，以至影響其回脹行為。結論如下： （1）當添加的碎石顆粒級配趨於優良級配時，碎石與碎石之接觸點較多，皂土之回脹可有效推擠碎石，反應出較大的外在自由回脹變形。 （2）且在體積受限時，因皂土的回脹壓力需透過多次碎石粒間應力分量的轉折傳送，實際反應於外的回脹壓力較小。 （3）在皂土內添加最大碎石粒徑較大者或碎石粒徑範圍較廣者，可獲得較高的回脹變形自癒能力。但此時欲以增大壓實密度來提高回脹變形之效益則較低。 （4）顆粒之粒徑大小對回填材回脹速率的影響均大於級配因素及初始單位重，三者重要性之權重比值約為4：1：1。 （5）而對最大回脹量之影響，初始壓實單位重的權重則大於顆粒之級配因素及粒徑範圍，其比值約為2：1：1。 Before closure of the radioactive waste repository, all the connecting shafts and rooms in a deep geological disposal are required to be backfilled. The backfill is proposed to consist of a mixture of 30% bentonite and 70% field crushed rock. The bentonite within the crushed rock is to be compacted to a high density to ensure sufficient swelling upon wetting to seal the voids. The Fuller maximum density curve is employed for the aggregates to achieve the optimal compaction property of backfill materials. However, the distribution of voids within the backfill materials is dominated by the gradation of crushed rocks. This study aims to investigate the swelling behavior of bentonite and crushed-rock backfill materials with various crushed-rock gradation using experimental swelling tests. It is found that the swelling behavior of bentonite and crushed-rock backfill material is strongly depended upon the gradation of crushed-rock. The crushed-rock gradation and grain size control the void distribution of backfill material and thus the swelling behaviors,could get the following conclusions: (1) Using the well-graded grain in bentonite-rock backfill material, the void is intercepted by the contacts of crushed rocks. (2) The swelling pressure of bentonite is reduced during the stress transmission. (3) However, the swelling deformation of bentonite is well delivered by the grain contacts and demonstrates a good self-sealing behavior. (4) The influence on the grain size to the swelling rate is bigger than the gradation factor and the initial unit weight, its influence ratio is 4:1:1 . (5) But the most greatly influence on the maximum swelling is that the initial compact unit weight is bigger than the gradation factors and the grain size, its ratio is 2:1:1 .
