目前對於放射性廢料的處置方法中較普遍的方法為利用深層處置場，封存放射性廢料。放射性廢料於地下深層處置中，常利用緩衝材料阻隔放射性核種外移，膨潤土具有特殊吸水性、高膨脹及低滲透性等特性，適合當作緩衝材料及回填材料。回填隧道的材料，多使用膨潤土與現地開挖之岩屑或礫石混和後回填，回填材料的功能為避免處置隧道成為地下水通道。在施工妥善的狀況下，可能造成回填材料體積產生變化的因素，主因是地震導致液化。另外亦考慮緩衝材料因地下水的侵蝕，使得緩衝材料整體的單位重降低，地震發生時可能有液化之虞。本研究對含有不同膨潤土與礫石混和比例之回填材料試體及不同統體單位重之緩衝材料試體，進行不排水之動力三軸試驗，以不同軸差應力振幅進行動態試驗，探討不同反覆剪應力作用下，回填材料及緩衝材料動態強度之變化趨勢。 所有試驗中，試體之超額孔隙水壓激發量皆不明顯，甚至無激發孔隙水壓，激發量皆未到達試體所受的有效圍壓，無液化現象發生。對於飽和單位重為20 kN/m3之回填材料試體，膨潤土含量越多之試體，隨著動態加載作用，所造成的軸向變形量較小，試驗中回填材料試體皆未因變形量過大而破壞的現象發生。飽和單位重為20 kN/m3及18 kN/m3緩衝材料試體，在動態加載下，所造成的雙軸向應變量亦不大，試體未因過大變形而破壞；飽和單位重16 kN/m3之緩衝材料試體，在動態加載下造成的雙軸向應變量變化較為明顯，雖然雙軸向應變量隨著反覆加載作用未超過5%，但試體會因累積之殘餘應變量過大而破壞。 ;Buffer materials are used to retard the migration of radionuclides emitted from high level wastes in a repository. Bentonite is the primary candidate for the buffer materials at the present day, because it has special water absorption, high expansion and low permeability. The materials used to backfill tunnel are mostly with bentonite and excavated in situ rock debris or gravels. After construction, liquefaction is the main cause of the backfill material volume generated change. In addition, the volume of buffer material would change because of the erosion of groundwater. It reduces the bulk density of backfill material, liquefaction would occur during earthquake. In this research, program undrained dynamical triaxial tests will be conducted to the backfill materials with different proportions of bentonite and gravel and buffer matrial with different bulk density to estimate cyclic strength of backfill and buffer materials. The excess pore water pressure excitations of specimens were not significant during the tests, even without water pressure excitations. There is no liquefaction occurred in all of tests. For the backill material with saturated unit weight of 20 kN/m3, axial displacement of specimens decreases with the increase of bentonite contents during cyclic loading. But axil deformations of backfill mater specimens were too small to cause failures. Buffer materials with saturated unit weight of 20 kN/m3 and 18 kN/m3, double amplitude axial strains of speciems were not significant during the tests, specimens were not faiulure. For buffer materials with saturated unit weight of 16 kN/m3, double amplitude axial strains of speciems were significant during cyclic loading. Although the amplitudel strain of specimens did not reach 5%, specimens were failure due to excessive accumulation of residual strain.
