| dc.description.abstract | 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. | en_US |