| Summary: | 碩士 === 國立臺灣大學 === 土木工程學研究所 === 102 === For understanding and modelling the behavior of saturated sand before, during, and after liquefaction, such as drainage, pore pressure build-up and dissipation, and settlement, the permeability of liquefied sand is one of the important soil properties. Previous researches on evaluating the changes of permeability of liquefied sand during and after liquefaction were proposed based on the assumption of drainage flow through the liquefied sand or the application of solidification and consolidation theory. However, these considerations of the water flow and the movements of soil particles did not truly represent the conditions within the soil during and after liquefaction, and the results were not well verified. In this study, a new experimental approach was proposed by combining the simple seepage test and the liquefaction test to evaluate the water flow within the saturated Vietnam silica sand before, during and after liquefaction. The experiments included: (1) simple seepage-induced failure (sand boiling) tests; (2) liquefaction tests without upward seepage; and (3) liquefaction tests with upward seepage. The pore water pressures at different depths of the sand column, the flow rate, and the sand surface settlement were recorded during the tests. The permeability of the sand specimen was calculated directly according to the hydraulic gradient which drove the water flow through the sand specimen. Results of the simple seepage-induced failure tests showed that the critical state of the specimen for sand boiling can be predicted well by using the Terzaghi’s theoretical equation. The peak hydraulic gradient for the failure of the specimen is about 1.2 times the critical hydraulic gradient. The permeability of liquefied sand during liquefaction was about 4 times the initial value, while it reduced to 0.9 times the initial value after full dissipation of the excess pore pressures.
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