液化砂土之滲透性試驗

Laboratory Experiments on Permeability of Liquefied Sand

王紫芳(Zih-Fang Wang)

指導教授 ： 翁作新

國立臺灣大學/工學院/土木工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.02490

摘要

為了解與模擬飽和砂土於液化前、液化中以及液化後之行為，如：排水、水壓激發與消散、沉陷等現象，液化砂土之滲透性為一重要之土壤參數。過去研究多假設液化砂土中之排水狀況，或藉由壓密理論及固化理論來探討液化砂土之滲透性變化。然而，前人針對水流及土顆粒運動之假設，與實際土壤液化時之情況並不相符，且研究結果並無一較可信之驗證。故本研究提出一套新的試驗方法，將滲流試驗與液化試驗相結合，以探討飽和越南石英砂於液化前、液化中以及液化後，試體內水流行為的變化。試驗內容包括：基本滲流試驗、無滲流液化試驗、向上滲流液化試驗等三部分。試驗過程中量測並記錄試體內不同深度之超額孔隙水壓、滲流量，以及砂面之沉陷量，並藉此求得試驗過程中之水力梯度與流量間之關係，直接計算試體之滲透係數。由基本滲流試驗結果發現：利用Terzaghi所提出之砂湧臨界水力梯度理論公式，可良好地預測試體破壞之臨界水力梯度。試體到達破壞時所對應之臨界水力梯度峰值，則約為1.2倍之臨界水力梯度。由液化試驗之結果發現：試體於液化過程中之滲透係數約為其初始滲透係數之4倍，而當液化後水壓完全消散時之土壤滲透係數則約為初始滲透係數之0.9倍。

關鍵字

飽和砂土 ； 砂湧 ； 液化 ； 滲透性 ； 水力梯度 ； 沉陷

並列摘要

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.

並列關鍵字

Saturated sand ； Sand boiling ； Liquefaction ； Permeability ； Hydraulic gradient ； Settlement

參考文獻

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