以實驗方法探討非飽和含細粒料砂土之液化行為研究

Experimental Investigation of the Liquefaction Behavior of Unsaturated Sand with Non-Plastic Fines

王偉丞(Wei-Cheng Wang)

指導教授 ： 郭安妮

國立臺灣大學/工學院/土木工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202103391

摘要

土壤液化行為研究主要建立在飽和且土壤為砂土的條件下，然而，非飽和土壤亦具有土壤液化潛能，如果滿足適當的條件可能會觸發非飽和土壤的液化，根據以往的研究指出飽和度較低的土壤具有較高的抗液化能力，並在實際液化發生後的土壤中發現含有細粒料，其細粒料會影響土壤之液化行為，因此細粒料含量與飽和度對於砂土的液化阻抗影響需要進一步的了解。本研究發展了以GDS開發的動力三軸試驗儀進行非飽和含細粒料砂土試驗的實驗流程，改良了傳統底座並鑲嵌高進氣陶板以利進行軸平移技術，採用濕夯法重模方式控制不同細粒料含量砂土試體的孔隙比，相對於常見的基質吸力控制方式使土壤達到非飽和狀態，本研究使用定流量汞以飽和度控制方式來降地土壤飽和度，並加入了純砂試體當作對照組探討含細粒料砂土在不同飽和度狀態下其循環載重過程中與液化行為的差異。
根據實驗結果可以發現初始液化後的行為在純砂與含細粒料砂土具有不同的特性，純砂試體在初始液化前無明顯勁度變化的趨勢且在液化發生後的應變變化行為呈現對稱之關係，然而在含細粒料砂土在加載階段開始時即不斷往以微小的增量在壓縮應變側增加，液化發生後的應變變化行為呈非對稱之關係，然而不同飽和度對於同一土壤組成而言無明顯之液化後行為差異。降低飽和度提升土壤試體抗液化潛能的程度在含細粒料砂土中的效果比純砂土更佳，發現基質吸力隨加載循環次數增加而遞減至零時即發生大應變的趨勢，透過一系列試驗結果的觀察討論本研究的實驗流程與改良設備以供後人進行非飽和土壤試驗做為參考。

關鍵字

非飽和土壤 ； 土壤液化 ； 動力三軸試驗 ； 軸平移技術 ； 定流量汞

並列摘要

Researches on soil liquefaction are mainly based on saturated condition. However, unsaturated soil has the potential to trigger soil liquefaction if appropriate conditions are met. According to previous studies, soil with the lower degree of saturation has higher liquefaction resistance. On the other hand, analyses of in-situ liquefied soil indicate that fines particles can greatly affect the liquefaction behavior. In this study, the influences of fines content and degree of saturation on liquefaction resistance of sand are investigated. The experimental procedures for evaluating the dynamic behavior of unsaturated sand with non-plastic fines are developed. The design of modified pedestal is improved and the high-entry-value ceramic plate is embedded into it to facilitate the axis translation technique. Wet tamping method is used to remold the soil specimens by controlling the void ratio of sand with different fines content. Although most of the past researches utilized suction-controlled tests, flow pump method was used in this study to control the degree of saturation of the specimens. Tests are also carried on clean sand specimens to serve as the baseline for subsequent comparison of liquefaction behavior and liquefaction resistance for.
From the test results of this study, it can be found that clean sand and sand with non-plastic fines have distinct properties during cyclic loading and after initial liquefaction happened. Clean sand specimens have no obvious tendency of stiffness reduction before initial liquefaction, and the variation of axial strain during cyclic loading is symmetric. In contrast, axial strain of sand with non-plastic fines continuously increases on the compression (strain) side with small increment at the beginning of the cyclic loading stage. Asymmetric form of axial strain variation is observed on sand with non-plastic fines. However, there is no significant effect on the soil behavior after initial liquefaction by different degrees of saturation when the specimens were under the same soil composition. By reducing the degree of saturation, the increase in liquefaction resistance is larger for sand with fines materials than for clean sand. With the use of the modified pedestal, matric suction can be observed. Also, it is found that suction decreases as the number of cycles increases. When suction becomes to zero, large strain occurs. The test procedures developed in this study and modified apparatus may serve as a reference for future research on dynamic testing of unsaturated soil.

並列關鍵字

unsaturated soil ； soil liquefaction ； cyclic triaxial test ； axis translation technique ； flow pump device

參考文獻

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4. ASTM D854–10. (2010). Standard test methods for specific gravity of soil solids by water pycnometer. ASTM International, West Conshohocken, PA.

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