台灣西部沿海一帶的土層多為沉泥質砂性土層，含有較高比例的無塑性細粒料，在進行液化潛能評估時，容易忽略無塑性細粒料對土壤液化阻抗之影響。故本研究以C.K.C.動力三軸試驗儀，採用高雄鼓山、鹽埕區近O1捷運車站之土壤，藉由控制試體不同的相對密度，改變試體中之無塑性細粒料含量，先對重模試體施加前期反覆荷重，再進行動力三軸試驗，探討砂土受前期反覆荷重後，相對密度與細粒料含量對於土壤抗液化強度之影響。

研究結果顯示，在相同之細粒料含量下，當試體相對密度愈大，土壤之抗液化強度亦愈高：不論試體相對密度Dr=45%或Dr=75%，土壤的液化阻抗會隨著粉土含量的增加而降低，當粉土含量超過25%時，其液化阻抗下降之趨勢會趨向於平緩。在以試體之單軸向應變達5%時，即視該試體發生液化破壞之定義下，純淨砂土試體液化阻抗約為60%細粒料含量試體液化阻抗之1.6倍。

前期反覆荷重影響方面，在不改變試體相對密度的情況下，當試體受前期反覆荷重後，體積應變及超額孔隙水壓激發百分比會隨粉土含量的增加而變大，故液化阻抗會增加。但隨著相對密度的增加，其體積應變量及孔隙水壓激發百分比也將隨之減少，但減少之趨勢則漸緩。

為模擬飽和土層受振動後，顆粒的排列與接觸性，本研究以顆粒微觀假想結構解釋；當細粒料含量較少時，土壤本身是以砂土為主體，其抗液化強度是由粗顆粒所控制，細粒料扮演著填充空隙之角色；當細粒料含量較多時，砂結構空隙比變大，土壤本身以細粒料為主體，粗粒料則扮演著次要或填充的角色，其抗液化強度乃由細粒料所控制。

關鍵詞：動力三軸試驗、無塑性細粒料含量、前期反覆荷重、液化強度、顆粒結構

The majority of the sand deposits along the western coast of Taiwan is with significant amounts of non-plastic fines. The assessment of soil liquefaction potential often neglected the effect of non-plastic fines. In this study, the non-plastic sand with fines content near O1 Station of Kaohsiung Metropolitan Mass Transit. The specimens are prepared by moist tamping at several relative density under different fine contents. Dynamic triaxial tests were conducted by CKC cyclic triaxial test system. Specimens were tested until soil is liquefied. The purpose of this reaserch is to investigate the effect of fines content on the liquefaction resistance of soils. The influence of previous cyclic loading and different relative density were also studied for the understanding of the relationship of fines content and liquefaction resistance.

The test results show that liquefaction resistance of specimens increases with increasing relative density of samples ; irrespective of the relative density, the liquefaction resistance of soils decrease as the fine content increases. The liquefaction resistance of the samples with pure sand is approximately 1.6 times of the soil with a silt content of 60%.

On the influence of previous cyclic loading, the volumetric strain and excess pore water ratio would increase when specimens are imposed with small previous cyclic loading.

The arrangement of soil particles as a saturated sand deposit subjected to a small ground vibration is also simulated in this study. It is indicated that as silt content is low, the soil can be described as consisting of silt content in a sand matrix and liquefaction strength is controlled by the coarse grain ; as silt content is high, the soil can be described as consisting of sand particles in a fines matrix and liquefaction strength is controlled by the fine grain.

Key words : Dynamic triaxial tests ; Non- Plastic ; Previous cyclic loading ; Liquefaction strength

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