Ko狀態下礫石-砂土混合物之液化行為探討

在集集大地震後於台灣中部地區發現數個礫石層液化案例，但受限於試驗設備與發生案例個數，對礫石土壤之液化強度與體積應變之相關研究甚少，對於礫石土壤之液化行為，礫石層在台灣分佈範圍很廣，因此有必要進行深入探討。本研究將礫石與越南砂以不同含量混合，並以濕搗法製作試驗試體，分別控制相同的壓密後砂結構孔隙比與礫石結構孔隙比之條件下，進行Ko狀態不等向不排水單剪液化試驗，根據試驗結果，並探討液化行為。根據研究結果，在相同砂結構孔隙比下，礫石含量由0%增加至40%，土壤抗液化強度變化不大，其土壤行為主要為越南砂堆積狀態控制，此外，剪力波速也隨礫石含量增加也增大，但體積應變量則無明顯差異；在相同礫石結構孔隙比下，砂含量由0%增加至20%，抗液化強度隨著砂含量增加也增大，而其土壤行為主要為礫石控制，剪力波速隨砂含量增加亦增大，體積應變量隨越南砂增加而減少。

關鍵字

砂結構孔隙比；礫石結構孔隙比；土壤抗液化強度；體積應變量；剪力波速；反覆單剪

並列摘要

Gravelly soils are widely spread in Taiwan and many liquefied sites had been observed in central Taiwan after 1999 Chi-Chi earthquake. Limited by laboratorial testing equipments and few case histories, systematic studies in liquefaction resistance and post-liquefaction volumetric strain of gravelly soils are rare. Undarined cyclic simple shear tests were performed on gravel-sand mixtures prepared by moisture tamping method to study the liquefaction characteristics in Ko conditions. Effects of sand skeleton void ratio and gravel skeleton void ratio on liquefaction resistance and subsequent volumetric strain are studied. The testing results revealed that liquefaction characteristics of specimens with a same sand skeleton void and gravel content less than 40% are predominately controlled by the packing condition of sand. For sand controlled mixtures, variations of liquefaction resistance and volumetric strain are insignificant but the shear wave velocity increases as gravel content increases. In contrast, the liquefaction characteristics of mixtures with a same gravel skeleton void ratio and sand content less than 20% are dominated by packing condition of gravel. For gravel controlled mixtures, increasing in sand content will increase the liquefaction resistance and shear wave velocity but reduce the volumetric strain.