飽和砂土液化後之受剪行為

Abstract

本研究採取南投市貓羅溪沿岸第二高速公路旁在集集地震中曾經發生過液化區域之土樣，並利用CKC動力三軸試驗儀進行試驗。試驗土壤包括以純粗料（＞200號篩）重模成相對密度40%、60%及70%的土壤試體，以及第二部分以控制乾密度為1400 kg/m3，細料含量分別為10%、20%及40%的重模土壤試體，以探討砂土受反覆荷重液化後受剪的行為。由純粗料土壤初始液化後試驗結果得知，相對密度越大時，剪力阻抗回升增加時的剪應變值越小且回升剪力模數越大。從不同細料含量貓羅溪砂土壤初始液化後試驗結果，當試體細料含量低於20%時，細料含量越多剪力阻抗回升時的剪應變值越小且回升剪力模數越大；當試體細料含量超過20%時，細料含量越多剪力阻抗回升增加時的剪應變值越大且回升剪力模數越小。而從純粗料土壤液化後回升剪力模數與設計所採用之靜態剪力模數相比，相對密度較大之粗料砂土，回升後之模數達原設計值較高的比例。由不同細料含量貓羅溪砂土壤回升剪力模數與設計靜態剪力模數相比，細料含量10%~20%之土壤，細料含量較多，回升後之模數可達原設計值較高的比例；細料含量20%~40%之土壤，細料含量越多，回升後之模數達原設計值的比例越少。

This research used Maoluo soil which had been liquefied during the Chi-Chi earthquake to study its behavior under shearing after initial liquefaction. The experiment used coarse portion（＞No. 200）of the Maoluo soil to make specimens with relative densities of 40%, 60% and 70%. Specimens with a dry density of 1400 kg/m3 and fines contents of 10%, 20% and 40% were also tested. According to test results of the coarse-grained soil, we found that the specimen with a higher relative density can recover its shear resistance at a smaller shear strain after liquefaction and can obtain a higher recovery shear modulus. For soil with fines contents lower than 20%, the specimen with a higher fines content can recover its shear resistance at a smaller shear strain and a higher recovery shear modulus. On the other hand, for fines contents higher than 20%, the specimen with a higher fines content recovers its shear resistance at a higher shear strain. Comparing with the static modulus which is usually used in design the coarse-grained soil with a higher relative density can recover a higher percentage of the original design shear modulus after liquefaction. Similarly, for fines contents of 10%~20%, the soil with a higher fines content can recover a higher percentage of the design shear modulus after liquefaction. For fines contents above 20%, the soil with a higher fines content can recover a less percentage of the original design shear modulus.