摘 要 本研究利用南崗工業區液化砂土，於室內製作35%、50%、90%三種相對密度的重模土壤試體，在三種不同有效圍壓下，分別進行排水與不排水靜態三軸試驗。試驗之主要構想係以增加反水壓的方式，模擬飽和砂土受初始剪應力作用下因液化效應所引致之強度弱化行為，建立觸發土壤弱化破壞時所需增加之孔隙水壓比與相關變形行為之關係。 本研究之試驗結果顯示，不論土壤的相對密度、有效圍壓為何，在一般工程設計之初始作用剪應力情況下，因超額孔隙水壓比約達60%時，即有觸發土壤產生弱化的危險，可作為判定土石結構液化穩定性之參考資料。 ABSTRACT In this research, we use the liquefied sand from Nan Kang Industrial Park, to prepare the remolded samples with relative densities of 35%, 50% and 90%. The drained and undrained triaxial shear tests were conducted on the samples consolidated in three different confining pressures. The main purpose of the tests is to simulate the softening behavior of the saturated sands when sustained to an initial shear stress by increasing the back pressure, which was considered as some kind of liquefaction effect. Finally, we establish the minimum excess pore water pressure ratio that required to trigger the softening behavior of the soil. The test results show that, no matter what relative density and effective confining pressure of the soil are, under the applications of the design initial shear stress, the minimum excess pore water pressure ratio is about 60%, to trigger the softening behavior of the soil due to liquefaction. This information may be helpful to assessing the liquefaction - induced stability of the soil structure.