反覆單剪試驗與動態三軸試驗常被用來求取土壤動態性質或液化阻抗；然而，兩者於壓密過程與加載方式上有所不同，所得結果亦常有差異。為此，本研究以反覆單剪試驗儀進行應變控制動態性質試驗、應變控制液化阻抗試驗與應力控制液化阻抗試驗，並將試驗分析結果與相同控制條件之動態三軸試驗成果(周伯儒，2022)進行比對。其中，應變控制動態性質試驗與應力控制液化阻抗試驗係參考ASTM-D8296-19來執行，應變控制液化阻抗試驗則以數個指定之剪應變振幅進行循環加載至液化，用以探討動態性質、剪應變及超額孔隙水壓間之關係。前述試驗中係選用越南石英砂製作試體，控制在兩種相對密度(Dr40%、Dr50%)、三種有效覆土應力(20、50、100 kPa)下，以加載頻率1赫茲進行循環加載。在與動態三軸試驗的比較中，發現兩試驗之剪力模數皆與剪應變、循環加載週數呈負相關，與有效覆土應力呈正相關，並於相對密度差異上皆無明顯差異。此外，以兩試驗之勁度大小進行比較發現，相同控制條件下反覆單剪試驗之剪力模數小於動態三軸試驗，勁度比例介於0.4~0.8之間；應力控制液化阻抗試驗之反覆剪應力比強度比例則約為0.38~0.5左右。而在超額孔隙水壓激發之過程中，發現兩試驗之超額孔隙水壓力皆隨著剪應變加載振幅及循環加載週數的增加而持續累積，並隨著有效覆土應力的增加而效降緩，惟降緩程度略有不同；另外，發現在超額孔隙水壓比約小於0.4的區段內，反覆單剪與動態三軸兩試驗之剪力模數會先略增在遞減，這是因為此範圍超額孔隙水壓所造成的土壤弱化影響小於土壤緻密化導致的勁度增加。

Cyclic simple shear (CSS) and cyclic triaxial (CTX) tests are commonly used to determine the dynamic properties and liquefaction resistance of soils. However, these two tests are different in the consolidation and loading processes. In this study, a series of CSS tests on Vietnam silica sand were conducted, including the strain-controlled tests for dynamic properties, and both stress-controlled and strain-controlled tests for liquefaction resistance. The results were compared with those of CTX tests under the same conditions (Chou, 2022). It was found that the shear modulus from both tests exhibited a negative correlation with shear strain and the loading cycles and a positive correlation with effective overburden stress. Furthermore, the shear modulus from CSS test was smaller than that from CTX test, with a stiffness ratio ranging from 0.4 to 0.8. Similarly, the CSS-to-CTX cyclic shear stress ratio obtained from the stress-controlled liquefaction resistance test was approximately 0.38 to 0.5. The excess pore water pressure generated during both tests was higher as the shear strain amplitude and number of loading cycles increased, and the buildup tendency was less significant at a larger effective overburden pressure, yet the decrement was slightly different. These findings led to a better understanding of the variation in mechanical properties of soil during the development of liquefaction and helped to clarify the discrepancies between CSS and CTX tests, which can serve as the reference in engineering practice.

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