土壤塑性程度包含塑性指數(PI)、液性限度(LL)及塑性限度(PL)，其能直接表達土壤基本特性，且於工程使用上為預測參數之重要指標。本研究以台北黏土為基礎，使用濕搗法製作添加皂土之重模試體，利用皂土之高液性限度特性改變試體塑性，並以三軸均向壓密不排水壓縮(CIUC)試驗及三軸K0壓密不排水壓縮(CK0UC)試驗結果為主，探討試體於正常壓密狀態下各參數受塑性程度之影響。試驗結果顯示，土壤破壞參數包含不排水剪力強度、有效剪抗角及破壞時超額孔隙水壓參數，與塑性指數成良好線性關係；將不同塑性土壤受K0壓密及均向壓密試驗結果與塑性指數比較，兩試驗正規化剪力強度之比值，隨塑性指數增加而增加；兩試驗有效剪抗角之比值，隨塑性指數增加而減少；破壞時超額孔隙水壓參數 隨塑性指數增加而增加。

Plasticity level is inclusive of plasticity index(PI), liquid limit(LL) and plasticity limit(PL). It could indicate basic characteristics of soil and also be an important index to predict other soil parameters for engineering use. In order to establish the relationship of soil parameters and plasticity level, the research conducted included triaxial isotropic consolidation undrained compression test (CIUC) and triaxial K0 consolidation undrained compression test (CK0UC) on three specimen with different plasticity index. The specimen was composed of Taipei clay and Bentonite, and was produced using the wet undercompaction method. Different percentages of Bentonite which has a higher liquid limit than Taipei clay was mixed with Taipei clay to change the plasticity index of reconstituted soil. From the experiments results, soil failure parameters which includes undrained shear strength, effective friction angle and excess pore pressure parameter at failure have good relations with plasticity index. The use of the ratio of CK0UC and CIUC to compare different consolidation procedures would be affected by plasticity index. The ratio of normalized undrained shear strength increases when plasticity index increases which is the same as the result for the excess pore pressure parameter at failure. In contrast, the ratio of effective friction angle will decrease when plasticity index increases.

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