黏土對土木工程的影響很大，往往在地層僅存在薄薄的一層，即對土層強度有很大的影響，並且造成施工上很大的困擾。因此工程師必須瞭解黏土之強度及力學行為，以期在土木工程中遭遇黏土的問題上，能有最適切之處理辦法。

本文想探討黏土在不同的有效圍壓、不同塑性指數狀態下，正常壓密及過壓密黏土的影響狀況。本研究以控制試驗黏土土樣初始孔隙比e = 1.25、添加三種不同皂土含量配合比(3%、6% 和10%)，三種不同過壓密比OCR(1.00、1.25 和1.50) 和三組不同之有效圍壓 (50 kPa、75 kPa 和100 kPa)，進行三軸壓密不排水兼量取孔隙水壓試驗。

主要目的乃在探討不同塑性指數黏土之不排水剪力強度，並藉由臨界破壞理論的Cam-clay模式和Modified Cam-clay模式，對所進行試驗之結果，探求兩個不同理論上的分析，進而探討模式是否能預測不同塑性土壤之適用性。

由實驗得知，模式對於正常壓密狀態之黏土模擬情況較為符合，且Cam-clay model對於塑性指數較高的黏土對塑性指數較低的黏土較能符合預期上之成果。相反的Modified Cam-clay model對於塑性指數較低的黏土反而較能符合試驗值。而對試驗強度上加以探討，試驗土樣隨著添加皂土含量的減少，其強度有顯著的增加趨勢，亦即不同塑性指數的黏土，對塑性指數較大的黏土而言，其強度變化靈敏度極高。

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