飽和砂土等向及非等向壓密不排水三軸試驗力學特性之研究

Behavior of Saturated Sand in Isotropic and Anisotropic Consolidation Triaxial Undrained Tests

陳嘉謙(Chia-Chien CHEN)

指導教授 ： 陳怡睿

共同指導教授 ： 謝舜傑

長榮大學/管理學院/土地管理與開發研究所/碩士(2008年)

https://doi.org/10.6833/CJCU.2008.00118

摘要

本研究針對雲林縣麥寮鄉海岸新興工業區之砂土，運用三軸剪力試驗，進行等向及非等向不排水試驗，用以探討飽和砂土之力學特性。試體之相對密度分別控制為40%、50%及60%，在等向壓密試驗控制平均有效正向應力分別為100、200及300kpa；在非等向壓密試驗控制不同初始 與 ， 值分別為0.4、0.5、0.67，進行三軸不排水單循環先壓縮及先伸張剪力試驗。
試驗結果發現，不同相對密度之飽和砂土，當相對密度愈大其抗剪強度愈大愈不容易破壞；當應力比大到足以導致試體破壞時，在壓縮及伸張側皆會發生相角轉換之現象。疏鬆土體呈現塑性收縮(對應於彈性膨脹)行為；緊密土壤呈現塑性膨脹(對應於彈性收縮)行為，顯示不同相對密度會有不同塑性收縮及塑性膨脹行為的發生。
飽和砂土受剪初期，孔隙水壓皆會急速上升。然而，隨著剪應變增加，孔隙水壓上升之速度會減緩，甚至開始下降。因此，砂土受剪塑性收縮與膨脹之趨勢，以及孔隙水壓之變化趨勢，皆與砂土本身之相對密度，和其所受之有效圍壓有關。
在非等向壓密先壓縮試驗結果，土體塑性收縮及塑性膨脹的力學行為，與等向壓密土體特性是一致的。當改變初始 及 之不同控制所設定 值，砂土最後殘餘應力路徑都很一致沿著破壞線的應力路徑，亦顯示在同一種相對密度下 值的不同，在等向或非等向試驗中均與初始 無關，不會影響土體破壞的應力路徑。

關鍵字

等向壓密 ； 非等向壓密 ； 飽和砂土 ； 力學特性 ； 三軸試驗 ； 收縮性 ； 膨脹性

並列摘要

In this research, isotropic and anisotropic consolidation triaxial undrained test was used to test Mai Liao sand. The mechanical characteristics of the saturated sand were investigated under various initial conditions and stress paths. Under the initial conditions: sand sample with three different relaqtive densities of 40%, 50%, 60%, cyclic undrained shear test was performed. In isotropic case, the initial effective normal stresses were 100, 200, 300kPa. In anisotropic case, the initial values of lateral earth pressure coefficient kc were 0.4, 0.5, 0.67 under various effective lateral and normal stresses.

The results showed that for saturated sand with different relative density the larger the relative density, the higher shear resistance and damage was not easy to occur. When stress ratio was so great that the sand sample failed, phase transformation occurred in both compression and tension sides. Loose sand showed plastic contraction (corresponding to elastic dilatancy), while dense sand shows plastic dilatancy (corresponding to elastic contraction). That is, with different relative density, plastic contraction or dilatancy may occur.

In the beginning of shear test, the pore pressure increased rapidly, and then slowly or even decreased with the increment of shear strain. Therefore, the changes of plastic contraction or dilatancy, and pore pressure depend on relative density of the sand and effective confined pressure.

The results in anisotropic case showed that the mechanical behavior of plastic contraction or dilatancy were the same as that in isotropic case. When the value of kc was changed, the residual stress path always followed the stress path of damage curve. It also showed that with the same relative density and different kc, initial effective lateral stresses did not affect stress path of damage of the sample in both isotropic and anisotropic cases.

並列關鍵字

isotropic consolidation ； anisotropic consolidation ； saturated sand ； mechanical characteristics ； triaxial test ； contraction ； dilatancy

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