有效圍壓與過壓密比對低塑性粉土液化之影響

Effects of Confining Pressure and Overconsolidation Ratio on Liquefaction of Low Plasticity Silt

周桓宇(Huan-Yu Chou)

指導教授 ： 葛宇甯

國立臺灣大學/工學院/土木工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.02726

摘要

本研究採用石英粉及鐵立庫粉土為試驗土樣，其粒徑介於砂土與黏土之間，並控制重模試體初始孔隙比為0.95，進行動力三軸試驗，了解純粉土之動態行為，並探討有無類似於砂土或黏土之動態行為。規劃石英粉及鐵立庫粉土在有效圍壓為80、160、320 kpa與過壓密比為1、2、4時進行動態試驗，探討有效圍壓及過壓密比對石英粉及鐵立庫粉土抗液化強度之影響。
根據研究結果顯示，石英粉受反覆應力作用，試體先達初始液化，再到達5%雙振幅軸向應變，類似砂質土讓破壞模式，但試驗中鐵立庫粉土先到達5%雙振幅軸向應變，爾後才達初始液化，此行為類似塑性土壤破壞模式。
根據石英粉與鐵立庫粉土在不同有效圍壓之動力三軸試驗結果，在相同反覆次數作用下，石英粉液化所需反覆剪應力比隨有效圍壓增加而增加，鐵立庫粉土液化所需反覆剪應力隨有效圍壓增加而增加，但反覆剪應力比隨有效圍壓增加而降低。
本研究探討過壓密比對石英粉及鐵立庫粉土抗液化強度影響，由試驗結果顯示石英粉及鐵立庫粉土反覆剪應力比隨過壓密比增加而增加，且兩者上升幅度相當。並與過往不同配比土樣之試驗結果進行比較，發現石英粉及鐵立庫粉土受過壓密作用後，抗液化強度上升幅度類似於砂質土壤，且上升幅度小於塑性土壤。

關鍵字

動力三軸試驗 ； 有效圍壓 ； 過壓密比 ； 反覆剪應力比

並列摘要

This study examines the liquefaction behavior of quartz powder and Tieliku silt using a CKC cyclic triaxial apparatus. It is aimed to distinguish the non-plastic silt’s cyclic behavior from sand or clay. Each tested specimen was remolded at an initial void ratio of 0.95. The tests were carried out under the effective confining pressures of 80, 160 and 320 kPa and at the over-consolidation ratios of 1, 2 and 4, respectively.
The results suggest that due to cyclic stress, the tested quartz powder reached initial liquefaction and then 5% double amplitude axial strain, resulting in a failure mode similar to sand. On the contrary, the tested Tieliku silt reached 5% double amplitude axial strain and then initial liquefaction, leading to a failure mode akin to clay.
Additionally, the results from the CKC triaxial tests under three different effective confining pressures were used to establish liquefaction resistance curves for both silty soil. Under a given number of cyclic load cycles, the cyclic stress ratio for quartz powder needed to liquefy rose as the effective confining pressure increased. The level of cyclic stress required for the liquefaction of Tieliku silt also increased, with its decreasing in cyclic stress ratio.
The effect of over-consolidation ratio on liquefaction resistance for quartz powder and Tieliku silt suggest that the corresponding levels of cyclic stress on both silty soils increased when over-consolidation ratio climbed up. Compared to other soil types, the tested over-consolidated silts provided a liquefaction resistance as much as that of sandy soil but less than that of clayey soil.

並列關鍵字

Triaxial test ； Effective confining pressures ； Over-consolidation ； Cyclic stress ratio

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