- 學位論文
共振柱試驗及動力三軸試驗下澎湖鈣質砂的動態性質
Dynamic Properties of Penghu Calcareous Sand by Resonant Column and Cyclic Triaxial Tests
摘要
鈣質砂基本上是通過生物降解形成的，由碳酸鈣組成，與石英砂相比結構較弱。鈣質砂具有高空隙率和有棱角的顆粒形狀。它們主要分佈在熱帶和亞熱帶淺水中，經常發生地震。因此，許多進入沿海的結構，例如港口設施，海基，以及由於缺乏能源而近期開發的海上風力渦輪機可能受到鈣質砂特徵的影響。鈣質砂的動態性質是本研究的重點。 在這項研究中，進行了共振柱試驗，以評估從澎湖沿海地區獲得的鈣質砂的小應變動力學特性。試樣採用夯實法重模，分別改變三種不同的空隙率、飽和度及圍壓。利用試驗結果探討圍壓、空隙率及飽和度對澎湖鈣質砂動態性質的影響，並建立澎湖鈣質砂最大剪切模量和最小阻尼比的相關方程。 本研究還進行對應於共振柱試驗三種空隙比的相對密度控制動力三軸試驗，用以得到澎湖鈣質砂在不同相對密度下的抗液化強度。 試驗結果顯示: 乾砂的剪力模數及阻尼小於濕砂，但正規化剪力模數比大於濕砂；需要分離乾砂和濕砂來預測Dmin和Gmax；飽和度不會影響濕砂的Dmin；澎湖鈣質砂的液化潛能明顯低於石英砂及其他現地土壤。
並列摘要
Calcareous sand is formed by biodegradation, composed of calcium carbonate, and weak structurally compared to quartz sand. Calcareous sand has high void ratio and angular particle shape. They can be found in tropical and subtropical shallow waters. It is highly likely that calcareous sand would be encountered in the construction of coastal and offshore structures, such as port facilities, sea base, and offshore wind turbines Hence, it is important to study the behavior of calcareous sand. Determination of the dynamic properties of calcareous sand is the focus of this study. In this study, resonant column tests were performed to evaluate the small-strain dynamic properties of calcareous sand, which was obtained from the coastal area of Penghu. Reconstituted specimens were prepared by the compaction method. Impact of void ratios, degrees of saturation and confining pressures on dynamic properties were investigated. Correlation relationships to estimate the maximum shear modulus and the minimum damping ratio of Penghu calcareous sand were developed. A relative density-controlled cyclic triaxial tests were performed on specimens with the same three void ratios as used in the resonant column test. Liquefaction resistance of Penghu calcareous sand with different relative densities were determined. The test results show that the shear modulus and damping of dry sand are smaller than those of wet sand, while the normalized shear modulus of dry sand is higher than that of wet sand. Separate correlation relationships were developed for dry sand and wet sand to predict Dmin and Gmax.In addition, degree of saturation would not affect Dmin of wet sand. Lastly, it is found that the liquefaction potential of Penghu calcareous sand is significantly lower than that of quartz sand and other in-situ soils.
參考文獻
延伸閱讀
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