含細料砂土的最大剪力模數之探討

在地動分析中，對於土層的影響一般會關注的是地震中地層對於地震波的放大效應，而其中有兩項用來描述土壤的動態參數，剪力模數和阻尼比，常用來代表土壤的動態特性。土層的動態參數會影響土壤的受震行為，而剪力模數會隨著剪應變不同而改變，當剪應變值很小的時候，剪力模數即為最大剪力模數。由最大剪力模數即可概算隨應變增大剪力模數之數值。在過去五十年間，許多學者曾利用動態實驗方法，探討各土壤基本參數與最大剪力模數之間的關聯，並建立相關的關係式。最常見的關係式形式是考慮孔隙比及平均有效應力，由Hardin和Richart(1963)建立的關係式。然而，過去的經驗公式常常是以單一種類的土壤，純砂或是黏土的實驗結果來建立，而在現地中通常不會是單一種類的土壤，因此對於混合土壤，需要判斷使用過去經驗公式是否合適。本研究利用一系列剪力元件(bender element)實驗，探討含細料砂土之最大剪力模數與細料對於最大剪力模數的影響。經由對不同細料含量和不同種類細料之砂土試體的實驗結果，找出孔隙比、平均有效應力、塑性指數、細料含量對最大剪力模數的影響趨勢。接著，經由收集過去研究中針對純砂和含細料砂土的動態實驗結果，檢算前人提出關係式所預測之最大剪力模數，了解各模型之預測精確度。最後，藉由非線性回歸方法，找出資料中最適合之關係式形式，並加入考慮細料之參數，得到含細料砂土之最大剪力模數經驗公式。

關鍵字

最大剪力模數；細料含量；剪力元件；混合土壤；土壤動態參數

並列摘要

Dynamic properties, such as strain-dependent shear modulus, damping ratio, are used to represent the behavior of a soil deposit subjected to dynamic loading. Furthermore, maximum shear modulus (G_(max⁡)) controls the behavior of soil under very small shear strain level. All of these properties control the propagation characteristics of earthquake waves. In the past fifty years, researchers investigated the relationship between maximum shear modulus and different basic soil properties through laboratory tests of pure soils, and developed empirical models for estimating maximum shear modulus. As we mostly encounter soil mixtures in the field, it is required to evaluate the applicability of these empirical models for estimating maximum shear modulus of soil mixtures. The objective of this study is to determine the maximum shear modulus of sands containing fines by bender element tests. Sands with different percentages of fines and fines types are used in preparing the reconstituted specimens. Effects of void ratio, mean effective stress, plasticity index, and over-consolidation ratio on maximum shear modulus would be examined. Furthermore, data from nine previous researches are collected, and the predictive power of previous empirical models on estimating maximum shear modulus is investigated. Lastly, with nonlinear regression method, the correlation relationship for sands containing fines is developed.

並列關鍵字

maximum shear modulus ； fines content ； bender element ； soil mixtures ； dynamic soil properties

參考文獻

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44. 簡才貴 (2006)。「土石壩材料之動態性質」，國立中央大學土木工程學系，碩士論文。

19. Jamiolkowski, M., Leroueil, S., and Lo Presti, D. C. F. (1991) “Theme lecture: Design parameters from theory to practice.” Proc. Geo-Coast ’91, Port and Harbour Research Institute, Japanese Ministry of Transport, pp.877– 917.

2. ASTM, D422. (2010). Standard Test Method for Particle-Size Analysis of Soils.

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含細料砂土的最大剪力模數之探討

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