顆粒材料於二元組構理論下之力學行為

Mechanical behaviors of granular materials under the framework of binary packing theory

卓雨璇(Yu-Syuan Jhuo)

指導教授 ： 葛宇甯

國立臺灣大學/工學院/土木工程學研究所/博士(2020年)

https://doi.org/10.6342/NTU202002270

摘要

為完整了解同一種材料來源之力學行為於不同細粒料含量 (FC)之變化，本研究設計一系列力學試驗，使用不同粒徑比之次稜角狀之粗顆粒與細粒料越南石英砂 (Type A: 6.375與Type B: 12.07)，進行並蒐集相同材料下單向度壓密、直接剪力、三軸試驗、彎曲元件與共振柱等試驗結果，目的在了解二元組構理論之下，透過靜態與動態等力學試驗，探討不同細粒料含量對力學行為之影響，以及粒間孔隙比概念對力學試驗結果解釋上之適用性。
研究結果顯示，並非所有試驗結果都能以粒間孔隙比的概念作解釋，二元混合材料的壓縮性會受到粒徑比、相對密度、試體尺寸與正向力或圍壓影響，而有不同趨勢，造成剪力強度與模數與粒間孔隙比成正比的可能原因有顆粒形狀與試體填製方法，而單向度壓密搭配彎曲元件試驗可看出不同相對密度下二元混合材料受到階段加載的剪力模數變化，疏鬆狀態下之二元混合材料容易受圍壓影響而改變FC 15到35%間之剪力模數趨勢之斜率。
當細粒料間可直接構成強烈力鏈時的細粒料含量稱為門檻細粒料含量 (CFth)，由於FC < CFth的二元混合材料性質不穩定性很高，此範圍亦是容易造成土壤液化之細粒料含量，大多研究聚焦於此，而本研究分析試驗結果造成該理論可能不適用之原因仍須進行更完整的試驗來釐清，此外，FC 85%的混合材料雖然不容易造成土壤液化，但於單向度壓密試驗 (I)的結果亦是讓人感興趣的部分，造成的原因可以再進一作探討。

關鍵字

二元混合材料 ； 二元材料微觀結構 ； 接觸力鏈 ； 顆粒接觸密度指數 ； 細粒料含量

並列摘要

This study analyzes the mechanical behaviors of binary granular materials through one-dimensional consolidation, direct shear, triaxial drained/undrained, bender element, and resonant column tests. Two particle size ratios of dry binary mixtures, 6.375 (Type A) and 12.070 (Type B), were adopted in the experiments. To understand the influences of fines content on mechanical behavior under binary packing, interpretation of the results was given by grain contact density indexes (intergranular void ratio).
The results show that the compression of binary mixtures was affected by size ratio, relative density, specimen size and normal stress or confining pressure. A possible reason for causing shear stress and shear modulus proportional to granular void ratio includes particle shape and the deposition methods. The variation of shear modulus under different loadings and relative densities can be seen by the results of one-dimensional consolidation test with bender element. Under loose sand condition, the shear modulus slope of FC 15~35% is easily affected by normal stresses.
The threshold fines content (CFth) is the fines content that makes fines compose strong force chain directly. The mixtures with fines content less than the threshold have higher unstable characteristic and easily cause liquefaction, many researchers focus on it. The results also present that not all the test results can be explained by the concept of intergranular void ratio, it needs more tests to figure out. The mixed material of FC 85% is not easy to cause soil liquefaction, however, the results of one-dimensional test (I) is also the interesting part, the cause can be further explored.

並列關鍵字

binary mixtures ； mircostructures ； contact force chain ； grain contact density indexes ； fines content

參考文獻

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