Analysis of Liquefaction Potential of Gravelly Soil- A Case Study at Wufeng Futian Bridge

摘要 由於台灣位處環太平洋地震帶上，地震頻繁，而災害性地震可能導致土壤液化而造成地層下陷與結構物破壞，帶來極大之損壞。一般認為飽和砂土或粉土質細砂較易液化；但在1999集集大地震時，曾於霧峰地區礫石土亦發生液化地區，因此對其發生液化行為需進一步研究。 本研究選定於921集集大地震時，曾發生礫石土液化之霧峰區福田橋下之高灘地作為研究場址，同時於室內進行之大型反覆三軸試驗(直徑15cm、高25cm)，探討不同相對密度與不同礫石含量對礫石土液化阻抗之影響，利用反覆三軸試驗之結果迴歸分析，並建立礫石土液化潛能評估公式，並嘗試建立孔隙水壓激發時，與土壤電阻率變化之關係。 研究結果顯示， 礫石土之液化阻抗，隨礫石含量或相對密度之增加而提高，因此可說明相對密度(Dr)與礫石含量(GC)皆為影響液化阻抗之主要因素。 由迴歸分析獲得礫石土抗液化強度〖CSR〗_(N1=15)=0.0031*(GC)+0.0045*(Dr)+0.041， 另外在反覆應力下，隨著礫石與相對密度增加，孔隙水壓上升趨緩，使得電阻減少亦趨緩，較不容易激發土體內部超額孔隙水壓與電阻之變化。abstract As Taiwan is located on the Pacific Rim seismic belt, frequent earthquakes, and severe earthquakes may lead to soil liquefaction caused by subsidence and structural damage, causing great damage. It is generally believed that saturated sand or silty fine sand is easier to liquefied. However, in the 1999 earthquake, the liquefied soil has also been liquefied in the fog peak area, so the liquefaction behavior should be further studied. In this study, we selected the high-lying beach under the fog peak area of the gravel soil as the research site, and carried out the large-scale repeated triaxial test (15cm in diameter and 25cm in height) at the same time. Relative density and different gravel content on the liquefaction resistance of gravel soil. Using the regression analysis of the results of repeated triaxial tests, the formula of liquefaction potential of gravel soil was established and the relationship between soil pressure and soil resistivity was established. The results show that the liquefaction resistance of gravel soil increases with the increase of gravel content or relative density, so it can show that the relative density (Dr) and gravel content (GC) are the main factors affecting the liquefaction resistance. (N1 = 15) = 0.0031 * (GC) + 0.0045 * (Dr) +0.041, and the gravel soil was obtained by regression analysis. In addition, under the repeated stress, with the increase of the gravel and the relative density, the pore water pressure increases slowly, which makes the decrease of the resistance also slow down, which is less likely to stimulate the excess pore water pressure and resistivity change in the soil.目錄 摘要 i abstract ii 目錄 iii 圖目錄 v 表目錄 viii 第一章 緒論 1 1.1 論文內容 1 1.2 研究背景與目的 1 1.3 研究方法 2 第二章 文獻回顧 4 2.1 礫石土液化案例之研究 4 2.2 液化定義與影響液化之因素 6 2.2.1 液化現象與液化名詞之定義 6 2.2.2 影響液化之因素 9 2.3 反覆三軸試驗 12 2.3.1反覆三軸試驗之原理與破壞準則 12 2.3.2反覆三軸試驗之原理 12 2.3.3探討反覆三軸試驗的電性量測探討和砂土液化潛能 16 2.4 室內試驗相關因素對液化抗阻之影響 19 第三章 液化評估方法之介紹 21 3.1 Seed 簡易分析法 24 3.2 反覆三軸試驗之液化潛能評估法 27 第四章 試驗內容 31 4.1 研究場址之地質狀況 31 4.2 試驗規劃 37 4.3 動力三軸反覆載重破壞之定義 39 4.4 反覆三軸試驗因子探討 39 4.4.1 模擬現地粒徑分佈曲線 40 4.4.2 橡皮膜貫入效應 (Membrane Compliance Effect) 41 4.4.3 橡皮膜貫入效應之控制 44 4.5 反覆三軸試驗儀器與設備 44 4.5.1 試體製作 52 4.5.2 儀器率定 53 第五章 試驗結果與討論 55 5.1 反覆三軸試驗結果 55 5.1.1不同礫石含量對液化阻抗之影響 55 5.1.2不同相對密度對液化阻抗之影響 63 第六章 結論與建議 73 6.1結論 73 6.2建議 74 參考文獻 7