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Title: | 土壤於二元組構理論下受振勁度折減之探討 Soil Stiffness Reduction due to Undrained Cyclic Loading under the Framework of Binary Packing |
Authors: | Yu-Hsuan Yang 楊予瑄 |
Advisor: | 葛宇甯(Yu-Ning Ge) |
Keyword: | 土壤液化,細顆粒含量,勁度折減曲線,循環荷載頻率,動態荷載,二元混和物, fines content,liquefaction,stiffness reduction,binary packing,cyclic loading, |
Publication Year : | 2020 |
Degree: | 碩士 |
Abstract: | 臺灣位於環太平洋地震帶上,每年約發生一萬六千餘次規模大小不一的地震,而地震的發生往往導致了土壤液化的災害,由於土壤液化的發生導致土壤的承載力不足,進一步使坐落於地表之建築物傾斜或引起地面有大量的沉陷,而近年來,許多研究皆探討土壤在地震過後土壤強度或勁度折減之行為。現地之土壤通常是由不同粒徑大小和不同類型組成,其土壤結構和顆粒排列會進一步改變土壤行為。 西元2016年於高雄市美濃區發生芮氏規模6.6之地震,對台南多處地區造成多起土壤液化之災情,造成很多建物傾斜、下陷及噴砂等災害,因此本研究選擇位於台南市新化區的場址,透過高品質低擾動Gel Push取樣器(簡稱GP取樣器)取得三種不同類型之原狀試體,並進行一系列的動三軸試驗,從現地土壤試驗結果得知低塑性粉土有更高的液化風險。 由於現地土壤在不同原狀試體之間有極高異相性,自1990年前後,許多學者也提出了二元混合物排列所產生變化之概念,並在近幾年廣泛應用在大地工程中,因此,該研究採用二元混和物的框架來探討不同細顆粒含量之砂土(15%、50%)在循環荷載下之行為,以二元混和物之框架解讀此兩種細顆粒含量值分別位於極限值之左側及右側,本研究藉由控制相同孔隙比施作了三種不同試驗,包含:靜態均向壓密不排水試驗、共振柱試驗以及動態均向壓密不排水試驗,並且所有試體皆以濕夯法進行製作,根據結果探討不同細粒料含量下之抗液化行為,並進一步探討循環應力比及循環荷載之頻率對液化曲線及勁度折減曲線,以及探討孔隙比對二元混和物之適用性。 根據本研究實驗結果顯示,循環荷載的頻率會影響液化曲線,尤其在細顆粒含量等於15%的試體上反應更為明顯,並且土壤勁度並一直隨著超額孔隙水壓比上升而下降,而細顆料含料越高,試體之抗液化能力越弱以及土讓勁度折減比例越高,和現地土觀察之現象得到相似的結論,並透過Thevanayagam在2007年提出的修正孔隙比公式計算出之孔隙比可以更有效的描述二元混和物實際之顆粒接觸情形。 Disasters along with liquefaction occur. Earthquakes may decrease the soil strength and make buildings tilted or cause ground settlement. The bearing capacity of soil is not enough due to liquefaction. In-situ soils are composed of various sizes and different types, where its fabric may change the behaviour of the mixtures. This study chose a site which is located on in Xinhua, Tainan to sample different soil types and carried out a series of cyclic triaxial tests with these undisturbed specimens. From the results of in-situ soils, the low-plastic silt exhibits the lowest liquefaction resistance in all in-situ soils. But, the degree of stiffness variability isn’t easy to compare with different types of soils because the fabric may change the behavior of the mixtures. The binary packing theory has been discussed in geotechnical engineering recently. Therefore, this research employed the framework of binary packing to examine the cyclic behavior of the granular mixtures. This study adopts different proportions of non-plastic fine sands by weight, including 15% and 50%. It carried out a series of isotropic consolidated undrained compression tests, resonant column tests and cyclic triaxial tests, where cyclic behaviours and stiffness reduction curve were evaluated under different cyclic stress ratio (CSR) and frequency of cyclic loading. The results indicate that different proportions of fine sands during the cyclic loading lead to different reduction factor in soil stiffness. Based on the experimental results, the frequency of 0.1 Hz has significant impact on the large cyclic stress ratio with fines content of 15%. It is easier to make the soils liquefied than the frequency of 1 Hz. The fines content of 50% possesses a lower liquefaction resistance lower than the fines content at 15%. The fines content plays an important role for the sandy soils regardless of in-situ soils and binary packing framework according to results, the higher fines content in the sand soils should be noticed during earthquake. The verified reduction factor of soil stiffness in the proposed framework will be applied to predict the stiffness reduction factor of in-situ soils. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/53684 |
DOI: | 10.6342/NTU202002403 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 土木工程學系 |
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U0001-0408202017513600.pdf Restricted Access | 10.95 MB | Adobe PDF |
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