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    Title: 軟弱黏土中層狀加勁砂柱試驗
    Other Titles: Model test for a laminated reinforced sand column embedded in soft clay
    Authors: 簡嘉緯;Chien, Chia-Wei
    Contributors: 淡江大學土木工程學系碩士班
    吳朝賢
    Keywords: 軟弱黏土;層狀加勁砂柱;地工合成材;模型試驗;承載力;側向腫脹;Soft clay;Laminated reinforced sand column;geosynthetic;Model test;Bearing capability;Lateral swelling
    Date: 2014
    Issue Date: 2015-05-01 16:12:58 (UTC+8)
    Abstract: 在基礎工程設計中,現地土壤過於軟弱無法提供足夠的承載力時,一般常使用砂柱工法進行土壤改良,砂石樁雖可承受軸力與剪力,但於近地表處由於側向圍束力不足,易造成砂樁頂層產生腫脹,進而限制砂土樁承載的能力。利用地工合成材加勁砂樁,防止砂柱頂端圍束力不足的現象,進而提升整體砂柱承載力,為近年發展的工法。

    本研究模擬現地軟弱黏土層中加勁砂柱之行為,依現地條件等比例縮小於適當之尺寸進行試驗。探討層狀加勁砂柱是否有效提升承載力以及提供頂層較好的圍束力。試驗使用三種不同勁度材料(GT1、GT2、GT3)以及5與10之加勁材層數進行模型試驗,並施做加勁材之雙向拉伸試驗得到加勁材的張力-應變關係,以解釋砂柱的行為。並量測加勁材於大載重下厚度壓縮試驗來修正整體砂柱的沉陷量。

    實驗結果顯示層狀加勁砂柱能有效提升軟弱黏土中砂柱的承載能力,當加勁材降伏前其張力勁度越大則能提供砂柱更大的承載能力,加勁材強度越大則使最終承載能力越好,設置加勁材也使上方載重傳遞更大應力至砂柱底部。安裝加勁材能提升砂柱整體勁度及抑制腫脹,但也讓上方力量向砂柱底部傳遞,使砂柱腫脹範圍向下延伸。層數配置部分,五層加勁砂柱除提供較少加勁效果外,加勁材層與層之間有較大的間距使加勁材的圍束效果不明顯,對頂部砂柱腫脹的抑制效果較少。十層加勁砂柱因有較密的間距能使加勁材提供的加勁範圍較大,使砂柱腫脹較小且平均於整體砂柱。延展性較差之地工合成材易於低應變下產生破壞,提供砂柱承載能力與抑制砂柱腫脹情況有限,使用多層加勁材仍無明顯增量。
    Sand columns have been used in engineering practice to improve the bearing capacity of soft clay in recent years. Although the sand column can bear axial stress and shear stress from surface load, but due to the lack of lateral confining pressure in the near-surface that often caused bulging failure in the top portion of the column, reduce the carrying capacity of the sand column. Reinforce a sand column with laminated geosynthetics is feasible and effective solution to improve bearing capability of a sand column.
    In this study, model test on single geosynthetic-laminated sand columns installed in soft clay was conducted. Similarity analysis was executed first to determine suitable properties of the constituents used in the model tests to ensure comparable behavior between the prototype-scale and model-scale reinforced granular columns. Three types of geosynthetics was employed to reinforce the sand columns either with 5 or 10 layers of geosynthetic sheets horizontally placed in these model sand columns.
    Experimental results showed that horizontally inserted reinforcements improve the bearing capability of the model sand columns; marked improvement was achieved for sand columns reinforced with geotextile of relatively medium to high stiffness. Horizontal reinforcement also restrained radial strain of the columns significantly. Additionally, horizontal reinforcements affected stress transmission character along the length of the sand column and thus the bearing capability of the column.
    Appears in Collections:[土木工程學系暨研究所] 學位論文

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