水平加勁砂柱之數值模擬

Numerical Modeling of Geosynthetic-Laminated Sand Columns

陳治夫(Jyh-Fu Chen)

指導教授 ： 洪勇善

淡江大學/工學院/土木工程學系碩士班/碩士(2012年)

https://doi.org/10.6846/TKU.2012.00178

摘要

對於現地基礎設計上，為了使土壤能夠承受上部載重，通常較軟弱之土壤需要進行一些工法來改良。而在各種工法之中，在軟弱土層中置入砂石樁可加速軟弱粘土層排水，並可傳遞荷重，降低後續階段壓縮潛能，以減少基礎完工後之土壤沉陷行為。砂石樁雖可承受軸力與剪力，但樁體接近地表處之結構，容易因側向束制力不足而產生徑向腫脹導致破壞，故工程師不斷地尋求砂石樁之加勁方式，以提高砂石樁頂部之承載力並減少該處之側向變形。而現在國內外也有許多學者皆進行了加勁砂石樁之相關研究，包括在砂土中混入聚酯纖維，以及於試體中水平置入或外包等方式加勁，以探討不同加勁方式對砂柱的影響。其中，地工合成材影響水平加勁效果的因素包括：加勁材層數、加勁材勁度與強度以及加勁材的擺放位置等，本研究即針對以上參數分別就加勁效果進行探討。研究主要以有限差分數值軟體FLAC撰寫計算分析程式，以探討層狀加勁砂柱的力學行為。首先，以塑性理論配合三軸試驗建立砂土力學行為模式，另由加勁材張力試驗與加勁材和砂土間之界面直剪試驗結果確立分析所需元素的性質。依據建立的層狀加勁數值模型，進行分析模擬並與試驗結果比對；在三種不同圍壓與加勁層數下，應力應變行為的模擬與試驗結果相近，而體積應變略微高估。此外，也觀察到試體內部加勁材漸進式破壞的行為，此部份也由試驗的最後觀察得到驗證。在參數研究的部份，以現場實體尺寸為分析標的，分別探討加勁材勁度、強度、樁徑、加勁材間距以及界面摩擦角等參數對層狀加勁的影響，分析結果並以砂土內部最小主應力分佈為基礎，剖析各條件下所反應的加勁性能。

關鍵字

地工合成材 ； 水平加勁 ； 數值模擬 ； 砂樁

並列摘要

Foundation construction on soft soil usually encounters weak bearing capacity and consolidation problems. The basal reinforcement and granular columns are the most commonly techniques used to solve these problems. The inclusion of granular material in soft soil reduces the drain path and improves the bearing capacity. However, insufficient lateral support at shallow column depth frequently causes bulging failure in the top portion of the column. In order to strengthen the column, the reinforcement can be achieved by enveloping a granular column with a flexible fabric or by placing horizontally laminated reinforcing sheets or induce the randomly oriented fibers on the column. This study numerically analyzes the mechanical performance of the laminated reinforced sand columns.In this study, numerical analysis using finite difference program FLAC. An elastic-plastic constitutive model with non-associated flow rule is used to characterize prominent expansive behavior of the medium to dense sands, and the elastic-perfectly plastic law for the reinforcement and the interface element between reinforcement and sand. The mechanical parameters of the materials are extracted from simple tests, e.g. triaxial compression test for pure sand, load-elongation test for reinforcement, and interface direct shear test for interface element. The results obtained from the proposed method were compared with those obtained from laboratory experimental triaxial tests. A series of parametric studies also provides elaborate work on the influence factors for the laminated reinforced columns. The parametric studies include the geosynthetic stiffness, strength, column diameter, geosynthetic horizontal spacing, and interface friction angle between geosynthetic and sand. Base on the distribution of the minor principle stress in reinforced sand can be dissected the performance of laminated reinforced columns under various conditions.

並列關鍵字

geotextile ； Laminated ； numerical modeling ； sand column

參考文獻

4. 鄭淳軒(2010) ，「張應變對針軋不織布開孔徑及滲透速率影響探討」，碩士論文，淡江大學土木研究系，臺北。

3. 黃振業(2009) ，「外包加勁砂柱之數值模擬」，碩士論文，淡江大學土木研究系，臺北。

2. 蔡伊雯(2007)，「地工合成物水準加勁砂柱試體之力學行為之探討」，碩士論文，淡江大學土木研究所，臺北。

5. Bergado, D. T., Chai, J. C., Alfaro, M. C. and Balasubremaniam, A. S. (1992), “Improvement Techniques of Soft Ground in Subsiding and Lowland Environment,” Division of Geotechnical and Transportation Engineering, Asian Institute of Technology, Bangkok, Thailand, pp.56-60.

9. Chandrasekaran, B., Broms, B. B. ＆ Wong, K. S. (1989), “Strength of Fabric Reinforced Sand under Axisymmetric Loading,” Geotextiles and Geomembranes, Vol. 8, pp.293-310.