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研究生:魏文韜
研究生(外文):Wun-Tao Wei
論文名稱:以耦合壓密有限元素分析探討基樁之負摩擦力行為
論文名稱(外文):Investgation of Negative Friction Behavior of Pile Using Coupled Consolidation Finite Element Analysis
指導教授:邱俊翔邱俊翔引用關係
口試委員:柯永彥鄒瑞卿
口試日期:2019-07-23
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:土木工程學研究所
學門:工程學門
學類:土木工程學類
論文種類:學術論文
論文出版年:2019
畢業學年度:107
語文別:中文
論文頁數:184
中文關鍵詞:樁基礎負摩擦力耦合壓密分析有限元素法中立點
DOI:10.6342/NTU201902834
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本研究採用有限元素軟體ABAQUS探討基樁受負摩擦力之行為,以耦合排水分析模擬超額孔隙水壓隨時間消散,土壤壓密沉陷對樁引致之負摩擦力。首先探討兩種土壤組成模式(Porous elastic+Modified Drucker-Prager/Cap與Porous elastic+Critical state plasticity)模擬黏性土壤行為之適用性。繼則利用前人在曼谷黏土中所施作之負摩擦力現地試驗,採用Porous elastic +Critical state plasticity模式模擬樁基礎周圍土壤以建立負摩擦力分析模型。最後以所建立之分析模型進行一系列參數研究,探討在土壤滲透係數、樁土間界面摩擦係數及門檻剪位移量、地表載重、樁頭載重、群樁效應等不同樁土系統條件下樁受負摩擦力之反應。
樁頭荷載對於不同承載型式樁的負摩擦力行為有不同的影響。對於摩擦樁,樁頭荷載會降低樁所受的負摩擦力,其降低幅度隨著樁頭力愈大而愈顯著,中立點深度約在0.3-0.7倍樁長處。對於座落於堅實砂土層之點承樁,樁頭受載亦會使樁所受的負摩擦力降低,其降低幅度小於摩擦樁,中立點位置約在0.6-0.8倍樁長處。對於座落於極堅硬層上方之理想點承樁,由於中立點位置位於樁底,樁頭載重對其負摩擦力行為的影響不顯著。
考量樁之使用性,樁頭變位也是重要的設計因子。雖然對於摩擦樁,樁頭荷載能大幅減少負摩擦力大小,但樁頭變位亦是前述三種承載型式的樁中最大者,且在較大的樁頭力作用下,亦可能發生承載破壞。考量樁之使用性及所受之軸力大小,對於座落於堅實砂土層上方之點承樁,當受到樁頭力,一方面會有負摩擦力減小的效果,另一方面,由於底層土壤較黏土層具有較高之勁度與強度,因此較摩擦樁具有較小的樁頭變位,且在較大的樁頭力情況下樁底較不會發生承載破壞。
In this study, the finite element software ABAQUS is used to investigate the behavior of piles subjected to negative friction. Coupled consolidation analysis is used to simulate the dissipation of excess pore water pressure of soil with time and the soil consolidation-induced negative friction. Firstly, the applicability of two soil constitutive models (Porous elastic+Modified Drucker-Prager/Cap and Porous elastic+Critical state plasticity) to simulate clay behavior is investigated. Then, field negative friction tests on Bangkok clay are utilized to build the negative friction analysis model, in which the soil is modeled using Porous elastic+Critical state plasticity model. Eventually, the established analytical model is further applied to carry out a series of parametric analyses for exploring the negative friction behaviors under different pile-soil system conditions, including soil permeability coefficient, friction coefficient and threshold shear displacement of pile-soil interfaces, soil surcharge, pile-head loading and group pile effect.
The application of pile-head loading has different effects on negative friction behavior for piles with different end-bearing types. For friction piles, the pile-head loading will reduce the negative friction force, and the drgree of reduction is significant with increasing pile-head loading. The depth of neutral point is located between 0.3-0.7 times the pile length. For piles whose tip is on dense sand, the negative friction reduction is less than for the friction piles, and the depth of neutral point is located between 0.6-0.8 times the pile legth. For piles whose tip is on a hard layer, the pile-head loading has no significant effect since the neutral point is located at the pile base.
Considering the serviceability of pile, the pile-head displacement is also an important design factor. Although the pile-head loading can greatly reduce the negative friction of friction piles, their pile-head displacement is the largest among the above three types of end bearing piles and they even have bearing failure under large pile-head loads. Therefore, considering the pile displacement and axial force, for an end bearing pile on dense sand, it will sustain smaller negative friction when subjected pile-head loading; on the other hand, compared to a friction pile, it has a smaller pile-head displacement and less bearing failure will occur under large pile-head loading because of larger stiffness and strength of the bottom soil than those of clay.
誌謝 i
摘要 ii
ABSTRACT iii
目錄 iv
圖目錄 vii
表目錄 xv
一、 緒論 1-1
1.1 研究背景及目的 1-1
1.2 研究方法 1-2
1.3 研究內容 1-2
二、 文獻回顧 2-1
2.1 基樁負摩擦力現象 2-1
2.1.1 基樁負摩擦力之發生原因 2-1
2.1.2 基樁負摩擦力之大小及範圍 2-1
2.1.3 基樁負摩擦力之影響 2-2
2.2 國內現行規範之負摩擦力設計考量 2-2
2.2.1 單樁中立點位置估計 2-2
2.2.2 單樁摩擦力計算方式 2-3
2.2.3 單樁負摩擦力評估 2-4
2.2.4 群樁負摩擦力評估 2-4
2.3 基樁負摩擦力研究之發展 2-5
2.4 數值模擬研究方法 2-11
2.5 小結 2-12
三、 土壤元素試驗模擬 3-1
3.1 數值分析軟體介紹 3-1
3.2 土壤元素試驗模型建立 3-2
3.2.1 模型基本假設 3-2
3.2.2 材料組成模式 3-2
3.2.3 模型尺寸與邊界條件 3-7
3.2.4 網格切割 3-7
3.2.5 元素類型 3-8
3.2.6 模擬流程 3-8
3.3 土壤三軸試驗模擬對象介紹 3-9
3.4 土壤元素模型參數設定 3-10
3.4.1 Critical state plasticity模式 3-10
3.4.2 Modified Drucker-Prager/Cap模式 3-11
3.5 模擬結果 3-14
3.6 小結 3-16
四、 基樁負摩擦力模型建立與驗證 4-1
4.1 模擬對象與前人驗證研究之介紹 4-1
4.1.1 模擬對象試驗場址 4-1
4.1.2 現地監測結果 4-2
4.1.3 前人對此現地試驗模擬結果 4-2
4.2 基樁負摩擦力驗證模型建立 4-4
4.2.1 模型基本假設 4-4
4.2.2 材料組成模式 4-4
4.2.3 土層參數設定與初始狀態驗證 4-4
4.2.4 模型尺寸與邊界條件 4-6
4.2.5 網格切割 4-6
4.2.6 元素類型 4-6
4.2.7 樁土間界面元素之性質 4-7
4.2.8 模擬流程 4-8
4.3 模擬結果 4-9
4.3.1 土層邊界 土堤加載模型分析結果 4-9
4.3.2 土層邊界大小對結果之影響 4-9
4.3.3 滲透係數放大10倍之結果比較 4-11
4.3.4 土層邊界大小與滲透係數大小對結果影響之綜合比較 4-12
4.3.5 土層邊界 模型分析結果討論 4-13
4.3.6 全範圍加載模型分析結果 4-14
4.4 小結 4-15
五、 參數研究 5-1
5.1 參數分析模型 5-1
5.1.1 基準分析模型 5-1
5.1.2 模擬流程 5-2
5.1.3 模擬結果 5-2
5.1.4 與摩擦樁中立點理論公式比較 5-3
5.2 參數研究 5-3
5.2.1 探討土壤滲透係數之影響 5-3
5.2.2 探討樁土間界面摩擦係數之影響 5-4
5.2.3 探討樁土間界面門檻剪位移之影響 5-5
5.2.4 探討地表均佈載重大小之影響 5-5
5.2.5 探討不同樁頭受載大小之下地表載重大小之影響 5-7
5.2.6 探討樁頭力大小對於不同承載型式樁之影響 5-9
5.2.7 群樁受負摩擦力情況之分析 5-13
5.3 小結 5-15
六、 結論與建議 6-1
6.1 結論 6-1
6.2 建議 6-3
七、 參考文獻 7-1
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