臺灣博碩士論文加值系統

利用直接剪力試驗求取土壤的摩擦角是相當常見的方法，但傳統的直剪試驗不易觀察直剪盒內部在受剪過程的微觀破壞機制，且前人研究(Terzaghi、Peck，1948、Saada、Townsend，1981)提出直剪試驗在剪動面應力分布不均勻。因此，本研究利用離散元素法進行數值模擬，從中監測剪動過程直剪盒整體的應力分布與孔隙率，並分析剪動面上平均應力之變異程度，也針對剪動面特定區域觀察應力路徑與主應力平面角度旋轉情形。此外，以單一尺寸粒徑與顆粒堆加入顆粒群(clump)兩種方法，改善微觀參數提高到偏高之數值摩擦角也無法提高的現象。
由以上研究可知：(1)顆粒粒徑增大與加入顆粒群(clump)皆會提高摩擦角。(2)直剪模擬體積的剪脹多來自剪動帶。(3)剪應力尖峰值出現於剪動帶正中央。(4)以應力路徑來看，剪動帶正中央的應力分布比靠近邊界的應力狀態單純許多。(5)主應力平面旋轉角度從初始剪動到破壞時會逆時針旋轉約45度。(6)剪應力之變異係數遠大於水平與垂直應力之變異係數。

Direct shear test has been among common laboratory tests to obtain the engineering properties of soils, especially for dry granular soils. However, the microscopic behavior during direct shear test of this type of material is not always easy to monitor What’s more, the non-uniformity of the stress and strain can be developed along the failure plane have been brought up by several previous studies by Terzaghi and Peck (1948), Saada and Townsend (1981). Therefore, a discrete element method was employed to study the microscopic behavior of the dry granular material and understand the stress and porosity distribution during direct shear test. Variations of average stress, stress path and major principal plane along the pre-determined failure plane were also observed. Furthermore, even though the microscopic parameters gets unreasonable larger, the friction angle of the particle assembly only increases to a certain bounding value. In this study, the issue was solved by using particles with larger sizes and clump-models.
The following summaries are addressed：(1) It is to say that the larger friction angle can also be by using the lager particles and the clump. (2) The dilation of the overall particle assembly comes from the dilation of the particles in the shear zone. (3) The maximum shear stress occurs in the middle of the pre-determined failure plane. (4)From the result of the stress path, the stress state in the middle of the shear plane is less complicated than that close to the edge of the shear box. (5) The directions of major principal plane are various between horizontal and 45 degrees in the counterclockwise direction until the test specimen has reached failure. (6)The coefficient of variation of the horizontal and vertical stress is much smaller than the shear stress.

目錄
第一章 緒論 1
1.1 研究動機及目的 1
1.2 研究內容 3
第二章 文獻回顧 5
2.1 離散元素法 5
2.1.1 PFC2D模擬概述 7
2.1.2二維模擬的限制 7
2.1.3應力與應變概述 8
2.1.4顆粒之質量計算方式 8
2.2建模步驟 9
2.2.1問題定義 9
2.2.2建立物理模型概念圖 9
2.2.3建立以及模擬簡單模型 10
2.2.4蒐集顆粒堆所需相關數據 10
2.2.5準備細部模型模擬 11
2.2.6數值分析測試 12
2.2.7現有結果的解釋 12
2.3觀測圓原理 13
2.3.1孔隙率計算 14
2.3.2應力計算 14
2.3.3應變率計算 17
2.4直剪試體內部應力分布情形 20
2.5使用離散元素法進行乾砂直剪試驗模擬 22
2.5.1直剪試驗模擬 22
2.5.2分析結果 23
2.5.3剪動帶的微觀機制 24
2.5.4結果整理 28
2.6直剪之物理試驗與數值模擬比較 28
第三章 研究方法 31
3.1 實驗室直接剪力試驗 31
3.2 模擬之模型 34
3.2.1設定參數 34
3.2.2顆粒填入 36
3.2.3設置觀測項目 41
3.2.4加載正向力 43
3.2.5剪動模擬速度的決定 44
3.3決定顆粒微觀參數 44
3.4 觀測圓直剪盒內應力分布情形 47
3.4.1觀測圓半徑 47
3.4.2觀測圓在直剪盒內的設置 52
3.4.3 觀測圓讀取的數據整理 54
3.5 直剪盒內應力路徑 59
3.5.1分析模型 59
3.5.2各種加載條件之下的應力路徑圖 59
3.5.3計算模擬剪動過程的應力路徑 61
3.6 分析項目與模型及微觀參數對照表 61
第四章 直剪模擬試驗結果 63
4.1基本結果 63
4.1.1模擬結果探討 63
4.1.2模擬結果展示 68
4.1.3改變微觀參數之影響 70
4.2 不同顆粒組成的模型 72
4.2.1加入顆粒群(clump) 72
4.2.2不同顆粒半徑模型對摩擦角的影響 73
4.2.3單一顆粒、兩顆顆粒群以及三顆顆粒群的影響 75
4.3結果整理 76
第五章 直剪過程中微觀組構以及應力分布 78
5.1概述 78
5.2孔隙率 82
5.3直剪盒內應力分布情形 85
5.3.1剪動前應力分布情形 85
5.3.2剪動位移達破壞一半時應力分布情形 91
5.3.3破壞時應力分布情形 96
5.4 應力路徑與主應力平面旋轉角度 101
5.4.1剪動帶的應力路徑 101
5.4.2最大主應力平面旋轉角度 106
5.5 剪動帶之平均應力 108
第六章 114
6.1 結論 114
6.2 未來展望 116
參考文獻 117
附錄 119

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