應用個別元素法探討人造岩石裂隙延伸行為

Using distinct element method to analyze fracture propagation behaviors of artificial rock

黃百懃(Pai-Chin Huang)

指導教授 ： 鄭富書

國立臺灣大學/工學院/土木工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.02644

摘要

裂隙的延伸發展為研究材料破裂行為之重要課題。材料受外力作用時，常於材料既存裂隙處發生應力集中現象，當裂隙周圍之集中應力大於材料強度時，裂隙周圍將發生局部破壞導致裂隙的延伸與發展，進而造成整體破壞。台灣地處板塊聚合帶，岩體多有不連續面，不連續面存岩體中可視為岩石材料中之預裂隙，對於岩體強度影響甚鉅。若能掌握並預測岩體在不同的應力態條件下既有裂隙如何發展與延伸，對於岩石邊坡穩定之工程實務問題，與地震相關之防災課題將有直接之助益。
有鑒於含裂隙之天然岩材取樣不異、岩材組成具變異性、實驗條件控制不易且裂隙觀察困難等，故本研究採數值方法進行裂隙延伸行為之研究。研究工具採個別元素法為理論基礎之顆粒流分析軟體進行數值模擬與分析，相較於連續體分析模式，個別元素法具有元素可分離的優勢，符合本研究對於裂隙延伸行為探討之需求。
為取得數值模擬所需之微觀參數與驗證對象。本研究以石膏製成人造岩石，進行單軸壓縮試驗與巴西人法間接張力試驗，再透過含有貫穿試體中心之預裂隙的圓盤試體(Central through Cracked Brazilian Disk，CCBD)，進行破裂力學實驗。微觀參數取得與數值建模流程驗證完成後，最終進行雙軸應力狀態下含預裂隙人造岩石之裂隙延伸行為的數值模擬，並探討不同側向壓力值與預裂隙幾何配置對於裂隙延伸行為之影響。分析結果顯示，側向壓力對於裂隙延伸行為有極大的影響。當側向壓力較高時，延伸裂隙之發展除受到抑制外，次要裂隙發展的方向介於低側向壓力時延伸裂隙的方向與預裂隙的方向，且破裂涵蓋的區域較集中於預裂隙附近，形成之破裂線條較寬；當側向壓應力值大於單壓強度之半，沿預裂隙方向之裂隙延伸行為不明顯，破壞集中於預裂隙所在之水平向帶狀範圍內。

關鍵字

裂隙延伸 ； 裂隙連通 ； 個別元素法 ； 雙軸應力 ； 人造岩石

並列摘要

The fracture propagation behavior plays an important role in material cracking. When compressed by external forces, stress concentration usually occurs near the pre-exist cracks. As concentration stress exceeds the strength of the material, local failure near the cracks can induce further extensions and development of the cracks, which could subsequently induce global failure. Due to the strong orogeny, the rock mass in Taiwan is plenty of discontinuities. The discontinuities, which are perceived as the pre-existing cracks in rock mass, can affect the strength of the rock mass. In this research, the pattern of fracture propagation behaviors of artificial rocks with pre-existing cracks under biaxial loading was discussed base on numerical analysis of data collected from lab simulation.
The numerical simulation is executed by the distinct element method (DEM) based software, Particle Flow Code 2D (PFC2D). DEM was preferred to continuous system analysis in simulating the fracture behaviors since the former possesses the advantage of particle separation.
In order to acquire the parameters for PFC2D simulating and verification the PFC2D results, artificial rocks are made to apply the uni-axial compression test, the Brazilian disk test and the Central through Cracked Brazilian Disc test(CCBD). When the verification completed, the parameter is applied in the simulation of the fracture propagation behaviors of pre-existing crack artificial rock sample under biaxial loading. The effect of lateral stress and geometry of pre-existing cracks was discussed. According to the simulation results, the lateral stress caused a great influence on fracture propagation behaviors. The following phenomena were found under high lateral stress level:
1. The development of wing crack was restrained.
2. The direction of secondary crack was veered. The new direction was between the direction of the pre-existing crack and the direction of the wing crack under lower stress level.
3. If the lateral stress were half as large as the uni-axial compression strength, the fracture propagation behaviors along the pre-existing crack was not obvious. The broken zone was bounded in the horizontal direction of the pre-existing cracks.
4. The fracture propagation behavior was not obvious under higher lateral stress level. The broken area was concentrated near the pre-exist cracks and formed broad fracture lines.

並列關鍵字

fracture propagation ； fracture coalescence ； DEM ； biaxial loading ； artificial rocks

參考文獻

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