利用個別元素法分析人造岩石之裂隙延伸及力學行為

Using DEM to Analyze Crack Extension and Mechanical Behavior of Artificial Rock

陳耀榮(Yao-Rong Chen)

指導教授 ： 鄭富書

共同指導教授 ： 李宏輝

國立臺灣大學/工學院/土木工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01385

摘要

自二戰以後，裂隙力學的發展漸趨完整。在岩石工程的領域上，裂隙的存在對岩體的強度有著重要的影響性，因此裂隙的延伸發展為研究材料破裂行為之重要課題。當岩石材料受外力作用引致破壞之破壞機制非由岩體的材料強度控制，而是由於岩體本身所含既有裂隙存在應力集中現象，導致岩體由既有裂隙延伸破壞，其破壞強度及破壞行為將迥異於完整岩塊的破壞行為。不同的破壞行為，在工程上無法以岩石力學來做分析、設計。以地質構造角度來看，台灣位於造山運動劇烈之板塊交接帶，由於菲律賓海板塊不斷的推擠歐亞大陸板塊，使得台灣本島的斷層密集，在板塊推擠持續作用下，斷層受力再錯動時，將順著原有的斷層線繼續發展延伸。有鑑於此，如能了解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在邊坡維護及地震相關之防災課題將有直接之助益。
然而岩石試體取得不易加上實驗儀器之限制，無法透過實驗室的力學實驗探求岩體的破壞行為。隨著計算機硬體運算能力的提升，以數值分析輔助研究已成為一趨勢，以往廣泛被使用之連續體分析方法在諸多研究領域皆受到重用。然而連續體分析方法在破裂模擬應用上有其限制，在材料受力後之大變形及裂隙發展延伸模擬，個別元素法(Distinct Element Method, DEM)能得到更好之結果。
本研究將先就實驗室力學試驗所得結果對數值模型做驗證，確認參數而後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。結果顯示，側向壓力對於裂隙延伸行為有顯著的影響。以較高圍壓狀況而言，試體單預裂隙破壞延伸行為與低圍壓狀態的預延伸行為截然不同，預裂隙發展將由垂直預裂隙方向向外延伸。雙預裂隙情況下，圍壓與預裂隙幾何配置均會影響裂隙連通現象，個別預裂隙之延伸行為會接近受同樣圍壓條件之試體，雙預裂隙之距離達到一定程度後，兩裂隙在不同圍壓之行為大不相同。

關鍵字

裂隙延伸 ； 個別元素法 ； 雙軸應力 ； 數值分析 ； 破裂力學

並列摘要

Since World War II, the development of fracture mechanics is becoming complete. In the rock engineering field, fracture plays an important role on rock strength, so crack propagation is a big issue for studying fracture behavior of material. When the rock material damage is caused not by material strength but stress concentration of the pre-exist cracks, it becomes different from intact rock on failure strength and failure behavior, so rock mechanics can not help us do the analysis, design on engineering.
On the side of geology, 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 view of this, it is benefit to know the pattern of fracture propagation behaviors of artificial rocks with pre-existing cracks under biaxial loading for earthquake disaster prevention.
This study was based on numerical analysis of data collected from laboratory test. The numerical simulation is executed by the distinct element method (DEM) based software, Particle Flow Code 2D.
In order to acquire the parameters for PFC2D simulating and verification the PFC2D results, this study refers to data of artificial rocks are made to apply the uni-axial compression test, the Brazilian disk test and the Central through Cracked Brazilian Disc test(Huang, 2010).
According to the simulation results, the lateral stress caused a great influence on fracture propagation behaviors. Behavior of specimen with single pre-exist crack is different between high and low confining pressure. 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 coalescence ； distinct element method ； biaxial loading ； numerical simulation ； fracture mechanics

參考文獻

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