岩石於正向貫切破壞試驗之數值模擬－以單一楔形刃口為例

Numerical modeling of normal indentation fracture of rock by a single wedge-shaped tool with lateral confinement

楊琳琰(Lin-Yan Yang)

指導教授 ： 陳立憲

國立臺北科技大學/工程學院/土木與防災研究所/碩士(2007年)

https://doi.org/10.6841/NTUT.2007.00071

摘要

依隧道與地下結構機械開挖之文獻可知，於相關工程實作及其理論分析上，多以貫切破壞試驗作簡化模擬以探索開挖機具之刃口對室內試體或室外實務施作之可挖性（cuttability）及其效率影響。鑑於楔形貫切破壞試驗之理論乃以二維之平面應變為分析模式，因此本研究以FLAC進行單一楔形刃口正向貫入於岩材之數值模擬，並配合孔洞擴展模式（Cavity Expansion Model, CEM）之理論進行研究。
本研究以大理岩試體進行數值模擬貫切破壞試驗，而相關變數為：（a）楔形刃口角度（α=90°、120°及150°）；及（b）水平側向圍壓( =0、5、10、20及30MPa)。從傳統巨觀角度可知，當楔形刃口角度越大時，材料延性或脆性破壞所需之最大貫切力增加及貫入深度隨之減少。再者，隨水平側向圍壓增加時，最大貫切力隨之增加，惟相對應之標稱貫切壓力則無增長趨勢；而其塑性區發展由密閉式形狀轉換為開放式；隨水平側向圍壓增大，最大張應力方向角 從2°增至58°。最後數值所求得無因次化之標稱貫切壓力p/q及無因次化之臨界塑性區半徑ξ*，再與理論解、實驗值比對顯示，數值結果落於理論解上下限範圍內，可驗證本研究之適確性。

關鍵字

貫切破壞試驗 ； 有限差分法 ； 孔洞擴展模式 ； 標稱貫切壓力.

並列摘要

To understand the in-depth mechanism of the cuttability and efficient cutting in underground excavation, literature review shows that the wedge indentation fracture test is a crucial way to examine. This study, based on the plane problem of indentation fracture theory, models the normal wedge indentation of rock using FLAC and compares numerical results with the Cavity Expansion Model (CEM).
In this investigation, the variables of numerical model are as below: (a) the wedge angles (α= 90°、120°及150°) and (b) the lateral confinement ( = 0、5、10、20及30MPa). In the view point of the macro-scope, the results show that the maximum indentation force increases and its corresponding indentation depth decreases with the increase in wedge angle. In other hand, when the lateral confinement increase, both the maximum indentation force and its corresponding indentation depth increases. However, nominal indentation pressure does not change significantly as increasing confinement. Besides, the shape of plastic zone depicts a transform from the closed mode to opened mode as the relative confinement increases up to 0.2, and the inclined angle (θ) between the critical tensile strength and the neutral axis increases in the range of 2°~58°with the increase in confinement.
At last, both numerical dimensionless indentation pressure (p/q) and dimensionless critical radius (ξ*) are estimated and compared with the experimental results as well as the analytical solutions adopted from CEM. Good agreement was found between the simulation and previous literature review in terms of p/q and ξ*. Therefore, this study proves that the suitability of the numerical solutions for indentation fracture.

並列關鍵字

Normal wedge indentation fracture test ； Finite difference program ； Cavity Expansion Model(CEM) ； Nominal indentation pressure.

參考文獻

文，國立台灣科技大學營建工程系，台北，2006。

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