磨耗與邊界效應對岩石貫切破壞之數值模擬

Numerical Approach to the Effect of Wear Flat and Lateral Boundary Conditions on Indentation Fracture in Rock

蘇億峰(I-Feng Su)

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(2008年)

https://doi.org/10.6841/NTUT.2008.00536

摘要

山岳隧道之機械式開挖可提升營建自動化及工程安全性之成效，惟因鑽掘切削之力學機制仍屬渾濛，因此常因切削刀頭之不當耗損，引致機械開挖效率不彰；又台灣地質複雜多變，隧道開挖遭遇斷層、弱面機會大增。因此對於鑽掘機具、弱面位置與岩石破壞三者間互制機理，值得深入探討。
本研究乃以二維數值軟體FLAC進行模擬楔刀正向貫入岩材之平面應變問題，藉由改變：(1) 楔刀之不同磨耗(wear flat)特徵模擬切削刀具耗損之影響，(2) 楔刀貫切位置模擬接近岩材開口弱面之行為，及(3) 楔刀貫切位置模擬接近岩材閉合弱面之行為，並試圖由上述三課題與理論解、實驗數據進行相關比對研析。
由數值分析得知，隨楔刀磨耗增加，受測岩材產生臨界塑性區所需之最大貫切力因之增加，而臨界貫入深度微增，故材料韌度亦因之增加；再者，無側壓且具相同楔形刀角條件下，隨貫切位置漸次靠近側向自由邊界，其最大貫切力與相對應之臨界貫入深度有隨之下降的趨勢；而依相對力量比、能量比、塑性面積比受側向自由邊界影響之敏感程度，求驗特定貫切條件下之臨界轉換區；另於漸次靠近側向束制邊界之控制變數下，其最大貫切力與相對應之臨界貫入深度有隨之上升的趨勢。另在束制邊界之模擬可簡化解析雙刀效應；即求算某一臨界刀距下，其脆性破壞所需最大貫切力之變動範圍，探求單刀轉為雙刀之應力重疊行為。由此得知，適當之刀距安排應有助於機械開挖能量之減耗。

關鍵字

岩石貫切 ； 磨耗效應 ； 側向邊界 ； 雙刀效應

並列摘要

Mechanical excavation in underground tunneling construction improves automatic efficiency as well as engineering safety. The cutting process, however, needs to understand better such that the inappropriate abrasion due to cutter’s indentation and scratch can be reduced. Especially, the frequency meeting some discontinuous geological conditions under tunnel cutting, such as jointed rocks or faults is quite often. Therefore, the interaction between the cutter and the position of weak plane during cutting becomes important in studying the mechanism of rock fragmentation in Taiwan.
This study presents a numerical approach simulating a plane problem under the normal wedge indentation in rock. By investigating three parts: (1) the effect of wear flat of indenter on the cutting abrasion, (2) the response under changing the position of cutter distanced from lateral free boundary to simulate opened joint situation and/or ripple cutting behavior, (3) the response under changing the position of cutter distanced from lateral fixed boundary to simulate closed joint situation and/or double-cutter effect, the numerical results then compares with related theoretical solutions and experimental data.
This analytical approach shows that, as increasing the wear flat of indenter, the maximum indentation force needed to develop critical plastic zone increases and its corresponding critical penetration enlarges slightly. It means that the ductility/toughness of rock-like material increases with adding wear flat. Moreover, under same wedge angle of indenter without lateral confinement, the closer the distance between indenter and lateral free boundary, the less the maximum indentation force and critical penetration. The transit zone regarding the critical distance between indenter and lateral free boundary can be determined with respect to the indentation force ratio, energy ratio, as well as plastic region ratio. In addition, as near the distance between indenter and lateral fixed boundary, the more the maximum indentation force and critical penetration. The final simulation with regard to the lateral fixed boundary can also be employed to examine the double-cutter effect by monitoring a rapid increase of maximum indentation force due to stress overlap under a critical cutter-to-cutter space. It implies that a proper cutter array in front of the cutting machine may save energy during the tunnel excavation.

並列關鍵字

Normal wedge indentation fracture ； Abrasion effect ； Lateral boundary ； Double-cutter effect

參考文獻

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