FLAC耦合PFC2D應用於雙楔刀貫切破壞之初探

Coupled FLAC/PFC2D Numerical Simulation to Indentation Fracture in Rock by Double Wedge Indenters

江明軒(Ming-Hsuan Chiang)

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.2008.00228

摘要

近來隧道工程多採用機械開挖，故提升鑽掘效率與施工安全性同等重要。參考相關工程實務及理論分析中，機械開挖多以簡化貫切破壞試驗作為之探索刃口對地質材料之互制行為，由於數值軟體FLAC為連體力學之架構探究，其功能除探求材料破壞形式與變形外，且於模擬運算速度上較其他數值軟體為快，但其缺點為無法完整模擬出試體破壞後之行為，故本研究首先建立FLAC（有限差分法）與PFC2D（分離元素法）同步執行模擬運算之耦合機制，藉由PFC2D可顯示裂縫發展趨勢之優點進行雙楔形刃口正向貫入岩材之模擬，並與文獻相關試驗結果進行比對研析。
本研究採用花崗岩（Lac du Bonnet Granite）之高強度岩材進行模擬，以楔形刃口角度150°及變化雙刃口之間距進行貫壓之系列研析。數值結果可由傳統巨觀行為察知，雙刃口間距較大時（Sr 3），刃口下方之延、脆性破壞演化趨勢不受另一鄰近刃口影響；反之，則有其互制效應。當雙刃刀距超過此一臨界間距時，則可視為單一楔形刃口之貫切破壞模式。而在微觀方面可由PFC所得結果之觀察，其塑性區張、剪微裂縫發展亦受臨界間距之影響。
藉由上述研究可知，當雙刃間距逐漸靠近時，其所需引致貫切脆性破壞之能量將逐步上升至1倍。另外，相對刀距（Sr）之臨界值為3時，其開裂行為將受應力區重疊之影響使裂縫偏離中心軸往兩側延伸，由此得知此趨勢可提升鑽掘開挖之效益。綜合以上討論可知，適當之刀距安排除有助於機械開挖能量之減耗外，亦可提升開挖效率。

關鍵字

FLAC ； PFC ； 貫切破壞 ； 機械開挖

並列摘要

Many of the underground excavation and tunnel engineering projects were designed by using mechanical excavation in Taiwan currently due the concerns of excavating efficiency and the construction security. However, this type of cutting process is not quite clear yet in terms of its contact mechanism to break rock. After referring to some literature reviews, this study therefore simplifies this cutting problem as two normal wedge cutting tools indented into an intact rock to make a fragmentation due to brittle fracture. Meanwhile, a coupling numerical algorism by linking a finite different method, so-called FLAC for continuum solids, to another distinct element code, so-named PFC2D for discrete packing materials is established to investigate the effect of doubled-indenters on the indentation fracture in the quasi-brittle material.
By penetrating into a high strength rock, Lac du Bonnet granite without lateral confinement, two adjacent indenters with same wedge angle of 150° are used in this approach. By varying the relative space between these two indenters (Sr), which is defined by the real space between indenters over the critical plastic radius induced by a single indenter, the effect of doubled-indenters on the indentation fracture can be examined through monitoring the maximum indentation force and its corresponding penetration depth numerically. In viewing the macroscopic behavior, the ductile and brittle failure tendency is influenced insignificantly by another neighbor wedge as long as Sr is larger than 3. On the other hand, the fracture characteristics by a single indentation then would be affected by another one also. As the two adjacent indenters draws closely, the microscopic failure aspects including the critical plastic zone and the development of micro-cracks can be changed significantly. The critical relative space Sr,c can then be determined. Note that the absorbed energy during indentation can even increase as large as double when Sr,c is reaching or less. Moreover, when Sr is less than critical value of Sr,c, the more bias of the orientation of the crack initiation from the vertical axis occurs as decreasing Sr.
This study depicts a suitable spacing arrangement between indenters may reduce the energy required to break rock, and may improve the efficiency during real excavating. .

並列關鍵字

FLAC ； PFC ； Indentation fracture ； The machinery excavation

參考文獻

【1】 王紹宇，「分離元素法於接觸破壞之刀刃磨耗與雙刀效應之模擬暨耦合有限差分法之數值初探」，碩士論文，國立台北科技大學土木工程系，台北，2008。

【2】 李昶佑，「應用電子點紋干涉術探討岩石貫切過程之破壞演化及破裂特徵」，碩士論文，國立台北科技大學土木工程系，台北，2007。

【3】 林郁修，「分離元素法於岩石貫切破壞試驗之模擬分析」，碩士論文，國立台北科技大學土木工程系，台北，2007。

【6】 楊琳琰，「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」，碩士論文，國立台北科技大學土木工程系，台北，2007。

【10】 蘇億峰，「磨耗與邊界效應對岩石貫切破壞之數值模擬」，碩士論文，國立台北科技大學，台北，2008。