本研究利用PFC2D軟體建立數值模式，選定四種不同覆岩深度(H=300、400、500、600 m)之圓形及馬蹄形隧道，於無節理岩盤中模擬隧道全斷面開挖且無支撐架設，在三種不同初始應力(K=0.5、1、2)作用下，開挖引致之力學行為探討。
研究結果顯示，馬蹄形主隧道開挖，K=1之鍵結拉力、鍵結壓力及顆粒合位移分布，受開挖面幾何形狀影響；K=0.5、2其分布主要受K值影響，其次為開挖面之幾何線型。其中最需要注意(危險)的是H=600、K=2之馬蹄形主隧道頂拱周遭，處置孔開挖使頂拱周遭之裂縫持續增加，其次為處置孔第二次降挖之底板周遭，裂縫垂直於最小主應力方向發展，形成三角形之破壞區。

In this study, the PFC2D code was used to explore the circular tunnel and horseshoe tunnel with four different overburden depths (H=300, 400, 500, 600 m).The tunnel was excavated in a hard rock (granite), and the whole section was excavated without support. The stress redistribution, displacement distribution and microcrack development during tunneling were analyzed under three different initial stresses (K=0.5, 1, 2).
The results show that the horseshoe main tunnel excavation, change of the micro bonding stress and particle displacement during tunneling are highly related different initial stresses and geometric linear shapes of Excavation face . The most need to pay attention to the roof of tunnel under K=2, the microcrack development in the three-stage tunnel excavation, has the maximum destruction area.

1. A. Lisjak, G. Grasselli, “A review of discrete modeling techniques for fracturing processes in discontinuous rock masses”, Journal of Rock Mechanics and Geotechnical Engineering (2014).
2. C.D. Martin, P.K. Kaiser, and D.R. McCreath., “Hoek–Brown parameters for predicting the depth of brittle failure around tunnels”, Can. Geotech. J. 36: 136–151 (1999)
3. D .O. Potyondy & P.A. Cundall, ”A bonded-particle model for rock”, International Journal of Rock Mechanics & Mining Science 41: 1329-1364. (2004).
4. E. Hoek , C.D. Martin, “Fracture initiation and propagation in intact rock e A review”, Journal of Rock Mechanics and Geotechnical Engineering (2014).
5. E. Hoek, and E.T. Brown, “Underground Excavations in Rock,” The Institution of Mining and Metallurgy, London, (1980).
6. E. T. Brown, “Rock CHARACTERIZTION TESTING & MONITORING ISRM Suggested Methods”, International Society for Rock Mechanics, pp.119-121, 125-127, (1981).
7. Itasca Consulting Group Inc. Particle Flow Code in Two Dimensions. Version 3.0., Itasca Consulting Group Inc., Minneapolis. (2004)
8. Nick Barton, Baotang Shen, “Risk of shear failure and extensional failure around over-stressed excavations in brittle rock,” Journal of Rock Mechanics and Geotechnical Engineering (2017).
9. R. E. Goodman, “Introduction to Rock Mechanics”, Second Ed, pp.90-91,226-228, John Wiley&Sons, New york,(1989).
10. Tomofumi Koyama, Lanru Jing,” Effects of model scale and particle size on micro-mechanical properties and failure processes of rocks—A particle mechanics approach”, Engineering Analysis with Boundary Elements Vol. 31, pp.458-472, Sweden (2007)
11. Xiaobin Ding, Lianyang Zhang, Hehua Zhu, Qi Zhang, “Effect of Model Scale and Particle Size Distribution on PFC3D Simulation Results”, Rock Mech Rock Eng, Vol. 47, pp.2139-2156, Austria, (2013)
12. 李宏輝，「砂岩力學行為之微觀機制-以個別元素法探討」，博士論文，國立臺灣大學土木工程研究所，台北，（2008）。

13. 陳冠州，「以PFC2D探討岩基加載之破壞演化」，碩士論文，國立台灣科技大學營建工程研究所，台北，（2012）。

14. 鄭文陵，「節理傾角變化對岩坡建物興建引致之裂縫發展探討」，碩士論文，國立台灣科技大學營建工程研究所，台北，（2014）。

15. 鄺寶山、王文禮(1993)，「FLAC程式於隧道工程之實例分析」，地工技術雜誌，第41期，第50-61頁。

16. 韓良蔚，「圓型隧道於無節理與一條節理岩盤中開挖引致之裂縫發展探討」，碩士論文，國立台灣科技大學營建工程研究所，台北，（2015）。

17. 羅科評，「於無節理及一條節理岩盤中隧道開挖引致之應力位移微觀發展探討」，碩士論文，國立台灣科技大學營建工程研究所，台北，（2016）。