BEARING MECHANISM OF TOP ARCH AND STABLE ARCH DESIGN METHOD FOR SURROUNDING ROCK OF UNDERGROUND CAVERNS
NIU Xinqiang1，DING Xiuli2
(1. Changjiang Institute of Survey，Planning，Design and Research，Changjiang Water Resources Commission，Wuhan，
Hubei 430010，China；2. Key Laboratory of Geotechnical Mechanics and Engineering of Ministry of Water Resources，
Yangtze River Scientific Research Institute，Wuhan，Hubei 430019，China)
Abstract：As restricted by project layout，geological and topographical conditions，the underground powerhouse of Three Gorges Project is arranged inside the mountain on right bank. The minimum thickness of rockmass over powerhouse is almost the same magnitude of powerhouse span. Obviously，it cannot meet the code?s requirement that overburden thickness of caverns should be not less than 2 times of the excavation span. For such shallowly buried underground cavern with large span and high sidewall，overburden thickness of rock mass is limited but initial geostress magnitude should be also taken into account. Therefore，the top arch stability is viewed as the primary issue that should be addressed. Based on rockmass structure and rock mass strength characteristics，and the concept that horizontal geostress controls surrounding rock stability，the bearing mechanism of surrounding rock at top arch area of underground cavern is studied. Definition of stable arch and its existence mechanical condition are presented. The method for determining stable arch of underground cavern is proposed as well. The feasibility of applying stable arch concept to determine overburden depth of underground cavern is analyzed. A methodology for stable arch design of overburden depth of shallowly buried underground cavern is then formed. It is revealed that surrounding rock at top arch area of underground powerhouse of Three Gorges Project possesses such stable arch formation conditions in terms of overburden depth and horizontal stress. Its minimum overburden thickness for stable arch formation is two-thirds of powerhouse span. The minimum and maximum values of horizontal lateral pressure coefficients for stable arch formation are 1.5 and 3.0，respectively. The proposed methodology was adopted in the arch design of underground powerhouse of Three Gorges Project. The observations of several years show that the surrounding rock at top arch area of underground powerhouse is stable，thus indicating that under given rock mass strength，rock mass structure and initial geostress conditions of Three Gorges Project，the overburden thickness determined by stable arch design methodology is appropriate and reliable. The surrounding rock stability and project safety can be both satisfied. The design of shallowly buried large scale caverns is therefore provided with reliable guidance.
钮新强1，丁秀丽2. 地下洞室围岩顶拱承载力学机制及稳定拱设计方法[J]. 岩石力学与工程学报, 2013, 32(4): 775-786.
NIU Xinqiang1，DING Xiuli2. BEARING MECHANISM OF TOP ARCH AND STABLE ARCH DESIGN METHOD FOR SURROUNDING ROCK OF UNDERGROUND CAVERNS. , 2013, 32(4): 775-786.
[1] 谷兆祺，彭守拙，李仲奎. 地下洞室工程[M]. 北京：清华大学出版社，1994：72–74.(GU Zhaoqi，PENG Shouzhuo，LI Zhongkui. Underground caverns engineering[M]. Beijing：Tsinghua University Press，1994：72–74.(in Chinese))
[2] 中华人民共和国行业标准编写组. SL266—2001水电站厂房设计规范[S]. 北京：中国水利水电出版社，2001.(The Professional Standards Compilation Group of People?s Republic of China. SL266—2001 Design code for hydropower house[S]. Beijing：China Water Power Press，2001.(in Chinese))
[3] 周述达. 长江三峡水利枢纽右岸地下电站招标设计报告[R]. 武汉：长江水利委员会长江勘测规划设计研究院，2004.(ZHOU Shuda. Tender design report for right bank underground powerhouse of Three Gorges Project on Yangtze River[R]. Wuhan：Changjiang Institute of Survey，Planning，Design and Research，Changjiang Water Resources Commission，2004.(in Chinese))
[4] 蔡美峰. 岩石力学与工程[M]. 北京：科学出版社，2002：330–336. (CAI Meifeng. Rock mechanics and engineering[M]. Beijing：Science Press，2002：330–336.(in Chinese))
[5] TERZAGHI K. Theoretical soil mechanics[M]. New York：John Wiley and Sons，Inc.，1943：66–76.
[6] EGGER P. Roof stability of shallow tunnels in isotropic and jointed rock[C]// Proceedings of the 5th ISRM Congress. [S. l.]：[s. n.]，1983：295–301.
[7] BARRY H G，BROWN E T. Rock mechanics：for underground mining[M]. 1st ed. London：George Allen and Unwin，1985：212–213.
[8] KOVARI K. Erroneous concepts behind the New Austrian Tunnelling Method[J]. Tunnels and Tunnelling，1994，(11)：38–41．
[9] BAE G J，SHIN H S，SICILIA C，et al. Homogenization framework for three-dimensional elastoplastic finite element analysis of a grouted pipe-roofing reinforcement method for tunnelling[J]. International Journal for Numerical and Analytical Methods in Geomechanics，2005，29(1)：1–24.
[10] 梁晓丹，刘 刚，赵 坚. 地下工程压力拱拱体的确定与成拱分析[J]. 河海大学学报：自然科学版，2005，33(3)：314–317.(LIANG Xiaodan，LIU Gang，ZHAO Jian. Definition and analysis of arching action in underground rock engineering[J]. Journal of Hohai University：Natural Sciences，2005，33(3)：314–317.(in Chinese))
[11] HUANG Z，BROCH E， LU M. Cavern roof stability—mechanism of arching and stabilization by rockbolting[J]. Tunnelling and Underground Space Technology，2002，17(3)：249–261.
[12] TSESARSKY M，HATZOR Y H. Tunnel roof deflection in blocky rock masses as a function of joint spacing and friction—a parametric study using discontinuous deformation analysis(DDA)[J]. Tunnelling and Underground Space Technology，2006，21(1)：29–45.
[13] HWANG J H，KIKUMOTO M，KISHIDA K，et al. Dynamic stability of multi-arch culvert tunnel using 3D FEM[J]. Tunnelling and Underground Space Technology，2006，21(3)：384–384.
[14] 邬爱清. 三峡工程中的岩石力学理论与实践[M]. 武汉：长江出版社，2009：661–670.(WU Aiqing. Theories and practices of rock mechanics in Three Gorges Project[M]. Wuhan：Changjiang Press，2009：661–670.(in Chinese))
2013, Vol. 32 
