CORING-INDUCED UNLOADING DAMAGE TO ROCK SAMPLES UNDER HIGH STRESS CONDITION AND ITS IMPACT ON ROCK STRENGTH
YAN Peng1，2，LU Wenbo1，2，CHEN Ming1，2，LI Tao1，2，ZHOU Chuangbing1，2
(1. State Key Laboratory of Water Resources and Hydropower Engineering Science，Wuhan University，Wuhan，Hubei 430072，China；2. Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering of Ministry of Education，
Wuhan University，Wuhan，Hubei 430072，China)
Abstract：The reasonable and accurate evaluation of deep rock strength has great importance on forecasting and controlling rock bursts and other dynamic geological disasters during excavation. Aiming at the problems of rock sample damage induced by coring-induced unloading，the damage zones and extent of rock samples under different stress levels are studied through numerical simulation and field sampling and indoor experiments. The results of numerical simulation and the corediscing phenomenon both confirm that the stress relieving sampling scheme suggested in this paper is effective，which can reduce stress of the sampling area by about 30%；and make it possible to core rock sample under different stress levels in same place. According to the result of the compaterized tomography(CT) scanning of the rock samples obtained from tunnels of Jinping II hydropower station with a buried depth of 1 900 m，unloading-induced damage extent may exceed 50% of the whole section of rock samples. The average uniaxial strengths of the rock samples by means of low stress sampling and over-coring increase by approximately 5% to 15% than conventional sampling under high stress condition and over-coring，with an average of about 8%；so the influence of coring-induced unloading damage on rock strength can?t be ignored. And the number of acoustic emission events of the former at early loading stage is significantly less than the latter，which indicates that the coring-induced unloading damage can?t be eliminated completely even by over-coring；and this result is in accordance with that of CT scanning.
严 鹏1，2，卢文波1，2，陈 明1，2，李 涛1，2，周创兵1，2 . 高应力取芯卸荷损伤及其对岩石强度的影响[J]. 岩石力学与工程学报, 2013, 32(4): 681-688.
YAN Peng1，2，LU Wenbo1，2，CHEN Ming1，2，LI Tao1，2，ZHOU Chuangbing1，2. CORING-INDUCED UNLOADING DAMAGE TO ROCK SAMPLES UNDER HIGH STRESS CONDITION AND ITS IMPACT ON ROCK STRENGTH. , 2013, 32(4): 681-688.
[1] 何满潮，谢和平，彭苏萍，等. 深部开采岩体力学研究[J]. 岩石力学与工程学报，2005，24(16)：2 803–2 813.(HE Manchao，XIE Heping，PENG Suping，et al. Study of rock mechanics in deep mining engineering[J]. Chinese Journal of Rock Mechanics and Engineering，2005，24(16)：2 803–2 813.(in Chinese))
[2] 王明洋，周泽平，钱七虎. 深部岩体的构造和变形与破坏问题[J]. 岩石力学与工程学报，2006，25(3)：448–455.(WANG Mingyang，ZHOU Zeping，QIAN Qihu. Tectonic，deformation and failure problems of deep rock mass[J]. Chinese Journal of Rock Mechanics and Engineering，2006，25(3)：448–455.(in Chinese))
[3] SHAN Z G，YAN P. Management of rock bursts during excavation of the deep tunnels in Jinping II hydropower station[J]. Bulletin of Engineering Geology and the Environment，2010，69(7)：353–363.
[4] 褚卫江. 深埋条件下隧洞围岩稳定与结构安全评估[R]. 杭州：中国水电工程顾问集团华东勘测设计研究院，2009.(ZHU Weijiang. Safety assessment of surrounding rocks and structures of deep tunnels[R]. Hangzhou：HydroChina Huadong Engineering Corporation，2009.(in Chinese))
[5] 赵兴东，唐春安，李元辉，等. 花岗岩破裂全过程的声发射特性研究[J]. 岩石力学与工程学报，2006，25(增2)：3 673–3 678.(ZHAO Xingdong，TANG Chun′an，LI Yuanhui，et al. Study on AE activity characters under uniaxial compression loading[J]. Chinese Journal of Rock Mechanics and Engineering，2006，25(Supp.2)：3 673–3 678. (in Chinese))
[6] DYKE C G. Core discing：its potential as an indicator of principal in situ stress directions[C]// MAURY V，FORMAINTRAUX D，ed. Rock at Great Depth. Rotterdam：A. A. Balkema，1989：1 057.
[7] CARLSON S，WANG H. Microcrack porosity and in situ stress in Illinois Borehole UPH–3[J]. Journal of Geophysical Research，1986，91(B10)：10 421–10 428.
[8] CHARLEZ P，HAMAMDJIAN C，DESPAX D. Is the microcracking of a rock a memory of its initial state of stress?[C]// Proceedings of International Symposium on Rock Stress and Rock Stress Measurements. Stockholm：[s. n.]，1986：341–50.
[9] HOLT R M，BRIGNOLI M，KENTER C J. Core quality：quantification of coring-induced rock alteration[J]. International Journal of Rock Mechanics and Mining Sciences，2000，37(6)：889–907.
[10] KENTER C J，BRIGNOLI M，HOLT R M. CMS(constant mean stress) vs UCS(unconfinned strength) tests：a tool to reduce core damage effects[J]. International Journal of Rock Mechanics and Mining Sciences，1997，34(3/4)：129.e1–129.e11.
[11] BRIGNOLI M，FANUEl P，HOLT RM，et al. Effects on core quality of a bias stress applied during coring[C]// Proceedings of EUROCK?98. [S. l.]：[s. n.]，1998：301.
[12] WITHJACK E M. Computerized Tomography for rock property determination and fluid flow visualization[J]. Society of Petroleum Engineers Formation Evaluation，1988，3(4)：696–704.
[13] 杨更社，谢定义，张长庆，等. 岩石损伤特性的CT识别[J]．岩石力学与工程学报，1996，15(1)：48–54.(YANG Gengshe，XIE Dingyi，ZHANG Changqing，et al. CT identification of rock damage properties[J]. Chinese Journal of Rock Mechanics and Engineering，1996，15(1)：48–54.(in Chinese))
[14] 葛修润，任建喜，蒲毅彬，等. 煤岩三轴细观损伤演化规律的CT动态试验[J]. 岩石力学与工程学报，1999，18(5)：497–502.(GE Xiurun，REN Jianxi，PU Yibin，et al. A real-time CT triaxial testing study off meso-damage evolution law of coal[J]. Chinese Journal of Rock Mechanics and Engineering，1999，18(5)：497–502.(in Chinese))
[15] 丁卫华，仵彦卿，蒲毅彬，等. 低应变率下岩石内部裂纹演化的X射线CT方法[J]. 岩石力学与工程学报，2003，22(11)：1 793–1797. (DING Wiehua，WU Yanqing，PU Yibin，et al. X-ray CT approach on rock-interior crack evolution under low strain rate[J]. Chinese Journal of Rock Mechanics and Engineering，2003，22(11)：1 793–1 797.(in Chinese))
[16] 周火明，杨 宇，张宜虎，等. 多裂纹岩石单轴压缩渐进破坏过程精细测试[J]. 岩石力学与工程学报，2010，29(3)：465–470.(ZHOU Huoming，YANG Yu，ZHANG Yihu，et al. Fine test on progressive fracturing of multi-crack rock samples under uiniaxial compression[J]. Chinese Journal of Rock Mechanics and Engineering，2010，29(3)：465–470.(in Chinese))
2013, Vol. 32 
