端部岩桥直剪破坏试验及断裂条件
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摘要
以重庆鸡尾山岩质滑坡为代表的前缘"关键块体"型滑坡具有较强的隐蔽性,研究"关键块体"前缘锁固段岩桥的破坏性质对滑坡预警具有重要意义。以鸡尾山滑坡地质条件为基础,在岩样端部预制不同长度边缘裂缝,填入软弱材料,形成软弱夹层节理,在不同法向压力下进行直剪试验,分析了前缘端部岩桥的裂纹扩展规律、块体剥落特征信息和岩桥断裂条件,提出了临滑阶段剪应力变化率k值。试验结果表明:软弱夹层节理长度对岩桥破坏模式和块体剥落剧烈程度有重要影响,且端部岩桥越长,破坏前临滑阶段剪应力增速k值越小。端部岩桥破坏模式为剪切破坏、拉剪破坏和张拉破坏,且不同破坏模式决定了相同节理岩桥块体剥落的剧烈程度。岩桥块体剥落点与破坏点剪应力比值百分数平均值为79.5%～92.2%,且端部岩桥临滑阶段时间快慢依次为短节理慢、中间节理居中和长节理快。端部岩桥3种破坏模式满足一定断裂条件,且呈现出3个阶段和裂纹稳定扩展。通过本直剪试验研究揭示的端部岩桥破坏特征信息和断裂条件,可对前缘"关键块体"锁固段型岩质边坡失稳破坏评价提供理论依据。
Since the Jiweishan landslide in Chongqing in the front edge of the "key block" is of certain concealment, it is of significance for the early warning of landslide to study the failure property the rock bridge in the front locking section of "key block". Based on the geological condition of Jiweishan, after prefabricating different length edge cracks, infilling soft materials and forming the joints of soft interlayer at the ends of the sample, direct shear tests were conducted on the prepared samples under different confining pressures. The propagation rules of crack, the characteristic information of the block spalling and the fracture condition of the rock bridge were analysed and the k value of changed rate of shear stress was proposed in a would-be sliding stage. The length of joint of the soft interlayer has a certain effect on the failure modes and the extent of block spalling, and the longer the end of rock bridge is, the smaller the k value of the growth rate of the shear stress is. The failure modes of the rock bridge at the end include shear failure, tensile-shear failure and tensile failure, however the extent of block spalling of the same joint is different under varied coalescent modes. The ratio of shear stress of spalling point to that of failure point is in the range of 79.5%-92.2%. The short joint is slower than the middle joint, but the long joint is faster than the middle joint in the time of would-be sliding stage. The three types of failure modes of the end rock bridge meet certain fracture conditions and present three stages and the crack growth stably. The conducted direct shear tests reveal the failure and characteristic information of rock bridge at the end and the fracture condition, and thus this study can provide a theoretical basis for the instability and failure estimate of the rock slope containing the front edge of the locking section which is called "key block".
Since the Jiweishan landslide in Chongqing in the front edge of the "key block" is of certain concealment, it is of significance for the early warning of landslide to study the failure property the rock bridge in the front locking section of "key block". Based on the geological condition of Jiweishan, after prefabricating different length edge cracks, infilling soft materials and forming the joints of soft interlayer at the ends of the sample, direct shear tests were conducted on the prepared samples under different confining pressures. The propagation rules of crack, the characteristic information of the block spalling and the fracture condition of the rock bridge were analysed and the k value of changed rate of shear stress was proposed in a would-be sliding stage. The length of joint of the soft interlayer has a certain effect on the failure modes and the extent of block spalling, and the longer the end of rock bridge is, the smaller the k value of the growth rate of the shear stress is. The failure modes of the rock bridge at the end include shear failure, tensile-shear failure and tensile failure, however the extent of block spalling of the same joint is different under varied coalescent modes. The ratio of shear stress of spalling point to that of failure point is in the range of 79.5%-92.2%. The short joint is slower than the middle joint, but the long joint is faster than the middle joint in the time of would-be sliding stage. The three types of failure modes of the end rock bridge meet certain fracture conditions and present three stages and the crack growth stably. The conducted direct shear tests reveal the failure and characteristic information of rock bridge at the end and the fracture condition, and thus this study can provide a theoretical basis for the instability and failure estimate of the rock slope containing the front edge of the locking section which is called "key block".
引文
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[19]李世愚,和泰名,尹祥础,等.岩石断裂力学导论[M].合肥:中国科学技术大学出版社,2010.LI Shi-yu,HE Tai-ming,YIN Xiang-chu,et al.The introduction of rock fracture mechanics[M].Hefei:University of Science and Technology of China Press,2010.
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[2]刘远明,夏才初.直剪条件下非贯通节理岩体岩桥力学性质弱化机制及贯通模型初步研究[J].岩石力学与工程学报,2010,31(3):695-701.LIU Yuan-ming,XIA Cai-chu.Weakening mechanism of mechanical behaviors and failure models of rock mass containing discontinuous joints under direct shear condition[J].Chinese Journal of Rock Mechanics and Engineering,2010,31(3):695-701.
[3]刘远明,夏才初.基于岩桥力学性质弱化机制的非贯通节理岩体直剪试验研究[J].岩石力学与工程学报,2010,29(7):1467-1472.LIU Yuan-ming,XIA Cai-chu.Research on rock mass containing discontinuous joints by direct shear test based on weakening mechanism of rock bridge mechanical properties[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(7):1467-1472.
[4]赵延林,彭青阳,万文,等.直剪作用下不共面断续节理岩桥破断试验与数值研究[J].土木建筑与环境工程,2014,36(1):59-66.ZHAO Yan-lin,PENG Qing-yang,WAN Wen,et al.Experimental and numerical analysis on rupture of rock bridge with non-coplanar intermittent joints under direct shear[J].Journal of Civil,Architectural&Environmental Engineering,2014,36(1):59-66.
[5]刘顺桂,刘海宁,王思敬,等.断续节理直剪试验与PFC2D数值模拟分析[J].岩石力学与工程学报,2008,27(9):1828-1836.LIU Shun-gui,LIU Hai-ning,WANG Si-jing,et al.Direct shear tests and PFC2D numerical simulation of intermittent joints[J].Chinese Journal of Rock Mechanics and Engineering,2008,27(9):1828-1836.
[6]蒋明镜,刘蔚,孙亚,等.考虑环境劣化非贯通节理岩体的直剪试验离散元模拟[J].岩土力学,2017,38(9):2728-2736.JIANG Ming-jing,LIU Wei,SUN Ya,et al.Discrete element simulation of direct shear test on rock mass containing discontinuous joints with environmental degradation[J].Rock and Soil Mechanics,2017,38(9):2728-2736.
[7]白世伟,任伟中,丰定祥,等.平面应力条件下闭合断续节理岩体破坏机制及强度特性[J].岩石力学与工程学报,1999,18(6):635-640.BAI Shi-wei,REN Wei-zhong,FENG Ding-xiang,et al.Failure mechanism and strength properties of rockmass containing close intermittent joints under plane stress condition[J].Chinese Journal of Rock Mechanics and Engineering,1999,18(6):635-640.
[8]任伟中,白世伟,丰定祥.平面应力条件下闭合断续节理岩体力学特性试验研究[J].实验力学,1999,14(4):520-527.REN Wei-zhong,BAI Shi-wei,FENG Ding-xiang.An experimental study on the mechanical characteristics of rockmass containing close intermittent joints under plane stress condition[J].Journal of Experimental Mechanics,1999,14(4):520-527.
[9]张国峰,陈国庆,敖昌啟,等.不同宽度岩桥节理岩体直剪试验研究[J].铁道建筑,2015,(11):81-91.ZHANG Guo-feng,CHEN Guo-qing,AO Chang-qi,et al.Direct shear test study on rock mass with rock bridge joints featuring different width[J].Railway Engineering,2015,(11):81-91.
[10]GEHLE C,KUTTER H K.Breakage and shear behavior of intermittent rock joints[J].International Journal of Rock Mechanics and Mining Sciences,2003,40(5):687-700.
[11]LAJTAI E Z.Shear strength of weakness planes in rock[J].International Journal of Rock Mechanics and Mining Sciences&Geomechanics Abstracts,1969,6(5):499-515.
[12]LAJTAI E Z.Strength of discontinuous rocks in direct shear[J].Geotechnique,1969,19(2):218-233.
[13]WONG R H C,CHAU K T,TSOI P M,et al.Pattern of coalescence of rock bridge between two joints under shear loading[C]//International Congress on Rock Mechanics.Rotterdam:A.A.Balkema,1999:735-738.
[14]SAVILABTI T,NORDLUND E,STEPANSSION O.Shear box testing and modelling of joint bridge[C]//Proceedings of the International Symposium on Rock Joints.Rotterdam:A.A.Balkema,1990:295-300.
[15]冯振,殷跃平,李滨,等.重庆武隆鸡尾山滑坡视向滑动机制分析[J].岩土力学,2012,33(9):2704-2712.FENG Zhen,YIN Yue-ping,LI Bin,et al.Mechanism analysis of apparent dip landslide of Jiweishan in Wulong,Chongqing[J].Rock and Soil Mechanics,2012,33(9):2704-2712.
[16]许强,黄润秋,殷跃平,等.2009年6.5重庆武隆鸡尾山崩滑灾害基本特征与成因机制初步研究[J].工程地质学报,2009,17(4):433-444.XU Qiang,HUANG Run-qin,YIN Yue-ping,et al.The Jiweishan landslide of June 5,2009 in Wulong,Chongqing:Characteristics and failure mechanism[J].Journal of Engineering Geology,2009,17(4):433-444.
[17]刘远明,夏才初.非贯通节理岩体直剪贯通模型和强度研究[J].岩土工程学报,2006,28(10):1242-1247.LIU Yuan-ming,XIA Cai-chu.Study on models and strength behavior of rock mass containing discontinuous joints in direct shear[J].Chinese Journal of Geotechnical Engineering,2006,28(10):1242-1247.
[18]刘远明.基于直剪试验的非贯通节理岩体扩展贯通研究[D].上海:同济大学,2007.LIU Yuan-ming.Study of failure models and strength of rockmass containing discontinuous joints indirect shear test[D].Shanghai:Tongji University,2007.
[19]李世愚,和泰名,尹祥础,等.岩石断裂力学导论[M].合肥:中国科学技术大学出版社,2010.LI Shi-yu,HE Tai-ming,YIN Xiang-chu,et al.The introduction of rock fracture mechanics[M].Hefei:University of Science and Technology of China Press,2010.
[20]孙逊方,方孝淑,关来泰,等.材料力学[M].北京:高等教育出版社,2009.SUI Xun-fang,FANG Xiao-shu,GUAN Lai-tai,et al.Material mechanics[M].Beijing:Higher Education Press,2009.
[21]温诗铸,黄平.摩擦学原理[M].北京:清华大学出版社,2008.WEN Shi-zhu,HUANG Ping.Principles of tribology[M].Beijing:Tsinghua University Press,2008.