基于降强法数值计算的复杂岩质边坡动力稳定性安全评价分析
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摘要
分析复杂岩质边坡在地震荷载作用下的动力稳定性的特点,提出基于降低材料强度算法的动力稳定性分析方法。先将软弱结构面抗剪强度指标降低,进行静力计算,在此基础上,再进行动力稳定分析,综合评估边坡的动力稳定性与降强倍数的关系,将边坡处于临界稳定状态下的降强倍数定义为动力稳定安全系数。借助数值计算程序,将上述方法应用于国内某拱坝坝轴线左岸岩质边坡的动力稳定性分析,取得满意的成果。
The failure of complex rock slope usually occurs along weak discontinuity.The numerical method based on reducing the shear strength of weak discontinuity has been efficiently applied to static stability analysis.Actually,before earthquake occurs,the substances existing in the weak discontinuity of rock mass have been changed in physical and chemical manners under the combined actions of mechanical field,hydraulic field,chemical field and thermal field.Accordingly,the shear strength of the weak discontinuity has been gradually decreased and the slope stress field has also been changed.When earthquake occurs,seismic load is exerted on the slope upon which a static stress field has existed.Earthquake may occur any time,but the initial mechanical property of rock mass and the static stress state are different at different times.The strength safety margin of rock mass is also different.Based on the above analysis of action mechanism about earthquake load,a new method of numerical seismic stability safety evaluation for rock slope is presented.The shear strengths of the weak discontinuities are divided by different strength-reduction ratios and the numerical seismic analysis is carried out after the accomplishment of the static analysis.As the duration of earthquake is usually very short,the shear strengths can be considered as constants in the earthquake process.Under the different shear strength-reduction ratios,the distribution features of deformation,stress,and plastic zone from numerical calculation results are also analyzed.The relationship between the shear strength-reduction ratios and permanent displacements of characteristic points and the failure situations are studied in detail.The seismic stability safety factor is finally defined as the strength-reduction ratio of shear strength when the rock slope is in the limiting stability state under earthquake load.As an application example of the above concepts,the seismic stability safety for a complex rock slope in a hydropower project in China is evaluated.The result of numerical analysis shows when the strength-reduction ratio of shear strength equals 0.99,the trend of large deformation and rigid movement begins to emerge,and the slope begins to lose stability.Therefore,the seismic stability safety factor of the slope is regarded as 0.99.The analysis of the example also shows that the presented method is convincing and it provides a new way for seismic stability safety evaluation of complex rock slopes.
The failure of complex rock slope usually occurs along weak discontinuity.The numerical method based on reducing the shear strength of weak discontinuity has been efficiently applied to static stability analysis.Actually,before earthquake occurs,the substances existing in the weak discontinuity of rock mass have been changed in physical and chemical manners under the combined actions of mechanical field,hydraulic field,chemical field and thermal field.Accordingly,the shear strength of the weak discontinuity has been gradually decreased and the slope stress field has also been changed.When earthquake occurs,seismic load is exerted on the slope upon which a static stress field has existed.Earthquake may occur any time,but the initial mechanical property of rock mass and the static stress state are different at different times.The strength safety margin of rock mass is also different.Based on the above analysis of action mechanism about earthquake load,a new method of numerical seismic stability safety evaluation for rock slope is presented.The shear strengths of the weak discontinuities are divided by different strength-reduction ratios and the numerical seismic analysis is carried out after the accomplishment of the static analysis.As the duration of earthquake is usually very short,the shear strengths can be considered as constants in the earthquake process.Under the different shear strength-reduction ratios,the distribution features of deformation,stress,and plastic zone from numerical calculation results are also analyzed.The relationship between the shear strength-reduction ratios and permanent displacements of characteristic points and the failure situations are studied in detail.The seismic stability safety factor is finally defined as the strength-reduction ratio of shear strength when the rock slope is in the limiting stability state under earthquake load.As an application example of the above concepts,the seismic stability safety for a complex rock slope in a hydropower project in China is evaluated.The result of numerical analysis shows when the strength-reduction ratio of shear strength equals 0.99,the trend of large deformation and rigid movement begins to emerge,and the slope begins to lose stability.Therefore,the seismic stability safety factor of the slope is regarded as 0.99.The analysis of the example also shows that the presented method is convincing and it provides a new way for seismic stability safety evaluation of complex rock slopes.
引文
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[2]李海波,蒋会军,赵坚,等.动荷载作用下岩体工程安全的几个问题[J].岩石力学与工程学报,2003,22(11):1 887–1 891.(LI HaiboJ,IANG Huijun,ZHAO Jian,et al.Some problems about safety analysis of rock engineering under dynamic load[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(11):1 887–1 891.(in Chinese))
[3]刘春玲,祁生文,童立强,等.利用FLAC3D分析某边坡地震稳定性[J].岩石力学与工程学报,2004,23(16):2 730–2 733.(LIU Chunling,QI Shengwen,TONG Liqiang,et al.Stability analysis of slope under earthquake with FLAC3D[J].Chinese Journal of Rock Mechanics and Engineering,2004,23(16):2 730–2 733.(in Chinese))
[4]刘汉龙,费康,高玉峰.边坡地震稳定性时程分析法[J].岩土力学,2003,24(4):553–560.(LIU Hanlong,FEI Kang,GAO Yufeng.Time history analysis method of slope seismic stability[J].Rock and Soil Mechanics,2003,24(4):553–560.(in Chinese))
[5]吴兆营,薄景山,刘洪帅,等.岩质边坡地震稳定性动安全系数分析方法[J].防灾减灾工程学报,2004,24(3):237–241.(WU Zhaoying,BO Jingshan,LIU Hongshuai,et al.A method for evaluating dynamic safety factor rock slope seismic stability[J].Journal of Disaster Prevention and Mitigation Engineering,2004,24(3):237–241.(in Chinese))
[6]赵尚毅,郑颖人,邓卫东.用有限元强度折减法进行节理岩质边坡稳定性分析[J].岩石力学与工程学报,2003,22(2):254–260.(ZHAO Shangyi,ZHANG Yingren,DENG Weidong.Stability analysis of jointed rock slope by strength reduction FEM[J].Chinese Journal of Rock Mechanics and Engineering,2003,22(2):254–260.(in Chinese))
[7]中华人民共和国行业标准编写组.DL 5073–2000水工建筑物抗震设计规范[S].北京:中国电力出版社,2001.(The Professional Standards Compilation Group of People′s Republic of China.DL 5073–2000 Specifications for seismic design of hydraulic structures[S].Beijing:China Electric Power Press,2001.(in Chinese))
[8]Itasca Consulting Group Inc..FLAC users manual,version5.0[R].Minneapolis,Minnesota:Itasca Consulting Group Inc.,2005.
[9]刘波,韩彦辉.FLAC原理、实例与应用指南[M].北京:人民交通出版社,2005.(LIU Bo,HAN Yanhui.Guidance of method,illustration and application about FLAC[M].Beijing:China Communications Press,2005.(in Chinese))
[10]王林,于亚伦.裂隙矿岩的动载特性[J].北京科技大学学报,1994,16(2):101–105.(WANG Lin,YU Yalun.The dynamic fracture properties of crack rocks[J].Journal of University of Science and Technology Beijing,1994,16(2):101–105.(in Chinese))
[11]周维垣.高等岩石力学[M].北京:水利电力出版社,1990.(ZHOU Weiyuan.The advanced rock mechanics[M].Beijing:Water Resources and Electric Power Press,1990.(in Chinese))
[12]JING L,STEPHANSSON O,NORDLUND E.Study on rock joints under cyclic loading conditions[J].Rock Mechanics and Rock Engineering,1993,26(3):215–232.
[13]中华人民共和国行业标准编写组.DL5180–2003水电枢纽工程等级划分及设计安全标准[S].北京:中国电力出版社,2003.(The Professional Standards Compilation Group of People′s Republic of China.DL5180–2003 Classification and design safety standard of hydropower projects[S].Beijing:China Electric Power Press,2003.(in Chinese))
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