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

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。

ANALYSIS OF DYNAMIC STABILITY SAFETY EVALUATION FOR COMPLEX ROCK SLOPES BY STRENGTH REDUCTION NUMERICAL METHOD

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.