Stability Analysis And Determination Of Critical Slip Surface For Slope Under Strong Earthquakes

China is an earthquake-prone country and the earthquake disasters lead in theworld. The instability and failure of slope under seismic is one of the major damage inWenchuan earthquake. Many researthers at home and abroad have done many studieson the stability of slope under earthquake. Now, the major methods about stability ofslope under earthauke are pseudo-static method, sliding block method, numericalsimulation method, experiment method and probability analysis method. Due to thesimple concept and it is convenient in the application of engineering, the pseudo-staticmethod has been widely performed in the pritical engineering. But we often presuposethe shape of slip surface of slope and use different assumptions to decrease the numbersof unkonwns when using traditional pseudo-static method. By satisfying the balance offorce and moment, the safety factor of slope under earthquake can be sloved. However,the slip surface of slope we obtain by traditional pseudo-static method is not real.Obviously, this kind of method has obvious error. In addition, it is generally assumedthat the instability and failure of slope is caused by the horizontal seismic inertia force,the effect of vertical earthquake can be ignored. However, slope damage cases alsoshow that the vertical motion has a significant effect on the stability of slope. In view ofthe above-mentioned factors, this thesis is based on the theory of limit equilibrium ofsoil, theoretical analysis, mathematical analytic method and numerical simulation, themethod of searching the real slip surface and the location of slip surface of slope aredeterminated, then the effect of non-homogeneous soil slope, pore pressure and thevertical earthquake is considered in the method of the slope seismic stability analysisand the determination of the slip surface. The main content and understandings obtainedare as follows:(1) The simplified method of determination of critical slip surface of slope underseismic, which considers the effect of vertical earthquake is introduced as follows: Thesimplified method is based on the theory of limit equilibrium, with the aid ofmathematical analytical method, satisfying the criteria of stress and kinematics underseismic and in accord with the geometrical compatibility condition of the deformationof slope. Then, the nonlinear equations of sloving the unkonwn soil slice is formed andthe fslove function in matlab is adopted to slove the equations. The method of searchingthe critical slip surface of slope and determining the stability of slope under seismic isestablished. By sloving the nonlinear equations, the acceptable minimum criticalacceleration and critical slip surface are obtained. Adopting the weigthed average of soilstrength parameters, the potential failure mechanism of slope between the boundary ofsoil stratum is considered. Using the average of pore pressure ratio method, the effect of pore pressure is considered. Then, the method above can be expanded to consider theeffect of pore pressure in non-homogeneous soil slope. Finally, the analytical method ofdetermining the critical slip surface and the stability of slope is established, whichconsider the effect of vertical earthquake.(2) Adopting the soil elastic-plastic yield surface model and the dynamic couplingprinciple of effective stress of soil, simulating the artificial boundary by free fieldboundary conditions, at the same time, using the soil two-phase medium theory toanalyze soil liquefaction, the method of considering the effect of soil liquefaction ofthree dimensional finite element analysis model and the corresponding calculationmethod is eatablished. Then the correctness of the analysis method is validated. Thefriendly interface of before and after processing of computing platform SlopeSAR isestablished, then the dynamic response characteristics of slope under earthquake isanalyzed.(3) Finally, the correctness of the is validated by the three-dimensional finiteelement method. Then the application of simplified method on the stability and criticalslip surface of slope is developed. The simplified method is mainly discussed on theconvergence of sloving the nonlinear equations. At the same time, the effect of soilstrengh on critical slip surface is analyzed, the effect of level of incremental Δx on thecritical slip surface of single soil slice and the whole slope are also discussed. The effectof pore pressure, heterogeneity of soil and vertical earthquake on the critical slip surfaceof slop are analyzed.