Study On Loess Slope Stability Based On The Method Of Double Reduction Parameters

Loess landslides induced by groundwater uplift or rainfall often develop in loess plateau, and around the residential quarters and along highways and railways. In the future, many similar hazards also will occur in the loess plateau, where the designation of the Belt and Road national strategy will cross. However, the methods of calculation of loesssoil slope safty factor are unchanged. So, lt has very important theoretical significance and practical value to further explore new methods of evlucating the safty factor of loess slope.Based on the effect of water content on the strength of unsaturated loess, the functional relationship between the reduction parameters of cohesion force and friction angle was deducted. A new double reduction method which fits for the the stability of loess slopes explored was determined. the reduction function F2=F1b, and the mathematical expression c’=c/Ftrial和φ’=arctan(tanφFtrialb) was presented. Meanwhile, the physical meaning and mechanical mechanism of the double reduction method was studied.The influence of using DP criterion and different parameters on the safty factor of loess slope was discussed, and the transformation of safty factor based on DP criterion was deducted. Research results show that: the results calculated through DP4 criterion is closely to that of strict slice method( Mprgenstern-Prince method); The difference of elasticity modulus E and poisson ratio v does not influence the safty factor, but that of dilatancy angle Ψ and strength of extension σt have great influence on the safty factor.The method of DRM-Morgenstern-Prince was presented and deducted, and used to analyse several typical slopes. The results show that: the value of DRM-Morgenstern-Prince method is higher than that of traditional single reduction method; To the loess slopes(slope angle θ≤45°), the error is about 19%, and to the loess slopes(slope angle θ≥55°), the error is less than 1%; the DRM-Morgenstern-Prince method can districtly reflect that the value of slope angle θ has a great influence on the safty factor of loess slope.The Finite Difference-Double Reduction Method(FD-DRM in abbreviaton) was presented and deducted, and then wast used to analyse stability of loess slope during excavation. The calculation results show that: the safty factor calculated by FD-DRM is higher than that of the Traditional Single Reduction Method and Morgenstern-Prince Method, the safty factor varies between Traditional Single Reduction(upper limit solution) and the Morgenstern-Prince Method(lower limit solution); In the stability analysis two criterion is reasonable, including the criterion of connectivity of plastic zone and the criterion of the abruptness of displacement, which can reflect the true shear capacity of geotechnical material.The two methods presented in this paper can reflect the characteristics of the reduction of cohesion force and friction angle separately. It also has explicit physical meaning and theoretical basis, and may be widely used in the analysis of stability of unsaturated loess slope.