Abstract: Seismic stability of Huaping bedding slope of Jinshajiang River bridge in Huali Expressway is studied. Safety factor, slip surface and scope of width 900 m and height 450 m are suggested by Janbu-simplified method based on slide. Safety factors and deformations of seven kinds of seismic working conditions such as horizontal acceleration being 0.00g, 0.10g, 0.15g, 0.20g, 0.25g, 0.30g and 0.35g are respectively computed by strength reduction method of finite elements on basis of Phase2D using quasi-static method, simulated object being model test. After curves of safety factor or defromation and horizontal acceleration of different seismic load conditions are compared with each other. The results show that: (1) Safety factor near to 1.0, the deviation is least, otherwise the deviation and discreteness increase, which is caused by disunity of limit condition defined by the two methods. Critical horizontal acceleration done by safety factor is 0.20g. (2) Fail mode presented by shear strain is bridge pier being tensile-shear fail, sliding in T2 tuff stratum and horizontally sheared out in front. Sensitivity order of deformation response in slope is horizontal displacement more sensitive than vertical displacement than shear strain. Limit value done by deformation evolution is 0.15g-0.20g, corresponding horizontal displacement being 10.2 mm. These are all proved by model test. (3) Finally, the critical horizontal acceleration of Huaping bedding slope comprehensively being 0.2g, safety factors of exceedance probability being 10% for 50 years and that of exceedance probability being 2% for 100 years are respectively 1.2 and 1.1. Huaping slope is safe under current seismic fortification criterion. In practice, safety factor considered material strength reserve is often selected as evaluating indicator of slope stability; but a strong operability and warning displacement considered deformation mechanism is selected for engineering safety monitoring. So, slope stability needed to be estimated by safety factor combined with critical displacement.

Key words: bedding slope, safety factor, critical displacement, critical horizontal earthquake acceleration, stability estimation