Abstract: Slope stability evaluation is a classic problem for soil mechanics. In order to study the stability of heterogeneous slopes, this paper uses the upper limit analysis method to establish the failure mechanism of segmented logarithmic spiral arcs for heterogeneous slope. Then fitting polynomial is used to approximately describe the logarithmic spiral arcs. External force power and internal energy dissipation power of the failure mechanism can be determined. The calculation process is applied to repeat the strength reduction until the slope gradually transition to the ultimate balance and the slope stability factor can be obtained. Taking the south slope in an open-pit mine as the background, the slope stability factor is determined by the method of repeated strength reduction. The stability of the calculation process is verified by the method of changing initial value, and the accuracy of the calculation result is verified by the method of strict Morgenstern-Price. The results show that the process is stable and is not affected by the initial value. Compared with the strict Morgenstern-Price method, the difference of stability factor calculation results between the two methods is less than 5%. The stability factor calculation results can fully satisfy the requirements of engineering practice. At the same time, the most dangerous slip surface formed by upper limit analysis method can satisfy the speed separation relationship.

Key words: heterogeneous slope, upper limit analysis, logarithmic spiral arc, fitting function, strength reduction