Abstract: The key to solving the safety factor of the vector sum method lies in determining the real stress state and the main sliding trend direction of the slope. The safety factor obtained by the vector sum method is closely related to the real stress state of the slope and the final sliding trend direction. The existing vector sum method is mostly based on a single anti-slide force or sliding force to determine the main sliding trend direction of the landslide. However, since slope sliding is actually the result of the combined action of the anti-slide force and the sliding force, the combined action of the two needs to be considered in the definition of the main sliding trend direction. In this study, we take the whole landslide body as an analysis object and the main sliding trend direction is first determined based on the overall vector resultant direction of the external load of the isolation body, the normal force, and the ultimate anti-sliding force at the bottom of the sliding body. After that, the safety factor of the landslide body is determined by the definition of the safety factor of the vector sum method. Finally, with the theoretical derivation and verification of standard test questions, the most dangerous sliding surface position, safety factor, and main sliding trend direction derived based on the new main sliding trend direction are comparable with those of the conventional slope stability method. What’s more, the slope safety evaluation based on the new main sliding trend direction are more safe, and more convenient for engineers to take more targeted slope support strategies.

Key words: slope stability, vector sum method, safety factor, main sliding trend direction