Abstract: The occurrence time of landslides has a significant periodical distribution and the gravitational tidal forces induced by the sun and the moon are the major contribution factors. This paper presents the formula of the tidal force acting on the landslide as well as the effect of the tidal force on the slope stability from the theory of the solid tide. The triggering mechanism of the tidal force on the landslide is explored throughout the improved factor of safety method that considering the action of tidal force. A slope stability example is considered in the paper to analysis the relationship between the diurnal period relationship and the landslide triggering time. The results indicate that a diurnal and half diurnal periods can be found in the tidal forces and their associated factors of safety.

Key words: Tidal Forces, Landslides, Triggering, Time Related; , Factor of Safety for Slope Stability