<p>Slope sliding in open-pit mines is a prevalent issue. While the mechanisms behind single influencing factors and their combinations that lead to slope sliding have been identified, the role of lithological differences in slope instability and failure remains unclear. This study focuses on a typical slope with distinct lithological variations and nearly vertical rock strata. Through a combination of field investigations and numerical simulations, the behaviors of adjacent soft rock and its overlying soil under varying excavation depths in hard rock areas and rainfall conditions were analyzed. Key findings include the impact of previous excavations on stress distribution within the slope. Shallow excavations in hard rock cause significant displacement differences in the overlying soil of adjacent soft rock, with maximum displacement and shear strain occurring at the excavation surface. Rainfall tends to concentrate displacement in the slope area. As excavation depth increases, substantial shear strain develops at the base of the soft rock near the free face, leading to noticeable unloading rebound effects. The compression zone of the unexcavated hard rock also expands. Shallow excavation decreases the slope safety factor by 32.5%, while deep excavation leads to an additional reduction of 9.2%. Rainfall significantly increases the potential sliding area, and when combined with deep excavations, it can lead to slope instability and failure.</p>