<p>Compared to natural slopes, differentially weathered slopes in valley areas (DWSVA) exhibit pronounced stage characteristics in their deformation and failure processes when subjected to excavation disturbances. Understanding these characteristics is essential for investigating failure mechanisms and formulating effective safety control measures. Through comprehensive case studies of roadcut slope failures in mountainous regions, this study conducted numerical simulations to investigate the evolutionary patterns of key variables across different excavation steps. The stage characteristics revealed by these multiple variables were synthesized to establish a generalized failure evolution curve for roadcut slopes. Furthermore, the horizontal elastic release force induced by excavation was quantified using empirical formulas, leading to a novel methodology for estimating reinforcement forces that incorporates both the self-bearing capacity of geomaterials and excavation-induced stress loss. The main conclusions are as follows: The sensitivity ranking of field variable responses is horizontal displacement &gt; vertical displacement &gt; horizontal stress &gt; vertical stress. The deformation process is divided into an elastic stage (stable, Fs ≥ Fst), a controllable elastoplastic stage (basically stable, 1.05 ≤ Fs &lt; Fst), and an uncontrollable failure stage (Fs &lt; 1.05). Excavation-induced stress loss exhibits an “inverted spoon” distribution, with significant release at the slope waist, highlighting the importance of “solidifying the base and strengthening the waist.“. The proposed analytical framework, utilizing theoretical earth pressure and horizontal elastic release force calculations, provides an efficient and practical approach for slope reinforcement design, effectively circumventing the complexities associated with numerical simulations while maintaining engineering relevance.</p>