# Numerical Study on Redbed Slope Stability Under Multi-Factor Conditions
###### Abstract  
Redbed soft rocks, widely distributed in China, are highly susceptible to weathering, disintegration, and strength reduction under environmental and engineering disturbances, posing critical challenges for slope stability. This study investigates the stability and failure mechanisms of high road-cut slopes in redbed regions under excavation, seismic, and rainfall conditions. Numerical simulations were conducted based on actual engineering sites, using the FLAC3D finite difference model to simulate conditions typical of these sites while incorporating realistic geological features such as weak interlayers and fluid-solid coupling effects. Results reveal that under excavation, the slope exhibits displacement discontinuities and stress concentration near weak interlayers. However, the safety factor of the redbed slope remains at 1.58 at this stage, suggesting that large-scale collapses or landslides are unlikely. Seismic loading amplifies displacements and accelerations, with the maximum deformation reaching a shear displacement of 0.81 m, observed in the upper sections of the redbed slope. Under prolonged rainfall, the slope experiences increased saturation and sliding along interlayer surfaces, driven by reduced shear strength. Combined influences of these factors highlight the vulnerability of redbed slopes to localized failure in weakly weathered zones, necessitating targeted reinforcement strategies. These findings provide a deeper understanding of redbed slope behavior under complex conditions, addressing key challenges in geotechnical and transportation infrastructure engineering. Article  
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soft rocks--including susceptibility to weathering, softening, and low strength--make redbed slopes particularly prone to geological hazards such as landslides, rockfalls, and debris flows (Figure 1) [2; 8; 9; 10; 11; 12; 13; 14]. During the rainy season, water infiltration exacerbates these vulnerabilities by inducing softening, swelling, and disintegration within the rock mass, further reducing its strength. This, combined with increased gravitational load and reduced shear strength due to prolonged rainfall, brings the slope closer to critical failure. Additionally, mechanical vibrations from construction activities, blasting, or seismic events further amplify slope instability [9; 10]. Landslide prediction in redbed regions has become a crucial task in engineering construction programs [15]. High and steep artificial cut slopes are particularly susceptible to instability, with numerous reported cases of slope failures triggered by rainfall or seismic events following excavation. Current research methods to analyze slope stability primarily include field investigations combined with monitoring data and numerical simulations [16; 17; 18]. Among these, numerical simulations, such as the finite element method and finite difference method, are increasingly favored due to their cost-effectiveness and ability to capture the complexities of real engineering projects [19; 20; 21; 22; 23]. For instance, [PERSON] et al. [24] conducted numerical simulations of basalt landslides with weak interlayers, highlighting the significant impact of excavation and inclined weak interlayers on slope stability. Similarly, [PERSON] et al. [25] employed FLAC3D finite difference modeling to explore the seismic response and dynamic failure modes of slopes. [PERSON] et al. [26] utilized GeoStudio 2.0 software to analyze the stability of three landslides under various water levels and rainfall conditions using the Bishop method. [PERSON] et al. [27] tested the hydraulic and mechanical properties of the residual soil and fully weathered granite, and the surface displacements on the slope were monitored. Geo-studio was utilized to establish a coupled seepage-deformation model to validate the numerical method and investigate the landslide-triggering factors of the cut slope.