The soft interlayer and rock structure play a significant role in controlling the deformation of the bedding slope, and it is necessary to consider the phenomenon of the sudden change of local response in these key parts under rainfall conditions, and then to clarify the mechanism of rainfall infiltration and damage mechanism of such slopes. In this paper, a large red-layered flat-dipping bedding landslide was selected as the research object, and numerical calculations based on the Van Genuchten model for saturated–unsaturated flow were performed in order to investigate the hydrological response and distribution patterns of water within the slope during rainfall. Moreover, stability analysis was performed based on the seepage field results and secondary development of FLAC^3D, and the landslide evolution process was simulated and reproduced using the constitutive model of double-variables and the strength reduction method (SRM). The results showed that the effects of heavy rainfall on the water distribution and stability of the highway slope are significant, while the effects on the natural slope are not significant. There are three phases of the slope destabilization: flexure and uplift state, deformation exacerbation state and shear failure state. The slope destabilization mechanism is a typical “sliding-bending-shearing” type. The results of the study can provide a theoretical basis for the study of the seepage, stability analysis and destabilization mechanism of bedding slopes.

The soft interlayer and rock structure play a significant role in controlling the deformation of the bedding slope, while previous studies seldom consider the phenomenon of sudden change of local response in these key parts under rainfall conditions, and it is not clear about the mechanism of rainfall infiltration and damage mechanism of such slopes. In this paper, a large red-layered flat-dipping bedding landslide was selected as the research object, and numerical calculations based on the van Genuchten model for saturated-unsaturated flow were performed. The hydrological response and distribution patterns of pore water pressure and water content within the slope during rainfall were studied, stability analysis was performed based on the seepage field results, and the landslide evolution process was simulated and reproduced. The results showed that rainfall infiltration produces local saturated areas and forms stagnant layers on the rock layers in the slope, and the thickness and range gradually extend to the vicinity of the weak interlayer. Moreover, slope stability is affected by rainfall infiltration, and the transient safety factor gradually decreases with rainfall. According to the macroscopic deformation process of the slope model, three stages of instability and failure of rainfall-induced red-layered bedding slopes are generalized: slight uplift stage, strong uplift stage, and sliding-bending failure stage. The results of the study can provide a theoretical basis for the study of seepage, destabilization mechanism and stability evaluation of bedding slopes.

Recurrent settlement of high-fill embankments along mountain expressways is difficult to diagnose because its underlying mechanism is often unclear. This study investigates the distressed K610 section of the G76 Xiamen–Chengdu Expressway between Rucheng and Chenzhou by integrating time-series InSAR, ground-settlement monitoring, boreholes, electrical resistivity imaging, ground-penetrating radar, hydrochemistry, engineering records, and three-dimensional finite-element analysis. These data establish a multi-source evidence chain linking deformation, geological structure, hydrological processes, and mechanical response. InSAR-derived line-of-sight velocities range from −30 to −8 mm/yr, and representative points show cumulative displacements of −40 to −50 mm. The anomalous zone extends from the high-fill embankment into the natural slope and spatially coincides with observed settlement, the inferred sliding direction, and radar-detected voids. Groundwater and karst cavities were encountered in 14 and 11 of 39 boreholes, respectively, while three resistivity profiles revealed low-resistivity anomalies beneath the core distressed section, indicating the control of shallow groundwater and karst structures. Water samples from the distressed zone contained an average fluoride concentration of 0.59 mg/L, far below the 17.54 mg/L in the tailings reservoir and similar to mountain surface water, identifying rainfall infiltration as the dominant recharge pathway. Strength-reduction analysis yielded factors of safety of 1.12 under natural conditions and 1.01 under extreme rainfall, a 9.8% decrease; simulated shear-strain concentration zones corresponded closely to field distress. Collectively, the evidence supports a progressive mechanism of rainfall infiltration, water-induced weakening, slope creep, and differential embankment settlement. The framework distinguishes slope-scale creep from localized settlement and supports treatment-boundary delineation and remediation design.