Multi-Source Evidence Chain Identification and Mechanistic Analysis of a Creep-Type Expressway Embankment Landslide in a Mountainous Karst Area: A Case Study of the K610 Section of the Rucheng-Chenzhou Expressway

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.