3D Seepage, Deformation, and Stability Analysis of the Yecha Concrete-Face Rockfill Dam Considering Defect Scenarios

Concrete-face rockfill dams (CFRDs) constructed in narrow valleys and on spatially heterogeneous foundations may experience nonuniform seepage and deformation, while local defects in the seepage-control system can further affect their operational safety. This study establishes a three-dimensional finite element model of the 90 m-high Yecha CFRD to systematically evaluate seepage behavior, stress–deformation response, face slab performance, and slope stability under normal, extreme-water-level, and representative defect scenarios. The seepage analysis considers different reservoir levels as well as peripheral-joint failure, face slab cracking at different elevations, and grout-curtain degradation, while the nonlinear mechanical behavior of the rockfill is described using the Duncan–Chang E–B model with parameters obtained from large-scale triaxial tests. Under normal storage, the seepage-control system remains effective, with a total seepage discharge of 3240.18 m3/d. The maximum dam settlement is 25.15 cm, corresponding to 0.279% of the dam height, and the slope safety factor is 1.48. Low-elevation face slab cracking is identified as a critical local seepage scenario, increasing the hydraulic gradient in the cushion material to 3.39, above the allowable value of 0.45. In addition, a 20% reduction in the mechanical parameters of the main rockfill zones increases the maximum settlement and face slab deflection by 84% and 74%, respectively, indicating a pronounced sensitivity to rockfill mechanical properties. Under the check flood level, the minimum slope safety factor decreases to 1.39 but remains above the code requirement. These results highlight low-elevation face slab integrity and rockfill compaction quality as key factors governing the seepage and deformation safety of CFRDs and provide a practical basis for defect-oriented monitoring and safety assessment.