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.

Clarifying the fracture mechanisms at the nanoscale is essential for constructing a multiscale framework of rock fracture. In this study, molecular dynamics simulation is employed to investigate the fracture behavior and associated strength evolution in defective α ‐quartz containing either a single hole or double holes under uniaxial compression. The effects of hole size, strain rate, and temperature are analyzed in relation to crack initiation, propagation, and coalescence, and the resulting evolution of uniaxial strength. The results show that the uniaxial strength in all cases is negatively correlated with hole size, while the influence of strain rate is generally limited but varies with hole size. Elevated temperature can reduce both the Young's modulus and peak stress of defective α ‐quartz. Moreover, amorphized zones forming around the lateral edges of holes serve as the primary sites for fracture initiation in all cases, and wing‐like shear fractures represent the dominant propagation mode. The configuration with double holes promotes indirect coalescence in the rock bridge region, while strain rate influences the coalescence patterns depending on hole size. These findings could offer useful insights for developing multiscale models for rock fracture.