Study on the reinforcement of weak structural surfaces in complex foundation of high arch dam based on stability evolution

High arch dams impose stringent requirements to ensure safety, requiring robust bearing capacity, deformation control, and resistance to seepage failure. The stability of the dam foundation serves as the cornerstone of the entire arch dam system. During operation, the enormous thrust generated by arch abutments acts on the dam-foundation interface, potentially inducing instability risks such as macroscopic fractures and shear sliding, particularly in weak foundation zones. These risks, if left unchecked, can compromise dam safety and may trigger catastrophic failure. Addressing weak zone reinforcement design in complex dam foundations poses a significant challenge, as no standardized system currently exists for prioritizing reinforcements or quantifying stability evaluation indicators.

To address this gap, this study proposes an energy-based method for stability evaluation and reinforcement design of weak dam foundation zones. A stability evolution analysis model was established using energy dissipation rate and domain integral variation, enabling the identification of critical weak zones and their evolutionary patterns. The study employed a three-dimensional numerical model of the arch dam-foundation system, accounting for complex geological factors such as faults, abutment slopes, and dam geometry. A thermodynamically driven creep constitutive model with internal variables was employed to conduct three-dimensional numerical simulations, revealing the stability evolution process of weak foundation zones. By analyzing energy dissipation rate curves and domain integrals, critical moments (marked by peak dissipation rates) and vulnerable areas (highlighted by energy concentration zones) were pinpointed. This method was then applied to parallel fault groups in a high arch dam foundation, with the reinforcement effectiveness analyzed in terms of energy dissipation rates, dam deformation, fault yield zones, and results from comparative testing using the super-water unit weight method.

Results indicate that energy dissipation rates and domain integrals for abutment faults initially increased rapidly after reservoir impoundment, gradually decreased, and eventually stabilized. The stability evolution of dam foundation faults under impoundment exhibits distinct time-dependent behavior, progressing through three phases: instability, transition, and stabilization. A significant observation is the delayed occurrence of peak energy dissipation rates in downstream faults, reflecting a spatiotemporal hysteresis in arch thrust transmission. During normal operations, the thrust from the arch extends its influence on deep foundation stability to a distance approximately twice the width of the arch abutment. However, its impact on downstream stability ranges between 2-3 times the abutment width. Comparative analysis using the super-water unit weight method demonstrated reduced dam deformation, improved fault yield zone distribution, and significant decreases in energy dissipation rates and domain integrals for critical faults after reinforcement.

The proposed method reveals spatiotemporal hysteresis in arch thrust transmission and its disturbance on structural stability. For multifault dam foundations, upstream faults exhibit less susceptibility to hydraulic disturbances when compared to downstream faults. Weak zones in downstream faults are primarily concentrated near their intersections with the dam abutment as well as along the strike direction. The f123 and f120 faults on the left bank were identified as critical to global stability, with key reinforcement areas at elevations of 2440-2470 m (f123) and 2395-2425 m (f120). Targeted reinforcement measures effectively enhanced fault and foundation stability, significantly improving the overall stability of the arch dam-foundation system.