Hydro-mechanical instability of concrete dam construction joints under hydraulic loading: aperture sensitivity, damage localization, and seepage-velocity acceleration

Seepage along construction joints can threaten the uplift stability and long-term safety of concrete dams. Although seepage-induced joint opening has been studied, the post-initiation transition from stable seepage to rapid uplift instability remains insufficiently understood. This study presents a coupled hydro-mechanical numerical framework with interfacial damage output to simulate the post-initiation uplift instability of concrete dam construction joints. The framework integrates hydraulic-head buildup, uplift separation, mechanically evaluated aperture evolution, interfacial damage analysis, and a seepage-velocity growth indicator. The results show that hydraulic head concentrates near the construction joint under anti-seepage constraint, reducing the effective normal stress and driving localized hydraulic separation. Uplift deformation develops near the jointed interface rather than as a uniform block deformation. Increasing the initial opening amplifies monitored uplift displacement and advances the transition from stable response to rapid separation and instability; the 3 mm opening loses stability earliest, followed by the 2 mm and 1 mm openings. The observed localization of interfacial degradation supports a damage-informed aperture interpretation in which interface deterioration may contribute to hydraulic-path development beyond mechanical opening alone. The magnitude of this additional contribution was not quantified because the damage-aperture coefficient was not independently calibrated. The normalized seepage-velocity response and velocity growth indicator further suggest that hydraulic acceleration may provide an early warning indicator of aperture-sensitive instability. These findings indicate that seepage-induced instability of dam construction joints should be evaluated through the combined evolution of hydraulic head, uplift separation, mechanically evaluated aperture, damage localization, and seepage-velocity, rather than through crack-opening initiation or displacement response alone. The proposed mechanism provides a basis for uplift instability assessment and monitoring of jointed hydraulic concrete structures.