库水位骤降下土石坝扩建渗流特性异化及对稳定性的影响OA

This study investigates the coupled seepage-stability response mechanism of heightened earth-rock dams under rapid reservoir drawdown,using the expansion project of Nanmuxi Reservoir as a case study.A multi-scenario coupled numerical model,based on unsaturated seepage theory and slope stability analysis,was developed to systematically examine the evolution of seepage patterns and changes in anti-sliding stability under different drawdown rates(0.5～4 m/d).The results reveal a pronounced hysteresis effect in seepage response during drawdown,manifested as a delayed adjustment of the phreatic line relative to the declining reservoir level.Within the inclined impervious layer,the saturation distribution reverses spatially from"bottom>middle>top"to"middle>bottom>top",with the timing of this reversal advancing as the drawdown rate increases.Pore-water pressure dissipation is highly dependent on material properties:rapid drainage in the highly permeable original shell promotes seepage flow concentration near the base of the inclined wall.The interface between the new and old dam sections is identified as a sensitive zone for hydraulic failure.When the water level abruptly drops below this interface,the strong suction effect induced by seepage forces causes hydraulic imbalance,triggering a cliff-edge decline of 12％～18％in the safety factor of the upstream slope.To mitigate these risks,it is recommended to incorporate a graded transition layer with a controlled permeability ratio(approximately k1:k2:k3=1:10:100),limit drawdown rates to less than 1 m/day,and implement real-time safety monitoring when the water level approach the interface elevation.This study provides theoretical and practical insights for the seepage control design and operational safety management of similar dam elevation projects.