Surge characteristics induced by deformation and instability of giant accumulation body under fluctuating reservoir water levels

Abstract

[Objective] During reservoir impoundment, reservoir-bank slopes are prone to deformation and instability due to hydraulic effects, which may subsequently generate surge hazards and pose serious threats to infrastructure and human safety in the reservoir area. The evolution process of instability-induced deformation of accumulation-body slopes and the characteristics of surge generation under fluctuating water levels are revealed. [Methods] A giant accumulation body in the reservoir area of a hydropower station on the Yalong River was selected as the research object. Field geological surveys were conducted to obtain fracture occurrence and deformation characteristics. The entire slope deformation evolution process was simulated using discrete element numerical modeling, while surge heights were calculated using the China Institute of Water Resources and Hydropower Research(IWHR) method and the Pan Jiazheng method. The synergistic effects of sliding velocity, volume, and terrain conditions were analyzed. [Results] The result showed that the deformation of the accumulation body exhibited a three-stage evolution characteristic of “creep, constant velocity, and acceleration.” The strength degradation of rock mass at the slope toe(cohesion decreased by 35% to 65% and internal friction angle reduced by 18% to 22%) was identified as the main cause of deformation initiation. The stability of locked segments at elevations of 2 905.65 m and 2 978.08 m served as the critical threshold controlling the transformation of deformation stages. After their failure, the sliding body acceleration increased from 0.06 m/s² to 0.418 m/s². Surge propagation showed significant nonlinear attenuation characteristics. The maximum surge heights calculated by the IWHR method and the Pan Jiazheng method at the opposite bank were 80.68 m and 53.53 m, respectively; at the tunnel entrance were 15.1 m and 15.09 m, respectively; and at the dam site were 3.63 m and 1.13 m, respectively. The differences revealed the terrain amplification effect. [Conclusion] The deformation-surge coupling mechanism is manifested as a chain response of “hydraulic degradation-locked segment failure-abrupt change in sliding velocity-surge propagation, ” with the stability of locked segments being the core for surge disaster prevention and control. A theoretical basis for early warning of similar landslide surges in reservoir areas is provided by these result.

Keywords

accumulation body deformation and instability / locked segment / surge disaster / coupling mechanism / landslide / discrete element / hydropower station / chain response mechanism