Impact of Jishishan Earthquake on the Gravel Rockfill Dam on the Right Bank of Dahejia Hydropower Station
Through field investigation and experiment results,combined with monitoring data,the seismic damage characteristics of the gravel rockfill dam of Dahejia Hydropower Station after the Jishishan earthquake are analyzed,and corresponding treatment measures are proposed based on a comprehensive evaluation of its post-earthquake safety.The study found that after the earthquake,two cracks appeared on the top of the dam,located on both sides of the concrete anti-seepage core wall along the dam axis.Crack No.1 is a continuous main crack caused by soil ten-sion;Crack No.2 is an intermittent secondary tensile crack caused by the deformation of the soil on the top of the anti-seepage wall upstream af-ter the formation of crack No.1.The parapet wall and the upstream dam slope,the parapet wall and the dam foundation surface,and the anti-seepage wall and the guide groove are in close contact without any void.The settlement of the gravel rockfill dam after the earthquake is 6.5～35 mm,with a larger settlement near the riverbed and a smaller settlement on the bank slope;the horizontal displacement change of the dam top a-long the river is-2.51 mm(upstream)to 1.14 mm(downstream),with the riverbed deforming downstream and the bank slope deforming up-stream.After comprehensive analysis,it is believed that although the Dahejia Hydropower Station is hit by an earthquake exceeding the standard,it does not affect the overall stability of the dam slope.It is preliminarily judged that the dam is in a safe and controllable state;it is recommen-ded to use geogrid layering and reservoir rolling replacement treatment measures to repair the dam top cracks.
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