Abstract: :Rarely seen abnormalities including settlement on the left and uplift deformation on the right with section 18^# as dividing line were found at Tongjiezi Hydropower Station after reservoir impoundment. Through mining the monitored information and analyzing the structural geology and hydrogeology condition, we concluded that the abnormalities are regional chain reactions resulted from the unique structure and hydrogeology, which caused the change of deep confined water after reservoir impoundment. Since the impoundment, water level has remained normal, seepage in the dam site has stablized, and the uplift deformation gradually tends to be stable. At present it is not yet a threat to the safety of dam.

Key words: Tongjeizi, uplift of dam body, safety monitoring, correlation analysis, confined water