Deformation analysis and treatment of the steeply dipping and bedding slope with thin layers at left bank tailwater outlet of Wudongde hydropower station

The tailwater outlet slope on the left bank of Wudongde hydropower station, as a key slope shared by the diversion outlet, tailwater outlet and flood discharging outlet, is characterized by the steeply dipping and bedding structure with thin layers, the hidden passage of a long-growth fault and the crossing of tunnels. This paper firstly analyses the reasons for the sudden deformation of the slope-tunnel system caused by the key problems encountered in geology, design and construction, and the corresponding treatment methods are discussed systematically. Through the implementation of a series of comprehensive measures, including systematic reinforcement, support by concrete retaining walls on the open face, strict adherence to the excavation sequence of “slope before tunnel”, strict limitation of the mass vibration rate of blasting, and strengthening of the construction of external waterproofing system, the excavation of the tunnels through the slope has been successfully completed under controlled deformation monitoring, and the excavation stabilization of the slope-tunnel system is solved after the emergence of sudden deformations during the construction period. Secondly, it is verified by numerical simulation analysis that the dynamically adjusted support measures can meet the safety requirements of the slope during the construction and operation periods. Finally, the overall response strategy and specific process after the sudden deformation of the slope-tunnel system are systematically elaborated. The long-term monitoring results show that the tailwater outlet slope has been operating safely for more than nine years. The research results have important reference significance for the excavation reinforcement and stabilization of similar projects.