Reservoir Deformation Mechanism During Impoundment And Operationand Its Influence To Safety Of High Arch Dam

The high arch dams in China are gradually going through the impounding and operation periods. Noteworthy deformationof reservoir slopes wasobserved during impoundment of Jinping-I and Xiluodu high arch dams,and afterwards the valley widths keptdecreasing. The deformation affects current working behavior and long-term safety of the dams. However, evaluation criterion for the influence of reservoir deformation is still limited in the design method of arch dam. In this paper, the deformation mechanism of fract ured rock mass during initial impoundment is explored, and valley width reduction andsome other phenomena of reservoir deformation are explained. Based on the limit analysis theory, some evaluation methods for long-term stability of high arch dam are presented. The major achievements are listed as below:(1) The Deformation Reinforcement Theory is extended to stability analysis of structure with multiple cracks. The plastic complementary energy is used to evaluate global stability, and theunbalanced force is used to predict initiation and propagation of fractures. Numerical simulation on compression failure of pre-crack specimens and overloading failure of high arch dams are performed, and compared with experimental results. The hazards of dam heel cracking and fracture propagation in dam bodyare assessed. Thepresented method is proved to be effective in the global stability and fracture analysis of arch dam, which is the basis of safety evaluation of arch dam during impounding and operation periods.(2) The features of reservoir deformation induced by impoundment are summarized, as well as the limitation of conventional calculation methods. Hydrostatic pressure is taken into consideration in the yield function of elasto-plastic model, and applied in the numerical simulation of Jinping-I arch dam. The calculated displacements agree well with observed values, which can phenomenologically explain valley width reduction and reservoirsettlement.(3) The mesoscopic mechanism of the effects of fracture pressure is explored. Water pressure distributed in intermittent fractures is self-balancing, which changes the equilibrium state of rock mass and causes plastic deformation. This view point is validated by various literature, monitoring data and numerical results. Furthermore, the influence of reservoir deformation during impoundment to the Jinping-I arch dam is evaluated. An approach to back analysis of strength parameters of rock mass is also presented.(4) The Boundary Displacement Method and the Stiffness and Strength Reduction Method are presented to assess the long-term safety of arch dam. The former method replacesthe constraintswith fixed displacements on model boundary in order to obtain long-term displacement field. The latter is based on the internal relation between elasto-plastic model and creep model, which is theoretically rigorous. The two methods are derived from the overload method and strength reduction method respectively, and both are used in the long-term limit analysis of reservoir and high arch dam.(5) Aviscoelastic-plastic creep model, Cvisc model, is applied in the numerical evaluation of reservoir deformation and its influence to the long-term safety of Jinping-I arch dam. Furthermore, the Boundary Displacement Method and the Stiffness and Strength Reduction Method are applied in the limit analysis. The results show that the long-term reservoir deformationwithin certain limits is beneficial for the global stability of Jinping-I high arch dam.