Study On The Mechanism And Control Of The Deformation And Failure Of Super High Arch Dams

Super high arch dams over 200 m high play a very important role in China's hydroelectric development.In the past 20 years,Jinping-I and other six super high arch dams have been completed and put into operation which accumulated valuable experience and rich data for the construction of super high arch dams.However,the problems of unloading relaxtion and valley contraction in engineering practices become more and more prominent,the conventional methods fail to quantitatively analyze them.In this research,the deformation and failure process of super high arch dams during overloading water pressure are calulated,and the mechanism of unloading relaxation and abnormal deformation with their effects on the dam body are studied.Finally,the above key problems of deformation and failure of super high arch dams are unified into the framework of unbalanced force.Meanwhile,typical features of super high arch dams are pointed out.The main achievements are listed as follows:(1)The unbalanced force and the plastic complementary energy norm(PCE)are used to evaluate the local and global failure of rock structures,respectively.The unbalanced force is demonstrated to be the result of the deformation compatibility condition which can not be relaxed in the nonlinear FEM calculation.Model tests and field monitoring data reveal that the unbalanced force is effective in the nonlinear deformation and failure simulation.Then,the deformation and failure process evolution of rock structures during loadingincreasing are elaborated.Treating the iterative step as time step,the minimum PCE principle is proved,which provides a theoretical basis for the nonlinear deformation and failure analysis.(2)The experimental techniques and evaluation criterion of the model test are organized and regulated,meanwhile,a digital operation system is developed based on VBA for real-time analysis and result exhibition.Based on these,the whole failure process is studied while looking into the deep meaning of 3K and searching for their key controls.An approximate method for solving 3K by numerical simulation is proposed with good consistency of the model tests.The key features of super high arch dams are pointed out,including their significant deficiency in safety compared with general high arch dams.The research also finds out the global nonlinear deformation safety factor K2 has a close relationship with compressive fractures near the dam toe,while the fillet near dam toe plays an important reinforcement role.(3)The mechanical parameters of concrete and rock masses are inverted for Jinping-I arch dam,then the inversion parameters are used to study the failure process of dam-foundation system.Model tests verify the simulated 3K safety factors and weakness zones.By correlation analogy,effects of foundation reinforcements and the reliability of design parameters are appraised.(4)The theoretical basis of using unbalanced force to evaluate the unloading relaxtion is demonstrated.The deformation and relaxtion during excavation of the left dam base surface of Baihetan are studied by unbalanced force,and verified by field monitoring.The control functions of protective layer and anchor cables are studied.The unloading relaxtion of dam base surface influencing the dam body deformation stability and overloading failure are proposed.Some advice from the author for the optimization of the dam base surface has been adopted in the engineering practice.(5)The reason why the Terzaghi effective stress principle cannot be used in the slope's abnormal deformation analysis during the initial impoundment is elaborated,and the effective stress principle for unsaturated fractured rock mass is proposed.The shrinkage of yield surface and even plastic deformation are induced by the imbalance between the pressure from fractures and that from pores in the fractured rock masses.This gives rise to the abnormal deformation of the slope,such as valley contractions,during initial impoundment.The slope's deformation field during the initial impoundment of Jinping-I is simulated by the effective stress principle for unsaturated fractured rock mass,and the calculated results tally well with the monitoring values.It's concluded that the slope's abnormal deformation has little influence on the stability of dam body.