Study On Permanent Deformation And Safety Evaluation Of High Rock-fill Dams Under Strong Earthquakes

With the progress of Grand Western Development Program and South-to-North Water Diversion, the seismic safety evaluation of high rock-fill dams has become a crucial problem in hydraulic engineering. Under the sponsorship 50639060 entitled 'Deformation analyses and security control of high rock-fill dam', some key issues including the evaluation of permanent deformation, aseismic measures and aseismic safety evaluation are discussed for high rock-fill dams:1. Equivalent linear analyses are widely used for estimation of site response of rock-fill dams under strong earthquakes. However, the average normalized curves of nonlinear soil properties incorporated in equivalent-linear iterative process can't depict precisely the relationships between nonlinear soil properties and shear strain for soil elements under a wide range of confining pressures. Thus, a more refined approach for determination of nonlinear properties for soil elements for 200 m high rock-fill dams is proposed. In this approach, the normalized confining-pressure-interpolating curves (CPI curves) of each soil element confined under different effective stress are obtained by interpolating from those normalized data under a wide range of confining pressures.2. Considering the facts that the equivalent nodal force method only considers the effect of inertial forces, the softening modulus method only considers the effect of modulus reduction and both of them can not characterize the development of permanent deformation, a simple modified procedure for permanent deformation evaluation of high rock-fill dam subjected to strong earthquake is presented based on seismic deformation analysis. In this approach, the increment of permanent deformation of dam can be determined on the basis of pseudostatic inertial loadings obtained by the equivalent nodal force method and the current modulus parameters which are adjusted by the accumulation of residual shear strain, residual volume strain and residual pore pressure.3. Based on the pseudostatic limited equilibrium method, the concept of average yielding acceleration of sliding body is brought forward, which takes into account the amplification of ground motion by elastic rockfill materials. In addition, the effects of time-history vertical acceleration, dynamic intensity and dynamic pore pressure on the average yielding acceleration and sliding displacement are investigated based on the modified decoupled Newmark sliding method. 4. A coupled analytical procedure based on the earthquake resistance mechanism of sliding structures, which captures simultaneously the acceleration of the sliding mass and the nonlinear stick-slip sliding response along the sliding plane, is presented. In this approach, the inertial force caused by the sliding acceleration of sliding body is included in the load vector. The sliding acceleration and dynamic response of sliding body are obtained by solving the coupled dynamic equilibrium equations and overall force equilibrium equation of sliding body simultaneously. As verification, a deformable soil columns sliding down an inclined plane is studied with the result compared with Wartman's shaking table experiment.5. The thin-layer element is utilized to model potential sliding faces in the earth dam. For the situation of potential sliding body and base sticking together, the thin-layer elements behave as ordinary solid elements to model the consistent deformation between the sliding body and base, while when sliding occurs, the thin-layer elements are taken as 'contact element' to simulate the coupled effects between the plastic sliding displacement and the dynamic response of sliding body. The general formulation of plastic sliding displacement is derived based on the energy conservation principle.6. Nowadays, the reinforced technology is commonly employed by high core rock-fill dams located in high seismic hazard zones. Therefore, the simulation of reinforcement and the evaluation of the reinforced effects are concerned by the engineers. In this text, the limit consistent strain between the reinforcement and rockfill material, intensity and added cohesion of composited material are determined on basis of the relationships between stress and strain of reinforced rockfill materials and rockfill materials. The degree of safety is judged by comparing with the results of time-history average yielding acceleration and the accumulation of sliding displacement of potential sliding bodies, which are determined by the modified Newmark sliding displacement method.7. Take the 260m Nuozhadu high core rock-fill dam for example, a new idea of safety evaluation based on the criterion of deformation is proposed. In this idea, the cumulative sliding displacement and location of potential sliding surface is determined by adjusting the input control parameters (including strength parameters and geometry parameters, etc). By the relationships between the sliding displacement and some key aseismic design parameters, the rationality of initial design parameters can be evaluated quantitatively.