Analysis And Research Of Seismic Effects And Slope Seismic Stability Of High Earth And Rockfill Dams

Many high earth and rockfill dams to be constructed in the west of China are mostly located at strong earthquake zone. The assurance of their secure operation is very important to the development of national economy and the safety of People's life and properties. Series of research about the seismic effects and slope seismic stability of high earth and rockfill dams are discussed in the paper. The distribution characteristic of the seismic acceleration along dam bodies and dam top in the direction of canyon of high earth and rockfill dams are analyzed with analytical method and finite element method in two and three dimensional space. Suggested dynamic seismic coefficient figure of high earth and rockfill dams 300m level in height is put forward. Furthermore, with improved limit equilibrium method and strength reduction technique, the influence of dynamic seismic coefficient upon slope safety factor and critical slide surface of high earth and rockfill dams is analyzed. When shear strength reduction technique is applied to analyze the slope stability problem, according to sudden increase characteristic of element strain inside the slide surface zone put forward by Academician Zhen Ying-ren, slope stability criterion by the sudden increase of the maximum element equivalent plastic strain inside the plastic coalescence zone is put forward. Considering large displacement and deformation will occur when dam loses stability status, large deformation theory based on the updated Lagrangian method is introduced to analyze dam slope seismic stability, and the results calculated by large deformation theory are compared with those by small deformation theory. The main research and results involved in the paper includes the following parts:1. With 1) analytical method based on shear beam theory including response spectrum method, iterative method considering nonlinear relationship between dynamic shear modulus G and dynamic shear strainγ, and simplified analysis method considering 3-dimensional effect. 2) finite element method including static computation program based on E-B nonlinear elastic constitutive model, and dynamic computation program based on equivalent linear viscoelastic model, seismic acceleration distribution characteristic analysis along dam bodies and dam top in the direction of canyon of six model dams with different height and engineering example of NuoZhaDu and ShuangJiangKou high earth and rockfill dams to be constructed is made. Influence of grade of canyon, seismic design intensity, slope grade, dam style, seismic wave input, and dam material parameters upon the seismic acceleration distribution of high earth and rockfill dams are also considered. Suggested dynamic seismic coefficient figure of high earth and rockfill dams 300m level in height is put forward ultimately.2. When simulating the loss of stability of a 300-meter-high earth and rockfill dam with strength reduction technique, the characteristic of sudden increase and unbalanced development of the element equivalent plastic strain in the plastic coalescence zone, the criterion of sudden increase of the maximum element equivalent plastic strain inside the plastic coalescence zone is put forward.3. With 1) limit equilibrium method considering nonlinear strength criterion of rock and dynamic strength criterion of soil, 2) strength reduction technique with some improvement about instability criterion and reduction step, influence of dynamic seismic coefficient and dam material strength criterion on the safety factor and slide surface of high earth and rockfill dams is analyzed. The results indicate that when earthquake load is calculated with the use of suggested dynamic seismic coefficient figure, seismic force in the dam body decreases, which result in the reduction of slide moment of soil trips and the increase of dam slope safety factor. The position of the critical slide surface is mostly determined by strength criterion of dam material, and the influence of dynamic seismic coefficient can be neglected.4. When high earth and rockfill dams lose stability, large dam slope displacement and deformation will occur. Therefore, with large deformation theory based on the updated Lagrangian method applied, using Modified Drucker-Prager constitutive model which reflects nonequivalence of tension and compression characteristic of geomaterials, discussion about seismic stability of high earth and rockfill dams with large deformation finite element method is made. The conclusion is when large deformation theory based on Continuous Medium Mechanics is considered to analyze slope stability problem, the value of safety factor will arise slightly. Results based on small deformation theory are sufficient for engineering practice. Finally, for modified Drucker-Prager constitutive model, influence of parameter K,dilation angleψ,cohesion C and internal frictional angleφ, and elastic modulus E and Poisson's ratioυupon dam slope safety factor is discussed.