Study Of The Worst Seismic Motion Input For Earth-dam Seismic Stability Under The Oblique Incidence Condition

With the inherent traits, the earth-dams become the most popular hydor-buildings distributed in the world. Seismic problem for earth-dam is a hot study that attracts more attention in academe. Lots of seismic disasters of the earth dams and the theoretic studies indicate that seismic responses of earth-dam not only are related to medium characteristics, geometry dimension, and boundary condition, but also are related to incidence orientation of the seismic motion. The effects of the worst seismic input on stability of earth dams arose more attention widely. Study of the worst seismic input for earth-dam stability was carried out intensively around the effects of oblique incidence on stability in the paper. Some studies as followed were completed.1. The history and actuality of seismic stability analysis was summarized systematically. The analysis methods for earth dam seismic stability were studied and commented on. The study history of earth dam seismic analysis was represented and summarized. At the same time, some problems in this field were pointed out. The problems to be studied in the paper were put forward.2. The input manners of seismic motion are related to the selection of boundary condition, considered the physical characteristics of the quiet boundary, seismic velocity was changed into stress, and the seismic input is realized. Furthermore, accorded to the orientation of oscillation face, the input boundary of model was modified, so as to consistent with the oscillation face. Hence, the oblique incidence was changed into the vertical incidence, and the nonsynchronous wave was changed into the synchronous wave, which not only increased the input precision but also achieved the oblique incidence.3. The advanced Fast Lagrangian Finite Difference method was adopted in the paper, the theory of the method was introduced in detail. Some problems about the method related to dynamic analysis were discussed too. The validation of quiet boundary and free-field boundary were verified with two 2-D compute models. Mohr-Coloumb plasticity constitutive model and Finn liquefaction model were selected in the paper. Based on the review of constitutive model development history, theories, physical signification and application scope of the two constitutive models were introduced in detail. Static analysis and dynamic analysis for a earth dam were conducted with the two constitutive models. The results indicate that the two models are valid and they can overcome the limitation of Duncan-Chang model that often happens in simulation storing water.4. The motion magnification effects of crest for a homogenous were studied systematically under the condition of oblique incidence. The relationship between magnification effects and canyon shapes, the characteristics of seismic motion were analyzed too. The results indicate that the magnification effects are related not only to the canyon shape, but also to the type of input, the frequency, the incidence angle, and wave length of input wave. Some other important conclusions were found.5. With the nonlinear dynamic analysis method, some analyses were carried out for an earth dam with full water under the condition of single incidence orientation. The four assessment factors for earth dam which are crest magnification coefficient, permanent deformation, pore pressure increment, and plasticity state were computed then. Based on study of the relation between the four factors and the incidence angle, the conclusion that SV-wave with incidence angle 30-45-degree is the worst seismic motion incidence angle was presented firstly in the paper. And when P-wave with high incidence angle (>45 degrees), the higher is the incidence angle, the more instable is the dam, which is the conclusion firstly presented in the paper. Furthermore, the response results indicate that the incidence orientation from downriver side is the worst incidence orientation for earth dam stability. These conclusions will be very important to seismic design for earth dam.6. As an example, the analysis method presented in the paper was performed on Jilin Erlong Lake earth dam. With the same PGV and the same duration, the artificial seismic motion and real seismic record were introduced as seismic input, the nonlinear response results were gained. The similar results indicate that the actual safety assessment is applicable for many instances.The mentioned points are the contents and conclusions found in the paper about the worst seismic incidence for earth dam stability, which verified that the conclusions presented in the paper were valid and applicable.