Research On Seismic Input Mechanism And Deformation Law Of Embankment Dams

Seismic safety issue of embankment dams is one of the most difficult and hotresearch problems that has attracted considerable attention in the field of civilengineering. On the basis of existing research findings, this thesis presented systematicresearch results on earthquake damage investigation, theoretical analysis, centrifugemodel tests, numerical modeling and engineering application. Special attention has beenpaid to nonuniform seismic input and its influence on the dynamic response anddeformation laws of embankment dams. The new main achievements are as follows:1. New dynamic analysis of embankment dams considering nonuniform seismicinput has been developed based on the virtual boundary method of wave scattering in anirregular canyon. Firstly, an actual time history of seismic wave is decomposed into aseries of incident harmonic waves that propagate to a dam base surface. Secondly, thevirtual boundary method is used as the first step to obtain the incident and scattereddisplacement field as well as the total displacement field along the base surface. Finally,the nonuniform total displacement field is input along the base surface as the secondstep, so as to induce seismic response and deformation of the embankment dam. Theeffectiveness of the first-step part of the virtual boundary method and the correctness ofseries of analytical formulas of the waves has been preliminarily confirmed through acomparison with exact solutions calculated by using existing analytical analysis.2. Effectiveness of the second-step part of the virtual boundary method has beenconfirmed with a series of dynamic centrifuge model tests on two types of embankmentdams including a CFRD and a combined dam. It is further found from numericalanalysis and dynamic centrifuge model tests that:(1) the acceleration amplificationeffects and permanent deformations of the two dams become more significantly largewith the increasing dam height;(2) the earthquake-induced permanent deformations ofthe combined dam display smaller than those of the CFRD with the same height andsize;(3) the maximum slope-direction stress of the CFRD occurrs on the middle and toppart of the face slabs, but the stress of the combined dam increases with the increasingdam height. 3. The above-mentioned numerical method considering nonuniform seismic inputhas been applied to dynamic response analysis of the Zipingpu concrete-faced rockfilldam (CFRD), which is the highest embankment dam located in the high seismicintensity region during the2008Wenchuan earthquake and the first CFRD experiencingstrong shallow earthquake of IX-X degrees in the world. A comparison is also madebetween two different methods considering nonuniform and uniform seismic input. It isshown that:(1) the new method of nonuniform seismic input can be used to simulatespacial variations of maximum accelerations and phases, and therefore it may providemore satisfactory results to access to actual earthquake response to a certain extent;(2)seismic responses of the dam calculated by the nonuniform seismic input method,including acceleration amplification and permanent deformation of the dam as well asthe permanent stress and deformation of the face slabs, appear significantly smaller inmagnitude than those obtained by the uniform seismic input method, however both ofthe results display the same patterns; and (3) nonuniform spacial variations of maximumaccelerations and phases on the dam base surface can decrease seismic motion of thedam.