چكيده به لاتين
Nowadays, more than 72 percent of world’s dams consist of earth dams. Factors such as possibility of construction on low rigidity foundations, possibility of construction in wide valleys, lower cost of construction, easier implementation and proper operation against earthquakes make earth dams as priority of dam construction in the world. Therefore, investigation of seismic performance of these geostructures has always been considered by researchers. One of the most important indicators of seismic performance of embankment dams is to evaluate permanent displacements under seismic excitations. On the other hand, in order to quantify the damage of different structure or non-structure parts, the probability of occurrence of a particular damage can be expressed in terms of an earthquake indicator. The repetition of these operations for different values of the earthquake indicator leads to a curve called fragility curve. Thus, in order to investigate seismic performance, the probabilistic fragility curves methods are used to evaluate the permanent displacements of the embankment dams during seismic excitation.
In this paper, the Anderson and the Lexington (Lenihan) dams, two earth dams in the state of California, have been chosen as case studies to evaluate seismic performance. Permanent displacement is chosen as an index of damage of the fragility analysis, and then by consulting the codes of earth dams' seismic design in the world, the no.624 code of Iran and engineering judgment, some of the damage limit states have been determined for case studies.
Numerical modeling of case studies has been conducted by finite difference software,FLAC 2D. The models’ verifications have been confirmed by using the results of the accurate instruments installed in the dams through real seismic loading. Also accuracy of the proposed models is checked by comparing these results with those presented by permanent displacements evaluating methods based on Newmark’s sliding block.
Finally, the fragility curves of case studies are calculated based on three different factors of earthquake intensity including Peak Ground Acceleration (PGA), Specific Energy Density (S.E.D) and Arias Intensity (Ia). Furthermore, the effect of earthquake energy on the fragility curve of case studies is evaluated by considering the concepts of near field and far field excitations.
Keywords: Earth dams, Permanent displacements, Fragility curves, Finite difference, Earthquake energy.
