Decoupledseismic Deformation Analysisofazoned Rockfill Dam

Abstract

The seismic safety, in terms ofcrest settlement, of a zoned rockfill dam designed by thetraditional empirical methods is evaluated. The proposed high dam of Bagmati MultipurposeProject (BMP), Nepalis taken as a typical case. 2D finite element method with plane strain assumption is used. The‘decoupled deformationanalysis’ technique is adopted in which thepeak crest acceleration response obtained bydynamic analysis is utilized to predict the potential permanent settlement of the crest usingthe chart developed based on Newmark’s analysis procedures.All calculations are performedon a PC using the available SAP2000 software package.The recorded N-S and the verticalacceleration components of the famous Imperial Valley earthquake of May 18, 1940 (ElCentro, California, USA)are taken as the prescribed input ground motion. Linear directintegration time history analysis based on Wilson-θ (θ = 1.42) incremental algorithm isadopted. Damping is introduced in terms of Rayleigh’sdamping coefficients.Four differentfinite element models: rigid and flexible foundation models, each with and without reservoir;designated by RF_WOR, FF_WOR, RF_WR and FF_WR are evaluated. For the models withflexible foundation, the effective part of foundation to be taken in the model isworked out bytrial procedure based on‘stresscriterion’. For calculating the hydrodynamic effects in thecase of the modelswith reservoir and also for the chart to predict the potential permanentsettlement of the crest, the IS guidelines is simply followed. Agreat deal of parametric studies on free vibration analysis and initial static deformationanalysis are carriedout.Theresults of the parametric studies compare well with the classicalsoil mechanics and the findings of the previous researches reviewed in this thesis, therebyjustifying the models exercised.It isrevealedthat the permanent crest settlement of the BMPdampredictedwiththefour different models are relatively higher.