SEISMIC RESPONSE ANALYSIS OF EMBANKMENT DAMS

Abstract

Indian embankment dams were mostly built in the second half of the 20th century. These embankment dams were designed for earthquake loading using outdated and obsolete analysis methods, with inadequate seismic and geotechnical site characterisation. Failure of a dam could have disastrous effects, increasing the likelihood of casualties and significant financial losses. Embankment dams in India are situated in regions with varying degrees of seismic risk, ranging from very high damage to low damage zones. Over the period, there have been revisions of earthquake zone maps, developments in seismic hazard assessment, enhancement of seismic design and performance criteria, upgradation of safety standards for large dams, the development of dynamic analysis methods that account for dam-reservoir interaction with the foundation, and the enactment of laws governing dam safety. Consequently, evaluating the seismic safety of existing embankment dams is necessary to ensure the safety of downstream areas. A comprehensive understanding of how embankment dams respond during earthquakes is essential, which can be accomplished by performing seismic response analysis for embankment dams. The primary focus of this thesis is to evaluate the seismic safety of an existing embankment dam as a case study by performing seismic response analysis. Firstly, a study on the existing literature on national and international practices on the seismic safety evaluation of embankment dams is carried out to develop the best practice addressing the issues in the current scenario. Secondly, a parametric study to examine the impact of hydrodynamic forces on the dynamic behaviour of embankment dams using PLAXIS 2D with a 2D Plane Strain Model of 15-noded elements. Finally, seismic performance of an existing large embankment dam was assessed evaluating its permanent crest settlements post governing earthquakes recommended by ICOLD. Hardening soil model with small strain stiffness, constitutive model was chosen to model the static and dynamic behaviour of the embankment dam to account for shear modulus reduction and damping in embankment dam materials. To this aim, numerical analysis results have been discussed, focussing on the effects of hydrodynamic forces on crest settlements and performance criteria of existing large embankment dam, according to ICOLD guidelines for dams.