STUDY ON SEISMIC ANALYSIS OF EARTH DAMS AND EMBANKMENT

Civil Engineering

Dams are mainly constructed of earth and rock-fill material. The earth-fill dams are simple structure which are able to prevent the sliding and overturning because of this self-weight. Dams are among the most critical civil-engineering structures because they supply water for domestic, agricultural, and industrial needs. Compared with other structures, earth embankments rank high in seismic vulnerability: their average fundamental period often exceeds 3 seconds, and their large footprint subjects them to substantial ground excitation. Historical earthquakes show that inadequately analyzed or designed embankment dams are prone to extensive liquefaction-induced damage. Seismic failure mechanisms include ground rupture beneath the embankment and seismic shaking that triggers liquefaction in supporting soils or the embankment itself. Failure from ground rupture is particularly likely when dams are sited across active faults or reactivated landslides. In this study, the seismic performance of an earth embankment under liquefaction potential is evaluated using field data and analytical procedures. The site under consideration lies in Seismic Zone IV, and soil properties are characterized through Standard Penetration Test (SPT) resistance values and sieve analysis. The soil layers have an average total unit weight of 18.5 kN/m³, and the embankment height is taken as 10 m on level ground. To comprehensively assess the liquefaction behavior, three different seismic zones and three importance factors are considered. In addition, seven different soil strata’s each soil stratum is characterized by its measured Standard Penetration Test (SPT) resistance and percentage fines. The seismic demand is estimated based on zone factor and importance factor, and liquefaction potential is determined by calculating the factor of safety as the ratio of cyclic resistance ratio (CRR) to cyclic stress ratio (CSR), derived from the simplified Seed and Idriss (1971) procedure and SPT-based correlations. A computational program is developed in Microsoft Excel using IITK-GSDMA guidelines for seismic design of earth dams and embankments to carry out these calculations, and in total, 63 different conditions are analyzed.

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