INFLUENCE OF ZONING ON DYNAMIC RESPONSE OF EARTH AND ROCKFILL DAM

Abstract

It will always be more economic if an earth and rockfill dam can be built with the materials available at the site itself. However, the materials available at a particular site may primarily be semipervious type; and In that case the semipervious materials can be placed in the shell of earth and rockfill dam. On the other hand, fill material characteristics and zoning affect the dynamic response of an earth and rockfill dam. In this study, a 200m high earth and rockfill dam with an inclined core is analysed to assess the influence of zoning on dynamic response of the darn. Static and dynamic analyses have been carried out by a two dimensional finite element program using four noded quadrilateral isotropic elements and assuming that the materials are linearly elastic. Three different cases of zoning have been studied, viz.-(i) shell with both pervious & semipervious material, (ii) shell with only pervious material, & (iii) shell with only semipervious ma terial. The static analysis has been carried out in both empty and Lull reservoir conditions and static displacements and stresses have been computed. Th' dynamic analysis has been performed only in full te most of the time the reservoir shall be full of water. The average acceleration spectra for 10% damping of the 15:1693-1984 has been used as the seismic input. Assuming that the damping shall remain constant in all the modes, the first five modes have been studied and mode shapes computed. The modal displacements and stresses in these five modes are combined by SflSS method and added to the corresponding static displacements and stresses respectively to have the most critical values of these parameters. The accelerations and time periods of the structure in all the five modes have also been computed; and it can be noticed that time period elongates in case when we provide semipervious material in the shell. Stress contours for both major & minor stresses in static and dynamic conditions have been drawn and studied. It is seen that arching takes place from the u/s core to the u/s shell. From the study it can be concluded that semipervious material can very well be provided in the shell of an earth and rockfill dam on a hard rock foundation.