EFFECT OF MATERIAL MODULII ON THE STABILITY OF A ROCK FILL DAM

Abstract

A parametric study has been carried out for an existing rock-fill dam to evaluate the influence of elastic modulii of fill and foundation materials on its stability in static (non-seismic) and dynamic (seismic) conditions. The shear characteristics of fill and foundation materials are known for the dam. The elastic modulii values for these materials have been worked out on the basis of shear wave velocities for such materials as available in the literature, taken into consideration their Poisson's ratio and densities. The analyses have been carried out by varying these values to the extent of 229 and 50% on either side, i.e. increase or reduction for the fill and foundation materials. Thus total nine cases have been considered. For static condition, in conventional approach, the safety factor is found out for the critical shear surface evolved by trials. But, in this investigation it has been obtained without trials, from maximum principal strain contours by FEM, for each of the nine cases. The results show that the elastic modulus has only marginal influence on the safety factor. However, it can be seen that the safety factor increases with the increase in modulus values for the materials. This increase is relatively more when the elastic modulus of foundation soils is increased as .compared to that of fill. The dynamic behaviour of the dam, as studied from modal, response spectrum and time history analyses, show that the fundamental time period and the dam crest displacement are maximum when fill modulus is reduced by 50%. While, the dam crest acceleration is maximum when elastic modulus of the fill is increased by 50%. The results of parametric study can be made use of in working out design of a rock-fill dam in seismic region.