Finite element modeling of the time-dependent deformation of a slope bounding a hydroelectric reservoir

The south slope of the Vernago hydroelectric reservoir in northern Italy is subjected to a slow time-dependent movement that produced some structural damages in a service shaft located within it. With their continuation, these movements could also damage the diversion tunnel of the reservoir, leading to possible operational problems for the power plant. Two nonlinear, plane strain, finite element models of the slope were developed to evaluate the effectiveness of a berm to be constructed at the slope toe to reduce its present rate of deformation. They are based on different constitutive laws (namely: Viscoplastic and elastoplastic softening) the parameters of which were calibrated on the basis of the available geotechnical information and through the back analysis of inclinometer measurements. The critical evaluation of the results of the two numerical models singled out the inherent limits of one of them, in spite of the satisfactory outcome of the mentioned back analysis. The conclusion that can be reached from this example is that a successful back analysis does not necessarily guarantee a successful forward analysis.