Effect of vertical input motion and excess pore pressures on the seismic performance of a zoned dam

This paper investigates the combined effect of the vertical component of the input motion and of the weakening effect associated to pore-pressure build-up with reference to a zoned earth dam for which the most recent probabilistic seismic hazard analyses promoted the need of evaluating its seismic performance. The two effects were studied through advanced plane-strain non-linear dynamic analyses using a finite difference numerical model calibrated on an accurate geotechnical characterisation. The occurrence of ultimate limit states in the dam embankment is checked using sets of horizontal and vertical input motions properly selected to account for possible frequency coupling with the dam. The analysis results are presented and discussed in the paper focusing on (i) the main features of the plastic mechanisms temporarily induced by the seismic actions, (ii) the amplification of the horizontal and vertical accelerations acting in the dam body, (iii) the role of the energy and frequency content of the input motion on the magnitude of earthquake-induced permanent displacements, (iv) the combined effect of frequency coupling and non-linear soil behaviour on the overall dam response.