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Stress-deformation analysis of Denis-Perron dam : verification and validation for better prediction of rockfill response Kolev, Boris Nikolaev


Rockfill dams present a challenge for engineers due to the many uncertainties revolving around the behaviour of rockfill. A governing factor in the behaviour of rockfill is the particle breakage due to change of moisture, which was observed in laboratory and field conditions. Alonso and Oldecop have proposed a rockfill model (RM), where the suction inside the cracks of the rockfill is a state variable that controls the breakage mechanism. This research focuses on verification and validation of stress-deformation analysis methodologies, for better prediction of rockfill response. It involves application of the RM in numerical simulation of a benchmark case study on the well instrumented Denis-Perron dam (SM3). Denis-Perron dam is a rockfill dam with a central till core, 171 metres high and 378 metres long, located on the Sainte-Marquerite river in northern Quebec, Canada. The instrumentation data was made available by Hydro-Qu´ebec, for a period of six years of construction, impoundment, and operation of the dam. Numerical simulations are conducted using Code Bright – a fully coupled three phase finite element program for unsaturated porous media. A validation stage was first carried out through modelling of Beliche dam – a well studied case by Alonso et al. The numerical model of the SM3 dam captures the staged construction, reservoir impoundment and rainfall history recorded. Model parameters for the till core and rockfill shoulders were either calibrated using limited available laboratory and field data, adopted from literature, or assumed with some rationale. Deformations measured by the inclinometers during construction and impoundment, both upstream and downstream, are simulated successfully. Piezometer and pressure cell measurements are replicated to a very good extent. Post-construction deformations are reproduced with reasonable success, given the limited data for detailed characterization of the various zones in the dam. Some important challenges around characterization of the rockfill compressibility and the related scaling issues for model calibration are presented and discussed. An attempt is made to quantify the amount of scaling observed through a back analysis of field measurements. Finally, the effect of permeability on rockfill in the development of deformations is discussed.

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