Prediction of Piezometric Levels at the Rock Concrete Interface Considering the Non-linearity of Permeability in the Foundations

Abstract

Being able to describe the state of a dam regarding the safety requirements is an obligation that dam owners have to fulfil. A constant surveillance is thus established, based on the measurement of structural behavioural parameters. The measurements are used to feed descriptive statistical models which are classically linear, such as the historical HST (Hydrostatic-Season-Time) model. This assumed linearity is a significant shortcoming, which only permit a poor description of the reality when it comes to analysing the piezometry in the foundations of arch dams, and more particularly at the rock-concrete interface. Indeed, the contact between rock and concrete evolves during seasons between an open and closed state, under the influence of the thermal loads, and of the hydrostatic load, but also during the years due to ageing effects. Thus, the effects of those three influencing loads on the piezometry are not merely additive. Consequently, analysing such a complex phenomenon with accuracy is only possible when considering complex interactions between the influencing quantities. This paper presents a model that describes the piezometry at the rock-concrete interface as being a fraction of the total upstream hydrostatic load. Since it has been empirically observed that the permeability variations and the piezometry are non-linearly correlated, this non-linearity is explicitly included into the model formulation. In this work, the resulting model is applied to analyse monitored piezometric levels recorded at the interface of a French arch dam. This approach greatly improves the analysis that could be made by HST, and it permits a thorough physical interpretation of the studied piezometry. Eventually, the temporal evolution of the state of aperture of the contact is assessed, which is a great improvement for dam surveillance.