ABSTRACT
Arch dam’s behavior is generally strongly influenced by thermal load. In summer, concrete expansion generates displacement of the arch toward upstream, which can lead in some cases to the opening of cracks on the downstream face and instability of gravity abutment. In winter, the arch moves toward downstream, increasing the opening of the dam-foundation interface at the upstream toe for the arch concerned by such issue.
Generally, for the evaluation of the arch dam behaviour during winter or summer load, average seasonal temperatures are used. In 2018, the French guidelines for the safety assessment of existing arch dam behavior proposed to carry out additional analyses which considers increased thermal loads. Such analyses should be performed for dams that show a particular vulnerability to thermal conditions such as very thin arches or arch dams in wide valley which are affected by opening of the dam-foundation interface.
The characterization of increased thermal loads is rather difficult because it is strongly dependent of the inertia of the structure itself: a thin arch dam will react quickly to a short but intense cold weather whereas the behavior of a thicker structure will depend on the temperature of the previous months.
The objective of this communication is to present a uniform methodology based on the monitoring on the dam’s crest and statistical analyses involving the HSTT (Hydrostatic Seasonal Temporal Thermal), (Penot,2009) method developed by EDF, to define increased thermal loads with a specified return period. In the same manner that statistical analyses of monitoring data allow to evaluate the radial displacement of the crest of an arch dam during seasonal effect, the methodology allows to define an increase of displacement of the arch under a ten-year return period in winter or summer. Numerical modellings can then be calibrated to represent such an increase of displacement and be used to evaluate the behavior of the dam for such situations.
