Safety assessment of the existing dam - HPP Mariborski otok

The dam of the HPP Mariborski otok on the Drava River, Slovenia was constructed in the last half of the forties of this century. At the beginning of the operation, the care of safety was limited to maintenance procedures and based mostly on visual observation of the dam. In the last twenty years, a regular monitoring system was introduced and used to observe the behavior of the structure and accumulation. Permanent periodic visual inspections, combined with surveying of vertical and horizontal displacements and piezometric measurements of the uplift pressures were introduced in the early seventies. In the year 1990 the refurbishment of HPP and uprating of the electro-mechanical equipment started At the same time, this was also an occasion for more complete safety analysis of the clam structure. The paper presents the procedure used for safety assessment of the existing dam. The statistic arm deterministic numerical models based on the measured data have been used. The results show satisfactory "condition" of the fifty years old dam at normal static loads. The earthquake analysis was introduced by means of pseudo-static loads. The dynamic anal ais has mot been performed. Such an analysis would be necessary, to complete the dam safety picture, particularly in some load cases where the results of the safety against sliding approached the minimum requested values.