The behaviour of the Ridracoli arch-gravity dam in the 2002-2020 operation years has been analysed, by applying "statistical" models of increasing complexity to the time series of pendulum and long-base extensometer measurements. The modelling approach has proved robust. A satisfactory estimate of the reservoir load, thermal and irreversible drift components has been obtained for most of the instruments. As expected, the influence of temperature is lower for the instruments deeply embedded in the rock mass. The deformations recorded on the left and right bank of the dam have shown a minor influence of the anisotropic proprieties of the rock mass, well characterized by the mechanical tests performed at the time of dam construction.
The monitoring of large dams relies on a wide network of instruments, primarily, to permit the continuous control of the structure during operation of the reservoir. The measurement of displacements and pore pressures is also instrumental to back-analyse the deformation properties of the foundation rock mass on a larger scale than that involved in any situ tests performed for the design of the dam. It is therefore possible, based on monitoring data, to verify the design hypotheses concerning the influence of elastic, thermal and irreversible deformations on dam behaviour.
This paper reports some results and considerations concerning the Ridracoli dam response during the last two decades of operation. The analysis focused on the assessment of the overall consistency of the deformation measurements recorded by instruments (pendulums and rock extensometers) at different location and depth, also considering the possible influence of the anisotropic structure of the rock mass (bedding planes). The elastic, thermal and irreversible drift components were recognized by a data regression analysis, based on "statistical" models derived from the experience of previous case histories.
The Ridracoli dam (figure 1) is located in the northern Apennines, at the confluence of two streams near the village of Santa Sofia (FC). Considering the width of the U-shaped valley and the overall geomechanical characteristics of the rock mass at the abutments, a concrete arch-gravity type was chosen. The dam is a double-curvature arch concrete structure 103.5 m high and 432 m long at the crest, subdivided into 27 blocks by vertical joints, resting on a pulvino (36.5 m width) along the total length of the excavation profile.
