GYPSUM’S ROLE IN THE SINKHOLES OF THE TAGLIAMENTO RIVER VALLEY (NE ITALY)

In an area of several kilometers in the Tagliamento Valley, between the villages of Ampezzo and Villa Santina (Friuli, NE Italy), are present frequent points of absorption associated with large and deep sinkholes collapsed in the shallow cemented fluvial-glacial deposits, in the recent alluvial deposits overlying a karstified evaporitic bedrock. In the Quinis village the situation is particularly complex, some houses are affected by failures and in the past, in the fields around the village sudden sinkholes were recorded and some building were demolished also in the centervillage. During the last years a tightening in the phenomena took to the necessity of a deep and multidisciplinary study in order to define the vulnerability of the different areas. For the purpose, were realized 20 piezometer (equipped with devices), 3 seismic lines, 1 electrical tomography, the establishment on the buildings of a topographical monitoring network, 2 assestimeters and a groundwater tracing test campaign. The main vulnerable areas were identified with the presence of holes or caves in the gypsum and soft and unconsolidates alluvial horizons. The big variations in the groundwater levels recorded during the past years and linked to the regime imposed by the dam outflow, underlined an increase in the karstification processes inside the gypsum bedrock and in the above deposits.