Continuous Monitoring of Masonry Arch Bridges to Evaluate the Scour Action

The shallow foundations that often characterizes multi-span masonry arch bridges are highly vulnerable to the soil settlements typically induced by riverbed scouring. Consequently, monitoring of scouring effects is of paramount importance to ensure the safe operation of these river bridges. Within a recent collaboration between Politecnico di Milano and Regione Lombardia, a multi-span masonry arch bridge has been selected to exemplify a quasi-static monitoring strategy capable of detecting the flood-induced scour. The structure, built during the second half of the 19th century, was subjected to numerous strengthening interventions, especially on the pier foundations resting on the riverbed. The installed heterogeneous sensor network consists of tiltmeters (measuring the rotation of the piers at the skewback level), 1 weather station, 1 hydrometer, and 1 echo-sounder. In addition, the detection of debris accumulation is performed with cameras taking pictures of the piers from the upstream side. After a concise description of the structure and the Sesia River, the paper focuses on the adopted measuring system and the results obtained in the first months of continuous monitoring.