# Interpretation of Bridge Health Monitoring Data from Satellite InSAR Technology
## 2 Case Study  
### A22 Po River Bridge  
The A22 Po River Bridge is part of the Italian A22 Highway. It is located in the Mantua province, Italy. It consists of two identical, parallel viaducts made entirely of reinforced concrete and prestressed concrete; it has 14 spans for a total length of 980 m. Each viaduct accommodates a separate highway carriageway. It was designed and built following the 1962 Italian standards for calculating loads of road bridges \"Circ. Min. LL.PP. 14/02/1962, n. 384\". Figure 1 shows a picture of the A22 Po River Bridge and a top view of the case-study area. Figure 2 shows the plant and prospect of the bridge.  
The structural system comprises 36 m-long internally simply supported spans that lean on shear keys at the end of 14.15 m-long cantilevers, resulting in a total span length of 72.8 m between the piers. The cantilevers' deck comprises a double box girder with variable heights ranging from approximately 2.3 m to 3.5 m. The supported span girders are 2.2 m high. In 2002, a widening work involved the symmetrical widening of the carriageways from 10 m to 11.3 m, increasing the thickness of the upper slab. The original slab thickness ranged from 20-22 cm, which was increased to an average thickness of 35-37 cm for the suspended spans and piers. Additionally, the transverse slope of the deck was increased from the original 2% to the current 2.5%. Consequently, the widening works significantly increased the overall deck mass (approximately 6 t/m). Figure 3 shows longitudinal and cross sections of the bridge in the current configuration.  
Figure 1: **(a)** Picture of the A22 Po River Bridge, Italy; **(b)** Top view of the case-study area.  
Figure 2: **(a)** Plant and **(b)** elevation of the A22 Po River Bridge. Dimensions in meters.  
The suspended spans lean on monodirectional and multidirectional steel-Teflon bearings in the north direction and fixed steel bearings in the south direction. Seismic dissipators connect the suspended spans to the cantilevers at the shear keys with fixed bearings. Figure 4 shows a scheme of the suspended span bearings and a picture of the seismic dissipators.  
Figure 4: (**a**) Scheme of the suspended span bearings; (**b**) picture of the seismic dissipators.  
Figure 3: (**a**) Longitudinal section of Piers 10 and 11 and (**b**) cross sections of the A22 Po River Bridge. Dimensions in meters.  
The bridge has 13 piers, with 5 piers within the riverbed and 9 on the floodplain (6 on the north side towards Mantua and 2 on the south side towards Modena). Each pier consists of 6 circular column elements with a diameter of 1.5 m. At the base of the columns is a reinforced concrete collar with dimensions 2.0 m \(\times\) 0.6 m. The foundation piles, also with a diameter of 1.5 m, extend below the collar and serve as natural extensions into the ground from the columns above. The piers in the riverbed have 10 m-neigh columns and approximately 28 m-long piles; the piers in the floodplain have 7 m-neigh columns and approximately 26 m-long piles.  
The last bathymetric survey was performed in 2009, and backfill soil was placed around Pier 11 to decrease its free length in 2012. As a result, the above-ground part of the foundation poles is approximately 8 m for Piers 8, 9, and 10, approximately 11.40 m for Pier 11, and approximately 1 m for the other piers. The erosion at the base of Pier 11 was essentially caused by the increased speed of the stream and the formation of vortexes at the base of the pier; these actions generated the progressive removal of material (solid transport) in the area surrounding the base of the pier with the consequent formation of a localised depression in the riverbed. Given this erosion phenomenon, some backfill soil might have been removed since 2012.