Centrifuge tests to evaluate performance of the Po river banks during earthquakes

On the behalf of the Italian Department for the Civil Protection, the Po River Basin Authority carried out a research project to evaluate the seismic hazard of about 90 km of the right bank of the Po river, from Boretto (Reggio Emilia Province) to Ro (Ferrara Province). The project aim is the assessment of 1) the regional seismic risk of the areas under study, 2) the soil properties of the embankment and the foundation ground via site investigation and laboratory tests, 3) the local seismic response of the ground foundation, 4) the liquefaction potential and 5) the stability under static and dynamic conditions of the bank. In order to investigate the seismic response of the embankment, a series of centrifuge dynamic tests on model embankments were performed using a single degree of freedom shaking table installed into the Italian centrifuge at ISMGEO. The models were reconstructed using silty and sandy soils retrieved in situ. Two soil profiles and two geometries were tested. Four time histories were applied to each model; the accelerograms were deduced from a local seismic response analysis carried out referring to one of the investigated site. The tests showed a significant tendency of the banks to amplify the input motions. The amplification is significant in a wide range of frequencies (from about 2.5 to 25 Hz) and increases from the base towards the top. The amplification is influenced by the soil inhomogeneity, especially near the top, also due to wave focalization. No signs of local instability were observed during tests. The experimental results are compared with the preliminary results of a numerical 2D response analyses of the banks.