A Laboratory and Numerical Investigation on a Post-Seismic Induced Settlement in Southern Italy

In the years following the Irpinia earthquake (1980), the old town of Bisaccia, located on a conglomerate hill overlaying a thick clay formation, experienced a slow subsidence revealed by topographic measurements. The paper summarizes the results of the numerical simulations of the effects of the Irpinia earthquake on the Bisaccia hill. The input data for the analyses were the acceleration records of the seismic event at the site and the geotechnical characterization obtained by dynamic and cyclic torsional tests on undisturbed clay shales. The analyses confirmed the hypothesis that the town subsidence was caused by a post-cyclic soil re-compression as a consequence of the earthquake-induced pore pressures. In fact, the computed shear strains generated by the earthquake within the clay shale deposit often trespassed the volumetric threshold strain; the consequent pore pressure buildup should then justify the observed settlements