The geotechnical seismic isolation of historical buildings through polyurethane injections: A numerical study

The seismic risk reduction is a topic of great interest among the earthquake engineering researchers, due to the high occurrence frequency of seismic events, responsible for extensive damages on vulnerable buildings. Many buildings needing protection against earthquakes belong to the historical and artistic heritage; some interventions for seismic risk reduction are based on the structural vulnerability reduction, but they are sometimes in contrast with the maintenance of the building's aesthetic. The paper aims at showing the efficiency of a Geotechnical Seismic Isolation method based on polyurethane injection in the soil, an already well-consolidated technique for ground improvement. For seismic purposes, this solution is based on the hazard reduction through the decrease of the surficial accelerations; it is an alternative to structural interventions and advantageous especially for the existing buildings, in terms of aspect conservation. Finite Element numerical analyses are performed to study the site effects of an historical building affected in the past by extensive damage related to a strong earthquake, after the modification of shallow soil layers with polyurethane injections. For the polyurethane expansion, changing according to the soil type and confinement, a previous developed method based on the theory of cavity expansion in elastic-plastic medium is used; this allows to have specific indication on the final geometry, density, and mechanical properties of the intervention to be simulated numerically.