Mitigate Seismic Liquefaction Risk with Nanosilica Grout Injection: Engineering Principle and Sustainability Assessment at the Urban Scale

Reducing liquefaction risk at the community level embraces a series of subsequent technical and non-technical steps, including communication strategies and political decisions, which are not explicitly discussed here. This study first presents the engineering design principles of nanosilicate grout injections and their application to mitigate the liquefaction risk. In a subsequent step, a cost–benefit analysis is defined and performed to evaluate the economic sustainability at the urban scale of this mitigation technique. Preliminary stages of the benefit–cost analysis consist in evaluating the liquefaction susceptibility of the area of interest, introducing the seismic hazard, and evaluating on an annual basis the resulting risk on the selected systems. The above implies the need to adopt adequate economic loss models and raises the question about the treatment of uncertainties affecting input data and propagating step by step. Bearing this goal in mind, the case study of Terre del Reno (Italy), hit by severe and enormous liquefaction following the 2012 Emilia Earthquake Sequence, is analyzed. After evaluating the liquefaction risk on buildings, the cost–benefit analysis is performed by introducing four nanosilica grout injection scenarios, highlighting the need to balance the technical goal and the cost-effectiveness.