Study on structural monitoring procedures for tunnels

Structural monitoring is a process used to assess stability and performance of structures over time and it consists of a measurement phase followed by a data processing phase. It is mainly applied on infrastructures of significant socioeconomic value, such as transportation networks. In Italy the recent investigation campaign following the legislative actions due to the Morandi Bridge collapse in Genova, has revealed a critical situation nationwide extended, whereby a significant portion of existing post-war infrastructure present such deficiencies that designers and policymakers often must face the decision between their restoration or reconstruction. This situation has made it clear how the almost total absence of monitoring data on the investigated structures, significantly limits the ability to define their effective health status. In such a context, it is essential for each structure, whether new or existing, to be equipped with a monitoring system suitable for the specific boundary conditions and aligned with technological advancements. In this thesis work, following a review about the most used tools for structural monitoring, attention was focused on the analysis of geotechnical structures behaviour, particularly tunnels. It is believed that the complexity and high degree of uncertainty associated with these structures make the study of an effective monitoring system even more significant. In underground works, boundary conditions can vary over time and space due to numerous phenomena related to the intersection with different geological formations frequently unexpected. These aspects may require interventions capable to restore the reliability level defined by the original design, but only an adequate monitoring system allows for the recognition of any anomalies and early determination of the most suitable solution. By conducting finite element modelling of tunnels with different imposed boundary conditions, it was possible to analyse the structural behaviour of the linings in terms of displacements and deformations. The results allowed to investigate what is the most appropriate quantities to monitor in order to ensure the safety during construction and operational phases as well. Considering the sensitivity of the most used instruments for structural monitoring, deformation in the linings has proved to be the most sensitive parameter to variations in boundary conditions. Therefore, its measurement is well-suitable for monitoring the structural health status and achieving an effective early warning system. Further study in this thesis has focused on the potential future scenarios associated with the continuous technological development. Nowadays, sensor components and complex algorithms are becoming increasingly accessible at reduced costs. As a result, there is a noticeable possibility of achieving a substantial automation level that can make measurements and subsequent data processing smarter. A direct consequence of such a monitoring system would be the creation of easily accessible data archives playing a prominent role - even with reference to BIM environment - in decision-making processes associated with the structures lifespan. These innovations would provide valuable cost savings for contracting authorities and/or executive companies, as well as an overall safety enhancement.