PSI - Issue 62

Carlo Alessio et al. / Procedia Structural Integrity 62 (2024) 1077–1088 Lapo Baccolini / Structural Integrity Procedia 00 (2022) 000 – 000

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The method has been implemented in a user-friendly spread sheet to iterate the calculation increasing vertical loads to the highest compatible with the structure. The thus found load is then compared with the expected one (Fig. 5b) based on rock mass quality designation (RQD) (Bieniawski). When the expected load is lower than the maximum one the performance of the lining is adequate and the global failure mechanism unlikely. 5.3. Local safety evaluation The methods to evaluate the residual safety factor associated to a local mechanism of failure of the structure is strictly linked to the local condition of the lining (construction and exogenous defects). Three methods are used to assess the influence of the anomalies of the concrete lining: ▪ punching check on the residual thickness; ▪ bending check on the concrete plate; ▪ critical temperature variations influence (Aiello et al.).

Fig. 6 Under thickness of the concrete.

In all cases a thin concrete layer is investigated for likely failures mode and mitigation measures consequently prescribed. Furthermore, that a more comprehensive approach is adopted by the Engineer who is in charge of evaluating the level of deterioration of the asset. Defects distribution, presence of cracks or water leakages and their combination feed a more complex engineering judgement process that leads to the definition of a monitoring and/or treatment plan on the tunnel. 6. Tunnel intervention strategy Level 4 purpose is to highlight the criticalities and possible solutions in terms of monitoring systems or intervention strategies. Tecne S.p.A., engineering company of Autostrade per l’Italia S.p.A., tends to group intervention strategies with the effect these have on asset conditions: ▪ IMS – is the treatment approach closer to extraordinary maintenance “ Intervento di Manutenzione Straordinaria ”. The aim is to reduce vulnerability for mainly local mechanisms of failure without increasing the strength of the structure. ▪ IRS – stands for structural reinforcement “ Intervento di Rinforzo Strutturale ”. In this, the aim is to reduce vulnerability for global mechanisms and increase the structural strength of the system. ▪ TRS – stands for “Tunnel Renewal Strategy”. The renewal solution is aimed to extend the tunnels life cycle of at least additional 50 years, through the construction of new lining, able to replace the structural function of the existing one and to ensure waterproof condition and suitable performance under seismic events. The optimal solution to be implemented mainly depends on Organization culture about preventive maintenance, existing lining conditions, impact on traffic, time, costs, waterproofing effectiveness, job-site organization, reusability of the solution, propensity to innovation.