PSI - Issue 62

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S. Aiello et al./ Structural Integrity Procedia 00 (2019) 000 – 000

Salvatore Aiello et al. / Procedia Structural Integrity 62 (2024) 1128–1136

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Initial observations were conducted considering a theoretical lining thickness of 50 cm. Subsequently, the calculation of the stress state in the lining generated by its own weight and the gravitational loads of the rock mass was carried out. The analyses were carried out parametrically, varying the magnitude and distribution of the geomechanical load and considering the non-linear behaviour of the concrete lining. The gravitational load of the rock mass, based on the GSI parameters obtained, was introduced parametrically with values varying from 40kPa to 500 kPA, assuming different load configurations (Table 1). Regarding the resistance of the concrete lining, given the limited knowledge on this matter, three resistance thresholds (Rck) of 10 MPa, 20 MPa, and 30 MPa were considered. Based on the structural checks carried out, an allowable load was defined for all load configurations considered for the intact lining as a function of the concrete's resistance.

Table 1. Allowable loads function of the concrete’ s Rck Rck [MPa]

Allowable load [kPa]

10 20 30

130 200 275

These threshold values allow the implementation of a monitoring system capable of providing an alert if it is exceeded. According to available literature on monitoring systems for determining the strength of a tunnel lining, the use of such strength thresholds can help prevent structural failure by anticipating areas of potential weakness and allowing timely interventions to ensure the structural safety of the tunnel. 4. Robust maintenance strategy: Synoptic tables synergy The concessionaire, recognizing the increasing importance of inspection and monitoring issues, plans to conduct in-depth inspections every six months. During these inspections, inspectors perform non-destructive defect detection through careful visual analysis and manual mechanical percussions to detect sound anomalies. These inspections provide detailed photographs of the work, contributing to a rich dataset for analysis and decision-making. The result of these inspections is a database and photographs of the tunnel for long lengths, i.e. for lengths of approximately 29 meters. Each photograph represents each defect of the tunnel vault, its “Image Qualité des Ouvrages d’Art” (IQOA) classification (Fig.2).

Fig. 2. Rating method “Image Qualité des Ouvrages d’Art” (IQOA) for civil engineering defects and water leakage (Lunardi et al., 2023)

The IQOA system, as reported in the CETU 2015 Guidelines, provides a comprehensive classification of defects observed during inspections. This system is divided into two parts: the first classifies civil defects, while the second classifies water leakage. The inspections also compile data relating to the extension of the individual defect in terms