PSI - Issue 84

I. Vangelisti et al. / Procedia Structural Integrity 84 (2026) 1239–1246

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o each attention class is modified in accordance with the new information introduced into the evaluation process, or confirmed where the additional documentation does not provide relevant elements; subsequently, the combination of the two classes is recalculated. 4. Comparative analysis between the updated and the original attention classes: o identification of variations in hazard, vulnerability, and exposure parameters, and consequently in the GSG and LS attention classes, together with a concise analysis of the underlying causes; o declaration of the updated final attention class for each lining inspection segment of the tunnel under consideration; o the outcome is deemed definitive for lining inspection segments for which no reduction in the investigated attention classes is observed. 5. Minimum set of investigations for lining inspection segments exhibiting a reduction in the attention class: o in order to confirm a reduction in the GSG or LS attention classes, the availability of a minimum set of structural tests is recommended. 6. Prescription of additional investigations, where required: o in addition to the investigations referred to in the previous step, and regardless of the outcome of the attention class recalculation process, the designer may request supplementary investigations for specific assessments or in preparation for the subsequent VAL4 level. Such investigations shall always be properly designed according to actual needs of the tunnel and included within a dedicated supplementary investigation plan. 7. Issuance of the VAL3 investigation plan: o issuance, as an annex to the VAL3 document, of the investigation plan including the tests derived from steps 4 and 5. 8. Updated attention class following the execution of investigations and the simplified verification for lining inspection segments exhibiting a reduction with respect to the original class: o detailed definition of the final attention class limited to the lining inspection segments subjected to the investigations referred to in steps 5 and 6, including a critical analysis of the results of stress related investigations and the possible confirmation of the reduction in the attention class. Within the VAL3 framework, for lining inspection segments for which the application of steps from 1 to 3 of the proposed framework leads to a downward assessment of either the Global Structural and Geotechnical or the Local Structural attention class, it is necessary to define a minimum set of stress measurements to be made available for the characterisation of the lining. Following the acquisition and evaluation of the test results, the reduction in the attention class is confirmed if the lining is found to be unloaded ; conversely, it is rejected—thus requiring the execution of VAL4—if the lining is found to be loaded . Specifically, it is deemed necessary to have available at least one assessment of the stress state, defined as the result of at least two individual tests performed on the same cross-section, for each homogeneous tunnel segment. A homogeneous tunnel segment is defined as a portion of the structure characterised by: • homogeneous geological and geotechnical properties of the rock mass or soil (e.g., identical Terzaghi classification or other geomechanical classifications and similar lithologies); • uniform overburden conditions; • identical excavation techniques and lining typologies and/or the presence of pre-support or ground improvement measures; • comparable defects related to the presence of water; • similar crack patterns in the lining. The proposed framework is sumarized in Figure 2. 4. Reduction of the original attention class